VOLUMETRIQ has reached its goal of developing a new, high power density automotive fuel cell stack (NM12) comprising components prepared at volume, and has achieved an exceptionally high stack power density of 5.38 W/l (excluding housing). By associating improvements in the ionomer used for the membrane, cathode catalyst construction, compression set, gas diffusion layers and by moving from baseline (NM5) to project improved (NM12) cell hardware, VOLUMETRIQ has achieved a leading single cell power density of 2.67 A/cm2 at 0.6 V (1.6 W/cm2) with catalyst coated membranes produced at volume. This exceeds the project target of 1.5 W/cm2. In parallel, and at automotive single cell level, VOLUMETRIQ has demonstrated 2700 hours of drive cycle testing, allowing reasonable expectation of 5000-6000 hours durability.
In WP2, BMW provided the stack and component specifications and defined test specifications. BMW specified stack requirements as well as automotive operating conditions that meet the system efficiency and dynamic requirements, and defined realistic geometrical dimensions for stack integration and requirements for environmental robustness. EK and JMFC broke down the requirements to component level specifications. The power density target achieved using the new cell hardware at single cell level in RP2 was reached using a short stack and in the full-size stack in RP3. This stack comprises 299 cells and provides a total power of 111 kW, which largely exceeds the original goal of 90 kW. The full stack was tested under various operating conditions, including the EU harmonised test protocol. A cost projection by EK for high volume production of a full stack, on the assumption of 50,000 units/year, led to 68 €/kW.
The objective of WP3 to demonstrate the manufacturability of a thin, low equivalent weight, nanofibre reinforced membrane using roll-to-roll high volume manufacturing processes was achieved in RP2. CNRS and JMFC collaborated to scale the electrospinning process with external industrial vendors equipped with off the shelf continuous electrospinning lines. CNRS introduced advanced grades of PBI to associate the requisite properties of feasibility of scale-up, mechanical resilience enabling its use in roll to roll processing, and compositional features compatible with its intended use. PBI electrospun roll material was then used successfully on JMFC casting line for membrane fabrication, and the scaled-up membrane was qualified for performance and durability at JMFC. Further evaluation of PBI reinforced Aquivion membranes confirmed the step changing improvement over the best ePTFE reinforced analogue containing the same ionomer and additive technology in in-cell relative humidity cycling durability assessment. Reduced rates of increase in gas crossover after the initial onset indicate subdued membrane deterioration after the onset of cracks at the anode or the cathode. In parallel, JMFC sourced ePTFE reinforcements having improved mechanical isotropy. Improved ionomer with different specifications and composition was prepared at high volume by Solvay for use in the membrane (RP1), while novel high oxygen permeability ionomers were developed in RP2 for the cathode catalyst layers that are currently undergoing final qualification, both in VOLUMETRIQ and also, by inter-project transfer, to INSPIRE.
WP4 has successfully demonstrated the manufacturing capability of an optimised high performance CCM compatible with high volume manufacturing, incorporating a low EW ionomer and both expanded PTFE and electrospun nanofibre reinforcements. For reasons of timing and relative product maturity, the CCMs produced for the NM12 stack comprise membranes reinforced with ePTFE. The CCMs developed exceed the performance milestone of 2.5 A/cm2 at 0.6 V. A CCM manufacturing process tailored to EK’s stack assembly process was developed and qualified. Risks and mitigations associated with the coating and converting of membranes to CCMs were considered in a process FMEA, and quality control systems were implemented. JMFC has supplied EK with 190 CCMs for use with the project baseline hardware, 753 CCMs for the project improved single cell and stack hardware and 350 linear metres of dummy CCM for trialling CCM feed into automatic stack assembly. JMFC trialled an automated visual system compatible with roll-to-roll production of membranes and catalyst layers. This was found to give good data relating to the location and types of defects and suggested strategies to reduce the defect frequency in membranes. Drive-cycle testing carried out over 2700 hours in automotive size single cell hardware on a CCM comprising a PBI-X reinforced membrane gave degradation rates well below 10 µV/hour at each of the various load points of the drive cycle.
WP5 is the development at EK of a high performance bipolar plate (NM12) for automotive applications with high volume manufacturing capabilities to deliver appropriate levels of yield and assuring the necessary drop in stack costs. All bipolar plate design improvement of flow field structures/pattern and other significant plate features, essential for manufacturing processes, were achieved. Tests assessing formability, weldability and quality control methods were conducted and the knowledge gained was used in developing an improved cell and bipolar plate design with optimised flow field pattern. Improved alignment features for stacking, welding and quality control processes were designed, their manufacturability tested in stamping test tools, their usability shown via assembly and/or measuring tests, and finally implemented in the bipolar plate design.
The manufacturing of an automated stack assembly line was completed and equipped at EK with a CCM supply unit enabling roll feeding in WP6. Fixtures and jigs were developed to improve handling and processing where necessary, and CCM punching and automated pick-and-place processes for MEA components were analysed to optimise the manufacturing processes and increase the assembling capability. In RP3, the focus in WP6 was on the assembly and testing of short stack and full-size NM12 stacks and on post-assembly quality control tests. Improvements of the stack components and the assembly processes made during the project lifetime were shown through increased performance at single cell, short stack and full-size stack levels, progressing from the baseline NM5 to the project NM12 cell hardware. JMFC developed a 15 minute CCM conditioning protocol, well below the 4 hour target, and commissioned an automotive drive cycle protocol on a short stack.
VOLUMETRIQ has communicated and disseminated results via its website, project flyer, and three annual newsletters, and by presentation at international conferences as well as at the recent INSPIRE PEMFC development workshop.
