Technology Status of Hydrogen Road Vehicles

The 11th WHEC shows increasing interest in FCs for transportation applications, but the ICE proponents are
still forcefully present. Provenzano et al. (1996) report on successful ICE operation of three hydrogen trucks,
as do Knorr et al. (1996) for a full-size city bus; Peschka (1996) favors a combination of early and late
injection of LH 2 to reach comparable performance as gasoline, but with very low NO x; he finds the FC
unattractive on a power/weight basis. Some major European car manufacturers such as Volvo (Ekdunge and
Råberg 1996) and Mercedes (Dönitz 1996; Friedrich and Noreikat 1996) report favorably on FCs; Friedrich
and Noreikat have been major developers of the hydrogen ICE, as summarized by Digeser et al. (1996).
4.2 Fuel Cells
The FC, like LH 2, was brought into widespread use in the space industry, and some versions have made
enormous strides during the past 5-10 years. Appendix 3 introduces FCs, enumerates the ones receiving most
attention in a general sense, and focuses on the two types of most interest for vehicles:
! The proton exchange membrane (PEM) FC, which operates at low temperature (~80 o C), has reasonable
efficiency (~55 %), starts up in seconds, has good dynamic response and a promising lifetime (~same as
vehicle); it is emerging as the favorite FC for vehicles (see in Tables 1 and 2).
! The alkaline fuel cell (AFC), which operates at about the same temperature as the PEM FC but with a
liquid electrolyte and a lower power density.
The main disadvantage of the PEM is its need for platinum (Pt) catalyst at the electrodes, at least an order of
magnitude greater than the Pt content of today’s catalytic converters for ICE mobile application. However,
the need for Pt in the PEM FC is decreasing. Another disadvantage is the cost of the solid polymer membrane,
which comes in several trademarked versions. But as Appleby (1992) points out, the basic polymer material
is quite cheap.
Dönitz (1996) states that in 1990 these two cost items were roughly equal per unit power output (320 DM/kW
for Pt loading of electrodes, 250 DM/kW for Nafion membrane). He claims that the Pt loading has sunk to
only 55 DM/kW in 1996, and can reach 6 DM/kW over the long run, making it no bar to commercialization.
However, only volume production and/or the development of new polymers can bring down the cost of the
membrane.
Rusanov (1996) states that a Russian solid polymer membrane costs several times less than Nafion.
Scherer et al. (1996) describe initial characterization tests on novel proton conducting membranes.
Bevers et al. (1996) describe potential improvements in mass production of reproducible PEM electrodes.
The AFC has different catalysts, and is intolerant to CO and CO 2. This may help explain its lack of favor:
only two projects--now terminated--figure on Table 1, and none on Table 2.
Although the PEM FC comes closest to the ICE on a specific power (kW/kg) basis, the 11th WHEC gives
some conflicting figures:
! Peschka (1996) claims that the hydrogen ICE will continue to enjoy the order-of-magnitude advantage
it has over H 2-air FC: 1 kW/kg vs. 0.1 today, increasing to 1.8 versus 0.2
! Ekdunge and Råberg (1996) give an ICE and an FC option for a five-passenger Volvo car: the 93-kW ICE
weighs 1,450 kg; a 75-kW FC would weigh 1820 kg plus 123 kg of buffer batteries for the same total peak
capability of 93 kW
! Friedrich and Noreikat (1996) quote 20 kg/kW for the Mercedes Benz PEM FC of Item 9 Table 1, and
claims that this can be improved by a factor 4 to 5; another author from the same company, Dönitz (1996)
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