Solving the Longstanding Durability Issues of Hydrogen VehiclesJuly 16, 2020 by Gary Elinoff
Can "oiling" the electrodes of automotive fuel cells prevent their degradation?
Unlike their larger, utility-scale counterparts that run continuously, automotive fuel cells are frequently turned off and on, allowing electrodes to corrode during the off state due to unwanted chemical reactions. The introduction of a specialized catalyst is shown to contain the problem.
A research team at Pohang University of Science and Technology (POSTECH) employed a catalyst to solve corrosion in fuel cells occurring when hydrogen cars are shut down.
The catalyst, platinum-hydrogen tungsten bronze (Pt/HxWO3), has been demonstrated to promote hydrogen oxidation and selectively suppress oxygen reduction reactions (ORR).
For some chemical insight, W is the chemical symbol for tungsten, and Pt, H and O stand for platinum, hydrogen, and oxygen, respectively. HxWO3 is familiar to chemists as hydrogen tungsten bronze.
The Metal-Insulator Transition Phenomena
The project focused on the Metal-Insulator Transition (MIT) phenomenon, which can selectively change materials' conductivity depending on the surrounding environment. In this study, insulator characteristics were obtained with high oxygen pressure and metal characteristics when hydrogen pressure is high.
Tungsten bronze changes conductivity through the insertion and removal of protons. When the fuel cell is operating, applying the MIT phenomenon of WO3 results in maintaining the H-WO3 conductor state with the insertion of a proton—when the fuel cell is off, mixed air is drawn in, increasing the oxygen pressure. This causes a change into WO3, which stops the unwanted electrode reaction, halting the cathode's corrosion.
When the automotive fuel cell turns off and oxygen rushes in, the MIT Phenomena provides protection against electrode degradation. Image credited to POSTECH
The Pt/HxWO3 served as a selective hydrogen oxidation reaction (HOR) catalyst that was imparted by the metal-insulator transition phenomenon. It showed significant results for membrane electrode assemblies, which are defined as an aggregation of electrolytic membranes, anode electrodes, and cathodic poles.
Automotive fuel cells employing the demonstrated catalyst exhibit over twice the durability of conventional commercial Pt/C catalyst materials during fuel cell shut-down conditions.
Professor Yong-Tae Kim, who led the research, commented, "This research has dramatically improved automotive fuel cells' durability." He added, "It is anticipated that hydrogen cars' commercialization may be further facilitated through these findings."
Some Misconceptions About Hydrogen
Hydrogen may be the most abundant material in the universe, and it's about number ten here on Earth. There are, literally, oceans of it – combined with oxygen to form water. To get the hydrogen gas, what's used by fuel cells, energy has to be applied to water in electrolysis. Then you get hydrogen and oxygen gasses, which can then combine with oxygen to drive a fuel cell or launch a rocket into space.
In chemistry, as in life, nothing is free, and hydrogen gas is highly flammable.
Even if the thought of a teenage pump jockey at the local fill-up station causing a mini-apocalypse doesn't fill you with terror, there are other disadvantages to using hydrogen as a fuel for vehicles.
The Hindenburg hydrogen balloon disaster. Image credited to the Smithsonian
Let's assume H2 gas is obtained from electrolysis powered by renewables. That process is 75% efficient. Then, H2 gas must be compressed, chilled, and transported to the hydrogen station. That process is about 90% efficient. Reconverting the hydrogen to electricity in the vehicle is 60% efficient. The motor driving the vehicle can be though to be 95% efficient.
For Electric Vehicles (EV), you lose 5% in the power's journey to the station, and another 10% for transferring energy to the battery and taking it out again to power the vehicle. The motor, as in the other case, loses 5%.
From 100 watts generated, a full 80 watts are available to move the vehicle. The image below illustrates the calculation. As noted in The Conversation, there are now about five million EVs on the road today, compared to a total of 7,500 hydrogen-powered vehicles. It's not hard to see why.
As noted in The Conversation, there are now about five million EVs on the road today, compared to a total of 7,500 hydrogen-powered vehicles. It’s not hard to see why.