Characterization of electroless Ni-based alloys for use in bipolar plates of direct methanol fuel cells

In this study, an electroless Ni–P deposit is employed as an anodic coating layer to protect the metallic bipolar plate of a direct methanol fuel cell (DMFC). An inductively coupled plasma-mass spectrometer, grazing incidence X-ray diffractometer, and potentiodynamic polarization measurements were used to study changes in the composition, crystalline structures and corrosion resistance of the Ni–P deposits at various bath pHs and temperatures. The crystalline structure of the Ni–P deposits was observed to change from crystal to amorphous as the P content increased, thus enhancing the corrosion resistance of the plate. The optimal conditions for obtaining the highest P content were found to be at pH 4.3 and 70 °C. Furthermore, the potentiostatic test for the Ni–P deposits prepared under the optimal condition was performed in a simulated anode working environment (0.5 M H2SO4 + 10 vol.% methanol), with the test showing that a negative corrosion current was observed at all times, therefore indicating that cathodic protection was employed throughout. Even after 10 h of potentiostatic treatment, no metal ions were found in a test solution. In addition, the result of a DMFC performance test demonstrated that bipolar plates using an anticorrosion coating of Ni–P deposits obtained a lower bulk resistance and an enhanced cell performance when compared to commercially available plates. Hence, the low-cost electroless Ni–P deposit demonstrates high potential for use as a corrosion protection layer in a DMFC bipolar plate with a Cu interlayer.