Thin carbon layer covered Co4N cubes encapsulated in N-doped porous carbon nanocage as tri-functional catalysts with enhanced charge-transfer efficiency for Zn-air battery and overall water-splitting

Abstract

High-efficiency bifunctional catalysts with high energy conversion efficiency and high cycling performance are urgently needed for traditional zinc-air batteries (ZABs). Herein, a composite of highly active carbon layer covered Co₄N cubes encapsulated in a nitrogen-doped porous carbon nanocage (Co₄NC@NC) as a cathode catalyst was prepared by a hydrothermal acid-assisted strategy combined with subsequent calcination. The precursor is treated with carbon coating and calcination to obtain a double-carbon-layer-coated structure of Co₄NC@NC. The inner carbon layer is tightly wrapped on the surface of the Co₄N particles, and the outer carbon layer presents a porous structure. Co₄NC@NC exhibits significantly enhanced electrocatalytic activities for ORR, OER and HER. In particular, the overpotential is only 166 mV for OER at a current density of 10 mA cm⁻². Density functional theory calculations reveal that the synergistic effect between the N-doped graphite carbon layer and Co₄N can improve the adsorption efficiency of intermediate products, accelerate the reaction kinetics, and reduce the free energy of rate determining steps. ZABs assembled with Co₄NC@NC showed excellent stability during 1050 cycles at 5 mA cm⁻². Furthermore, Co₄NC@CN can also be used as an HER catalyst for overall water splitting, driven by Co₄NC@CN-ZABs. The above results indicate that Co₄NC@CN can be used as a high-performance three-function catalyst for ZABs and overall water splitting.