Proton-exchange membrane fuel cells (PEMFCs) are currently widely investigated for the development of space power systems for future deep-space exploration and lunar research stations in China. Key technological research pertaining to PEMFCs for space applications must be conducted urgently. The bipolar plate, which is the core component of PEMFCs, significantly affects the weight and cost of the battery stack. Titanium is the preferred metal-plate material for lightweight space fuel-cells owing to its low density (only 0.6 times that of stainless steel) and high specific strength. However, they are susceptible to corrosion when used in weak acidic environments for long durations.To improve the corrosion resistance of titanium bipolar plates, a Ti / TiN composite coating composed of a Ti transition layer and a TiN surface layer is prepared on the surface of titanium via multi-arc ion plating technology, which is a physical vapor deposition technique. The effects of preparation process parameters such as the substratetemperature and arc current on the microstructure and mechanical / electrochemical properties of the Ti / TiN composite coating are investigated. The cathode sputtering target material is imported titanium metal (purity=99.995%), the sputtering gas is high-purity argon (purity=99.99%), and the reaction gas is high-purity nitrogen (purity=99.99%). The sheet of titanium was sequentially sonicated in acetone, anhydrous ethanol, and deionized water for 15 minutes to remove oil stains and attachments on the surface of the sample. Then, nitrogen flow was used to blow dry the surface moisture of the sample to ensure that there were no residual water stains on the surface. After that, the sample was placed in a drying dish for later use. When the vacuum degree of the equipment is better than 5.0 mPa, perform ion source cleaning to remove the oxide layer on the surface of the Ti substrate and activate the surface of the Ti substrate. When preparing the Ti transition layer on the titanium metal substrate, the target substrate distance is set to 23 cm, the arc current is 70 A, the substrate temperature is 150 degrees C, and the deposition time is 10 min. When preparing TiN layers on the Ti transition layer, two different substrate temperatures (150, 230 degrees C) and arc currents (50, 120 A) are selected. A field-emission scanning electron microscope (Carl Zeiss AG Corporation) is used to analyze the micromorphology of the Ti / TiN composite coating. An X-ray diffractometer (Rigaku Corporation) is used to analyze the phase composition of the coating. A nanoindentation instrument (Anton Paar) is used to evaluate the mechanical properties of the coating. The indentation depth is controlled to be less than 10% of the thickness of the Ti / TiN composite coating. During testing, the maximum load is increased linearly to 5 mN at a loading and unloading rate of 10 mN / min. A TalySurf CCI Lite optical interferometric surface profilometer (Taylor Hobson) is used to test the surface roughness and thickness of the Ti / TiN composite coating. An electrochemical workstation is used to evaluate the corrosion resistance of the coating under a simulated operating environment of a PEMFC cathode. The results show that the Ti / TiN composite coating prepared under a substrate temperature of 150 degrees C and an arc current of 50 A offers the best surface quality, the lowest surface roughness, and the lowest corrosion current density. The Ti / TiN composite coating with optimized preparation process parameters exhibits excellent surface quality and high corrosion resistance, with a corrosion current density of 6.383 mu A / cm(2) (i.e., 0.6 times the corrosion current density of titanium). Furthermore, the Ti / TiN composite coating significantly improves the corrosion resistance of titanium. This study provides technical support for the surface modification of metal bipolar plates used in space fuel-cells
