The effect of duty cycle and bias voltage for graphite-like carbon film coated 304 stainless steel as metallic bipolar plate

Abstract Graphite-like carbon films are deposited on 304SS substrates with different duty cycles and bias voltages by unbalanced magnetron sputtering, both the alternating current (AC) twinned and direct current (DC) single graphite targets are used. The microstructures and properties are investigated as bipolar plate for proton exchange membrane fuel cell (PEMFC). It is found that the surface compactness and sp2 fraction are significantly affected by the duty cycle and bias voltage. The electrical resistivity and interface contact resistance (ICR) first decrease and then increase with increasing duty cycle, which is completely dominated by the sp2 fraction. However, although the electrical resistivity and sp3/sp2 ratio monotonously increases with increasing bias voltage, the ICR values show an initial decrease and final increase for appearing a difference between 0 V and −75 V, a mechanism of electronic channels is put forward to explain this result. The lowest ICR of carbon films reaches 8.4 mΩcm 2 at a compaction force of 140 N/cm 2 , which is hopeful to replace commercial graphitic plate. In addition, the corrosion potential and current density are closely related to the surface morphology. The perfect duty cycle and bias voltage are 40% and −75 V respectively in this research, which promotes a most conductive, moderate corrosion resistant and well hydrophobic carbon film to form.