Coordination engineering of Ru–N-C based OER catalysts guided by the ΔG*OH descriptor: a theoretical study

Abstract

A Ru–N-C single-atom catalyst is intrinsically limited in the oxygen evolution reaction (OER) by excessively strong oxygen adsorption, which renders the *O → *OOH step rate-determining. Here, rather than focusing on a single coordination motif, we establish a unified activity–stability comparison framework for Ru–N-C based OER catalysts through five representative coordination engineering strategies: axial non-metal coordination, axial metal coordination, axial N-bridged metal motifs, in-plane dual-metal sites, and in-plane N-bridged dual-metal motifs. Using ΔG_*OH (1.23–1.53 eV) (X. M. Zhang, Z. X. Xia, H. Q. Li, S. S. Yu, S. L. Wang and G. Q. Sun, J. Colloid Interface Sci., 2023, 640, 170–178) as a primary screening descriptor, we first identify promising candidates from more than 100 Ru-based structures and then evaluate their complete four-step OER free-energy pathways and stability. Specifically, (i) axial CH₃ and NH groups lower the overpotential (η) to 0.58 V and 0.59 V, with binding energies ΔE_b = −6.42 eV and −6.08 eV; (ii) axial Mn, Fe, Co, Ni, and Cu give η = 0.38–0.48 V, among which Ru–N₄Mn-C achieves η = 0.38 V and ΔE_b = −5.59 eV; (iii) axial N-bridged Ni and Cu produce η ≈ 0.50 V and exceptionally high ΔE_b ≈ −9.20 eV; (iv) in-plane N-bridged oxidized structures, especially RuIr–O3, exhibit an ultra-low η of 0.18 V (ΔE_b = −4.24 eV), while RuRh–O3R(Rh) and RuIr–O3R(Ir) balance η = 0.55 V/0.37 V with ΔE_b = −6.42 eV/−5.92 eV. Cross-system comparison identifies Ru–NiN₄ and RuIr–O3R as top integrated performers. Operando simulations reveal that *O specific adsorption, especially when coupled with an electric field (0.3 V Å⁻¹), weakens metal–support binding by up to 2.01 eV, while ab initio molecular dynamics confirms the dynamic stability of RuIr–O3R (±0.03 eV over 5000 fs). This work provides a quantitative library of Ru-based OER catalysts and establishes *O-induced destabilization as the primary degradation mechanism.