Anode Degradation Effects in PEMFC Stacks by Localized Fuel Starvation

摘要

A study is presented of the anode degradation in a proton exchange membrane fuel cell (PEMFC), due to fuel starvation. First the basic principles of fuel starvation are discussed. We find that fuel starvation may be attained either below a limiting flow rate or below a limiting partial pressure, giving rise to two different processes in the cell, that we name starvation-by-current and starvation-by-voltage, respectively. Then, experimental results are presented and analyzed for anodes working under different conditions in a PEMFC stack. Severe degradation occurs in the anodes of PEMFCs affected by fuel starvation. Degraded anodes become visibly thinner, cracked, and appear firmly adhered to the bipolar plates when disassembling the stack. Thermogravimetric analysis coupled with mass spectrometry shows degradation occurring in the microporous gas diffusion layer and the hydrophobic agent (PTFE), as well as the carbon fibres of the macroporous support (carbon cloth). The initial oxidation of the gas diffusion substrate in the anodes provokes massive flooding of the affected cells and exacerbates their progressive degradation.