Nissan Develops Automotive Solid-Oxide Fuel Cell System

Nissan Motor Co. is developing a bi-ethanol solid-oxide fuel cell (SOFC) system that it aims to use as a primary power source to help lower the cost and improve the driving range and safety of fuel cell vehicles.

Current fuel cell vehicles use proton-exchange-membrane stacks with expensive precious metal catalysts, coupled with a high-pressure hydrogen storage tank with the fuel pumped in by a traditional refueling process. SOFC systems use a solid-oxide electrolyte and an onboard reformation process to derive hydrogen from other fuel sources—biofuel in the case of in the Nissan system.

SOFCs have long been used in stationary power generation systems and in some cases as an auxiliary power source in vehicles. But operating temperature and power limitations have prevented them from being a vehicle’s main power source.   

Nissan is working to resolve these concerns with its new system, which it hopes to launch in a production vehicle in about four years. Improvements still are needed in the heat-management system and start-up performance, the company says.

Nissan estimates that an SOFC vehicle using bio-fuel could have a driving range of more than 600 km (400 miles) in cars and as far as 800 km (500 miles) in larger vehicles. It notes there already is an existing infrastructure for such fuels, which are derived from renewable crops such as corn and sugarcane. The mixture used by the Nissan system can contain as much as 55% water to further reduce cost.

Using ethanol also would eliminate the need to store highly flammable hydrogen onboard a vehicle in high-pressure fuel tanks, which typically are made of costly carbon fiber materials. And higher operating temperatures would eliminate the need for platinum catalysts.

Unlike PEM fuel cell vehicles, which release only heat and water vapor, Nissan’s bio-ethanol SOFC system also emits carbon dioxide as a byproduct of the onboard hydrogen reformation process. Nissan maintains the system is carbon neutral because the carbon dioxide released is eventually sequestered in the crops that are harvested to make ethanol.

Nissan says it will continue to develop traditional PEM-based fuel cell technology, which it has been working on with Daimler AG for several years.