More efficient fuel-cells, thanks to a new catalyst

Over the past decades climate change and its consequences for life on our planet have given rise to a growing scientific interest in the development of alternative energies. The fossil fuels that currently dominate our energy map are not only becoming scarce, but are moreover generating large quantities of contaminating gases. Within the field of renewable energies the scientific community is today devoting great efforts to investigating and developing fuel cells, capable of creating electrical energy from a chemical reaction between a fuel and oxygen. For fuel cells to be a competitive option amongst alternative energies, advances in a number of fields are required, amongst these being the development of new catalysts, i.e. substances that are responsible for accelerating the chemical reaction required for electricity to be produced. It is in here that José E. Barranco’s focused when he presented his PhD thesis, Development of new metallic materials of an amorphous nature for use in direct methanol fuel cells, at the UPV/EHU. José Enrique Barranco Riveros is a graduate in Chemical Sciences and is currently working as a researcher employed by the Polytechnic University School in the Basque city of Donostia-San Sebastián. His PhD was awarded excellent cum laude unanimously and was led by Dr. Ángel Rodríguez Pierna of the Department of Chemical Engineering and the Environment at the University School.

Methanol as an alternative

Most current research is focused on hydrogen cells the biggest advantage of which is that they do not generate contaminant gases, except water vapour as the only waste product. However, hydrogen is very expensive, both in producing it and in distributing it using traditional overland transport methods. Moreover, its energy density is less than that of methanol, meaning that, in order to obtain the same energy from a similar amount of fuel, the hydrogen has to be kept and stored under conditions of very high pressure (more than 800 bars). This is why hydrogen is dangerous, and even more so when stored in vehicles travelling at high speed – a small crack in the storage container could have fatal consequences. These and other reasons mean that methanol (a type of alcohol derived from methane gas) is a good option for charging fuel cells.

More efficient and sustainable catalysts

In order for the fuel cell to generate electricity, a chemical reaction called electro-oxidation has to take place and this, in turn, requires a catalyst to accelerate the process. This catalyst is inserted in the fuel cell membrane and, in the case of methanol, the basic accelerator is platinum, a scarce and expensive metal. This is why the aim of Dr. Barranco’s thesis was to devise a catalyst composed of a metal alloy in which the amount of platinum is significantly reduced. His research focused on a fundamental problem: the electro-oxidation of methanol produces carbon monoxide, a molecule that adheres to the metal and inhibits the latter’s catalysing capacity, i.e. it impedes the accelerator from doing its work and energy production is halted.

After investigating the composition of numerous metals, Dr. Barranco made alloys that enabled the reduction of the proportion of platinum to 1%. These alloys, composed of elements such as nickel, niobium, antimony or ruthenium, amongst others, have the unique property of converting molecules of carbon monoxide (CO) into carbon dioxide (CO2) efficiently. The CO2, being gaseous, does not adhere to the catalyst which in the long term favours the catalytic process.

This means that the methanol fuel cell will emit a small quantity of CO2 which, according to Dr. Barranco, is easily tolerable by nature given that this can be incorporated into the photosynthesis cycle of plants. According to a study by the American Methanol Institute, it is forecast that, by the year 2020, there will be 40 million cars powered by methanol fuel cells, meaning that CO2 emissions will be cut by 104 million tons with respect to emissions from petrol.

Catalysts in powder form

Once the suitable catalyst was found, Dr. Barranco set out to increase its efficiency. The conclusions of his PhD thesis point to the fact that, if the platinum alloy is structured amorphously, its electrical conduction properties are enhanced and it undergoes less corrosion (advantages for the medium in which it has to operate). Moreover, it has an operational capacity in the order of 80-100 times greater than platinum in a crystalline structure. Amorphous materials are those with a disordered molecular structure and which, in this case, are obtained by the sudden cooling of metal alloys.

Also, for the catalyst made on this basis of amorphous metal alloys to be incorporated into the fuel cell membrane, Dr. Barranco decided to change its form. The result is a very fine powder that is placed in a container to “spray paint” the membrane. Not only this: as it is a substance made of minute particles, the operating capacity of the catalyst is enhanced by 9 to 13 times.

Looking to a fuel cell completely built at the UPV/EHU

Taking into account that the catalyst improves the efficiency of the cell by more than 50%, this new material developed at the UPV/EHU is a giant step forward in fuel cell research. But the PhD thesis of Mr Barranco is not limited to describing and producing the new catalyst. His work falls within the remit of the overall Alcohols Oxidation Fuel Cell Research being undertaken at the Industrial Chemistry and Electrochemical Engineering Laboratory of the Polytechnic University School in Donostia-San Sebastián, research work being led by Dr. Ángel Rodríguez Pierna the target of which is to achieve a methanol fuel cell solely and totally devised and developed at this laboratory.

Source: Elhuyar Fundazioa