In situ constructing lamella-heterostructured nanoporous CoFe/CoFe2O4 and CeO2−x 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/CoFe₂O₄ 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 (η₁₀ = 227 mV; η₅₀₀ = 450 mV) and hydrogen evolution (η₁₀ = 35 mV; η₄₀₈ = 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.

Graphical abstract