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.