Programmable Geometric Core–Shell In₂O₃@Cu₂O Catalysts for Near-Unity CO Selectivity in Electrocatalytic CO₂ Reduction

The electrocatalytic CO 2 reduction reaction (CO 2 RR) to carbon monoxide (CO) represents a promising strategy for carbon recycling; however, achieving high selectivity under industrially relevant current densities remains a significant challenge. In this study, we report the development of a geometrically programmable core–shell catalyst (In 2 O 3 @Cu 2 O) fabricated via spray pyrolysis, in which the In 2 O 3 core size precisely controls strain effects, interfacial electronic properties, and spatial confinement. The optimized In 2 O 3 @Cu 2 O catalyst exhibits near-unity Faradaic efficiency for CO (99%) across a broad current density range of 50–200 mA cm –2, while effectively suppressing both the hydrogen evolution reaction (HER) and C–C coupling. In situ spectroscopic analysis confirms the absence of C 2 reaction intermediates (*OCCOH) and reveals a strain-induced redshift in the *CO vibrational frequency (from 2090 to 2052 cm –1 ), indicating weakened adsorption strength. Core-size-dependent performance evaluations further illustrate that a balanced geometric configuration effectively blocks In 2 O 3 -mediated formate generation pathways while optimizing active site exposure. This synergistic integration of spatial confinement, electronic modulation, and strain engineering establishes a robust design principle for selective CO 2 -to-CO conversion, offering a scalable and rational strategy for catalyst development in industrial CO 2 RR applications.