Tuning the CO₂ electrocatalytic reduction pathway via oxygen-locking effect in CuCr₂O₄/CuO heterostructures

Electrocatalytic conversion of carbon dioxide (CO₂) into high-value chemicals or fuels is a key approach to simultaneously optimize carbon cycling and energy conversion, providing significant environmental and energetic benefits. Copper-based catalysts, because of their unique selectivity toward multi‑carbon (C₂₊) products, have become preferred electrode materials for electrocatalytic CO₂ reduction reactions (CO₂RR). However, during electrochemical polarization, they tend to undergo valence state changes and structural rearrangements, resulting in a decline in catalytic activity and limited long-term stability, which greatly restricts their practical use. To overcome those drawbacks, this study promoted the formation of CuCr₂O₄/CuO heterojunction by Cr doping during the synthesis of CuO. The strong interactions at the heterojunction interface trapped oxygen atoms within the catalyst, preventing the loss of lattice oxygen as well as stabilizing copper valence states. The heterostructure altered the interface electronic configuration to lower charge transfer resistance and reduced CC coupling energy barriers. The results demonstrated that the as-prepared CuCr₂O₄/CuO catalyst exhibited excellent CO₂RR performance, achieving a C₂₊ product selectivity of 50.1% at a potential of -0.95 V (vs. RHE), which significantly surpassed that of the undoped CuO catalyst. Additionally, detailed X-ray photoelectron spectroscopy (XPS) analysis before and after the reaction confirmed that the elemental composition and copper valence state of the catalyst remained relatively stable during electrochemical polarization, verifying the integrity of the heterojunction structure and the long-term stability of the catalyst. The 'oxygen-locking effect' proposed in this study offers a new approach for designing highly selective and stable copper-based CO₂RR catalysts.