Metal–Organic Frameworks for Electrocatalysis: Catalyst or Precatalyst?

Metal-Organic Frameworks for Electrocatalysis:Catalyst or Precatalyst?Metal-organic frameworks (MOFs) have popularly been engaged directly in electrochemical applications, particularly as electrocatalysts in energy-related reactions.[1][2][3][4] The well-demonstrated efficiency and selectivity of MOFs are commonly attributed to their structures: their high specific surface area can expose abundant catalytic active sites to the surface; their pores of predetermined size/geometry allow rapid mass transport of selected substrates to the active sites; and the isolated metal nodes (typically, ions and clusters) of MOFs can serve as the active sites, providing great mono-dispersibility and atomic efficiency close to 100 %.Meanwhile, the functionalization of organic ligands enables extra chemical and structural selectivity over both reactants and products.However, the coordinate bonding between metal nodes and organic linkers, by nature, is generally weaker than the ionic bonding in inorganic solids.Therefore, the structural robustness of MOFs under electrochemical environments is questionable.A typical electrocatalysis involves chemical species in the electrolyte, dynamic electrochemical double layer interface, inner sphere electron transfer, and surface redox reactions that break and form bond(s).These can be classified as chemical and electrochemical environments (Figure 1).The possible reconstruction of MOFs under these environments brings a question to their role during electrocatalysis: are they the real catalysts or merely the precatalysts that produce active phases during the electrochemical treatment?Furthermore, depending on the reaction conditions (potential, electrolyte, pH, etc.), a robust electrocatalyst for one reaction may be a vulnerable precatalyst for another.The blurred line between catalyst and precatalyst has previously raised concerns in transition metal carbides-, pnictides-, and chalcogenides-based catalysts.[5][6][7] To initiate a deeper discussion on MOFs, in this This is the Pre-Published Version.