Abstract
The dependency of the Nernst potential in an operating proton exchange membrane fuel cell (PEMFC) on the temperature, inlet pressure and relative humidity (RH) is examined, highlighting the synergistic dependence of measured open circuit potential (OCP) on all three parameters. An alternative model of the Nernst equation is derived to more appropriately represent the PEMFC system where reactant concentration is instead considered as the activity. Ex situ gas diffusion electrode (GDE) measurements are used to examine the dependency of temperature, electrolyte concentration, catalyst surface area and composition on the measured OCP in the absence of H2 crossover. This is supported by single-cell OCP measurements, wherein RH was also investigated. This contribution provides clarity on the parameters that affect the practically measured OCP as well as highlighting further studies into the effects of catalyst particle surrounding environment on OCP as a promising way of improving PEMFC performance in the low current density regime.
Highlights
Proton exchange membrane fuel cells (PEMFCs) have a promising future in the energy sector due to their ability to generate energy from H2 gas at low temperatures, with no harmful pollutants
Initial examination of the Nernst equation showed the synergistic effects of cell temperature, inlet pressure and relative humidity (RH) on the theoretical maximum potential that can be achieved in a PEMFC system
Using ex situ gas diffusion electrode (GDE) tests, the temperature dependency was examined further, where an approximate >150 mV disparity between the measured open circuit potential (OCP) and theoretical OCP was found as a result of oxidative currents such as the mixed potential, all in the absence of H2 crossover
Summary
Proton exchange membrane fuel cells (PEMFCs) have a promising future in the energy sector due to their ability to generate energy from H2 gas at low temperatures, with no harmful pollutants. Ation of the measured cell potential in comparison to the theoretical maximum Nernst equation While these efficiency losses affect the overall polarisation performance, when net. It can be seen that even with net zero current across the fuel cell, i.e., at OCP, the logathrimic function does not collapse as a result of the crossover currents and so there is an induced activation overpotential [18] This contribution firstly analyses the theoretically achievable PEMFC potential at OCP as defined by the Nernst equation with an illustration of the dependences on temperature, inlet gas pressure and relative humidity (RH). The effect of RH on OCP is examined in the single cell whereby deviations from the theoretical dependency highlights the need to consider not just catalyst materials and the entire catalyst/ionomer system at low current densities
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