Atomically isolated copper on titanium dioxide for ammonia photosynthesis via nitrate reduction with unprecedently high apparent quantum yield

Photocatalytic nitrate (NO3-) reduction to NH3 (PcNRA) is a sustainable alternative that is considered advantageous over N2 fixation, which suffers from the high dissociation energy and sluggish activation of inactive N2. Although PcNRA has recently been shown to achieve excellent selectivity, its sluggish kinetics restrict the NH3 production efficiency. Herein, we present a single-atom Cu-incorporated TiO2 nanosheet (Cu-TNS) photocatalyst for efficient and selective PcNRA. Single Cu atoms displacing Ti sites accumulate photogenerated electrons, ensuring efficient charge separation and surface NO3- reduction. Moreover, introducing Cu atoms into the TiO2 - matrix induces spontaneous defect formation, resulting in oxygen vacancies and lattice strain that promote NO3 adsorption and activation. The simultaneous presence of single Cu atoms and structural defects in Cu-TNS synergistically stimulates PcNRA, leading to a 62-fold enhancement over pristine TiO2 in NH3 production with 97.6% selectivity and an unprecedently high apparent quantum yield of 11.7% at 330 nm under optimized conditions.