Influence of graphene sheet properties as supports of iridium-based N-heterocyclic carbene hybrid materials for water oxidation electrocatalysis

Abstract

The effect of the structural properties of graphene materials on the local structure of –OH anchored Ir(I)–NHC complexes is herein investigated. For that, two partially reduced graphene oxides exhibiting different sheet properties due to an adequate selection of the crystalline characteristics of their parent graphite were used. The main differences among them were the size of Csp2 domains within their graphenic layers and the distribution of functional groups at the basal planes and edges. Anchoring of N-methylimidazolium moieties through the graphene –OH functional groups and subsequent formation of the Ir(I)–NHC complexes resulted in graphene-based hybrid materials. The structural differences of the support have an influence in the interaction of the supported iridium compounds with the graphene sheet. The oxygenated functional groups in the material with a smaller graphene sheet are closer leaving larger Csp2 domains in the graphene layer, favoring their interaction with the supported iridium atoms therefore displacing the chlorido ligand from the first coordination shell. In contrast, the hybrid material in which the distribution of the oxygenated functional groups within the basal planes of the graphenic layer is more homogeneous shows partial chlorido displacement. This fact has an influence on the electrocatalytic performance of the iridium-based hybrid materials as water oxidation catalysts (WOCs), exhibiting improved catalytic activity the catalyst having coordinated chlorido ligands.