Toyota MIRAI Fuel Cell Vehicle and Progress Toward a Future Hydrogen Society

In anticipation of the diversification of primary energy resources such as oil, natural gas, coal, electricity, and renewable resources, Toyota launched the Prius Hybrid vehicle in 1997 and has also made available Electric Vehicle (EV) and Plug-in Hybrid Vehicle (PHV) versions to improve fuel consumption efficiency and reduce exhaust gas emissions as compared to conventional combustion-engine vehicles. Moreover, Toyota has developed a Fuel Cell Vehicle (FCV) and regards a sustainable society as the future energy scenario. In such a scenario, the energy supply relies not only on fossil fuels, but also on environment-friendly renewable resources. Electricity and hydrogen are used as energy carriers in a common idealized infrastructure in the sustainable society, as shown in Fig. 1. Toyota believes hydrogen will be a leading energy carrier and has just started sales of the MIRAI FCV, introduced with an affordable price (approximately 7 million Japanese yen or $57,500), in December 2014. Toyota’s FCV development started in 1992, with the Fuel Cell Hybrid Vehicle (FCHV), which was first leased in 2002. Three big technical issues were addressed over several years: the cruising range was increased to more than 500 km, cold start was enabled from −30 °C, and refueling times were lowered to about 3 minutes. 1 This led to the FCHV-adv being leased in 2008, with around 100 cars tested worldwide. A FC bus was developed with Hino Motor Ltd, with field-testing beginning with a Tokyo city route bus in 2003 and subsequent demonstration tests conducted on many routes in Japan. Toyota made use of the customers’ experiences of the FCHV-adv and the FC bus to help guide the design of the MIRAI FCV. The MIRAI retains FCHV-adv’s excellent qualities of zero emissions, large cruising range, cold start, and short refueling time, with further improvements towards quiet operation and better acceleration. A power supply function is also added for emergency use. Currently, overcoming the cost hurdle to bring FCVs to commercial reality is of paramount importance. This paper presents new technologies introduced to reduce cost and improve performance as steady progress is made towards a hydrogen society. A New Concept in Flow Field Structure A conventional flow field is made up of a rib and channel architecture. The rib contacts against and presses into the gas diffusion layer (GDL) on the membrane electrode assembly (MEA) to reduce contact resistance. However, the rib partially covers the GDL and the resultant gas-transport distance become longer than the inter-channel distance. Thus, the width of the rib results in lower V-I performance. 2