(October 12th, 2017) Fuel cells require platinum to function but this chemical element is scarce and expensive. French researchers replaced it with bacterial enzymes.
Most of us have probably heard of fuel cells and know they are a kind of green technology that might one day replace fossil fuels. However, few of us in the Life Science field really know what they are or how they work. Fuel cells essentially produce electricity from a chemical reaction, due to the production of positive and negative ions through oxidation and reduction reactions. This is comparable with what happens in a battery, except unlike a battery, the fuel cells require a constant source of fuel – which, in modern designs, is a supply of hydrogen and oxygen. Perhaps surprisingly to most people, fuel cells are not a new technology – the first one was developed in 1938, although unlike the modern fuel cells, it used sulphuric acid and water as the fuels. The benefit of producing electricity from hydrogen fuel cells is that the only waste product is water, making this a promising green technology.
You may be wondering what this all has to do with biology? Well, in a recent publication, resulting from research conducted in France, in the French National Centre for Scientific Research (CNRS), it was shown that enzymes from bacteria can be incorporated into fuel cells to act as biocatalysts to speed up the reaction, negating the need for platinum catalysts that are normally used. Elisabeth Lojou, a Director of research at CNRS, led the study. “At the beginning of my career, I was working on Lithium batteries. I moved to Marseille in 1995 and started to look at the way enzymes can communicate with electrodes, as they do in the bacterial cell.”
In her current work, Lojou and her team was able to replace platinum by bacterial enzymes, i.e. hydrogenase for H2 oxidation and bilirubin oxidase for O2 reduction. Lojou went on to describe how this involved “chemical modification of electrodes that can allow fast electron transfer between enzymes and electrodes, mimicking the way electrons are transferred in energy metabolic chains in bacteria”. When questioned about the advantages of using enzymes rather than platinum, Lojou explained that enzymes are more efficient, specific and have lower overpotentials. “Platinum is scarce on earth, so very expensive and only produced by South Africa and Russia, thus leading to political issues,” she adds.
In this study, the group first identified two thermostable enzymes: hydrogenase for H2 oxidation and bilirubin oxidase for O2 reduction, which can operate at temperatures as high as 80°C. They then developed the fuel cell and were able to “demonstrate that the enzymes are as efficient as platinum, when immobilised on the carbon material”. Finally, they optimised the dimensions of the electrodes.
Lojou commented that she was very surprised by the high current they could achieve and “more fundamentally, it was more than ten years that we, and other researchers, tried to detect the signals of the enzymes that can allow to quantify the operating enzymes. And we failed…until this work”.
Evidently, the publication was a long time in the making, only made possible by 50 years of work on the enzymes. “Concerning the biofuel cell itself, I began working on the immobilisation of the hydrogenase ten years ago. The first biofuel cell was designed five years ago. The main problem was to find the suitable chemical functionalities to connect the enzymes, and then to provide the environment that can make the enzymes stable enough.”
The publication clearly marks a huge success for the group but Lojou explained that, “We still have much to do. First because we know now that only 10% of the enzymes are participating to (generate) the current. That means we still have to search for new structures, new chemical functionalisation, perhaps some enzyme engineering to improve the electron transfer rate (…) Then we have to work with engineers to improve the design of the cell and enhance the supply of gases, which is one of the limitations of our system. Finally, we are still looking at the biodiversity to find new enzymes with new outstanding properties.” Certainly enough ideas to keep the group busy for the foreseeable future!