Metal termination of Pd(111) enables selective electrochemical nitrogen oxidation reaction under anodic polarization

The electrochemical nitrogen oxidation reaction (NOR) on solid-state electrodes represents a potential alternative to the traditional industrial process for nitric acid (HNO 3 ) production. However, development is hampered by limited knowledge of the mechanistic pathways that leads to HNO 3 formation and how to suppress the competing oxygen evolution reaction (OER). Here, we present a first-principles investigation of NOR and OER on Pd(111) using density functional theory (DFT) calculations using the computational hydrogen electrode (CHE) approach, combined with a descriptor-based analysis to comprehend activity and selectivity trends at the atomic level. We systematically assess a range of competing NOR pathways, including multiple routes for N 2 activation, using oxygen-covered Pd(111) surface models. Our DFT calculations identify an electrochemical activation mechanism in which N 2 reacts with surface-bound *OH to form *NO 2 via a concerted proton-electron transfer step. A selectivity analysis under operational conditions suggests that N 2 O is the dominant NOR product, prevailing even over OER. Based on these results, we propose that experimentally observed NOR selectivity on Pd-based electrodes is closely linked to the presence of metallic surface regions, highlighting the importance of developing strategies to stabilize Pd islands maintain and coverage composition under anodic reaction polarization.