Highly efficient CO₂electrolysis within a wide operation window using octahedral tin oxide single crystals

Electrocatalytic CO₂reduction is an effective way to close the global carbon cycle. Tin oxides have been demonstrated as promising catalysts to convert CO₂into formate with high selectivity but with low reactivity and within a narrow potential window. Herein, octahedral tin oxide (SnO₂) single crystals have been well tuned and exhibited a high formate selectivity within a 500 mV wide operation range and a remarkable high formate partial current density of ∼500 mA cm⁻².In situRaman spectroscopy and DFT calculations indicate that high-energy facets of SnO₂favor the adsorption of *OCHO and the desorption of HCOOH*, which breaks the limitation of the scaling relationship of these intermediates on the (110) facet of conventional SnO₂nanoparticles and thus enhances formate selectivity. More interestingly, a maximum formate selectivity of 95% is achieved on SnO₂(111) due to the deeply suppressed hydrogen evolution in seawater. These catalysts have been further coupled with chlor-alkali electrolyzers to convert greenhouse gas CO₂into formate and produce higher-value Cl₂simultaneously. The present work will advance the development of practical CO₂electrolyzers.