Integration of an aminopyridine derived cobalt based homogenous cocatalyst with a composite photocatalyst to promote H2evolution from water

Article abstract of DOI:10.1039/d1nj00086a

Inexpensive cocatalysts are promising materials to improve the performance of photocatalytic systems. However, a cocatalyst can be anchored onto a photosensitizer in certain amount and further loading can hinder the visible light by blocking the active si

Full text of DOI:10.1039/d1nj00086a

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Integration of an aminopyridine derived cobalt
based homogenous cocatalyst with a composite
photocatalyst to promote H2 evolution from
Cite this: New J. Chem., 2021,
45, 5561
water†
a
Rana Muhammad Irfan,
Sayed Ali Khan,b Mudassir Hussain Tahir,c
Tauqeer Ahmad,d Liaqat Ali,d Masood Afzal,d Hazrat Ali,d Anees Abbas,d
Khuram Shahzad Munawar,
Jianqing Zhao*a and Lijun Gao*a
d
Inexpensive cocatalysts are promising materials to improve the performance of photocatalytic systems.
However, a cocatalyst can be anchored onto a photosensitizer in certain amount and further loading
can hinder the visible light by blocking the active sites of the photosensitizer. Herein, we introduce the
utilization of a cobalt based homogenous cocatalyst with composite photocatalyst CdS/Ni3C. The
homogenous cocatalyst did not occupy the physical space on the photosensitizer and the performance
of CdS/Ni3C was significantly enhanced from 263 mmol hÀ1 to 750 mmol hÀ1. The present study showed
that homogenous cocatalysts paved a way to further capture the electrons from photoexcited compo-
site photocatalysts and have great potential to enhance the photocatalytic performance for low cost H2
evolution under visible light.
Received 6th January 2021,
Accepted 25th February 2021
DOI: 10.1039/d1nj00086a
rsc.li/njc
Water splitting using solar energy has been considered as one of anchoring a cocatalyst and integration of another suitable
the best strategies to overcome the global energy and environ- semiconductor.14,15 In the past few years, it has been well
mental crises since 1972.1,2 H2 can replace the non-renewable demonstrated that cocatalysts can efficiently suppress the
fossil fuels owing to its several advantages such as straightforward charge recombination and photocorrosion of CdS by accepting
synthesis pathway, benign burning products and superior photogenerated electrons.16,17 However, state of the art photo-
chemical energy.3–5 Semiconductor photosensitizers have become catalytic systems are based on noble metal cocatalysts, which
prominent candidates for photocatalytic systems due to their high suppress their industrial applications.20,21 Recently, numerous
catalytic activity and excellent durability under catalytic condi- inexpensive and earth-abundant cocatalysts have been thor-
tions.6,7 Among them, TiO2 and CdS have been studied broadly oughly studied such as metal sulfides, selenides, nitrides,
because of their excellent catalytic abilities for H2 produc- oxides and carbides. However, a single cocatalyst on a photo-
tion.8–11 Contrary to TiO2, the advantage of visible light activity sensitizer cannot hamper the charge recombination suffi-
of CdS made it the apple of researcher’s eye. Unfortunately, CdS ciently. Particularly, an anchored cocatalyst can boost H2
suffers from photocorrosion with the passage of time and the H2 production up to a certain loading amount. Further loading
production yield decreases gradually under irradiation.12,13
of the cocatalyst may result in decreased H2 evolution due to
Several strategies have been adopted to overcome these the shielding of visible light and blocking the active sites of the
rudimentary issues of CdS, such as doping, ligand attachment, photosensitizer.18,19 Therefore, it is highly demanding to utilize
some additional strategies to further capture the photogenerated
electrons from photosensitizers to sufficiently suppress charge
a College of Energy, Soochow Institute for Energy and Materials Innovations
recombination.20,21
(SIEMIS), Soochow University, Suzhou 215006, China.
Homogeneous cocatalysts proved themselves as highly efficient
E-mail: jqzhao@suda.edu.cn, gaolijun@suda.edu.cn
b School of Electronic Science and Engineering, Xiamen University, Xiamen 361005,
electron capturing species in homogenous photocatalytic reac-
tions.22,23 The utilization of molecular cocatalysts in composite
photocatalytic systems can be a promising strategy to further
capture photogenerated electrons from photosensitizers. In the
past decades, several homogenous cocatalysts based on particular
ligands such as salen, porphyrin and phthalocyanine have been
reported to exhibit excellent photocatalytic activities. However, less
China
c School of Power and Energy Engineering, Shandong University, Jinan 250100,
China
d School of Chemistry, University of Mianwali, 42200, Mianwali, Pakistan
† Electronic supplementary information (ESI) available: ICP-AES data, XRD
patterns, SEM image, HRTEM image, EDX spectrum and TRPL spectra. See
DOI: 10.1039/d1nj00086a
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attention has been paid to simple bidentate ligand-based com-
plexes and their utilization in composite photocatalysts.
Herein, we report a highly efficient photocatalytic system
consisting of an aminopyridine derived Co-complex as a homo-
genous cocatalyst integrated with a composite photocatalyst to
boost its H2 evolution activity from water under visible light.
CdS/Ni3C NR composites were chosen for this study as Ni3C has
been reported to be a promising alternative to noble-metal
cocatalysts.24,25 The photocatalytic performance of CdS was
enhanced to 263 mmol hÀ1 on the usage of Ni3C as a cocatalyst
and further boosted remarkably on integration with a Co-molecular
cocatalyst. The highest rate of 750 mmol hÀ1 was achieved under
optimal conditions and the system demonstrated robust stability of
80 hours. The maximum apparent quantum yield of 53.2% was
obtained using monochromatic 420 nm light.
Fig. 1 (a) Photocatalytic H2 activities of CdS/Ni3C NR samples and pure
CdS NRs. Photocatalytic samples contained 1.0 mg photocatalyst, 0.75 M
Na2S and 1.05 M Na2SO3 in 20 mL Millipore water. (b) Effect of concen-
tration of electron donors: (A) 0.5 M Na2S, 0.7 M Na2SO3; (B) 0.75 M Na2S,
Results and discussion
The as-synthesized photocatalysts were utilized for the investiga- 1.05 M Na2SO3; (C) 1.0 M Na2S, 1.40 M Na2SO3; (D) 1.25 M Na2S, 1.75 M
Na2SO3; (E) 1.5 M Na2S, 2.1 M Na2SO3. (c) H2 evolution profiles of 0.01 mM
tion of photocatalytic H2 evolution performances under visible
light (l 4 420 nm). The real amount of nickel in each sample
was investigated by ICP-AES and is given in Table S1 (ESI†).
cocatalysts PX1, PX2, Co2+ and ligand of PX1 on 1 mg NC3 using 1.0 M
Na2S and 1.40 M Na2SO3 as sacrificial reagents in 20 mL Millipore water.
(d) Molecular structures of cobalt-based homogenous cocatalysts.
Fig. 1a shows the comparison of photocatalytic outcomes of
pristine CdS and samples NC1–NC5. The reaction mixtures were
prepared using 1 mg photocatalyst, 1.05 M Na2SO3 and 0.75 M photocatalytic H2 production rate of NC3. The concentration
Na2S in 20 mL Millipore water. The results demonstrate a ratio of Na2S and Na2SO3 was kept constant at 5 : 7. At the low
relatively poor H2 production rate of 27 mmol hÀ1 mgÀ1 for pure concentration of 0.5 M Na2S and 0.7 M Na2SO3, the H2 evolu-
CdS NRs. This deficient performance of CdS NRs may be due to tion rate was 145 mmol hÀ1. An enhancement was observed with
the fast recombination of photogenerated electron–hole pairs. the increased concentration of sacrificial reagents. The optimum
Loading of Ni3C on CdS NRs enhances the H2 production rate to concentration was 1.0 M : 1.4 M (Na2S : Na2SO3) at which the
63 mmol hÀ1 and it further improves with the increasing content highest H2 evolution rate of 263 mmol hÀ1 was observed. Further
of Ni3C. The highest H2 evolution rate of 182 mmol hÀ1 was increase in concentration showed a decrease in the rate of H2
detected for NC3 suggesting the optimum amount of Ni3C on evolution. Initially, the increased amount of sacrificial reagents
CdS NRs. After this, a decrease in H2 production rate was enhances the H2 evolution by reducing the increased number of
observed for samples NC4 and NC5. This phenomenon proves photogenerated holes. As the concentration of sacrificial
that loading of an optimum amount of cocatalyst to semicon- reagents further increases, the solution becomes over saturated
ductor photocatalysts is critical for enhanced photocatalytic and solid particles can shield the visible light, which leads to a
activity.26,27
Initially, Ni3C offers catalytic active sites to CdS NRs for the
decrease in the H2 production rate.30
Furthermore, the effect of molecular cocatalysts on the H2
transfer of photogenerated electrons, which suppress the rapid evolution rate of the current photocatalytic system was thoroughly
recombination of photogenerated charges. The photo-induced studied (Fig. 1c). Molecular cocatalysts PX1 and PX2 (Fig. 1d) show
electron transfer enhances with the increased content of Ni3C increased H2 evolution rate than the composite photocatalyst. The
on CdS NRs, and therefore enhances the H2 production rate. highest H2 production rate of 554 mmol hÀ1 was obtained for PX1
Further loading of Ni3C than the optimal amount hinders the probably due to its higher solubility in water as compared to PX2.
active sites of CdS NRs and inhibits the visible light absorption. The enhanced solubility of a molecular cocatalyst enables it to
Ultimately, a decrease in the photogenerated electrons is interact more with a photosensitizer, which results in a high
observed, which leads to a decreased rate of H2 evolution.18,28 electron capturing ability. On the other hand, poor solubility of a
Moreover, pure Ni3C did not show H2 evolution while all the molecular cocatalyst results in the formation of aggregates, which
CdS/Ni3C NR samples exhibited higher H2 evolution rate than leads to low electron transfer processes. Ultimately, the H2 evolu-
CdS NRs proving that Ni3C alone cannot produce H2 but it plays tion rate of the photocatalytic system decreases.30 Besides, Co ions
a crucial role to enhance the photocatalytic activity of CdS NRs were employed as the cocatalyst, which resulted in lower H2
as cocatalyst.
production than PX1, inferring the significant role of the homo-
The concentration of the sacrificial reagent critically affects genous cocatalyst. On the other hand, the ligand of PX1 did not
the rate of H2 evolution in a photocatalytic system.29,30 Fig. 1b show enhancement, which means that a ligand without central
shows the effect of concentration of Na2S and Na2SO3 on the metal ions is not effective. Moreover, the concentration of the
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Fig. 2 (a) Comparison of H2 evolution rates of different samples. (b) Com-
parison of inexpensive cocatalysts with 1 wt% Pt on CdS and NC3 (CdS/Ni3C),
respectively. Photocatalytic samples contained 1.0 mg photocatalyst, 1.0 M
Na2S and 1.40 M Na2SO3 in 20 mL Millipore water.
molecular cocatalyst has a significant effect on the H2 evolution
rate of the photocatalytic system. Fig. S4 (ESI†) shows that with
the increase in the concentration of PX1, the H2 evolution rate
increases. This result illustrates that a greater number of PX1
molecules can capture more electrons from NC3 photosensitizer,
suppressing the charge recombination effectively. The highest H2
evolution rate of 750 mmol hÀ1 was observed for 0.02 mM of PX1
depicting it as the optimal concentration of the molecular
cocatalyst for the current photocatalytic system. Further increase
in the concentration of the molecular cocatalyst can shield the
visible light, resulting in a decreased H2 evolution rate.31
Fig. 3 (a) Apparent quantum yield of sample NC3/PX1. The photocatalytic
system contained 1.0 mg photocatalyst, 0.02 mM molecular cocatalyst
(PX1), 1.0 M Na2S and 1.4 M Na2SO3 in 20 mL Millipore water. (b) Long-
term H2 production using 2.5 mg NC3 as photocatalyst, 0.02 mM molecular
cocatalyst (PX1), 1.0 M Na2S and 1.4 M Na2SO3 as sacrificial reagents in
50 mL Millipore water under visible light (l 4 420 nm). (c) The cyclic runs of
photocatalytic H2 evolution. (d) Comparison of photocatalytic H2 evolution
under air and inert atmosphere. Photocatalytic samples contained 1.0 mg
NC3 as photocatalyst, 0.02 mM molecular cocatalyst (PX1), 1.0 M Na2S and
1.4 M Na2SO3 in 20 mL Millipore water.
Fig. 2a shows the comparison of different photocatalytic
samples. Ni3C/PX1 produced no H2 in the absence of a photo- (l 4 420 nm). A total of 50.1 mmol H2 was produced with the
sensitizer, suggesting that neither Ni3C nor PX1 is visible light highest rate of 758 mmol hÀ1 indicating good stability of the
active and their role in the current photocatalytic system is current photocatalytic system. The reusability of the photocatalyst
merely as cocatalysts. Moreover, CdS integrated with molecular was also confirmed by time course analysis of H2 evolution
cocatalyst PX1 showed an enhanced H2 evolution rate of (Fig. 3c). Four consecutive runs were performed in 1.0 M Na2S
321 mmol hÀ1, indicating the efficient charge separation ability and 1.4 M Na2SO3 aqueous solution. The produced H2 was
of molecular cocatalysts. When CdS was simply mixed with removed from the flask after each run of 3 hours. No significant
Ni3C, poor H2 evolution rate (105 mmol hÀ1) than that of CdS/ decrease was observed during four consecutive runs suggesting
Ni3C composite was observed indicating the crucial role of the the good stability and reusability of the photocatalyst. Fig. 3d
interfacial contact of CdS and Ni3C in NC3. Employment of shows the photocatalytic activity of NC3/PX1 NRs in 1.0 M Na2S
molecular cocatalyst PX1 with NC3 results in the highest H2 and 1.4 M Na2SO3 aqueous solution under air and inert atmo-
evolution rate of 750 mmol hÀ1, which might be due to the sphere. The results describe a higher H2 production rate under
synergistic electron capturing effect of Ni3C and PX1, resulting in inert atmosphere than air. The lower H2 evolution rate under air
the effective suppression of charge recombination. To confirm can be assigned to the presence of O2, which may lead the
the efficiencies of current cocatalysts, their performances were reaction backward and produce H2O on the catalytic surface.32
compared with that of well-known noble metal cocatalyst, 1 wt%
The successful synthesis of photocatalysts and particular
loaded Pt. Fig. 2b depicts the higher H2 evolution rates of CdS/ role of cocatalysts was thoroughly analyzed using several analytical
Ni3C and CdS/Ni3C/PX1 NRs than that of CdS/Pt and CdS/Ni3C/Pt techniques. Fig. 4a shows the XRD patterns of Ni3C. It is obvious
NRs, respectively. These results prove that Ni3C and PX1 are from the diffraction peaks that the currently synthesized Ni3C is a
highly efficient cocatalysts for CdS under present conditions.
hexagonal Ni3C (JCPDS No. 06-0697). The peaks located at 39.271,
The apparent quantum yields (AQYs) of the photocatalytic 41.761, 44.521, 58.631, 71.211 and 78.101 can be assigned to (110),
reaction system were estimated in 1.0 M Na2S and 1.4 M Na2SO3 (006), (113), (116), (300) and (119) crystal planes, respectively.33
aqueous solution under monochromatic visible light (l = 420 nm). Pure CdS NRs presented its typical hexagonal structure (JCPDS No.
Fig. 3a shows that an average AQY of 47% was obtained during 77-2306).31,34 Furthermore, similar structure of CdS NRs was
6 hours of irradiation. The maximum AQY value reached to detected in samples NC1–NC5 (Fig. 4b). No distinguished peak
53.2%, indicating the efficient catalytic performance of NC3/PX1 of Ni3C was found in samples NC1-NC3, which may be due to the
NR photocatalyst for H2 evolution from water. Furthermore, the less content of Ni3C on CdS NRs or due to the less crystalline
stability of the photocatalytic system was evaluated over long- nature of Ni3C as compared to CdS. However, a new peak can be
term irradiation (Fig. 2b). The current photocatalytic system seen in sample NC4 at 44.851 corresponding to the (113) face of
showed good stability over 80 hours of visible light irradiation Ni3C. Moreover, three additional peaks were observed in sample
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spectrum of Cd showed two binding energies at 404.5 eV and
411.1 eV corresponding to Cd 3d3/2 and Cd 3d1/2 (Fig. 6b).35 In
Fig. 6c, two peaks appeared that can be attributed to S 2p3/2
(160.9 eV) and S 2p1/2 (162.1 eV). The Ni 2p3/2 and Ni 2p1/2 peaks
were observed at 853.2 eV and 870.4 eV, respectively (Fig. 6d).36,37
The peak at 284.7 eV can be attributed to C 1s, which is
consistent with the previous reports (Fig. 6e).38,39 Moreover, no
peak of metallic Ni was observed. These outcomes prove the
successful formation of pure CdS/Ni3C NR photocatalysts. Fig. 6f
Fig. 4 (a) Powder XRD patterns of pristine Ni3C. (b) Powder XRD patterns shows the high resolution spectrum of Co 2p having peaks at
of CdS, CdS/Ni3C samples and Ni3C (* shows the peak positions of Ni3C in
CdS/Ni3C samples).
780.64 eV and 796.46 eV corresponding to Co 2p3/2 and Co 2p1/2
,
respectively.31
To investigate the stable behavior of the NC3 photocatalyst
and molecular role of PX1 during the photocatalytic reaction,
XRD patterns, SEM image, EDX and XPS spectra were obtained.
The photocatalyst was collected after 6 hours of irradiation and
thoroughly washed with water. The diffraction peaks of the
samples before and after irradiation are well aligned with each
other suggesting the stable crystal structure of NC3 (Fig. S6a,
ESI†). SEM images were obtained to examine the variation in
the morphology of the photocatalyst. Fig. S6b (ESI†) shows the
intact nanorod morphology of the photocatalyst during irradia-
tion. Furthermore, EDX data was attained to confirm the elemental
composition of the photocatalyst after irradiation. Fig. S7 (ESI†)
displays the presence of all building elements of NC3, Cd, S, Ni
and C, which demonstrates the excellent stability of CdS/Ni3C NRs.
Furthermore, no Co peak was detected, suggesting the absence of
elemental Co after irradiation. Besides, XPS spectra were collected
to investigate the changes in the photocatalyst after irradiation.
Fig. S8 (ESI†) illustrates that no change in the shape and position
of peaks occurred in the high resolution spectra of Cd and Ni,
further confirming the robust stability of the present photocatalytic
system. However, the characteristic peak of Co 2p was absent
after irradiation, which confirms that PX1 did not decompose to
elemental cobalt and plays a crucial role in current enhancement
as a molecular cocatalyst.
NS5 at 39.491, 41.851and 44.851, which can be attributed to (100),
(002) and (101) planes, respectively.
The morphologies of the photocatalysts were studied using
SEM and TEM images. Fig. 5a displays the SEM image of pure
CdS NRs proving the nanorod morphology with diameters of
40–95 nm and lengths of 0.4–2 mm. On the other hand, the SEM
image of NC3 shows a solid mass, which is in well contact with
CdS NRs suggesting the presence of Ni3C (Fig. 5b). Moreover,
the TEM image also shows the existence of black mass over CdS
NRs further confirming the presence of Ni3C (Fig. 5c). Fig. S5
(ESI†) displays the HRTEM image having lattice fringes of
0.33 nm and 0.20 nm, which can be attributed to 002 and
113 crystal faces of CdS and Ni3C, respectively.19,25 EDX data
was collected to confirm the presence of expected elements in
the sample. In Fig. 5d, the EDX spectrum of NC3 shows the
existence of Ni, C, Cd, S, Au and Cu. Au appeared as it was
sprayed on the sample for better conductivity and the signal of
Cu was detected due to the Cu grid.
X-ray photoelectron spectroscopy (XPS) was performed to
explore the presence and valence state of elemental composition
of sample NC3/PX1. In Fig. 6a, the XPS survey spectrum showed
the presence of Cd, S, Ni, C and Co. The high resolution
The optical properties of the photosensitizer and cocatalysts
were studied using UV-vis diffuse reflectance absorption spec-
trosopy. Fig. S8a (ESI†) shows that CdS NRs depicted its
Fig. 6 (a) XPS survey spectrum of NC3. (b) High resolution spectrum of Cd
3d. (c) High resolution spectrum of S 2p. (d) High resolution spectrum of Ni 2p.
(e) High resolution spectrum of C 1s. (f) High resolution spectrum of Co 2p.
Fig. 5 (a) SEM image of CdS NRs. (b) SEM image of NC3. (c) TEM image of
NC3. (d) EDX spectrum of NC3.
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characteristic absorption at 520 nm corresponding to a band CdS/Ni3C/PX1 NRs was used as the working electrode, Pt wire as
gap of 2.39 eV and molecular cocatalyst PX1 showed a broad the counter electrode and Ag/AgCl as the reference electrode.
absorption peak (Fig. S9a, ESI†).28 Moreover, Ni3C does not 0.5 M solution of Na2SO4 was used as the electrolyte. A consider-
show significant absorption edge in the visible region describing able photocurrent response was observed for both samples under
the metallic character of Ni3C. CdS/Ni3C NRs (NC3) sample visible light irradiation. Fig. 7b displays the higher photocurrent
proves that it cannot change the band gap of photocatalyst of CdS/Ni3C NRs sample as compared to pure CdS NRs. Besides,
(Fig. S9b, ESI†).30 Furthermore, no change in the absorption significant enhancement in photocurrent was observed for CdS/
edge of sample NC3 was observed upon loading of PX1, which Ni3C/PX1 NRs inferring that it possesses the highest charge
confirms that PX1 does not affect the band gap of the photo- transport ability, which enhances the photocatalytic activity.
catalyst and the enhanced H2 evolution rate might be due to the Furthermore, electrochemical impedance spectra were obtained
efficient electron transfer process. To further investigate the role to elucidate the charge transfer resistance of present photocata-
of cocatalysts, steady state photoluminescence (PL) spectroscopy lysts. Fig. S10 (ESI†) clearly shows that the arc radius of NC3/PX1
was used. Fig. 7a shows the obtained PL spectra of CdS NRs, is the smallest as compared to pure CdS and NC3 (CdS/Ni3C).
CdS/Ni3C NRs and CdS/Ni3C/PX1 NRs. Two distinct PL peaks It shows that PX1 effectively separated the photogenerated charge
were observed for pristine CdS NRs at B504 nm and B700 nm carriers and significantly supressed the charge recombination.44
using an excitation wavelength of 405 nm.40 The intense peak at These results are consistent with PL analysis and photocatalytic
504 nm probably corresponds to the near-band-edge emission H2 production experiments, further proving that Ni3C and PX1
and a broad peak at 700 nm may appear due to surface can synergistically enhance the performance of CdS NRs as
defects.32,41 The intensity of these PL emission bands reduces cocatalysts under optimized conditions.
notably upon loading of Ni3C on CdS NRs (NC3) and further
To know more about the mechanistic role of PX1 in the
decrease was observed in the case of NC3/PX1, indicating the fast present photocatalytic system, cyclic voltammetric (CV) mea-
electron transfer processes at their interfaces. Besides, a low PL surements were performed. Experiments were carried out using
intensity at 700 nm was also observed, which confirms the 0.5 mM PX1 in dry acetonitrile containing 0.1 M TBAPF6 as
passivation of surface defects. These phenomena increase the electrolyte and 0.2 M ferrocene as internal standard. Fig. 7c
opportunity of the photoinduced electron to produce more shows the reductive scan having an obvious wave at À8.45 (V vs
photocatalytic H2.42,43
Fc+/Fc), which can be assigned to Co(II)/Co(I). Upon addition of
The photoelectrochemical measurements were achieved to acetic acid, the Co(II)/Co(I) peak remains nearly constant but an
examine the electron transfer process between the photosensitizer increase in current was observed, which continuously increased
and cocatalysts under visible light irradiation. The fluorine-doped with the increasing concentration of acetic acid. This observa-
tin oxide (FTO) electrode coated with CdS NRs, CdS/Ni3C NRs and tion can be attributed to the production of H2 involving the
formation of Co(I) species as an essential step (Fig. 7d).
Comprehensively, visible light excites CdS NRs and produces
electron–hole pairs. From the conduction band of CdS, photo-
generated electrons move towards the nearby Ni3C. The more
number of Ni3C entities can guarantee the rescue of more number
of electrons from recombination to holes. Consequently, this can
result in an increased photocatalytic H2 evolution. However,
further loading of Ni3C than the optimal amount is not fruitful
as it can block the visible light active sites of the photosensitizer.
Besides, the Co-based molecular cocatalyst swiftly accepts the
excess photogenerated electrons. After accepting the electrons, the
Fig. 7 (a) Photoluminescence spectra of CdS, CdS/Ni3C (NC3) and CdS/
Ni3C/PX1 excited at a wavelength of 405 nm. (b) Transient photocurrent
responses of CdS, CdS/Ni3C and CdS/Ni3C/PX1 samples. (c) Cyclic voltam-
mogram (CV) of 0.5 mM PX1 prepared in dry acetonitrile. The solution
contained 0.1 M TBAPF6 as the electrolyte and 0.2 M ferrocene as the
internal standard. (d) CVs of 0.5 mM PX1 in the presence of different
concentrations of acetic acid. The scan rate of CV was kept at 50 mV sÀ1
using a glassy carbon working electrode.
Scheme 1 Schematic depiction of CdS/Ni3C/PX1 photocatalytic system.
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Conclusions
In summary, a molecular cocatalyst was synthesized by a facile
method and successfully employed with a composite photocatalyst
CdS/Ni3C NRs for highly improved photocatalytic H2 evolution. The
photocatalytic activity of the system was boosted to 750 mmol hÀ1
due to the efficient electron capturing ability of molecular cocata-
lyst PX1. The highest apparent quantum yield of 53.2% was
attained using monochromatic 420 nm light. The present photo-
catalytic system demonstrated excellent durability and long-term
stability reached to 80 hours under visible light irradiation. PL
spectra and photocurrent responses inferred the swift electron
transfer at the interface of cocatalysts and CdS NRs, which
hindered the rapid recombination of charge carriers. Interestingly,
Ni3C and PX1 synergistically enhanced the H2 production ability of
CdS NRs, which also reinforced the stability by inhibiting the
photocorrosion process. This study presents an excellent strategy to
build highly productive and non-noble metal photocatalytic system
for H2 evolution having potential large-scale applications.
Conflicts of interest
23 R. S. Khnayzer, B. S. Olaiya, K. A. El Roz and F. N. Castellano,
ChemPlusChem, 2016, 81, 1015.
There are no conflicts to declare.
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Acknowledgements
This work was supported by the National Natural Science
Foundation of China [grant number 21703147 and U1401248,
51850410508]; the Natural Science Foundations for the Young
Scientist of Jiangsu Province [grant number BK20170338]; The
Open Fund of Jiangsu Key Laboratory of Materials and Tech-
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