Self‐Assembly of Hydroxyl Metal–Organic Polyhedra and Polymer into Cu‐Based Hollow Spheres for Product‐Selective CO₂ Electroreduction

The electrochemical CO₂ reduction reaction (CO₂RR), an elegant solution to mitigate the greenhouse effect and produce high‐value feedstock, has significant hurdles in selective production of target products. Herein, a series of Cu‐based hollow spheres is synthesized through the self‐assembly of hydroxyl metal–organic polyhedra and a polymer. The obtained materials with tunable morphology and compositions enable precise generation of varied products in a flow cell. Specifically, polymer‐induced sol–gel (PISG)‐3 shows 61.1% (−0.9 V, −143 mA cm⁻²) Faradaic efficiency (FE) of C₂H₄ and negligible CH₄, higher than that of PISG‐1 ( 46.7%) with solid‐sphere morphology. Interestingly, the products can be well tuned from C₂H₄ to CH₄ by introducing CaCO₃, along with increased hydrocarbon selectivity and CO₂ reduction efficiency. Notably, PISG‐8 with modified composition displays drastically changed products ( 55.8% and 22.2%, −162 mA cm⁻², −0.9 V). As certified by density functional theory calculations, CaCO₃ is proven to decrease the possibility for coexistence of two adjacent *CHO to restrain the dimerization process and enhance the CH₄ selectivity.