The exploitation of a low-cost catalyst is desirable for hydrogen generation from electrolysis or photoelectrolysis. In this study we have demonstrated that nickel phosphide (Ni12P5) nanoparticles have efficient and stable catalytic activity for the hydrogen evolution reaction. The catalytic performance of Ni12P5 nanoparticles is favorably comparable to those of recently reported efficient nonprecious catalysts. The optimal overpotential required for 20 mA/cm(2) current density is 143 ± 3 mV in acidic solution (H2SO4, 0.5 M). The catalytic activity of Ni12P5 is likely to be correlated with the charged natures of Ni and P. Ni12P5 nanoparticles were introduced to silicon nanowires, and the power conversion efficiency of the resulting composite is larger than that of silicon nanowires decorated with platinum particles. This result demonstrates the promising application potential of metal phosphide in photoelectrochemical hydrogen generation.

Cobalt phosphide (Co 2 P) nanorods are found to exhibit efficient catalytic activity in hydrogen evolution reaction (HER), with the overpotential required for the current density of 20 mA/cm 2 as small as 167 mV in acidic solution and 171 mV in basic solution. In addition, the Co 2 P nanorods can work stably in both acidic and basic solution during hydrogen production. This performance can be favorably comparable to typical high efficiently non-precious catalysts, and suggest the promising application potential of the Co 2 P nanorods in the field of hydrogen production. The HER process follows a Volmer-Heyrovsky mechanism, and the rates of the discharge step and desorption step appear to be comparable during the HER process. The similarity of charged natures of Co and P in the Co 2 P nanorods to those of the hydride-acceptor and proton-acceptor in high efficient Ni 2 P catalyst, [NiFe] hydrogenase, and its analogues implies that the HER catalytic activity of Co 2 P nanorods might be correlated with the charged natures of Co and P.

Hydrogen (H2) has a significant potential to enable the global energy transition from the current fossil‐dominant system to a clean, sustainable, and low‐carbon energy system. While presently global H2 production is predominated by fossil‐fuel feedstocks, for future widespread utilization it is of paramount importance to produce H2 in a decarbonized manner. To this end, photoelectrochemical (PEC) water splitting has been proposed to be a highly desirable approach with minimal negative impact on the environment. Both semiconductor light‐absorbers and hydrogen/oxygen evolution reaction (HER/OER) catalysts are essential components of an efficient PEC cell. It is well documented that loading electrocatalysts on semiconductor photoelectrodes plays significant roles in accelerating the HER/OER kinetics, suppressing surface recombination, reducing overpotentials needed to accomplish HER/OER, and extending the operational lifetime of semiconductors. Herein, how electrocatalyst coupling influences the PEC performance of semiconductor photoelectrodes is outlined. The focus is then placed on the major strategies developed so far for semiconductor/electrocatalyst coupling, including a variety of dry processes and wet chemical approaches. This Review provides a comprehensive account of advanced methodologies adopted for semiconductor/electrocatalyst coupling and can serve as a guideline for the design of efficient and stable semiconductor photoelectrodes for use in water splitting.

Discovering efficient and promising non-noble catalysts toward the alkaline hydrogen evolution reaction (HER) is vital for a clean energy system. Here, we design an efficient alkaline HER electrocatalyst, coating of WN nanowire core with a Ni­(OH)2 shell supported on a carbon fiber paper (WN-Ni­(OH)2). In a 1 M KOH solution, the hierarchical electrocatalyst affords a current density of 20 mA cm–2 at an overpotential of 170 mV and 100 mA cm–2 at 245 mV. The enhanced performance of WN-Ni­(OH)2 in the HER is attributed to the synergy between WN and Ni­(OH)2: during water dissociation, hydroxyl groups are preferentially adsorbed on WN and hydrogen on Ni­(OH)2; meanwhile, Ni­(OH)2 could promote hydroxyl group desorption from WN. Thus, the full-surface Volmer reaction kinetics could be enhanced. As a consequence, the WN-Ni­(OH)2 has a reduced activation energy of the HER and enhanced intrinsic activity performance. Meanwhile, the hybrid can reach a current density of 100 mA cm–2 at an overpotential of 339 mV for the oxygen evolution reaction (OER), and an overpotential of 510 mV for the full water-splitting reaction. This interfacial cooperation offers a promising bifunctional electrocatalyst, as well as a hopeful strategy for fabricating efficient nitride-based electrocatalysts in alkaline media.

The development of effective non-precious electrocatalyst for hydrogen evolution reaction (HER) is highly desirable for the commercial application of hydrogen as a clean and renewable energy, whereas remains a big challenge. Here the hierarchical nanowires array (HNA) of iron phosphide (FeP) nanowires coated with iron phosphide nanorods grown on carbon fiber paper (CFP) was constructed, and exhibited remarkable catalytic activity in the HER. The overpotential required for the current density of 20 mA cm -2 is as small as 45 and 221 mV in acidic and basic solution, and the corresponding Tafel slope is 53 and 134 mV dec -1 , respectively. The effective catalytic activity of the CFP-FeP HNA in the HER, together with its long-term stability and nearly 100% faradaic efficiency in water electrolysis, make the CFP-FeP HNA one of the best non-noble electrocatalysts descried to date. The prominent catalytic activity of CFP-FeP HNA is correlated to a large number of active sites for the HER, and the fast electron transport from the CFP to the FeP nanorods mediated by FeP nanowires.

Tungsten sulfides, including WS2 (crystalline) and WS3 (amorphous), were introduced to silicon nanowires, and both can promote the photoelectrochemical hydrogen production of silicon nanowires. In addition, more enhancement of energy conversion efficiency can be achieved by the loading of WS3, in comparison with loading of WS2. Polarization curves of WS3 and WS2 suggest that WS3 has higher catalytic activity in the hydrogen evolution reaction than WS2, affording higher energy conversion efficiency in silicon nanowires decorated with WS3. The higher electrocatalytic activity of WS3 correlates with the amorphous structure of WS3 and larger surface area of WS3, which result in more active sites in comparison with crystalline WS2.

A facile and scalable approach to synthesize trinickel monophosphide (Ni 3 P) porous hollow nanospheres (PHNs) has been developed, the resultant Ni 3 P PHNs exhibiting excellent catalytic activity in the hydrogen evolution reaction (HER). The formation of the Ni 3 P PHNs correlates with phase separation during the thermal annealing of amorphous nickel-phosphorus nanospheres that affords crystalline Ni-Ni 3 P nanoparticles, and the subsequent selective removal of nickel. The overpotential required for the current density of 20 mA cm À2 is as small as 99 mV in acidic solution. The performance compares favorably with that of other metal phosphides, and is superior to that of transition metal dichalcogenides, carbides, borides, and nitrides. The faradaic efficiency of the Ni 3 P PHNs is 96%, and the Ni 3 P PHNs are stable during the long-term electrolysis of water. Density functional theory calculations suggest that a Ni-Ni bridge site and the sites on the top of the P atoms are the active sites during the HER. The scalable production, low cost, excellent catalytic activity, and long-term stability suggest promising application potential for Ni 3 P PHNs.

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