Phase-Induced Strain Effect to Synthesize an Iron-Doped Orthogonal Cobalt Selenide Electrocatalyst for the Oxygen Evolution Reaction.

The etching effect has the capability to control atom doping and trigger phase transformation, thereby enhancing the electrocatalytic reaction. Herein, iron-doped cobalt selenide (Fe-CoSe 2 ) nanoparticle-decorated carbon nanofibers (Fe-CoSe 2 /CNFs) are synthesized by assembling an FeCo-Prussian blue analogue (FeCo-PBA) cube precursor with polyacrylonitrile fibers and then treating with hydrochloric acid, followed by gas phase selenization. The Fe-CoSe 2 /CNFs catalyst exhibits a large surface area and a porous structure, facilitating the permeation of electrolytes. Moreover, orthorhombic CoSe 2 is obtained, which is in favor of improving the oxygen evolution reaction (OER). By modulating the etching time, the ideal crystal phase and the optimal amount of the dopant (Fe) can be achieved, thus showing favorable OER activity. Specifically, the Fe-CoSe 2 /CNFs electrocatalyst enables high electrocatalytic activity for the OER with a low overpotential of 263 mV to drive a current density of 10 mA cm -2 in 1 M KOH. A small Tafel slope of 51 mV dec -1 shows fast charge transfer kinetics. Density functional theory (DFT) calculations reveal that Fe-doped orthorhombic CoSe 2 (111) can modulate the electron structure, contributing to OH - adsorption ability. Given this, a strategy for phase transformation induced by etching technology is proposed to improve the intrinsic activity of the catalyst.