Local magnetic moment and adsorption energetics as intrinsic activity indicators for bimetallic 2D π-d conjugated BHT frameworks in oxygen evolution electrocatalysis

Abstract

Bimetallic two-dimensional π-d conjugated benzenehexathiol (BHT) frameworks are emerging as a versatile platform for oxygen evolution reaction (OER) electrocatalysis, yet the vast compositional space and the known limitations of computational hydrogen electrode (CHE)-based free-energy rankings make purely thermodynamic screening unreliable. Building on our previous combined experimental–computational study of NiFe–BHT, we here use the local magnetic moment of the transition-metal node and the *OH adsorption energy (E_ad) as physically motivated, intrinsic activity indicators to evaluate a series of monometallic TM–BHT (TM = Cu, Zn, Cd, Pd, Ni, Co, Fe, Mn) and Mn-based bimetallic MnTM–BHT (TM = Fe, Co, Ni, Cu) frameworks at two stoichiometries (MnTM_5 : 1 and MnTM_1 : 5). Density functional theory (DFT) calculations reveal an apparent trend between the TM local magnetic moment and E_ad(*OH), with high-spin Mn–BHT exhibiting nearly neutral binding (E_ad = −0.015 eV). Among the bimetallic compositions examined, MnFe_5 : 1–BHT uniquely shifts E_ad(*OH) on the Mn site into the moderately negative regime (−0.647 eV) while preserving the high local Mn spin moment (2.757 µB). CHE-level Gibbs free-energy profiles, used here only as an internal mechanistic consistency check, suggest a dual-site picture in which Fe acts as the kinetic hotspot and electronically tunes the neighboring Mn centers. Convex-hull and Boltzmann-transport calculations further indicate that MnFe_5 : 1–BHT is metastable to an extent comparable with already-synthesized monometallic BHTs and retains adequate intrinsic conductivity. The convergence of four independent criteria, moderated *OH binding on Mn, preserved Mn high-spin character, accessible metastability, and adequate conductivity, rather than any single ΔG value, supports MnFe_5 : 1–BHT as a concrete target for experimental realization.