Solar‐Driven Spin‐State Optimization in Co‐Based Catalysts for Enhanced Photothermal Ammonia Synthesis

ABSTRACT Spin‐state engineering of active sites represents a key strategy for boosting catalytic performance, as demonstrated in thermal ammonia synthesis. However, conventional promoter‐mediated ground‐state spin modulation is inherently limited by the electronic structure of the catalyst, imposing a ceiling on achievable spin tuning efficacy and hindering further advances. In this work, we developed a series of cobalt (Co) nanoparticle‐based catalysts for photothermal ammonia synthesis. By introducing Ru single atom into the Co nanoparticles, along with the addition of barium as a promoter, spin‐state engineering of Co nanoparticles was optimized under light irradiation, boosting the production rate by 3 times compared to thermal catalytic conditions. In‐situ characterization studies revealed that the hot electrons accumulate on the catalyst surface and shift the Co active sites toward a lower‐spin configuration. Supported by density functional theory (DFT) calculations, we demonstrate that this light‐induced spin state change modulates the electronic interaction between Co and N 2 , weakening the N≡N bond and lowering its dissociation energy barrier, thereby facilitating N 2 activation. This work demonstrates that spin regulation in Co‐based catalysts is an innovative design principle for developing more efficient photothermal catalysts for ammonia synthesis and other applications.