First-principles design of hetero CoM (M = 3d, 4d, 5d block metals) double-atom catalysts for oxygen evolution reaction under alkaline conditions

Abstract

As an extension of single-atom catalysts, the development of double-atom catalysts with high electrocatalytic activity for the oxygen evolution reaction (OER) is vital to facilitate hydrogen production and industrial applications. The CoM (M = 3d, 4d, 5d block metals) homo and double-atom catalysts supported on nitrogen-doped graphene (CoM/N₄G) were prepared for electrochemical water oxidation under alkaline conditions, and the electrocatalytic activity was studied through density functional theory (DFT) calculations. The hetero CoCu/N₄G double-atom catalyst indicated the highest OER activity with an onset potential of 0.83 V, while the homo Co₂/N₄G catalyst showed a higher onset potential of 1.69 V. The decoupled strain, dopant, and configurational effects based on the notable differences between the homo Co₂/N₄G and CoCu/N₄G explained the enhanced OER activity, implying that the Cu dopant has a crucial impact on boosting the reactivity by reducing the affinity of reaction intermediates. The enhancement could also be understood from the perspective of the electron structure characteristic through d-orbital resolved density of states (ORDOS) (d_z², d_xz, d_yz, d_xy, and d_x²−y²) analysis. From the ORDOS analysis, we found an apparent alteration of the key orbitals between Co₂/N₄G (d_z², d_xz, and d_yz) and CoCu/N₄G (d_z2, d_xz, d_yz, and d_xy) with a substantial change in the overlap ratio (X_d). This theoretical study offers beneficial insights into developing a strategy for efficient OER catalysts utilizing a double-atom structure.