Electrocatalysis of Poly-Neutral Red for Hydrogen Evolution Reaction in Acidic Media (Supporting Information)

Metal-free hydrogen-bonding conductive polymer catalysts (HCPCs) are emerging alternatives to platinum-group-metals (PGMs) for electrocatalytic hydrogen evolution reaction (HER). In this study, electrodes coated with poly-neutral red (PNR) films were fabricated by oxidative chemical vapor deposition (oCVD) and electropolymerization deposition (EPD) to study their activities as HER-electrocatalysts in acidic media. PNR (EPD) exhibited a superior performance, i.e., an overpotential of 194 mV (at 10 mA cm⁻²) owing to a high exchange current density of 0.711 mA cm⁻². The activity is substantiated by spectroelectrochemical measurements and time-dependent density functional theory (TDDFT) calculation unveiling a doubly reduced and doubly protonated PNRH₂ as the reaction intermediate for the evolution of H₂. It resulted in a first-order kinetic constant of k = 9.98 × 10⁻⁴ s⁻¹ to indicate a slow dissociation of PNRH₂ to release H₂. Large Tafel slope of 176 mV dec⁻¹ also limits the electrocatalytic activity of PNR.