(600e) Oxide-Derived Tin Microspheres for Efficient CO2 Electroreduction to Formic Acid

Rational design and engineering of electrocatalysts for electrochemical CO₂ reduction (CO₂RR) is crucial to effectively, selectively converting CO₂ into carbon-neutral chemicals and fuels. In this work, we have developed low-cost hierarchical tin oxide microsphere electrocatalysts to boost the production of formic acid. Three-dimensional (3D) SnO₂ spheres constructed from small crystalline nanoparticles exhibit high Faradaic efficiencies (70-80%) and high selectivities (77-90%) toward formic acid in a wide potential window of -0.9 V to -1.3 V vs. the reversible hydrogen electrode (RHE) at total current densities of 30-100 mA/cm². A peak 80.3% Faradaic efficiency is obtained at -1.2 V vs. RHE with superior HCOOH partial current density of 50.4 mA/cm². Such unique 3D spherical catalysts outperform non-spherical nanoparticles and commercially available SnO₂ benchmarking catalysts due to special hierarchical porous structure, enlarged surface area, larger number of electrochemically active sites, and strongly suppressed H₂ evolution. The spherical oxide-derived Sn catalysts are highly stable up to 36 hours over many start/stop cycles at -1.2 V vs. RHE, preserving long-term partial current density of 45 mA/cm² and 90% selectivity for formic acid. Our results may provide more guidelines for the introduction of hierarchical porosity into CO₂RR electrocatalysts for large-scale applications.