Biomolecules as hydrogen oxidation catalyst in fuel cells – BIOPAC

BIOPAC project has developed an interdisciplinary strategy thanks to the original association of theoretical chemists, material chemists and biolectrochemists. This consortium allows to define, modelize and finally optimize the structural and physico-chemical parameters which control the interaction between and O2-and CO-resistant hydrogenase and a conductive support for efficient H2 oxidation. The modelisation of the interaction between hydrogenases and electrochemical interfaces has allowed to define the required structural and chemical modification of the carbon support. New nanostructured carbon materials presenting a controlled porosity have been synthesized and characterized to achieve an increase in the amount of electrically connected enzymes. The knowledge of the parameters that control enzyme immobilization has allowed the design of a bioanode based on hydrogenase in nanostructured materials for H2/O2 biofuel cell development.

A hydrogenase, an enzymatic catalyst has been identified and produced. It is as efficient as platinum catalyst and is able to oxidize H2 over a large range of temperature even in the presence of O2. It is furthermore insensitive to CO. Thanks to molecular dynamics, the physico-chemical parameters that unable its efficient immobilization on a conductive support has been defined. The study in-depth of its incorporation in a network of mesoporous carbon nanofibers has allowed a 100 times increase in the current density for H2 oxidation. A first prototype of H2/O2 biofuel cell, the first one in France, has been designed which delivers power density in the range of 300 µW/cm2. BIOPAC partners have thus an international leadership in the domain. They are invited to communicate about their results in many international scientific conferences, but also towards a wider audience.

BIOPAC project has allowed to highlight the main factors that limit the functional immobilization of enzymes, including membrane ones, on conductive supports. These key findings will have important fallouts on various biotechnological processes involving enzymes (biofuel cells but also bioreactors and biosensors). From a fundamental point of view, they will help in the understanding of how enzymes work in constraint environments. The data that have been obtained by molecular dynamics, although not fully determined yet, constitute a strong basis toward a complete image of enzyme immobilisation n electrode surface.
BIOPAC has also allowed to develop and to strengthen the H2/O2 biofuel cell devices. The increase of both the performances and stability of the whole system will require to modelize the mass transport inside the mesoporous network, and to couple electrochemistry and modelization to spectroscopies to control the spatio-temporal activity of the enzyme.
.

19 publications have been published in high impact factor international journals. They are already largely cited by the scientific community. Multipartner publications describe the control of hydrogenase orientation allowing an increase in the interfacial electron transfer rate. They demonstrate how to control the immobilisation of membrane enzymes, which was a challenge by itself. They underline the key role played by modelization and deep knowledge and characterisation of carbon materials in order to reach the high current densities reached within this project. One paper dedicated to the scale up of the bioanode in under preparation.
The other publications deal with the key role of detergent on protein stability and catalytic current, and investigate the electrochemistry of hydrogenase on analytical electrodes, either gold or graphite electrodes. Three reviews have also been published in the domain.
One paper describes the design and performances of the first H2/O2 biofuel cell.
More than 30 oral presentations have been given in national and international conferences, including 13 invited lectures.

With the objective of a forthcoming hydrogen economy, supposed to eliminate carbon-based fossil fuels and thus reduce carbon dioxide emissions, the development of innovative technology is required. Actually much can be learnt from microbial world. Reversible interconversion of H2 and H+ is crucial in microbial energy cycling. In a future “green” hydrogen economy, use of biocatalysts as hydrogenases instead of highly cost and poisonous chemical catalysts in fuel cells is very attractive. Moreover the existance of hydrogenases from extremophylic bacteria supposed to be resistant to various extreme conditions (T°, pH, presence of inhibitors) will help in succeeding in the removing of biotechnological bottlenecks. With this aim, new conductive materials, highly porous and divided for electrode supports are a key point so that an increase in enzyme volumic density is achieved for the same surface coverage.
Intermolecular and intramolecular electron transfer within isolated protein and enzyme have been performed in the last decade using electrochemical methods in order to study electron transfer kinetics, thermodynamics, and electrocatalytic reactions. New strategies in which electrons to/from redox enzymes are coupled more closely to electrodes are needed in order to bring essential information for the knowledge of in vivo enzymatic machinery.
We propose in this project to explore new materials and processes for immobilization of hydrogenases with main goals: (i) which hydrogenases for an optimum resistance and stability (ii) how to ensure efficient electron transfer between electrodes and enzymes, and in particular how to control the orientation of the enzyme at the electrode in order to avoid the use of redox mediators, (iii) how to reach and control high enzyme surface concentrations, (iii) how to increase stability of the immobilized enzyme.
For that purpose progressive steps will be followed to understand
-the role of surface chemistry by using flat surfaces such as gold and graphite
-the role of an increase of the surface area by the use of commercial carbon black or carbon nanotubes, already proved to be efficient in hydrogenase immobilization
-the study of mass transfer limitation in these materials
-the influence of encapsulation in mesoporous materials on stability by using porous carbon materials with controlled pore size, pore organization and pore curvature, maintaining the accessibility of both enzyme and substrate
-the influence of encapsulation in mesoporous materials presenting an open structure that can increase the accessibility of both enzyme and substrate by using carbon fibers with controlled pore size, surface chemistry and topology.
Molecular modeling of hydrogenase will help to characterize its surface properties, determine essential conformational changes required for biological activity and describe important features of its interaction with the surface.
BIOPAC brings together experts in enzymology, bioelectrochemistry, molecular modeling and materials chemistry, necessary to improve the knowledge of enzyme immobilization and develop compatible supports for efficient hydrogenase immobilization. The expected progresses are technological via the development and characterization of new conductive carbon materials, as well as the design of new composite electrodes allowing the control of the orientation of the immobilized enzyme, the quantification and the physico-chemical study of the enzyme for hydrogen oxydation. They are also fundamental because one may expect from this project i) an improvement of the knowledge of the enzymatic reaction via an immobilized enzyme, ii) a method to design electrode supports that mimic the enzyme environment, and iii) an enhancement of the stability and the catalytic efficiency of the immobilized biocatalyst, so that use for biotechnological processes such as replacement of the chemical catalyst in fuel cells, can be considered.