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.