Metal, Not Hydrogen?
[Dr. Bortrum returns June 21]
Am I doomed? Yesterday I awoke, looked at the clock and it
was 6:06 AM on 6/06/06 – how Satanic can it be? Last week I
discussed hybrid vehicles, and as an example chose the Toyota
Prius, the first hybrid to garner any significant market here in the
U.S. At the polls yesterday (it was primary election day in NJ),
one of the poll workers is our friend who owns a Prius. I told her
that I thought I heard of a recall on the news last week. She
hadn’t heard any such news and said they’d have to take it away
from her by force – she loves the car! Keeping the ominous 666
date in mind, I checked on msnbc.com and, sure enough, there is
a massive worldwide recall by Toyota that includes about
170,000 Priuses in the U.S. for a possible steering defect. Maybe
I’ll keep my 1997 VW Jetta a bit longer.
In last week’s column, I expressed skepticism about the future of
hydrogen fuel cells as power sources for cars and about the
future of pure battery-powered electric vehicles. Then I realized
that for quite some time I have not been following the battery
field as closely as I should. For example, an article by Owen
Edwards in the June issue of Smithsonian told me that I’d missed
a battery-related funeral at the Hollywood Forever Cemetery in
Los Angeles in 2003. To the strains of a bagpipe, a white hearse
circled the cemetery followed by a procession of mourners
driving their General Motors EV1s. The EV1 was GM’s sleek
production model battery-powered electric vehicle. There were
about 1,100 of them manufactured and they were leased to
drivers in California and Arizona starting in 1996. The mourners
in LA found their leases expiring and almost all the EV1s were
to be destroyed. So much for GM’s electric vehicle, with its
range of about 100 miles.
At the bottom of my pile of unread journals, I found the Autumn
2005 issue of Batteries & Energy Storage Technology (BEST), a
magazine targeting manufacturers and users of electrochemical
power. One of the articles, “Hydrogen future? What Future?”,
dealt with the views of one Ulf Bossel of the European Fuel Cell
Forum. Ulf concludes that cars powered by hydrogen fuel cells
don’t have a chance. He considers biomass fuels such as ethanol
or biodiesel in hybrid vehicles as the way to go.
What really caught my attention in the BEST magazine was a
section on a different kind of fuel cell, the zinc-air fuel cell
(ZAFC). If you’re hard of hearing, you’ve used many small
button cells to power your hearing aid. The overwhelming
majority of these cells are zinc-air batteries. Zinc is the active
material in one electrode while oxygen (from the air) is the active
material in the other electrode. The hearing aid battery is neat in
that you don’t have to store the oxygen in the battery. It’s free,
comprising about 20% of our air.
When you put the battery in your hearing aid, you open a tab to
let the air in and the battery starts working. Because you don’t
have to pack oxygen in the battery initially, you have room for
more zinc and the battery lasts longer. Although the chemistry is
a bit more complicated, as the battery discharges zinc reacts with
oxygen to form zinc oxide. In the hydrogen fuel cell, hydrogen
reacts with oxygen to form a “hydrogen oxide”, water.
With a hydrogen fuel cell in your car, when you run low on
hydrogen you would stop at your “gas” station and fill up your
(pressurized) tank with hydrogen. Having had a relatively mild
hydrogen explosion in my lab at Bell Labs, I wouldn’t feel all
that comfortable with the operation. Suppose, instead of a
hydrogen fuel cell, we use a very large version of a hearing aid
battery to drive our car. What happens when most of the zinc
has turned to zinc oxide? We drive into a “zinc” station, pull out
the zinc electrode and replace it with a new one. Now we have a
zinc-air fuel cell, ZAFC, with zinc being the fuel we replace.
Oxygen in the air is the other fuel.
What happens to that zinc oxide? It’s returned to the plant where
it’s converted back to zinc for refueling another vehicle. The
ZAFC compares favorably with the hydrogen fuel cell. The
latter forms water, a benign compound, and the ZAFC forms zinc
oxide, a nontoxic and recyclable material. Zinc also has the
advantage that the most of your common “dry” cells, e.g., those
ubiquitous AA and 9-volt batteries, have zinc electrodes – we’re
comfortable with zinc and know how to handle it.
ZAFCs have received little media attention in spite of some
promising results in powering vehicles. The costs of ZFAC
technology were not competitive until the recent run-up in gas
prices. However, at current levels, ZAFCs become more
competitive and several companies have entered the arena with
serious programs in the automotive field.
One of the companies is the Electric Fuel Transportation
Company (EFTC), which conducted an impressive two-year test
of zinc-air powered postal vans in Germany and Sweden back in
the late 1990s. A subsidiary, Electric Fuel Ltd., built a full-size
(40-foot) bus capable of a full day’s operation on battery power.
General Electric cooperated in the development of the propulsion
system. The bus was demonstrated in various cities including
Washington, D.C. and reportedly received positive responses
from the public as well as various government officials. With
today’s fuel prices, it may be that zinc-air powered buses will be
cheaper to run than diesel-powered buses. EFTC hopes to have a
thousand of their buses running in North America by 2013.
A subsidiary of Reveo, Inc. called eVionyx has worked with
smaller vehicles. The company’s “Vision” as detailed on its
Web site is certainly a laudable one. It points out the problems
inherent in the much touted “hydrogen economy” in which
hydrogen fuel cells play the key role. The problems include the
high cost of producing, handling and shipping of hydrogen. The
company’s solution is a “metal economy” in which metals such
as zinc, aluminum and magnesium are the energy carriers.
In a zinc metal economy, the zinc oxide from the zinc-air fuel
cells would be recycled and converted back to zinc metal by
using electrochemical means. The power to do this would be
derived from hydro, wind or solar in the ideal scenario. The
company envisions using metal-air technology to power small
and larger vehicles and has demonstrated ZAFCs in vehicles
ranging from motor scooters to cars. In 2000, eVionyx set what
they say is the Guinness Book of Records world record of 214.7
miles on public roads for a modified production automobile
powered by a metal-air fuel cell on a single charge/refueling.
In 2003 in Malaysia, eVionyx ran a trial of a hybrid Honda
Insight, a two-seater car, modified to have an all-electric drive.
In this case a zinc-air fuel cell was combined with a nickel-zinc
rechargeable battery. The range on public roads was over 300
miles, another world record, according to the BEST article. With
ranges of 200-300 miles, metal-air powered vehicles seem a
more practical approach than the lamented battery-powered EV1.
Years ago when I was in the battery game, an aluminum-air
battery was hot for a while. We used to joke that if we ran out of
power we could round up discarded beer cans to power our way
home. In a “metal economy” that might not be as ridiculous as
NOTE: No column next week – Bortrum’s attending his 60th
college reunion and visiting his wife’s relatives in Pennsylvania.
Allen F. Bortrum