Efficient electrocatalytic hydrogen gas evolution by a cobalt–porphyrin-based crystalline polymer

Abstract

Herein, we report a crystalline CoTcPP-based [TcPP = the anion of meso-tetra(4-carboxyphenyl)porphyrin] polymeric system, 1, as a hydrogen evolution reaction (HER) electrocatalyst in acidic aqueous media. The material was characterized by powder X-ray diffraction (p-XRD), Fourier transform infrared (FT-IR) spectroscopy, and energy dispersive X-ray (EDX) analysis and its morphology was probed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Polymer 1 shows a surface area of 441.74 m³ g⁻¹, while the discrete CoTcPP molecule (2) shows a surface area of 3.44 m³ g⁻¹. The HER catalytic performance was evaluated by means of linear sweep voltammetry in the presence of 0.5 M H₂SO₄ aqueous solution. To achieve 10 mA cm⁻² cathodic current density, 1 and 2 respectively require an overpotential of 0.475 V and 0.666 V, providing strong evidence that the extended network of cobalt-based porphyrin leads to enhanced HER efficiency. The polymer also shows great tolerance for HER electrolysis in the presence of an acid remaining active over 10 hours.