Current trends and perspectives on emerging Fe-derived noble-metal-free oxygen electrocatalysts

Abstract

Oxygen electrochemistry that comprises oxygen evolution and reduction reactions (OER/ORR) is vital for sustainable, clean, and efficient energy generation. However, the high activation barrier due to the multi-electron transfer process makes them sluggish and requires noble metals (e.g. Ir, Ru, or Pt) to overcome the kinetic barrier. This increases the cost of sustainable devices such as metal–air batteries and fuel cells and, in turn, obstructs their wide-scale applications. In this context, it is necessary to explore noble-metal-free efficient oxygen electrocatalysts to produce a surge in the practical applicability of these technologies. Since Fe facilitates these reactions and is widely available, it has emerged as an element of interest in different forms, such as oxides, phosphides, chalcogenides, layered double hydroxides, Fe–N–C, single atoms, and some other hetero-structured composites with carbon-based (graphene, carbon nanotubes, etc.) materials. This review assesses the strategies utilized in the development of Fe-derived materials without involving noble metals in the catalysis under alkaline conditions. It also focuses on the approaches used to transform well-known Fe-derived ORR materials to OER and vice versa or into bifunctional catalysts. Furthermore, we highlight the significant role of modifying various fundamentally important parameters, such as the fabrication methods and their consequent morphological and electronic deviations in establishing promising new Fe-based catalytic materials. This assessment will bring valuable fit to the existing literature and assist in gaining important information to extract practical applications from Fe-derived noble-metal-free electrocatalysts.