Nanoparticles of nickel phosphide (Ni2P) have been investigated for electrocatalytic activity and stability for the hydrogen evolution reaction (HER) in acidic solutions, under which proton exchange membrane-based electrolysis is operational. The catalytically active Ni2P nanoparticles were hollow and faceted to expose a high density of the Ni2P(001) surface, which has previously been predicted based on theory to be an active HER catalyst. The Ni2P nanoparticles had among the highest HER activity of any non-noble metal electrocatalyst reported to date, producing H2(g) with nearly quantitative faradaic yield, while also affording stability in aqueous acidic media.

Nanoparticles of cobalt phosphide, CoP, have been prepared and evaluated as electrocatalysts for the hydrogen evolution reaction (HER) under strongly acidic conditions (0.50 M H2SO4, pH 0.3). Uniform, multi-faceted CoP nanoparticles were synthesized by reacting Co nanoparticles with trioctylphosphine. Electrodes comprised of CoP nanoparticles on a Ti support (2 mg cm(-2) mass loading) produced a cathodic current density of 20 mA cm(-2) at an overpotential of -85 mV. The CoP/Ti electrodes were stable over 24 h of sustained hydrogen production in 0.50 M H2SO4. The activity was essentially unchanged after 400 cyclic voltammetric sweeps, suggesting long-term viability under operating conditions. CoP is therefore amongst the most active, acid-stable, earth-abundant HER electrocatalysts reported to date.

Hydrogen gas obtained by the electrolysis of water has long been proposed as a clean and sustainable alternative to fossil fuels. Noble metals such as Pt are capable of splitting water at low overpotentials, but the implementation of inexpensive solar-driven water-splitting systems and electrolyzers could benefit from the development of robust, efficient, and abundant alternatives to noble metal catalysts. Transition metal phosphides (M x P y ) have recently been identified as a promising family of Earth abundant electrocatalysts for the hydrogen-evolution reaction (HER) and are capable of operating with low overpotentials at operationally relevant current densities while exhibiting stability under strongly acidic conditions. In this review, we highlight the progress that has been made in this field and provide insights into the synthesis, characterization, and electrochemical behavior of transition metal phosphides as HER electrocatalysts. We also discuss strategies for the incorporation of metal phosphides into integrated solar-driven water-splitting systems and highlight key considerations involved in the testing and benchmarking of such devices.

Nanoparticles of cobalt phosphide, CoP, have been prepared and evaluated as electrocatalysts for the hydrogen evolution reaction (HER) under strongly acidic conditions (0.50 M H2SO4, pH 0.3). Uniform, multi‐faceted CoP nanoparticles were synthesized by reacting Co nanoparticles with trioctylphosphine. Electrodes comprised of CoP nanoparticles on a Ti support (2 mg cm−2 mass loading) produced a cathodic current density of 20 mA cm−2 at an overpotential of −85 mV. The CoP/Ti electrodes were stable over 24 h of sustained hydrogen production in 0.50 M H2SO4. The activity was essentially unchanged after 400 cyclic voltammetric sweeps, suggesting long‐term viability under operating conditions. CoP is therefore amongst the most active, acid‐stable, earth‐abundant HER electrocatalysts reported to date.