FUEL CELL USE IN
Gray Davis, Governor
Arthur D. Little, Inc.
Cupertino, CA 95014
Contract No. 500-00-002 (WA 8)
Transportation Technology Office
Transportation Energy Division
This report was prepared as a result of work sponsored by the California Energy Commission. It
does not necessarily represent the views of the Energy Commission, its employees or the State of
California. The Energy Commission, the State of California, its employees, contractors and
subcontractors make no warrant, express or implied, and assume no legal liability for the
information in this report; nor does any party represent that the uses of this information will not
infringe upon privately owned rights. This report has not been approved or disapproved by the
California Energy Commission nor has the California Energy Commission passed upon the
accuracy or adequacy of the information in this report.
PROJECTED AUTOMOTIVE FUEL CELL
USE IN CALIFORNIA
CALIFORNIA ENERGY COMMISSION
1516 Ninth Street
ARTHUR D. LITTLE, INC.
10061 Bubb Road
Cupertino, CA 95014
Fuel cell vehicles hold the promise of high efficiency and zero or near-zero emissions.
While it will take many years if not decades for fuel cell vehicles to be mainstream, high-
efficiency fuel cells have the potential to deliver comparable power, range and
performance to today’s conventional vehicles. High costs will remain the biggest
challenge to automakers before commercial viability can be achieved.
This summary uses a Delphi method of opinions from experts to project technology,
cost, and performance of fuel cell vehicles during the next 30 years. While much of the
information is speculative due to the adolescent nature of this technology, it does give an
idea of what is to come in the near and mid-term.
2. Fuel Cell Technologies
A fuel cell is similar to a battery in that electrochemical energy is used to produce
electrical energy. Like batteries, multiple fuel cells can be stacked in series to increase
the voltage of the system. However, unlike a battery, fuel cells never need to be
recharged; instead, they utilize hydrogen fuel from an external tank and oxygen from air
to derive power. Thus, fuel cells are essentially engines that combine the best attributes
of both batteries (electrochemical energy conversion) and internal combustion engines
(rapid refueling via an external fuel supply).
The fundamental power-producing unit of a basic hydrogen fuel cell is the membrane-
electrode assembly (MEA) consisting of a cathode, an anode, and an electrolyte.
Oxygen (usually from ambient air) enters through the cathode while hydrogen enters
through the anode. Usually in the presence of a catalyst on the membrane, the
hydrogen molecules split into protons and electrons, with the protons passing through
the electrolyte and the electrons passing through an external circuit. At the cathode
side, water and electricity are produced, resulting in electrical current that can be used
as a power source.
Fuel cell stack conversion efficiency is from 45 to 70 percent compared to the 30 to 40
percent typical of internal combustion (IC) engines. Each hydrogen fuel cell – consisting
of a single MEA and a bipolar plate – generates around 0.6 to 0.8 volts. Single cells are
combined end-to-end into a fuel cell stack to produce the desired level of electrical
power. Fuel cells tend to have high efficiency at low loads while IC engines typically
have high efficiency at high loads. Another key advantage of fuel cells is that they
provide zero emissions in the case of direct-hydrogen systems, and near-zero emissions
in the case of systems that use on-board reformers (discussed further below).
There are several types of fuel cells, distinguished mostly by the chemistry, electrolyte,
and fuel feedstock. These are shown in Table 1. Of these, two show the most promise
Table 1. Characteristics of Fuel Cell Types
Fuel Cell Type
large size and
from fuel and
Sources: NAVC, “Future Wheels,” November 2000; Arthur D. Little Analysis.
for automotive applications, namely the Proton Exchange Membrane1 Fuel Cell
(PEMFC) and the planar Solid Oxide Fuel Cell (SOFC), which are discussed below.
Proton Exchange Membrane
The proton exchange membrane fuel cell (PEMFC) is favored for automobile propulsion
because it has a relatively high power density, operates at low temperatures (see Table
1), permits adjustable power output, and can be started relatively rapidly. These positive
attributes outweigh its disadvantages (compared with other fuel cells) of lower efficiency
levels and its low tolerance for carbon monoxide contamination. Almost all fuel cell
demonstration vehicles currently under development by the world’s major automotive
manufacturers use PEMFC stacks.
PEMFCs use hydrogen as a fuel, which can be stored as pure hydrogen on-board or
produced on-board from other fuels using a fuel processor or reformer.
1 Also know as a Polymer Electrolyte Membrane fuel cell.
A special type of PEMFC is the Direct Methanol-Air Fuel Cell (DMFC), which utilizes
methanol, combined with water, directly as a fuel and ambient air for oxygen. This could
be a less expensive, more convenient technology because it enables use of a liquid fuel
without the need for an on-board reformer, while still providing a zero-emissions system.
However, current research has demonstrated power density lower than other PEMFCs,
significant research effort will be required to improve this.
Solid Oxide Fuel Cells
Planar Solid Oxide Fuel Cells (SOFCs) operate at relatively high temperatures (500 to
800°C), can use carbon monoxide (CO) and hydrogen (H2) fuel, have a good tolerance
to fuel impurities, and use ceramic as an electrolyte. Transportation applications of this
type of fuel cell will be limited to heavy-duty vehicle propulsion or auxillary power unit
(APU) service due to its size and warm-up requirements. BMW is currently developing
an APU using an SOFC with Delphi and Global Thermoelectric. Although SOFCs may
eventually accept fuels directly, currently use of gasoline requires a simple reformer.
As discussed in the next chapter, hydrogen storage on-board a vehicle is one of the
largest technical problems to overcome with direct hydrogen PEMFC vehicles. On-
board reformation of a hydrocarbon fuel into hydrogen allows the use of more
established infrastructure, but adds additional weight and cost, reduces vehicle
efficiency, and creates some emissions.
Reformers are high temperature devices that convert hydrocarbon fuels to CO and H2.
SOFCs can use this mixture directly, PEMFCs must combined these gases with steam
to produce additional H2 and convert the CO to carbon dioxide (CO2). The CO2 is then
released to the atmosphere. On-board reformers are currently being developed by
several companies. Reformer technologies include steam reforming, partial oxidation,
and autothermal reforming. Fuel reformer development activities are shown in Table 2.
Steam reforming (SR) uses a catalyst to convert fuel and steam to hydrogen, carbon
monoxide and carbon dioxide. The carbon monoxide is further reformed with steam to
form more hydrogen and carbon dioxide. A purification step then removes carbon
monoxide, carbon dioxide, and any impurities to achieve a high hydrogen purity level (97
to 99.9 percent). SR of methanol is the most developed and least expensive method for
producing hydrogen from a hydrocarbon fuel on a vehicle, resulting in a 45 to 70 percent
conversion efficiency that is limited by the endothermic nature of the reactions.
Partial oxidation (POX) reforming is similar to SR in combining fuel and steam, but this
process adds oxygen in an additional step, making the reaction exothermic. The process
is less efficient than SR, but the exothermic nature of the reaction makes it more
responsive than SR to variable load, an important feature of on-board reforming.
Heavier hydrocarbons can be used in POX, but they have lower carbon-to-hydrogen
ratios, which limit hydrogen production. This process is more expensive than SR. POX
reformers are not widely used due to their lower efficiencies.
Table 2. Automotive Fuel Reformer Development Activities
Delphi, GM, Opel
Low Temperature SR
On-vehicle (50 kW)
Low Temperature SR
On-vehicle (57 kW)
Low Temperature SR
Transit bus (100 kW) Submarine
R&D for on-vehicle (50 kW)
Prototype (3 kW), various
International Fuel Cells
High Temperature SR
Natural Gas, LPG,
PC25 fuel cell (200 kW) Transit
Low Temperature SR
Laboratory burner reformer
Laboratory membrane Joule II,
Argonne National Lab
various applications 50 kW
Stationary demo (5 kW) and
small on-vehicle demo (25 kW
battery charger) for Chevy S-10
50 kW compact design for mobile
and stationary use
500 kW for marine use and 50
kW multifuel processor for
Natural Gas, LPG,
POX Industrial hydrogen
production (50 kW, 300 kW)
Prototype for vehicle (50 kW)
Hot Spot™ partial
Designed for industrial hydrogen
and vehicles (10 kW) – able to
Sources: Unnasch, “Evaluation of Fuel Cell Reformer Emissions,” 1999, company literature.
Autothermal reforming (ATR) combines both SR and POX so that the heat production
from POX offsets the heat needs of SR. ATR produces a better concentration of
hydrogen than POX but less than SR. ATR offers good response to variable loads and a
good efficiency rate. The efficiency of an ATR depends upon the heat transfer between
the burner and reformer.
A fundamental problem with fuel cell technology whether to store hydrogen or convert it
from other fuels on-board the vehicle. All four principal fuels that automakers are
considering – hydrogen, methanol, ethanol, and gasoline – pose serious challenges.
While direct hydrogen is the approach most favored because of its higher efficiency and
zero emissions, it has significant storage problems. On the other hand, methanol,
ethanol, and gasoline offer the advantages of liquid fuels, but require on-board reformers
to convert the fuel to hydrogen. A discussion of each fuel option follows.
Approximately 40 million tons of hydrogen gas are produced annually on a global scale,
but very little of this is used as an energy source. Most of the hydrogen produced is
used in oil refining, and methanol and ammonia production. Most U.S. companies
produce their own hydrogen through steam reformation of natural gas and consume it
on-site. Only 5 percent of hydrogen production is sold to other facilities.
Hydrogen is colorless and odorless, thus hydrogen refueling stations will need leak
detection devices to alarm personnel. With its low ignition temperature and wide
flammability range, hydrogen poses unique fire hazards. In properly ventilated areas,
however, hydrogen dissipates quickly, reducing this risk.
A vehicle hydrogen fueling station at the Chicago Transit Authority used liquid hydrogen
delivered by truck from an industrial plant 300 miles away. During refueling, the
hydrogen was pumped out and pressurized into compressed hydrogen storage tanks on
the bus roof. This station was recently dismantled. Ford Motor Company has a similar
station in Dearborn, Michigan. The California Fuel Cell Partnership also has a liquid to
compressed hydrogen 16 vehicle fueling station in West Sacramento and is adding
fueling for liquid hydrogen vehicles in late 2001.
Coast Mountain Transit (formerly British Columbia Transit) in Vancouver, Canada and
SunLine Transit Agency in Palm Springs, California utilize on-site electrolysis (splitting of
water into hydrogen and oxygen) to supply hydrogen to their fuel cell vehicles. Fleet-
sized (1 to 200 vehicles) electrolysers are commercially available with residential-sized
electrolysers expected to be available in 2004. Power for electrolysers is usually
provided from renewable energy sources such as hydroelectric (Coast Mountain Transit)
or photovoltaic arrays (SunLine Transit). SunLine Transit also has a 4200 scf per hour
POX reformer system using natural gas as a feedstock and a Stuart Energy Systems
electrolyser. In the summer of 2001, Honda developed a fueling station using solar
photovoltaic arrays for electrolyzing hydrogen in Torrance, California.
The ability to use hydrogen directly in a fuel cell provides the highest efficiency and zero
tailpipe emissions. However, hydrogen has a low energy density and boiling point, thus
on-board storage tends to be large and heavy. There are three types of hydrogen
storage under development: compressed hydrogen, liquefied hydrogen, and binding
hydrogenate to solids in metal hydrides or carbon compounds. Table 3 compares on-
board hydrogen storage methods to an vehicle range-equivalent amount of gasoline.
Each is described in the following subsections.
Table 3. On-Board Hydrogen Storage Options
Fuel Weight (kg)
Tank Weight (kg)
63.3 – 86
Total Fuel System Weight (kg)
67.9 – 90.5
409 – 227
Vehicle Range (km)
Source: NAVC, “Future Wheels,” November 2000.
Compressed hydrogen offers the least expensive method for on-board storage of
hydrogen. However, at normal CNG operating pressures of 24 MPa (3500 psi),
reasonably-sized commercially-available pressure vessels will provide limited range for a
fuel cell car (about 190 km or 120 mi). Pressure vessels capable of 34 MPa (5000 psi)
are now being used by DaimlerChrysler and Hyundai. Quantum is conducting research
of high performance hydrogen storage systems, looking at pressure vessels capable of
up to 69 MPa (10000 psi), which would permit a 645 km (400 mi) driving range with a
total vessel mass less than 68 kg (150 lb). However, the real problem is size -- unlike
heavy-duty vehicles such as transit buses -- automobiles offer relatively small platforms
to accommodate multiple pressure vessels.
Liquefied hydrogen does not have the high storage size and weight penalty as
compressed hydrogen, but it is still bulkier than gasoline storage. Hydrogen’s low boiling
point requires excellent insulation of storage containers, similar to the way in which
liquefied natural gas is currently stored on heavy-duty vehicles. Maintaining the extreme
cold temperature (-253°C) during refueling and on-board storage currently poses a great
technical challenge. Under worst case conditions, 25 percent of liquid hydrogen can be
boiled off during refueling and about 1 percent is lost per day in on-board storage.
Systems using liquefied hydrogen have been developed by DaimlerChrysler and others.
Another option for hydrogen storage is to use materials that absorb hydrogen into their
crystal structure (metal hydrides). Hydrogen bonds to more than 80 metallic compounds
forming a weak attraction that stores hydrogen until heated. Metal hydride systems can
be categorized as either low temperature (<150°C) or high (300°C). Since heat is
required to release the hydrogen, hydride systems avoid safety concerns surrounding
compressed or liquefied hydrogen. However, the metal compounds used to attract
hydrogen tend to be very heavy resulting in only 1.0 to 1.5 percent hydrogen by weight.