Effects of carbon corrosion on mass transfer losses in proton exchange membrane fuel cells

Abstract

Carbon corrosion in proton exchange membrane fuel cells (PEMFC) causes not only kinetic degradation, but also damages to electrode microstructure and hydrophobicity, which can lead to increases in mass transport resistance. While much attention has been paid to catalyst degradation and kinetic losses, the increases in mass transfer loss is also a very serious problem and thus it is the focus of this work. To induce carbon corrosion, accelerated stress test (AST) by holding the cell potential at 1.4 V is used. The AST procedure is interrupted periodically to record cell performance after each period of AST at three different current densities. Experiment results show that at low current density, the decrease in cell voltage is linear with time of AST, but the rate in cell voltage decrease accelerates after some period of AST at medium and high current densities. It is hypothesized that such an accelerated voltage decrease is from the increase in mass transfer loss due to water flooding in the MEA. Further experiments with either reduced inlet air humidification or reduce air flow rate confirm that water flooding in the MEA is the cause for the sharp decline in cell voltages. A phenomenon that the cell voltage increases, or the rate in cell voltage reduction decreases as cell degradation progresses is repeatedly observed. It is determined that such a phenomenon is mainly caused by the enhanced phase-change-induced flow (PCI) due to the higher heat generation rate in a more severely degraded cell. The experimental results also provide some insights on how to optimize operating conditions for degraded fuel cells.

Gas diffusion layer wettability determination by cyclic voltammetry for automotive fuel cells

“…The increased specific capacitance after immersion is in accordance with literature, showing increased capacitance of electro-or liquid-oxidized electrodes [22], carbon fibers [44][45][46][47], and GDLs [22,23,26]. The increase of capacitance and thus of the wetted surface area after carbon corrosion is also in accordance with findings of Zhang et al, showing increased mass transfer losses due to carbon corrosion of the MEA [48]. In addition, several studies are reporting increased water accumulation during fuel cell operation within GDLs being pre-viously immersed in H 2 O 2 as compared to reference samples [33,[38][39][40].…”

Electrocatalysts for PEM Fuel Cells

“…[51] Several investigations have been performed to elucidate the kinetics of carbon corrosion inside an actual PEMFC cathode by detecting CO 2 emission. [51] Several investigations have been performed to elucidate the kinetics of carbon corrosion inside an actual PEMFC cathode by detecting CO 2 emission.…”

“…The corrosion of carbon black leads to not only a decrease in catalytic activity but also an increase in the hydrophilicity of the carbon surface, which results in flooding in the catalyst layer . Several investigations have been performed to elucidate the kinetics of carbon corrosion inside an actual PEMFC cathode by detecting CO 2 emission .…”

Performance Degradation of Proton Exchange Membrane Fuel Cell Caused by an Accelerated Stress Test

“…Besides, it may seem to be contra‐intuitive that the overall resistance is the highest at AST 6 h. Decoupling of the resistances at both current densities confirms the increases of mass transport loss from BOL to AST 6 h, and then decrease from AST 6 h to AST 9 h. In contrast to what happens under the voltage‐controlled operation, water production is constant under the current‐controlled operation in the EIS measurement. Under these conditions, the phase change induced flow (PCI) resulted from greater internal temperature gradient along the through‐plane direction plays a vital role in the removal of liquid water , .…”