Dopant redox stability as a design principle for selective CO2 electroreduction on Cu.

The rational design of selective Cu-based electrocatalysts for CO2 electroreduction requires an understanding of how dopants modify catalytic pathways under realistic conditions. However, the active surface often evolves dynamically during electrolysis, hindering direct comparison between theoretical predictions and experimental selectivity. Herein, we investigate how dopant redox stability influences reaction pathways on Cu by combining controlled sputter-based synthesis of Ti- and Sn-modified Cu thin films with electrochemical measurements and dispersion-corrected density functional theory (DFT-D) within the computational hydrogen electrode framework. Composition-spread electrodes enable systematic comparison of dopant effects, while DFT-D quantifies how Ti and Sn modify the thermodynamics of key intermediates (H*, COOH*, CO*, and OCHO*). Experiments reveal that Ti-modified Cu favors hydrogen evolution, whereas Sn-modified Cu produces CO with unaccounted charge consistent with liquid products. Post-electrolysis XRD shows TiO2 formation on Cu@Ti and Cu3Sn intermetallic phases on Cu@Sn, indicating distinct phase evolution during reaction. Combined experimental-theoretical analysis reveals a stability-selectivity relationship in doped Cu catalysts: oxophilic Ti oxidizes into HER-active oxide motifs, whereas redox-stable Sn forms metallic or intermetallic environments that stabilize O-bound intermediates and promote CO/formate pathways. This experimentally validated framework provides a transferable guideline for designing Cu-based CO2 reduction catalysts and may enable future high-throughput screening of dopant chemistries.