Magnetic transition of 1D ferromagnetic catalysts during the NO electroreduction

Abstract

Exploration of magnetic phase transitions during electrochemical processes is of great importance for rational design of supported magnetic-metal electrocatalysts. Herein, we systematically investigated the magnetic transition between ferromagnetism (FM) and anti-ferromagnetism (AFM) in one-dimensional ferromagnetic Co chain supported on graphene (Co4N8-gra) during NO electroreduction (NORR) process, focusing on the impact of potential and acidity on the catalytic property and magnetic transition. A combination of catalytic kinetics calculations and microkinetic simulations reveals that the Co4N8-gra exhibits excellent NH3 selectivity and thermal stability. In the implicit solvent model, the general reaction follows optimal pathway: * + NO(g) → *NO → *HNO → *H2NO → *H2NOH → *NH2 → *NH3 → * + NH3, with the potential-determining step (PDS) identified as *NO → *HNO. In acidic solvent, the magnetic transitions follow the pathway (FM → AFM2 → AFM2 → AFM2 → AFM1 → AFM1 → AFM1 → FM) under an applied potential of −0.20 V/RHE. In neutral solvent, the magnetic transitions occur according to this pathway (FM → AFM2 → AFM2 → FM → AFM1 → AFM1 → AFM1 → FM) under an applied potential of −0.14 V/RHE. In an alkaline solvent, the magnetic transitions proceed along this sequence (FM → AFM1 → AFM2 → FM → AFM1 → AFM1 → AFM1 → FM) under an ultralow potential of −0.08 V/RHE. Essentially, the improvement of catalytic property is attributed to the synergistic influence of external potential and magnetic-state transition on the adsorption of reaction species (e.g., NO and NH3). Magnetic transitions are closely associated with ligand field effect of metal site with variable valence electron induced by applied potential. In general, this study provides valuable insights for the controllable design of magnetic metal catalysts.