Cobalt−Iron Pyrophosphate Porous Nanosheets as Highly Active Electrocatalysts for the Oxygen Evolution Reaction

Abstract One of the challenges to realize large‐scale water splitting is the sluggish kinetics of the anode reaction. Nowadays, metal phosphates are widely used as high‐efficiency catalysts for the oxygen evolution reaction (OER). In this work, we studied common phosphoric acid salts including orthophosphate, pyrophosphate, and tripolyphosphate in a bimetallic catalyst to explore the effect of the anion in phosphate‐based OER electrocatalysts. Co−Fe‐Pi, Co−Fe‐Pyro, and Co−Fe‐Pyro were successfully synthesized through a simple and convenient co‐precipitation method. Among them, Co−Fe‐Pyro exhibits the best electrocatalytic activity, with a low overpotential of 276 mV at a current density of 10 mA cm −2 , a small Tafel slope of 32 mV dec −1 , and a durable stability of about 90 % after 30000 s at 1.62 V vs. RHE in 1 M KOH. XRD reveals the amorphous structure of the materials and XPS confirms the formation of Co−Fe‐Pyro. SEM and TEM present the nanosheets with a porous structure on the surface of Co−Fe‐Pyro. The distribution and ratio of the elements in Co−Fe‐Pyro are confirmed by using EDS and ICP‐AES. Therefore, this work promotes a new thought regarding the anion structure in the phosphate‐based electrocatalysts.