Unprotected and interconnected Ru0 nano-chain networks: Advantages of unprotected surfaces in catalysis and electrocatalysis

Article abstract of DOI:10.1039/c5sc04714e

Seedless, surfactantless and support-free unprotected, metallic, interconnected nano-chain networks of ruthenium nanoparticles (NPs) were successfully synthesized via the reduction of ruthenium(iii) chloride (RuCl₃) with sodium borohydride (NaBH₄) at three different temperatures, viz. 30 °C, 45 °C and 60 °C. The molar ratio of RuCl₃ solution and borohydride was optimized to be 1:1.5 to produce stable colloids with the optimum final solution pH of 9.7 ± 0.2. Average diameters of the interconnected nano-chain networks prepared at 30 °C (Ru-30), 45 °C (Ru-45) and 60 °C (Ru-60) were 3.5 ± 0.5 nm, 3.0 ± 0.2 nm and 2.6 ± 0.2 nm respectively. The morphology and composition dependent catalytic and electrocatalytic activities of these unprotected Ru nano-chain networks (Ru-30, Ru-45 and Ru-60) were studied in detail. The catalysis study was performed by investigating the transfer hydrogenation of several substituted aromatic nitro compounds. It was observed that Ru-60 was relatively more active compared to Ru-30 and Ru-45, which was reflected in their rate constant values. The electrocatalytic activities of Ru-30, Ru-45 and Ru-60 were screened for anodic water splitting in alkaline medium (0.1 M NaOH) and it was found that all of them showed almost the same activity which required an over-voltage of 308 ± 2 mV to obtain an anodic current density of 10 mA cm^-2. The catalytic and electrocatalytic performances of these unprotected Ru⁰ networks were compared with Ru⁰ nanomaterials prepared under similar conditions with three different surfactants, viz. CTAB, SDS and TX-100, which revealed that unprotected Ru⁰ networks are better catalysts than those stabilized with surfactants. The superior catalytic and electrocatalytic performance is due to the availability of unprotected Ru⁰ surfaces. The present route may provide a new possibility of synthesizing other surfactant-free, unprotected metal colloids for enhanced catalytic and electrocatalytic applications.

Full text of DOI:10.1039/c5sc04714e

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0
Unprotected and Interconnected Ru Nano-chain Networks:
Advantages of Unprotected Surfaces in Catalysis and
Electrocatalysis
S. Anantharaj, M. Jayachandran and Subrata Kundu*
Electrochemical Materials Science (ECMS) Division, CSIR-Central Electrochemical Research
Institute (CECRI), Karaikudi-630006, Tamilnadu, India.
*
To whom correspondence should be addressed, E-mail: skundu@cecri.res.in and
subrata_kundu2004@yahoo.co.in, Fax: +91 4565-227651; Tel: +91 4565-241487.
ABSTRACT
Seedless, surfactantless and support free unprotected, metallic, interconnected
nano-chain networks of ruthenium (Ru) nanoparticles (NPs) had been successfully
synthesized via the reduction of ruthenium(III) chloride (RuCl ) with sodium borohydride
3
(
NaBH ) at three different temperatures, viz. 30 °C, 45 °C and 60 °C. The molar ratio of
4
RuCl solution and borohydride was optimized to be 1:1.5 to get stable colloids with the
3
optimum final solution pH of 9.7 ± 0.2. Average diameter of the interconnected nano-chain
networks prepared at 30 °C (Ru-30), 45 °C (Ru-45) and 60 °C (Ru-60) were 3.5 ± 0.5 nm,
3
.0 ± 0.2 nm and 2.6 ± 0.2 nm respectively. The morphology and composition dependent
catalytic and electrocatalytic activities of these unprotected Ru nano-chain networks (Ru-
0, Ru-45 and Ru-60) were studied in-detail. The catalysis study was done by taking the
3
transfer hydrogenation of several substituted aromatic nitro compounds. It was observed
that Ru-60 was relatively more active compared to Ru-30 and Ru-45 which was reflected in
their rate constant values. The electrocatalytic activities of Ru-30, Ru-45 and Ru-60 were
screened for anodic water splitting in alkaline medium (0.1 M NaOH) and found that all of
them showed almost the same activity which required an over voltage of 308 ± 2 mV to get
2
an anodic current density of 10 mA/cm . Meanwhile, the catalytic and elctrocatalytic
0
0
performances of these unprotected Ru networks were compared with Ru nanomaterials
prepared under similar conditions with three different surfactants viz., CTAB, SDS and

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0
TX-100 which in turn revealed that unprotected Ru networks are better catalysts than the
ones stabilized with surfactants. The superior catalytic and electrocatalytic performance is
0
due to the availability of unprotected Ru surfaces. The present route may provide a new
possibility of synthesizing other surfactant free, unprotected metal colloids for enhanced
catalytic and electrocatalytic applications.
Introduction
Despite enjoying many advances in the field of nanostructured zero-valent metals
for the past two decades, interesting results, findings, methodologies and applications have made
them as one of the fascinating field of research in the scientific community around the globe.
Stabilizing metals at the nanoscale and their subsequent applications in various fields such as
electronics, optics, catalysis, energy conversion and in other emerging fields have become an
unavoidable and essential requirement in the field of materials science. Among the various forms
1
2,3
of metal based nanostructures, fabrication/synthesis of nanoparticles (NPs), thin films (TFs),
4
5
6
7
nano-chains, nanowires (NWs), nanorods (NRs), and nanofoams (NFs) were studied in depth
8
5
9
by various physical and chemical routes. The chemistry of metal NPs such as Au, Ag, Pd and
10
Pt with different morphologies have been focused more compared to relatively more reactive
7
11
12,13
14
15
metals such as Ir, Rh, Os,
Cu, and Ru. Among the several transition metals with
0
standard reduction potential (E ) higher than that of hydrogen, Au, Ag, Pt and Pd are the most
studied metals at nanoscale level compared to others. Beyond the successful reduction and
stabilization of metal NPs at nano level, morphology, size and shape control are also
significantly essential for many specialized applications. For the synthesis and control over
1
6
morphological parameters, many physical and chemical methods such as hydrothermal, sol-
1
7
18
19
20
gel, laser ablation, physical vapor deposition (PVD), chemical vapor deposition (CVD),
2
1
22,23
7,24–26
microwave assisted synthesis, sonochemical synthesis
and wet chemical reductions
are employed. Among them, wet chemical reduction at various reaction conditions is the most
preferred. As wet chemical synthesis is a bottom-up approach, it offers a better control over size
and shape of metal nanostructures. Besides, the morphology selectivity or control is usually
achieved by adding external additives such as stabilizers, surfactants, templates, scaffolds,

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layered materials and other 3D matrices. The nature of these additives varies from a simple
2
7
28
chemical to bio-macromolecules such as DNA and cellulose and even up to naturally
2
9-31
occurring 3D matrices like alumina, clay and minerals like ferrite and silica.
All these
materials basically offer selectivity over size, shape, morphology by acting as a structure
determining platform for growth and as a host material. However, wet chemical routes to prepare
metal nanomaterials with desired morphology without the addition of any such additives and
external agents are highly limited and reported occasionally for the preparation of metal NPs
3
2-34
35
36
37
such as Au,
Pd, Pt, ternary metal nanocomposites like CuAgSe and some metal
3
8,39
oxides.
Obviously, it is highly desired to prepare materials without any additives when it
comes to practical applications to avoid many unwanted loss in efficiency due to these additives.
Moreover, a nanomaterial synthesized without any support and surfactant will offer larger
surface area compared to the ones with the additives.
Among the various transition metals, ruthenium is the one with a positive standard
3
+
0
electrode potential of 0.68 V (Ru to Ru in water) that makes it possible to reduce at the
nanoscale and stabilize for further applications. In bulk, it is a hard metal with a color of silvery
white. Moreover, it is one of the metals with melting point higher than 2300 °C with a density of
3
1
2.41 g/cm . Applications of Ru as metal, metal oxide and as its complexes both in bulk and in
4
0–46
nanoscale levels had been studied in catalysis and in electrocatalysis.
There are many reports
available for the synthesis of Ru metal nanomaterials with different morphology for specific
applications. Chau et al. reported the β-cyclodextrin stabilized Ru NPs for hydrogenation
4
7
48,49
reactions. Salas et al. reported the preparation of Ru NPs in ionic liquids.
Stabilization of
Ru NPs was achieved by heavily fluorinated compounds as reported by Tristany and co-
5
0
51
workers. Ru NPs was prepared by a facile polyol reduction by Viau et al. In addition to these
studies, reports on supported Ru metal NPs for catalytic applications are also available where β-
5
2
29,53–55
15,56
57
58
Zeolite, Fe O ,
Graphene/reduced graphene oxide,
silica, rutile, montmorillonite
3
4
3
1
59
60
clay, nanostructured carbon and polystyrene are the common solid supports. Ru metal based
6
1–67
nanoalloys and composites have been also prepared and used for many specific applications.
6
2,63
68
Besides, spherical Ru NPs, Ru and Pt-Ru metal nanowires
and nano-chains were also
reported earlier where surfactants were employed to stabilize them. However, there is no report
for the synthesis and stabilization of Ru metal nano-chain networks without any external
stabilizer such as surfactant, solid support, scaffolds, templates or structure warping agents. The

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only metal which is frequently reported at nanoscale without any external stabilizing agents is
3
2–34
Au,
for which phrases ‘surfactant free synthesis’ and the term ‘unprotected’ are often
employed.
On considering its unique catalysis application, Ru is one among the most used transition
0
metals for catalysis along with Pt, Pd, Ni, Ir, Au and Ag. Ruthenium, as Ru , RuO , mononuclear
2
complexes, multinuclear complexes, bimetallic NPs such Pt-Ru, Ru-Ir and as composites with
6
2,65–67,69–71
some other metal oxides were used extensively in many catalytic studies.
Among
4
9
47
them, the important chemical transformations are hydrogenations of alkenes, arenes, carbonyl
7
2
40,59,73
29
compounds and nitroarenes,
N-alkylation of sulfonamides, sulfinamides and amines,
5
2
54
conversion of syngas to isoparaffins, conversion of nitriles and Heck and Suzuki type
7
4
coupling reactions. On the other hand, Ru, RuO and its bimetallic and oxide composites have
2
extensively been studied as electrocatalysts for various reactions such as oxygen evolution
reaction (OER), hydrogen evolution reaction (HER), HCl oxidation and in methanol oxidation
6
1–64,66,67,75
reaction.
Water splitting by anodic oxidation with Ru electrocatalyst is the well
documented electrocatalytic application in which it competes with the state-of-the-art catalyst
7
6
Ir. Nowadays, non-noble metal catalysts are also used as anodes in water electrolyzer but in
our case the main reason for choosing Ru for OER is to emphaize the advantages of the
0
unprotected Ru surfaces over the protected ones. While considering the versatile applicability of
Ru and its compounds, surfactant and any kind of supports free Ru nanomaterial is highly
desired and required as the surface area offered by surfactant free nanomaterials is obviously
higher than the other nanomaterials surrounded by scaffolds, surfactants, templates and supports.
To the best of our knowledge, this is the first ever report on the synthesis of unprotected Ru
metal nano-chain networks, which is surfactant free and synthesized without any solid support
and external stabilizers and the examination of their catalytic and electrocatalytic performances.
In this article, for the first time, we present the facile and fast synthesis of surfactant and
support free unprotected metallic Ru interconnected nano-chain networks of three different
average chain diameter by a simple wet chemical reduction of known RuCl .xH O solution with
3
2
sodium borohydride at three different temperatures viz., 30 °C, 45 °C and 60 °C. The molar ratio
of RuCl .xH O solution and sodium borohydride solution were optimized accordingly to get a
3
2
0
stable colloidal solution of Ru nano-chain networks and the optimum final solution pH in all the

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three was found to be 9.7 ± 0.2. The eventual average chain diameter of Ru-30, Ru-45 and Ru-60
networks were 3.5 ± 0.5 nm, 3.0 ± 0.2 nm and 2.6 ± 0.2 nm respectively. The synthesized
materials were characterized using all essential spectroscopic and microscopic techniques to
elucidate the morphology and chemical nature of the sample and a detailed discussion is
elaborated in the results and discussions section. The catalytic performance of Ru-30, Ru-45 and
Ru-60 were inspected by taking several, different nitro compounds viz., nitrobenzene, 4-
nitrophenol (4-NP), 4-nitroaniline (4-NP), 4-nitrostyrene (4-NS), 2-nitrophenol (2-NP), 2-
nitroaniline (2-NA) and 2-bromo-6-nitrotoluene (2-B-6-NT). Moreover, the electrocatalytic
activity of Ru-30, Ru-45 and Ru-60 nanomaterials for anodic water splitting for OER in alkaline
medium were tested and discussed in subsequent sections.
Experimental Section
0
Synthesis of Interconnected Ru Nano-chain Networks.
A stock solution of ruthenium(III) chloride hydrate (RuCl .xH O) of concentration 0.01
3
2
M was prepared using Milli Q water. A solution of 0.1 M sodium borohydride was prepared
freshly in ice-cold condition and used for each trial. In a typical synthesis, desired amount of
3
+
Ru stock solution was taken into 250 mL beaker and stirred on a hot plate magnetic stirrer.
3
+
Then the freshly prepared borohydride solution was added into the Ru solution at the rate of 10
mL per 30 s. From the color change and the primary absorption spectral results the successful
0
formation of Ru NPs was confirmed. To find out the optimum molar ratio between RuCl .xH O
3
2
0
and the borohydride to get a stable colloidal solution of interconnected Ru nano-chain networks,
the ratio was systematically changed and the results are as tabulated in Table 1 along with the
final pH of each solutions. Depending on the reaction scheme, the rate of addition of borohydride
was also varied wherever required. From Table 1, we can infer that at 30 °C, 45 °C and 60 °C,
except the molar ratio of 1:1.5 others were found unable to produce a stable colloidal solution of
0
interconnected Ru nano-chain networks. Depending on the molar ratio and the temperature, the
0
aggregation and precipitation time of Ru particles varied from 1 min to 55 min. The stable dark-
0
brown colloidal solution of interconnected Ru nano-chain networks obtained at 30 °C, 45 °C
and 60 °C when the ratio of metal precursor and borohydride was 1:1.5 and the final pH was
about 9.7 ± 0.2. Other than 30 °C, 45 °C and 60 °C, we also tried our synthesis at 75 °C and 90
°
C but as borohydride is a vigorously reacting reductant, we experienced drastic spillage and

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3
+
bumping of the reaction mixture at 75 °C and 90 °C. To ensure the complete reduction of Ru to
0
Ru , reaction mixtures were continuously stirred for 3 h further. Moreover, to find out the
stability of the colloidal solution obtained, a part from all the three solutions were kept in light
under ambient conditions and another part was kept in dark and at 5°C. The later ones were
found stable for more than a month and the one kept in light and in ambient conditions got
precipitated in 12-15 days. However, when the settled solutions were sonicated for 10 min, we
obtained the stable dark-brown colloidal solution with the stability that almost equals to that of
the freshly prepared solutions. This implies that though the colloidal solutions are not stable for a
long period of time, it can be made stable at any time by a simple sonication assisted re-
dispersion. The catalytic performance was evaluated for the as-synthesized solutions of
0
interconnected Ru nano-chain networks obtained at 30° C, 45 °C and 60° C. The electrocatalytic
0
water splitting was carried out using the interconnected Ru nano-chain networks modified GC
electrodes. The visible changes during the synthesis were captured and the complete synthesis
sequence is depicted as Scheme 1.
Catalytic Hydrogenation of Nitroarenes to Aminoarenes.
Hydrogenation of nitroarenes to aminoarenes is solely catalyzed metals and metal NPs
and has been studied intensively with various catalysts and various nitro compounds. The
0
catalytic performance of interconnected Ru nano-chain networks viz., Ru-30, Ru-45 and Ru-60
were examined for the hydrogenation of seven different nitroarenes. In all these catalysis
reactions, the volume catalyst solutions were kept about 20 µL. Similarly, the volume and
concentration of the borohydride solution were also kept constant which were about 100 µL and
0
.1 M respectively. To find out the actual concentration of nitro compound at each point,
calibration curve for all the nitro compounds has been prepared using standard solutions of
known concentration. The details of concentrations of each nitro compound are tabulated in
Table S1 (online SI section). The details on volume and concentration of the nitro compounds
taken are listed in Table S2 in online supporting information (SI) section. For a typical
-6
hydrogenation reaction of 4-Nitrtostyrene (4-NS) with these three catalysts, 0.5 mL of 10 M
stock solution of 4-NS was taken into a glass vial of 15 mL volume into which 20 µL of Ru-30,
Ru-45 and Ru-60 were added and shaken well for homogeneity. Then the volume of the reaction
mixtures was made 4 mL with water. Soon after adding a freshly prepared ice-cold solution of

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1
00 µL of 0.1 M sodium borohydride, the mixture was shaken for a moment and then about 3.5
2
mL of the solution was taken out into quartz cuvette of path length 1 cm and analyzed through a
double beam UV-Visible spectrophotometer. Time-dependent UV-Vis analyses at a regular time
interval of 60 sec were done after the addition of borohydride. The resultant UV-Vis spectra of
other nitroarenes hydrogenation reactions were plotted together and discussed in results and
discussion section (under main text) and in online SI section. The same procedure was followed
for other nitroarenes with required change in their concentration depending on their molar
absorptivity.
0
Electrocatalytic Study on the Interconnected Ru Nano-chain Networks by Taking Oxygen
Evolution as a Test Reaction.
As the catalytic study on the hydrogenation of nitroarenes, electrocatalytic water splitting
0
ability of interconnected Ru nano-chain networks viz., Ru-30, Ru-45 and Ru-60 were also
2
examined. GC electrode of 0.0732 cm area was taken as bare working electrode. For better
adhesion of our catalyst, binder nafion (5%) solution was mixed with our catalysts solution in the
ratio of 1:9 by sonication. About 3 mg of each Ru-30, Ru-45 and Ru-60 were homogenized with
1
mL of water and 5% nafion (9:1) solution by sonication separately. About 5 µL of the resultant
ink was casted carefully on the calibrated GC surface ensuring a catalyst loading of 0.015 mg in
each GC surface and dried in ambient conditions for 10 h. In each modification, the catalyst
2
loading was kept constant about 0.205 mg/cm . The modified GC electrodes were then used as
working electrode. About 20 mL of 0.1 M NaOH is taken with a Pt-foil counter electrode and an
Hg/HgO reference electrode. The electrocatalytic activity was studied by running cyclic
voltammetry (CV) at a scan rate of 10 mV/s. Stability and the kinetics were analyzed by
chronoamperometry, steady state polarization techniques and electro impedance spectroscopy
and other required electrochemical characterizations. The detailed discussion is given in the
results and discussions section.
Results and Discussions
UV-Visible Spectroscopic Study.
The UV-Visible absorption spectroscopic studies were done to follow the chemical
0
changes that occurred during and after the syntheses of colloidal Ru nanomaterials at different

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temperatures viz., 30 °C, 45 °C and 60 °C. The absorption spectrum for the metal ion precursor
3
+
0
(
Ru ) and the synthesized colloidal Ru nanomaterials at different time intervals after the
addition of borohydride was recorded and given as Figure 1. Curve a in Figure 1 is the
3
+
absorption spectrum of the Ru solution in which two humps at 487 nm and 304 nm are
3
+
observed which is as expected for Ru solution and also in good agreement with earlier
7
7
3+
reports. Curves b, c and d, e are the absorption spectra of the reaction mixture of Ru solution
and borohydride at 30 °C and 45 °C after 5 and 30 min from the addition of borohydride
respectively. Curve b and d have a sharp and intense peak at 257 nm which is due to the
2
+
3+
77
formation of Ru ions intermediate by the reduction of Ru ions at the initial stage. Curves c
and e are the absorption spectra of the same reaction mixture after 30 min where we can see the
2
+
clear and sharp drop almost about 99% in the intensity of Ru peak observed at 257 nm. This
clearly indicates that when the synthesis was done at 30 °C and 45 °C, initial reduction product
2
+
0
2+
was Ru rather than Ru and on continued stirring further reduction of Ru took place to form
0
metallic Ru particles. However, there in curve c and e still a small hump is seen indicating the
2
+
unreacted Ru ions. Curves f and g are the absorption spectra of the reaction mixture performed
at 60 °C. Curve d was recorded at 5 min from the addition of borohydride and curve e was
recorded when it was 30 min. Unlike the curves observed at 30 °C, the absorption spectra of
reaction mixture performed at 60 °C showed a gradual steep increase in the absorption while
approaching the lower wavelength regions. This is attributed to the interference caused by the
4
2,51,77
rapid evolution of H gas from the reaction mixture as the temperature was high.
This rapid
2
3
+
0
evolution assisted the rapid reduction of Ru to Ru within 5 min unlike the one performed at 30
0
°
C where it took more than 30 min. Even though the reduction was rapid and formed Ru in 5
2
+
min, a very small hump in curve f at 256 nm indicates the existence of some unreacted Ru ion
at this stage. When the stirring was further continued and temperature kept constant about 60 °C
for 30 min, the resultant absorption spectra (curve g) almost had no peak in the region
2
+
characteristic to Ru ions. Moreover, the total reduction in the absorption from higher to lower
wavelength side is noted which is due to the reduced evolution of H gas from the reaction
2
mixture. One more absorption spectrum of Ru-60 was taken after 3 h from the synthesis and
given as curve h which is of comparable intensity to that of Ru-30 and Ru-45. This in turn
strongly supports our attribution to the increased intensity in the reaction mixture performed at
0
6
0 °C. The overall UV-Visible studies showed the successful formation of metallic Ru particles

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3
+
by the reduction of Ru solution by borohydride. These results are in good resonance with the
7
7
earlier report of Li et al.
Transmission Electron Microscopic (TEM) Studies.
Transmission electron microscopic (TEM) and high resolution transmission electron
microscopic (HR-TEM) studies were carried out to find the morphology, size, nature of the
material and their fine structures. Figures 2, A-I are the TEM, HR-TEM and SAED pattern
images of Ru-30, Ru-45 and Ru-75 respectively where Figures 2, A-C are of Ru-30, Figures 2,
D-F are of Ru-45 and Figures 2, G-I are of Ru-60. Figure 2A, 2D and 2G reveal overall
morphologies of Ru-30, Ru-45 and Ru-60 at low magnification respectively. It is clear from
these images that all of them have almost the similar morphology of dense, interconnected
0
networks of Ru nano-chains. However, it can also be observed that the nature of the
interconnected chains gradually becomes less dense while going from Ru-30 to Ru-60. This is
because of the rapid evolution of H gases and short reaction time taken at high temperatures that
2
0
restricted the adjacent chain fusion by not providing sufficient time for the Ru particles formed
initially. On the other hand, inset histograms of 2A, 2D and 2G reveal a linear variation in the
average chain diameter of interconnected chains and the average diameters are 3.5 ± 0.5 nm, 3.0
±
0.2 nm and 2.6 ± 0.2 nm for Ru-30, Ru-45 and Ru-60 respectively. Figures 2B, 2E and 2H are
the HR-TEM images that project the lattice fringes and fine structures of Ru-30, Ru-45 and Ru-
0 respectively. From the measured d-spacing values various planes are assigned accordingly.
6
Figures 2C, 2F and 2I are selected area electron diffraction (SAED) of Ru-30, Ru-45 and Ru-60
respectively. The observed ring patterns are calibrated according to the diffraction planes from
which they originate and found that both SAED and XRD analysis (given in online SI section as
7
8
Figure S2) are in good agreement and with the ICDD card data of number 88-1734. The overall
TEM, HR-TEM and SAED analyses had revealed that the morphologies of Ru-30, Ru-45 and
Ru-60 are interconnected nano-chain networks with the difference in the density of the network
structures and the average chain diameter of the individual chains that are fused together with the
adjacent chains.
X-ray Photoelectron Spectroscopic (XPS) Analysis.
X-ray photoelectron spectroscopic (XPS) studies were done for Ru-30, Ru-45 and Ru-60.
Figure 3A is the survey spectra of Ru-30, Ru-45 and Ru-60 where various peaks for Ru 3d, Ru

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3
4
p3/2 and Ru 3p , Ru 2s, Na 1s and O 1s are observed at the binding energy values of 280.2 eV,
1/2
61.9 eV, 484.8 eV, 740.7 eV, 1071 eV and 529.9 eV respectively. All these peaks and their
corresponding binding energy values are in agreement with the previous studies of zero-valent
79-81
Ru atoms.
A peak with considerable intensity for O 1s is also observed due to the
spontaneous formation of passive RuO film on the unprotected Ru surface when it is drawn out
x
of the colloidal solution and dried for making XPS samples. The characteristic peak of OKLL is
also observed at 980.7 eV. The peak at 1071 eV is of Na 1s come from the reductant sodium
borohydride used. High resolution spectra of Ru 3d and Ru 3p for all three catalysts were taken
and given as Figures 3, B-G. Figures 3B, 3C and 3D are the high resolution scan of Ru 3d in Ru-
3
0, Ru-45 and Ru-60 respectively in which the corresponding binding energy values of Ru 3d5/2
and Ru 3d3/2 are observed at 280.50 eV and 284.9 eV for Ru-30, 280.52 eV and 284.83 eV for
Ru-45 and 280.49 eV and 284.78 eV for Ru-60 respectively. It is also found that all these Ru 3d
peaks have two comparatively poor intense peaks at the binding energy values of 282.1 ± 0.02
eV for Ru 3d and of 286.06 ± 0.03 eV for Ru 3d which arise mainly from the passive oxide
5
/2
3/2
film formed on the metallic Ru surface as observed earlier because of its reactive nature in open
7
9-81
atmosphere.
Ru-30, Ru-45 and Ru-60 where a doublet due to spin orbit coupling that resulted two states as Ru
p3/2 and Ru 3p with a peak to peak separation of ~22.9 eV was observed. The positions of the
Figures 3E, 3F and 3G are the respective high resolution scans of Ru 3p state of
3
1/2
doublets were 461.90 eV and 484.81 eV for Ru-30, 461.88 eV and 484.85 eV for Ru-45 and
61.87 eV and 484.77 eV for Ru-60. Like Ru 3d, each Ru-3p states also have two less intense
4
peaks due to the passive oxide film were observed at 464.07 ± 0.03 eV, and at 486.64 ± 0.05eV.
All the observed binding energy values are nicely matching with the earlier reports of metallic
7
9–81
0
Ru in many forms.
From the XPS results, it is concluded that the formation of metallic Ru
nanomaterials was successful under the stated conditions. Survey scans are in agreement with the
EDS analyses (given in online SI section as Figures S3, (A-C) and proved that synthesized
0
unprotected Ru nano-chains are free from foreign stabilizers.
Mechanism for the Formation of Interconnected Ru Nano-chain Networks.
The probable formation mechanism of these interconnected Ru nano-chain networks is
proposed from the spectroscopic and microscopic studies carried out. The reaction happens here
is given below.

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3+
-
RuCl .xH 0
Ru + 3Cl ------------- (1)
3
2
+
-
4
NaBH4
Na + BH ------------- (2)
-
-
2
BH + 2H O
BO + 4[H] ------------ (3)
4
2
3+
0
+
Ru + 3[H]
Ru + 3H ------------- (4)
+
-
+
-
(
H O + BO
H BO3
H O + BO )
3
2
3
3
2
3
+
Thus the reduction of Ru was effected in aqueous medium. The last step given inside
the parenthesis is the formation of boric acid and the equilibrium between the boric acid and
borate oxyanion which is one of the conjugate base of boric acid. Depending on the pH of the
medium, the concentration of the boric acid and the borate oxyanion will vary. UV-Vis spectra
(Figure 1) of precursors and the reaction mixture at different stages revealed that the reduction of
3
+
0
Ru to Ru was so fast when it is done in high temperature (60 °C) compared to 30 °C and 45
C. Moreover, the HR-TEM analyses revealed the interconnected nano-chain networks
°
morphology for Ru-30, Ru-45 and Ru-60. But the actual difference among them was in the
density (density in the sense how much closer the individual chains are in the network structures)
and in the average diameter of the interconnected chains. When the synthesis was carried out at
3
0 °C, the rate of evolution of hydrogen was relatively slower which allowed the nucleation and
growth to proceed for a longer time thereby resulting in larger individual particles (3.5 ± 0.5 nm)
and the formed particles had grown along their own preferred direction and got fused with the
adjacent particles that ultimately resulted in chains. These chains had further undergone cross
fusion with other chains in the vicinity and hence created denser network like structures. Curve c
2
+
of Figure 1 shows that for complete reduction of the intermediate Ru ions took a longer time of
3
0 min by borohydride. The same was witnessed by visual observation also. The initial pale
2
+
brown color of the Ru ions in solutions changed to dark brown after 30 min. This was the main
factor for forming larger particles and more interconnections within the network structure.
2
+
Besides, when the reaction was carried out at a 45 °C, the initial reduction product (Ru ) took

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0
nearly 17 min for the complete reduction to Ru (curve e, Figure 1). The average chain diameter
of the networks formed at 45 °C is 3.0 ± 0.2 nm which is relatively less than that of Ru-30. This
indicates that relatively faster reduction at 45 °C decreases growth of the particles by not
providing sufficient time. However, the density of the network structure looks almost similar.
This tells us that though the average diameter of the ultimate chain structures is less than Ru-30,
the time of 17 min is still more than sufficient for cross fusion that resulted in interconnected
nano-chain networks as denser as Ru-30. On the other hand, when the same reaction was carried
3
+
0
out at the temperature of 60 °C, the reduction Ru to Ru was completed within a short time (5
min). The corresponding absorption curves are shown in curve f and g in Figure 1. Curve f in
Figure 1 is the absorption spectrum of the reaction mixture (carried at 60 °C) obtained
immediately after the addition of borohydride where there was no / a weak peak characteristic to
2
+
3+
0
the intermediate Ru ions was observed. This indicated the immediate reduction of Ru to Ru
at higher temperature. Curve g is the absorption spectrum of the same reaction mixture 5 min
after the reduction borohydride which in turn clearly supports fact of immediate reduction of
3
+
2+
Ru and the non-existence of Ru for a long period of time unlike the ones observed in the
previous cases. These observations leads to the fact for the formation of interconnected nano-
0
chain networks of unprotected Ru particles with the smaller average diameter (2.6 ± 0.2 nm)
and lesser interconnections across individual chains of the network structure requires high
temperature to initiate and complete the reaction in a shorter time. Further, reason for the smaller
average chain diameter and less number of interconnections among the chains might be due to
the rapid reduction caused by the rapid evolution of hydrogen gas. As the reduction was so fast
2
+
and there was no chance for the existence of intermediate Ru ions for a significant period of
time in the reaction mixture to assist the further growth of the individual particles, the reaction
terminates with the smaller particles and had less number of interconnections than Ru-30 and
Ru-45. These observations clearly tell us that temperature is the main factor that took control
over average diameter and nature of the network structure.
To confirm that the observed morphology is the actual morphology in its native state too,
laser diffraction particle sizing (LDPS) technique was used. This is the technique which
measures the average size of the particles in its native state. In our case, it is not just the particle
but it is interconnected nano-chain network. The measured average particle diameter for Ru-30,
Ru-45 and Ru-60 are 721 nm, 708 nm and 632 nm respectively (Figure S4, A-C). This clearly

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indicates that in solution, Ru is not present just like a particle whereas it has the same
morphology what had been observed through TEM analysis. Moreover, it reveals that the
observed morphology is not just due to the evaporation phenomena on TEM grid. If it is present
as large particles with the sizes measured through LDPS, the same size of particle could be
detected in TEM. However, it is not the case. Apart from this, we also believe that a larger
particle might not be transformed into an interconnected chain-like structure upon drying with an
average chain diameter of 2.5 to 3.5 nm. Hence, it is clear that the synthesized colloids have the
same morphology in its native states too.
0
Stability of Unprotected Ru Nano-chain Networks and Its Dependence on pH.
Stability of material prepared without any external stabilizing agents mainly depends on
other coexisting byproducts and residual ions along with it in solution. In reaction mechanism
section above, we proposed that boric acid and its conjugate base will be in equilibrium which
+
-
depends on pH of the solution. Besides, Na and Cl ions are also there. Hence we strongly
believe that these are the actual stabilizer that stabilizes them by electrostatic interactions.
3
2
Similar stabilization of Au NPs by these ions in solution was observed by Deraedt et al. where
they find an exceptional stabilizing activity of excess borohydride on Au NPs by forming the
hydridic bonds on the surface. As in our synthesis of Ru colloids, no external agent was added.
Hence, obviously the only thing that is stabilizing should be the excess borohydride. However,
borohydride is reactive and it won’t be in the solution after some time. Hence, in later time
-
-
electrostatic interactions between the Cl ions and B(OH ) ions adsorbed on the surface of Ru
4
+
NPs and the Na ions in the solution would stabilize the unprotected Ru nano-chains. The same
3
2
mechanism was proposed for the stabilization of Au NPs was proposed by Deraedt et al. The
proposed formation and stabilization mechanism are depicted as Scheme 2. Moreover, we also
believe that the formation of the interconnected chains can also be a significant factor in the
stabilizing action.
Apart from this, we have carried out a detailed study on the relation between the stability
and the final solution pH. From Table 1, it can be seen that the final solution pH varied
3
+
-
depending on the molar ratio of the reactants (Ru :BH ). The formed Ru colloidal solution is
4
stable only when the pH is 9.7 ± 0.2 which is of 1:1.5 ratio. With the molar ratio of 1:1 and 1.5:1,

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the resultant solution is neutral (7.0 ± 0.1) and slightly acidic (6.7 ± 0.07) respectively. Here the
stability is of considerable time and order of stability is Ru-60>Ru-45>Ru-30. With all other
molar ratio, the resultant solution is not as stable as the ones discussed above. The pH of those
solutions was either acidic or highly alkaline (see Table 1 for details). In these conditions,
temperature played a little role over the stability. In acidic and highly basic conditions, at low
temperature, precipitation was not effected quickly. This may be due to the slow reduction of
3
+
2+
2+
Ru and the existence of Ru in solution for a considerable time. When those Ru gets reduced
0
to Ru , precipitation occurred immediately. To check the role of pH, we had taken 3 mL of Ru-
3
0, Ru-45 and Ru-60 prepared using the ratio of 1:1.5 separately and increased the pH gradually
by adding 1 M NaOH drop by drop and observed that when the pH reached 10.50, precipitation
began and on continued addition of NaOH, precipitation occurred with enhanced rate. Similarly,
we had reduced the pH of these stable colloids by adding 0.5 M H SO drop by drop and found
2
4
that when the pH reached 6.60 precipitation occurred and the rate was enhanced upon continued
addition. Hence, we concluded that the stability was mainly due to the byproducts and other
coexisting ions that provided appropriate electrostatic environment depending on the overall
solution pH and in our present case, the optimum pH is 9.7 ± 0.2.
Catalytic Nitroarenes Hydrogenation.
The detailed procedure of the catalytic reduction reactions of all the nitro compounds (4-
NP, 4-NA, 4-NS, 2-NP, 2-NA, 2-B-6-NT and NB) are already explained in the experimental
part. Nitroarenes hydrogenation is the conventional and most studied catalytic reaction using
4
0,53,59
zero valent metal NPs that includes both noble and non-noble metals.
Despite being a well-
studied and well documented reaction, nitroarenes hydrogenation by metal NPs continues to
draw greater attention when it is about enhancement in the catalytic activity. Hence, any attempt
to increase the catalytic rate and reducing the reaction time will be a fruitful outcome. In our case
0
we have comparatively examined the catalytic activity of our unprotected Ru catalysts (Ru-30,
Ru-45 and Ru-60). Though we tried all the above nitro compounds for their hydrogenation, only
the following five compounds viz., 4-NP, 4-NS, 4-NA, 2-NP and 2-NA are completely reduced
by Ru-30, Ru-45 and Ru-60. Interestingly, Ru-60 was able to hydrogenate 2-B-6-NT whereas
Ru-30 and Ru-45 were inactive. This is may be due to larger average diameter and denser
interconnected chains in Ru-30 and Ru-45 networks that restrict the coordination of 2-B-6-NT in

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a preferred direction to effect the hydrogenation whereas with Ru-60 this hindrance was
overcome by the smaller size and lesser interconnections. Besides the size and dense nature, we
2
+
also believe that the retention of considerable amount of Ru ions on Ru-30 and Ru-45 surfaces
may also be the key factor showing a significant reluctance in this reaction. Moreover, the same
may be the reason for having lower rate constant values in all the reaction relative to Ru-60.
However, the hydrogenation of 2-B-6-NT by Ru-60 was also not a complete one. Apart from
this, none of them catalyzed the reduction of NB hydrogenation. Here, the catalytic reduction
reaction of 4-NS is discussed in details and others are included in the SI section. For the
hydrogenation of 4-NS, the time dependent UV-Vis spectra and respective ln(conc) vs time plots
for Ru-30, Ru-45 and Ru-60 are given as Figures 4, A-F. It can be seen from the figures that, the
rate constant value is the highest for Ru-60 and also the time taken by Ru-60 is relatively less.
All the reactions followed first order kinetics with respect to the nitro arenes and the
-1
-1
-1
corresponding rate constant values for Ru-30, Ru-45 and Ru-60 are 4.00×10 min , 4.10 × 10
-1
-1
-1
min and 4.8×10 min respectively. This indicates that Ru-60 is more active than the other two.
Similarly, the time dependent UV-Vis spectra for other nitro compounds hydrogenations by Ru-
3
4
0, Ru-45 and Ru-60 are given in online SI section as Figures S5, A-M which is in the order of
-NP, 4-NA, 2-NP, 2-NA and 2-B-6-NT (only for Ru-60) respectively. The corresponding first
order plots for Ru-30, Ru-45 and Ru-60 are also provided in the same order in the online SI
section as Figures S5, N-Z. Moreover, for a comparative interpretation, the catalytic activity of
Ru-30, Ru-45 and Ru-60, C /C vs. Time (T) were plotted for each catalytic hydrogenation
t
0
reaction and given as Figure 5. From Figure 5, it is clear that the rate of disappearance of reactant
in all the catalytic hydrogenation reaction was faster for Ru-60 than Ru-30, Ru-45. Similarly, the
rate of disappearance of reactants with Ru-45 is almost parallel with Ru-30. Beyond the time of
the reaction, order and rate of the reaction, other quantitative parameters like conversion,
selectivity, yield, turnover number and turnover frequency for each reaction were also calculated
4
0,56,59,72-73
according to the literature reports
and the detailed calculations are provided in online
SI section. The results are provided as Table 2.
0
To find the superiority of our unprotected catalyst, we have prepared Ru nanomaterials
with three different surfactants such as cetyltrimethylammonium bromide (CTAB), sodium
dodecyl sulphate (SDS) and Trixon-100 (TX-100) which are cationic, anionic and neutral
0
surfactants respectively. Formation of Ru nanomaterials with these surfactants were primarily

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confirmed from their absorption spectra, TEM micrographs and their electron diffraction patterns
which are given as Figures S5, A-G in online SI section. We have chosen only the hydrogenation
of 4-NS and studied their catalytic activities under the same conditions. The resultant time-
dependent UV-Vis spectra and their corresponding kinetic plots are given as Figures S7, A-F in
0
online SI section. From this, it can easily be evidenced that unprotected Ru catalysts are better
than the ones capped by surfactants. Results of this comparative study are given in Table 2. We
have also compared our results with other reports where the same metallic Ru NPs in other forms
were used to hydrogenate nitroarenes are also compared and tabulated as Table S3 in online SI
section. The chosen works are the closely related to the catalytic studies of this report where we
found that our catalysts are comparatively better than others in terms of time and yield. However,
7
3
it was observed that the dendrimer encapsulated Ru NPs of less average individual particle size
than our catalysts showed slightly higher rate constant value than ours. The much higher k values
5
6
59
observed for Ru/rGO and Ru/CNF catalysts are due to different reaction conditions they
employed such as high pressure and temperature unlike us where we carried out our reaction at
room temperature. The catalytic performance of our catalysts with noble metal catalysts and
other non-ruthenium catalysts for 4-NP reduction was also compared and given as Table S4 in
online SI section. From these, we found that very few reports were reported with slightly higher
rate constant values than our catalysts. Hence, we strongly believe that the unprotected surfaces
of the Ru particles are the reason for the enhanced catalytic activity. The overall catalytic study
revealed that Ru-60 is relatively a more active catalyst than Ru-30 and Ru-45and all of them
were are significantly more active than Ru-TX-100, Ru-CTAB and Ru-SDS prepared under
similar conditions. Interestingly, when compared with other Ru catalyst for the same and similar
5
9,73
reactions, our catalysts were almost superior with few exceptional cases.
catalytic activity of Ru-30, Ru-45 and Ru-60 are depicted in Scheme 3.
The overall
Electrocatalytic Water Splitting.
Interesting results obtained in the catalytic hydrogenation of nitroarenes triggered us to
study the electrocatalytic performances of Ru-30, Ru-45 and Ru-60. Ru is one of the most
studied transition metal along with Ir for anodic water splitting. As the need for renewable
energy got much attention over the globe, the inevitability of producing H at cheaper cost has
2
becomes one of the essential things in energy sector. Ru and RuO are studied in many forms.
2

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8
2
Among them following are some important reports where Ru is used as a metal, as its oxide
8
3
69,70
71,84
(
RuO ), as its mononuclear/polynuclear complexes,
as bimetallic materials
and as metal
2
6
7
oxide composite materials.
Hence, it is essential to study the electrocatalytic activity of
unprotected Ru-30, Ru-45 and Ru-60 catalysts for OER. As described in the experimental
section, the electrocatalytic studies were carried out initially for Ru-30, Ru-45 and Ru-60 by
running a cyclic voltammogram at a sweep rate of 10 mV/s in 0.1 M NaOH. The resultant CV is
given as Figure S8 in online SI section. The drop due to uncompensated resistance (R ) was
u
corrected by carrying out electro impedance spectroscopic analysis the corresponding Nyquist
and Bode plots are given as Figures 6, A-B. From these Nyquist and Bode plots, the R value
u
2
found was about 22.36 Ohm/cm . From these figures, we can see that Ru-30, Ru-45 and Ru-60
2
required an overvoltage of 308 ± 2 mV to produce 10 mA/cm of OER current density. Unlike
catalysis results, almost similar electrocatalytic activity was observed for all the three catalysts. It
can be explained as follows, the catalytic property of any metallic catalyst is mainly dependent
on the atoms on the surface. In our case, Ru-30 and Ru-45 were found to be having considerable
2
+
Ru ions on their surfaces as evidenced by respective UV-Vis and XPS analyses whereas with
Ru-60, it is not the case. However, when it comes to electrocatalysis, especially when it is anodic
water splitting, the metal taken will undergo vigorous oxidation known as anodization. These
oxides are the actual catalysts that cause the water splitting. In our case all the Ru atoms was
oxidized to RuO that catalyzed the water splitting. This might be the reason for the similar
2
electrocatalytic activity. Hence, we chose Ru-60 and done further electrochemical analysis.
Figure 7A is the cyclic voltammogram (CV) of Ru-60 modified GC electrode with
uncompensated resistance (curve a) and iR free CV (curve b) ran at 10 mV/s in 0.1 M NaOH. It
2
can be seen that the benchmarking OER current density of 10 mA/cm is achieved at 1.538 V
(vs. RHE). Hence, the overvoltage is 308 mV which is significantly lower. Figure 7B is the
chronoamperometric curve of Ru-60 modified GC under the same experimental condition at 1.55
V and it is observed that the modified catalyst is stable for more than 10 h.
Like catalysis study, we also conducted similar comparative electrocatalytic study with
the Ru-CTAB, Ru-SDS and Ru-TX-100 adapting the same procedure. Figure 7C is the CV of
Ru-60, Ru-CTAB, Ru-SDS and Ru-TX-100 ran at 10 mV/s in 0.1 M NaOH where curve a is the
CV of Ru-60, curve b is of Ru-CTAB, curve c is of Ru-SDS and curve d is of Ru-TX-100. The
2
required over voltages for getting an anodic current density of 10 mA/cm by these surfactant

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0
stabilized Ru nanomaterials are 361 mV, 385 mV and 441 mV for Ru-CTAB, Ru-SDS and Ru-
0
TX-100. From this, unprotected Ru catalysts were found more reactive than the ones covered
with surfactants which in turn emphasize the significance of unprotected surfaces in
electrocatalysis. In all the cases backward sweep is taken for the calculation of overvoltage to
avoid any non-faradaic contribution to the total current and the same was extended for Tafel
analyses also. The corresponding steady state polarization curves for Ru-60, Ru-CTAB, Ru-SDS
and Ru-TX-100 are given together as Figure 7D from which the order of the Tafel slopes were
found to be 95 mV/dec for Ru-60, 215 mV/dec for Ru-CTAB, 202 mV/dec for SDS and 163
mV/dec for Ru-TX-100. This again implies that the kinetics is sluggish when the catalysts were
stabilized with surfactants. The comparative electrocatalytic OER results are tabulated as Table
3
. Though the chronoamperometric analysis showed the robustness of our catalyst, we carried
out post cyclic CV under the same condition again after a vigorous electrolysis for 10 h which is
given as Figure S8 in the online SI section. From Figure S9, a loss which was not beyond 0.05 V
in terms of overpotential was observed. It may be due to leaching of catalyst in alkaline solutions
which was observed earlier by others for Ru catalysts in OER where the leaching product was
85,86
the volatile RuO4.
Moreover, the stability of the Ru-60 modified GC was examined by a
potential sweeping between the same potential window at a scan rate of 10 mV/s. The reultant
voltammograms are given together as Figure 8 from which a stedy decrease in the oveerall
activity as well as a stedy increae in the overpotential can be obsereved and the increase in the
overpotential is not more than 0.05 V. Both constant potential electrolysis and potential
sweeping caused the similar change in the electrocatalytic activity of the Ru-60 modified GC and
imply its robutness under these harsh conditionns.
Besides, determination of real surface area or the electrochemical surface area (ECSA) of
the working electrode is an important parameter in an electrocatalytic reaction which will
provide quantitative information about the electrocatalytic processes. In our case, we have
determined the ECSA from the double layer capacitance (C ) of the Ru-60 modified GC
DL
8
7,88
electrode as done by others.
non-faradaic region from the CV curves ran at different scan rates such as 1 mV/sec, 5 mV/sec,
0 mV/sec, 30 mV/sec, 50 mV/sec, 70 mV/sec, 100 mV/sec, 150 mV/sec, 200 mV/sec, 240
The double layer charging currents (i ) were measured in the
c
1
mV/sec, 300 mV/sec, 500 mV/sec and 800 mV/sec in the same potential window. The resultant
CVs are given together as Figure 9. The double layer charging current was increased as expected

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due to the gradual increase in the scan rates. The relationship between double layer charging
current (i ) and the scan rate ( is given in equation (3).
c
ic = CDL
(3)
Hence, the plot of double layer charging currents (i ) against the scan rates yielded straight lines
c
the slope of which is a direct measure of the double layer capacitance of the electrode as seen in
Figure 10. The relationship between the ECSA and the double layer capacitance (C )is given in
DL
equation (4).
ECSA = C /C
(4)
DL
s
Where, C is the specific capacitance of RuO .The detailed study on the specific capacitance of
s
2
RuO was carried out by many under identical experimental conditions both in alkaline and
2
acidic media. Typically in alkaline medium RuO is reported to have the specific capacitance
2
2
2 89–95
that vary from 0.013 mF/cm to 0.019 mF/cm .
In our calculation we have used the specific
2
capacitance (C ) value of 0.015 mF/cm . Detailed calculation is provided in the online SI section.
s
The real or the electrochemical chemical surface area (ECSA) determined through this method
2
for Ru-60 modified GC electrode was 99.2 cm . Based on the ECSA, the specific activity of our
-2
material is found to be 0.1008 mAcm
(see SI section for detailed calculation). The
ECSA
8
2
observed value is is higher than the report of Lee et al. and comparable to the report of
9
6
McCrory et al. where they have taken the measured current density at 1.59 V vs RHE, whereas,
we have taken at 1.54 V vs RHE. The turnover frequency (TOF) of our catalyst was calculated
by assuming Ru monolayer formation upon modifying GC with Ru-60, as we and others reported
9
7-98
earlier for other similar noble metal electrocatalysis.
The number of Ru atoms on Ru
9
9
monolayer was taken from the report of Brongersma et al. (pp-217-218). Detailed TOF
-1
calculation is given in online SI section. The calculated TOF value is 4.72 s . The overall
electrocatalytic study revealed that Ru-30, Ru-45 and Ru-60 had similar electrocatalytic activity
in alkaline water splitting (OER) which required an overvoltage of 308 ± 2 mV to generate 10
2
2
mA/cm of OER current density with an ECSA value of 99.2 cm . However, the electrocatalytic
study had also revealed the advantage of having unprotected Ru catalyst form its lower
2
overvoltage (308 ± 2 mV) required to generate a current density of 10 mA/cm and with a
-1
67,69-71,82-84
significant TOF value of 4.72 s .While comparing our results with the other reports
where Ru was used in many forms, it can be concluded here that the unprotected Ru surfaces

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2
showed good activity in terms of lower oxygen overpotential (10 mA/cm OER current density at
2
-1
3
08 ± 2 mV), loading (0.205 mg/cm ) and the TOF value (4.72 s ). Although our catalysts have
shown better electrocatalytic activity, there are reports with comparable activity in terms of
8
2,84,96
overpotential and specific activities.
Moreover, it should not be forgotten that though the
0
synthesized material remains as Ru in solution when it is exposed to atmosphere the surface gets
oxidized to some of its oxides RuO and upon anodizing which are the actual catalysts that do
x
0
water splitting. However, in case of surfactants protected Ru nanomaterials such kind of
oxidation likely to be harder at lower over potential regions which may render down their
electrocatalytic activity.
Conclusion.
In summary, three different interconnected, unprotected Ru NPs as nano-chain networks
were prepared by a simple wet chemical reduction route using borohydride without any external
stabilizer at three different temperatures viz., 30 °C, 45 °C and 60 °C. The optimum molar ratio
3
+
-
between Ru and BH4 and the pH for getting stable colloids are 1:1.5 and 9.7 ± 0.2.
Temperature was increased systematically to vary the average chain diameter as 3.5 ± 0.5 nm,
3
.0 ± 0.2 nm and 2.6 ± 0.2 nm for Ru-30, Ru-45 and Ru-60 respectively. Comparative and
systematic studies on catalytic nitroarenes hydrogenation and electrocatalytic water splitting in
0
alkaline solution were done and found that unprotected Ru catalysts are better catalysts than the
ones stabilized by surfactants in both catalysis and electrocatalysis. Among Ru-30, Ru-45 and
Ru-60, significant difference in the catalytic behavior was noticed which was attributed mainly
2
+
due to the presence of Ru ions on the surface of Ru-30 and Ru-45.In all the reactions, Ru-60
was found to be more active. Interestingly, all of them were found to show supreme catalytic
activity over other Ru catalysts in many forms with solid supports for the same and similar
reactions with few exceptions. The highest first order rate constants for Ru-30, Ru-45 and Ru-60
-1
-1
-1
-1
-1
-1
were found to be 4.0 × 10 min , 4.1 × 10 min and 4.8 × 10 min respectively. The
0
unprotected Ru nano-chain networks were found to be superior with noble metal catalysts in
terms of catalytic activity. Electrocatalytic anodic water splitting was catalyzed by all of them
with almost similar efficiency. The required overvoltage for generating the OER current density
2
of 10 mA/cm was just 308 ± 2 mV which is better than many other reported values for Ru
2
-1
catalysts. The ECSA was determined to be 99.2 cm and the TOF was 4.72 s . The specific

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-2
activity is as good as very few earlier reports which is 0.1008 mAcm ECSA. As a consequence of
0
unprotected Ru nano-chain networks, superior catalytic activity and good performance in
electrocatalytic water splitting were achieved. In future, the same protocol can be extended to
prepare many other metal nanomaterials with unprotected surfaces for better catalytic and
electrocatalytic performances without contaminating the system by the use of any foreign
stabilizing agents such as stabilizers, surfactants, supports, scaffolds and templates.
Online Supporting Inormation (SI) Available.
Information on reagents, instrumentation and analytical techniques employed are
elaborated. Detailed calculation of conversion, selectivity, yield, TON, TOF and the rate
constants for catalytic nitroarenes hydrogenation is given. TOF calculation for the
electrocatalytic water splitting is explained. Calibration curves for finding the real concentrations
of the nitro compounds as Figures S1, A-F and the corresponding concentration are provided as
Table S1. Details on the construction of calibration curves are given. XRD and EDS spectra are
given as Figures S2 and S3, A-C. The detailed concentration of nitroarenes taken for catalytic
study and other reaction parameters are tabulated as Table S2. The comparative interpretation for
0
the catalytic activity of unprotected Ru nano-chain networks with the Ru catalysts in other
forms and noble metal catalysts are provided as Table S3 and Table S4. The LDPS particle size
distribution is provided as Figure S4, A-C. The time dependent UV-Vis spectra and the
corresponding first order kinetic plots for all other nitroarenes except 4-NS are provided as
Figures S5, A-M and Figures S5, N-Z. UV-Vis spectra, TEM micrographs and electron
diffraction patterns of Ru-CTAB, Ru-SDS and Ru-TX-100 are provided as Figures S6, A-I. The
time-dependent UV-Vis spectra for the hydrogenation of 4-NS by Ru-CTAB, Ru-SDS and Ru-
TX-100 and their corresponding ln(conc.) vs time plots are given as Figures S7, A-F. CV of Ru-
3
0, Ru-45 and Ru-60 are given together as Figure S8. Post cycle CV for Ru-60 after 10 h of
chronoamperometric analysis is given as Figure S9. CV of Ru-60 modified GC with the -1 to 1 V
of potential window for identifying non-faradaic region is given as Figure S10. This material is
available free of charge via the Internet at http://pubs.rsc.org.
Acknowledgements: We wish to acknowledge Dr. Vijayamohanan K. Pillai, Director CSIR-
CECRI for his continuous support and encouragement. S. Anantharaj wishes to acknowledge

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DOI: 10.1039/C5SC04714E
council of scientific and industrial research (CSIR) for JRF fellowship. Authors wish to thank
Dr. B. Subramaniam, Sr. Scientist, ECMS division for his extended help in allowing
electrochemical studies, Dr. P. E. Karthik, EEC division, discussion related to OER study and
support from the Central Instrumental Facility (CIF), help from Mr. A. Rathishkumar (TEM in-
charge, CIF) are greatly acknowledged.
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Figure Captions:
3
+
Figure 1: UV-Visible (UV-Vis) absorption spectra of Ru solution and the reaction mixtures for
0
the formation Interconnected unprotected Ru nano-chain networks.
Figure 2: (A-I) TEM, HR-TEM micrographs and SAED patterns of the interconnected
0
unprotected Ru nano-chain networks. Figure 2, A-C are of Ru-30, D-F are of Ru-45 and G-I are
of Ru-60 respectively.
Figure 3: X-ray photoelectron spectroscopic (XPS) analysis of interconnected, unprotected Ru
nano-chain networks:(A) is the survey spectra of Ru-30, Ru-45 and Ru-60; (B-D) are the high
resolution 3d scans of Ru-30, Ru-45 and Ru-60 respectively; (E-G) are the high resolution Ru 3p
scans of Ru-30, Ru-45 and Ru-60 respectively.
Figure 4: (A) is the time dependent UV-Vis absorption spectra of the catalytic hydrogenation of
4
-NS by Ru-30; (C) is the time dependent UV-Vis absorption spectra of the catalytic
hydrogenation of 4-NS by Ru-45; (E) is the time dependent UV-Vis absorption spectra of the
catalytic hydrogenation of 4-NS by Ru-60; (B), (D) and (F) are the corresponding first order
plots.
Figure 5: C /C vs. Time plot of all the catalytic hydrogenation reactions studie by Ru-30, Ru-45
t
0
and Ru-60. Note: In all the cases the rate of disappearance of reactant when catalysed by Ru-60
is comparatively higher than Ru-30, Ru-45.
Figure 6: (A)and (B) are the Nyquist Bode impedance plots for the electrochemical system
under study for finding Ru.
Figure 7: (A) Cyclic voltammogram (CV) of electrocatalytic water splitting by Ru-60 modified
GC electrode where curve a is the CV of the same with uncompensated resistance (R ), curve b
u
is the CV of the same with iR drop correction. (B) is chronoamperometric i-t profile for the same
Ru-60 modified GC electrode. (C) Cyclic voltammogram (CV) of electrocatalytic water splitting
by Ru-60, Ru-CTAB, Ru-SDS and Ru-TX-100 modified GC electrodes respectively. (D) is the
corresponding steady state polarization curves.