Exploring the role of polymer interactions during water electrolysis under basic conditions with bifunctional cobalt corroles

Abstract

With green hydrogen fuel continuing to be an important option for energy storage, studies on water-splitting reactions have attracted increasing attention. Within a multitude of parameters that have the potential to be explored to enhance water electrolysis, one of the most consequential factors is the development of an efficient electrocatalyst. The effectiveness of Co(III) corroles as electrocatalysts has largely been investigated in homogenous, non-aqueous or acidic environments. We report the use of heterogenized Co(III) corroles as bifunctional catalysts for water splitting under basic conditions, finding that the inclusion of alkyl chains on the ligand framework has a beneficial impact on electrocatalytic properties. Two new corroles have been isolated where the para positions in the fluorophenyl meso substituents of the parent cobalt(III) 5,10,15-tris(pentafluorophenyl)corrole Co(tpfpc) 1 have been modified with heptyl, [Co(ttfphc)] 2 and dodecyl [Co(ttfpdc)] 3 amines via a nucleophilic aromatic substitution reaction. The electronic structure of these new complexes and properties of the resultant catalyst inks are significantly altered relative to the parent complex by the presence of the alkyl chains, as evidenced by changes in catalytic onset potentials and Tafel behavior during water splitting at pH 14. All catalysts were found to exhibit bifunctional behavior with reasonable stability, and the interactions of the alkyl amine groups with the supporting polymer in the catalyst ink have been found to have an important role in altering corrole aggregation and therefore Co active site accessibility during deposition of the catalyst inks.