Micro-electroforming metallic bipolar electrodes for mini-DMFC stacks

Abstract

This paper describes the development of metallic bipolar plate fabrication using micro-electroforming process for mini-DMFC (direct methanol fuel cell) stacks. Ultraviolet (UV) lithography was used to define micro-fluidic channels using a photomask and exposure process. Micro-fluidic channels mold with 300 mu m thick and 500 mu m wide were firstly fabricated in a negative photoresist onto a stainless steel plate. Copper micro-electroforming was used to replicate the micro-fluidic channels mold. Following by sputtering silver (Ag) with 1.2 mu m thick, the metallic bipolar plates were completed. The silver layer is used for corrosive resistance. The completed mini-DMFC stack is a 3.5 x 3.5 cm(2) fuel cell stack including a 1.5 x 1.5 cm(2) MEA (membrane electrode assembly). Several MEAs were assembly into mini-DMFC stacks using the completed metallic bipolar plates. All test results showed the metallic bipolar plates suitable for mini-DMFC stacks. The maximum output power density is 9.3 mW/cm(2) and current density is 100 mA/cm(2) when using 8 vol.% methanol as fuel and operated at temperature 30A degrees C. The output power result is similar to other reports by using conventional graphite bipolar plates. However, conventional graphite bipolar plates have certain difficulty to be machined to such micro-fluidic channels. The proposed micro-electroforming metallic bipolar plates are feasible to miniaturize DMFC stacks for further portable 3C applications.