Study On The High-throughput Screening Of High Performance Coatings For PEMFC Metallic Bipolar Plates

Proton exchange membrane fuel cell(PEMFC)is a highly efficient and environmentally friendly energy device that can convert hydrogen energy into electricity.It has broad application prospects in industrial fields such as automotive power and distributed power generation systems.However,one of the key components,bipolar plate,has become one of the main obstacles to the further commercialization of PEMFC because it cannot reach the performance and duration standard given by US DOE.In order to solve this problem,conductive and corrosion-resistant coatings are often deposit on metal bipolar plates to meet PEMFC performance and duration requirements.The current coating material design method follows the same idea as the traditional material design,that is,the pattern of"experience-guided experiment,experimental trial-and-error".However,with the maturity of high-precision material property calculation tools and the emergence of high-throughput calculation methods under the material genome initiative,the application-oriented material design method based on the concept of "calculation-prediction then experimental verification"provides a new way of bipolar plate coating design.Based on the performance requirements of bipolar plates,this paper designed a first principle high-throughput calculation and screening scheme focusing on conductivity,corrosion resistance and bonding force.The scheme was carried out this way:1)calculate electrical conductivity and PB ratio of elements.2)assess stability and corrosion-resistance of compounds by Pourbaix diagram and energy above hull.3)calculate electrical conductivity of compounds.4)evaluate interface strength by calculation of separation work.Several coatings were obtained after the screening scheme.The calculation result was compared to existing experiment outputs so the feasibility of the screening scheme and the correctness of the calculation were verified.Gold was successfully prepared on a 316L stainless steel substrate by magnetron sputtering method due to its superior electrical conductivity and high chemical inertness.The effects of bias voltage,gas flow rate and sputtering time on the properties and microstructure of the gold coating were investigated.The corrosion resistance and electrical conductivity of the gold coatings were evaluated by potentiodynamic polarization test in simulating PEMFC environment and surface contact resistance test.The phase composition and microstructure of the coating were analyzed and characterized by XRD,AFM and SEM.The results show that the conductivity and corrosion resistance of the gold coating increase first and then decrease with the increase of the bias voltage.When the bias voltage is-200V,the surface of the coating is island-like agglomerated,the distribution of which is uniform and compact,and the performance of the coating is best in all bias voltage.The working gas flow has little effect on the coating performance,but when the gas flow rate drops to 5 sccm,the low plasma concentration reduces the uniformity of the coating,resulting in a decrease in coating performance.When the sputtering time reaches 5 minutes,the thickness and compactness of the coating can provide good corrosion protection to the stainless steel substrate.Under the optimal process parameter,the corrosion current density of the coating decreased to 0.25μA/cm2,and the ICR decreased to 1.5 mQ·cm2(140N/cm-2 compact force).Comparing to stainless steel(17.91μA/cm2,123 mΩ·cm2),the performance has been greatly improved.