Supervisor:
Torsten Berning

Co-Supervisor:
Vincenzo Liso

Assessment Committee:
Kim Sørensen (Chair)
Frano Barbir, Faculty of Electrical Engineering, Mechanical Engineering and Naval Architecture University of Split
Martin Andersson, Lund University, Faculty of Engineering

Moderator:
Simon Lennart Sahlin

Abstract:

A proton exchange membrane fuel cells is an efficient power generation device that converts chemical energy into electrical energy.

It has the advantages of high energy conversion efficiency and environmental friendliness.

This type of fuel cell uses hydrogen as fuel, oxygen as oxidant, and separates the anode and cathode through a proton exchange membrane, allowing hydrogen to oxidize at the anode and produce protons and electrons.

Protons reach the cathode through the membrane, while electrons form an electric current through an external circuit.

Overall, this PhD project includes two main scientific parts: the first part focuses on the modelling while the second part focuses on the experimental study of the proton exchange membrane fuel cell.

In the simulation section, firstly, an anode side of a proton exchange membrane fuel cell single-phase model based on computational fluid dynamics is used to investigate the possibility of operating a fuel cell at low stoichiometric flow ratios and dry hydrogen at the inlet.

The results indicate that proton exchange membrane fuel cells can potentially be operated with a stoichiometric flow ratio as low as 1.01 on the anode side.

Such operation enables an open-ended anode configuration, eliminating the need for a recirculation system.

Moreover, a multiphase model of a fuel cell, encompassing both the anode and cathode sides, is introduced.

It is studied with a particular focus on enabling fuel cells to operate at high current densities under conditions of variable inlet relative humidity.

High current densities can be achieved when perforated metal plates replace traditional carbon fiber papers as the gas diffusion layer to improve waste heat dissipation.

The outcomes indicate that the predicted current densities across all the case studies fall within the range of 5–6 A cm\(^{-2}\).

Significantly, the model's results imply that it is feasible for fuel cells to perform at a high current density.

Additionally, based on this multiphase model, further research on operating a proton exchange membrane fuel cell with high current densities at a constant humidity from the inlet to the outlet is presented.

The results show that the constant humidity operation conditions at the cathode side appear feasible and results for a current density above 6 A cm\(^{-2}\) were obtained.

Furthermore, the operation of proton exchange membrane fuel cells at low stoichiometry and high current densities on the order of 10 A cm\(^{-2}\) is presented.

Importantly, these findings suggest that fuel cell can operate at low stoichiometric flow ratios and high current densities, in conjunction with low inlet relative humidity.

In terms of the experimental part, based on previous simulation results with a multiphase computational fluid dynamics model, which proposed a structure named the water uptake layer, a layer between the cathode catalyst layer and the membrane with a high specific surface area, we verified our hypothesis through experiments.

The test results are in very good agreement with the previous simulation predictions.

Overall, the polarization curves showed that the water uptake layer could improve the performance more pronounced in low humidity conditions.

However, a too high ionomer/carbon ratio can reduce the reaction mass transport.