fuels for fuel cell vehicles

Fuels for he1 cell vehicles By Joan M. Ogden, Thomas G. Kreutz and Margaret M. Steinbugler (Center for Energy & Environmental Studies,

Princeton University, USA)

The issue of fuel choice impacts both fuel cell vehicle design and infrastructure

development. In general, there is a trade-off between simpler vehicle design (hydrogen vehicles are inherently simpler than those with onboard fuel

processors) and simpler infrastructure issues (liquid fuels such as gasoline or methanol are easier to store and handle, and are more compatible with the

existing refueling infrastructure). In this article we compare fuel cell vehicle characteristics and infrastructure requirements for four possible fuel options:

compressed hydrogen gas, methanol, gasoline and synthetic liquids derived from

natural gas. The advantages and disadvantages of various fuels are discussed, and possible fuel strategies leading towards the commercialisation of fuel cell vehicles

are explored.

All fuel cells currently being developed for use

in vehicles require hydrogen as a fuel.

Hydrogen can either be stored directly or

produced onboard the vehicle by reforming a

liquid fuel such as gasoline, methanol, or

synthetic liquids from natural gas. The vehicle

design is simpler with direct hydrogen storage,

but requires developing a more complex

refueling infrastructure. While many in the

fuel cell vehicle community would agree that

widespread public use of hydrogen in fuel cell

automobiles is the ultimate aim, there is an

ongoing debate about the best path towards

this goal. Much of this debate centres on which

fuel to use, and when in the commercialisation

process to use it.

Here we compare, with respect to vehicle

characteristics and infrastructure requirements,

four possible fuel options for use with fuel cell

vehicles (see Figure 1):

l Compressed hydrogen gas.

l Methanol with onboard steam reforming. l Gasoline with onboard partial oxidation.

l Synthetic liquids (such as synthetic middle distillates) derived from natural gas with

onboard partial oxidation.

Automakers have demonstrated fuel cell

vehicles which use hydrogen or methanol, and

commercialisation of these technologies is

planned within the next five years. Several

groups are developing onboard gasoline

reformer/fuel cell systems, although this is

generally thought to be a longer-term option

than methanol. Synthetic middle distillate

(SMD) is a leading contender as a low-

polluting fuel for advanced internal

combustion engine vehicles, and it has been ;

proposed that SMD could be used in fuel cell

vehicles as well.

Comparison of alternative- fueled fuel cell vehicles Researchers at Princeton University’s Center for

Energy & Environmental Studies have

developed computer models of proton exchange

membrane (PEM) fuel cell vehicles, as a tool for

estimating the performance, fuel economy and

cost of alternative fuel cell vehicle designs.[1-3]

Input parameters to the model include:

l The driving schedule (for example, the

Federal Urban Driving Schedule (FUDS), Federal Highway Driving Schedule (FHDS)

or others may be used).

l Vehicle parameters (base vehicle weight

without the power train, aerodynamic drag, rolling resistance, vehicle frontal area, accessory loads).

l Fuel cell system parameters (fuel cell current/voltage characteristic, fuel cell

system weight). l Peak power battery characteristics (behaviour

on charging and discharging, weight).

l Fuel processor parameters (conversion efhciency, response time, weight, hydrogen

utilisation in the fuel cell). l Type of fuel storage (hydrogen, methanol,

gasoline or SMD).

First, the fuel cell system and peak power device

are sized according to the following performance

criteria, which are consistent with the goals set by

the US Partnership for a New Generation of

Vehicles (PNGV):

l The fuel cell system alone must provide

enough power to sustain a speed of 55 mph (88 km/h) on a 6.5% gradient.

l The output of the fuel cell system plus the

peak power device must allow acceleration

for high speed passing of 3 mph/second (5 km/h per second) at 65 mph (105 km/h).

Once the components are sized, the vehicle weight

is calculated. The program then estimates the

power needed at the wheels and the fuel consumed

Gear )J r Gear 2 r Gear f-.~

Fuel Cells Bulletin No. 16

ar each time step of the driving schedule,

accounting for energy conversion losses in the fuel

processor, fuel cell, motor etc. Fuel consumption is

summed over the drive cycle and divided into the

distance travelled to give a fuel economy, expressed

in miles per equivalent gallon of gasoline.

Table 1 summarises the assumptions used in

the model. The base vehicle is a streamlined,

lightweight, 4-5 passenger mid-size

automobile with an 800 kg “glider” weight,

aerodynamic drag of 0.20 and rolling

resistance of 0.007. Table 2 shows modelling

results for fuel cell vehicles fueled with

hydrogen, methanol, gasoline or SMD. Each

vehicle is designed to satisfy identical

performance criteria.

The results in Table 2 illustrate how fuel

choice affects vehicle design.

Vehicle weight Vehicles with onboard fuel processors are heavier

because: (1) the fuel processor adds weight, and

(2) the fuel cell/fuel processor system is less

energy-efficient than a pure hydrogen system, so

a larger, heavier fuel cell is needed to provide the

same power output.

Power requirements for fuel cell and peak power device For hydrogen, a lower fuel cell capacity and

overall peak power output are needed, because

the vehicle is lighter. The fuel cell and battery

each provide about half the peak power.

Fuel economy The energy efficiency of the methanol, gasoune

and SMD fuel cell vehicles is about 2/3 that of

the hydrogen fuel cell vehicle. The loss of

efftciency is due to several effects. First, there is _

15-25% energy loss in converting methanol,

gasoline or SMD to hydrogen. Secondly,

operation on reformate means that the fuel cell

has a lower efficiency. Thirdly, the vehicle weighs

IO-20% more with an onboard fuel processor.

Finally, for the methanol steam reformer, the

assumed 5 s reformer response time implies that

a significant fraction (40-50%) of the energy

must be routed through the peak power battery,

with energy losses in charging and discharging.

Range The vehicle range exceeds the PNGV goal of 380

miles (610 km), for all the fuel cell vehicle cases

considered in Table 2.

Vehicle capital cost Table 3 summarises our cost assumptions for fuel

cell vehicle drive train and fuel storage components

in high-volume mass production, based on a range

of estimates in the literature. Recognising that there

is still considerable uncertainty in these numbers,

two sets of assumptions are shown - one

corresponding to a “low” range of cost values for

mass-produced fuel cell, fuel processor, battery,

motor/controller and hydrogen storage, and the

other to a “high” range of values. Using projected

mass-produced component costs in Table 3 and

component sizes from Table 2, we can estimate the

total capital cost of drive train and fuel storage

components for each case (Table 4). The total drive

train cost ranges from about US$3400 to over

$7000, depending on the assumptions. Fuel cell

vehicles with onboard fuel processor systems have a

higher first cost than those with direct hydrogen

storage. This is due to extra costs for the fuel


processor, and because a larger capacity (and more

costly) fuel cell is needed to achieve the same

performance. The first cost of fuel cell vehicles with

onboard methanol steam reformers would be

higher than that for hydrogen fuel cell vehicles by

about $500-600/tar. We estimate gasoline or

SMD partial oxidation (POX) fuel cell cars would

cost $850-12OO/car more than hydrogen fuel cell

vehicles.

In summary, for the same performance,

hydrogen fuel cell vehicles are estimated to be

simpler in design, lighter, more energy-efficient

and less expensive than methanol, gasoline or

SMD fuel cell vehicles.

Comparison of refueling infrastructure requirements The relative simplicity and lower cost of the

hydrogen fuel cell vehicle must be weighed

against the complexity and cost of developing a

hydrogen refueling infrastructure. Here we

discuss the feasibility and cost of building new

fuel production, transmission and distribution

systems, comparing hydrogen to liquid fuels:

methanol, gasoline and SMD.

Development of refueling infrastructure for hydrogen vehicles Although hydrogen infrastructure is often cited

as a “show-stopper” for hydrogen vehicles, the

issue is not about technical feasibility. Large

quantities of hydrogen are produced and

delivered routinely for chemical applications

today, and the technologies to produce, store and

transport hydrogen are mature, well established

and commercially available. However, based on

studies conducted in the late 1980s and early

1990~,[~1 the cost of hydrogen infrastructure is

widely regarded as much higher than that for

other fuels. We have revisited this issue, and here

we summarise our results assessing the technical

feasibility and economics of developing a

hydrogen vehicle refueling infrastructure.15, ‘1

(Another comprehensive study on this topic was

undertaken by Directed Technologies Inc for

Ford Motor Company.[‘l)

A number of near-term possibilities exist for

producing and delivering gaseous hydrogen

transportation fuel, which employ commercial

technologies for hydrogen production, storage

and distribution. These include (see Figure 2):

(c) Hydrogen from chemical industry sources

(for example, excess capacity in refineries

which have recently upgraded their

hydrogen production capacity etc.), with

pipeline delivery to a refueling station.

(u’) Hydrogen produced at the refueling station

via small-scale steam reforming of natural

gas (in either a conventional steam reformer

or an advanced steam reformer of the type

developed as part of fuel cell cogeneration

systems).

(e) Hydrogen produced via small-scale water

electrolysis at the refueling station.

(a) Hydrogen produced from natural gas in a

large, centralised steam reforming plant, and

delivered by truck as a liquid to refueling

stations.

(6) Hydrogen produced in a large, centralised

steam reforming plant, and delivered via

local, small-diameter hydrogen gas pipeline

to refueling stations.

Fuel Cells Bulletin No. 16 0

In the longer term, other methods of hydrogen

production might be used, including gasification

of biomass, coal or municipal solid waste, or

electrolysis powered by off-peak hydropower,

wind, solar or nuclear power (Figure 3).

Sequestration of byproduct CO, (for example,

in deep aquifers or depleted gas wells) might be

done to reduce greenhouse emissions from

hydrogen derived from hydrocarbonsI’

Centralized reforming

(4 TRUCK DELIVERY

LH2 pump+ Er H2

W n PIPELINE DELIVERY

NG_ H2 I

Chemical by-product hydrogen

w Refinery EF H2 or Chemical Plant

H2 -

Onsite reforming reformer COMP. H2

Cd)

NG_

Onsite electrolysis (e) ELECTRICITY

1 , ,

,

I

Delivered cost of hydrogen transportation fuel

In Figure 4, we estimate the levelised cost of

compressed gas hydrogen transportation fuel

delivered to the vehicle at 5000 psi (350 bar), for

the near-term supply options shown in Figure 2.

Fuel costs are given in US$/GJ (on a higher

heating value basis, the energy cost of $l/gallon

gasoline is equivalent to $7,7/GJ). In this

example, we have calculated hydrogen costs based

on energy prices in the Los Angeles area, where

the natural gas cost is low ($28/GJ), and the cost

of off-peak power is relatively high (3 cents/kWh):

l Delivered fuel costs range from abet

$12-25/GJ or $1.6-3.3/gallon gasolin

equivalent.

l Truck delivery or onsite production vi steam reforming or electrolysis have th

advantage that the hydrogen could b provided where it was needed (at th

refueling site), without the need fc developing hydrogen pipelin infrastructure.

l Liquid hydrogen delivery might be attractiv

for early demonstration projects, since th

capital requirements for the refueling statio

would be relatively small.

If

.e

a :

e j

le I

e :

lr ’

e :

e :

e j n i

Onsite production of hydrogen via small-

scale steam reforming of natural gas is

economically attractive, based on advanced, low-cost reformers, which have recently

been introduced for stationary hydrogen production.L91

Onsite electrolysis would be somewhat more expensive than other options, largely because

of the relatively high cost of off-peak power

(3 cents/kWh) assumed here. If the cost of off-peak power were reduced from 3 to

l-l .5 cents/kWh (costs which are available in some locations with off-peak hydropower,

and may become more common in a future

deregulated electric utility), hydrogen costs would become more competitive.

A local gas pipeline bringing centrally

produced hydrogen to users could offer low delivered costs if there was a large, fa .!y

localised demand. Alternatively, a stl,lll demand might be served by a nearby, 1,. 3:-

cost supply of hydrogen (for example, a 1:~~ garage located near a chemical plant with

excess byproduct hydrogen).

Capital cost of building hydrogen refueling infrastructure In Figure 5 we show the capital cost of building a

hydrogen refueling infrastructure for various

near-term options. The range of infrastructure

capital costs for a hydrogen refueling system is

about $3 1 O-620 per car served by the system.

Some of the lower capital cost options (such as

liquid hydrogen delivery) can give a higher

delivered fuel cost than pipeline delivery or

ansite reforming (see Figure 4). Onsite small-

scale steam reforming is attractive with both a

relatively low capital cost (for advanced fuel cell

type reformers), and a low delivered fuel cost.

Developing refueling infrastructure for methanol FC vehicles In I995 the worldwide methanol production

capacity was about 28 million metric tonnes per

year, and about 23 million metric tonnes were

actually produced. About 90% of methanol is

produced from natural gas, although it would be

possible to produce methanol via gasification of

coal, heavy liquids, biomass or wastes (Figure 6).

The main uses of methanol are the production

of formaldehyde, MTBE and acetic acid.

A significant methanol distribution already

system exists. Of total world production,

roughly half (I2 million metric tonnes) was

shipped to remote users, 70% by sea and 30% by

rail, tank wagon or barge. Typically, tanker ships

transport methanol from production plants sited

near inexpensive sources of natural gas to marine

terminals. At the terminals, the methanol is

loaded into tank trucks and delivered to users.

If the entire 1995 methanol production

capacity were dedicated to producing fuel for


methanol fuel cell cars, we estimate that about

30 million cars could be fueled. Since the

capacity is not fully utilised at present, this

suggests that excess production capacity might

be enough to fuel up to a few million methanol

fuel cell cars worldwide.

Initially, to serve relatively small numbers of

methanol fuel cell cars, it would probably be

possible to provide methanol transportation fuel

using the existing methanol distribution system,

without building new methanol production

capacity. The only capital costs would be

conversion of gasoline refueling stations, marine

terminals and delivery trucks to methanol.[41

This has been estimated to cost about $50/car.[21

This strategy would work until the market for

automotive methanol exceeded the excess

production capacity in the system.

Bringing methanol to millions of fuel cell cars

would involve increases in methanol production

capacity and tanker capacity as well. The capital

cost for new tankers would be modest on a per

car basis, perhaps $4-25/tar. However, the

capital costs for new production capacity would

be significant. For a new 2500 tonne/day plant,

serving 0.9 million methanol fuel cell cars, the

capital cost wouid be about $440-75O/car. At a

larger plant size (10,000 tonnes of methanol per

day) serving 3.8 million cars, the capital cost

would be $290-500/tar.

At low market penetrations of methanol fuel

cell vehicles, infrastructure capital costs will be

small (probably less than $50/tar). However,

once methanol is used in more than perhaps a

million fuel cell vehicles, new production

capacity would be needed, bringing the capital

costs per car to levels similar to those for

hydrogen, about $340-800/ear, depending on

the assumptions (see Figure 7).

This is a surprising result. One would expect

that infrastructure costs for a liquid fuel like

methanol would be inherently much lower than

for a gaseous fuel like hydrogen. Certainly, if one

compares only distribution and refueling station,

costs, a methanol infrastructure is much less

costly to implement than a hydrogen

infrastructure, a view supported by earlier

studies of methanol and hydrogen

infrastructure.l*l But once a large level of

alternative fuel use is assumed, the picture

changes. In this case, the majority (about 90% or

more) of the capital cost of methanol

infrastructure development is due to building

new production capacity, rather than to

distribution systems and refueling stations.

Hydrogen production is somewhat less costly

than methanol production per unit of energy

output from the plant. (This is true because the

conversion efficiency of natural gas to fuel is

higher for hydrogen than for methanol

production.) Moreover,

H2 via Biomass, Coal or MSW Gasification BIOMASS, COAL or

H2 b

Solar or wind electrolytic hydrogen PV

Wind Turbine

H2 from hydrocarbons w/CO2 sequestration AA

NG. BIOMASS or COAL

IO underground storage

i-

S-

Reformer

Natural gas

q Central H2 production

n Pipeline H2 T&D

n Electrolyzer capital+O&M

n Storage cylinders

0 Compressor capital+O&M

q Electricity

q Liquid hydrogen

LH2 tank+pump

q Dispenser

q Labor

For Southern California energy prices. NG costs $3/MBTU; off-peak power costs 3 centsfkwh. Each refueling station dispenses 1 million scf H2/day.

Fuel Cells Bulletin No. 16 0 9

600

Natural Gas -> Methanol

q H2 production

n Liquefaction

Cntrl camp. +sto

0 Delivery

n Refueling station

Each refueling station dispenses 1 million scf H2 per day, serving a fleet of 9200 H2 fuel cell cars.

Central SMR plant produces 160 million scf/day, serving a total fleet of 1.4 million H2 fuel cell cars. Low demand case has 300 cars/sq.mi, high demand has 3000 cars/sq.mi.

MeOH Tanker

Marine

Terminal

t storage MeOH

Biomass, Coal or MSW -> Methanol

BIOMASS.

COAL OR

MSW n

MeOH !!L Gasifier

vehicles are estimated to be 50% more energy

effkient than methanol fuel cell cars (Table 2),

so that a given energy production capacity will

serve a larger number of cars.

The overall effect is that even with

hydrogen’s much higher distribution and

refueling station costs, the total capital cost of

infrastructure development per car

comparable for methanol and hydrogen, once

high level of fuel cell vehicle use is achieve<

The high cost of new methanol productio

capacity and the hydrogen vehicle’s hight

energy efficiency combine to “level the playin

field”.

is : a :

i. n I

:r :

g i

Cost of infrastructure for gasoline FC vehicles For this study, we have assumed that there is no

extra capital cost for developing gasoline

infrastructure for fuel cell vehicles. This may be

an oversimplification. For example, if a new type

of gasoline (e.g. very low sulfur) is needed for

gasoline/POX (partial oxidation) fuel cell

vehicles, this would entail extra costs at the

refinery. The costs of maintaining (and gradually

replacing existing equipment with new) or

expanding the existing gasoline infrastructure are

not considered.

Cost of refueling infrastructure development for SMD FC vehicles Modest-sized plants producing synthetic mic ‘le

distillates (SMDs) from natural gas have b :n

built, and construction of larger plants is bclng

considered. Shell currently operates a 12,500

bbl/day plant producing SMD from natural gas.

Assuming that the energy content of SMD is the

same as diesel fuel, this plant produces 76,875

GJ/day, enough to fuel a fleet of 1.36 million

SMD/POX automobiles. The capital cost is

$55,00O/bbl/day (or $687.5 million). The

capital cost per car for the production plant is

then about $505/tar. A proposed 50-100,000

bbllday plant by Exxon has been estimated to

cost $24,000/bbl/day.[101 The capital cost of the

production plant would be about $22O/car, for

this scale of production, which could serve

perhaps 5.5-l 1 million SMD/POX cars.

The total capital cost of developing a refueling

infrastructure for SMD is comparable to that for

methanol or hydrogen, assuming that no extra

costs for SMD are incurred at refueling stations,

marine terminals or in ocean shipping.

Comparison of total infrastructure costs (on and off the vehicle) If we define “infrastructure” to mean all the

equipment (both on and off the vehicle)

required to bring hydrogen to the fuel cell, it is

clear that hydrogen, methanol, gasoline and

SMD fuel cell vehicles all entail infrastructure

capital costs. For gasoline vehicles, these costs are

entirely for onboard fuel processing, assuming

that no extra off-vehicle gasoline infrastructure

costs are incurred for using fuel cells. For

methanol and SMD, there are “infrastructure”

costs both on the vehicle (for fuel processors)

and off the vehicle (for fuel production,

distribution and refueling systems). In the case

of hydrogen, there is no “onboard” infrastructure

cost (i.e. no fuel processor) and all the

infrastructure capital cost is paid by the fuel

producer (and passed along to the consumer as a

higher fuel cost).


In Figure 7 we combine our estimates of the

costs of alternative fuel cell vehicles and off-

board refueling infrastructure. Our estimates

show that methanol fuel cell cars are likely to

cost $500-600/tar more and gasoline or

SMD/POX fuel cell vehicles $850-1200/ear

more than comparable hydrogen fuel cell

vehicles. The added cost of off-board refueling

infrastructure for hydrogen is in the range of

$310-620/vehicle. For methanol the off-board

refueling infrastructure costs will be small (less

than $50/tar) until new production capacity is

needed (for example, until the methanol fuel cell

car fleet exceeds perhaps 1 million cars). Once

new methanol production capacity is needed,

methanol infrastructure capital costs off the

vehicle would be $340-800/ear. For methanol

the total on and off the car is then about

$840-1400/tar. For SMD, the capital cost for

off-vehicle infrastructure development would be

$220-500/tar (for new SMD production plants)

and $850-1200/ear on the vehicle, for a total of

$1070-1700/tar.

To within the accuracy of our cost projections,

it appears that the total -capital cost for

infrastructure on and off the vehicle would be

roughly comparable for methanol and gasoline

fuel cell vehicles, with hydrogen costing

somewhat less and SMD somewhat more. In the

longer term (once new production capacity is

needed), hydrogen appears to be the least costly

alternative.

Fuel strategies for fuel cell automobiles Automobile manufacturers developing fuel cell

vehicles are exploring several fuel possibilities,

especially hydrogen, methanol and gasoline.

Automakers are emphasising methanol or

hydrogen as near-term fuel options in their

demonstration vehicles. DaimlerChrysler and

Honda are both developing methanol and

hydrogen experimental fuel cell automobiles.

Although DaimlerChrysler’s plan is to launch

commercialisation in 2004 with methanol, it is

keeping the hydrogen option open, particularly for

fleet vehicles (hydrogen heel cell cars are planned as

part of the California Fuel Cell Partnership). Ford

and Mazda are in a joint project with

DaimlerChrysler. Ford has done a significant

amount of work with hydrogen, as shown in its

recent I’2000 car. Toyota, Opel (General Motors)

and Nissan are each developing methanol fuel cell

cars. GM has worked with methanol reformers,

but is reportedly examining all options.

For the longer term, DaimlerChrysler and

Shell are pursuing onboard reformation of

gasoline in partial oxidation (POX) systems. In

addition Epyx is developing a multi-fuel-capable

1250 r 1000

1 1 Fuel production

n Fuel delivery

n Refueling station

0 Onboard fuel processor

0 z al -a

Early Large scale 8% infrastructure infrastructure Q

devel. No new production capacity

Off-vehicle Extra cost of fuel infrastructure processors on vehicles

POX fuel processor for use in fuel cell vehicles.

This approach would have the important

advantage of using the existing gasoline

infrastructure. However, many technical

challenges remain in developing onboard

gasoline fuel processors, and gasoline is generally

seen as a longer-term possibility than methanol.

Assuming that onboard gasoline reformers are

successfully developed, there are several

evolutionary fuels strategies which have been

proposed for fuel cell automobiles.

Scenario 1: Gasoline/POX fuel cell cars + Hydrogen fuel cell cars Introduction of fuel cell cars with onboard

gasoline fuel processors would allow the rapid

introduction of large numbers of fuel cell

automobiles to general consumers without

changes in the refueling infrastructure. This

might reduce the cost of fuel cells via mass

production to levels where they could compete

with advanced internal combustion engine

vehicles. Once the cost of fuel cells is reduced, it

can be argued that there would be economic

pressure to move to hydrogen fuel cell vehicles,

because of their lower first cost and lifecycle

cost.[2] Environmental and energy supply

concerns would be key motivations for switching

from gasoline. In the longer term, a widespread

hydrogen refueling infrastructure would be

implemented for hydrogen fuel cell cars. This

would allow diverse primary sources to be used

for fuel production, and enable significant

reductions in greenhouse gas emissions.

Scenario 2: Hydrogen moves from centrally refueled fleets to general automotive markets In this scenario, hydrogen is implemented first

in centrally refueled fleet vehicles (such as buses

and vans), and later moves to general automotive

markets. Figure 7 suggests that this strategy

might involve the lowest overall capital outlay,

counting both vehicle costs and infrastructure

costs. However, this scenario faces a “chicken

and egg” problem in reaching beyond niche

markets, and getting enough fuel cell cars on the

road to bring down costs. (Until large numbers

of hydrogen cars are present, it will be difficult to

justify a geographically widespread hydrogen

fuel distribution system. But general automotive


use depends on widespread availability of fuel.)

Implementing this strategy would assume a

societal decision to move towards a zero-

emissions transportation system, because of

environmental concerns.

Scenario 3: Methanol FC vehicles are introduced for fleet applications, moving to general automotive markets; eventually a switch to hydrogen may be implemented In this scenario, methanol fuel cell vehicles are

introduced first in centrally refueled fleet

applications. The advantages are that methanol

is easier to store and handle than hydrogen, and

easier to reform than gasoline. The

disadvantages are that methanol faces the same

“chicken and egg” problem as hydrogen in

reaching general automotive markets, and that

the methanol vehicle will be more costly than

one with hydrogen. Initially, methanol

infrastructure costs will be much less than those

for hydrogen, but once methanol makes

significant penetration into automotive

markets, costly new production capacity will be

needed, so that off-vehicle infrastructure costs

alone might be comparable to those for

hydrogen.

In the near term the most likely source for

methanol production is remote natural gas.

Ultimately, other feedstocks for making methanol

could be used such as biomass, wastes or coal.

Eventually, a switch from methanol to hydrogen

might occur, because hydrogen vehicles would be

lower-cost, and the capital costs for developing a

new fuel production and delivery infrastructure

would probably be comparable for hydrogen and

methanol. Moreover, a hydrogen-based

transportation system would allow lower

greenhouse gas emissions than one based on

methanol. (Greenhouse gas emissions would be

lower, since less primary energy would be used

with hydrogen than with methanol. Also,

sequestration of CO, might be possible if

hydrogen is produced from hydrocarbons.) A

serious disadvantage of this scenario is that the

fuel infrastructure would have to be changed

twice (from gasoline to methanol, then from

methanol to hydrogen.)

In the near term (the next five years or so), it

seems clear that methanol or hydrogen will be the

fuels of choice for fuel cell vehicles. The optimum

mid-term fuel strategy for fuel cell vehicles is

uncertain, awaiting the results of demonstrations

of alternative fuel cell vehicle types. In the long

term, it appears that hydrogen has advantages over

gasoline, methanol and SMD in terms of vehicle

cost, complexity and fuel economy, and

environmental and energy supply benefits. The

total capital cost of implementing fuel cell vehicles

(counting both onboard fuel processors and off-

vehicle fuel supply infrastructure) appears to be

lowest for hydrogen, as well.

Conclusions Our simulations indicate that for the same

performance, hydrogen fuel cell vehicles are

simpler in design, lighter in weight, more\

energy-efficient and lower-cost than those with

onboard fuel processors.

Vehicles with onboard steam reforming of

methanol or partial oxidation of gasoline have

about two-thirds of the fuel economy of direct

hydrogen vehicles. The efficiency is lower because

of the conversion losses in the fuel processor

(losses in making hydrogen from another fuel),

reduced fuel cell performance on reformate,

added weight of fuel processor components, and

effects of fuel processor response time.

For mid-size automobiles with PNGV type

characteristics (base vehicle weight - without

power train and fuel storage - of 800 kg,

aerodynamic drag of 0.20, and roliing resistance

of 0.007), fuel economies (on the combined

FUDSlFHDS driving cycle) are projected to be

about 106 miles per equivalent gallon of gasoline

(mpeg) for hydrogen fuel cell vehicles, 69 mpeg

for fuel cell vehicles with onboard methanol

steam reforming, 71 mpg for onboard gasoline

partial oxidation, and 71 mpeg for onboard

partial oxidation of SMD.

Based on projections for mass-produced fuel

cell vehicles, methanol fuel cell automobiles are

projected to cost about $500-600/tar more than

comparable hydrogen fuel cell vehicles. Gasoline

or SMD/POX fuel cell automobiles are

projected to cost @SO-I200 more than

hydrogen fuel cell vehicles.

The capital cost of developing hydrogen

refueling infrastructure based on near-term

technologies would be about $3 lo-620/tar,

depending on the type of hydrogen supply.

Methanol infrastructure capital costs should be

low initially (less than $50/tar), but would

increase to $340-800/tar once new methanol

production capacity was needed. For SMD the

cost would be about $220-500/tar for new

production capacity only. No extra costs are

assumed for developing gasoline infrastructure.

Given the projected increasing demand for

transportation fuels worldwide (which would

require new gasoline production capacity), this

may be an underestimate.

If we define “infrastructure” to mean all the

equipment (both on and off the vehicle)

required to bring hydrogen to the fuel cell, we

find that the cost is roughly comparable for

methanol, gasoline and SMD/POX fuel cell

0 Fuel Cells Bulletin No. 16

vehicles. Surprisingly, hydrogen appears to entail

the lowest overall capital costs in the longer

term, when new fuel production capacity is

needed for methanol or SMD.

Our simulations indicate that hydrogen is the

preferred fuel for fuel cell vehicles in terms of

vehicle weight, simplicity, cost and fuel

economy. The lifecycle cost of transportation is

projected to be less with hydrogen, because the

vehicle first cost is lower, and the fuel economy

about 50% higher. This suggests that there will

be an internal market dynamic that will drive the

system towards the development of a hydrogen

infrastructure once fuel cell vehicles have been

commercialised in large enough numbers to

bring down the cost via mass production.

Moreover, use of hydrogen fuel opens -be

possibility of a future low COz-emitting, fo *iI-

based energy system in which CO, is genec :d

as a by-product of H, manufacture at centrali cd

facilities and sequestered underground, at low

incremental cost.[81

Like compressed natural gas or methanol,

hydrogen faces the issue of reaching beyond

centrally refueled fleet markets. In addition,

technical issues remain to be resolved for fuel

processors. The choice of fuel for the first

generation of commercial fuel cell automobiles

will be informed by data from demonstrations of

alternative types of fuel cell vehicles over the next

few years. Ideally, this choice should be made to

give fuel cells the best chance of reaching general

mass markets, paving the way for economically

competitive, mass-produced fuel cell vehicles

and long-term use of hydrogen.

Acknowledgments We would like to thank the US Department of

Energy Hydrogen R&D Program, the Energy

Foundation, the Link Energy Foundation and

the American Association of Universiry Women

Educational Foundation for their support.

References 1. M. Steinbugler: “How far, how fast, how

much fuel: Evaluating fuel cell vehicle

configurations”. Presented at Commercializing

Fuel Cell Vehicles Conference, Chicago,

September 1996 (Intertech Conferences, USA).

2. J. Ogden, T. Kreutz, M. Steinbugler: “Fuels for

fuel cell vehicles: Vehicle design and infrastructure

issues”. Society of Automotive Engineers

Technical Paper 982500, October 1998.

3. J.M. Ogden, M.M. Steinbugler, T.G. Kreutz:

“A comparison of hydrogen, methanol and

gasoline as fuels for fuel cell vehicles:

Implications for vehicle design and

infrastructure development”, J Power Sources

79(2) (June 1999) 143-168.

4. “Assessment of costs and benefits of flexible

5. J.M. Ogden: “Developing an infrastructure

for hydrogen vehicles: A Southern California

case study”, Znt. J Hydrogen Energy 24(8)

and alternative fuel use in the US transportation

(August 1999) 709-730.

6. J. Ogden: “Prospects for building a hydrogen

sector”. US Department of Energy (Policy,

energy infrastructure”, to appear as a chapter in

Annual Reviews of Energy and the Environment

Planning & Analysis) report DOE/PE-0095P

24 (1999).

Washington, DC, August 1990.

7. “Hydrogen Infrastructure Report”. Directed

8. R.H. Williams: “Fuel decarbonization for fuel

Technologies Inc, Air Products & Chemicals,

cell applications and sequestering of the

separated CO,“. Princeton University, Center

for Energy & Environmental Studies, Report

BOC Gases, Electrolyser Corporation and Praxair

no. 296 (January 1996).

9. T. Halvorson, I? Farris: “Onsite hydrogen

Inc; prepared for Ford Motor Company under

generator for vehicle refueling application”.

Proceedings of I997 World Car Conference,

US Department of Energy contract DE-AC02-

Riverside, California (January 1997) 33 l-338.

94CE50389 (July 1997).

10. P. Grimes, Patrick Grimes & Associates,

private communications (1998).

11. C.E. Thomas, R. Sims: “Overview of

onboard liquid fuel storage and reforming

systems, fueling aspects of hydrogen fuel cell

powered vehicles”. Society of Automotive

Engineers, Proceedings of Fuel Cells for

Transportation TopTec Conference, Arlington,

Virginia, USA (April 1996).

For more information, contact: Dr Joan M.

Ogden, Center for Energy & Environmental Studies,

Princeton University, Princeton, NJ 08544, USA. Email: [email protected]

Research Trends DMFCs for road transportation The direct methanol-air fuel cell is reviewed here

with special attention to its use in road

transportation applications. The history of the

technology is discussed, and the various problems

associated with its commercial development are

assessed, in particular the mechanisms of the

electrode reactions, the development of effective

catalysts, and the possible electrolytes which

can be used. The barriers to successful

commercialisation are reviewed and suggestions

for future work are given.

B.D. McNicol, D.A.J. Rand, K.R. Williams: J

Power Sources83(1/2) 15-31 (October 1999).

Corrosion of stainless steel Corrosion of cell components is a major problem

in MCFC development. This work describes the

effect of sensitisation on the corrosion

characteristics of AISI-type 3 16L stainless steel in

a 62/38 lithium-potassium carbonate eutectic

melt in the cathode-gas environment. Increasing

the sensitisation treatment time causes the

corrosion potential to shift in the cathodic

direction. The passive film becomes more

unstable and supports a high passive current, i.e.

the substrate is more susceptible to intergranular

corrosion (IGC). Morphological observation of

samples immersed in a carbonate melt reveal a

change from initial IGC to localised corrosion. A

combination of a Cr-depleted region due to

sensitisation and decreasing oxygen concentration

from top to bottom of the oxide layer, explains the

change in corrosion morphology.

K.S. Lee, K. Cho,T.H. Lim, S.-A. Hong, H. Kim:

J Power Sources 83(1/2) 32-40 (October 1999).

Gas channel height in MCFC stack An investigation was made of the relationships

between the gas channel height, gas-flow

characteristics and gas-diffusion characteristics

in a plate heat-exchanger type MCFC stack. The

effects of the channel height on the uniformity

and pressure loss of the gas flow are evaluated by

numerical analysis using CFD code. The effects

of the channel height on the reactive gas

concentration distribution perpendicular to the

channel flow are evaluated by analytical solution

of the 2D concentration transport equation. The

appropriate gas channel height in the MCFC

stack was investigated in view of the results for

uniformity and pressure loss of the gas flow, and

for distribution of the reactive gas concentration.

H. Hirata, ‘T. Nakagaki, M. Hori: 1. Power

Sources 83(1/2) 41-49 (October 1999).

New MCFC cathode The solubility of a nickel oxide cathode in

electrolyte is a major technical obstacle to MCFC

commercialisation. Lithium cobalt oxide is a

candidate material for MCFC cathodes because of

its low solubility and the rate of dissolution into

the melt is slower than for nickel oxide, although

the electrical conductivity of LiCo02 is lower

than that of nickel oxide. Thus, nickel oxide has

been coated with stable LiCoO, in carbonate by a

PVA-assisted sol-gel method to give a LiCoOz-

coated NiO (LC-NiO) cathode. Raman spectra

show that the structure of LC-NiO is different

from of nickel oxide, and that a LiCo l-yNpZ phase is formed during heat-treatment of the

cathode. The mean voltage of the unit cells is

0.80 V using a NiO cathode and 0.85 V with a

LC-NiO cathode at a current density of 150

mA/cm*. The solubility of the LC-NiO cathode

in molten carbonate electrolyte is half that of the

NiO cathode after 300 h at 650°C.

S.T. Kuk, Y.S. Song, K. Kim: J Power Sources

83(1/2) 50-56 (October 1999).

SOFC stacks using extruded honeycomb elements This SOFC stack concept comprises “condensed

tubes” like extruded honeycomb sections of

ceramic electrolyte (Zr02-based) and

interconnectors of nickel sheet, allowing low-

cost production. The cells are self-supported

with in-plane conduction. A demonstrator

model stack of five honeycomb elements and six

nickel sheet seals/interconnectors was built and

operated for 860 h at 1000°C. Volumetric power

densities of 160 kW/m3 were obtained with

H,lair, and close to 200 kW/m3 with H,/O,. A

power density of more than 2 kW/m’ active area

should be attainable with air as oxidant. A

module consisting of 100 honeycomb sections of

each 6x6 cells with overall active dimensions of

6x6~12 cm3 could provide 1 kW (230 kW/m3).

The elimination of expensive materials such as

lanthanum chromite and/or high-temperature

alloys is also favourable. Extrusion and sintering

of honeycomb elements should be possible at

costs per active area comparable to tape-cast

electrolyte foils.

M. Wetzko, A. Belzner, F.J. Rohr, E Harbach: J

Power Sources 83(1/2) 148-155 (October 1999).

Medium-temperature SOFC anode The polarisation properties and microstructure

of Ni-SDC (samaria-doped ceria) cermet anodes

prepared from spray pyrolysis composite powder,

and element interface diffusion between the

anode and a Lao,sSr,.lGa0,8Mg0.203-6 (LSGM)

electrolyte are investigated as a function of anode

sintering temperature. The anode sintered at

1250°C displays minimum anode polarisation,

while 1300°C gives the best electrochemical

overpotential (27 mV at 300 mAlcm* at SOO’C).

The anode ohmic loss gradually increases with

increasing sintering temperature below 1300°C

and sharply increases at 1350°C. SEM shows a

clear grain growth at sintering temperatures

above 1300°C. The anode microstructure

appears optimal at 13OO”C, in which nickel

particles form a network with well-connected

SDC particles finely distributed over the nickel

particle surfaces. The anode sintered at 1350°C

has severe grain growth and an apparent


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