Manganese oxides have shown promise as co-catalysts for platinum- and palladium-based alcohol electrooxidation catalysts. In this investigation, the effect of adding MnO 2 to a gold-based catalyst system was explored for the glycerol electrooxidation reaction. It was found that modification of the carbon support with MnO 2 had the effect of stabilising gold nanoparticles, giving rise to smaller gold particles with a more uniform particle size distribution than on the carbon alone. All gold-based catalysts gave very high currents for glycerol oxidation (1–5Amg −1 cat) and catalysts with MnO 2 contents of 5 and 9wt% yielded the highest mass activities (35–37Amg −1 Au). This is believed to be partly due to MnO 2 preventing gold agglomeration, creating a larger gold surface area for reaction. In addition, it is believed that MnO 2 may act as an active co-catalyst, especially at higher potentials, by means of oxygen spillover onto gold – leading to higher activities and lower peak potentials. MnO 2 was also found to activate the glycerol oxidation reaction earlier, giving lower onset potentials. Stability and impedance studies showed that MnO 2 -modified catalysts were less stable at a low potential (0V) than Au/C. This could be due to blocking of mixed-valence manganese oxide sites or poisoning of the smaller gold particles on these catalysts. However, at a higher potential of 0.2V, Au/5% MnO 2 /C demonstrated the best activity and stability overall. All our catalysts are more active than the palladium- and platinum-based catalysts reported in literature, with our best-performing catalyst on a mass activity basis (Au/9% MnO 2 /C) being at least 12 times more active. This effectively demonstrates the advantage of using a gold-based catalyst for glycerol oxidation, especially when supported by MnO 2 which aids in lowering the overpotential for glycerol oxidation over gold.
Financed by the National Centre for Research and Development under grant No. SP/I/1/77065/10 by the strategic scientific research and experimental development program:
SYNAT - “Interdisciplinary System for Interactive Scientific and Scientific-Technical Information”.