Today, two innovations lead the roster of answers in the
search for pollution-free sources of energy. The first, electric
batteries, are already marketable but also plagued by concerns over high
recharge-time and suboptimal performance in cold climes.
Hydrogen
fuel cells (HFCs), the other solution, face a different problem. Asian
car-makers are ready with HFCs running at 60 per cent efficiency and
already 50 per cent cheaper to make than in 2011.
However, there is a
conspicuous absence of hydrogen-refuelling stations owing to logistics
issue.
Nonetheless, hydrogen fuel cells continue to
receive upgrades. This week, researchers from the Illinois Institute of
Technology (IIT), Chicago, announced another one that increased their
performance and lifetime by altering just one component.
In a paper published in the Proceedings of the National Academy of Sciences, the researchers detail how an alternative support to disperse the cell’s catalyst is the key.
An
HFC works by consuming hydrogen that reacts with oxygen from the
atmosphere over platinum nanoparticles as catalyst to produce water and
electricity; the electricity powers a motor stationed in an external
circuit between the anode and the cathode of the cell.
The
platinum is dispersed by high surface-area carbon (HSAC) supports. The
HSAC supports have a tendency to corrode during vehicle start-up and
shutdown because of electric potentials at the anode and cathode.
“As
the carbon support is lost, more of the platinum nanoparticles are
detached from the support surface and become inaccessible for reaction,”
Dr. Vijay Ramani, professor of chemical engineering at IIT and
principal investigator in the project said in an email to this
Correspondent.
However, carbon has been the substance of choice because it is cheap, abundant, and has high electronic conductivity.
Instead,
Dr. Ramani and his colleagues synthesised a compound called
titanium-ruthenium oxide (TRO) to support the platinum nanoparticles.
Titanium oxide formed the rigid, corrosion-resistant support structure
while a coating of ruthenium oxide allowed electrons to be conducted
through the frame.
Neither titanium- or
ruthenium-oxide can be further oxidized, leaving them less harmed by
corrosion. — an oxidation reaction — which commonly occurs during
start-up and shutdown of the cell.
In fact, after
5,000 start–stop cycles during a test, the team found the loss in
surface area due to corrosion was 16 per cent for TRO, against 39 per
cent for HSAC. Also, with TRO, losses in catalyst activity were
diminished by 70 per cent, increasing performance.
Additionally,
Dr. Ramani found that their compound was also able to prevent the
platinum nanoparticles from oxidising. This happens when platinum gets
exposed to potentials of 0.9-1 V—values reached when the HFC transitions
between full- and no-load, 0.65-0.95 V.
“Due to
beneficial electronic interactions between the nanoparticles and the
TRO, called strong metal support interactions, platinum dissolution was
far lesser than it would have been with HSAC, with which the
nanoparticles wouldn’t have had such interactions,” explained Dr.
Ramani.
Even though titanium and ruthenium are
costlier than carbon, an analysis by the IIT team found that more than
90 per cent of the cell’s costs were incurred by the use of platinum as
catalyst, irrespective of scale.
By no means an incentive, Dr. Ramani feels this is not prohibitive, either.
The
distinction for that is taken by the absence of hydrogen-refuelling
stations. “Economy of scale in manufacturing will necessitate a market
for fuel-cell vehicles, which in turn will require a hydrogen-fuelling
station to be in place. This is a classic chicken-egg issue,” quipped
Dr. Ramani.
