Reversible Structural Evolution of Metal‐Nitrogen‐Doped Carbon Catalysts During CO₂ Electroreduction: An Operando X‐ray Absorption Spectroscopy Study

Abstract Electrochemical CO₂ reduction (CO₂RR) is a rising technology, aiming to reduce the energy sector dependence on fossil fuels and to produce carbon‐neutral raw materials. Metal‐nitrogen‐doped carbons (M‐N‐C) are emerging, cost‐effective catalysts for this reaction; however, their long‐term stability is a major issue. To overcome this, understanding their structural evolution is crucial, requiring systematic in‐depth operando studies. Here a series of M‐N‐C catalysts (M = Fe, Sn, Cu, Co, Ni, Zn) is investigated using operando X‐ray absorption spectroscopy. It is found that the Fe‐N‐C and Sn‐N‐C are prone to oxide clusters formation even before CO₂RR. In contrast, the respective metal cations are singly dispersed in the as‐prepared Cu‐N‐C, Co‐N‐C, Ni‐N‐C, and (Zn)‐N‐C. During CO₂RR, metallic clusters/nanoparticles reversibly formed in all catalysts, except for the Ni‐N‐C. This phenomenon, previously observed only in Cu‐N‐C, thus is ubiquitous in M‐N‐C catalysts. The competition between M‐O and M‐N interactions is an important factor determining the mobility of metal species in M‐N‐C. Specifically, the strong interaction between the Ni centers and the N‐functional groups of the carbon support results in higher stability of the Ni single‐sites, leading to the excellent performance of Ni‐N‐C in the CO₂ to CO conversion, in comparison to other transition metals.