PEM Fuel Cell Start-Up/Shut-Down Losses vs Relative Humidity: The Impact of Water in the Electrode Layer on Carbon Corrosion

Abstract

For automotive applications, one of the main challenges for proton exchange membrane fuel cells (PEMFCs) is to increase the lifetime of membrane electrode assemblies (MEAs), especially during transient operating conditions such as start-up/shut-down (SUSD) cycles. During SUSD, the carbon support in the cathode layer is known to be oxidized as a consequence of hydrogen/air anode gas fronts moving through the anode. In this work, we focus on the effect of relative humidity (RH) during SUSD events. Here we show the significant impact on PEMFC performance by both experiments with 50 cm 2 single-cell PEMFCs and by a simple SUSD model using the RH-dependent kinetics for the carbon oxidation reaction (COR) rate. The kinetic parameters of the COR are determined by on-line mass spectrometry, yielding a COR reaction order with respect to RH of one. Utilizing the thus determined COR kinetics in the SUSD model predicts a ≈ 3-fold lower COR during SUSD events at 80 • C for an MEA with a conventional high surface area carbon support when the RH is decreased from 100% to 25%. This agrees perfectly well with the experimentally determined factor of ≈ 3.

WITHDRAWN: Corrosion resistant fluorine-doped graphene nanoribbons for an highly durable PEMFC: combined experiment and ab-initio studies

“…However, the abundant defect and edge sites of a GNR can also be a disadvantage in using support materials because they would inevitably be the initial point of carbon corrosion 20 . Carbon corrosion is one of the most problematic degradation mechanisms in carbon-based support materials because it leads to side effects such as Pt agglomeration and detachment under carbon corrosion conditions [21][22][23] . Therefore, GNR might not be suitable as a support material because it is imperatively vulnerable to carbon corrosion.…”

Mapping of Heterogeneous Catalyst Degradation in Polymer Electrolyte Fuel Cells

“…In our voltage cycling AST between 0.60 V and open circuit potential (OCV, approximately 0.94 V), the major electrocatalyst degradation mechanisms are expected to be Pt oxidation and reduction/dissolution and redisposition. Carbon-support corrosion is expected to be less severe at these conditions compared to those at high potentials above 1.2 V [24,25] . The loss of ECSA was observed to be 70% after voltage cycling, expected to be mostly due to Pt nano-particle size growth.…”

Temperature Effects in Polymer Electrolyte Membrane Fuel Cells

“…Figure 14 shows Polarization curves recorded before and after 60 SUSD cycles at 0.25, 0.4, 0.66, 0.80, 1.00 and wet RH, where "wet" denotes overhumidified gas at the inlet, with a minimum RH of 1.20. [131] For MEAs with electrodes based on Pt catalyst supported on high surface area carbon, the SUSD-induced degradation rate (expressed as mV cycle À 1 s À 1 ) was found to decrease by a factor of about 3 when the RH was reduced from 1.00 to 0.25 at 80°C during SUSD events. Very recent studies confirmed this finding under similar operating conditions.…”

“…[51] Mittermeier et al reported a study on the prediction and experimental determination of the SUSD damage induced by extended H 2 /air anode gas fronts as a function of RH. [131] To achieve this goal, the authors utilized on-line mass spectrometry in order to quantitatively determine the COR rate at 80°C vs potential and RH, and therefore determined the COR reaction order with respect to the RH. Figure 14 shows Polarization curves recorded before and after 60 SUSD cycles at 0.25, 0.4, 0.66, 0.80, 1.00 and wet RH, where "wet" denotes overhumidified gas at the inlet, with a minimum RH of 1.20.…”