Electrocatalytic hydrogen production by CN– substituted cobalt triaryl corroles

Abstract

Four cobalt corrole complexes bearing 0–3 cyano groups on the para-position of the three meso-phenyl rings of the macrocycle were synthesized, characterized and applied for electrocatalytic H₂ production in both organic solvent and neutral aqueous media. Each of the complexes is an efficient electrocatalyst for hydrogen production at the potential of the Co(II/I) couple, with turnover frequencies ranging from 40 to 400 s⁻¹ in 18 mM TFA and TsOH. In our study, the reaction path and reaction rate are affected by both the proton source and the substituent. In organic solvent, the catalysis may undergo two competing catalytic routes (EECC and ECEC pathways). The rate of catalysis can be improved remarkably by increasing the number of cyano-substituents. For the three cyano-substituent complex 4, a TOF of 381 s⁻¹ is obtained in low concentration of p-toluenesulfonic acid (TsOH) which is 9 times higher than that of the unsubstituted complex 1. Complex 4 is also an efficient electrocatalyst for the HER in neutral aqueous systems, and a turnover number (TON) of 1675 and Faraday efficiency of 98% have been observed in aqueous medium. This work can provide some evidence for the influence of the cyano-substituent on corroles for the HER.