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

Abstract

© The Royal Society of Chemistry 2021. 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 H-2 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 N-2-quenching method can significantly inhibit the migration tendency of Rh single-atoms (Rh-SA), thereby stabilizing an similar to 200% higher loading of Rh-SA sites (Rh-SA-S-Co3O4; bulk loading similar to 6.6 wt%/surface loading similar to 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.