Spin modulation of single Fe atoms with thiolate-poisoned Pd nanoclusters for highly efficient ammonia synthesis

Nitrate reduction toward ammonia is pivotal in energy and environmental domains but faces challenges in achieving simultaneous high selectivity and activity. Manipulating interactions between intermediates and metal species is deemed effective for catalytic enhancement. In this study, a uniformly configured Fe₁-N₄ single-atom catalyst with four-coordination was synthesized. Subsequent deposition of thiol-poisoned Pd nanoclusters provided a platform to investigate the neighboring effect of Pd nanoclusters, excluding activity influences from Pd catalysts. Through this neighbor engineering, the Fe 3d electron spin configuration shifted from low spin to medium spin (MS). Experimental and theoretical analyses affirmed that MS Fe species optimized nitrate reduction by enhancing the *NO desorption process. This spin-modulated Fe single-atom catalyst demonstrated superior activity (392.16 mmol⁻¹ g_cat⁻¹ h⁻¹, ~40 mol⁻¹ g_Fe⁻¹ h⁻¹) and a Faraday efficiency of 98.6% at −0.5 V vs. RHE, surpassing reported values. This study presents a promising strategy for nitrogen-chemistry transition metal catalysts.