(254a) Electrode Performance in An Alkaline Microfluidic H2/O2 Fuel Cell

Fuel cells have been extensively investigated as alternative power sources due to their high efficiency and potential for achieving high energy densities [1]. Operating fuel cells in alkaline media, as opposed to acidic media, is advantageous as enhanced fuel oxidation and oxygen reduction kinetics improve fuel cell energetic efficiency [2]. Furthermore, cheap non-precious metal catalysts, i.e. silver (Ag) cathodes and nickel (Ni) anodes, may be used in place of expensive Pt-based catalysts without significant performance reduction. Historically, the major technical concerns for traditional alkaline fuel cells (AFCs) operated with stationary liquid electrolytes are water management at the electrodes, electrode durability in highly caustic environments, and carbonate formation when using organic fuels or reactant streams containing carbon dioxide. Emerging high performance alkaline anion exchange membrane (AAEM) technologies demonstrate improved conductivity, stability and robustness compared to liquid electrolytes but remain limited by membrane-related disadvantages notably water management (electrode dry-out/flooding) and fuel crossover [3]. Additionally, the inherent alkalinity of the AAEM limits ways to fine tune electrolyte composition with respect to optimizing electrode reaction kinetics (e.g., optimize pH). Furthermore carbonate formation on and within the gas diffusion electrode structures in the membrane-electrode assembly (MEA) remain an issue.

Previously, we have developed a microfluidic H₂/O₂ fuel cell with a flowing electrolyte which functions as an electrode/catalyst characterization platform [4,5]. Autonomous control of electrolyte parameters (i.e. flow rate, composition, pH) enables detailed in-situ analyses of individual electrode performance and degradation without fuel cell disassembly. Here, we probe the performance of Pt/C electrodes, both anode and cathode, in an alkaline microfluidic H₂/O₂ fuel cell as a function of electrode preparation procedures and fuel cell operating conditions. Furthermore, we characterize electrode durability as function of the aforementioned parameters using both electrochemical (i.e., electrochemical impedance spectroscopy) and imaging (i.e., microtomography) methods. Understanding electrode performance in AFCs will enable rational design and optimization of alkaline MEAs and provide valuable insight for developing alkaline direct liquid fuel cells.

References

[1] L. Carrette, K. A. Friedrich and U. Stimming, ChemPhysChem, 1, 2000, 162.

[2] J.S. Spendelow, A. Wieckowski, Phys. Chem. Chem. Phys., 9, 2007, 2654.

[3] J.R. Varcoe, R.C.T. Slade, Fuel Cells, 5, 2005, 187.

[4] R.S. Jayashree, M. Mitchell, D. Natarjan, P.J.A. Kenis, Langmuir, 23, 2007, 6871.

[5] F.R. Brushett, W.P. Zhou, R.S. Jayashree, P.J.A. Kenis, J. Electrochem Soc., 156, 2009, B565