The electrochemical nitrogen reduction reaction (eNRR) is a sustainable pathway for ammonia production, yet its practical implementation is hindered by the inherent thermodynamic stability of nitrogen and the competitive hydrogen evolution reaction (HER). Therefore, designing efficient electrocatalysts with superior eNRR activity and selectivity remains challenging. In this work, ultrasmall molybdenum oxide quantum dots (MoO_3−x QDs) rich in oxygen vacancies (OVs) were synthesized through an ultrafast wet-chemical approach. Owing to the exceptionally high surface-to-volume ratio, the 3 nm quantum-confined architecture of the MoO_3−x QDs has a high density of accessible active sites, facilitating charge transfer kinetics at the nanoscale. The number of OVs within MoO_3−x QDs can be precisely tailored by adjusting the amount of ligand introduced and effectively modifying the electronic structure of neighboring Mo sites in favor of the adsorption and hydrogenation of nitrogen, enhancing eNRR selectivity. Owing to the synergistic effects of quantum confinement and vacany engineering, the optimized MoO_3−x QD catalysts exhibit outstanding eNRR performance, achieving a good NH₃ yield rate of 38.55 μg·h⁻¹·mg⁻¹ with a Faradaic efficiency of 8.2% at −0.15 V (vs. RHE), which surpasses that of most reported Mo-based eNRR catalysts under comparable conditions. Furthermore, in situ Fourier transform infrared (FTIR) characterization revealed that the eNRR reaction pathway of MoO_3−x QDs follows an associative distal mechanism. This work establishes a dual-modulation strategy that integrates quantum size effects with vacancy engineering, providing a promising avenue for designing transition metal oxide catalysts with enhanced activity and selectivity in multielectron transfer reactions.

Covalent organic frameworks (COFs) represent an emerging class of crystalline porous polymers with high porosity, good stability, and adjustable structure, and their excellent characteristics lay a solid foundation for electrocatalysis. This review systematically introduces the design principles of the catalytic sites in two-dimensional (2D) COF-based electrocatalysts and analyzes the relationship between 2D COF structure and their electrocatalytic performances. In particular, the recent progress in the field of 2D COFs as electrocatalysts is comprehensively summarized. Finally, we discuss the current shortcomings and challenges on tailoring 2D COF for high-performance electrocatalysts in details, and look forward to promoting more researches on 2D COF-based electrocatalysts.

The commercial application of non-precious metal-based electrocatalysts is not only limited by the intrinsic activity of the catalysts, but also the stability of the catalysts is extremely important. Herein, we fabricated an ultra-stable NiFe armored catalyst (Ar-NiFe/NC) by a simple secondary pyrolysis strategy. The as-obtained Ar-NiFe/NC electrocatalyst exhibits an excellent bifunctional oxygen electrocatalytic performance with an activity indicator ∆E of 0.74 V vs. reversible hydrogen electrode (RHE). More importantly, the Ar-NiFe/NC electrocatalyst also shows a remarkable operational and storage stability. After accelerated durability test (ADT) cycles, no obvious degradation of oxygen electrocatalytic performance could be observed. In addition, the Ar-NiFe/NC electrocatalyst still exhibits an unbated oxygen electrocatalytic performance comparable to fresh catalysts after three months of air-exposed storage. The assembled liquid and flexible quasi-solid-state rechargeable Zn–air batteries with the Ar-NiFe/NC electrocatalyst exhibit impressive performance. The liquid rechargeable Zn–air batteries possess a high open-circuit voltage (OCV) of 1.43 V and a salient peak power density of 146.40 mW·cm⁻², while the flexible quasi-solid-state rechargeable Zn–air batteries also exhibit an excellent OCV of 1.60 V and an exciting peak power density of 41.99 mW·cm⁻².