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

• Published in: Advanced materials (Weinheim) 2024-01, Vol.36 (4), p.e2307809-n/a
• Main Authors: Hursán, Dorottya, Timoshenko, Janis, Ortega, Eduardo, Jeon, Hyo Sang, Rüscher, Martina, Herzog, Antonia, Rettenmaier, Clara, Chee, See Wee, Martini, Andrea, Koshy, David, Roldán Cuenya, Beatriz
• Format: Article
• Language: English
• Subjects: Absorption spectroscopy; active sites; Carbon; Carbon dioxide; Catalysts; cluster formation; Clusters; CO2 conversion; Copper; Evolution; Functional groups; Nickel; Nitrogen; operando XAS; Raw materials; Single atom catalysts; Spectrum analysis; Transition metals; Zinc
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.202307809

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. Metal‐nitrogen doped carbon catalysts containing Co, Zn, or Cu single atomic sites in their as prepared state tend to reversibly form metallic clusters during CO2 electroreduction as evidenced by operando X‐ray absorption spectroscopy. The formed metallic cluster with the remaining single atomic species jointly determines the catalytic functionality of these materials.