Dissolution of the Heteroatom Dopants and Formation of Ortho-Quinone Moieties in the Doped Carbon Materials during Water Electrooxidation

Abstract

Heteroatom-doped carbon materials are widely used as metal-free electrocatalysts and supporting substrates for many metal-based composites. However, almost all the current researches are based on the assumption of the self-stability of the heteroatom-doped carbon materials, neglecting their possible structural evolution during electrocatalysis, especially under harsh oxygen evolution reaction (OER) conditions. Besides, previous researches always focused on the dropcast carbon-based materials with only a few participated dopants, leading to unobservable structural evolution during the electrolysis. Here, heteroatom-doped graphite flakes (GP) with a large quantity of participated dopants are chosen as the research model to multiply the transformation during the electrolysis. Through the combination of theoretical calculations and experiments, we present the nearly complete dissolution of the heteroatoms in N-, P-, and Se-doped carbon materials in the form of the high-valence oxoanions during OER. The oxygen-abundant residues are proven to be responsible for the OER activity. Among the oxygen-containing functional groups in the residues, the ortho-quinone moieties, whose structures change with the doping elements, are finally identified as the active sites. Heteroatom-doped carbon materials as the supporting substrates for the metal-based composite experience a similar transformation, leading to unexpectedly different activity origins. Our work not only reveals the real active sites of the heteroatom-doped carbon materials for OER but also provides new insight into understanding the heteroatom-doped carbon materials as the supporting substrates for other anodic reactions.