CoxFeyN nanoparticles decorated on graphene sheets as high-performance electrocatalysts for the oxygen evolution reaction

Abstract

Exploring highly efficient non-noble metal based catalysts for the oxygen evolution reaction (OER) is of great importance for the development of renewable energy conversion technologies, such as water-splitting devices and rechargeable metal–air batteries. Co-based electrocatalysts have been regarded as a class of highly active and earth-abundant catalysts for the OER, but most of them are semiconductors or insulators that may limit the OER efficiency. Herein, we report the facile preparation of Co_xFe_yN nanoparticles uniformly loaded on graphene sheets (Co_xFe_yN/graphene) with amazing OER activity and stability, attributed to the intrinsic metallic characteristics. Through partial Fe heteroatom substitution in Co₄N lattices, the disorder of the crystalline structure could be increased, thus forming a more favorable electronic structure for the catalysis of the OER. By adjusting the atomic ratios of Co/Fe elements, we found that the Co₃Fe₁N/graphene catalyst exhibited the highest activity for the OER under alkaline conditions among the Co_xFe_yN/graphene samples, showing the lowest overpotential of 266 mV at 10 mA cm⁻², the highest current density of 105.83 mA cm⁻² at 1.53 V, and the lowest Tafel slope of 32 mV dec⁻¹. Moreover, the freestanding electrodes of Co_xFe_yN/graphene catalysts loaded on carbon paper (CP) also exhibited excellent long-term stability for the OER, and the overpotentials only slightly increased after continuously testing for 16 h at 10 mA cm⁻². Among all the Co_xFe_yN/graphene/CP samples, the Co₃Fe₁N/graphene/CP sample also displayed the best long-term stability and the lowest overpotential (270 mV) after 16 h. This work presents the great potential of Co_xFe_yN/graphene catalysts as promising non-noble metal electrocatalysts for the OER for application in clean energy conversion devices.