Studies on surface modification of polypropylene composite bipolar plates using an electroless deposition technique

Abstract

A direct methanol fuel cell (DMFC) is predominantly noticeable because it can convert chemical energy directly into electrical energy with higher energy conversion efficiency (∼65%) compared to the efficiency of traditional combustion engines (40%) and with lower emissions. Henceforth, it is one of the new electrical generators that is becoming an important source of cleaner power in modern life. One of the key obstacles in designing and assembling the DMFC is contact resistance between interfaces of fuel cell components. A major source of the contact resistance in the DMFC arises from the contact between gas diffusion layers (GDLs) and the bipolar plates (BPs). A poor interface contact decreases the actual contact area, leading to an electrical voltage drop across these interfaces. Decreasing surface resistivity of BPs is one of the major approaches to reduce contact resistance in fuel cells. Present-day methods use a polypropylene composite as BPs to replace metallic or graphite BPs to reduce the overall weight of the DMFC stack. Unfortunately, polymeric composites typically provide higher surface resistance than the other BPs do. Coating copper on polypropylene composite plates was strategically manipulated by an electroless deposition (ELD) technique to decrease surface resistance. The coating process consists of pretreatment, adhesion improvement, and electroless deposition. Prior to ELD, the surfaces of the composite plates were treated by plasma treatment and then silanization was conducted using N-3-(trimetylpropylsilyl)diethylenetriamine (TMS) to improve adhesion. Palladium(II) chloride (PdCl₂) was used as a catalyst for the ELD process. Successful modification of the surfaces was confirmed by morphology investigation via scanning electron microscopy, diagnoses of chemical surface characteristics using ATR-Fourier-transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS), physical surface characterizations with a contact angle measurement, electrical conductivity measurements, and surface adhesion test, while also observing corrosion behavior. In order to complete a viability study of using modified copper-coated BP for the DMFC, an in situ cell performance test was conducted. The results of the experiments pave the way for a feasible modification of the BP surfaces to be considered as suitable BPs for usage in fuel cells.