Ni₂P as a Janus catalyst for water splitting: the oxygen evolution activity of Ni₂P nanoparticles

TLDR

Electrochemical water splitting is a promising solar energy storage method, yet catalysts active for both hydrogen and oxygen evolution are rare. We demonstrate that nickel phosphide (Ni₂P), known as an excellent hydrogen evolution catalyst, is also highly active for oxygen evolution. Ni₂P nanoparticles achieve 10 mA cm⁻² at 290 mV overpotential in 1 M KOH and, due to a core–shell Ni₂P/NiOx structure, can function as both cathode and anode, delivering 10 mA cm⁻² at 1.63 V in an alkaline electrolyzer.

Abstract

Electrochemical water splitting into hydrogen and oxygen is a promising method for solar energy storage. The development of efficient electrocatalysts for water splitting has drawn much attention. However, catalysts that are active for both the hydrogen evolution and oxygen evolution reactions are rare. Herein, we show for the first time that nickel phosphide (Ni2P), an excellent hydrogen evolving catalyst, is also highly active for oxygen evolution. A current density of 10 mA cm−2 is generated at an overpotential of only 290 mV in 1 M KOH. The high activity is attributed to the core–shell (Ni2P/NiOx) structure that the material adopts under catalytic conditions. The Ni2P nanoparticles can serve as both cathode and anode catalysts for an alkaline electrolyzer, which generates 10 mA cm−2 at 1.63 V.