Cobalt phosphide nanorods as an efficient electrocatalyst for the hydrogen evolution reaction

Cobalt phosphide (Co2P) nanorods are found to exhibit efficient catalytic activity for the hydrogen evolution reaction (HER), with the overpotential required for the current density of 20mA/cm2 as small as 167mV in acidic solution and 171mV in basic solution. In addition, the Co2P nanorods can work stably in both acidic and basic solution during hydrogen production. This performance can be favorably compared to typical high efficient non-precious catalysts, and suggests the promising application potential of Co2P 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 Co2P nanorods to those of the hydride-acceptor and proton-acceptor in highly efficient Ni2P catalysts, [NiFe] hydrogenase, and its analogues implies that the HER catalytic activity of the Co2P nanorods might be correlated with the charged natures of Co and P

Phase separation synthesis of trinickel monophosphide porous hollow nanospheres for efficient hydrogen evolution

A facile and scalable approach to synthesize trinickel monophosphide (Ni₃P) porous hollow nanospheres (PHNs) has been developed, the resultant Ni₃P PHNs exhibiting excellent catalytic activity in the hydrogen evolution reaction (HER). The formation of the Ni₃P PHNs correlates with phase separation during the thermal annealing of amorphous nickel–phosphorus nanospheres that affords crystalline Ni–Ni₃P nanoparticles, and the subsequent selective removal of nickel. The overpotential required for the current density of 20 mA cm−2 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 Ni₃P PHNs is 96%, and the Ni₃P 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 Ni₃P PHNs.This research was financially supported by the National Natural Science Foundation of China (61006049, 51432006, 51172100), the Ministry of Science and Technology of China (2011DFG52970), the Ministry of Education of China (IRT14R23), 111 Project (B13025), Jiangsu Province (2011-XCL019 and 2013-479), and the Natural Science Foundation of Jiangsu (BK20131252)

Strategies for Semiconductor/Electrocatalyst Coupling toward Solar-Driven Water Splitting

Hydrogen (H-2) 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 H-2 production is predominated by fossil-fuel feedstocks, for future widespread utilization it is of paramount importance to produce H-2 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

A Self-Supported Porous Hierarchical Core–Shell Nanostructure of Cobalt Oxide for Efficient Oxygen Evolution Reaction

Increasing the active surface area of an electrocatalyst is crucial for effective oxygen evolution reaction (OER). Here, a sophisticated electrode that uses the advantages of porous/hollow nanostructure, hierarchical nanostructure, and self-supported structure simultaneously is demonstrated for the first time. A self-supported porous hierarchical core–shell structure (PHCS) of cobalt oxide is synthesized by the combination of electrochemical deposition and electrochemical treatment. The treatment introduces numerous pores into the core of a core–shell structure, and it decreases the particle size of cobalt oxide to <5 nm, markedly increasing the surface area of the resultant structures. The electrochemical surface area of PHCS is 1.6 greater than that of hierarchical core–shell cobalt oxide, and is ∼20 times greater than that of cobalt oxide nanowires. The PHCS is extremely active in the OER, with the overpotential required for a current density of 100 mA cm^–2 being as small as 300 mV. The Tafel slope is 40.3 mV dec^–1, and the PHCS can work stably for more than 40 h

Ni₁₂P₅ Nanoparticles as an Efficient Catalyst for Hydrogen Generation <i>via</i> Electrolysis and Photoelectrolysis

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/cm² 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

Tungsten Sulfide Enhancing Solar-Driven Hydrogen Production from Silicon 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