A polyoxometalate@covalent triazine framework as a robust electrocatalyst for selective benzyl alcohol oxidation coupled with hydrogen production

Article abstract of DOI:10.1039/d0ta09421h

Electrocatalytic oxidation has been proven as a sustainable and promising alternative to traditional chemical transformation, but its further development is limited by the use of noble-metal electrocatalysts. Herein, a polyoxometalate-based electrode material,H₅PMo₁₀V₂O₄₀@CTF(denoted asPMo₁₀V₂@CTF), has been successfully fabricated through electrostatic assembly of a molecular polyoxometalate catalyst,PMo₁₀V₂, with a porous cationic covalent triazine framework (CTF), which, to our knowledge, represents the first combination of polyoxometalate with a cationic CTF. The resultingPMo₁₀V₂@CTFexhibits high activity for the selective electrocatalytic oxidation of alcohols to aldehydes, achieving 99% conversion of benzyl alcohol, over 99% selectivity of benzyl aldehyde, and at the same time near unity H₂production. Notably, the reported electrocatalytic system presents good atom economy, high energy conversion (96% faradaic efficiency), remarkable catalytic activity and robustness for at least eight recycles. Based on the various experimental and spectroscopic analyses, a possible catalytic mechanism was proposed, revealing that such excellent electrocatalytic performance is attributed to the versatile redox ability ofPMo₁₀V₂and the good porosity and adsorption property of the CTF in the constructedPMo₁₀V₂@CTFcomposite.

Full text of DOI:10.1039/d0ta09421h

View Article Online
View Journal
Journal of
Materials Chemistry A
Materials for energy and sustainability
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: Z. Li, J. Zhang, X.
Jing, J. Dong, H. Liu, H. Lv, Y. Chi and C. Hu, J. Mater. Chem. A, 2020, DOI: 10.1039/D0TA09421H.
Volume
Number 12
28 March 2018
Pages 4883-5230
6
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Journal of
Materials Chemistry A
Materials for energy and sustainability
rsc.li/materials-a
Accepted Manuscripts are published online shortly after acceptance,
before technical editing, formatting and proof reading. Using this free
service, authors can make their results available to the community, in
citable form, before we publish the edited article. We will replace this
Accepted Manuscript with the edited and formatted Advance Article as
soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes to the
text and/or graphics, which may alter content. The journal’s standard
Terms & Conditions and the Ethical guidelines still apply. In no event
shall the Royal Society of Chemistry be held responsible for any errors
or omissions in this Accepted Manuscript or any consequences arising
from the use of any information it contains.
ISSN 2050-7488
COMMUNICATION
Zhenhai Wen et al.
An electrochemically neutralized energy-assisted low-cost
acid-alkaline electrolyzer for energy-saving electrolysis
hydrogen generation
rsc.li/materials-a

Please do not adjust margins
Journal of Materials Chemistry A
Page 1 of 9
View Article Online
DOI: 10.1039/D0TA09421H
ARTICLE
Polyoxometalate@covalent triazine framework as robust
electrocatalyst for selective benzyl alcohol oxidation coupled
hydrogen production
Received 00th January 20xx,
Accepted 00th January 20xx
Zhen Li, Junhao Zhang, Xiaoting Jing, Jing Dong, Huifang Liu, Hongjin Lv,* Yingnan Chi* and
Changwen Hu
DOI: 10.1039/x0xx00000x
Electrocatalytic oxidation has been proven as a sustainable and promising alternative to traditional chemical transformation,
but its further development is limited by the use of noble-metal electrocatalysts. Herein, a polyoxometalate-based electrode
material, H5PMo10V2O40@CTF (denoted as PMo10V2@CTF), has been successfully fabricated through electrostatic assembly
of molecular polyoxometalate catalyst, PMo10V2, with the porous cationic covalent triazine framework (CTF), which, to our
knowledge, represents the first combination of polyoxometalate with cationic CTF. The resulting PMo10V2@CTF exhibits high
activity for the selective electrocatalytic oxidation of alcohols to aldehydes, achieving 99% conversion of benzyl alcohol, over
99% selectivity of benzyl aldehyde, and at the same time near unity H2 production. Notably, the reported electrocatalytic
system presents good atom economy, high energy conversion (96% Faradaic efficiency), remarkable catalytic activity and
robustness for at least eight recycles. Based on the various experimental and spectroscopic analyses, a possible catalytic
mechanism was proposed, revealing that such excellent electrocatalytic performance is attributed to the versatile redox
ability of PMo10V2 and the good porosity and adsorption property of CTF in the constructed PMo10V2@CTF composite.
homogeneous
2,2,6,6-tetramethyl-1-piperidine-N-oxyl
Introduction
(TEMPO) as an electrocatalyst or co-catalyst, rendering this
approach less attractive.10, 20, 25-30 Therefore, the development
of facile catalytic systems using earth-abundant and effective
catalyst under mild conditions is of scientific significance.
As an emerging type of catalysts, polyoxometalates (POMs)
have been attracting tremendous attention due to their
atomically well-defined structures and unique acid-base and
redox properties.31-35 POMs as a kind of promising molecular
electrocatalysts can undergo fast and reversible stepwise
electron transfer usually coupling with proton transfer.36 For
example, Neumann et al. explored the electrochemical
hydroxylation of arenes catalyzed by homogeneous
[CoIIIW12O40]5- catalyst; Hill et al reported the tetra Ru-
Electrocatalytic organic synthesis has attracted increasing
attention as a potential sustainable alternative to conventional
chemical synthetic approach.1-9 To date, important progress has
been made on the anodic oxidations of alcohols, biomass-
driven molecules, arenes, and aliphatic hydrocarbons,10-14 but
most of these oxidation processes require the use of noble-
metal-based electrocatalysts (such as Pt, Rh, Ru and Pd).15-19 To
achieve economic and value-added transformation of organic
substrates, some works have been reported on electrocatalytic
oxidation of alcohols, in the meanwhile, coupling with hydrogen
production. In these works, the organic substrates are
electrocatalytically oxidized to fine chemicals on the anodic
working electrode; while hydrogen as a clean and renewable
containing POMs for the effectively electrocatalytic oxidation of
38
ethanol and methanol.37,
Nevertheless, the direct use of
energy is simultaneously released from cathodic counter
POMs as electrode materials are limited due to their poor
attachment onto the electrode surface, low surface area, and
poor electrical conductivity. To overcome these disadvantages,
carbon-based materials and metal organic frameworks were
largely developed to immobilize POMs. And these previous
investigations reveal that nature of supports and
immobilization strategy have significant influence on the
stability and electrocatalytic activity of POMs.34, 39-42
20-22
electrode.3,
However, the challenges facing by these
systems still remain in the following aspects. For example,
electrooxidized carboxylic acid products (such as benzoic acid or
2,5-furandicarboxylic acid) were generally obtained and the
selective oxidation of alcohols to corresponding aldehydes
remains still a big challenge.23, 24 The high selectivity towards
aldehydes in some systems requires the use of expensive
Covalent triazine frameworks (CTFs) are crosslinked porous
polymers based on aromatic triazine units, which provide a
Key Laboratory of Cluster Science Ministry of Education, Beijing Key Laboratory of
Photoelectroic/Electrophotonic Conversion Materials, School of Chemistry and
Chemical Engineering, Beijing Institute of Technology, Beijing, 100081, People’s promising platform for the immobilization of electrocatalysts
Republic of China. E-mail: chiyingnan7887@bit.edu.cn; hlv@bit.edu.cn
†Electronic Supplementary Information (ESI) available: [proposed mechanism
process for the selective electrocatalytic oxidation of BA coupled with H2 evolution].
See DOI: 10.1039/x0xx00000x
owing to their large surface area, excellent chemical stability,
good conductivity, and unique structure flexibility.43-45 To date,
some active metal centers (such as Ru, Pt, Cu, and Pd etc.) have
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry A
Page 2 of 9
ARTICLE
Journal Name
been combined with CTFs and the resulting metal-modified from the FT-IR spectrum of PMo10V2@CTF, indicating the
View Article Online
CTFs exhibited remarkable activities in the electrochemical structural integrity of PMo10V2 after immDoObIi:li1z0a.1t0io3n9/.DC0oTmA0p9a4r2e1Hd
oxygen reduction reaction.46-51 However, the combination of with bare PMo10V2, the vibrations at 1049 cm−1 for P–Oa (a:
POM catalysts with CTFs are rarely reported.52 Herein, a novel tetrahedral oxygen atoms), 945 cm−1 for M=Od (d: terminal
electrocatalytic material, PMo10V2@CTF, has been successfully oxygen atoms), and 877 cm−1 for M–Ob–M (b: corner shared
fabricated by using cationic CTF as support, where the active oxygen atoms) are nearly unchanged, but a slight blue shift of
anionic Keggin-type clusters are evenly dispersed on the CTF M–Oc–M (c: edge-shared oxygen atoms) from 771 to 786 cm-1
and immobilized onto the support through electrostatic is found, which is probably caused by the strong electrostatic
interactions. The synthesized PMo10V2@CTF as a noble metal interaction between POMs and CTF. According to the structural
free anode can effectively catalyze the selective oxidation of feature of CTF, we speculate that PMo10V2 could be anchored
benzyl alcohol to benzaldehyde coupled with simultaneous H2 around the imidazolium group. According to inductively
production (Scheme 1), achieving high Faradaic efficiency (96%) coupled plasma atomic emission spectrometry (ICP-AES), the
and selectivity (>99%).
maximun loading amount of PMo10V2 is calculated to be 28 wt%
and the molar ratio of Mo to V is 4.8:1, which is close to the
theoretical ratio of 5:1.
Scheme 1. Schematic of PMo10V2@CTF fabrication and PMo10V2@CTF as
electrocatalyst for selective oxidation of benzyl alcohol coupled H2
production.
Results and discussion
The cationic CTFs were synthesized through the trimerization of
1,3-bis(4-cyanophenyl)imidazolium chloride in molten ZnCl2
(Scheme 1).53 As shown in Fig. 1, comparing with FT-IR spectrum
of monomer, the disappearance of characteristic C≡N stretching
band at 2228 cm-1 indicates the complete transformation of
nitrile group to triazine, while the board peaks at 1500-1616 cm-
Fig. 1. FT-IR spectra of monomer, CTF, PMo10V2@CTF, and PMo10V2.
The observation of a broad peak in powder X-ray diffraction
(PXRD) pattern suggests that PMo10V2@CTF is amorphous (Fig.
S4) and there is no characteristic diffraction of POMs, displaying
that PMo10V2 are evenly dispersed on the CTF support. The
Raman spectra of CTFs and PMo10V2@CTF (Fig. S5) show a G
band at 1584 cm-1 and a D band at 1341 cm-1, which are
attributed to sp2-hybridized carbon and disordered sp3 carbon,
respectively. Interestingly, the value of ID / IG ratio increases
after the incorporation of POMs, reflecting the increase of
defects and disorders in PMo10V2@CTF.
1
and 1384-1463 cm-1 reveal the presence of triazine and
imidazole groups. Moreover, the formation of triazine rings was
further confirmed by solid-state 13C cross-polarization magic-
angle spinning nuclear magnetic resonance (13C CP/MAS NMR)
spectrum (Fig. S2), where the peaks at 176 ppm and 129 ppm
can be assigned to triazine carbon atoms and the phenyl group,
respectively. For ionothermal method conducted at high
temperature (500 °C), irreversible carbonization reactions occur
in the synthesis of CTF, which could improve the conductivity of
CTF due to the partial graphitization. As a result, the molar ratio
of N to C (0.09) in CTF is far less than the theoretical value (0.27).
Considering the outstanding oxidizing activity of Keggin-
type H5PMo10V2O40 (PMo10V2) for mediating electron transfer,
it was chosen as the catalytic active species to combine with
cationic CTFs. As shown in Scheme 1 and Fig. S3, when cationic
CTFs were impregnated into the aqueous solution of PMo10V2,
the color of PMo10V2 gradually disappeared, revealing the
successful ion exchange of POMs with Cl¯. As shown in Fig. 1, all
the characteristic peaks of PMo12V2 can be clearly observed
Fig. 2. XPS spectra (a) Mo 3d and (b) V 2p of PMo10V2 and PMo10V2@CTF.
To confirm the elemental composition and their chemical
oxidation state, X-ray photoelectron spectroscopy (XPS)
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 3 of 9
Journal of Materials Chemistry A
Please do not adjust margins
Journal Name
ARTICLE
measurements were performed on both PMo10V2@CTF and fringe in the HRTEM image due to its amorphous structure and
View Article Online
DOI: 10.1039/D0TA09421H
PMo10V2 samples (Fig. 2, Fig. S6-S9). The P 2p, Mo 3d, and V 2p POMs clusters (the black spots) are homogeneously dispersed
signals are clearly detected in the XPS spectra of PMo10V2. The in the support. By using high-angle annular dark-field scanning
peaks with the binding energies of 236.2 eV (Mo 3d3/2) and transmission electron microscopy (HAADF-STEM), bright spots
233.05 eV (Mo 3d5/2) confirm the +6 oxidation state of Mo corresponding to single PMo10V2 cluster of about 1 nm and
atoms. In the V 2p region, two peaks at 525.1 eV and 517.7eV double clusters of about 2 nm can be clearly observed (Fig. 3b).
are assigned to V 2p1/2 and V 2p3/2, respectively, consistent with Energy-dispersive X-ray (EDX) elemental mapping analysis of
V5+ oxidation state, another two peaks at 523.7 eV (V 2p1/2) and PMo10V2@CTF (Fig. 3c-3g) further reveals that Mo, V, P, and C
516.45eV (V 2p3/2) are assigned to V4+ oxidation state, atoms are uniformly distributed in the framework of CTF.54, 55
respectively (Fig. 2b). Notably, after immobilization the binding We speculate that the uniform distribution of POMs is possibly
energy of Mo 3d (235.8 and 232.65 eV are assigned to Mo 3d3/2 related to the special structure of cationic CTF. The synthesized
and Mo 3d5/2, respectively) in the PMo10V2@CTF composite PMo10V2@CTF with mesoporous structure and evenly dispersed
shifts to lower region, meanwhile the ratio of V4+ (523.2 and PMo10V2 is expected to be a promising electrode material for
515.95 eV are assigned to V 2p1/2 and V 2p3/2) species in the selective oxidation of alcohols as proved in the following
composite also obviously increases,42 and the binding energy of experiments.
V 2p (PMo10V2@CTF) shifts to lower region about 0.5 eV,
N2 adsorption and desorption isotherms of CTF and
indicating partial electron transfer from CTF to PMo10V2 during PMo10V2@CTF are present in Fig. S13. Cationic CTF exhibits a
the formation of PMo10V2@CTF composite. The observed type Ⅳ isotherm with a significant hysteresis loop in the range
electron transfer behavior and coexistence of V5+ and V4+ are of 0.6 < p/p0 < 0.9, suggesting a mesoporous structure.
proven to be helpful for the improvement of electrocatalytic However, the shape of curve is changed after loading POMs.
activity. The existence of P in PMo10V2@CTF has been further PMo10V2@CTF has a Brunauer−Emmett−Teller (BET) surface
proven by solid-state 31P NMR spectroscopy (Fig. S10), where area of 399 m2 g-1, which is much lower than that of CTF (1154
the slight peak shift relative to PMo10V2 was found, probably m2 g-1). Notably, the surface area of PMo10V2@CTF is much
due to the chemical environment change around P after larger than many reported POMs-containing porous materials
combination with CTF. In addition, the strong interaction (Table S1). The pore size distribution of CTF (Fig. S14 and Table
between PMo10V2 and CTF support is further confirmed by S2) contains both micropores of 1.7 nm and mesopores of 4-35
leaching test. After soaking PMo10V2@CTF composite in nm. After incorporation of Keggin-type POMs (~1.2 nm size), the
water/acetonitrile for 8 h, no characteristic absorption of POMs pores of 1.7 nm disappear and the distribution range of
was detected by UV-vis spectroscopy (Fig. S11).
mesopores (4-20 nm) becomes narrower relative to that of CTF
(4-35 nm). The decrease of specific surface area and pore size
(Table S2) shows that PMo10V2 cluster is successfully
incorporated into the pores of CTF.
Fig.4. (a) CVs of 1 mM PMo10V2 in acetonitrile containing LiClO4 (1.5 mmol)
without benzyl alcohol (BA) and with 0.6 mmol BA, obtained at carbon cloth
working electrode with a scan rate of 50 mV s-1; (b) CVs of PMo10V2@CTF
without BA, or with 0.6 mmol BA, or with 0.6 mmol BA and 0.18 mmol Et3N,
obtained at carbon cloth working electrode modified with PMo10V2@CTF
(0.3 mg/cm2) with a scan rate of 50 mV s-1 using LiClO4 (1.5 mmol) as
electrolyte; (c) CVs of PMo10V2@CTF upon addition of three different
Brønsted bases (0.18 mmol) and BA (0.6 mmol), LiClO4 (1.5 mmol), obtained
at carbon cloth working electrode modified with PMo10V2@CTF (0.3
Fig. 3. (a) HRTEM image; (b) HAADF-STEM; (c)-(g) EDX elemental mapping of
PMo10V2@CTF.
Moreover, the structure of PMo10V2@CTF composite is
characterized by high-resolution transmission electron
microscopy (HRTEM). As shown in Fig. 3a, there is no lattice
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry A
Page 4 of 9
ARTICLE
Journal Name
mg/cm2) with a scan rate of 50 mV s-1; (d) Recycle test for the selective of 1.6 V (vs. Ag/Ag+ reference electrode) was appliVeiedw. AArsticslehOonwlinne
DOI: 10.1039/D0TA09421H
electrocatalytic oxidation of BA using PMo10V2@CTF.
in Fig. 5a, the conversion of BA linearly increases with
electrolysis time and 99% of BA is converted in 12 h under
ambient conditions. More importantly, no undesired over-
oxidation product (benzoic acid) was detected by gas
chromatography (GC) (Fig. S16) and the selectivity for
benzaldehyde reaches over 99%, corresponding to a Faradaic
efficiency (FE) of 96%. The FE of hydrogen production is 98%.
During the electrolysis process, a large amount of hydrogen gas
was generated over time at the cathode part (as shown in the
supporting Video clip). Moreover, the H2 evolution rate is
proportional to the conversion rate of substrate. After 12 h,
~0.639 mmol H2 was measured by GC. Recently, nitrogen-doped
carbon@CuCo2Nx (NC@CuCo)21 and nickel hydroxide
nanosheets, h-Ni(OH)256, have been proven to be active for the
selective electrocatalytic oxidation of alcohols to aldehydes
with simultaneous H2 production, but in their experiments
TEMPO was used to improve the selectivity for benzaldehydes.
The catalytic performance of PMo10V2@CTF (conversion: 99%,
selectivity: >99%, FE: 96%) reported in our work outperforms
that of NC@CuCo (conversion: 97%, selectivity: >98%, FE:
76%)21 and h-Ni(OH)2 (conversion: >90%, selectivity: >94%, FE:
81.3%)56 (Table S3).
In addition, we find that organic bases play a crucial role in
the electrocatalytic reaction. As shown in Fig. 5b, a negligible
amount of benzaldehyde is detected in the absence of organic
base. In contrast, the addition of a small amount of organic
bases (30 mol% relative to BA) greatly improved both
conversion and selectivity. Under otherwise identical
conditions, the catalytic performance of Et3N (conversion: 99%,
selectivity: >99%) is better than that of NMI (conversion: 89%,
selectivity: 90%) and DMP (conversion: 86%, selectivity: 79%).
The order of Et3N > NMI > DMAP in controlled potential
electrolysis is consistent with the results of CV measurements
(Fig. 4b). The influence of Et3N amount on electrocatalytic
activity was also studied. As shown in Fig. 5c, with the increase
of Et3N amount both conversion and selectivity show a first
increasing and then decreasing trend, and the optimal amount
of added organic base is 30%. As POMs are sensitive to pH, the
addition of more Et3N (above 30%) would lead to the
decomposition of PMo10V2, accordingly leading to the
The electrocatalytic activities of PMo10V2@CTF was initially
evaluated by cyclic voltammetry method. Fig. 4a presents the
cyclic voltammograms (CV) of 1 mM PMo10V2 acetonitrile
solution in the absence or presence of benzyl alcohol (BA). Upon
addition of BA, a significant increase in the anodic peak current
was observed, reflecting that quick catalytic response of
PMo10V2 towards the electrochemical oxidation of BA. Then the
CV studies were performed using PMo10V2@CTF-modified
carbon cloth electrode (Fig. 4b). Similar to that observed in
PMo10V2 solution, the addition of BA results in an increase in
catalytic current. To further confirm the catalytic role of
PMo10V2 in the oxidation of BA, the CV curves of CTF without BA
and with BA were recorded. Different from PMo10V2 and
PMo10V2@CTF, the addition of BA leads to a negligible increase
in the anodic peak current (Fig. S15). Notably, the above-
mentioned anodic current is further improved by addition of
triethylamine (Et3N) (Fig. 4b), which is consistent with previous
literature report that Brønsted bases could enhance the
electrocatalytic oxidation of alcohols. As shown in Fig. 4c, the
addition of different organic bases (N-methylimidazole (NMI),
4-(dimethylamino)pyridine (DMAP), and Et3N) could all
promote the oxidation of BA, among which Et3N base is
particularly effective.
Fig. 5. (a) Time profile for the electrocatalytic oxidation of BA and decreased catalytic activity. Based on above results, we
simultaneous H2 production using PMo10V2@CTF as anode; (b) The influence speculate that in our system Et3N probably works as the proton-
of different organic bases on the selective electrocatalytic oxidation of BA transfer mediator: it accepts the proton at the anode to form
catalyzed by PMo10V2@CTF; (c) The influence of Et3N amount on the Et3NH+, which is subsequently reduced to H2 and Et3N at the
selective electrocatalytic oxidation of BA catalyzed by PMo10V2@CTF; (d) cathode.
Selective electrocatalytic oxidation of BA using different catalysts. Reaction
To assess the influence of POMs and CTF on the
conditions: BA (0.6 mmol), anhydrous acetonitrile (10 mL), Et3N (0.18 mmol), electrocatalytic activity, a series of control experiments were
and LiClO4 (1.5 mmol) at ambient conditions for 12 h with the potential of conducted under the otherwise identical conditions. As shown
1.6 V vs. Ag/Ag+.
in Fig. 5d, 72% of BA was converted by CTF electrode, showing
CTF support is active for the electrochemical oxidation of BA,
but the selectivity for benzaldehyde (65%) is unsatisfactory.
After incorporation of PMo10V2, both the conversion and
selectivity were significantly improved. When PMo12@CTF
(PMo12: H3PMo12O40, the other Keggin-type cluster) was used as
electrocatalyst, an obvious decrease in catalytic performance
was found (Fig. 5d). Such different catalytic performances of
Bulk electrolysis experiment of BA was performed in an
electrolysis cell using PMo10V2@CTF-modified carbon cloth (1.0
cm2) as working electrode, platinum foil as counter electrode,
and Ag/Ag+ electrode as reference electrode, respectively. The
acetonitrile solution containing BA, Et3N (30 mol% relative to
BA), and LiClO4 electrolyte was added to the cell and a potential
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 5 of 9
Journal of Materials Chemistry A
Please do not adjust margins
Journal Name
ARTICLE
PMo10V2@CTF (conversion: 99%, selectivity: >99%) and
PMo12@CTF (conversion: 79%, selectivity: >69%) indicates the
important contribution of substituted V atoms in PMo10V2 (Fig.
5d). The electrochemical oxidation of BA with homogeneous
PMo10V2 using CTF-modified carbon cloth as electrode was also
tested (Fig. 5d). The addition of PMo10V2 yields a high selectivity
(>99%) of the electrocatalytic oxidation reaction showing the
important role of PMo10V2, but the conversion (60%) of BA in
the presence of homogeneous PMo10V2 is much lower than that
of PMo10V2@CTF composite. During the electrocatalytic
reaction using PMo10V2 as homogeneous catalyst, the reaction
solution gradually changed from yellow to green, indicating that
PMo10V2 was reduced. However, the re-oxidation of reduced-
PMo10V2 only occurs when it diffuses to the surface of anode,
which hinders the turnover of homogeneous POM in some
degree. When PMo10V2 is immobilized on CTF to fabricate
electrode material, electron transfer between PMo10V2 and
electrode can go smoothly, leading to its remarkable
performance.
View Article Online
DOI: 10.1039/D0TA09421H
Fig. 6. XPS spectra of PMo10V2@CTF (a) Mo 3d and (b) V 2p of before and
after the reaction.
The excellent electrocatalytic activity, stability, and
recyclability of PMo10V2@CTF in the selective oxidation of BA
prompted us to assess its performance in the oxidation of other
benzylic alcohols (Fig. S20). Without any further optimization,
PMo10V2@CTF is active for the electrochemical oxidation of
benzylic alcohols to the corresponding aldehydes with the
conversion of 91-99% and selectivity of 91-99% (Table 1, entries
1-5). It is noteworthy that the remarkable selectivity (>99%) was
obtained for the benzylic alcohols with electron donating
groups. In most cases, FE is higher than 80%. Although 90% of
diphenylmethanol was converted, the reaction only gave a
selectivity of 50% for diphenyl ketone due to the formation of
by-product tetraphenylethylene (Table 1, entry 6).
For electrocatalytic materials, their recyclability and stability
are key issues for potential practical applications. As shown in
Fig. 4d, the PMo10V2@CTF catalyst is highly recyclable and even
after 8 consecutive cycles the conversion of BA remained above
98% and a FE of 90% was achieved. Impressively, during the
recycle process no over-oxidation product (e.g. benzoic acid)
was detected. To confirm the stability of PMo10V2@CTF
composite in the presence of Et3N, the composite was soaked
in the reaction solution for 7 days and FT-IR spectrum of isolated
samples remains unchanged (Fig. S17). In addition, after the
electrocatalytic reaction the catalyst on electrode and reaction
solution were collected. For the post-reaction solution, no
characteristic absorption of PMo10V2 is detected by UV-vis
spectrum (Fig. S18), while for the catalyst there is no obvious
change found in the FT-IR spectra before and after the
electrocatalysis (Fig. S19). The XPS spectrum of the recycled
catalyst was also measured, where the V 2p (Fig. 6a) and Mo 3d
(Fig. 6b) peaks are basically unchanged relative to the pristine
sample. Interestingly, the ratio of V4+ oxidation state increases
in PMo10V2@CTF after the electrocatalytic reaction.
Furthermore, the Mo 3d peaks could be deconvoluted into
Table 1. Electrochemical oxidation of alcohols using PMo10V2@CTFa
Entry
Substrate
Product
Conv.b Sele.b
FE (%)
96
99
93
95
99
91
90
99
99
99
91
95
50
1
2
3
4
5
6
87
83
95
85
77
235.8 eV (3d3/2, Mo6+), 233.8 eV (3d3/2, Mo5+), 232.65 eV (3d5/2
,
a Reaction conditions: alcohols (0.6 mmol), anhydrous acetonitrile (10 mL), Et3N
(0.18 mmol), LiClO4 (1.5 mmol), reaction time: 12 h, E: 1.6 V vs. Ag/Ag+. b The
product conversion and selectivity were determined by GC analysis.
Mo6+), and 232.05 eV (3d5/2, Mo5+). Moreover, the V 2p peaks
could be deconvoluted into 524.6 eV (2p1/2, V5+), 517.1 eV
(2p3/2, V5+), 523.2 eV (2p1/2, V4+), and 515.95 eV (2p3/2, V4+),
respectively. The presence of Mo5+ and the increase of V4+ imply
that PMo10V2@CTF could accept the electrons by oxidizing BA
substrate during the electrocatalytic reaction. Though, with
some oxidation state variation, the structure and catalytic
performance of PMo10V2@CTF are basically maintained for
eight successive recycling test.
Scheme 2. Proposed mechanism for the selective electrocatalytic oxidation of
benzyl alcohol by PMo10V2@CTF.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry A
Page 6 of 9
ARTICLE
Journal Name
We also conducted the adsorption test of BA on
Experimental
View Article Online
DOI: 10.1039/D0TA09421H
PMo10V2@CTF and quantified the amount of adsorbed BA by
GC. Since PMo10V2@CTF has relative higher specific surface
area and well-defined mesoporous structure, it exhibits
substrate adsorption capacity towards BA and the maximum
adsorbed amount is about 28 mmol/g (Fig. S21). We speculate
that BA possibly interacts with CTF by hydrogen bonding
between the hydroxyl group of BA and nitrogen sites of CTF.
According to previous investigations, we guess that a radical
process might be involved in the electrochemical reaction. To
verify our speculation, Ph2NH as oxygen radical scavenger and
tert-butanol as a hydroxyl radical scavenger were added into
the reaction system. As shown in Table S4, the oxidation of BA
was effectively prohibited by the addition of Ph2NH. On the
basis of above experimental results and XPS analysis, we
propose a plausible mechanism for the selective electrocatalytic
oxidation of BA coupled with H2 evolution (Scheme 2). In the
first stage, BA is adsorbed by CTF that is readily accessible to the
immobilized POMs cluster. Then, the oxidized state of
PMo10V2(ox)@CTF catalyzes BA to benzyl aldehyde through
proton coupled electron transfer (PCET), generating the
reduced state of H2PMo10V2(red)@CTF. In addition, an oxygen
radical species (PhCH2O) might be involved in this step. The
electron transfer from substrate to PMo10V2 is partially
supported by XPS data, where ratios of Mo5+ and V4+ increase
after the electrocatalytic oxidation. In the meanwhile, the
protons are removed from H2PMo10V2(red)@CTF by Et3N
forming Et3NH+ and the catalyst is oxidized to
PMo10V2(ox)@CTF at anode completing a catalytic cycle. The
mesoporous structure of CTF and electrostatic interactions
between POMs and the CTF support facilitate the electron and
proton transfer. In the cathodic electrode, Et3NH+ is reduced to
release H2 and regenerate Et3N at the same time.
Materials and Methods.
All the starting materials and organic solvents were purchased
from commercial suppliers and used without further
purification unless otherwise noted. H5PMo10V2O40·nH2O57 and
1,3-bis(4-cyanophenyl)imidazolium chloride58 were prepared
according to literature methods. Solid-state 13C and 31P CP/MAS
spectroscopy of PMo10V2@CTF and PMo10V2 were performed at
room temperature on a 700 MHz Bruker Ascend spectrometer
at a MAS rate of 5 kHz. PXRD measurements were carried out
on the Rigaku SmartLab X-ray diffractometer with Cu-Kα
radiation (40 kV, 30 mA, λ = 1.5418 Å) and a scanning step of
0.01°. The morphology and microstructure of the samples were
observed by scanning electron microscopy (SEM, JOEL JSE-
7500F) and transmission electron microscopy (TEM, JOEL JEM-
2010). The atomic resolution scanning transition electron
microscopy (STEM) and energy-dispersive spectroscopy (EDS)
experiments were performed on an aberration-corrected
transmission electron microscope FEI Titan Cubed Themis G2
300. The FT-IR spectra were collected on a Nicolet 170SXFT-IR
spectrophotometer in the range 400-4000 cm-1. N2 adsorption-
desorption isotherms and pore size distribution were obtained
at 77 K by using a Belsorp-max surface area detecting
instrument. The XPS spectra of the samples were performed on
Thermo ESCALAB 250Xi. The UV-vis spectra were measured on
UV-2600. The Raman spectra were obtained on SNFT-
SRLab1000. The Inductively coupled plasma mass spectrometry
(ICP-MS) were measured on Thermo Scientific iCAP Q. Gas
chromatograph analyses were performed on a Shimadzu GC-
2014C instrument with an FID detector equipped with an HP 5
ms capillary column. The quantity of hydrogen evolved was
determined using a Techcomp GC-9700 gas chromatograph
with a 5Å molecular sieve column (2 m*2 mm) and a thermal
conductivity detector (TCD). The thermogravimetric analysis
(TGA) of the samples was performed using a Shimadzu DTG-
60AH thermal analyzer under the N2 atmosphere from room
temperature to 800 ºC with a heating rate of 5 °C min−1.
Elemental analyses (C, H and N) were performed on an
ElementarVario EL cube Elmer CHN elemental analyzer.
Conclusions
In summary, we demonstrate a facile and effective strategy to
fabricate POMs electrode material through electrostatic
assembly of active PMo10V2 cluster with cationic CTF support.
The synthesized PMo10V2@CTF works as effective
electrocatalyst for the selective oxidation of BA coupling with
H2 generation with near unity yield. The selectivity (>99%) and
FE (96%) of PMo10V2@CTF is higher than those of the reported
heterogeneous catalysts. Moreover, the catalyst is highly robust
and recyclable and its catalytic activity is maintained even after
eight successive cycles. Such catalytic system is also applicable
to a variety of BA derivatives with very high conversion and
selectivity. The exhibited electrocatalytic performance is mainly
attributed to the versatile redox ability of PMo10V2, the porous
architecture, highly dispersed POMs, and the cooperative effect
between CTF and POMs. The reported investigations have
important implications for the development of POMs-based
electrocatalytic materials and also provides some insightful
guidelines for oxidation of other organic substrates beyond
alcohol oxidation.
Synthesis of CTF
The cationic CTF was synthesized according to the reported
ionothermal method.53 In a typical experiment, a mixture of
0.613 g (2 mmol) of 1,3-bis(4-cyanophenyl)imidazolium chloride
and 1.363 g (10 mmol) of desiccated ZnCl2 was placed into a
quartz ampule under an inert atmosphere. The ampule was
then evacuated, flame-sealed and transferred into a furnace for
heating treatment at 500 °C for 40 h. The solid monolith
obtained was subsequently grounded and then washed
thoroughly with water to remove most of the ZnCl2. Further
stirring in 0.1 M HCl for 12 h was carried out to remove the
residual salt. The resulting black powder was washed
successively with water and THF and dried in vacuum at 120 °C
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 7 of 9
Journal of Materials Chemistry A
Please do not adjust margins
Journal Name
ARTICLE
for 12 h. The C, H and N elemental analysis (%) for CTF: 66.09,
2.243, 6.031.
Notes and references
View Article Online
DOI: 10.1039/D0TA09421H
1.
2.
3.
4.
5.
6.
W. Zhong, H. Liu, C. Bai, S. Liao and Y. Li, ACS Catalysis,
2015, 5, 1850-1856.
J. E. Nutting, M. Rafiee and S. S. Stahl, Chem. Rev., 2018,
118, 4834-4885.
A. Das and S. S. Stahl, Angew Chem Int Ed., 2017, 56, 8892-
8897.
A. J. J. Lennox, J. E. Nutting and S. S. Stahl, Chem Sci, 2018,
9, 356-361.
Q. L. Yang, Y. Q. Li, C. Ma, P. Fang, X. J. Zhang and T. S. Mei,
J. Am. Chem. Soc., 2017, 139, 3293-3298.
C. Tian, L. Massignan, T. H. Meyer and L. Ackermann,
Angew Chem Int Ed., 2018, 57, 2383-2387.
C. Y. Cai and H. C. Xu, Nat Commun, 2018, 9, 3551.
B. Schille, N. O. Giltzau and R. Francke, Angew Chem Int Ed.,
2018, 57, 422-426.
Synthesis of PMo10V2@CTF
PMo10V2 (0.05 g) was dissolved in deionized water (15 mL) and
then CTF (100 mg) was added. The mixture was stirred at room
temperature for 8 h and during the process the characteristic
color of PMo10V2 gradually disappeared. Finally, a black solid of
PMo10V2@CTF was obtained after washing with a large amount
of deionized water and drying at 80 °C for 12 h.
Electrochemical Oxidation of Benzyl Alcohols
Preparation of PMo10V2@CTF electrode. The PMo10V2@CTF
working electrode was prepared as follows: PMo10V2@CTF (5
mg) was dispersed in isopropanol (1 mL) containing 5 wt%
Nafion under ultrasonic conditions. 50 µL of this suspension was
drop-casted onto a piece of carbon cloth (1 cm2) and then dried
under vacuum.
Cyclic Voltammetry Experiments. Voltammetric experiments
were performed in anhydrous acetonitrile (10 mL) containing
supporting electrolyte LiClO4 (1.5 mmol) at room temperature.
7.
8.
9.
D. T. Yang, M. Zhu, Z. J. Schiffer, K. Williams, X. Song, X. Liu
and K. Manthiram, ACS Catalysis, 2019, 9, 4699-4705.
A. Badalyan and S. S. Stahl, Nature, 2016, 535, 406-410.
B. You, X. Liu, N. Jiang and Y. Sun, J. Am. Chem. Soc., 2016,
138, 13639-13646.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
E. J. Horn, B. R. Rosen, Y. Chen, J. Tang, K. Chen, M. D.
Eastgate and P. S. Baran, Nature, 2016, 533, 77-81.
Y. Kawamata, M. Yan, Z. Liu, D. H. Bao, J. Chen, J. T. Starr
and P. S. Baran, J. Am. Chem. Soc., 2017, 139, 7448-7451.
J. A. Marko, A. Durgham, S. L. Bretz and W. Liu, Chem
Commun (Camb), 2019, 55, 937-940.
M. YASUZAWA, K. KAN, A. KIJNUGI, Z. OGUMI and Z.
TAKEHARA, Electrochim. Acta, 1995, 40, 1785-1787.
A. L. B. Marques, W. Li, E. P. Marques and J. Zhang,
Electrochim. Acta, 2004, 49, 879-885.
S. Yamazaki, M. Yao, N. Fujiwara, Z. Siroma, K. Yasuda and
T. Ioroi, Chem Commun, 2012, 48, 4353-4355.
A. L. Wang, H. Xu, J. X. Feng, L. X. Ding, Y. X. Tong and G. R.
Li, J. Am. Chem. Soc., 2013, 135, 10703-10709.
Z. Daşdelen, Y. Yıldız, S. Eriş and F. Şen, Appl. Catal., B,
2017, 219, 511-516.
All potentials were measured by
a CH Instruments
Electrochemical Analyzer (CHI660E) with a scan rate of 50 mV s-
1. The CV tests of homogeneous PMo10V2 (10mM) were
performed using a three-electrode setup with glassy carbon
(GC) working electrode (3 mm diameter), a platinum plate (1
cm2) electrode as counter electrode and Ag/AgNO3 as reference
electrode. The CV tests of PMo10V2@CTF were performed with
PMo10V2@CTF modified carbon cloth as working electrode (1
cm2 effective area), a platinum foil as counter electrode and
Ag/AgNO3 electrode as reference electrode.
Controlled Potential Electrolysis Experiments. Bulk electrolysis
experiments were performed in an undivided cell using a three-
electrode setup with a PMo10V2@CTF-modified carbon cloth
(1.0 cm2) as working electrode, a platinum foil as counter
electrode, and a Ag/AgNO3 electrode as reference electrode. To
the cell was added 10 mL of anhydrous acetonitrile solution
containing LiClO4 (1.5 mmol), Et3N (0.18mmol), and benzyl
alcohol (0.6 mmol) and a potential of 1.6 V vs Ag/AgNO3 was
M. Rafiee, Z. M. Konz, M. D. Graaf, H. F. Koolman and S. S.
Stahl, ACS Catalysis, 2018, 8, 6738-6744.
J. Zheng, X. Chen, X. Zhong, S. Li, T. Liu, G. Zhuang, X. Li, S.
Deng, D. Mei and J.-G. Wang, Adv. Funct. Mater., 2017, 27,
1704169.
applied. At the end of electrolysis, biphenyl as internal standard 22.
was added in the reaction solution and the products were
X. Cui, M. Chen, R. Xiong, J. Sun, X. Liu and B. Geng, J.
Mater. Chem. A, 2019, 7, 16501-16507.
N. Zhang, Y. Zou, L. Tao, W. Chen, L. Zhou, Z. Liu, B. Zhou,
G. Huang, H. Lin and S. Wang, Angew Chem Int Ed., 2019,
58, 15895-15903.
Z. Yin, Y. Zheng, H. Wang, J. Li, Q. Zhu, Y. Wang, N. Ma, G.
Hu, B. He, A. Knop-Gericke, R. Schlogl and D. Ma, ACS Nano,
2017, 11, 12365-12377.
23.
qualitatively analyzed by GC. For the recycle test, after the
reaction the working electrode, PMo10V2@CTF-modified
carbon cloth, was gently washed with acetonitrile and ethyl
alcohol for three times, dried and used for the next cycle.
24.
25.
26.
27.
28.
29.
M. Rafiee, K. C. Miles and S. S. Stahl, J. Am. Chem. Soc.,
2015, 137, 14751-14757.
C. J. Weiss, E. S. Wiedner, J. A. Roberts and A. M. Appel,
Chem Commun, 2015, 51, 6172-6174.
M. T. Masatoshi Shibuya, and Yoshiharu Iwabuchi, J. Org.
Chem., 2008, 73, 4750-4752.
B. L. Ryland and S. S. Stahl, Angew Chem Int Ed., 2014, 53,
8824-8838.
Conflicts of interest
There are no conflict interest to declare.
Acknowledgements
This work was financially supported by the National Natural
Science Foundation of China (21871025, 21831001, 21671019,
21871026, 21771020, and 21971010).
M. H. A. Janssen, J. F. Chesa Castellana, H. Jackman, P. J.
Dunn and R. A. Sheldon, Green Chem., 2011, 13, 905.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry A
Page 8 of 9
ARTICLE
30.
Journal Name
X. L. Renhua Liu, Chunyan Dong, and Xinquan Hu, J. Am. 56.
Chem. Soc., 2004, 126, 4112-4113.
J. Macht, M. J. Janik, M. Neurock and E. Iglesia, Angew
X. Chen, X. Zhong, B. Yuan, S. Li, Y. Gu, Q. ZhaVniegw, GAr.tiZclheuOannlinge,
X. Li, S. Deng and J. G. Wang, GreeDnOCIh: 1e0m.1.0,3290/1D90,T2A019, 452718H-
588.
31.
Chem Int Ed., 2007, 46, 7864-7868.
I. A. Weinstock, R. E. Schreiber and R. Neumann, Chem. 58.
Rev., 2018, 118, 2680-2717.
57.
R. N. a. M. Lissel, J. Org. Chem., 1989, 54, 4607-4610.
R. S. Crees, M. L. Cole, L. R. Hanton and C. J. Sumby, Inorg.
Chem., 2010, 49, 1712-1719.
32.
33.
E. D. Anne Dolbecq, Ce´dric R. Mayer, and Pierre Mialane,
Chem. Rev., 2010, 110, 6009-6048.
34.
F. M. Toma, A. Sartorel, M. Iurlo, M. Carraro, P. Parisse, C.
Maccato, S. Rapino, B. R. Gonzalez, H. Amenitsch, T. Da
Ros, L. Casalis, A. Goldoni, M. Marcaccio, G. Scorrano, G.
Scoles, F. Paolucci, M. Prato and M. Bonchio, Nat Chem,
2010, 2, 826-831.
35.
V. Y. Evtushok, A. N. Suboch, O. Y. Podyacheva, O. A.
Stonkus, V. I. Zaikovskii, Y. A. Chesalov, L. S. Kibis and O. A.
Kholdeeva, ACS Catalysis, 2018, 8, 1297-1307.
Y. Ji, L. Huang, J. Hu, C. Streb and Y. F. Song, Energy Environ.
Sci., 2015, 8, 776-789.
A. M. Khenkin, M. Somekh, R. Carmieli and R. Neumann,
Angew Chem Int Ed., 2018, 57, 5403-5407.
Y. Liu, S. F. Zhao, S. X. Guo, A. M. Bond, J. Zhang, G. Zhu, C.
L. Hill and Y. V. Geletii, J. Am. Chem. Soc., 2016, 138, 2617-
2628.
36.
37.
38.
39.
40.
41.
42.
C. Zou, Z. Zhang, X. Xu, Q. Gong, J. Li and C. D. Wu, J. Am.
Chem. Soc., 2012, 134, 87-90.
S. Mukhopadhyay, J. Debgupta, C. Singh, A. Kar and S. K.
Das, Angew Chem Int Ed., 2018, 57, 1918-1923.
H. Ma, B. Liu, B. Li, L. Zhang, Y. G. Li, H. Q. Tan, H. Y. Zang
and G. Zhu, J. Am. Chem. Soc., 2016, 138, 5897-5903.
J. Song, Y. Li, P. Cao, X. Jing, M. Faheem, Y. Matsuo, Y. Zhu,
Y. Tian, X. Wang and G. Zhu, Adv. Mater., 2019, 31,
e1902444.
43.
44.
P. Kuhn, M. Antonietti and A. Thomas, Angew Chem Int Ed.,
2008, 47, 3450-3453.
A. l. F. Pierre Kuhn, Dangsheng Su, Arne Thomas, and
Markus Antonietti, J Am Chem Soc, 2008, 130, 13333-
13337.
45.
X. Zhu, C. Tian, S. M. Mahurin, S. H. Chai, C. Wang, S. Brown,
G. M. Veith, H. Luo, H. Liu and S. Dai, J. Am. Chem. Soc.,
2012, 134, 10478-10484.
46.
47.
48.
49.
50.
51.
52.
J. Artz, S. Mallmann and R. Palkovits, ChemSusChem, 2015,
8, 672-679.
R. Palkovits, M. Antonietti, P. Kuhn, A. Thomas and F.
Schuth, Angew Chem Int Ed., 2009, 48, 6909-6912.
K. Iwase, T. Yoshioka, S. Nakanishi, K. Hashimoto and K.
Kamiya, Angew. Chem. Int. Ed., 2015, 54, 11068-11072.
Z. Wang, C. Liu, Y. Huang, Y. Hu and B. Zhang, Chem
Commun, 2016, 52, 2960-2963.
L. Zhao, S. Shi, G. Zhu, M. Liu, J. Gao and J. Xu, Green Chem.,
2019, 21, 6707-6716.
M. Pilaski, J. Artz, H.-U. Islam, A. M. Beale and R. Palkovits,
Microporous Mesoporous Mater., 2016, 227, 219-227.
S. Zhang, O. Oms, L. Hao, R. Liu, M. Wang, Y. Zhang, H. Y.
He, A. Dolbecq, J. Marrot, B. Keita, L. Zhi, P. Mialane, B. Li
and G. Zhang, ACS Appl. Mater. Interfaces, 2017, 9, 38486-
38498.
53.
54.
55.
T.-T. Liu, R. Xu, J.-D. Yi, J. Liang, X.-S. Wang, P.-C. Shi, Y.-B.
Huang and R. Cao, ChemCatChem, 2018, 10, 2036–2040.
P. H. Qingda Liu, Hongde Yu, Lin Gu, Bing Ni, Dong Wang,
Xun Wang, Science Advances, 2019, 5, eaax1081.
J. Liu, W. Shi, B. Ni, Y. Yang, S. Li, J. Zhuang and X. Wang,
Nat Chem, 2019, 11, 839-845.
8 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 9 of 9
Journal of Materials Chemistry A
View Article Online
DOI: 10.1039/D0TA09421H
Table of Contents