Ultrathin Iron‐Cobalt Oxide Nanosheets with Abundant Oxygen Vacancies for the Oxygen Evolution Reaction

TLDR

Electrochemical water splitting is a promising method for storing light/electrical energy as H₂ fuel, but its progress is hindered by the sluggish anodic oxygen evolution reaction (OER). To enhance H₂ production, the study aims to develop an efficient, low‑cost OER catalyst with a large surface area, abundant active sites, and good stability. A facile solution‑reduction approach using NaBH₄ produces iron‑cobalt oxide nanosheets (FeₓCoᵧ‑ONSs) with a specific surface area up to 261.1 m² g⁻¹, an ultrathin thickness of 1.2 nm, and abundant oxygen vacancies. Fe₁Co₁‑ONS delivers a mass activity of 54.9 A g⁻¹ at 350 mV and a Tafel slope of 36.8 mV dec⁻¹, surpassing commercial RuO₂, crystalline Fe₁Co₁‑ONP, and most reported OER catalysts, thanks to its ultrathin nanosheet structure that facilitates mass transport and oxygen vacancies that enhance electronic conductivity and water adsorption.

Abstract

Electrochemical water splitting is a promising method for storing light/electrical energy in the form of H 2 fuel; however, it is limited by the sluggish anodic oxygen evolution reaction (OER). To improve the accessibility of H 2 production, it is necessary to develop an efficient OER catalyst with large surface area, abundant active sites, and good stability, through a low‐cost fabrication route. Herein, a facile solution reduction method using NaBH 4 as a reductant is developed to prepare iron‐cobalt oxide nanosheets (Fe x Co y ‐ONSs) with a large specific surface area (up to 261.1 m 2 g −1 ), ultrathin thickness (1.2 nm), and, importantly, abundant oxygen vacancies. The mass activity of Fe 1 Co 1 ‐ONS measured at an overpotential of 350 mV reaches up to 54.9 A g −1 , while its Tafel slope is 36.8 mV dec −1 ; both of which are superior to those of commercial RuO 2 , crystalline Fe 1 Co 1 ‐ONP, and most reported OER catalysts. The excellent OER catalytic activity of Fe 1 Co 1 ‐ONS can be attributed to its specific structure, e.g., ultrathin nanosheets that could facilitate mass diffusion/transport of OH − ions and provide more active sites for OER catalysis, and oxygen vacancies that could improve electronic conductivity and facilitate adsorption of H 2 O onto nearby Co 3+ sites.