Development of porous silicon-based miniature fuel cells

Nowadays the rise in portable electronics requires energy sources compatible with the environmental constraints. We demonstrate, in this paper, how microfabrication techniques allow the development of low-cost miniature fuel cells fully integrated on silicon. Contrary to usual proton-conducting membranes made of ionomers ensuring the proton conductivity of proton-exchange membrane fuel cells (PEMFCs), we present here another way to proceed. It consists in the chemical grafting of molecules bearing acid groups on the pore walls of a porous silicon membrane to mimic the structure of an ionomer, such as Nafion. We obtain an inorganic, dimensionally stable, proton-conducting membrane with many optimizable parameters such as the pore size and the pore structure of the membrane or the nature of the grafted molecules. Moreover, the use of a silicon substrate offers advantages of serial and parallel integration, the possibility of encapsulation by wafer bonding and gas feed and electrical contacts may be included into the membrane etching process, thanks to simple KOH wet etching processes and metal sputtering.