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

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 N₂, weakening the N≡N bond and lowering its dissociation energy barrier, thereby facilitating N₂ 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.