X-Ray Photoelectron Spectroscopy Studies of Carbon-Based Electrocatalytic Materials

Abstract

X-ray photoelectron spectroscopy (XPS) was used for investigation of carbon-based electrocatalysts. According to the measurements, in a majority of samples, the main components were carbon, nitrogen and oxygen, as expected. In metal-nitrogen-carbon catalysts, the presence of iron and cobalt, introduced during preparation, was proved and in carbide-derived carbon catalysts zirconium and silicon were found. The results of N1s measurements showed 7 different nitrogen species in samples such as pyridinic-N, pyrrolic-N, amines/metal-Nx, imine-N, graphitic-N, NO and bulk N-H. The quantitative analysis of C1s demonstrated 7 states of carbon (sp2 C, sp3 C, C-O-C, C=O, C-O=C, π-π*, and carbide) with significant dominance of sp2 carbon. In O1s spectrum the following different oxygen-containing groups were observed: metal oxide, O=C-OH carboxyl, C=O carbonyl, C-O, C-OH, and chemisorbed O. The chemical composition of the samples was determined. The study of different carbon-oxygen functionalities and nitrogen species on the catalyst surface was of particular importance. The electrocatalytic properties of the catalyst material for the oxygen reduction reaction are related to the active sites on the catalyst surface. Determined peaks agree, in general, well with literature findings in different electrocatalysts.