Regulative Electronic States around Ruthenium/Ruthenium Disulphide Heterointerfaces for Efficient Water Splitting in Acidic Media

Article abstract of DOI:10.1002/anie.202101539

Theoretical calculations unveil the charge redistribution over abundant interfaces and the enhanced electronic states of Ru/RuS₂ heterostructure. The resulting surface electron-deficient Ru sites display optimized adsorption behavior toward diverse reaction intermediates, thereby reducing the thermodynamic energy barriers. Experimentally, for the first time the laminar Ru/RuS₂ heterostructure is rationally engineered by virtue of the synchronous reduction and sulfurization under eutectic salt system. Impressively, it exhibits extremely high catalytic activity for both OER (201 mV @ 10 mA cm^?2) and HER (45 mV @ 10 mA cm^?2) in acidic media due to favorable kinetics and excellent specific activity, consequently leading to a terrific performance in acidic overall water splitting devices (1.501 V @ 10 mA cm^?2). The in-depth insight into the internal activity origin of interfacial effect could offer precise guidance for the rational establishment of hybrid interfaces.

Full text of DOI:10.1002/anie.202101539

Angewandte
Communications
Chemie
How to cite:
International Edition: doi.org/10.1002/anie.202101539
German Edition: doi.org/10.1002/ange.202101539
Water Splitting Very Important Paper
Regulative Electronic States around Ruthenium/Ruthenium
Disulphide Heterointerfaces for Efficient Water Splitting in Acidic
Media
Jiawei Zhu, Yao Guo, Fang Liu, Hanwen Xu, Lei Gong, Wenjie Shi, Ding Chen, Pengyan Wang,
Yue Yang, Chengtian Zhang, Jinsong Wu, Jiahuan Luo, and Shichun Mu*
Abstract: Theoretical calculations unveil the charge redistrib-
ution over abundant interfaces and the enhanced electronic
states of Ru/RuS2 heterostructure. The resulting surface
electron-deficient Ru sites display optimized adsorption behav-
ior toward diverse reaction intermediates, thereby reducing the
thermodynamic energy barriers. Experimentally, for the first
time the laminar Ru/RuS2 heterostructure is rationally engi-
neered by virtue of the synchronous reduction and sulfuriza-
tion under eutectic salt system. Impressively, it exhibits
extremely high catalytic activity for both OER (201 mV @
10 mAcmꢀ2) and HER (45 mV @ 10 mAcmꢀ2) in acidic media
due to favorable kinetics and excellent specific activity,
consequently leading to a terrific performance in acidic overall
water splitting devices (1.501 V @ 10 mAcmꢀ2). The in-depth
insight into the internal activity origin of interfacial effect could
offer precise guidance for the rational establishment of hybrid
interfaces.
conduction, fewer side effects and convenient gas separa-
tion.[2b,3] However, both electrodes of PEM-water splitting
(PEMWS) devices require certain electrocatalysts to effec-
tively facilitate the sluggish kinetic processes.[1a,4] Metal-based
nanocatalysts have been extensively developed to hasten their
anodic oxygen evolution (OER) and cathodic hydrogen
evolution reaction (HER).[5] Nevertheless, extreme acidity
in PEMWS is liable to cause the dissolution and degradation
of metal-based active centers, thereby resulting in inferior
activity and durability.[5a,6] Hitherto, precious metal-based
materials (Pt/C, IrO2 and RuO2) are still the benchmark
electrocatalysts due to their satisfying activity.[7] However, the
required mismatched operating environment of these sepa-
rate monofunctional catalysts in integrated PEMWS electro-
lyzer hinders their practical implementation.[8] Thus, highly
active and stable bifunctional electrocatalysts in acidic media
need to be rationally designed.
Relative to other noble metals, ruthenium (Ru) catches
more attention in electrocatalysis, because of its extremely
high cost performance, appropriate binding energy with
reactive intermediates, ultra-strong thermostability and
resistance to corrosive electrolyte.[9] Its oxide (RuO2) is
widely regarded as an efficient commercial catalyst for OER.
But the oxidation behavior at high voltage would cause
devitalization, and the effusion of lattice oxygen would result
in the dissolution of active species, rendering them unstable
during OER process.[10] Thus, designing oxygen-free Ru-
based catalysts with suitable morphology and electron
structure might alleviate the deactivation behavior, mean-
while promote their intrinsic activity and durability.[3,11]
Interface engineering is an effective strategy to improve
the electrocatalytic activity of hybrid nanomaterials by means
of the synergistic effect of double or even multiple active
sites.[12] Different active components might be favorable for
different stepwise reactions, while judiciously adjusted heter-
ostructure enables these separate processes to happen over
different sites at close quarters, thereby accelerating the
kinetics of overall reaction.[13] Furthermore, such coupling can
effectively modulate the electronic state of electrocatalysts.[14]
For example, benefited by the Mott-Schottky effect on the
strong coupled interface, the interfacial electronic structure of
Janus metal/semiconductor nanomaterials would be rear-
ranged. The multielectron transfer during electrocatalytic
reactions can be implemented rapidly over the interface,
resulting in promoted intrinsic activity.[15] However, the
interfacial effect of Ru-based electrocatalysts has rarely
been reported, primarily because of the difficulty in obtaining
H
ydrogen energy, as a significant secondary energy source,
attracts tremendous attention due to its cleanliness, affluence
and sustainability.[1] As for the hydrogen production, the
acidic water splitting devices employing mature proton
exchange membrane (PEM) technology afford excellent
hardware environment for large-scale commercial applica-
tions.[1a,2] The use of PEM and favorable reaction mechanism
bring multiple strengths, such as cost advantage, high proton
[*] J. Zhu, F. Liu, H. Xu, L. Gong, W. Shi, D. Chen, P. Wang, Y. Yang,
C. Zhang, Prof. J. Wu, Prof. S. Mu
State Key Laboratory of Advanced Technology for Materials Synthesis
and Processing, Wuhan University of Technology
Wuhan 430070 (P. R. China)
E-mail: msc@whut.edu.cn
J. Zhu, Prof. S. Mu
Foshan Xianhu Laboratory of the Advanced Energy Science and
Technology Guangdong Laboratory, Xianhu Hydrogen Valley
Foshan 528200 (P. R. China)
Dr. Y. Guo, Dr. J. Luo
Department of Chemical and Environmental Engineering
Anyang Institute of Technology
Anyang 455000 (P. R. China)
F. Liu, Prof. J. Wu
NRC (Nanostructure Research Centre)
Wuhan University of Technology
Wuhan 430070 (P. R. China)
Supporting information and the ORCID identification number(s) for
the author(s) of this article can be found under:
https://doi.org/10.1002/anie.202101539.
Angew. Chem. Int. Ed. 2021, 60, 1 – 8
ꢀ 2021 Wiley-VCH GmbH
1
These are not the final page numbers!

Angewandte
Communications
Chemie
appropriate heterostructures with the conventional high-flux
heteroatom sources.
the improved electronic transmission capability of hetero-
structures in electrocatalytic reactions (Figure 1b).[16] To
disclose the superiority of electronic structure in heterostruc-
ture, charge density of two compound models was analyzed
with visualized two-dimensional slices (Figure 1c and S3). It
reveals that upon constructing the heterointerface, the charge
density can be redistributed, leading to the electron transfer
from Ru atoms to S atoms. These surface electron-deficient
Ru sites might serve as the active centers for the appropriate
adsorption behavior of various reaction intermediates.[17]
On basis of this, the adsorption energy of key intermedi-
ates in OER (OH*, O* and OOH*) was calculated, and the
relevant adsorption structure is shown in Figure S4. The
Gibbs free energy diagrams exhibit that the rate-determining
steps for these four models are all the formation of OOH*
from O* (Figure 1d and S5). Comparatively speaking,
benefiting from the strong adsorption of O* upon the surface
electron-deficient Ru sites of heterostructures, the theoretical
overpotentials of Ru-RuS2 (0.49 V) and RuS2-Ru (0.66 V) are
much lower than those of Ru (0.78 V) and RuS2 (0.94 V),
demonstrating the more favorable OER kinetics on hetero-
structures. As for HER, the hydrogen adsorption free energy
(DGH*) was calculated in the similar way (Figure S6). As
shown in Figure 1e, the adsorption of H* over heterointer-
faces can be also optimized, making the DGH* values of Ru-
RuS2 (0.26 eV) and RuS2-Ru (ꢀ0.37 eV) closer to ideal 0 eV,
as compared to pure Ru (ꢀ0.50 eV) and RuS2 (0.61 eV). This
suggests the superior HER performance on heterointerfaces.
In brief, the construction of heterostructures can cause the
charge density redistribution upon the interfaces and improve
the inner electron conduction. The surface electron-deficient
Ru atoms of such heterostructures, as the potential active sites
for electrocatalytic reactions, are expected to regulate the
adsorption behavior of key intermediates, thereby reducing
the reaction energy barrier.
Herein, we systematically investigate the regulative
electronic states, activity origin and practical catalytic perfor-
mance of ruthenium/ruthenium disulphide heterostructure
(Ru/RuS2) for the first time. The density functional theory
(DFT) calculations first reveal the superiority and activity
origin of the Ru/RuS2 heterostructures. Such heterostructures
can possess higher electronic conductivity due to larger
density of state at the Fermi level. The charge density around
the heterointerface would be rearranged, sequentially regu-
lating the adsorption behavior of key intermediates. In
consequence, the thermodynamic energy barriers of such
heterostructures are reduced, leading to the high theoretical
activity toward acidic water electrolysis. Importantly, the thin
Ru/RuS2 nanosheet heterostructure (Ru/RuS2-2) is con-
structed through a well-designed isochronous reduction-
sulphuration strategy. As expected, such material displays
excellent electrocatalytic performance in acidic media. When
employed as OER catalyst, Ru/RuS2-2 displays ultralow
overpotential, favorable kinetics, superb intrinsic activity and
excellent long-term stability. Besides, it also exhibits great
acidic HER performance. Encouraged by this, to demonstrate
the practical water splitting capability of this catalyst, the
acidic electrolytic device is assembled with Ru/RuS2-2
heterostructure material as bifunctional catalyst for both
electrodes.
To deeply understand the activity origin and reaction
mechanism, DFT calculations were first conducted. The
heterostructure models (Ru-RuS2 and RuS2-Ru) were pro-
posed based on the Ru (101) and RuS2 (200) planes, as shown
in Figure S1. From the calculated band structures, the
introduction of strong metallic Ru would bring absolute
metallicity to the heterostructures, independent of the RuS2
with a tiny band gap (Figure S2). We further compared the
partial density of states (PDOS) of surface Ru atoms in these
models. Interestingly, the Ru atoms in Ru-RuS2 and RuS2-Ru
display higher density states across the Fermi level, suggesting
To experimentally verify the interfacial effect of Ru/RuS2
on the electrochemical activity, an elaborated strategy was
designed, as shown in Figure 2a. Eutectic salt system
Figure 1. a) Diagram of Ru-RuS2 heterostructure for OER and HER pathways; b) partial density of states (PDOS) of surface Ru sites on as-built
models; c) charge density difference of two-dimensional slice on RuS2-Ru model; Gibbs free energy diagrams of Ru, RuS2, Ru-RuS2 and RuS2-Ru
models for d) OER and e) HER.
2
www.angewandte.org
ꢀ 2021 Wiley-VCH GmbH
Angew. Chem. Int. Ed. 2021, 60, 1 – 8
These are not the final page numbers!

Angewandte
Communications
Chemie
pure metallic Ru can be obtained (labelled as Ru-1).
Reversely, phase-pure RuS2 (labelled as RuS2-8) can be
prepared if the excess dosage is used (nK S :nRuO = 8), result-
2
2
ing from the dominating sulphuration. Predictably, the crucial
Ru/RuS2-2 and Ru/RuS2-4 heterostructures can be synthe-
sized with moderate proportion.
X-ray photoelectron spectroscopy was employed to reveal
the elemental compositions and chemical states. Take the vital
Ru/RuS2-2 as an example, the survey spectrum exhibits that it
is composed of Ru, S and O elements, and the atomic ratio of
Ru:S is about 1.13:1 (Figure S8). Thereout, we can roughly
infer that the approximate phase percentage of Ru:RuS2 is
55.7%:44.3%. From the deconvoluted spectrum of Ru 3p
state, the couple peaks at 462.1 and 484.3 eV are associated
with Ru 3p3/2 and Ru 3p1/2, respectively (Figure 2c).[3,18]
Figure 2d shows that the separate subpeaks at 163.0 and
164.2 eV are consistent with S 2p3/2 and S 2p1/2 states,
respectively.[19] To compare the chemical states of hetero-
structure material with phase-pure materials, further XPS
analyses were conducted. As shown in Figure S9, relative to
the pure Ru-1 and RuS2-8, the positive shift of Ru 3p states in
Ru/RuS2-2 can be observed, indicating the slight electron loss
and valence ascension of ruthenium atoms once the hetero-
interface is constructed, in consistence with the DFT pre-
diction.[18,20]
The morphology of the vital Ru-RuS2-2 heterostructure
was first investigated by high resolution transmission electron
microscopy (HRTEM), as shown in Figure 2e. Such material
consists of plentiful stacked thin nanosheets with the plane
dimension of about 40–60 nm. Spherical aberration-corrected
scanning transmission electron microscopy (ac-STEM) image
displays the abundant heterointerfaces between Ru and RuS2
(Figure 2 f, enlarged image shown in Figure S10). In the
upper-left corner, the Ru atoms are arranged within the
hexagonal close packed (hcp) structure, well consistent with
the XRD results. A lattice spacing of 0.202 nm could be
indexed to the (101) crystal face of Ru (Figure S11). Besides,
at the bottom and top-right corner, the legible lattice fringes
of 0.283 nm and 0.325 nm can be observed, corresponding to
the (200) and (111) lattice planes of RuS2. Thus, the copious
Ru/RuS2 heterointerfaces can be formed between the over-
lapped regions, which are further confirmed by more STEM
images (Figure S12). High-angle annular dark-field scanning
transmission electron microscopy (HAADF-STEM) image
and its relevant energy-dispersive spectroscopy (EDX) ele-
mental mapping images manifest that the Ru and S elements
are evenly distributed across the whole regions (Figure 2g–
i and S13). Based on the above results, it could be concluded
that the Ru/RuS2 heterostructure was successfully con-
structed.
Figure 2. a) Preparation method of Ru/RuS2 heterostructure; b) XRD
patterns of synthesized materials; c) Ru 3p and d) S 2p fitting results
of Ru/RuS2-2; e) HRTEM image, f) ac-STEM image and g–i) EDX
elemental mappings of Ru/RuS2-2.
(LiCl:KCl = 45:55 wt%, Tm.p. = 3528C) served as the marvel-
ous high-temperature liquid-phase reaction medium, where
the ruthenium oxide (RuO2) and potassium sulfide (K2S)
were chosen as Ru and S source, respectively. These
ingredients were drastically mingled under inert atmosphere
and then transferred into a corundum crucible, followed by
the heat treatment at 8008C for 2 h. After furnace cooling, the
hydrosoluble molten salts and residuals were totally removed
with ultrapure water. The final products were collected by
vacuum filtration and desiccation.
Notably, owing to the dual effect of reducibility and
sulfidation for K2S, products with different phase composi-
tions can be acquired as the K2S/RuO2 ratio changes. As
shown in the X-Ray diffraction (XRD) patterns (Figure 2b),
the 2-theta peaks at 38.48, 42.28, 44.08, 58.38, 69.48, 78.48 are
attributed to (100), (002), (101), (102), (110), (103) crystal
planes of hexagonal Ru (PDF#89-4903), respectively. Besides,
other peaks at 27.58, 31.98, 35.88, 39.38, 45.78, 54.28, 56.88,
59.48, 61.88, 66.68, 73.58, 75.88 and 78.08 are indexed to (111),
(200), (210), (211), (220), (311), (222), (023), (321), (400),
(331), (024) and (421) crystal faces of cubic RuS2 (PDF#73-
1677), respectively. When the dosage of K2S is relatively low
(nK S :nRuO = 1), the reducibility prevails so that almost phase-
The practical electrochemical OER performance of these
as-prepared materials in acidic media was then tested. The
representative iR-compensated polarization curves show that
the heterostructural Ru/RuS2-2 with optimal phase constitu-
tion possesses the best catalytic activity in acidic media, as
compared with other contrast samples (Figure 3a). Specifi-
cally, to deliver the current density of 10 mAcmꢀ2, Ru/RuS2-2
merely needs an overpotential of 201 mV, which is much
superior to that of commercial RuO2 catalyst. The over-
2
2
Angew. Chem. Int. Ed. 2021, 60, 1 – 8
ꢀ 2021 Wiley-VCH GmbH
www.angewandte.org
3
These are not the final page numbers!

Angewandte
Communications
Chemie
normalized LSV curves were employed to estimate the
intrinsic activity. Figure S16 demonstrates that Ru/RuS2-2
still possesses the most outstanding OER performance with
the least overpotential of 270 mV at 0.02 mAcmꢀ2
.
ECSA
Besides, Ru/RuS2-2 has the highest turnover frequency
(TOF) per active site (0.61 sꢀ1 at an OER overpotential of
350 mV) among these samples (Figure S17). And the amount
of evolved oxygen is close to the theoretical value on the Ru/
RuS2-2 electrode, suggesting a high faraday efficiency of
nearly 100% (Figure S18). These results illustrate that Ru/
RuS2-2 owns not only the maximum active sites, but also the
highest intrinsic activity for every single site, thereby resulting
in the supreme OER performance. Another proof for the
improved electrochemical kinetics is the electrochemical
impedance spectroscopy (EIS), as conducted in Figure 3e.
The extracted charge transfer resistance (Rct) of Ru/RuS2-2 is
distinctly lower than other contrast samples, implying the
ultrafast electron transfer contributed by the interfacial
charge redistribution. All these suggest that the construction
of heterointerface with appropriate phase constitution might
cause the electronic interaction effect upon the interface,
thereby improving the OER kinetics. To be specific, benefited
by the interface electronic transmission, the amount and the
specific activity of active sites can be elevated simultaneously,
and the promotion of conductivity might be favorable for the
fast electron transfer process during the OER reaction.[12a,21]
The durability of Ru/RuS2-2 was evaluated by CV cycles
and chronoamperometry. Figure 3 f shows that there is only
a negligible activity decay after 3000 CV cycles on Ru/RuS2-2
electrode. And the inset illustrates that the Ru/RuS2-2 can
achieve a steady current output at 10 mAcmꢀ2 for 24 h. The
excellent long-term stability of Ru/RuS2-2 can be put down to
the meliority of novel hybrid construction. After long-term
test, the sample was collected, and its morphology as well as
structural composition was further analyzed. HRTEM images
show that Ru/RuS2-2 retains its laminated structure and
ample heterointerfaces, with the lattice fringes corresponding
to Ru (101) and RuS2 (210) found in Figure S19. As shown in
Figure S20, further XRD analysis also validates the main-
tained phase composition. XPS was utilized to understand the
change of elemental chemical states. The tiny rise of O 1s
peak after OER test might be originated from the slight
surface oxidation, which is also verified by the emergence of
S–O groups in S 2p spectrum (Figure S21 and S22).[18]
Moreover, compared with the pristine one, the Ru 3p states
in Ru/RuS2-2 after OER test present positive shifts because of
valence ascension of Ru atoms (Figure S23).[20] However,
such phenomenon in Ru/RuS2-2 heterostructures is unworthy
of being mentioned, as compared with the strong oxidation
(Ru4+ to Ru8+) in commercial RuO2 catalyst during OER
reaction.[10b,22] These indicate that the Ru/RuS2-2 heterostruc-
ture owns terrific OER stability.
Figure 3. OER performance in acidic media. a) LSV curves with iR
correction, b) corresponding overpotentials and c) Tafel plots of Ru-1,
Ru/RuS2-2, Ru/RuS2-4, RuS2-8 and commercial RuO2 catalysts;
d) double-layer capacitances (Cdl) and e) electrochemical impedance
spectroscopy (EIS) of Ru-1, Ru/RuS2-2, Ru/RuS2-4 and RuS2-8; f) LSV
curves before and after 3000 cycles and inserted i-t chronoamperomet-
ric response of Ru/RuS2-2.
potential advantage of Ru/RuS2-2 over RuO2 becomes
greater with the increasing current density (Dh = 37@10,
64@50, 90@100 mV@mAcmꢀ2), as shown in Figure 3b. Fur-
thermore, the superiority of Ru/RuS2-2 over other reported
Ru/Ir-based anodic electrocatalysts in acidic media is also
confirmed, as shown in Table S1. Note that although the onset
potential of phase-pure RuS2-8 is quite low, its overpotentials
at frequently-used current density indicators are unsatisfying,
especially at high current densities.
To assess the OER kinetics, relevant Tafel plots were
further drawn. Figure 3c exhibits that Ru/RuS2-2 owns the
minimal Tafel slope of 47.2 mVdecꢀ1 as compared with RuO2
(48.2 mVdecꢀ1),
Ru-1
(51.3 mVdecꢀ1),
Ru/RuS2-4
(81.2 mVdecꢀ1) and RuS2-8 (166 mVdecꢀ1), illuminating the
optimum dynamic mechanism for Ru/RuS2-2.[16a] Besides,
electrochemical active surface area (ECSA) was deduced
through double-layer capacitance (Cdl) from the cyclic
voltammetry (CV) curves within the non-Faradaic range
(Figure S15). Ru/RuS2-2 possesses the largest Cdl value of
11.5 mFcmꢀ2, as compared with Ru-1 (9.9 mFcmꢀ2), Ru/
RuS2-4 (9.1 mFcmꢀ2) and RuS2-8 (6.7 mFcmꢀ2). Correspond-
ingly, it has the highest ECSA value (191.7 cmꢀ2; 165 cmꢀ2 for
Ru-1, 151.7 cmꢀ2 for Ru/RuS2-4 and 111.7 cmꢀ2 for RuS2-8),
testifying the promoted active site density over the appro-
priate heterostructure (Figure 3d). Based on this, the ESCA-
Likewise, the cathodic HER performance was also
measured. As shown in Figure 4a, the catalytic activity of
pure RuS2-8 is poor in acidic media. While combined with Ru
to form a certain amount of heterointerface, the activity of
Ru/RuS2-4 is raised but still mediocre. Impressively, Ru/RuS2-
2 with the optimal interface design presents the best HER
performance. To afford the current density of 10 mAcmꢀ2, it
4
www.angewandte.org
ꢀ 2021 Wiley-VCH GmbH
Angew. Chem. Int. Ed. 2021, 60, 1 – 8
These are not the final page numbers!

Angewandte
Communications
Chemie
overall water splitting (OWS) devices were assembled with
Ru/RuS2-2 as catalysts. The voltage difference (DV= hHER
+
hOER) at designated current density was first used to estimate
the full performance of electrocatalysts. Ru/RuS2-2 has lower
DV values (1.48 V @ 10 mAcmꢀ2) than commercial Pt/C and
RuO2 couple (1.51 V @ 10 mAcmꢀ2), presaging prominent
application prospect of Ru/RuS2-2 for full water splitting
(Figure 5a). Unsurprisingly, when applied in actual assembly
of the water splitting device, Ru/RuS2-2 k Ru/RuS2-2 couple
simply needs a cell voltage of 1.501 V to drive the current
density of 10 mAcmꢀ2, which is 69 mV lower than that of Pt/C
k RuO2 couple (Figure 5b). Such OWS performance also
outperforms most of the reported precious metal-based
electrocatalysts, implying the distinguished candidacy for
concurrent electrocatalytic H2 and O2 production (Table S3).
Meanwhile, the i-t chronoamperometric response of Ru/
RuS2-2 k Ru/RuS2-2 couple proves its splendid long-term
durability for overall water splitting (Figure 5c). That can be
revalidated by the inappreciable overpotential decline from
LSV curves before and after 3000 CV cycles (Figure S29).
Further, H-type electrolytic cell with proton exchange
membrane was used to accomplish the separate H2/O2 gas
collection that was quantitatively evaluated by drainage
method (Video S1). By recording the gas volume at a series
of operating time, the volume ratio of H2 to O2 can be
reckoned to be 2.02:1, approaching the theoretical value in
water electrolysis (Figure 5d and S30). It suggests the almost
100% faradic efficiency of our catalysts toward overall water
splitting. The above results indicate that Ru/RuS2-2 can be
one of the most promising options for practical acidic PEM
water splitting applications.
Figure 4. HER performance in acidic media. a) LSV polarization curves
with iR correction, b) relevant overpotentials at different current
densities and c) Tafel plots of Ru-1, Ru/RuS2-2, Ru/RuS2-4, RuS2-8 and
state-of-the-art Pt/C catalysts; d) current density variation versus
various scan rates and e) EIS plots of Ru-1, Ru/RuS2-2, Ru/RuS2-4 and
RuS2-8; f) stability tests of Ru/RuS2-2.
In summary, theoretical calculations first disclosed the
interfacial charge rearrangement and the boosted electron
conduction over the Ru/RuS2 heterostructures. Such effects
can optimize the adsorption of key intermediates upon the
requires a low overpotential of 45 mV, which could bear
comparison with that of the commercial Pt/C catalyst (39 mV)
and be very competitive as compared with other noble metal-
based HER catalysts (Table S2). While at the large current
density of 100 mAcmꢀ2, the overpotential of Ru/RuS2-2 is
almost in line with the Pt/C catalyst (111 mV). The dominant
Ru disrupts the interface structure, thus, the catalytic activity
of Ru-1 is restricted. The HER pathway of Ru/RuS2-2 was
certified to be the Volmer-Tafel mechanism by virtue of
ultralow Tafel slope of 24.4 mVdecꢀ1 (Figure 4c).[23] Besides,
as calculated from a series of CV curves outside HER voltage
range (Figure S25), Ru/RuS2-2 possesses the largest Cdl value
(Figure 4d). Accordingly, the intrinsic activity of Ru/RuS2-2 is
also superior to other samples, suggesting the synchronously
uppermost active site density and specific activity (Fig-
ure S26).In addition, Ru/RuS2-2 also owns the highest TOF
value (0.71 sꢀ1 at an HER overpotential of 100 mV) (Fig-
ure S27). And the hydrogen is evolved with a high Faradic
efficiency as well (Figure S28). The promotion of conductivity
on the Ru/RuS2-2 electrode can be further proven via Nyquist
plots at the HER overpotentials (Figure 4e). Apparently, Ru/
RuS2-2 displays remarkable stability no matter in the CV
accelerating test or i-t chronoamperometric response test
(Figure 4 f). Therefore, Ru/RuS2-2 can be an excellent
substitute for Pt/C in acidic HER.
Figure 5. OWS performance in acidic media. a) Polarization curves of
Ru/RuS2-2, Pt/C and RuO2 catalyst for HER and OER; b) LSV curves of
two-electrode overall water splitting devices with Ru/RuS2-2 k Ru/RuS2-
2 and commercial Pt/C k RuO2 catalysts; c) i-t curve of Ru/RuS2-2 k
Ru/RuS2-2 couple; d) volume of collected H2 and O2 versus time.
Considering the superb bifunctional catalytic feature of
Ru/RuS2-2 for acidic OER and HER reactions, two-electrode
Angew. Chem. Int. Ed. 2021, 60, 1 – 8
ꢀ 2021 Wiley-VCH GmbH
www.angewandte.org
5
These are not the final page numbers!

Angewandte
Communications
Chemie
Zhang, Y. Yan, C. Wu, Y. Hu, C. Yan, T. Lei, W. Chen, C. Fan, J.
Xiong, Angew. Chem. Int. Ed. 2019, 58, 4484 – 4502; Angew.
Chem. 2019, 131, 4532 – 4551.
surface electron-deficient Ru atoms, sequentially reducing
the reaction energy barriers. Given such interfacial effect, we
designed and constructed the ruthenium/ruthenium disulfide
(Ru/RuS2) heterostructure for the first time, based on the
dual effect of reducibility and sulfidation of K2S with
assistance of eutectic salt system. The as-prepared laminar
Ru/RuS2-2 displays outstanding bifunctional catalytic perfor-
mance for both OER and HER in acidic media. Specifically, it
possesses extremely low overpotential (201 mV for OER,
45 mV for HER @10 mAcmꢀ2), favorable reaction kinetics,
massive catalytic active sites, prominent intrinsic activity,
ultrafast electron transfer, as well as excellent long-term
stability. In particular, as the catalysts for both electrodes, it
can drive the acidic overall water splitting with a significantly
reduced cell potential (1.501 V @ 10 mAcmꢀ2). Thus, this
paper profoundly explores the inherent catalytic mechanism
of Ru/RuS2-2 heterostructure, and provides instructive guid-
ance for the feasible construction of heterostructures with
optimal interfacial design to achieve high catalytic perfor-
mance in PEM-water splitting devices.
[6] T. Reier, Z. Pawolek, S. Cherevko, M. Bruns, T. Jones, D.
Teschner, S. Selve, A. Bergmann, H. N. Nong, R. Schlçgl, K. J. J.
Mayrhofer, P. Strasser, J. Am. Chem. Soc. 2015, 137, 13031 –
13040.
[7] a) Y. Pi, Q. Shao, P. Wang, J. Guo, X. Huang, Adv. Funct. Mater.
2017, 27, 1700886; b) J. Zhu, Y. Huang, W. Mei, C. Zhao, C.
Zhang, J. Zhang, I. S. Amiinu, S. Mu, Angew. Chem. Int. Ed.
2019, 58, 3859 – 3864; Angew. Chem. 2019, 131, 3899 – 3904.
[8] a) T. Zheng, C. Shang, Z. He, X. Wang, C. Cao, H. Li, R. Si, B.
Pan, S. Zhou, J. Zeng, Angew. Chem. Int. Ed. 2019, 58, 14764 –
14769; Angew. Chem. 2019, 131, 14906 – 14911; b) J. Zhu, S. Mu,
Adv. Funct. Mater. 2020, 30, 2001097.
[9] a) S. Y. Bae, J. Mahmood, I. Y. Jeon, J. B. Baek, Nanoscale
Horiz. 2020, 5, 43 – 56; b) X. Ai, X. Zou, H. Chen, Y. Su, X. Feng,
Q. Li, Y. Liu, Y. Zhang, X. Zou, Angew. Chem. Int. Ed. 2020, 59,
3961 – 3965; Angew. Chem. 2020, 132, 3989 – 3993; c) Y. Zhao, X.
Wang, G. Cheng, W. Luo, ACS Catal. 2020, 10, 11751 – 11757.
[10] a) Y. Yao, S. Hu, W. Chen, Z. Q. Huang, W. Wei, T. Yao, R. Liu,
K. Zang, X. Wang, G. Wu, W. Yuan, T. Yuan, B. Zhu, W. Liu, Z.
Li, D. He, Z. Xue, Y. Wang, X. Zheng, J. Dong, C. R. Chang, Y.
Chen, X. Hong, J. Luo, S. Wei, W. X. Li, P. Strasser, Y. Wu, Y. Li,
Nat. Catal. 2019, 2, 304 – 313; b) J. Shan, C. Guo, Y. Zhu, S. Chen,
L. Song, M. Jaroniec, Y. Zheng, S. Z. Qiao, Chem 2019, 5, 445 –
459; c) T. Reier, H. N. Nong, D. Teschner, R. Schlçgl, P. Strasser,
Adv. Energy Mater. 2017, 7, 1601275.
Acknowledgements
This work was financially sponsored by the National Natural
Science Foundation of China (Grant No. 22075223, 51672204,
21801005, 21901008) and the Fundamental Research Funds
for the Central Universities (No. 2020-YB-012). We wish to
thank Xiaoqing Liu and Tingting Luo (Materials Analysis
Center of Wuhan University of Technology) for TEM (JEM-
2100F) measurement support.
[11] a) H. Chen, X. Ai, W. Liu, Z. Xie, W. Feng, W. Chen, X. Zou,
Angew. Chem. Int. Ed. 2019, 58, 11409 – 11413; Angew. Chem.
2019, 131, 11531 – 11535; b) Y. Zhao, H. Cong, P. Li, D. Wu, S.
Chen, W. Luo, Angew. Chem. Int. Ed. 2021, 60, 7013 – 7017;
Angew. Chem. 2021, 133, 7089 – 7093.
[12] a) Y. Wang, P. Han, X. Lv, L. Zhang, G. Zheng, Joule 2018, 2,
2551 – 2582; b) W. Li, Z. Y. Hu, Z. Zhang, P. Wei, J. Zhang, Z. Pu,
J. Zhu, D. He, S. Mu, G. Van Tendeloo, J. Catal. 2019, 375, 164 –
170.
[13] Y. P. Zhu, C. Guo, Y. Zheng, S. Z. Qiao, Acc. Chem. Res. 2017,
50, 915 – 923.
Conflict of interest
[14] J. Zhang, J. Qian, J. Ran, P. Xi, L. Yang, D. Gao, ACS Catal. 2020,
10, 12376 – 12384.
The authors declare no conflict of interest.
[15] Z. H. Xue, H. Su, Q. Y. Yu, B. Zhang, H. H. Wang, X. H. Li, J. S.
Chen, Adv. Energy Mater. 2017, 7, 1602355.
[16] a) D. Chen, R. Lu, Z. Pu, J. Zhu, H. W. Li, F. Liu, S. Hu, X. Luo,
J. Wu, Y. Zhao, S. Mu, Appl. Catal. B 2020, 279, 119396; b) J.
Wang, L. Han, B. Huang, Q. Shao, H. L. Xin, X. Huang, Nat.
Commun. 2019, 10, 5692.
[17] a) Y. X. Lin, S. N. Zhang, Z. H. Xue, J. J. Zhang, H. Su, T. J.
Zhao, G. Y. Zhai, X. H. Li, M. Antonietti, J. S. Chen, Nat.
Commun. 2019, 10, 4380; b) T. Qiu, Z. Liang, W. Guo, S. Gao, C.
Qu, H. Tabassum, H. Zhang, B. Zhu, R. Zou, Y. Shao-Horn,
Nano Energy 2019, 58, 1 – 10.
Keywords: acidic water electrolysis ·
bifunctional electrocatalyst · DFT calculation · heterostructure ·
Ru-based nanomaterial
[1] a) F. Podjaski, D. Weber, S. Zhang, L. Diehl, R. Eger, V. Duppel,
E. Alarcꢀn-Lladꢀ, G. Richter, F. Haase, A. Fontcuberta i Mor-
ral, C. Scheu, B. V. Lotsch, Nat. Catal. 2020, 3, 55 – 63; b) Z. Pu, J.
Zhao, I. S. Amiinu, W. Li, M. Wang, D. He, S. Mu, Energy
Environ. Sci. 2019, 12, 952 – 957; c) J. A. Turner, Science 2004,
305, 972; d) S. S. Wang, L. Jiao, Y. Qian, W. C. Hu, G. Y. Xu, C.
Wang, H. L. Jiang, Angew. Chem. Int. Ed. 2019, 58, 10713 –
10717; Angew. Chem. 2019, 131, 10823 – 10827.
[2] a) P. Wang, R. Qin, P. Ji, Z. Pu, J. Zhu, C. Lin, Y. Zhao, H. Tang,
W. Li, S. Mu, Small 2020, 16, 2001642; b) J. Yu, Q. He, G. Yang,
W. Zhou, Z. Shao, M. Ni, ACS Catal. 2019, 9, 9973 – 10011; c) J.
Shan, T. Ling, K. Davey, Y. Zheng, S. Z. Qiao, Adv. Mater. 2019,
31, 1900510.
[18] Y. Li, J. Li, J. Chen, P. Cai, G. Wang, Y. Hou, L. Lei, Z. Wen, J.
Power Sources 2020, 472, 228625.
[19] K. Krishnamoorthy, P. Pazhamalai, S. J. Kim, Electrochim. Acta
2017, 227, 85 – 94.
[20] Y. Zhu, H. A. Tahini, Y. Wang, Q. Lin, Y. Liang, C. M. Doherty,
Y. Liu, X. Li, J. Lu, S. C. Smith, C. Selomulya, X. Zhang, Z. Shao,
H. Wang, J. Mater. Chem. A 2019, 7, 14222 – 14232.
[21] a) Z. Xue, X. Li, Q. Liu, M. Cai, K. Liu, M. Liu, Z. Ke, X. Liu, G.
Li, Adv. Mater. 2019, 31, 1900430; b) Q. Zhang, X. Liang, H.
Chen, W. Yan, L. Shi, Y. Liu, J. Li, X. Zou, Chem. Mater. 2020,
32, 3904 – 3910.
[22] J. Chen, P. Cui, G. Zhao, K. Rui, M. Lao, Y. Chen, X. Zheng, Y.
Jiang, H. Pan, S. X. Dou, W. Sun, Angew. Chem. Int. Ed. 2019, 58,
12540; Angew. Chem. 2019, 131, 12670.
[3] D. Chen, T. Liu, P. Wang, J. Zhao, C. Zhang, R. Cheng, W. Li, P.
Ji, Z. Pu, S. Mu, ACS Energy Lett. 2020, 5, 2909 – 2915.
[4] L. C. Seitz, C. F. Dickens, K. Nishio, Y. Hikita, J. Montoya, A.
Doyle, C. Kirk, A. Vojvodic, H. Y. Hwang, J. K. Norskov, T. F.
Jaramillo, Science 2016, 353, 1011.
[5] a) H. Wang, H. W. Lee, Y. Deng, Z. Lu, P. C. Hsu, Y. Liu, D. Lin,
Y. Cui, Nat. Commun. 2015, 6, 7261; b) X. Du, J. Huang, J.
6
www.angewandte.org
ꢀ 2021 Wiley-VCH GmbH
Angew. Chem. Int. Ed. 2021, 60, 1 – 8
These are not the final page numbers!

Angewandte
Communications
Chemie
[23] a) D. H. Kweon, M. S. Okyay, S. J. Kim, J. P. Jeon, H. J. Noh, N.
b) Y. Pi, Y. Xu, L. Li, T. Sun, B. Huang, L. Bu, Y. Ma, Z. Hu,
C. W. Pao, X. Huang, Adv. Funct. Mater. 2020, 30, 2004375.
Park, J. Mahmood, J. B. Baek, Nat. Commun. 2020, 11, 1278;
Manuscript received: February 1, 2021
Accepted manuscript online: February 25, 2021
Version of record online: && &&, &&&&
Angew. Chem. Int. Ed. 2021, 60, 1 – 8
ꢀ 2021 Wiley-VCH GmbH
www.angewandte.org
7
These are not the final page numbers!

Angewandte
Communications
Chemie
Communications
Water Splitting
Profiting from the rearranged charge
density around the abundant interface
and the enhanced electronic states, in
acidic media, the Ru/RuS2 hetero-
structure exhibits prominent catalytic
activity toward oxygen and hydrogen
evolution reactions, and consequent
remarkably high overall water splitting
performance, demonstrating promising
application prospect for industrial proton
exchange membrane-water electrolysis.
J. Zhu, Y. Guo, F. Liu, H. Xu, L. Gong,
W. Shi, D. Chen, P. Wang, Y. Yang,
C. Zhang, J. Wu, J. Luo,
S. Mu*
&&&& — &&&&
Regulative Electronic States around
Ruthenium/Ruthenium Disulphide
Heterointerfaces for Efficient Water
Splitting in Acidic Media
8
www.angewandte.org
ꢀ 2021 Wiley-VCH GmbH
Angew. Chem. Int. Ed. 2021, 60, 1 – 8
These are not the final page numbers!