La-doped HKUST-1-derived catalysts for stable and selective CO₂-to-CH₄ conversion via Cu oxidation state stabilization

During the electrocatalytic CO₂ reduction (ECO₂R) process, the active oxidation states of Cu-based catalysts (e.g., Cu⁺) are unstable and prone to reduction to metallic Cu (Cu⁰), leading to decreased product selectivity and catalyst stability. To address this issue, this study proposed a catalyst design strategy involving lanthanum (La) doping to stabilize Cu oxidation states. Using typical Cu₃(BTC)₂ (HKUST-1) as a precursor, a series of x La/HKUST-1 materials with varying La doping levels were synthesized via a wet-chemical method, followed by electrochemical activation to obtain A-x La/HKUST-1 derived catalysts. Characterization revealed that appropriate La doping (Cu:La = 8:1) effectively modulated the electronic structure around Cu, suppressing its excessive reduction during the reaction and promoting the formation and stabilization of active Cu⁺ sites. Electrochemical performance tests in an H-cell demonstrated that A-0.1 La/HKUST-1 achieved a CH₄ Faradaic efficiency (FE_CH4) of 60.81% with a corresponding partial current density of −25.93 mA·cm⁻² at −1.37 V (vs. reversible hydrogen electrode (RHE)), significantly outperforming other catalysts. Furthermore, this catalyst exhibited excellent stability during a 24-h continuous test, maintaining an FE_CH4 above 55%. This research provides a novel material design concept and mechanistic insight for enhancing the CO₂ methanation pathway by stabilizing Cu oxidation states via rare-earth La doping.