Electrochemical CO2 reduction to fuels and chemicals is a promising approach for CO2 utilization. Developing highly active, selective, and cost-effective electrocatalysts is the key to the large-scale application of this technology. Here, we report that defective indium/indium oxide heterostructures selectively catalyze CO2 electroreduction into C-1 products in a broad potential range from -0.7 to -1.2 V vs RHE in aqueous media with the faradaic efficiency approaching 100%. This electrocatalyst enables an efficient CO2-to-formate conversion with excellent selectivity (up to 93 /o), activity (up to 50.8 mA cm(-2)), and durability (>25 h). The collaboration between metallic In and In oxide of the heterostructures attributes to the boosted electrochemical CO2 reduction: Metallic In mainly facilitates formate production, while In oxide suppresses the competing hydrogen evolution reaction. This study highlights the integration of different functional components/defects into heterostrticttires as an effective strategy for enhancing CO2 electrocatalysis.