Orbital-Engineered CuTi-NC/BiOBr Schottky Junction for Efficient Photocatalytic N ₂ Fixation

The development of efficient photocatalytic systems for nitrogen fixation hinges on the precise regulation of charge separation and electron transfer kinetics. Here, we present a chemically bonded Schottky junction, CuTi 0.25 -NC/BiOBr, in which a nitrogen-doped carbon (NC) layer protects the embedded transition metals from overoxidation. In a sacrificial-agent-free aqueous environment, the CuTi 0.25 -NC/BOB heterojunction achieves an ammonia production rate of 764.1 μmol g –1 h –1 under simulated solar irradiation. This performance represents a 10-fold enhancement relative to pristine BOB and substantially surpasses that of metal-free NC/BOB and single-metal control systems. Mechanistic studies reveal that CuTi 0.25 -NC and BiOBr form Cu/Ti–O–Bi chemical bonds through d–p orbital interactions, which increase the electron density at the active Bi sites. This coupled modulation precisely tunes the p-band center of Bi, promoting N 2 activation while enhancing interfacial stability and providing an atomic-level pathway for charge transfer. Our findings underscore the critical role of interfacial orbital coupling in heterostructure design and establish a strategic paradigm for constructing high-performance nitrogen fixation systems that transcend conventional heterojunction engineering.