An improved miniature direct formic acid fuel cell based on nanoporous silicon for portable power generation

Silicon-based fuel cells are under active development for power generation for portable electronic devices. Previous work has demonstrated that an acid loaded nanoporous silicon membrane could be a suitable proton conducting material that is compatible with silicon microfabrication technology. In this design, the acid acts as an electrolyte while the porous silicon acts as a separator that limits fuel crossover. Unfortunately, the power output of the previous nanoporous-silicon based fuel cells was far below Nafion-based fuel cells. In this paper a new design for a nanoporous-silicon based miniature direct formic acid fuel cell is proposed and tested. The effects of the thickness, pore size, and formic acid concentration on the nanoporous silicon miniature fuel cell performance are studied. At room temperature in ambient air the fuel cell peak power density reached 94 mW/cm(2) with a current density level of 314 mA/cm(2), using 5 M formic acid fuel with 0.5 M sulfuric acid electrolyte. This power output is three times higher than in previous work. These results show that the new design is a substantial improvement and that microfabricated silicon fuel cells using nanoporous silicon are potentially excellent power sources for portable electronic devices. (c) 2006 The Electrochemical Society.