Ultralow‐Overpotential CO Production from Electroreduction of CO 2 on a Hydroxyl‐Enriched Heterojunction

ABSTRACT Electrochemical CO 2 reduction (eCO 2 R) to valuable chemicals or fuels offers an effective solution to alleviate the energy crisis and environmental challenges. Reducing the overpotential of a desired product for eCO 2 R is paramount to achieving high energy efficiency. Herein, CuO/In 2 O 3 (Cu 4.2 In 1 ) nanosheets (NSs) p‐n heterojunction with the built‐in electric field which enhances the surficial hydroxyl coverage achieving the greatly decreased overpotential for CO production by eCO 2 R. The Faraday efficiency of CO attains 96.5% under an impressively low overpotential (130 mV), which is one of the lowest among the reported catalysts for CO production. Additionally, the eCO 2 R system integrates with a commercial triple‐junction solar cell exhibiting an average solar‐to‐CO conversion energy efficiency of 7.9%, with the CO production rate of 0.73 mmol h −1 cm −2 . The built‐in electric field between the CuO/In 2 O 3 (Cu 4.2 In 1 ) NSs heterojunction increases the oxidation states of Cu ions (Cu δ+ , δ = 2.14), which enhances the surficial hydroxyl coverage by the strong electrostatic attraction at low overpotentials, consequently stabilizing * COOH intermediate and facilitating the desorption of * CO. This work provides a new solution to achieve energy efficient eCO 2 R by the surficial hydroxyl coverage manipulation.