Investigation on role of nitrogen as a second active site of Fe-N-C for oxygen reduction reaction in alkaline medium

Abstract

As a cheap and effective electrocatalyst for oxygen reduction reaction (ORR) in alkaline and acidic medium, FeNC has been vigorously studied in a recent decade. Since hydroperoxide is a well-known factor that damages the polymer membrane, many studies have been reported to remove iron oxides or carbides using acid treatment and heat treatment because these are the main source of the hydroperoxide during the oxygen reduction reaction. In this study, the performance of the FeNC catalyst under alkaline condition was improved by increasing the active sites such as pyridinic and graphitic nitrogen. Simple methods were used like introducing a nitrogen-rich material such as melamine to FeNC or performing heat treatment in a mixed hydrogen and nitrogen atmosphere. For physical characterization, X-ray photoelectron spectroscopy (XPS) and nitrogen adsorption/desorption technique were used. Content and composition of nitrogen species were estimated by the deconvolution of the XPS spectra. To investigate electrochemical properties, rotating-ring disk electrode (RRDE) technique was used, which is effective to measure the generation of hydroperoxide. Performance for ORR was tested at 0.1 M KOH solution with a sweep rate of 10 mV/s from 1.2 V to 0.1 V using Hg/HgO as a reference electrode. The activity related to the composition of nitrogen species in the catalysts will be discussed.