Fe(II)-Coordinated Polymer/Polyaniline Dual Nanocomposite as a Binder-Free pH-Universal Electrocatalyst for Durable Hydrogen Evolution Reaction

Abstract

A rationally engineered nanocomposite of Fe(II)-coordinated polymer and polyaniline (PANI) was developed for efficient hydrogen evolution reaction (HER) catalysis, exhibiting low overpotentials and excellent long-term durability. A discrete Fe(II) coordination complex was first synthesized using an asymmetric azo ligand at a ligand-to-metal ratio of 2:1, enabling precise control over the coordination environment and electronic structure. In contrast, a three-dimensional Fe(II) coordination polymer was hydrothermally assembled at a 1:3 ligand-to-metal ratio, generating a spherical Fe-rich framework with uniformly distributed active domains that provide abundant electrochemically accessible catalytic sites. Integration of this Fe(II) motif with PANI produced the hybrid nanocomposite of FePHP. Electrochemical evaluation demonstrated that FePHP exhibits enhanced HER performance in both acidic and alkaline media, requiring overpotentials of only 106 and 189 mV, respectively, to achieve a current density of 10 mA/cm2, with corresponding Tafel slopes of 55 mV/dec and 67 mV/dec. The improved catalytic performance is attributed to the formation of nanostructured Fe-PANI architecture, which maximizes the exposure of catalytically active Fe sites, increases the electrochemically active surface area, facilitates rapid electron and proton transport, and promotes efficient interfacial charge transfer, thereby delivering enhanced HER kinetics and excellent operational stability.