(Invited) Development of Second Generation New Structure Fuel Cell Stack
Authors: Kanaoka Nagayuki 
Published: December 2024

Honda and GM have started co-development program for fuel cell system in 2013. In January of 2024, FCSM (Fuel Cell System Manufacturing, LLC), which was established in 2017 at Brownstown in Michigan, USA, as the joint venture company between Honda and GM, has launched new generation fuel cell system in the world. This new system has adopted new generation (GEN2) fuel cell stack, which has achieved 1/3 cost and 2-time durability compared to previous generation (GEN1) stack with satisfied basic performance.

GEN2 stack has also achieved equivalent net power to GEN1 stack even though the stacking number of the cells is reduced in terms of cost reduction. Main features of GEN2 cost reduction are below; 1) Elimination of the outer peripheral structure of the rubber for Bipolar Plate (BPP) with the combination of metal bead seal for BPP and the filters for stack case, 2) Reduction of total Pt amount by adopting Pt alloy catalyst and reduction of polymer electrolyte membrane thickness, 3) Complete automated stack assembly line from Unitized Electrode Assembly (UEA ; membrane electrode assembly with subgasket), cell unitization of UEA and BPP to cell stacking.

In order to achieve 2-time durability of the stack, the novel coating for BPP is applied for the reduction of Fe elution from the plate material, and cell-by-cell cooling concept is adopted to improve the cooling performance of the stack.

New designed BPP has adopted the novel coating, metal bead seal and welding seal structure to achieve both durability improvement and cost reduction. The novel coating is applied to the coil material before stamping. The BPP for GEN1 stack had adopted gold coating, which resulted higher cost for this specific parts. The novel coating can balance good conductivity and durability of the plate against elution. As a result, the new plate can eliminate expensive material for the coating. New metal bead seal and welding seal structure also help cost reduction. Previous BPP design adopted the rubber seal for the outer peripheral by injection molding. This manufacturing method takes longer time for the molding process. By the combination of metal bead seal and filter concept for stack case, that can realize to eliminate the rubber seal structure for BPP. As a result, the tact time for the manufacturing process of BPP is significantly reduced to help total cost reduction of the parts.

New designed UEA has adopted Pt alloy catalyst for electrode, thinner polymer electrolyte membrane and general purpose plastic material for the subgasket. Pt alloy catalyst can enhance the electrode activity for the reaction in the cell, and helps to reduce the total amount of Pt. Precise degradation models for electrode performance and membrane degradation have been developed. That also helps to reduce the amount of catalyst down to 1/5 and membrane thickness down to 3/5 compared to GEN1 model by providing appropriate operating condition in terms of total fuel cell system control. For subgasket, GEN1 model had adopted injection molding plastic. That process takes longer tact time for manufacturing as same as that for the previous BPP. New designed BPP flow field helps to adopt simple structure of UEA subgasket. As a result, general purpose plastic material can be applied as subgasket material. That contributes to reduce material cost and significant reduction of tact time for the manufacturing process.

New design stack has adopted stack case instead of panel type structure for GEN1 model. By reconsidering functions of BPP and stack structural parts, that contributes to reduce the number of the structural parts of the stack.

New designed stack assembly line has achieved highly efficient stack manufacturing process. By redesign of BPP and UEA, complete automated stack assembly line from UEA to cell stacking can be realized. As a result, the new stack assembly line has achieved significant reduction of stack manufacturing tact time.

This new generation fuel cell system with GEN2 stack is installed to brand-new CR-V e:FCEV in 2024. Honda will also provide this system to the customers for the various application such like as commercial vehicles, stationary power stations and construction machinery and so on to contribute to achieving carbon neutrality of the world.