Efficient and Robust Carbon Dioxide Electroreduction Enabled by Atomically Dispersed Sn^δ ⁺ Sites.

Abstract

Electrocatalytic CO₂ reduction at considerably low overpotentials still remains a great challenge. Here, a positively charged single-atom metal electrocatalyst to largely reduce the overpotentials is designed and hence CO₂ electroreduction performance is accelerated. Taking the metal Sn as an example, kilogram-scale single-atom Sn^δ ⁺ on N-doped graphene is first fabricated by a quick freeze-vacuum drying-calcination method. Synchrotron-radiation X-ray absorption fine structure and high-angle annular dark-field scanning transmission electron microscopy demonstrate the atomically dispersed Sn atoms are positively charged, which enables CO₂ activation and protonation to proceed spontaneously through stabilizing CO₂ ^•- * and HCOO^- *, affirmed by in situ Fourier transform infrared spectra and Gibbs free energy calculations. Furthermore, N-doping facilitates the rate-limiting formate desorption step, verified by the decreased desorption energy from 2.16 to 1.01 eV and the elongated SnHCOO^- bond length. As an result, single-atom Sn^δ ⁺ on N-doped graphene exhibits a very low onset overpotential down to 60 mV for formate production and shows a very large turnover frequency up to 11930 h^-1 , while its electroreduction activity proceeds without deactivation even after 200 h. This work offers a new pathway for manipulating electrocatalytic performance.