Cathode and Anode Rationalization for an OUtstanding H2/O2 biofuel CELL – CAROUCELL

Our planet is facing energetic, climatic and economic crisis implying mutations in our ways of producing, converting, and consuming energy. Fuel cells are one of the promising alternatives. However, hydrogen and oxygen conversions rely on noble metals, such as platinum. Its availability severely limits the large scale development of fuel cells. Furthermore, classical process for H2 production is based on gas reforming, which yields H2 polluted with impurities (in particular CO) that inhibit platinum. Hydrogen can alternatively be produced from biomass, but again CO will be a major contaminant. Besides, high purity hydrogen produced through electrolysis of water is energy consuming. As for the cathodic part, the presence of pollutants in air may also poison the platinum catalyst.
The development of noble metal free fuel cells is thus highly desirable.
An efficient alternative to platinum resides in enzymes or bio-inspired catalysts immobilized onto anode and cathode materials so as to design a H2/O2 biofuel cell.
H2 conversion in many microorganisms is carried out by a key enzyme, namely hydrogenase. In addition to bioavailability and biodegradability, it presents high turn-over and low over-potential for H2 oxidation. The specificity of this enzyme compared to platinum, may allow feeding the fuel cell by non purified hydrogen, such as hydrogen issued from biomass fermentation. For a long time, the extreme sensitivity of hydrogenase has prevented its use as a biocatalyst. A solution may arise from hydrogenases that have been recently identified to be naturally oxygen and CO tolerant, or from others that have been mutated so that they can present some oxygen tolerance. Some of these hydrogenases are even able to work in a large range of temperatures thus allowing them to be potentially used in extreme environments. Alternatively, nickel-based bio-inspired catalysts immobilized on carbon nanotubes proved active for catalyzing the conversion of H2 with protons and with no over-potential. This material displays remarkable stability over cycling together with tolerance to CO and may represent another good alternative to platinum catalysts. On the cathodic side, multi-copper enzymes, such as bilirubine oxidase, are known to be able to reduce O2 with high efficiency and low over-potentials, although with low affinity for oxygen and poor thermostability.
Based on two O2-tolerant hydrogenases and bilirubine oxidase, two preliminary H2/O2 biofuel cells have been reported during the last year, one developed by partner 1 of the present project and highlighted by the French ADEME innovation award in 2012. Although delivering low power densities, they act as a proof of concept that needs now to be validated by fundamental explorations.
In that context, CAROUCELL is a fundamental project that seeks to design and to evaluate the performances of the first efficient green Biofuel cell, in which H2 and O2 transformations are catalyzed by the most efficient redox biocouple, either enzymes or bio-inspired catalysts.
It aims at i) identifying new enzyme or bio-inspired catalyst couples that present high affinity for H2 and O2, and transform the substrates with low over-potentials and high current densities, so that a final high power density can be envisioned, ii) enhancing the current by a rational design in the electrode structure: better electrochemical connection of the enzymes to both cathode and anode, iii) the innovative advanced characterization of 3D structured electrodes, iv) the demonstration of the possible use of the designed bioelectrodes in actual-operating biofuel cell devices, and the evaluation of the performances when fed with H2 produced directly from biomass.
For the first time, the expertise of our five groups, BIP, CRPP, DCM, LCBM and SPrAM in bioanode and biocathode design offers the opportunity to take an international leadership in the field of biofuel cells.