Anodic SnO 2 porous nanostructures with rich grain boundaries for efficient CO 2 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 (CO 2 ) 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 SnO 2 porous nanostructures with high surface area (90.1 m 2 g -1 ), large porosity (0.74 cm 3 g -1 ), and rich grain boundaries for electrochemical CO 2 reduction (CO 2 RR). They exhibit stable 95% faradaic efficiency (FE) towards CO 2 RR and 73% FE for formate at -0.8 V RHE . The notable performance of such SnO 2 nanostructures can be attributed to their unique structural and chemical properties, which provide active sites for CO 2 adsorption and conversion, and easy access for CO 2 to the active sites. The insights gained from the structure/property relationships might be beneficial for designing superior electrocatalysts for CO 2 electroreduction into formate.