In situ constructing lamella‐heterostructured nanoporous CoFe/CoFe ₂ O ₄ and CeO _{2− <i>x</i>} as bifunctional electrocatalyst for high‐current‐density water splitting

Abstract The stability and electrocatalytic efficiency of transition metal oxides for water splitting is determined by geometric and electronic structure, especially under high current densities. Herein, a newly designed lamella‐heterostructured nanoporous CoFe/CoFe 2 O 4 and CeO 2− x , in situ grown on nickel foam (NF), holds great promise as a high‐efficient bifunctional electrocatalyst (named R‐CoFe/Ce/NF) for water splitting. Experimental characterization verifies surface reconstruction from CoFe alloy/oxide to highly active CoFeOOH during in situ electrochemical polarization. By virtues of three‐dimensional nanoporous architecture and abundant electroactive CoFeOOH/CeO 2− x heterostructure interfaces, the R‐CoFe/Ce/NF electrode achieves low overpotentials for oxygen evolution ( η 10 = 227 mV; η 500 = 450 mV) and hydrogen evolution ( η 10 = 35 mV; η 408 = 560 mV) reactions with high normalized electrochemical active surface areas, respectively. Additionally, the alkaline full water splitting electrolyzer of R‐CoFe/Ce/NF||R‐CoFe/Ce/NF achieves a current density of 50 mA·cm −2 only at 1.75 V; the decline of activity is satisfactory after 100‐h durability test at 300 mA·cm −2 . Density functional theory also demonstrates that the electron can transfer from CeO 2− x by virtue of O atom to CoFeOOH at CoFeOOH/CeO 2− x heterointerfaces and enhancing the adsorption of reactant, thus optimizing electronic structure and Gibbs free energies for the improvement of the activity for water splitting.