Preparation of Ni2P on twinned Zn0.5Cd0.5S nanocrystals for high-efficient photocatalytic hydrogen production


Developing efficient non-precious metal semiconductor photocatalysts is highly desirable for photocatalytically splitting water. In this work, the composite of the nanocrystal twinned Zn0.5Cd0.5S (ZCS) solid solution decorated with highly dispersed Ni2P nanoparticles was successfully formed by in situ growth method, and it exhibited remarkable photocatalytic hydrogen production activity of visible light. A high rate of hydrogen production of 30473 µmol h−1 g−1 was achieved, and the apparent quantum yield (AQY) was as high as 83.5% at 420 nm. Moreover, the sample could maintain outstanding photocatalytic hydrogenation activity after 4-cycle continuous catalytic process. The unique nano-twinned structure of ZCS and synergistic effects between the Ni2P and the twinned ZCS are responsible for the dramatically improved catalytic activities of photocatalysts composite.

Graphic abstract

Ni2P is highly dispersible on the surface of ZCS with distinctive double lattice structure, and it exhibits remarkable visible-light photocatalytic hydrogen production activity


Hydrogen energy has been widely recognized as an effective substitute to fossil fuels for its cleanliness and high-energy density.1 Photocatalytic hydrogen evolution, which uses solar power to produce hydrogen efficiently, is a promising hydrogen production strategy.2 Since the discovery of photocatalytic splitting water for hydrogen production with TiO2, the development of new semiconductor catalysts presented an accelerating trend.3 As is well known, photocatalytic activity is determined by the efficiency of transport and separation of electrons and holes generated by light, which greatly depends on the band energy levels and the microcrystal structure of the catalysts.4 Therefore, it is highly desirable to refine the microstructure and reduce the band gap energy of semiconductor photocatalysts, which is advantageous for not only the separation of photoelectrons and holes, but also for the transport of holes.5

In the past decades, various semiconductors were discovered, such as oxides, metal sulfides and oxynitrides,6,7,8,9 which have been identified as valid catalysts for photocatalytic hydrogen production.10 Among them, cadmium sulfide (CdS) has gained extensive attention because of its relatively narrow band gap of 2.42 eV, which is more easily responsive for visible-light and more negative than the redox potential of H+/H2.11 However, the practical application of CdS is limited due to its low apparent quantum yield resulting from rapid electron recombination and severe photo-corrosion. To solve these problems, the construction of ternary metal sulfides provides a feasible strategy.4,12,13 Ternary ZnxCd1−xS is one of the widely used photocatalysts, because the band gap of ZnxCd1−xS can be controlled and its conduction band can be shifted to a more negative position to improve the photocatalytic H2 production activity. Even so, the single nanocrystal structure of ZnxCd1−xS does not have a high enough efficiency for space charge separation, which greatly shortens the life of photo-generated carriers. Recently, some works reveal that the ZnxCd1−xS with nano-twinned structure can improve the charge transport properties (due to its highly ordered structures) and offer effective spatial isolation of photo-generated electrons/holes to prevent their recombination (due to the possibility of forming electrostatic field).5 This twinning structure is formed by alternating arrangements of zinc blende/wurtzite (ZB/WZ) and arranging the twinning superlattice periodically. The homojunctions between two different phases within the same nanocrystals can improve the separation efficiency of electron-hole pairs and reduce their recombination.14,15 Supporting suitable cocatalysts onto semiconductors has been proved an effective method for further improving photocatalytic activity.16 The cocatalyst can trap photogenerated charge, restrain the rapid recombination of electron/hole pairs and decrease the activation energy or overpotential of H2 decomposition. At present, most reported cocatalysts are noble metals (such as Au and Pt),17,18 however, the high price of precious metals makes their applications in hydrogen production impractical. Consequently, it is very crucial to develop the non-precious metal catalysts with cost-effective.19 With the efforts of many groups, various promising cocatalysts including transition metal sulfides (Cu2S, Cu1.94S, NiS, Mo2S and CoS),20,21,22,23,24 hydroxides Ni(OH)2, Co(OH)2)25,26 and transition metal phosphides (Cu3P, Co2P, CoP and Ni2P)27,28,29,30 have been developed. Among them, Ni2P has particular optoelectronic properties and has been reported as a highly efficient and earth-abundant cocatalyst,31 which significantly improves the activity of photocatalytic hydrogen production. Taking into account the characteristics of ZnxCd1−xS and Ni2P, it will be significant to couple N2P with twinned ZnxCd1−xS, which can fully exploit the advantages of Ni2P and ZnxCd1−xS. We expected that excellent photocatalytic performance can be achieved.

Herein, we develop a facile approach to grow Ni2P on pre-synthesized twinned Zn0.5Cd0.5S (ZCS) nanocrystals coupled with hydrothermal synthesis. To our knowledge, there is seldom research on photocatalytic performance of combining Ni2P with twinned ZCS.4 The as-prepared photocatalyst (Ni2P-ZCS) exhibited excellent visible-light photocatalytic activity for hydrogen evolution with a high hydrogen production rate of 30473 µmol h−1 g−1. The apparent quantum yield (AQY) could reach as high as 83.5% under visible light (λ ≥ 420 nm), and the activity retention rate could maintain 90.5% of primitive H2-evolution rate after 4-cycle continuous catalytic process for 16 h. Twinned ZCS offers high electron-hole pairs separation rate to a large extent, and Ni2P not only restrains the rapid recombination of electron-hole pairs but also decreases the activation energy. Meanwhile, the synergistic effect between Ni2P and ZCS can dramatically elevate the photocatalytic performance as well. The results reveal great potential of Ni2P-ZCS as high-performance photocatalytic materials. Besides, the simple and scalable method employed in this work may be feasible for preparing other transition metal oxides (hydroxides)-ZCS-based composites with excellent photocatalytic performance, extending their potential applications in many fields.


Synthesis of twinned ZCS

The twinned ZCS was formed by a hydrothermal precipitation method (Figure 1).5 A certain amount of cadmium acetate (0.01 mmol) and zinc acetate (0.01 mmol) were added to the deionized water (40 mL), and then 10 mL of sodium hydroxide was added after mixing well. Next, 0.25 mmol of thioacetamide were added into suspension by stirring for 30 min and then transferred into a 100 mL Teflon-lined stainless-steel autoclave and maintained at 180 °C for 24 h. Twinned ZCS was obtained by rinsing the above solid with anhydrous ethanol and deionized water for three times, followed by vacuum drying at 60 °C for 12 h.

Figure 1

Schematic diagram of the synthesis procedures of Ni2P-ZCS composite photocatalysts.

Synthesis of Ni2P-ZCS

Ni2P-ZCS composites were prepared by an in situ growth method (Figure 1).32 0.4 g of the as-prepared twinned ZCS was dissolved in ethylenediamine (60 mL), and then after stirring uniformly, a certain amount of Ni(NO3)2·6H2O and excess red phosphorus nanoparticles (molar ratio of Ni to P is 1:5) were added to ensure completely phosphating. After continuous socinate for half an hour, the mixed homogeneous solution was transferred to 100 mL Teflon-lined autoclave and maintained at 160 °C for 24 h. Subsequently, the product was collected and washed with deionized water and anhydrous ethanol for three times. Finally, the product was dried in a vacuum oven at 80 °C for 5 h to obtain Ni2P-ZCS. For comparison, pure Ni2P was also synthesized using the same method without adding of ZCS.


X-ray diffraction (XRD) patterns of the prepared photocatalysts were confirmed by an X-ray diffractometer using a Cu K irradiation source (=1.54056 Å), and all the samples were scanned between 10° and 90°. Scanning electron microscopy (SEM) were obtained by Hitachi S2400 to observe the morphologies of the samples. Transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) were acquired on a FEI Talos f200s to characterize the microstructures of the samples. X-ray photoelectron spectroscopy (XPS) measurement was enforced on a Thermo Scientific ESCALAB 250 instrument with Al Ka source to analyze the element composition. UV-visible (UV-vis) absorption spectra were acquired from a HITACHI U4100 spectrophotometer. Photoluminescence (PL) spectra were obtained using a Hitachi F-700 fluorescence spectrophotometer. Electrochemical impedance spectroscopy (EIS) and photocurrent response were measured by Chenhua CHI660E. Nitrogen adsorption-desorption isotherms were tested on the Quantachrone Autosorb iQ-MP-C.

Photocatalytic measurement

Photocatalytic hydrogen evolution experiments were performed in a 100 mL vacuum reactor (Perfect light Labsolar-III AG photocatalytic online analysis system), which was connected to a cryostat to maintain the reaction temperature at 9 °C during the characterization. The photocatalyst powder (10 mg) was uniformly dispersed in a 100 mL aqueous solution containing 0.35 M Na2S and 0.25 M Na2SO3, and the system was vacuumed for 0.5 h to remove air. The reaction vessel was then illuminated with a 300 W xenon lamp (PLS-SXE 300C) with a cut-off filter (420 nm). Hydrogen production was tested every 0.5 h for 3 h using a gas chromatograph (FULI GC 9790) equipped with a thermal conductivity detector (TCD), and high purity Argon as the carrier gas. In the cycling test, 0.5 h dark conditions and gas draws were taken between every cycle and each cycle last for 4 h.

AQY refers to the utilization rate of photoquantum in photochemical reaction, which was gauged using visible light (420 nm) and calculated according to the following formula:33

$$ \begin{aligned} {\text{AQY}} & = \frac{{ {\text{the number of reacted electrons}}}}{{ {\text{the number of incident photons}}}} \times 1 0 0 {\text{\% }} \\ & = \frac{{ 2\times N_{{H_{2} }} }}{{\frac{I \times A \times T \times \lambda }{h \times c}}} \times 1 0 0 {\text{\% }} \\ \end{aligned} $$

In this formula, I = 15 A is the light intensity; t = 10800 s is the irradiation time; A is the irradiation area (about 38.5 cm2); λ is the incident wavelength of the light source (nm); h = 6.626 × 10−34 Js is the Planck constant; c is the speed of light (3.0 × 108 m s−1). All the source conditions of the above data are consistent with the hydrogen production performance test conditions.

Electrochemical measurements

The saturated calomel electrode (SCE) was used as the reference electrode, the platinum plate was used as the counter electrode, and the photocurrent was measured by an electrochemical analyzer (CHI660E) under a standard three-electrode structure. The working electrode was produced by three drops (30 μL per drop) of the photocatalyst suspension in 5% nafion solution/ethanol (20 mg mL−1) on the surface of fluorine-doped tin oxide (FTO) glass, and then dried at room temperature. The photocurrent density at a bias voltage of 0.1 V was measured under irradiation with a 300 W Xe-lamp (optical switching period of 50 s) equipped with a 420 nm cut-off filter. The supporting electrolyte is 0.5 M of Na2SO4 solution. EIS were recorded in potentiation mode with a 10 mV sinusoidal wave with frequencies ranging from 100 kHz to 0.05 Hz.

Results and Discussion

Characterization of samples

The crystal structure of the as-prepared samples were determined by XRD analysis (Figure 2). Compared to the standard diffraction patterns of cubic phase ZnS (JCPDS card no. 05-0566) and hexagonal phase CdS (JCPDS card no. 41-1049), it can be seen that the diffraction pattern of Zn0.5Cd0.5S exhibits multiphase characteristics.4 After a certain amount of Cd were added into the ZnS crystal (for the Zn0.5Cd0.5S sample), the diffraction peaks of Zn0.5Cd0.5S showed an evident shift to the lower angle.14 This phenomenon is attributed to the larger radius of Cd2+ than that of the Zn2+ ion. These results indicated the formation of the twinned Zn0.5Cd0.5S solid solution.17 All the peaks of Ni2P-ZCS maintain nearly at the same position, indicating that the crystal structure of Zn0.5Cd0.5S is not affected by the deposition of Ni2P. However, the apparent peaks of ZCS move to a little higher angle, suggesting that ions of Zn2+ doped into CdS lattice. Notably, the characteristic diffraction peak of Ni2P (Figure S1, Supplementary Information) is not observed in Ni2P-ZCS composite, attributing to low content of Ni2P in Ni2P-ZCS composite which exceeds the sensitive of XRD characterization and fine particles of Ni2P. Nevertheless, the presence of Ni2P in Ni2P-ZCS can be easily proved by TEM and XPS techniques, which will be discussed later.

Figure 2

The XRD patterns of pure twinned ZCS and Ni2P-ZCS nanocomposite.

To observe the microstructure of Ni2P-ZCS, the prepared samples were characterized by SEM, TEM and HRTEM. SEM shows that Ni2P-ZCS exists as an irregular granule with a size range of 30–100 nm Figure 3(a), which appears same as ZCS (Figure S2, Supplementary Information). As revealed in Figure 3(b), the twin nanocrystal structure of ZCS is confirmed by the lattice fringes of the zinc blende/wurtzite (ZB/WZ) arranged alternately and periodically arranged in twinning superlattice.17 In addition, the black and white strips on the surface of ZCS can be observed in the TEM images (the inset of Figure 3(b)), also suggesting the existence of twinned structure of ZCS.4 In the TEM image of Ni2P-ZCS composite in (Figure 3(c)), some fine Ni2P particles are found on the twinned ZCS surface with high dispersion compared with pure ZCS (Figure S3, Supplementary Information). In Figure 3(d), the identified lattice fringes of 0.32 nm correspond to the (111) lattice plane of twinned ZCS phase,34 and the interplanar spacing of 0.22 nm is ascribed to Ni2P (111).35 These results indicate that Ni2P and twinned ZCS components form a close contacted interface in the composite samples, which contributes to the efficient transfer of the charges between the components, thereby increasing the photocatalytic activity.16 The corresponding energy-dispersive X-ray (EDX) spectra are shown in Figure 3(e–j), further demonstrating the distribution of the two substances. Obviously, the elements of Zn, Cd, S, Ni and P are coexist and distributed uniformly in the surface of Ni2P-ZCS, further confirming that Ni2P-ZCS composite photocatalysts are successfully prepared. In addition, the EDX results show that the molar ratio of Zn to Cd is approximately 1:1, which is consistent with the theoretical value. However, the loading amount of Ni2P is lower than the theoretical value (4wt%), which is mainly because Ni2+ in the solution is not completely deposited on the surface of ZCS during the hydrothermal process. (Table 1, Table S1 and Figure S4, Supplementary Information).

Figure 3

(a) SEM image of Ni2P-ZCS composite; (b) Coherent twin boundaries of alternative ZB/WZ segments. (c) TEM image of Ni2P-ZCS composite. (d) HRTEM image of Ni2P-ZCS composite; (e-j) EDX spectra of Ni2P-ZCS.

Table 1 EDX analysis result of Ni2P- Zn0.5Cd0.5S.

The XPS was tested to analyze the surface chemistry and bonds of the photocatalysts. As shown in Figure 4(a), the survey spectrum provides the signal peaks of Zn, Cd, Ni, S and P elements, which is accorded with the results of EDX (Figure 3). In the high-resolution XPS spectrum of Zn 2p in Figure 4(b), two peaks at 1021.9 and 1044.9 eV correspond to Zn 2p3/2 and Zn 2p1/2, respectively, which indicates that the valence state of Zn is +2. Two peaks at 404.8 and 411.7 eV in Figure 4(c) are attributed to Cd 2p3/2 and Cd 2p1/2, which confirms the presence of Cd2+. Another two peaks at 161.5 and 162.6 eV in Figure 4(d) can be assigned to S 2p3/2 and S 2p1/2, respectively.36 The Ni 2p spectrum shows six fitted peaks (Figure 4(e)), which are related to the Ni 2p1/2 and Ni 2p3/2 energy levels. The peaks at 853.3 and 871.3 eV are ascribed to Niδ+ (0 < δ < 2) in Ni2P, while two peaks at 856.3 and 876.1 eV result from the surface oxidation, and the other two peaks at 861.7 and 881.2 eV are the shake-up satellite signal related with multi-electron excitation of Ni.15,37,38 For the P 2p spectrum in Figure 4(f), the binding energies at 129.5 and 132.9 eV are attributed to Pδ of metal phosphides, following two satellite peaks at 130.6 and 133.9 eV.38,39 These results suggest that Ni2P is obtained and grows successfully on the surface of ZCS. Furthermore, it is noteworthy that the Zn 2p, Cd 3d and S 2p peaks of Ni2P-ZCS composite move a little to higher binding energies compared with those of pure ZCS in Figure 4(b–d). These shifts indicate that there exists a strong interaction between ZCS and Ni2P, which can lead to effective migration of photogenerated electrons from ZCS to Ni2P and is expected to have superior photocatalytic performance.35 This result is in good accordance with the above XRD, SEM, TEM, HRTEM and EDX analyses, and further demonstrate the existence of Ni, P, Cd, Zn and S for Ni2P-ZCS. According to the XPS characterization results, we can conclude that Ni2P was successfully deposited on the surface of Zn0.5Cd0.5S.

Figure 4

XPS spectra of Ni2P-ZCS: (a) survey; (b) Zn 2p; (c) Cd 3d; (d) S 2p; (e) Ni 2p; (f) P 2p.

Photocatalytic H2-evolution activity and stability

The photocatalytic H2 evolution rates of the ZCS with different loading of Ni2P and pure Ni2P were carried out in visible light (λ ≥ 420 nm). As presented in Figure 5, Ni2P is inactive for photocatalytic H2 evolution, and pure twinned ZCS has a low H2 producing rate of 20.3 mmol h−1 g−1. With the increase in the loading of Ni2P, the hydrogen production rate of the product increased gradually. This can be attributed to the improved separation efficiency of photo-generated electrons at the interface between Ni2P and ZCS and higher surface area of Ni2P-ZCS compared to ZCS (11.03 vs 8.32 m2 g−1, Figure S6, Supplementary Information). The hydrogen production rate can reach the maximum value of 30.3 mmol h−1 g−1 when the Ni2P is 4wt%. Moreover, an excess of Ni2P may result in the marked decrease of H2 evolution rate. These results show that Ni2P is an effective cocatalyst for water splitting, and at the same time, excessive Ni2P in the hybrid photocatalyst will shield the absorption of light and reduce the number of surface-active sites.

Figure 5

The rate of H2-evolution of different samples.

In addition to hydrogen production rate, the AQY is also a crucial parameter used to evaluate the activity for photocatalytic hydrogen production. The AQY was measured and calculated under the same conditions. The AQY value of 4wt% Ni2P-ZCS can reach the highest value of 83.5%. Higher apparent quantum yield means higher utilization efficiency of photons in the photochemical reaction and higher photocatalytic hydrogen production rate.38 Compared with other ZCS-based composite photocatalysts reported (Table 2), 4wt%Ni2P-ZCS exhibits a relatively high level of H2 evolution rate and AQY, implying its great potential application as photocatalyst. Compared with other similar systems, the excellent hydrogen production performance of Ni2P-ZCS is mainly attributed to the following aspects: (i) ZCS has a distinctive double lattice structure (Figure 3(b)). (ii) Ni2P is highly dispersed on the surface of ZCS with special structure (Figure 3(c)). (iii) ZCS has unique nano-twinned structure and there exists synergistic effects between the Ni2P and the twinned ZCS (iv) The close contact between Ni2P and twinned ZCS interface can accelerate the charge transfer.

Table 2 Comparative summary of photocatalytic H2 evolution rate and AQY of different composite photocatalysts.

The stability of the photocatalysts is an important factor for their practical applications. Consequently, Ni2P-ZCS (4wt%) was used in continuous photocatalytic process to investigate its durability (Figure 6). It is noticed that the hydrogen production rate has a slight decrease after 4-cycle continuous running, and Ni2P-ZCS composite can maintain 90.5% of its original H2-evolution rate. However, the activity of the pure twinned ZCS remains only 60% after four cycles. This result illustrates that 4wt%Ni2P-ZCS composite can maintain a high stability for photocatalytic process.

Figure 6

The cycle process of hydrogen production by photocatalysis.

Optical and electrochemical analysis

In order to explore the optical absorption characteristic of the as-prepared samples, the UV-vis absorption spectra were shown in Figure 7(a). It can be observed that twinned ZCS and Ni2P-ZCS have almost the same steep absorption edge in the wavelength range of 400–490 nm. The absorbance of twinned ZCS with different Ni2P contents at the visible region (λ > 490 nm) are significantly higher than that of pure twinned ZCS, which is attributed to the absorption of Ni2P.35 The band gaps of the prepared samples are further calculated according to the Kubelka-Munk (KM) method through the ultraviolet pattern by the equation:40

$$ \alpha h\nu = A(h\nu - {\text{E}}_{g} )^{1/2} $$
Figure 7

(a) UV–vis diffuse reflectance spectrum of pure twinned ZCS and Ni2P-ZCS composites with different molar ratios of Ni2P and energy band gap of 4wt%Ni2P-ZCS; (b) photoluminescence spectra of pure twinned ZCS and 4wt%Ni2P-ZCS.

Here, α is the absorption coefficient; hν is the photon energy; Eg is the direct band gap, and A is a constant. By calculation, the band gap width of the 4wt%Ni2P-ZCS is 2.45 eV, which is smaller than ZCS (2.53 eV), leading to an enhancement in photoactivity.36 Furthermore, the band gap width decreases with the increasing of Ni2P loading amounts (Figure S5, Supplementary Information). The smaller band gap width means that electrons can be easily excited from valence band (VB) to conduction band (CB), which leads to higher intrinsic carrier concentration and higher conductivity. However, it should be noted that excessive Ni2P would hinder the absorption of twinned ZCS in visible light range, which reduces the photogenic electrons and decreases the photocatalytic activity ultimately.41

Photoluminescence (PL) spectra of pure twinned ZCS and 4wt%Ni2P-ZCS were obtained under an excitation wavelength of 345 nm as shown in Figure 7(b). The pure twinned ZCS has a relatively powerful emission peak at 565 nm, however, the emission intensity of Ni2P-ZCS is significantly reduced.24 The weak emission of Ni2P-ZCS indicates that the Ni2P can act as charge carrier trapping center to improve separation efficiency of electron-hole pairs and decrease their recombination, thus improving the activity and stability of Ni2P-ZCS catalyst.42

The transient photocurrent was used to investigate the behavior of charge separation (Figure 8(a)). Compared with response photocurrent of pure twinned ZCS, the 4wt%Ni2P-ZCS exhibits a more rapid response rate and higher photocurrent. The photocurrent density of the Ni2P-ZCS electrode is about three times of pure twinned ZCS. Moreover, the photocurrent response capability of pure twinned ZCS weakens gradually. The result is in good agreement with the results described above, which further proves that the Ni2P plays an important role in improving the separation efficiency of photoelectrons at the interface of composite materials.43

Figure 8

(a) The transient photocurrent of pure twinned ZCS and 4wt%Ni2P-ZCS under visible light; (b) Nyquist diagram of EIS of pure twinned ZCS and 4wt%Ni2P-ZCS.

The charge transfers resistance (RCT) of the photocatalyst was measured using EIS. Under visible-light irradiation, the pure twinned ZCS exhibits a much higher interfacial charge transfer resistance with a larger diameter than that of Ni2P-ZCS composites (Figure 8(b)), indicating that after the introduction of Ni2P, a faster charge transfer occurs on their interfaces. This result is consistent with the photocurrent test.44

The mechanism of photocatalytic H2 evolution

On the basis of the above results, a possible photocatalytic mechanism for photocatalytic hydrogen production using Ni2P-ZCS is proposed as depicted in Figure 9. Under the irradiation of visible light, the twinned ZCS can effectively absorb photons, and the electrons on VB are excited onto CB and the holes stayed on the VB to form photogenerated hole-electron pairs. However, without the cocatalyst, carriers may recombine rapidly, resulting in a lower rate of photocatalytic H2 evolution of twinned ZCS. The valence band edge of ZCS is located at 2.28 eV,4 and the conduction band edge of ZCS is calculated to be −0.25 eV, according to the formula EVB = ECB + Eg. The potential of Ni2P is about −0.17 eV, which locates between the CB of ZCS and the potential of H+ reduced to hydrogen molecule (E 0H+/H2 = 0). With the presence of Ni2P catalyst, Ni2P-ZCS exhibits high electron trapping ability due to its lower Fermi level than the pure ZCS, which makes photogenerated electron energy excite rapidly from the CB of the twinned ZCS to the surface of Ni2P, thus effectively separating photoexcited hole-electron pairs.34,36 Ni2P acts as an electron collector to trap photogenerated electrons and suppress the combination of the photogenerated carriers. The electrons on Ni2P will reduce H+ into H2, and the holes on the VB of ZCS are captured and consumed by the sacrificial agent in the solution. In addition, the lower H2 adsorption energy on the surface of the Ni2P is beneficial to the reduction of H+. Ni2P serves as an active reaction center in the evolution of photocatalytic H2 and can accelerate the reaction rate.36 Besides, the subtle atomic-level intimate contact and strong interaction between ZCS and Ni2P provide a larger dynamic specific surface area and maximize the efficiency of electron-to-electron transmission between the two components, and thus leads to a highly efficient photocatalytic activity. Using Ni2P-ZCS as photocatalyst under visible light (λ ≥ 420 nm), the main reaction of photocatalytic H2-evolution in an aqueous solution containing S2−/SO32− can be expressed by the following eqns. (1)–(6):

$$ {\text{Ni}}_{2} {\text{P-ZCS}} \mathop \to \limits^{h\nu } {\text{Ni}}_{2} {\text{P }}\left( {{\text{e}}^{ - } } \right) + {\text{ZCS}}\,\left( {{\text{h}}^{ + } } \right) $$
$$ {\text{Ni}}_{2} {\text{P}}\,\left( {2{\text{e}}^{ - } } \right) + 2{\text{H}}^{ + } \to {\text{Ni}}_{2} {\text{P}} + {\text{H}}_{2} \uparrow $$
$$ {\text{SO}}_{3}^{2 - } + {\text{H}}_{2} {\text{O}} + {\text{ZCS}}\,\left( {{\text{h}}^{ + } } \right) \to {\text{SO}}_{4}^{2 - } + 2{\text{H}}^{ + } + {\text{ZCS}} $$
$$ 2{\text{S}}^{2 - } + {\text{ZCS}}\,\left( {{\text{h}}^{ + } } \right) \to {\text{S}}_{2}^{2 - } + {\text{ZCS}} $$
$$ {\text{S}}_{2}^{2 - } + {\text{SO}}_{3}^{2 - } \to {\text{S}}_{2} {\text{O}}_{3}^{2 - } + {\text{S}}^{2 - } $$
$$ {\text{SO}}_{3}^{2 - } + {\text{S}}^{2 - } + {\text{ZCS}}\,\left( {{\text{h}}^{ + } } \right) \to {\text{S}}_{2} {\text{O}}_{3}^{2 - } + {\text{ZCS}} $$
Figure 9

Schematic illustration for the charge transfer and separation in Ni2P-ZCS system.


To sum up, we successfully synthesized high-efficiency catalysts by in-situ growth of Ni2P on the twinned ZCS nanocrystals. The Ni2P were scattered uniformly on the surface of twinned ZCS nanoparticles. The highest rate hydrogen evolution of 4wt%Ni2P-ZCS can reach as high as 30473 µmol h−1 g−1 and AQY reaches 83.5% at 420 nm. Moreover, the activity retention rate could maintain 90.5% of primitive H2-evolution rate after 4-cycle continuous catalytic process for 16 h. A possible photocatalytic mechanism was proposed to explain the enhanced evolution of H2 in Ni2P modified ZCS. The unique nano-twinned structure of ZCS, the close interaction between the components, and the special properties of Ni2P can effectively isolate photogenerated electrons/holes and improve their transfer, which is instrumental to boost photocatalytic hydrogen production activity. These results indicate that Ni2P is an effectively co-catalyst for twinned ZCS and has a potential application in the process of photocatalytic hydrogen production.


  1. 1.

    Liu Y, Zhang J, Guan H, Zhao Y, Yang and Zhang B 2018 Preparation of bimetallic Cu-Co nanocatalysts on poly (diallyldimethylammonium chloride) functionalized halloysite nanotubes for hydrolytic dehydrogenation of ammonia borane Appl. Surf. Sci. 427 106

    CAS  Google Scholar 

  2. 2.

    Feng J, Liu J, Cheng X, Liu J, Xu M and Zhang J 2018 Hydrothermal cation exchange enabled gradual evolution of Au@ZnS–AgAuS yolk–Shell nanocrystals and their visible light photocatalytic applications Adv. Sci. 5 1700376

    Google Scholar 

  3. 3.

    Clark R J and Felsenfeld G 1972 Electrochemcial photolysis of water at a semiconductor electrode Nature New Biol. 240 226

    CAS  Google Scholar 

  4. 4.

    Song J, Zhao H, Sun R, Li X and Sun D 2017 An efficient hydrogen evolution catalyst composed of palladium phosphorous sulphide (PdP~0.33S~1.67) and twin nanocrystal Zn0.5Cd0.5S solid solution with both homo- and hetero-junctions Energy Environ. Sci. 10 225

    CAS  Google Scholar 

  5. 5.

    Liu M, Wang L, Lu G, Yao X and Guo L 2011 Twins in Cd1−xZnxS solid solution: Highly efficient photocatalyst for hydrogen generation from water Energy Environ. Sci. 4 1372

    CAS  Google Scholar 

  6. 6.

    Tijare S N, Bakardjieva S, Subrt J, Joshi M V, Rayalu S S, Hishita S and Labhsetwar N 2014 Synthesis and visible light photocatalytic activity of nanocrystalline PrFeO3 perovskite for hydrogen generation in ethanol–water system J. Chem. Sci. 126 517

    CAS  Google Scholar 

  7. 7.

    Lou Y, Zhang Y, Cheng L, Chen J and Zhao Y 2018 A stable plasmonic Cu@Cu2O/ZnO heterojunction for enhanced photocatalytic hydrogen generation ChemSusChem. 11 1505

    CAS  PubMed  Google Scholar 

  8. 8.

    Iwashina K, Iwase A, Ng Y H, Amal R and Kudo A 2015 Z-schematic water splitting into H2 and O2 using metal sulfide as a hydrogen-evolving photocatalyst and reduced graphene oxide as a solid-state electron mediator J. Am. Chem. Soc. 137 604

    CAS  PubMed  Google Scholar 

  9. 9.

    Liang Y-H, Liao M-W, Mishra M and Perng T-P 2019 Fabrication of Ta3N5ZnO direct Z-scheme photocatalyst for hydrogen generation Int. J. Hydrogen Energy 44 19162

  10. 10.

    Reshak A H 2018 Active photocatalytic water splitting solar-to-hydrogen energy conversion: Chalcogenide photocatalyst Ba2ZnSe3 under visible irradiation Appl. Catal. B Environ. 221 17

    CAS  Google Scholar 

  11. 11.

    Xiang Z, Nan J, Deng J, Shi Y, Zhao Y, Zhang B and Xiang X 2019 Uniform CdS-decorated carbon microsheets with enhanced photocatalytic hydrogen evolution under visible-light irradiation J. Alloys Compd. 770 886

    CAS  Google Scholar 

  12. 12.

    Song K, Zhu R, Tian F, Cao G and Ouyang F 2015 Journal of solid state chemistry effects of indium contents on photocatalytic performance of ZnIn2S4 for hydrogen evolution under visible light J. Solid State Chem. 232 138

    CAS  Google Scholar 

  13. 13.

    Ma D, Shi J-W, Zou Y, Fan Z, Shi J, Cheng L, Sun D, Wang Z and Niu C 2018 Multiple carrier-transfer pathways in a flower-like In2S3/CdIn2S4/In2O3 ternary heterostructure for enhanced photocatalytic hydrogen production Nanoscale 10 7860

    CAS  PubMed  Google Scholar 

  14. 14.

    Li Q, Meng H, Zhou P, Zheng Y, Wang J, Yu J and Gong J 2013 Zn1−xCdxS solid solutions with controlled bandgap and enhanced visible-Light photocatalytic H2-production activity ACS Catal. 3 882

    CAS  Google Scholar 

  15. 15.

    Zhao H, Liu H, Sun R, Chen Y and Li X 2018 A Zn0.5Cd0.5S photocatalyst modified by 2D black phosphorus for efficient hydrogen evolution from water ChemCatChem.10 4395

    CAS  Google Scholar 

  16. 16.

    Li X-l, Wang X-j, Zhu J-Y, Li Y-P, Zhao J and Li F-T 2018 Fabrication of two-dimensional Ni2P/ZnIn2S4 heterostructures for enhanced photocatalytic hydrogen evolution Chem. Eng. J. 353 15

    CAS  Google Scholar 

  17. 17.

    Ng B-J, Putri L K, Kong X Y, Shak K P Y, Pasbakhsh P, Chai S-P and Mohamed A R 2018 Sub-2nm Pt-decorated Zn0.5Cd0.5S nanocrystals with twin-induced homojunctions for efficient visible-light-driven photocatalytic H2 evolution Appl. Catal. B Environ. 224 360

    CAS  Google Scholar 

  18. 18.

    Abdel M and Al-johani H 2017 Enhancement of visible light irradiation photocatalytic activity of SrTiO3 nanoparticles by Pt doping for oxidation of cyclohexane J. Chem. Sci. 129 1687

    Google Scholar 

  19. 19.

    Manbeck G F, Fujita E and Brewer K J 2017 Tetra and Heptametallic Ru(II), Rh(III) Supramolecular Hydrogen Production Photocatalysts J. Am. Chem. Soc. 139 7843

    CAS  PubMed  Google Scholar 

  20. 20.

    Wang C-C, Chang J-W and Lu S-Y 2017 p-Cu2S/n-ZnxCd1−xS nanocrystals dispersed in a 3D porous graphene nanostructure: an excellent photocatalyst for hydrogen generation through sunlight driven water splitting Cat. Sci. Technol. 7 1305

    CAS  Google Scholar 

  21. 21.

    Chen Y, Zhao S, Wang X, Peng Q, Lin R, Wang Y, Shen R, Cao X, Zhang L, Zhou G, Li J, Xia A and Li Y 2016 Synergetic integration of Cu1.94S-ZnxCd1−xS heteronanorods for enhanced visible-light-driven photocatalytic hydrogen production J. Am. Chem. Soc. 138 4286

    CAS  PubMed  Google Scholar 

  22. 22.

    Liu M, Chen Y, Su J, Shi J, Wang X and Guo L 2016 Photocatalytic hydrogen production using twinned nanocrystals and an unanchored NiSx co-catalyst Nat. Energy 1 16151

    CAS  Google Scholar 

  23. 23.

    Yin M, Zhang W, Qiao F, Sun J, Fan Y and Li Z 2019 Hydrothermal synthesis of MoS2-NiS/CdS with enhanced photocatalytic hydrogen production activity and stability J. Solid State Chem. 270 531

    CAS  Google Scholar 

  24. 24.

    Zheng M, Ding Y, Yu L, Du X and Zhao Y 2017 In situ grown pristine cobalt sulfide as bifunctional photocatalyst for hydrogen and oxygen evolution Adv. Funct. Mater. 27 1605846

    Google Scholar 

  25. 25.

    Wang P, Lu Y, Wang X and Yu H 2017 Co-modification of amorphous-Ti(IV) hole cocatalyst and Ni(OH)2 electron cocatalyst for enhanced photocatalytic H2-production performance of TiO2 Appl. Surf. Sci. 391 259

    CAS  Google Scholar 

  26. 26.

    Zhou X, Jin J, Zhu X, Huang J, Yu J, Wong W-Y and Wong W-K 2016 New Co(OH)2/CdS nanowires for efficient visible light photocatalytic hydrogen production J. Mater. Chem. A 4 5282

    CAS  Google Scholar 

  27. 27.

    Yue X, Yi S, Wang R, Zhang Z and Qiu S 2016 A novel and highly efficient earth-abundant Cu3P with TiO2 “P-N” heterojunction nanophotocatalyst for hydrogen evolution from water Nanoscale 8 17516

    CAS  PubMed  Google Scholar 

  28. 28.

    Zeng D, Ong W-J, Chen Y, Tee S Y, Chua C S, Peng D-L and Han M-Y, 2018 Co2P nanorods as an efficient cocatalyst decorated porous g-C3N4 nanosheets for photocatalytic hydrogen production under visible light irradiation Part. Part. Syst. Char. 35 1700251

    Google Scholar 

  29. 29.

    Qiu B, Zhu Q, Xing M and Zhang J 2017 A robust and efficient catalyst of CdxZn1−xSe motivated by CoP for photocatalytic hydrogen evolution under sunlight irradiation Chem. Commun. 53 897

    CAS  Google Scholar 

  30. 30.

    Sun Z, Zheng H, Li J and Du P 2015 Extraordinarily efficient photocatalytic hydrogen evolution in water using semiconductor nanorods integrated with crystalline Ni2P cocatalysts Energy Environ Sci. 8 2668

    CAS  Google Scholar 

  31. 31.

    Wu T, Wang P, Ao Y and Wang C 2018 Enhanced visible light activated hydrogen evolution activity over cadmium sulfide nanorods by the synergetic effect of a thin carbon layer and noble metal-free nickel phosphide cocatalyst J. Colloid Interface Sci. 525 107

    CAS  PubMed  Google Scholar 

  32. 32.

    Qin Z, Xue F, Chen Y, Shen S and Guo L 2017 Spatial charge separation of one-dimensional Ni2P-Cd09Zn01S/g-C3N4 heterostructure for high-quantum-yield photocatalytic hydrogen production Appl. Catal. B Environ. 217 551

    CAS  Google Scholar 

  33. 33.

    Lin H, Li Y, Li H and Wang X 2017 Multi-node CdS hetero-nanowires grown with defect-rich oxygen-doped MoS2 ultrathin nanosheets for efficient visible-light photocatalytic H2 evolution Nano Res. 10 1377

    CAS  Google Scholar 

  34. 34.

    Dai D, Xu H, Ge L, Han C, Gao Y, Li S and Lu Y 2017 In-situ synthesis of CoP co-catalyst decorated Zn05Cd05S photocatalysts with enhanced photocatalytic hydrogen production activity under visible light irradiation Appl. Catal. B Environ. 217 429

    CAS  Google Scholar 

  35. 35.

    Peng S, Yang Y, Tan J, Gan C and Li Y 2018 In situ loading of Ni2P on Cd05Zn05S with red phosphorus for enhanced visible light photocatalytic H2 evolution Appl. Surf. Sci. 447 822

    CAS  Google Scholar 

  36. 36.

    Shao Z, He Y, Zeng T, Yang Y, Pu X, Ge B and Dou J 2018 Highly efficient photocatalytic H2 evolution using the Ni2P-Zn05Cd05S photocatalyst under visible light irradiation J. Alloys Compd. 769 889

    CAS  Google Scholar 

  37. 37.

    Zhou D, Xue L-P and Wang N 2019 Robustly immobilized Ni2P nanoparticles in porous carbon networks promotes high-performance sodium-ion storage J. Alloys Compd. 776 912

    CAS  Google Scholar 

  38. 38.

    Calvinho K, Laursen A and Yap K 2018 Selective CO2 reduction to C3 and C4 oxyhydrocarbons on nickel phosphides at overpotentials as low as 10 mV Energy Environ. Sci. 11 2550

    CAS  Google Scholar 

  39. 39.

    Wang Z, Jin Z, Yuan H, Wang G and Ma B 2018 Orderly-designed Ni2P nanoparticles on g-C3N4 and UiO-66 for efficient solar water splitting J. Colloid Interf. Sci. 532 287

    CAS  Google Scholar 

  40. 40.

    Li Y, Ouyang S, Xu H, Wang X, Bi Y, Zhang Y and Ye J 2016 Constructing solid-gas-interfacial fenton reaction over alkalinized-C3N4 photocatalyst to achieve apparent quantum yield of 49% at 420 nm J. Am. Chem. Soc. 138 13289

    CAS  PubMed  Google Scholar 

  41. 41.

    Lu Y, Shang H, Guan H, Zhao Y and Zhang B 2015 Enhanced visible-light photocatalytic activity of BiVO4 microstructures via annealing process Superlattic Microst. 88 591

    CAS  Google Scholar 

  42. 42.

    Ran J, Gao G, Li F T, Ma T Y, Du A and Qiao S-Z 2017 Ti3C2 MXene co-catalyst on metal sulfide photo-absorbers for enhanced visible-light photocatalytic hydrogen production Nat. Commun. 8 13907

    CAS  PubMed  PubMed Central  Google Scholar 

  43. 43.

    Zhang J, Qi L, Ran J, Yu J and Qiao S-Z 2014 Ternary NiS/ZnxCd1−xS/Reduced Graphene Oxide Nanocomposites for Enhanced Solar Photocatalytic H2-Production Activity Adv. Energy Mater. 4 1301925

    Google Scholar 

  44. 44.

    Lu Z, Li C, Han J, Wang L, Wang S, Ni L and Wang Y 2018 Construction 0D/2D heterojunction by highly dispersed Ni2P QDs loaded on the ultrathin g-C3N4 surface towards superhigh photocatalytic and photoelectric performance Appl. Catal. B Environ. 237 919

    CAS  Google Scholar 

  45. 45.

    Xu Y, Gong Y, Ren H, Liu W, Li C, Liu X and Niu L 2018 Insight into enhanced photocatalytic H2 production by Ni(OH)2-decorated ZnxCd1−xS nanocomposite photocatalysts J. Alloys Compd. 735 2551

    CAS  Google Scholar 

  46. 46.

    An C, Feng J, Liu J, Wei G, Du J and Wang H 2017 NiS nanoparticle decorated MoS2 nanosheets as efficient promoters for enhanced solar H2 evolution over ZnxCd1−xS nanorods as efficient promoters for enhanced solar H2 Inorg. Chem. Front. 4 1042

    CAS  Google Scholar 

  47. 47.

    Zhang J, Qi L, Ran J, Yu J and Qiao S-Z 2014 Ternary NiS/ZnxCd1−xS/reduced graphene oxide nanocomposites for enhanced solar photocatalytic H2-production activity Adv. Energy Mater. 4 1301925

    Google Scholar 

  48. 48.

    Wang P, Zhan S, Wang H, Xia Y, Hou Q, Zhou Q, Li Y and Kumar R R 2018 Cobalt phosphide nanowires as efficient co-catalyst for photocatalytic hydrogen evolution over Zn05Cd05S Appl. Catal. B Environ. 230 210

    CAS  Google Scholar 

  49. 49.

    Dai D, Wang L, Xiao N, Li S, Xu H, Liu S, Xu B, Lv D, Gao Y, Song W, Ge L and Liu J 2018 In-situ synthesis of Ni2P co-catalyst decorated Zn05Cd05S nanorods for high-quantum-yield photocatalytic hydrogen production under visible light irradiation Appl. Catal. B Environ. 233 194

    CAS  Google Scholar 

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This work was supported by the National Natural Science Foundation of China (Grants 21706242, 21576247, and U1804140).

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Correspondence to Yafei Zhao.

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Zhou, X., Yin, L., Dai, K. et al. Preparation of Ni2P on twinned Zn0.5Cd0.5S nanocrystals for high-efficient photocatalytic hydrogen production. J Chem Sci 132, 26 (2020).

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  • photocatalysts
  • Ni2P-Zn0.5Cd0.5S
  • hydrogen production
  • water splitting