In-situ characterization of gas distribution in proton exchange membrane fuel cell stacks

Uniform gas distribution contributes greatly to output performance, operating reliability, and durability of fuel cell stacks, which still lacks detection means and remains a great challenge. In this study, a non-invasive and in -situ characterization method of gas distribution is originally presented, based on the dual-chamber model that describes the mathematical relationship among gas flow, hydrogen crossover, and hydrogen transfer in the cathode side during electrochemical testing (N-2/H-2). By means of micro-current excitation, the hydrogen crossover of every cell in a stack is synchronously identified and then the gas distribution can be decoupled. In a specially designed step-current test that aims for direct evidence, the voltage response characteristics to artifi-cially induced air starvation coincide perfectly with the identified gas distribution. Typically, as the current density steps up to 175 mA.cm(-2), the voltages of under-supplied cells, classified by the identified stoichiometric ratios of nearly-one and within 1.13-1.15, decline rapidly to around zero and abnormally to around only 0.5 V, respectively, while the sufficiently supplied cells remain normal. Based on the in-situ method, the artificially channel-choked fuel cell is precisely recognized, and different choke degrees can be distinguished. As identified at the corresponding current densities of 50, 100, and 500 mA.cm(-2) and the average stoichiometric ratio of two, the gas flow rate of a certain cell only reduces by 22.8 %, 20.2 %, and 13.7 %, respectively, even with all the cathodic channels choked. The significant role of convection in the mass transfer is experimentally confirmed in fuel cells, and correspondingly, the mass transfer indicators are available by this electrochemical means.