Influence of Current Ripple on Proton Exchange Membrane Fuel Cell Degradation
H.E. Wesseling (TU Delft - Mechanical Engineering)
H. Polinder – Mentor (TU Delft - Transport Engineering and Logistics)
Linder van Biert – Graduation committee member (TU Delft - Ship Design, Production and Operations)
J. W. Haverkort – Graduation committee member (TU Delft - Energy Technology)
J. Bruinsma – Graduation committee member (Nedstack Fuel Cell Technology)
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Abstract
The ongoing transition towards sustainable energy has resulted in a large interest in alternative sources. Proton exchange membrane fuel cells (PEMFC) use hydrogen to produce energy without harmful emissions, and they can be used in a range of applications, from mobility to industrial power generation.
One hurdle that still stands between PEMFC and widespread commercial adoption is the durability. The electrodes, catalyst and membrane of the fuel cells degrade due to the reactive environment inside the fuel cell (temperature, acidity and the presence of catalysts). This is worsened by situations with dynamic loads or start-stop cycling.
Another factor that can affect the degradation of fuel cells is the interaction between the fuel cell and the power electronics it interfaces with. The power electronics are necessary to boost and stabilize the voltages from the fuel cell, but they introduce current ripple into the fuel cell. The main objective of this research is to investigate how current ripple influences fuel cell degradation. The relevance is that the desired lifetime plays a significant role during the design of fuel cell systems, and quantitative information about the relationship between current ripple and fuel cell degradation can be used in the design process of the power electronics, where trade-offs need to be made between ripple amplitude, complexity and costs.
An analysis has been made concerning current ripple in fuel cells. Two current ripple types are mentioned in literature, low frequency current ripple and high frequency current ripple. Low frequency current ripple is created by the conversion from DC to AC by a single phase inverter, it has a frequency of 100Hz or 120Hz. High frequency current ripple is caused by the high frequency switching that occurs in any power converter. The link between these current ripple types and fuel cell degradation has mainly been investigated using experiments, but only for very specific parameters, a handful of frequencies and amplitudes. There is an absence of a quantitative analysis on the effect of different current ripple shapes on PEMFC degradation.
In this report, a model is developed which predicts the degradation of the PEMFC catalyst caused by current ripple. The model consists of two sub-models. The steady state degradation model predicts the decrease of the electrochemically active surface area (ECSA) due to the average current of the current ripple. It models the influence of electrochemical dissolution, chemical dissolution and Ostwald ripening on the ECSA over time. The ripple degradation model predicts the ECSA degradation as a function of the ripple amplitude and frequency, using an electrical representation of the fuel cell and experimental degradation data. The model can be used to help in the design process of power electronics that interface with fuel cells.