Catalytically active sites of MOF-derived electrocatalysts: synthesis, characterization, theoretical calculations, and functional mechanisms

Electrocatalysts play critical roles in electrochemical energy storage and conversion technologies such as fuel cells, metal–air batteries, and H2O/CO2/N2 electrolysis. Recently, metal–organic framework (MOF)-derived electrocatalysts have been extensively explored not only because of their superior electrocatalytic activities but also their well-defined active sites, particularly those of single-atom active sites, which have been recognized as role-model electrocatalysts for fundamental understanding of the catalytic mechanisms at both the molecular and electronic levels. In this paper, we have reviewed the recent progress in MOF-derived electrocatalysts with focus on the characterization of the catalytically active sites, their functional mechanisms and performance validation/optimization of the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), carbon dioxide reduction reaction (CO2RR), and nitrogen reduction reaction (NRR). Regarding the synthesis of the electrocatalysts with active sites, the alloy and composite formation and the edge-defect/oxygen vacancy engineering are discussed. Regarding the characterization for fundamental understanding, some advanced in situ/ex situ characterization and theoretical calculations using first-principles Density Functional Theory (DFT) are summarized. Some technical challenges are analyzed and the corresponding further research directions for overcoming the challenges are also proposed for future research and development of practicable MOF-derived electrocatalysts.