SURFACE CHARACTERIZATION OF NON-NOBLE METALS EMBEDDED IN N-DOPED CARBON CATALYSTS: THE IMPORTANCE OF HYDROPHILICITY ON OXYGEN REDUCTION REACTION ACTIVITY

Oxygen reduction reaction (ORR) is a fundamental step in many electrochemical applications, e.g. fuel cells and zinc/air batteries. Being kinetically hindered, ORR requires efficient catalysts typically based on Platinum Group Metals [1]. Finding cheaper substitutes with similar or better electrocatalytic properties and stability is a challenge for the scientific community [2]. This works highlights the importance of the hydrophilicity of the catalyst active sites on oxygen reduction reaction (ORR) through an extensive study on catalysts based on nitrogen-modified carbon doped with different metals (Fe, Cu, and a mixture of them). Different analytical techniques, such as BET, XRPD, micro-Raman, XPS, SEM, STEM and hydrophilicity measurements were performed. In particular, XPS was used to assess the concentration and the chemical oxidation state of metal species. Moreover, N1s core level spectra were investigated to put in evidence different types of nitrogen-species on the surface of carbon catalysts, as well as C1s core level spectra to determine the total amount of carbon-oxygen functionalities (CxOy), considered as a measure of defects or edge sites in the graphene-like network [3]. From surface measurements, in combination with the results obtained from the other techniques, it was clearly demonstrated that the hydrophilicity of active sites plays a key role in electrocatalytic properties of ORR catalysts.