(553b) Nanostructured Particles of Manganese Oxide for ORR in Alkaline-Based Fuel Cells

The world’s energy demand has been rapidly increasing over the past few decades; however, questions have been raised about the ability of traditional sources of energy such as oil and coal to keep pace with the demand. One potential solution to this problem is the development of regenerative fuel cells which are able to use renewable electricity (e.g. wind and solar) to split water and form H₂, and when necessary, reverse operation and use the H₂ to produce electricity.¹However, current regenerative fuel cells use Pt and Pt/Ir catalyst which are very expensive; hence there is a need to develop alternative oxygen electrocatalysts comprised of earth-abundant materials. 

Manganese oxide (MnO_x) electrocatalysts are potential candidates for reversible oxygen catalysis in a regenerative fuel cell due to their high activity, low toxicity and low cost.² Previously, we have synthesized thin films of nanostrucutred MnO_x via electrodeposition, and the activity for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) is comparable to that of the best known precious metal catalysts such as Pt, Ir and Ru.³ However, the MnO_xfilms are deposited onto a flat glassy carbon (GC) disk and in this particular form, the catalyst is not suitable for use in a regenerative fuel cell. Hence the goal is to translate this active catalyst to a fuel cell environment.

The high temperature calcination involved in the synthesis procedure necessitates a support that is heat-resistant. We have found that traditional high-surface area carbon supports for fuel cells degrade rapidly in the calcination environment required to produce active MnO_x catalysts. We thus turned our attention to GC particles which we found are appropriate for this application due to their high temperature resistance, high corrosion resistance which is needed due to the harsh alkaline testing environment, and high conductivity to enhance electron transport to and away from the catalyst surface. MnO_x was deposited onto GC particles via an impregnation technique followed by calcination, which resulted in a nanostructured surface dominated by Mn₂O₃ as determined from SEM and XPS analysis. Electrochemical testing in a rotating disk electrode setup revealed that the ORR activity is similar to the MnO_x thin films, while the OER activity is only slightly lower. The active MnO_x-GC particles were then loaded onto carbon paper to form a gas diffusion electrode which can be further processed to form a membrane electrode assembly for use in fuel cells.

 References

1. K.A. Burke, International Energy Conversion Engineering Conference. 2003, AIAA 2003-5939
2. J.O.M. Bockris, Int. J. Hydrogen Energ. 1999, 24, 15
3. Y. Gorlin, T.F. Jaramillo, J. Am. Chem. Soc. 2010, 132, 13612