Investigation on electrocatalytic performance and material degradation of an N-doped graphene-MOF nanocatalyst in emulated electrochemical environments†

Abstract

To develop graphene-based nanomaterials as reliable catalysts for electrochemical energy conversion and storage systems (e.g. PEM fuel cells, metal–air batteries, etc.), it is imperative to critically understand their performance changes and correlated material degradation processes under different operational conditions. In these systems, hydrogen peroxide (H₂O₂) is often an inevitable byproduct of the catalytic oxygen reduction reaction, which can be detrimental to the catalysts, electrodes, and electrolyte materials. Here, we studied how the electrocatalytic performance changes for a heterogeneous nanocatalyst named nitrogen-doped graphene integrated with a metal–organic framework (N-G/MOF) by the effect of H₂O₂, and correlated the degradation process of the catalyst in terms of the changes in elemental compositions, chemical bonds, crystal structures, and morphology. The catalyst samples were treated with five different concentrations of H₂O₂ to emulate the operational conditions and examined to quantify the changes in electrocatalytic performances in an alkaline medium, elemental composition and chemical bonds, crystal structure, and morphology. The electrocatalytic performance considerably declined as the H₂O₂ concentration reached above 0.1 M. The XPS analyses suggest the formation of different oxygen functional groups on the material surface, the breakdown of the material's C–C bonds, and a sharp decline in pyridinic-N functional groups due to gradually harsher H₂O₂ treatments. In higher concentrations, the H₂O₂-derived radicals altered the crystalline and morphological features of the catalyst.

Keywords: Nitrogen-doped graphene-based electrocatalyst; Metal–organic framework; Hydrogen peroxide effect on catalyst; Electrocatalytic performance; Material degradation.