Operando Reconstruction of NiB Precatalyst Into Adaptive Heterointerfaces for CO 2 Photoreduction via Tandem Hydrogen Relay

ABSTRACT Photocatalytic CO 2 reduction is a transformative carbon neutrality technology, yet the electronic competition between water‐derived proton generation and CO 2 activation over intrinsic sites leads to parasitic H 2 evolution over a static catalytic surface. Here we demonstrate that crystalline nickel boride (NiB) precatalyst, previously unexplored for photocatalysis, undergoes spontaneous operando reconstruction under illumination to form adaptive Ni/B 2 O 3 /NiB heterointerfaces as the genuine catalytically active phases. The reaction‐driven reconstructed interfaces enable a tandem hydrogen relay across the NiB→Ni→B 2 O 3 interface, in which hydrogen species evolve sequentially from H 2 O to H 2 and are subsequently converted into surface‐active hydrogen (H 2 O→H 2 →H*) via Ni‐mediated dissociation and hydrogen spillover. The H* species assist CO 2 activation and hydrogenation on the electron‐deficient B 2 O 3 domains. This dynamic process progressively redirects the reaction pathway from water‐splitting‐dominated activity to highly efficient CO 2 ‐to‐CO conversion, achieving a CO evolution rate of 4.5 mmol·g −1 ·h −1 with promoted utilization of in situ formed hydrogen species, thus presenting an order‐of‐magnitude enhancement over reported photocatalytic systems. This work unlocks crystalline transition‐metal borides as an untapped material platform for photocatalytic CO 2 reduction and demonstrates that reaction‐driven interfacial reconstruction can establish adaptive hydrogen‐relay pathways to mitigate multi‐reaction competition in solar‐to‐chemical conversion.