MOdelling of Porous Electrodes for an Optimized MAterial Design – MOMA

This project is dedicated to a bottom-up approach to optimize the design of porous electrode materials devoted to biofuel cells and biosensors. These devices operate on the basis of complex enzymatic electrochemical redox reactions coupled to mass transfer of substrates (glucose and O2) and electron transfer within the pores of the structure and from/to the pore surfaces. The advantage of using porous materials for these devices lies in the very large internal surface area (where electron exchange takes place) to overall material volume ratio, yielding much larger current densities than on a simple solid bare electrode. The global performance of the electrode is intimately related to the choice of the reagents and the placement within the pore structure but, above all, to the architecture of the material at the pore-scale. Some very interesting techniques, based on templating silica beads with a Langmuir-Blodgett deposition step followed by electroplating of a conducting material and beads dissolution have been elaborated to synthetize porous materials having a typical pore size on the order of the micrometer. This technique, well controlled by one of the partner of the project, yields materials with a tunable pore architecture. However, these materials have always been designed so far on an empirical basis regarding the thickness of the material and its pore size and organization. These parameters have a crucial impact on the competition between mass transport, enzymatic turn-over and heterogeneous electron transfer rate. A rational approach is hence really needed, based on a direct interplay between materials design and modelling to reach optimal performance.
The objective of the present project is four-fold. In a first step, careful models will be derived at the pore-scale. For tractable computational subsequent treatment, macroscale models will be obtained by upscaling their pore-scale analogues. Solutions of the pore-scale models, obtained from Direct Numerical Simulations on simple porous structures, will be compared to the solution of the corresponding upscaled model as a validation step of the upscaling process. Validation of the overall modelling approach will be further performed by comparisons with experimental results using images of the real structure. In a second step, the electrode current-to-potential dependency with respect to the microstructure obtained by modelling will be exploited to optimize the porous architecture. To do so, the macroscale model will be employed in order to identify the optimal pore structure yielding the maximum output power. The optimization will be first focused on a restricted set of parameters (pore size, their connecting window size and a pore size gradient along the direction of the electrode thickness). This choice relies on the fact that these parameters can be controlled by the actual experimental protocols, ensuring an effective optimization that will be carried out using image analysis and virtual materials simulations. The set of parameters will be progressively enriched (pore-shape and size distribution) till further optimization remains feasible. Optimal thicknesses will be also analyzed with this procedure. In a third step, engineering of electrode prototypes, based on the resulting optimized materials, will be then carried out by conveniently tuning the pore structure. In the final part of the project, after a key step of enzymes (and electron mediator) immobilization within the porous structure to achieve a DET or MET operating mode, experiments on the synthetized electrodes will be performed using electroanalytical tests. This recursive and rational approach should lead to a real and decisive breakthrough in the efficiency improvement of the bio-devices to which these porous electrodes are dedicated.