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.
