The need for an alternative to combustion engine cars is a growing concern in many countries. Hybrid cars and more recently electric cars rose as an obvious solution to this problem. But a third option has been overlooked and dismissed since 2015 when Hyundai and Honda presented their firsts commercially available hydrogen fuel cell cars.
While electric cars may seem a perfect solution for the problem, the capacity of the batteries and the long recharging time can be a detriment for the total replacement of the combustion engine cars. The higher energy density of hydrogen allows these cars to have a driving range comparable to traditional cars. The refuelling is as simple and fast as with a combustion car. The existence of an infrastructure to distribute and provide petroleum based fuel could be converted to the hydrogen technology.
The hydrogen fuel cell car works by combining the hydrogen with oxygen from the air in the fuel cell. The cell works as a catalyst of this reaction and allows to harvest the energy produced in the form of electricity, a more efficient way compared to combustion. Also, any excess of energy produced can be easily stored in a battery. The hydrogen fuel cell must still improve to be competitive compared to electric cars.
One of the areas in which it has been tried to improve is in the removal of the water produced while bringing air inside the cell to use the oxygen in the reaction. This problem is known as water management, and it is a hard problem to solve. On one hand, the cell must be sufficiently wet so that protons can travel from the anode to the cathode. But on the other hand, too much water could suffocate the cell by not allowing oxygen to get to the cathode.
The way where this exchange of water and air is made is in the gas diffusion layer. This gas diffusion layer is usually made of carbon fibres. Capillary pressure is the driving force for this exchange and for this reason the fibres are usually coated with hydrophobic polymers. Hydrophobic polymers are made of molecules whose interaction are very unfavourable with water. They are the base of the always-clean fabric technology, by avoiding the absorbance of water and water based liquids in the fabric.
The coating of the membrane with these polymers improves its performance but it still has the problem that the water tries to take the least resistance path in the membrane, which means that those paths are usually tortuous or sometimes lead to a dead end.
Another attempt tried to stack hydrophobic membranes with hydrophilic ones. Hydrophilic polymers are those whose interaction is favourable with water, and therefore water prefers to be in contact with them rather than with the hydrophobic polymers. This also provided an improvement, but this approach had a limited design flexibility. This drawback made it rather limited in its scale-up potential.
A new method was presented a couple years back. It allowed to create specific pathways for the air and water inside the same membrane. The research explains the preparation method of this new kind of gas diffusion layers and their capabilities. In this case the design is very flexible and can be easily adapted to new condition and configurations. Furthermore, it is ready to be scaled up to a production level.
The research also shows X-ray images that allow to see the distribution of the hydrophobic and hydrophilic areas and neutron spectroscopy, which allows to study the water distribution inside the layer and its behaviour in different conditions.
If you want to know more about this research don’t miss our video making a short sum up. But if you are still intrigued as to how this works and how the research was made you can check it yourself. The papers are open-access and therefore downloadable for free.
Also you can read this article from nature, the scientific journal, about hydrogen on the rise.