Phase engineering of Cu@Cu₂O core-shell nanospheres for boosting tandem electrochemical CO₂ reduction to C₂₊ products

Cu-based CO₂ electrochemical reduction (CO₂ER) is promising for reducing greenhouse gas emission and producing high-value multicarbon (C₂₊) chemicals and fuels. Unfortunately, the C₂₊ selectivity is still quite low. In this work, well-defined Cu@Cu₂O core–shell nanospheres with time-dependent evolution of phase composition, crystallinity and morphology were specifically designed by a facile chemically induced self-transformation strategy. A maximum C₂₊ Faradaic efficiency (FE) exceeding 79%, including FE_C2H4 reaching 44%, was achieved using phase-engineered Cu@Cu₂O nanospheres. Based on the temperature-programmed desorption analyses and in-situ Raman spectroscopy, the adsorption behaviors of both CO₂ reactant and *CO intermediate can be synergistically tuned by phase engineering of Cu@Cu₂O nanospheres: Cu₂O shell enhances *CO₂ and *CO adsorption coverage, while porous Cu core concentrate and strengthens *CO intermediates for subsequent CO-CO coupling towards C₂₊ products. This work will shed new light on the phase engineering of Cu-based tandem electrocatalysts for tuning CO₂/CO-catalyst interaction and modulating CO₂ER processes and selectivity.