Preparation And Oxygen Reduction Performance Of Graphene Supported Chromium Based Catalyst

Traditionally, platinum(Pt) is regarded as the best ORR catalyst for oxygen reduction. Unfortunately, limited resources and high cost are the primary barriers for Pt-based catalysts of commercial market fuel cells. To eliminate the usage of Pt/Pt-alloy based catalysts at the cathode of fuel cells, great efforts are taken to identify the Pt free catalysts that are readily available, cost effective, and comparable or even better catalytic effects than Pt for cathodic ORR in fuel cells. Transition metal oxides have been widely investigated for ORR catalysis and provide some of the best alternates, though none of these systems match the activity and stability of Pt under PEMFC operating conditions.This paper studied the catalytic activity and its durability for oxygen reduction reaction of graphene loaded chromium compounds. The specific content of the work and the results of the study are summarized as follows:(1) Graphene based non precious metal catalysts for oxygen reduction reaction(ORR) have been successfully fabricated through pyrolysis of a mixture of Cr salt, urea, and graphene oxide(GO). Cr2O3/rGO was prepared by calcination of the mixture at 600? in nitrogen atmosphere. CrN/rGO was prepared by calcination of the mixture at 800? in ammonia atmosphere. The structure, composition, particle size and morphology of the samples of Cr2O3/rGO and CrN/rGO were examined by X-ray diffraction(XRD), scanning electron microscopy(SEM), high-resolution transmission electron microscopy(HRTEM) and X-ray photoelectron spectroscopy(XPS) tests. The performance of catalyst(Cr2O3/rGO and CrN/rGO) for oxygen reduction reaction was tested by CV, LSV, EIS, I-t in oxygen saturated 0.1 M KOH electrolyte.(2) In the matter of Cr2O3/rGO, the experimental evidence from clearly reveal that Cr2O3 nanocrystals are deposited uniformly on the surface of the graphene sheets. The resulting chromium oxides embedded graphene with rather low cost and rich sources shows an approaching ORR onset potential to Pt/C catalyst but has a superior stability than Pt/C catalyst toward O2 reduction in alkaline, which shows potential application in fuel cells.(3) In terms of CrN/rGO,the experimental evidence from clearly reveal that CrN crystal is cubic structure. Some small CrN particles dispersed on graphene, but there are agglomerating graphene sheets. So the less reaction center in catalyst surface will affect the activity of the catalyst. According to the oxygen reduction performance data shows, the onset voltage and peak current density are with the Pt/C catalyst in a level, but it's not ideal. The structure and properties of the catalyst are closely related, which requires further improvement of the catalyst structure, thus improving the performance of the catalyst.