Thermodynamic control of Cu-I nanotopologies enables solar-driven CO2-to-multicarbon conversion

Solar-driven electrochemical CO 2 reduction to multicarbon (C 2+ ) products presents a promising avenue for artificial photosynthesis, yet remains constrained by high overpotentials and limited conversion efficiency. Here, we developed an alkaline environment-modulated prereduction strategy that capitalizes on the divergent thermodynamic stabilities of precursors, enabling the precise synthesis of iodine-doped copper nanotopologies (Cu-I NTs). Featuring tunable under-coordination defects and stabilized high-energy adsorption sites, the Cu-I NTs achieve an onset potential of only −0.37 V versus the reversible hydrogen electrode for C 2+ formation. Operando Raman measurement and density functional theory calculation reveal that the tailored surface topologies favor Cu-CO rotation adsorption, enabling dynamic reorientation from bridge- to atop-binding configurations, which collectively lowers the barrier for CO-CO coupling. Impressively, powering the electrolyzer by a perovskite/silicon tandem together with a single-junction silicon photovoltaic device, the system delivers a photocurrent of 12.34 mA cm −2 at 2.17 V under standard AM 1.5 illumination, achieving a solar-to-C 2+ conversion efficiency of 8.64%.