Bimetallic iron cobalt oxide nanoclusters embedded on three-dimensional flower-like iron cobalt oxide nanosheets for improved oxygen evolution reaction

Abstract

The design of the nanoarchitecture of hierarchical three-dimensional (3D) nanosheets for use as free-standing, non-precious electrocatalysts for oxygen evolution reaction (OER) is critical for building commercial water-splitting systems. Herein, we report a facile, scalable, efficient and binder-free fabrication of earth-abundant bimetallic iron cobalt oxide nanoclusters embedded on 3D flower-like iron cobalt oxide nanosheets (FeCoO NC@3D-FeCoO NS) grown on a nickel foam (NF) substrate for the improved OER under an alkaline electrolyte. The as-developed FeCoO NC@3D-FeCoO NS|NF electrode materials exhibited an excellent OER catalytic activity with low OER onset potential (∼1.37 V), small overpotential (η) (∼0.22 V) @ 10 mA cm⁻² and Tafel slope (∼53 mV dec⁻¹), high mass activity (500 A g⁻¹) and turn over frequency (TOF) (2.83 s⁻¹), and long-term durability (over 100 h) in 1.0 M KOH. The attained high catalytic OER performance of the FeCoO NC@3D-FeCoO NS|NF electrode is due to its unique bimetallic heterostructure, rich in oxygen deficient sites and active sites, large electrochemical active surface area (ECASA), low polarization resistance, rapid charge-transfer kinetics, facilitation of mass diffusion/transport of OH⁻ ions and improved electronic conductivity, and ease of H₂O adsorption onto nearby active sites. Impressively, the FeCoO NC@3D-FeCoO NS|NF‖PtC/C couple exhibited less positive potential (∼1.82 V) to attain a current density of ∼50 mA cm⁻² and high catalytic OER performance, which is ∼150.0 mV smaller than that of the benchmark RuO₂‖Pt/C couple in the alkaline electrolysis cell, suggesting good practicability.