Novel Cu3P/g-C3N4 p-n heterojunction photocatalysts for solar hydrogen generation

Science China Materials, Jan 2018

Developing efficient heterostructured photocatalysts to accelerate charge separation and transfer is crucial to improving photocatalytic hydrogen generation using solar energy. Herein, we report for the first time that p-type copper phosphide (Cu3P) coupled with n-type graphitic carbon nitride (g-C3N4) forms a p-n junction to accelerate charge separation and transfer for enhanced photocatalytic activity. The optimized Cu3P/g-C3N4 p-n heterojunction photocatalyst exhibits 95 times higher activity than bare g-C3N4, with an apparent quantum efficiency of 2.6% at 420 nm. A detail analysis of the reaction mechanism by photoluminescence, surface photovoltaics and electrochemical measurements revealed that the improved photocatalytic activity can be ascribed to efficient separation of photo-induced charge carriers. This work demonstrates that p-n junction structure is a useful strategy for developing efficient heterostructured photocatalysts.

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Novel Cu3P/g-C3N4 p-n heterojunction photocatalysts for solar hydrogen generation

Novel Cu3P/g-C3N4 p-n heterojunction photocatalysts for solar hydrogen generation Zhixiao Qin 0 Menglong Wang 0 Rui Li 0 Yubin Chen 0 0 International Research Center for Renewable Energy, State Key Laboratory of Multiphase Flow in Power Engineering, Xi'an Jiaotong University , Shaanxi 710049 , China Developing efficient heterostructured photocatalysts to accelerate charge separation and transfer is crucial to improving photocatalytic hydrogen generation using solar energy. Herein, we report for the first time that p-type copper phosphide (Cu3P) coupled with n-type graphitic carbon nitride (g-C3N4) forms a p-n junction to accelerate charge separation and transfer for enhanced photocatalytic activity. The optimized Cu3P/g-C3N4 p-n heterojunction photocatalyst exhibits 95 times higher activity than bare g-C3N4, with an apparent quantum efficiency of 2.6% at 420 nm. A detail analysis of the reaction mechanism by photoluminescence, surface photovoltaics and electrochemical measurements revealed that the improved photocatalytic activity can be ascribed to efficient separation of photo-induced charge carriers. This work demonstrates that p-n junction structure is a useful strategy for developing efficient heterostructured photocatalysts. photocatalysis; copper phosphide; p-n junction; heterostructure; hydrogen production INTRODUCTION Hydrogen is considered to be an ideal energy source to substitute fossil fuel due to its high energy capacity and environmental friendliness [1]. Since the discovery of the Honda-Fujishima effect in 1972 [2], photocatalytic hydrogen production from water has attracted much attention as an ideal solution to global energy and environmental issues [3–6]. Developing highly active, long-term stable and low-cost photocatalysts is still a key to their commercial application. Recently, graphitic carbon nitride (g-C3N4) has emerged as an attractive metalfree polymeric semiconductor for photocatalytic hydrogen generation due to its specific laminar structure, high stability and capability of visible-light harvest [7–11]. However, the severe photo-induced charge recombination and surface reaction still restrict the photocatalytic performance. Loading suitable cocatalysts seems to be a useful approach to boost photocatalytic hydrogen generation [12–14]. To date, Pt has been widely utilized as an efficient cocatalyst with g-C3N4, leading to significantly improved performances [15]. However, the high cost and low reserve of Pt limit the large-scale application and hence the development of non-precious photocatalytic system is quite appealing. Recently, it has been demonstrated that a series of transition-metal phosphides could promote the photocatalytic hydrogen generation superior to g-C3N4 as cocatalysts [16–19]. For instance, our previous work demonstrated that Ni2P cocatalyst could significantly increase photocatalytic performance for hydrogen generation over g-C3N4 [16]. Jiang et al. [17] reported that CoP was also an efficient cocatalyst to enhance the photocatalytic activity of g-C3N4. Besides g-C3N4, the photocatalytic properties of various semiconductor photocatalysts such as CdS [20–22], TiO2 [16,23], and CdxZn1-xS [24] could also be increased by coupling with transitionmetal phosphides. However, the reported reaction mechanisms of these transition-metal phosphides are quite different. It is necessary to investigate more general coupling principle between photocatalysts and transitionmetal phosphides as a guidance to develop efficient noble-metal-free hybrid photocatalysts. Coupling semiconductors with different band structures to form heterojunction structure has been proved to be an effective way to promote the charge separation and photocatalytic performance [24–26]. When p-type semiconductor is combined with n-type semiconductor, a built-in electric field is achieved across the p-n junction region, which can efficiently promote the separation of photo-induced charges [27]. Copper phosphide (Cu3P) is a p-type semiconductor with a band gap of 1.5 eV [23]. Due to its low cost and earth-abundant elements, Cu3P was previously reported for application in lithium ion batteries [28–30]. However, the utilization of Cu3P in photocatalytic hydrogen generation is still limited. Herein, we report a novel and low-cost Cu3P/g-C3N4 p-n heterojunction photocatalyst for highly efficient hydrogen generation. Nanoscale p-n junctions developed in the hybrid photocatalysts could efficiently improve the photo-induced charge separation, leading to the significantly enhanced photocatalytic performance. EXPERIMENTAL SECTION Synthesis procedure All chemicals in the present study are of analytical grade and used as received without further purification. g-C3N4 was synthesized by heating 10 g of urea at 550°C for 2 h in the air to obtain yellow powder. In a typical synthesis, Cu(OH)2/g-C3N4 was prepared by a simple precipitation method. 0.4 g of g-C3N4 was dispersed in 100 mL of 0.25 mol L–1 NaOH aqueous solution, and then Cu(NO3)2·3 H2O was added under stirring. The mixed solution was stirred for 6 h at room temperature. The products were collected and washed three times with deionized water and ethanol. Then the precipitates were dried in a vacuum oven at 80°C for 5 h. Finally, Cu3P/g-C3N4 photocatalyst was synthesized through a solid-state reaction. Typically, 0.2 g of the prepared Cu(OH)2/g-C3N4 and 0.1 g of NaH2PO2 were blended mechanically and ground into fine power. Then, the fine power was annealed at 300°C for 2 h in a quartz tube with a heating rate of 5 °C min−1 under Ar flow. The obtained products were washed with deionized water to remove residual salts, and dried under vacuum at 50°C. The Cu3P was also prepared using a similar procedure. The loading weight of Cu3P in Cu3P/ g-C3N4 was measured by X-ray photoelectron spectroscopy (XPS) analysis and the results were shown in Table S1. The practical loading concentrations of Cu3P were close to the theoretical values. Characterization X-ray powder diffraction (XRD) patterns were obtained from a PANalytical X’pert MPD Pro X-ray diffractometer. Transmission electron microscopy (TEM) images were obtained using a FEI Tecnai G2 F30 S-Twin microscope attached with an OXFORD MAX-80 energy dispersive X-ray (EDX) system. UV-visible (UV-vis) absorption spectra were measured on a HITACHI U4100 spectrophotometer. XPS measurements were conducted on a Kratos Axis-Ultra multifunctional X-ray spectrometer. All binding energies were referenced to the C 1s peak at 284.8 eV. Photoluminescence (PL) spectra were examined using a PTI QM-4 fluorescence spectrophotometer with an excitation wavelength of 320 nm. The lock-in-based surface photovoltage (SPV) spectra were obtained using a surface photovoltage spectroscope. The measurement system consists of a source of monochromatic light (Omni-λ300), a lock-in amplifier (SR830) with a light chopper (SR540), and a sample chamber. Visible-light-driven photocatalytic measurement Photocatalytic hydrogen generation was performed in a side irradiation Pyrex cell with a magnetic stirring. Typically, 20 mg of the as-prepared photocatalyst was added into 80 mL of aqueous solution containing 10 vol% triethanolamine (TEOA) as the electron donors. Before irradiation, nitrogen was purged into the reaction cell for 30 min to remove air in the dark. The reaction temperature was kept at 35°C. A 300 W Xe-lamp equipped with a 420 nm cutoff filter was employed to provide the visible-light irradiation. The amount of generated hydrogen was measured by gas chromatography using a thermal conductivity detector (TCD). The apparent quantum efficiency (AQE) could be calculated as AQE(%) =(The number of evolved hydrogen molecules×2/The number of incident photons)×100%. RESULTS AND DISCUSSION Physicochemical properties of Cu3P/g-C3N4 heterostructure The crystal structures of the as-prepared samples were investigated by XRD. As shown in Fig. 1, two distinct diffraction peaks of bare g-C3N4 could be attributed to the graphitic phase with tri-s-triazine units. The Cu3P sample shows diffraction peaks located at 36.0°, 39.0°, 41.5°, 45.1°, and 46.2°, corresponding to the (112), (202), (211), (300), and (213) planes of hexagonal Cu3P (PDF#712261) [22]. It has been reported that trace amount of Cu was involved in the Cu3P sample, which was prepared via a phosphatization method [23]. The main diffraction peaks of Cu3P/g-C3N4 could be attributed to the graphitic phase g-C3N4. There were not apparent peaks corresponding to Cu3P, possibly due to the low amount and high dispersity. We further investigated the morphology of g-C3N4 photocatalysts after loading Cu3P. As displayed in Fig. 2a, the hybrid samples had uniformly dispersed Cu3P nanoparticles anchored on the surface of g-C3N4 nanosheets 2. . . . . . . . . . . . . . . . . . . . . . . . . .©. .Sc.ie.nc.e.C.hi.na. P.r.es.s a.n.d.Sp.r.in.ge.r-.V.er.lag. G.m.b.H. G.e.rm.a.n.y .20.18. . . . . . . . . . . . . . . . . . . . . . . . . . . SCIENCE CHINA Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ARTICLES (Fig. 2b). The lattice distance of 0.25 nm corresponded to the (112) plane of hexagonal Cu3P. To determine the composition and element distribution of Cu3P/g-C3N4, the elemental mapping of C, N, Cu, and P species was carried out (Fig. 2c). It was proved that Cu3P nanoparticles were successfully distributed on the surface of gC3N4. The specific surface area of Cu3P/g-C3N4 was 70.2 m2 g−1, which was close to that of single g-C3N4 (73.1 m2 g−1). This result indicated that the fabrication of hybrid samples did not lead to agglomeration of g-C3N4. XPS measurements were performed to investigate the surface chemical states of Cu3P/g-C3N4. As shown in Fig. 3a, the typical values for C–C, C–NH2, and N–C=N in gC3N4 were respectively presented at binding energies of 284.8, 286.1, and 288.1 eV [31]. Meanwhile, the peaks at 398.4, 399.6, 401.1, and 404.2 eV of N 1s spectrum (Fig. 3b) could be assigned to the binding energies of C–N=C, N–(C)3, C–N–H, and π excitations of g-C3N4, respectively [24]. Fig. 3c shows the Cu 2p profile with a peak located at 932.3 eV, and the P 2p region has a single peak at 133.6 eV (Fig. 3d). The peak at 932.3 eV could be ascribed to Cu–P in Cu3P, and the peak at 133.6 eV arose from oxidized P species probably due to the air exposure [23]. The XPS results further demonstrated the successful synthesis of Cu3P and g-C3N4 in the heterostructure. The optical properties of the as-prepared samples were measured by UV-vis spectrophotometer. As shown in Fig. 4a, the spectrum of bare g-C3N4 displayed a sharp edge at around 450 nm. After the coupling of Cu3P onto the gC3N4 surface, an increased absorption in visible range of 400–800 nm was observed. Meanwhile, the UV-vis absorption spectrum of pure Cu3P (Fig. 4b) showed an apparent absorption from 300 to 800 nm. The absorption peak around 550 nm could be attributed to the plasmon peak of Cu nanoparticles in as-prepared Cu3P sample [32]. The optical band gaps (Eg) of g-C3N4 and Cu3P were estimated from Tauc plots of (αhν)n vs. photon energy (hν) [33]. The insets show that the band gaps of g-C3N4 and Cu3P were respectively determined to be 2.72 and 1.50 eV, which were consistent with the previous studies [23,34]. Photocatalytic hydrogen production The photocatalytic hydrogen generation was subsequently . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ©.. .S.ci.e.n.ce. .C.h.in.a. .P.re.s.s.a.n.d. S.p.r.i n.g.e.r-. V.e.r.la.g. G..m. b. H..G. e.r.m. a.n.y. 2.0.1.8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 investigated in triethanolamine (TEOA) aqueous solution under visible-light irradiation. As shown in Fig. 5a, the hydrogen production rate of bare g-C3N4 was rather low, and Cu3P could significantly boost the photocatalytic hydrogen generation of g-C3N4. The rate of hydrogen generation initially increased and then decreased with increasing amount of Cu3P. With the optimal loading amount of Cu3P, Cu3P/g-C3N4 showed the highest hydrogen production rate of 284 μmol h−1 g−1, which was about 95 times higher than that of bare g-C3N4. The apparent quantum efficiency (AQE) for hydrogen generation was calculated to be 2.6% at 420 nm. However, no appreciable hydrogen generation could be detected in bare Cu3P, indicating that Cu3P was not an active photocatalyst [22]. By comparison, the activity of physically mixed Cu3P@g-C3N4 was measured under the same condition. The hydrogen production rate of Cu3P@gC3N4 was much lower than that of Cu3P/g-C3N4, revealing that the intimate contact between Cu3P and g-C3N4 takes effect on the performance [24]. Long-term photocatalytic test of Cu3P/g-C3N4 for hydrogen generation was carried out to evaluate the stability of Cu3P/g-C3N4 hybrid photocatalysts. As displayed in Fig. 5b, there was no apparent decrease in the photocatalytic activity over the 20 h reaction, indicating its good stability. Mechanism study PL spectra of the as-prepared samples were measured to explore the charge separation and migration behaviors in the photocatalyst. As shown in Fig. 6a, both g-C3N4 and Cu3P/g-C3N4 exhibited broad emission peaks centered around 450 nm, corresponding to the band gap of g-C3N4. Compared to pure g-C3N4, Cu3P/g-C3N4 showed apparently decreased PL intensity, which indicated that loading Cu3P could facilitate the charge transfer so as to inhibit the charge recombination in g-C3N4 [35], which was beneficial to photocatalytic performance. The lock-in-based SPV spectra were also carried out to reveal the transfer properties of the photo-induced charge carriers. The signal of SPV can be attributed to the variation of surface potential barriers during the light irradiation, which can identify the light-responsive wavelength range and the separation efficiency of the electron-hole pairs in the photocatalysts [36]. As shown in Fig. 6b, positive photovoltaic responses ranging from 300 to 400 nm were observed for g-C3N4, indicating that g-C3N4 is a typical n-type semiconductor [37]. After loading Cu3P on the surface of g-C3N4, the response signal of Cu3P/g-C3N4 was obviously enhanced. The enhanced SPV signal intensity indicated that the introduction of Cu3P was beneficial to the photo-induced charge separation in Cu3P/g-C3N4 heterostructures [38]. In addition to the charge-transfer behavior in the photocatalyst, the charge-transfer at the photocatalyst/ solution interface is also crucial to the photocatalytic performance. Therefore, g-C3N4 and Cu3P/g-C3N4 electrodes were fabricated (see Supplementary information) and the electrochemical impedance spectroscopy (EIS) was performed to elucidate the charge-transfer resistances. As shown in Fig. 7a, the Nyquist impedance plots for the electrodes could be fitted to an equivalent circuit (the inset) consisting of the series resistance (Rs), charge transfer resistance from the electrode to the electrolyte (Rct), recombination resistance at the electrode interface (Rrec), and constant phase elements (CPE1 and CPE2). As summarized in Table S2, the values of Rct and Rrec for Cu3P/g-C3N4 were lower than those of g-C3N4, indicating that the Cu3P/g-C3N4 had efficient chargetransfer behavior at the photocatalyst/solution interface [16,39]. The transient photocurrent responses of g-C3N4 4. . . . . . . . . . . . . . . . . . . . . . . . . .©. .Sc.ie.nc.e.C.hi.na. P.r.es.s a.n.d.Sp.r.in.ge.r-.V.er.lag. G.m.b.H. G.e.rm.a.n.y .20.18. . . . . . . . . . . . . . . . . . . . . . . . . . . and Cu3P/g-C3N4 were also investigated to examine their photoelectrochemical properties. As shown in Fig. 7b, Cu3P/g-C3N4 exhibited a much higher photocurrent density than that of pure g-C3N4, suggesting a noticeable improvement in the suppression of charge recombination [40], which was consistent with PL and SPV results. The spectroscopic and electrochemical analyses revealed that Cu3P/g-C3N4 owns efficient charge separation, which is essential to achieve high photocatalytic activity. To better understand the photo-induced charge carrier dynamics involved in the Cu3P/g-C3N4 heterojunction, the band alignment of Cu3P and g-C3N4 were investigated. The valence band positions (EVB) of Cu3P and g-C3N4 were firstly measured by XPS valence band spectra. As displayed in Fig. 8a, b, the EVB of Cu3P and gC3N4 were determined to be 0.71 and 1.74 eV, respectively. Since the band gaps (Eg) of Cu3P and g-C3N4 were 1.50 and 2.72 eV, respectively, the conduction band positions (ECB) of Cu3P and g-C3N4 were calculated to be −0.79 and −0.98 eV, according to the equation: EVB = ECB + Eg [41]. Mott-Schottky plot of g-C3N4 showed (Fig. 8c) a positive slope, indicating that it is an n-type semiconductor, while a negative slope of Cu3P (Fig. 8d) corresponds to a p-type semiconductor [42]. The flat-band potentials of Cu3P and g-C3N4 were estimated to be 0.56 and −0.88 V vs. RHE, which were close to the determined EVB of Cu3P and ECB of g-C3N4. As shown in Fig. S1, Cu3P/ g-C3N4 exhibited the similar feature as pristine g-C3N4 owing to the low amount of Cu3P. A positive slope was observed for Cu3P/g-C3N4, and the flat band potential was determined to be −0.75 V vs. RHE, which was close to that of g-C3N4. Therefore, the energy band structures of Cu3P and gC3N4 before forming the heterojunction are shown in Fig. 9a. The Fermi level (EF) of g-C3N4 is higher than that of Cu3P. When p-type Cu3P is coupled with n-type g-C3N4, electrons will transfer from g-C3N4 to Cu3P until the Fermi levels to be equal for both phases [43]. As shown in Fig. 9b, a built-in electric field is formed across the p-n junction, where the p-type Cu3P region is negatively charged, and the n-type g-C3N4 region is positively . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ©.. .S.ci.e.n.ce. .C.h.in.a. .P.re.s.s.a.n.d. S.p.r.i n.g.e.r-. V.e.r.la.g. G..m. b. H..G. e.r.m. a.n.y. 2.0.1.8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 charged. When Cu3P/g-C3N4 photocatalysts are irradiated with visible light, the photo-induced electrons and holes will be obtained in Cu3P and g-C3N4. As a result of the built-in electric field, the photo-induced electrons in the CB of Cu3P will diffuse into the CB of g-C3N4 through the p-n junction, giving rise to the accumulation of photoinduced electrons in g-C3N4. Meanwhile, the photo-induced holes in the VB of g-C3N4 will diffuse into the VB of Cu3P, leading to the accumulation of photo-induced holes in Cu3P. Subsequently, the accumulated photo-induced electrons can transfer to the surface of g-C3N4 to reduce H+ for hydrogen production, and the accumulated photo-induced holes can migrate to the surface of Cu3P to oxidize TEOA. As a consequence, the efficient charge separation is successfully achieved by the p-n junctions in hybrid Cu3P/g-C3N4. During the photocatalytic reaction, Cu3P captured the photo-induced holes in g-C3N4 and functioned as the active sites for the surface oxidation reaction. CONCLUSIONS In summary, Cu3P/g-C3N4 heterostructures were successfully constructed to achieve the efficient separation of photo-induced charges. Cu3P nanoparticles were tightly attached to the surface of g-C3N4, leading to the formation of p-n junctions between p-type Cu3P and n-type gC3N4. The p-n junctions could promote charge transfer and reduce charge recombination, leading to an enhanced photocatalytic activity. The optimized Cu3P/g-C3N4 p-n heterojunction photocatalyst exhibits 95 times higher activity than bare g-C3N4, with an apparent quantum efficiency of 2.6% at 420 nm. This work proposes an effective guidance to develop efficient noble-metal-free hybrid photocatalysts by p-n junction structure. Received 30 October 2017; accepted 28 November 2017; published online 15 January 2018 6. . . . . . . . . . . . . . . . . . . . . . . . . .©. .Sc.ie.nc.e.C.hi.na. P.r.es.s a.n.d .Sp.r.in.ge.r-.V.er.lag. G. m.b.H. G.e.rm.a.n.y .20.18. . . . . . . . . . . . . . . . . . . . . . . . . . . 26 27 28 29 30 31 32 33 34 35 36 Supplementary information online version of the paper. Supporting data are available in the . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ©.. .S.ci.e.n.ce. .C.h.in.a. .P.re.s.s.a.n.d. S.p.r.i n.g.e.r-. V.e.r.la.g. G..m. b. H..G. e.r.m. a.n.y. 2.0.1.8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Zhixiao Qin received his bachelor degree from Xi’an Jiaotong University in 2013. He is currently a PhD student at Xi’an Jiaotong University. His research interests focus on photocatalytic and photoelectrochemical water splitting. 秦知校, 王朦胧, 李锐, 陈玉彬* Liu G , Wang T , Zhang H , et al. Nature-inspired environmental “phosphorylation” boosts photocatalytic H2 production over carbon nitride nanosheets under visible-light irradiation . Angew Chem , 2015 , 127 : 13765 - 13769 Liu J , Liu Y , Liu N , et al. Metal-free efficient photocatalyst for stable visible water splitting via a two-electron pathway . Science , 2015 , 347 : 970 - 974 Li Y , Xu H , Ouyang S , et al. In situ surface alkalinized g-C3N4 toward enhancement of photocatalytic H2 evolution under visiblelight irradiation . J Mater Chem A , 2016 , 4 : 2943 -2950 Ong WJ , Tan LL , Ng YH , et al. Graphitic carbon nitride (g-C3N4 )- based photocatalysts for artificial photosynthesis and environmental remediation: are we a step closer to achieving sustainability? Chem Rev , 2016 , 116 : 7159 - 7329 Qin Z , Chen Y , Wang X , et al. Intergrowth of cocatalysts with host photocatalysts for improved solar-to-hydrogen conversion . ACS Appl Mater Interfaces , 2016 , 8 : 1264 - 1272 Chang K , Mei Z , Wang T , et al. MoS2/Graphene cocatalyst for efficient photocatalytic H2 evolution under visible light irradiation . ACS Nano , 2014 , 8 : 7078 - 7087 Yang J , Wang D , Han H , et al. Roles of cocatalysts in photocatalysis and photoelectrocatalysis . Acc Chem Res , 2013 , 46 : 1900 -1909 Maeda K , Wang X , Nishihara Y , et al. Photocatalytic activities of graphitic carbon nitride powder for water reduction and oxidation under visible light . J Phys Chem C , 2009 , 113 : 4940 -4947 Chen Y , Qin Z. General applicability of nanocrystalline Ni2P as a noble-metal-free cocatalyst to boost photocatalytic hydrogen generation . Catal Sci Technol , 2016 , 6 : 8212 -8221 Yi SS , Yan JM , Wulan BR , et al. Noble-metal-free cobalt phosphide modified carbon nitride: an efficient photocatalyst for hydrogen generation . Appl Catal B-Environ , 2017 , 200 : 477 -483 Indra A , Acharjya A , Menezes PW , et al. Boosting visible-lightdriven photocatalytic hydrogen evolution with an integrated nickel phosphide-carbon nitride system . Angew Chem Int Ed , 2017 , 56 : 1653 - 1657 Zhao H , Sun S , Jiang P , et al. Graphitic C3N4 modified by Ni2P cocatalyst: an efficient, robust and low cost photocatalyst for visible-light-driven H2 evolution from water . Chem Eng J , 2017 , 315 : 296 - 303 Sun Z , Zheng H , Li J , et al. Extraordinarily efficient photocatalytic hydrogen evolution in water using semiconductor nanorods integrated with crystalline Ni2P cocatalysts . Energy Environ Sci , 2015 , 8 : 2668 - 2676 Cao S , Chen Y , Wang CJ , et al. Spectacular photocatalytic hydrogen evolution using metal-phosphide/CdS hybrid catalysts under sunlight irradiation . Chem Commun , 2015 , 51 : 8708 - 8711 Sun Z , Yue Q , Li J , et al. Copper phosphide modified cadmium sulfide nanorods as a novel p-n heterojunction for highly efficient visible-light-driven hydrogen production in water . J Mater Chem A , 2015 , 3 : 10243 - 10247 Yue X , Yi S , Wang R , et al. A novel and highly efficient earthabundant Cu3P with TiO2 “P-N” heterojunction nanophotocatalyst for hydrogen evolution from water . Nanoscale , 2016 , 8 : 17516 - 17523 Qin Z , Xue F , Chen Y , et al. Spatial charge separation of onedimensional Ni2P-Cd0 . 9Zn0 . 1S/g-C3N4 heterostructure for highquantum-yield photocatalytic hydrogen production . Appl Catal BEnviron , 2017 , 217 : 551 - 559 Chen Y , Qin Z , Wang X , et al. Noble-metal-free Cu2S-modified photocatalysts for enhanced photocatalytic hydrogen production by forming nanoscale p-n junction structure . RSC Adv , 2015 , 5 : 18159 - 18166 Chen Y , Wang L , Lu GM , et al. Nanoparticles enwrapped with nanotubes: a unique architecture of CdS/titanate nanotubes for efficient photocatalytic hydrogen production from water . J Mater Chem , 2011 , 21 : 5134 - 5141 Meng F , Li J , Cushing SK , et al. Solar hydrogen generation by nanoscale p-n junction of p-type molybdenum disulfide/n-type nitrogen-doped reduced graphene oxide . J Am Chem Soc , 2013 , 135 : 10286 - 10289 Manna G , Bose R , Pradhan N. Semiconducting and plasmonic copper phosphide platelets . Angew Chem Int Ed , 2013 , 52 : 6762 - 6766 Ni S , Ma J , Lv X , et al. The fine electrochemical performance of porous Cu3P/Cu and the high energy density of Cu3P as anode for Li-ion batteries . J Mater Chem A , 2014 , 2 : 20506 -20509 Villevieille C , Robert F , Taberna PL , et al. The good reactivity of lithium with nanostructured copper phosphide . J Mater Chem , 2008 , 18 : 5956 - 5960 Liang Q , Li Z , Yu X , et al. Macroscopic 3D porous graphitic carbon nitride monolith for enhanced photocatalytic hydrogen evolution . Adv Mater , 2015 , 27 : 4634 - 4639 Xiong J , Wang Y , Xue Q , et al. Synthesis of highly stable dispersions of nanosized copper particles using L-ascorbic acid . Green Chem , 2011 , 13 : 900 - 904 Butler MA . Photoelectrolysis and physical properties of the semiconducting electrode WO2 . J Appl Phys , 1977 , 48 : 1914 -1920 Zhang G , Lan ZA , Lin L , et al. Overall water splitting by Pt/g-C3N4 photocatalysts without using sacrificial agents . Chem Sci , 2016 , 7 : 3062 - 3066 Chen Z , Berciaud S , Nuckolls C , et al. Energy transfer from individual semiconductor nanocrystals to graphene . ACS Nano , 2010 , 4 : 2964 - 2968 Han C , Wu L , Ge L , et al. AuPd bimetallic nanoparticles decorated graphitic carbon nitride for highly efficient reduction of water to H2 under visible light irradiation . Carbon , 2015 , 92 : 31 - 40 37 38 39 40 41 42 43 Bi L , Xu D , Zhang L , et al. Metal Ni-loaded g-C3N4 for enhanced photocatalytic H2 evolution activity: the change in surface band bending . Phys Chem Chem Phys , 2015 , 17 : 29899 -29905 Cao S , Low J , Yu J , et al. Polymeric photocatalysts based on graphitic carbon nitride . Adv Mater , 2015 , 27 : 2150 - 2176 Qin Z, Chen Y , Huang Z , et al. Composition-dependent catalytic activities of noble-metal-free NiS/Ni3S4 for hydrogen evolution reaction . J Phys Chem C , 2016 , 120 : 14581 -14589 Zhang J , Qi L , Ran J , et al. Ternary NiS/Znx Cd1-xS/reduced graphene oxide nanocomposites for enhanced solar photocatalytic H2- production activity . Adv Energy Mater , 2014 , 4 : 1301925 Chen J , Shen S , Guo P , et al. In-situ reduction synthesis of nanosized Cu2O particles modifying g-C3N4 for enhanced photocatalytic hydrogen production . Appl Catal B-Environ , 2014 , 152 - 153 : 335 - 341 Chen Y , Qin Z , Chen T , et al. Optimization of (Cu2Sn)xZn3(1−x)S3/ CdS pn junction photoelectrodes for solar water reduction . RSC Adv , 2016 , 6 : 58409 - 58416 Kronik L , Shapira Y . Surface photovoltage phenomena: theory, experiment, and applications . Surf Sci Rep , 1999 , 37 : 1 - 206 Acknowledgements The authors thank the financial support from the National Natural Science Foundation of China (21606175), the grant support from the China Postdoctoral Science Foundation (2014M560768), and the China Fundamental Research Funds for the Central Universities ( xjj2015041 ).


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Zhixiao Qin 秦知校, Menglong Wang 王朦胧, Rui Li 李锐, Yubin Chen 陈玉彬. Novel Cu3P/g-C3N4 p-n heterojunction photocatalysts for solar hydrogen generation, Science China Materials, 2018, 1-8, DOI: 10.1007/s40843-017-9171-9