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

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 CoxFeyN nanoparticles uniformly loaded on graphene sheets (CoxFeyN/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 CoxFeyN/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 CoxFeyN/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 CoxFeyN/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 CoxFeyN/graphene catalysts as promising non-noble metal electrocatalysts for the OER for application in clean energy conversion devices.