Proton exchange membrane fuel cell relative humidity

A. M. Kannan, L. Cindrella, and L. Munukutla. Functionally graded nanopo-rous gas diffusion layer for proton exchange membrane fuel cells under low relative humidity conditions. Electrochimica Acta 53 (2008) 2416-2422. 

Figure 6.7. Polarization curves for different concentrations of NO . Cell temperature 60°C, H2/air (1.2/3.3) relative humidity H2 95% and air 0% backpressure 1.5 atm [49], (Reprinted from Electrochimica Acta, 51(19), Yang Daijun, Ma Jianxin, Xu Lin, Wu Minzhong and Wang Haijiang, The effect of nitrogen oxides in air on the performance of proton exchange membrane fuel cell, 4039-44, 2006, with permission from Elsevier.)...

Table 16.1. The equilibrium concentration, in ppm, of CO with vaiying temperature, relative humidity and total pressure. CO concentration for a total pressure of 3 atm is given in parentheses while the values not in parentheses are the result of a total pressure of 1 atm. The initial concentration of dry gas is 25% CO2 and 75% H2 [96]. (From Baschuk J, Li X, Carbon monoxide poisoning of proton exchange membrane fuel cells. International Journal of Energy Research, 2001 John Wiley Sons Limited. Reproduced with permission.)...

Discover and develop proton exchange membranes (PEMs) capable of extended fuel cell operation at higher temperatures of 120 to 150°C, at low relative humidity (RH), and without leachable components... 

The efficiency of the automotive proton exchange membrane (PEM) fuel cell is dependent on many factors, one of which is the humidification of the inlet air. If the inlet air is not sufficiently humid (saturated), then the stack can develop dry spots in the membrane and efficiency and voltage will drop. Therefore, it is necessary to ensure that humid inlet air at the proper elevated temperature is supplied to the stack. Current methods involve utilizing a spray nozzle to atomize water droplets onto a cloth or wire mesh substrate. As the ambient inlet air passes over the cloth it picks up moisture however, the relative humidity drops as the air is heated in the fuel cell. If heat could be supplied to the water efficiently, the system would become independent of the ambient conditions, the inlet air could become more humid at the proper temperatures, and the overall stack could maintain a high level of efficiency. Previous work with power electronic heat sinks and automotive radiators has demonstrated the high efficiency of carbon foam for heat transfer. Utilizing the carbon foam in the PEM fuel cell may reduce the inlet air humidification problems. 

Conventional proton exchange membrane (PEM) fuel cells (typically operated at <90 °C) make use of a perfluorosulfonic acid (PFSA) membrane (e.g. Nafion membrane) as the PEM. A certain level of relative humidity (RH), typically near saturation (>80% RH) is required to achieve high PEM fuel cell... 

Typical bulk through-plane conductivity of Nafion as proton exchange membrane is around 0.1 Scm at 100% relative humidity (RH) and room temperature [24] with typical membrane thickness of 50-200 pm. In contrast, the conductivity of 0.5 M sulfuric acid as a common supporting electrolyte is on the order of 0.2 S cm . Anode to cathode spacing in a membraneless LFFC generally ranges from 0.5 to 1.5 mm, which results in higher total ohmic losses rather than PEM fuel cells. 

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