Spin-Order Effects of Single-Atom Catalyst on Electrocatalytic Oxygen Reduction

Magnetic property (spin order) of support is of great importance in the rational design of heterogeneous catalysts. Herein, we taken the Ni-supported ferromagnetic CrBr3 support (Nix/CrBr3) to thorough investigate the effect of spin-order on electrocatalytic oxygen reduction reaction (ORR) via spin-polarized density functional theory (DFT) calculations. Specifically, Ni loading induces anti-ferromagnetic coupling in Ni-Cr, leading to a transition from ferromagnetic ( FM )-to-ferrimagnetic ( FIM ) properties, while Ni-Ni metallic bonds create a robust ferromagnetic direct exchange, benefiting the improvement of the phase transition temperature. Interestingly, with the increase of Ni loading, the easy magnetic axis changes from out of plane (2D-Heisenberg) to in plane (2D-XY). The adsorption properties of Nix/CrBr3, involving O2 adsorption energy and configuration, are not governed by the d-band center and strongly correlate with magnetic anisotropy. It is noteworthy that the applied potential and electrolyte acidity triggers spin-order transition phenomena during the ORR and induces the catalytic pathway change from the 4e- ORR to 2e- ORR with the excellent onset potential of 0.93 V/RHE, comparable to the existing most excellent noble-metal catalysts. Generally, these findings offer new avenues to understand and design the heterogeneous catalysts with magnetic support.