Water Management in an Alkaline-Exchange-Membrane Fuel Cell

Among the existing fuel cell types, alkaline exchange membrane fuel cells (AEMFC) have intriguing features as compared to proton exchange membrane fuel cells. For example, their advantage is the high current density and mainly the possibility of using non-noble catalysts due to faster ORR kinetics in the alkaline media than in the acidic media. However, CO₂, reacting with hydroxide ions to form carbonate ions, has a harmful effect on the air-breathing AEMFC by reducing the number of hydroxide available for the hydrogen oxidation reaction at the anode. Thus, AEMFC typically operates on pure oxygen, which dramatically increases its cost. Herein, we developed a first electrochemical model that can predict the response of AEMFC according to variations of operating parameters, such as the CO₂ concentration in the oxidant flow and the relative humidity of inlet gases. The result in Figure 1 shows that current density significantly decays with higher CO₂ concentration mainly due to hydroxide depletion by carbonate formation at the cathode. Other possible reactions are also accounted for in the model, such as the reverse water-gas shift reaction (RWGS) and the participation of carbonate ions in the hydrogen oxidation reaction. Water management and mass transport characteristics of an AEMFC assembly are discussed in detailed. With experimental verification, our model can be used to demonstrate different strategies for reducing harmful effects of CO₂ poisoning, significantly increasing the possibility of AEMFC commercialization.