Electron-Rich Cobalt Corroles as Potent Electrocatalysts for the Hydrogen Evolution Reaction.

The development of efficient, earth-abundant electrocatalysts for the hydrogen evolution reaction (HER) is central to advancing sustainable hydrogen production. Here, we report a systematic investigation of three cobalt corroles featuring progressively stronger electron-donating meso-positions and β-pyrrole substituents. The highly electron-rich β-octaalkyl-substituted cobalt corrole was synthesized and fully characterized by single-crystal X-ray diffraction, NMR, UV-vis spectroscopy, and high-resolution mass spectrometry. Electrochemical studies reveal a monotonic shift of the Co-centered redox couples to more negative potentials with increasing electron donation by the macrocycle. The difference between the redox and catalytic onset potentials was determined to be largest for the most electron-rich corrole when examined under homogeneous conditions using acetic acid as the proton source. HER catalysis by this complex was also most efficient, proceeding with a turnover frequency of up to 5105 s-1. All three complexes were successfully immobilized onto high-surface-area carbon (BP2000) and used for catalyzing HER in acidic aqueous media. Under these heterogeneous conditions, the catalysts with 2,6-dimethoxyphenyl substituents on the meso-positions perform best, with a low overpotential of 0.2 V. These findings demonstrate that proper tuning of the electron-donating capability of the cobalt-chelating corroles can be used for enhancing HER catalytic efficacy.