Size-engineered cMOF/o-Cu2O heterostructures activate the *CHO selectivity switch for the C2 versus C1 pathway during CO2 electroreduction

Abstract

The rational control of heterostructure motifs and the corresponding electronic environment in heterocatalysts offers an effective strategy to regulate CO₂RR selectivity, yet it remains challenging. The precise regulation of the reaction intermediates is therefore a critical determinant. In this work, the size-engineered cMOF/o-Cu₂O was introduced to modulate heterostructure motifs, thereby modulating the *CHO intermediate selectivity switch and steering C2 or C1 reaction pathways. We elucidated the divergent CO₂RR pathways governed by the differential growth degrees of the cMOF/o-Cu₂O heterostructures. The minimized cMOF/o-Cu₂O-s (∼361.8 nm), comprising a high proportion of –OH terminations, accelerated the continuous hydrogenation of *CHO and promoted their conversion into *CH_xO intermediates. The moderate cMOF/o-Cu₂O-m (∼870.1 nm) achieved an optimal balance between the intermediate concentrations and interfacial transfer, enabling a preferential *CHO–*CO coupling pathway through the rationally designed heterostructure motifs. In contrast, the enlarged cMOF/o-Cu₂O-l (∼2.7 µm) exhibited an indistinguishable force toward the key intermediates of *CHO, thereby failing to differentiate between the subsequent reaction pathways. The intensified *CH_xO and *CHO–*CO signals observed in the in situ ATR-FTIR further verified the bifurcated reaction pathways, featuring a C1-dominated pathway on cMOF/o-Cu₂O-s and C2 pathway on cMOF/o-Cu₂O-m. cMOF/o-Cu₂O-m achieved a Faraday efficiency of 71.1% for C2 products at −1.3 V vs. RHE. This work offers crucial insights into the significance of size engineering in modulating the heterostructure motifs to regulate the selectivity switch of key intermediates.