General Motors’ hydrogen fuel cell development program has been operating in “stealth” mode in recent years, as the collaboration with Honda quietly focuses on delivering production-ready stacks, power electronics, and hydrogen storage systems for use by both OEMs by 2020. But there have been intriguing developments, as Andrew Bosco, GM’s Fuel Cell Chief Engineer, revealed at the recent SAE Hybrid and EV Technologies Symposium in Los Angeles.
Engineers in the SAE audience, as well as some GM executives in the audience, were surprised to see a yellow U.S. Navy research submersible pictured in one of Bosco’s presentation slides.
“It’s a UUV—an unmanned undersea vehicle that’s powered by a GM automotive fuel-cell stack similar to those used in our fleet of 118 Equinox FCV test vehicles,” he noted. GM has been involved with the Navy UUV program since 2011, and Bosco said open-water testing of the fuel-cell sub are coming up. The program, for which GM is financially compensated for its technical contribution, “helps offset some of our costs” on the automotive FC side, he said.
In the Q&A session following his presentation, Bosco noted that when the UUV is submerged the fuel cell “breathes” through a sophisticated closed-loop oxygen storage system.
The UUV stack is a proton-exchange-memory (PEM) type that is well proven in the Equinox FCV program. In that project GM has accumulated over 3 million miles’ actual operational data over seven years. “We have clocked about 91 million cell hours of use, and in that time individual cell failures have been rare; we sample each cell electronically every 25 ms,” he noted. Most component failures in the field have been unrelated to the fuel-cell powertrain.
The GM-Honda collaboration is progressing through what Bosco called Gen1 and Gen2 stack development, the latter being the design they will establish for production in the 2020 timeframe. In addition to optimizing the Gen2 stack’s overall efficiency, the team is “attacking” cost in every detail, Bosco claimed, “because that’s what is hindering mass adoption of this technology.”
To cite a few examples, much analysis is going into reducing the amount of carbon fiber in the gaseous hydrogen storage tank that must withstand 700-bar (10,000-psi) internal pressure. Also, the volatility in stainless-steel commodity prices (due to the rise and fall of the constituent nickel’s prices) caused the team to change the stack’s bi-polar plate material from austenitic stainless to ferritic-stainless alloys. The latter have little or no nickel content. Ferritics also are magnetic, making them easier to handle in an automated production environment, but they also present a formability challenge.
Coatings of the bi-polar plates in the 300-cell stack are critical to its internal efficiency. The team is currently using a non-precious-metal coating, which saves cost while maintaining conductivity over time. The plates themselves have transitioned from the original composite type coated with 80 g of platinum (Pt) in the Equinox stack, to stamped (austenitic) stainless coated with 30 g Pt in the latest Gen1 stack, to the ferritic SS coated with 11 g Pt currently slated for Gen2.
Net power for the Gen2 production stack is targeted at approximately 95 kW (127 hp), slightly more than the 93-kW (125-hp) Equinox unit. Power density, however, will be significantly improved as the engineers have methodically reduced the stacks’ mass from 240 kg (530 lb) in the Equinox to 120 kg (265 lb) in the Gen1 and are targeting 105 kg (230 lb) in Gen2.
Other comparative specifications shared by Bosco include 115°C (239°F) maximum thermal excursion in the Gen2 stack, vs. 86°C (187°F) in Equinox, and -40°C (-40°F) cold operation, compared with a -25°C (-13°F) extreme in the Equinox unit.
Optimized air-delivery systems are critical for providing oxygen to the stack, and the GM-Honda team is currently using a small turbomachine running at what Bosco said is “higher pressures” than past systems, which helps improve the cathode’s performance. “The turbine allows us to move a lot of air quickly—1 g/s per kW,” he noted.
Collaborative development is a significant trend in automotive FCVs, as automakers share engineering and scientific resources, and cost, as they race toward series production and customer sales later this decade. Besides Honda and GM, other partners include BMW and Toyota; Volkwagen and Ballard; and Ford with Daimler and Nissan. FCVs are expected to play a major role in enabling OEMs to meet the tough new U.S. CO2 standards.
FCV350s, so named because they offer 350-mi (563-km) range between fill-ups, earn OEMs four zero-emission vehicle (ZEV) credits per vehicle under the new regs, vs. 1.5 ZEV credits for a BEV100 (battery electric with 100-mi/161-km range).