WP2 focused on the evaluation and prediction of the durability of the heavy-duty specific MEAs developed in IMMORTAL. Effort focused on the development and application of load profile tests (LPTs) and accelerated stress tests (ASTs) and correlation between the sets of results. An improved practicable modal load profile test protocol was developed using the results in WP6 of four selected simulated load profiles amongst those of 450 actual truck missions.
New materials (support, catalyst, membrane) were developed and upscaled in WP3 and WP4 respectively, and were integrated into a Gen1 heavy-duty MEA in WP5. The performance of these MEAs came within 93% of the final power density target at 0.675 V in short-stack testing in WP2 using the improved LPT. Information derived from post-test analysis of Gen1 MEAs was used to develop materials for Gen2 MEAs. Gen2 MEAs achieved 0.642 V at 1.77 A/cm2, i.e. within 5% of the final target. However, Gen1 and Gen2 MEAs displayed a higher voltage loss during LPT than the project target. End-of-test analyses of the Gen1 and Gen2 MEAs were conducted and the predominant ageing mechanism was determined. Future work (e.g. in HIGHLANDER) will use the learning from IMMORTAL to develop more robust alloy catalysts.
Testing over the targeted 30,000 h of lifetime was beyond the scope of IMMORTAL, and lifetime prediction methods were essential. WP2 developed a parameterised ageing model that was used to simulate voltage loss, which was compared with actual voltage loss during 1500 hours of LPT for the IMMORTAL baseline MEA which, although it gave slightly lower performance, was more stable over time (Pt-only catalyst). The simulated voltage loss with the baseline MEAs was 10% after 30,000 hours, which corresponds to the project, AWP and SRIA targets.
More than 7,200 hours of LPT were carried out on a total of five short stacks, using two types of stack hardware, and using an initial and an improved modal load profile test protocol, with no catastrophic MEA failure, but with a voltage decay, the origin of which is well understood.
AST was carried out with the baseline MEAs (Pt-only catalysts) with sensitivity analysis of the operating conditions influencing platinum dissolution. These important results provide guidelines for minimising loss of platinum surface area in the catalyst by keeping the fuel cell in a benign operation regime via systems control.
WP3 was dedicated to the development of active and stable anode and cathode catalysts and of new and stable supports, as well as anode catalysts stable to cell reversal. A wide library of Pt-rare earth alloys was developed, and extensive characterisation was conducted to determine their structure-property relationships, including by using operando X-ray measurements at the European synchrotron. The results of this research have laid the groundwork for the targeted development of Pt-base metal alloy catalysts with specific crystal structure for higher stability. Several carbon supports with improved durability against electrochemical corrosion were identified, catalysed with Pt or Pt alloys and screened in single cells. Two supports provided significant improvement in terms of corrosion resistance compared to the reference carbon and multiple hundreds-of-gram batches were catalysed with Pt or PtCo and transferred to WP5. Anode catalysts stable to start-up and shut-down events were developed with Pt alloy anode catalysts that are highly active towards the hydrogen oxidation reaction but less active for the oxygen reduction reaction.
The objectives of WP4 were to develop an exceptionally durable membrane specific to heavy-duty truck application. An ionomer was selected that best satisfied durability and performance requirements. The formulation and processing of thermostable nanofibre reinforcements were further improved, and the webs produced at several linear metres for nanofibre reinforced membrane production on a coating line. Extensive ex situ and in situ characterisation of the resulting membranes produced results that demonstrate that the IMMORTAL reinforced 10 µm membrane significantly extends the state of the art in terms of durability under accelerated ageing conditions of high temperature and relative humidity cycling at open circuit voltage. The heavy-duty-specific membrane was transferred to WP5 for use in the first and second generations of MEAs.
WP5 on MEA development was central to IMMORTAL. More than 100 IMMORTAL baseline full-size MEAs were produced, and more than 80 Gen1 and 20 Gen2 MEAs for stack manufacture and testing. Systematic work on catalyst layer optimisation using catalyst materials from WP3, and improved PtCo/C alloy catalysts were instrumental in the excellent progress made in reaching the project performance target. Their use has delivered significant benefits, resulting in a 20% increase in power density at 0.675 V compared with the benchmark MEA, and brought the performance to within 5% of the project power density target at 1.8 A/cm2. Importantly, strides forward were made with platinum thrifting, illustrated by the Pt per kW metric which was decreased from 0.84 g Pt/kW at 0.675 V in the baseline MEAs, to 0.31 g Pt/kW in the high performance Gen2 MEAs.
WP6 aimed at validating the project results for heavy-duty fuel cell truck application. Methods were developed for a regression model for fuel cell degradation forecasting, along with the necessary criteria for selection of the most appropriate model, and a method for creating accelerated durability tests for fuel cells, based on Markov chains. Simulations were performed to improve understanding of the impact of fuel cell and battery dimensioning, vehicle and mission characteristics, as well as power split and ambient conditions on the overall fuel cell heavy duty truck performance and fuel consumption in combination with fuel cell stack degradation. Technoeconomic analysis confirmed the dominant role of fuel price in the total cost of ownership of heavy-duty trucks. Improvements in the cost of the fuel cell, powertrain, efficiency, and durability are also decisive, given the high part of fuel cost in the total cost of ownership, and the high part of the electrified powertrain cost in the total vehicle cost.
In WP7, IMMORTAL partners have published 5 articles, and a further manuscript has been submitted. IMMORTAL results were presented at international conferences and during international discussion meetings with the US M2FCT and Japanese FC Platform partners. IMMORTAL held an on-line workshop in March 2024 that assembled 120 attendees. Two newsletters were produced, and a third is in the pipeline.
