Crucial Role of Self‐Exsolved Heterostructured Cermet Nanoparticles in Highly Active Spinel Electrodes for CO2/H2O Co‐Electrolysis

Abstract The versatility of the spinel (AB 2 O 4 ) oxides means they are of great interest for a variety of catalysis and energy conversion applications, involving gas reactions and reforming. CuFe 2 O 4 spinel is identified as a highly efficient fuel electrode for CO 2 /H 2 O co‐electrolysis due to its promising electrocatalytic activity. To identify the actual active sites, the electrochemical characteristics, composition, chemical state, and microstructure are systematically investigated while optimizing the electrolysis performance by varying the feed gas composition. Markedly enhanced electrolysis current density is achieved under a CO 2 ‐enriched composition of 50%CO 2 /10%H 2 O‐Ar. This promising performance is attributed to the in situ exsolution of heterostructural “Cu/Fe 3 O 4 ” nanoparticles on the parent CuFe 2 O 4 surface during co‐electrolysis. Interestingly, a strong correlation of the electrolysis performance with the amount of the formed heterostructural cermet is observed. The exsolved cermet heterostructure plays a crucial role in CO 2 /H 2 O electroreduction, as also confirmed by density‐functional‐theory studies. The self‐exsolved Cu/Fe 3 O 4 nanoparticles present exceptional strength due to a strong interaction between the formed metallic Cu and Fe 3 O 4 , enabling the electrode to remain active and stable under such high electrical polarization. The excellent durability and stability of the self‐exsolved heterostructural nanoparticles are clearly confirmed by long‐term operation at high‐working voltage with an outstanding Faradaic efficiency (nearly 100%).