Synergistic effect customized for cobalt pentlandite (Co,Ni,Fe)9S8 accelerated charge transfer toward highly efficient oxygen evolution reaction

Abstract

The oxygen evolution reaction (OER) is one of the core reaction modules of important renewable energy technologies with applications in water splitting, metal-air (oxygen) cells and regenerative fuel cells. However, OER catalysts are forced to operate with a significant intrinsic overpotential and inefficient charge transfer due to the adsorption energy scaling balance between the reaction intermediates. It is critical to develop an understanding of structure-activity relationship of catalysts, determine the speed control steps and improve catalytic activity. In this work, cobalt pentlandite (Co,Ni,Fe)9S8 (CNFS) electrocatalysts were successfully prepared by combining the earth-abundant transition metal elements Co, Ni and Fe into a single structure. Benefiting from the structure, nanoflower morphology, and the synergistic effect among the three elements, the optimized sample requires an overpotential of only 335 mV to drive a current density of 50 mA cm–2 under alkaline conditions. The experimental results establish a composition-structure-function relationship, and the density functional theory results further indicate that the Fe sites bind more moderately to the intermediates and the electron synergistic effect occurs dynamically during the OER cycle reaction. This work not only provides a very promising catalyst candidate for efficient OER processes but also highlights the superiority of the cobalt pentlandite structure in the rational design of efficient OER electrocatalysts.