The triple structure design of 2D amorphous Fe-doped indium phosphate nanosheets as a highly efficient electrocatalyst for water oxidation

Abstract

Metal phosphates have been developed into a promising category of highly efficient and low-cost electrocatalyst candidates for the oxygen evolution reaction (OER). However, their catalytic activities are still inferior to noble-metal-based oxides. Although increasing the number of catalytically active sites and improving the intrinsic activity via structural engineering at the atomic level are of great significance for improving the activity during electrocatalysis, it still remains challenging to actualize this in a desirable manner. Here, a triple structure design combining amorphization, 2D nanosheet fabrication, and Fe doping simultaneously is developed to promote the activity of InPO₄, an electrochemically inert metal phosphate, as a model catalyst for highly efficient water oxidation. Systematic experiments and density functional theory calculations demonstrate that the triple structure design induces unique structural merits, including the maximum exposure of Fe-dopant highly active sites, an outer 2D morphology with a thickness of 1.57 nm, and a local structure with inner disorder and abundant surface defects; these contribute to a simultaneous increase in the number of catalytically active sites and an enhancement in the intrinsic activity of the model catalyst. The engineered InPO₄ model catalyst exhibits outstanding OER performance (requiring overpotentials of only 230 and 284 mV for current densities of 10 and 100 mA cm⁻², which are comparable and even better values than most state-of-the-art OER electrocatalysts). Furthermore, the triple structure design strategy could also be explored to enhance the OER performance of other metal phosphates, such as M_x(PO₄)_Y (M = Co, Ni, Bi, V), indicating its generality and efficiency.