(147e) Unraveling the Problem of Carbonate Formation in Alkaline Fuel Cells

Session: 16D07 Fuel Cell Technology

Fuel cells are promising power sources due to their ability to bypass Carnot efficiency limitations by directly converting chemical energy into electrical energy. However, the high costs of catalysts and membranes, as well as component durability issues, have barred widespread implementation. Alkaline fuel cells (AFCs) have gained increasing attention due to superior electrode kinetics in alkaline media, compared to acidic media, which enables the use of non-noble metal catalysts [1]. Unfortunately, carbonate formation is a major barrier to mass commercialization of AFC technologies. Hydroxide anions in the electrolyte react with carbon dioxide from organic fuel oxidation and/or air to form carbonates. This reaction reduces electrolyte conductivity and can deactivate electrodes through carbonate precipitation with an available cation [2].

The effects of carbonate formation are largely determined by the fuel cell electrolyte. The electrolyte can be a solid polymeric membrane or a liquid electrolyte, either of which have an initial concentration of hydroxide anions. With a stagnant liquid electrolyte, carbonates can easily precipitate onto electrodes when the nearby solution is saturated, while a flowing electrolyte remains dissolved in solution as long as the entire solution volume remains unsaturated [3]. Metal cation-free membrane systems do not suffer from carbonate issues since no mobile cations are present to facilitate precipitation onto an electrode or within the membrane [4]. Nevertheless, overall fuel cell performance is still hampered by conductivity losses and the precise effects of carbonate formation have yet to be researched in detail.

We present research quantifying the effect and rate of carbonate formation in a microfluidic fuel cell operating with a flowing alkaline electrolyte and utilizing either hydrogen or methanol as the fuel. Precise control over electrolyte composition enables the study of carbonate formation effects in an operating fuel cell by varying carbonate-electrolyte ratios. The membraneless design allows for individual analyses of anode and cathode performances via an external reference electrode.

[1] Tewari et al., Journal of Power Sources, 2006, 153, 1-10

[2] Rolla et al., Journal of Power Sources, 1980, 5, 189-196

[3] Brushett et al., Journal of the Electrochemical Society, 2009, 156, B565

[4] Lu et al., Proceedings of the National Academy of Sciences, 2008,105 52, 20611-20614