Comparative study of plasma-treated non-precious catalysts for oxygen and hydrogen peroxide reduction reactions

Abstract

The performance of plasma-treated non-precious catalysts is discussed in the light of their application for oxygen and hydrogen peroxide reduction reactions. Six different Fe and Co porphyrins and phthalocyanines were used as precursors. The precursors were mixed with a carbon support and treated with an Ar-, N₂- and Ar : O₂-radio frequency (RF) plasma to obtain carbon supported Fe–N/C or Co–N/C catalysts. Additionally, the effect of plasma pretreatment of the catalyst's support was studied. The electrochemical properties of these catalysts were evaluated by cyclic voltammetry (CV) and rotating disc electrode (RDE) techniques (ORR) and for hydrogen peroxide (H₂O₂) reduction reaction. The difference in activity of the porphyrin-based catalyst treated by plasma and the Pt catalyst was less for H₂O₂ reduction reaction than for ORR. Selected samples were also tested in a HCOOH/H₂O₂ proton exchange membrane fuel cell (PEMFC). The maximum power of the HCOOH/H₂O₂ fuel cell with plasma treated catalyst was 1.4-fold higher than that of the fuel cell with noble metal based catalysts (Pt/C). The catalysts were also characterized in terms of their morphology, structure and composition by atomic force microscopy (AFM), attenuated total reflection infrared spectroscopy (ATR FT-IR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). A correlation was found between the activity and concentration of nitrogen on the surface of the catalysts. The AFM investigations revealed morphological changes which accompanied the transformation of the catalyst precursor into the catalytic material.