Discovering ultrahigh loading of single-metal-atoms via surface tensile-strain for unprecedented urea electrolysis

Abstract

Single-atom-catalysts (SACs) have recently gained significant attention in energy conversion/storage applications, while the low-loading amount due to their easy-to-migrate tendency causes a major bottleneck. For energy-saving H₂ generation, replacing the sluggish oxygen evolution reaction with the thermodynamically favorable urea oxidation reaction (UOR) offers great promise, additionally mitigating the issue of urea-rich water contamination. However, the lack of efficient catalysts to overcome the intrinsically slow kinetics limits its scalable applications. Herein, we discover that incorporating tensile-strain on the surface of a Co₃O₄ (strained-Co₃O₄; S-Co₃O₄) support by the liquid N₂-quenching method can significantly inhibit the migration tendency of Rh single-atoms (Rh_SA), thereby stabilizing an ∼200% higher loading of Rh_SA sites (Rh_SA-S-Co₃O₄; bulk loading ∼6.6 wt%/surface loading ∼11.6 wt%) compared to pristine-Co₃O₄ (P-Co₃O₄). Theoretical calculations revealed a significantly increased migration energy barrier of Rh_SA on the S-Co₃O₄ surface than on P-Co₃O₄, inhibiting their migration/agglomeration. Surprisingly, Rh_SA-S-Co₃O₄ exhibited exceptional pH-universal UOR activity, requiring record-low working potentials and surpassing Pt/Rh-C, this was due to superior urea adsorption and stabilization of CO*/NH* intermediates, revealed by DFT simulations. Meanwhile, the assembled urea-electrolyzer delivered 10 mA cm⁻² at only 1.33 V with robust stability in alkaline media. This work provides a general methodology towards high-loading SACs for scalable applications.