Electrocatalytic nitrogen reduction reaction (NRR) is a promising approach for renewable NH 3 production, while developing the NRR electrocatalysis systems with both high activity and selectivity remains a significant challenge. Herein, we combine catalyst and electrolyte engineering to achieve a high-efficiency NRR enabled by a Se-vacancy-rich WSe 2−x catalyst in water-in-salt electrolyte (WISE). Extensive characterizations, theoretical calculations, and in situ X-ray photoelectron/Raman spectroscopy reveal that WISE ensures suppressed H 2 evolution, improved N 2 affinity on the catalyst surface, as well as an enhanced π-back-donation ability of active sites, thereby promoting both activity and selectivity for the NRR. As a result, an excellent faradaic efficiency of 62.5% and NH 3 yield of 181.3 μg h −1 mg −1 is achieved with WSe 2−x in 12 m LiClO 4 , which is among the highest NRR performances reported to date.

The electrochemical N2 reduction reaction (NRR) offers a promising approach for sustainable NH3 production, and modulating the structural/electronic configurations of the catalyst materials with optimized electrocatalytic properties is pivotal for achieving high‐efficiency NRR electrocatalysis. Herein, vacancy and heterostructure engineering are rationally integrated to explore O‐vacancy‐rich MoO3‐x anchored on Ti3C2Tx‐MXene (MoO3‐x/MXene) as a highly active and selective NRR electrocatalyst, achieving an exceptional NRR activity with an NH3 yield of 95.8 µg h−1 mg−1 (−0.4 V) and a Faradaic efficiency of 22.3% (−0.3 V). A combination of in situ spectroscopy, molecular dynamics simulations and density functional theory computations is employed to unveil the synergistic effect of O‐vacancies and heterostructures for the NRR, which demonstrates that O‐vacancies on MoO3‐x serve as the active sites for N2 chemisorption and activation, while the MXene substrate can further regulate the O‐vacancy sites to break the scaling relation to effectively stabilize *N2/*N2H while destabilizing *NH2/*NH3, resulting in more optimized binding affinity of NRR intermediates toward reduced energy barriers and an enhanced NRR activity for MoO3‐x/MXene.

The electrochemical nitrate reduction to ammonia reaction (NO3RR) has emerged as an appealing route for achieving both wastewater treatment and ammonia production. Herein, sub-nm RuO x clusters anchored on a Pd metallene (RuO x /Pd) are reported as a highly effective NO3RR catalyst, delivering a maximum NH3-Faradaic efficiency of 98.6% with a corresponding NH3 yield rate of 23.5 mg h–1 cm–2 and partial a current density of 296.3 mA cm–2 at −0.5 V vs RHE. Operando spectroscopic characterizations combined with theoretical computations unveil the synergy of RuO x and Pd to enhance the NO3RR energetics through a mechanism of hydrogen spillover and hydrogen-bond interactions. In detail, RuO x activates NO3 – to form intermediates, while Pd dissociates H2O to generate *H, which spontaneously migrates to the RuO x /Pd interface via a hydrogen spillover process. Further hydrogen-bond interactions between spillovered *H and intermediates makes spillovered *H desorb from the RuO x /Pd interface and participate in the intermediate hydrogenation, contributing to the enhanced activity of RuO x /Pd for NO3 –-to-NH3 conversion.

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