A miniature fuel cell with monolithically fabricated Si electrodes – Reduction of residual porous Si on catalyst layer

• Porous Pt layer was formed on a Si substrate using anodized porous Si.
• Miniature fuel cell was build using the porous Pt as a catalyst.
• Residual porous Si layer was observed on the porous Pt catalyst layer and could not be removed by additional etching.
• Process condition was optimized to reduce the residual porous Si.
• Highest power density of 450 mW cm−2 comparable to large scale fuel cells was obtained by a cell having least residual porous Si.

Higher performance was obtained in our miniature fuel cells by reducing the residual porous Si on catalyst layers. We have developed a miniature polymer electrolyte fuel cell by forming monolithic Si electrodes with MEMS techniques, in which a catalyst layer was synthesized on a Si chip by modifying porous Si to porous Pt by a wet plating process. As a result of technical limitations in the fabrication process, porous Si was left on the porous Pt catalyst layer. The residual porous Si was intended to lower the fuel cell performance by blocking reactant gas supply, and the effect of the residual porous Si on fuel cell performance was studied. The anodization conditions for porous Si formation were varied, and several prototype fuel cells were prepared with residual porous Si of different thickness. It was confirmed that a thick residual porous Si layer reduced cell performance, and high power density comparable to conventional large scale fuel cells was obtained with the least residual porous Si.