Dynamic Switching Spin State of Fe Single Atoms for Piezoelectric-Mediated Overall Nitrogen Fixation Photosynthesis

Solar-driven one-step disproportionation overall nitrogen fixation (ONF) for synchronously synthesizing ammonia and nitrate presents a promising alternative to conventional Haber-Bosch and Ostwald processes, but suffers from ultra-low efficiency. Single atoms (SAs) featured by maximized atomic utilization exhibit superb catalytic activity, while the definite electronic configurations confine SAs to function solely as reduction or oxidation sites, limiting the possibility for both reduction and oxidation reactions. Herein, an efficient approach is presented for ammonia and nitrate co-synthesis by introducing Fe SAs and alternating piezoelectric field into a defective piezoelectric BaTiO₃ (OvBTO-Fe), enabling the formation spatially-separated redox regions and dynamic bidirectional switching of Fe spin states. At positive and negative polarization ends, Fe spin state transitions to high and low spin states through d-electrons relocation, respectively, thermodynamically and kinetically facilitate nitrogen reduction and oxidation reactions. Thus, OvBTO-Fe exhibits unprecedented piezo-photocatalytic ONF activity, achieving a record solar-to-chemical conversion efficiency of 0.82% and total energy-to-chemical conversion efficiency of 0.53%. This work proposes a methodology for dynamic multi-directional manipulation of spin states and overall catalytic synthesis reaction.