First-Principles Design of Janus ABSe ₃ Monolayers for NO-to-NH ₃ Electrocatalysis

The electrochemical nitric oxide reduction reaction (NORR) offers a promising pathway for both ammonia synthesis and environmental pollutant removal. However, achieving high activity and selectivity remains a significant challenge. In this work, we design and screen a series of two-dimensional (2D) Janus ABSe3 monolayers using first-principles calculations and identify HfVSe3 and ReMoSe3 as dynamically and thermally stable metallic candidates. Among them, only HfVSe3 exhibits strong NO adsorption and activation at the V site, with an adsorption energy of −2.11 eV. The most favorable NORR pathway proceeds through NO* → NOH* → N* → NH* → NH2* → NH3, with a low limiting potential of 0.49 V associated with the potential-determining step NO* → NOH*. HfVSe3 also demonstrates high selectivity over the hydrogen evolution reaction and strong resistance to hydroxyl poisoning, thereby ensuring high Faradaic efficiency. An intrinsic built-in electric field, directed from the V-side to the Hf-side with a potential difference of 0.22 eV, further enhances electron transfer and NORR kinetics. This study expands the family of Janus 2D materials and provides fundamental insights and design principles for developing high-performance NORR electrocatalysts.