Oxygen-Vacancy-Mediated d–p Hybridization in RuO2 Nanosheets for Efficient Nitrate-to-Ammonia Electrosynthesis

Abstract

Nitrate electroreduction to ammonia (NRA) has emerged as a promising green alternative to the energy-intensive Haber–Bosch process, offering a dual-benefit strategy for mitigating nitrate pollution while enabling carbon-neutral ammonia synthesis. However, its intrinsic multi-step proton-coupled electron transfer (PCET) faces a fundamental issue, which requires achieving the selective coupling of nitrogen intermediates (*NHxOy) with protons (*H) while simultaneously suppressing parasitic side reactions. To address this, density functional theory (DFT) calculations were employed to rationally screen the hybridization of Ru 4d and O 2p orbitals in oxygen-deficient RuO2, systematically evaluating it as a decisive descriptor for the adsorption characteristics of key intermediates. Building on this theoretical guidance, we synthesized monolayered RuO2 nanosheets through wet-chemical exfoliation, with oxygen-vacancy (Ovac) mediation to precisely modulate the targeted d–p hybridization. As a result, the RuO2 nanosheet with high Ovac (RuO2-HO) achieves a Faradaic efficiency of 94.3% and a production rate of 466.4 mmol h–1 g–1 at –0.4 V vs the reversible hydrogen electrode (RHE), outperforming its low-Ovac counterparts (RuO2-LO) by approximately fivefold. Complementary operando investigations and DFT calculations demonstrate that the optimized d–p hybridization in RuO2-HO balances the binding strengths toward *NHxOy and *H, thereby promoting nitrate activation and facilitating subsequent N–H coupling steps. This DFT-guided, vacancy-mediated d–p hybridization engineering establishes a versatile paradigm for the design of high-performance NRA electrocatalysts.