Frank Markus
NEWS I OPINION I GOSSIP I STUFFTechnologue
It’s also possible
to burn ammonia
in an internal
combustion
engine, but it’s
tricky to ignite
and burns slowly,
so at best it’d
be a tractor/
agricultural fuel.22 MOTORTREND.COM JUNE 2020I
’ve long been a hydrogen fuel cell skeptic. But after
laying out my case against “the fuel of the future” in
a recent drive comparison of the Toyota Mirai and
Hyundai Nexo, a reader from Down Under pointed
me to recent research by Australia’s Common-
wealth Scientific and Industrial Research Organisation
(CSIRO) that promises to address many of my concerns
regarding hydrogen distribution by making hydrogen
from ammonia at the pump.
These days hydrogen is typically shipped in ready-
to-use liquid or gas form, but the liquifying process
consumes 30 percent of its eventual energy content, and
further losses occur from inevitable boil-off
in transit. What the Aussies are proposing is
to transport it as liquid ammonia and then
convert it to hydrogen at the point of sale.
Oz has access to far more renewable energy
than it knows what to do with. It’s the globe’s
most solar-energy-rich country, receiving 7 to
8 kW-hr per square meter of solar radiation per
day across the entire continent; there’s also abundant
ocean tide energy and plenty of wind, as well. So the
government is keen to export that green energy, and
easily transportable liquid ammonia (NH 3 ) produced
without generating any CO 2 looks like a great way to do so.
Most ammonia produced today involves hydro-
carbon feedstocks and hence produces CO 2. CSIRO
proposes producing hydrogen by electrolyzing water
and combining it with nitrogen separated from air.These gases are then compressed and fed into the same
Haber–Bosch synthesis reactor used for hydrocarbon-
based ammonia production (which involves iron-based
catalysts, temperatures of 750 to 930 degrees, and pres-
sures of 2,200 to 3,600 psi). Total energy input is roughly
10 to 12 kW-hr/kilogram of ammonia—all of it clean.
There are no ocean-going hydrogen tanker ships, but
ammonia is routinely shipped by sea. Now CSIRO, in
conjunction with Fortescue Metals Group, has devel-
oped a novel two-step process to convert ammonia into
pure hydrogen gas.
The chemical reaction starts off in a ruthenium catalyst
that cracks the ammonia into hydrogen
and nitrogen at 840 degrees. Then it flows
through a second set of tubes involving a
vanadium membrane, which filters the H 2
from N 2 at 640 degrees. The hydrogen then
gets bubbled through a water bath to remove
any remaining ammonia gas, which is toxic to
a proton-exchange membrane fuel cell. The
proof-of-concept prototype has produced 99.99 percent
pure hydrogen. A commercial-scale version is currently
under development.
The cracking process requires energy, and it also
involves losses—some ammonia boils off or fails to crack,
and some hydrogen escapes, as well, plus it must then be
pressurized for dispensing into a vehicle. The American
Chemical Society conducted research into the “round-trip
efficiency,” or net useful propulsion energy available at the
wheels of the fuel cell vehicle divided by the total energy
required to produce, transport, compress, and dispense
the hydrogen. It found the process efficiencies to be as
follows: ammonia production: 58.8 percent; ammonia
cracker/separator: 75.9 percent; hydrogen compression/
dispensing: 88.0 percent; fuel cell vehicle: 48.0 percent.
Overall RTE: 19 percent.
California Fuel Cell Partnership research pegs
California hydrogen production/distribution efficiency
at 65 percent, with vehicle efficiency averages ranging
from 36 to 44 percent, for RTE of 23 to 29 percent. But
remember that in the Aussie analysis all the hydrogen/
ammonia production energy was renewable and carbon
free. Only about a third of California’s hydrogen currently
comes from carbon-free renewable sources.
I just feel better knowing that in this scenario, every
hydrogen atom can be happily married to a
nitrogen right up until it’s ready to board my
FCEV, shortly after which it will be reunited
with its true love, oxygen. These happier
hydrogens are almost never plotting an escape,
and they seem way greener than the ones we’re
driving around using as fuel nowadays. QFertilizing fuel cells by making
H
2from ammonia at the pump
TRAMINO(^) NH 3