Positive self-reconstruction in an FeNiMo phosphide electrocatalyst for enhanced overall water splitting

Abstract

Searching for low-cost and highly active bifunctional electrocatalysts toward hydrogen/oxygen evolution reactions is a grand challenge for water splitting hydrogen production. Herein, we prepare a trimetallic nickel, iron, and molybdenum phosphide (FeNiMoP) grown on nickel foam (NF) via a facile two-step process and employ it as a bifunctional electrocatalyst for full water splitting. In virtue of the superior hydrogen/oxygen evolution activity, the cell with the bifunctional FeNiMoP as both anode and cathode exhibits an initial low cell voltage of 1.50 V at a current density of 10 mA cm⁻² in 1.0 M KOH electrolyte solution. Impressively, the full cell voltage decreases to 1.44 V through favorable self-reconstruction on both the anode and cathode during the electrocatalytic overall water splitting process. On the anode side, the FeNiMoP is transformed into FeNiOOH while Mo and P elements are dissolved into the electrolyte. Such transformation leads to a continuously increasing active surface area, and the dissolved Mo forms MoO₄²⁻ in the electrolyte which improves the OER performance. On the cathode side, the dissolution and re-deposition of Mo oxides on the surface of the electrode greatly increase the active surface sites towards the electrolytes, and the surface absorbed Mo oxides play key roles, leading to a positive effect on HER performance. The new synthesis strategy, taking advantage of favorable structural self-reconstruction in the catalysts can be extended to other catalytic systems.