Transition metal nitrides (TMNs) have recently attracted increasing attention as a robust alternative to platinum electrocatalysts in alkaline oxygen reduction reaction (ORR). However, the fundamental understanding of the catalytic nature of the TMNs remains elusive, impeding the further catalyst design and optimization. Here, using ZrN as a model catalyst, we demonstrate that the unexpected catalytic activity of TMNs originates from the self-adaptive behavior of surface-reconstructed oxynitride monolayers under ORR conditions. Our first-principles calculations reveal that oxygen adsorption triggers a square-to-hexagonal symmetry transition on the ZrN surface, stabilizing a hexagonal ZrNO monolayer. At quarter-hydroxyl coverage, this reconstruction generates semi-elliptical cavities that confine the highly active Zr sites. Crucially, the flexible Zr–N–Zr linkages connecting these Zr sites and the underlying ZrN substrate undergo dynamic bond-length variations during ORR, which precisely regulate oxygen intermediate adsorption and significantly enhance catalytic activity. Experimental characterization aligns well with these theoretical predictions. The as-designed ZrNO monolayer catalyst delivers a 0.882 V half-wave potential for ORR and enables zinc–air batteries with 240 mW·cm⁻² peak power density—metrics that exceed state-of-the-art Pt/C. This study provides atomic-level insights into the nature of TMNs’ catalytic monolayers, paving the way for stable and active catalyst engineering in next-generation energy technologies.

Bi is a promising anode material for potassium-ion batteries (PIBs) due to its high theoretical capacity. However, severe pulverization upon cycling limits its practical applications. In this work, we propose a new approach of using metastable alloys with Bi elements. Metastable Bi:Co and Bi:Fe alloys nanodots@carbon anode materials (Bi:Co and Bi:Fe@C) are synthesized for the first time via simple annealing of their metal-organic frameworks (MOF) precursors. These prepared materials are demonstrated as ideal hosts for high-rate K-ion storage. Bi_0.85Co_0.15@C and Bi_0.83Fe_0.17@C electrodes respectively deliver superior 178 and 253 mAh·g⁻¹ at 20 A·g⁻¹, as well as stable cycling performance at 2 A·g⁻¹. Ex situ scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and transmission electron microscopy (TEM) studies on Bi:Co@C indicate that the elemental Co separates out during the initial potassiation and stands during the following discharge/charge cycles. In situ formed Co precipitates can act as (1) “conductive binders” as well as (2) “separators” to prevent the severe aggregation of adjacent active elemental Bi nanoparticles and (3) accelerate the potassiation/de-potassiation kinetics in elemental Bi precipitates after initial discharge/charge cycles. This work could inspire the development of metal-type anodes.