Development of protective coatings for metallic bipolar plates for PEM fuel cell applications

Cooper, Liam Travis (2024). Development of protective coatings for metallic bipolar plates for PEM fuel cell applications. University of Birmingham. Ph.D.

Preview

Cooper2024PhD.pdf
Text - Accepted Version
Available under License All rights reserved.
Download (7MB) | Preview

Abstract

Polymer electrolyte membrane fuel cells have the potential to progress the worlds energy cycle toward a greener future. PEM fuel cells have the potential to power data centres, drones, auxiliary power units on planes, heavy and light duty vehicles but are still hindered by high costs and low hydrogen supply. For PEM fuel cells to become a mainstream power source, the price of stacks needs to be reduced. In addition, some applications require improvements in the gravimetric power density currently produced by systems.

Metallic bipolar plates have become the standard for modern fuel cell systems but plates often require expensive coatings. For this reason cheaper alternatives to PVD coating were investigated for stainless steel plates. Polyaniline/TiN - TiN bilayer coatings were investigated due to the simple equipment needed for coating and the low cost raw materials. Contact resistance was reduced by increasing TiN surface layer loading. This also improved the corrosion resistance of the sample. The optimised coating however failed to meet DoE contact resistance targets.

Reducing PVD coating thickness is another method to reduce coating costs. PVD coatings have already been shown to achieve DoE contact resistance targets. To increase gravimetric power density the mass of bipolar plates needs to be reduced. Aluminium was selected as the density is 40% that of stainless steel. Aluminium however readily corrodes in simulated fuel cell conditions, the metal is also covered in an insulating oxide layer which would lead to unacceptable contact resistance values. For this reason the substrate must be coated. In this work, TiN, TiC, CrC and TiAu, PVD coatings were applied to 99.0% pure aluminium and TiC, CrC and TiAu coatings to Alloy Al6082 substrates. All coated samples, except the TiC 99.0% coated sample, possessed excellent contact resistance values that far exceed DoE targets. However all the samples displayed typical aluminium corrosion phenomena. The corrosion resistance of materials was probed by means of linear sweep voltammetry and chronoamperometry, with ICPOES, EDX and SEM analysis characterisation techniques utilised to investigate the corrosion solutions and the samples.

Further investigations on the feasibility of aluminium bipolar plates were carried out by means of in situ degradation testing. In situ degradation was carried out by a duty cycle whereby the voltage was cycled between 0.9 V and 0.6 V. Polarisation curves and impedance spectroscopy measurements were carried out at the start of tests and every 12 hours to assess the performance degradation. The TiAu coating displayed superior performance to the graphitic bipolar plate at beginning of life but degraded through the test. Further work is required to achieve durability requirements. However PVD coated aluminium bipolar plates show promise in increasing the volumetric power density of PEM fuel cells.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):