Pentacyanonitrosylferrate-Based Metal Coordination Frameworks for Oxygen Evolution Reaction: Coordination Regulation Inducing Unique Active Catalytic Species

Non-noble metal MOFs hold great potential for the alkaline oxygen evolution reaction (OER). In this work, cyano-bridged nickel-iron MOFs derived from pentacyanonitrosylferrate ([Fe(CN)5NO]2-) were fabricated to explore their feasibility as oxygen evolution electrocatalysts via coordination modulation with ethylenediamine (en). The structural evolution and structure-activity mechanism of the as-prepared Ni-Fe-MOF@(1:n)en (n = 1, 2, 3) coordination polymers were systematically investigated before and after the OER process. Interestingly, en effectively adjusts the dimensionality of cyano-bridged Ni-Fe moieties, transforming the initial 3D Prussian blue structure into one-dimensional metal chains. Upon compositing with carbon nanotubes (CNTs), the obtained material exhibits efficient OER catalytic activity (η10 = 290 mV at 10 mA·cm-2; Tafel slope = 55 mV·dec-1). Further studies reveal that the partial cleavage of Ni-NC bonds triggers surface reconstruction, generating highly active Ni(en)2OH-Fe(CN)5NO metal active units. This finding challenges the conventional view that cyano groups poison metal active sites and degrade catalytic performance. Density functional theory (DFT) calculations further confirm that the uniquely reconstructed structural unit can effectively optimize the adsorption-desorption kinetics of reaction intermediates. This work proposes a facile chelating ligand modulation strategy to regulate the structure and electrocatalytic properties of strongly coordinated non-noble metal MOFs.