X-ray Diffraction Investigation of Oxygen Reaction Catalysts

Introduction

Rising greenhouse gas concentrations in the atmosphere and their effects on the climate have increased the interest in searching alternative, more environmentally friendly energy sources. Based on, for example, the non-toxicity, the ease of transportation, and the high-energy density, ethanol is considered a major future alternative to fossil fuels. (1) Alkaline direct ethanol fuel cells (ADEFCs) are devices that utilize ethanol to efficiently produce clean power. However, the commercialization of ADEFCs has been hindered strongly by the cost of noble metals that are commonly used in the cathode. For example, platinum has been the state-of-the art electrocatalyst for the oxygen reduction reaction (ORR) occurring during the ethanol conversion. The activity of the catalyst towards the ORR can be strongly affected by their physico-chemical properties dependent on, for example, their crystallographic structure. Furthermore, the catalyst activity is not only influenced by the catalyst itself, but also the material it is deposited on. The most frequently applied type of support material is reduced graphene oxide (rGO). Research has been extensively focused on identifying Pt-free catalysts for this application, including metal (oxide) / graphene composite materials. Previously, mixtures of silver and manganese oxide deposited onto graphene (Ag-Mn_xO_y/C), were found to be promising catalysts due to their high current density as well as the tolerance to alcohol fuel crossover. (2) As for the manganese oxides, the catalytic activity is especially dependent on the Mn oxidation state as well as on the oxide structure. It was also reported in the literature that doping the graphene material with heteroatoms such as nitrogen, resulting in N-doped graphene oxide (NGO), can be beneficial for ORRs. However, the structural implication of the combination of Ag-Mn_xO_y deposited on NGO had not been reported previously, which, in combination with a comparison to the rGO, is the purpose of this report. X ray diffraction (XRD) using the Automated Multipurpose Powder X-ray Diffractometer XRDynamic 500 from Anton Paar was the optimal tool to analyze the crystallographic features of this catalyst combination

References:

1. Kamarudin, M. Z. F., et al. "Direct ethanol fuel cells." International journal of hydrogen energy 38.22 (2013): 9438-9453.
2. Wolf, Sigrid, et al. "Ag-MnxOy on graphene oxide derivatives as oxygen reduction reaction catalyst in alkaline direct ethanol fuel cells." Catalysts 12.7 (2022): 780.