Anodic SnO₂ porous nanostructures with rich grain boundaries for efficient CO₂ electroreduction to formate

Formic acid (HCOOH), the acidic form of formate, is an important hydrogen carrier which can be directly used in fuel cells. Development of earth-abundant element-based catalysts to convert carbon dioxide (CO₂) into HCOOH or formate with high selectivity and high efficiency has been a vigorous research activity in recent years but remains an unsolved challenge. In this contribution, using one-step anodization, we prepare nanotubular SnO₂ porous nanostructures with high surface area (90.1 m² g^-1), large porosity (0.74 cm³ g^-1), and rich grain boundaries for electrochemical CO₂ reduction (CO₂RR). They exhibit stable 95% faradaic efficiency (FE) towards CO₂RR and 73% FE for formate at -0.8 V_RHE. The notable performance of such SnO₂ nanostructures can be attributed to their unique structural and chemical properties, which provide active sites for CO₂ adsorption and conversion, and easy access for CO₂ to the active sites. The insights gained from the structure/property relationships might be beneficial for designing superior electrocatalysts for CO₂ electroreduction into formate.