Study On Fuel Cell Stainless Steel Bipolar Plate Modified By Tantalum And Tantalum Carbide

Proton exchange membrane fuel cells(PEMFC)have the advantages 'of fast start up at room temperature,low operating temperature,and high energy conversion efficiency.They have very broad application prospects in transportation and portable power sources.Metal bipolar plates are superior to graphite plates due to their higher mechanical strength,lower cost and better electrical conductivity.However,an oxide layer will appear on the stainless steel metal bipolar plate that reduces the surface conductivity of bipolar plate under the working environment of PEMFC,reducing the efficiency of the fuel cell.Therefore,the corrosion resistance and interface contact resistance(ICR)of the metal bipolar plate are the main problems to be solved.Focusing on the above problems,this article adopts double glow plasma surface modification technology,a tantalum modified coating and tantalum carbon alloy layer are prepared on the 316 L stainless steel(316L SS).First,investigating the process,and then analyzing the composition and structure,hydrophobic properties,the corrosion resistance and conductivity of the modified layer.By studying the influence of voltage,temperature,air pressure and holding time on the formation of the modified layer,the best process parameters for tantalum,modified 316L SS(Ta-316L SS)has been obtained:source voltage is-850?-900 V,cathode voltage is-550?600 V,Temperature is 1073 K,air pressure is 40 Pa,time is held for 2 h,the distance of two electrode is 15 mm.The tantalum modified layer is mainly composed of a tantalum surface layer and a diffusion sub-surface layer,and the surface morphology is dense and the Ta modified coating is well metallurgical bonding on the surface of 316L SS.Investigating the hydrophobicity of Ta-316L SS,and its corrosion resistance and surface conductivity in simulated PEMFC environment(70?,0.05 M H2SO4+2 ppm HF solution,purged with air to simulate the cathodic environment and purged with H2 to simulate the anodic environment).The hydrophobicity,corrosion resistance and ICR of 316L SS modified by tantalum have been improved.The corrosion resistance of bipolar plate was evaluated by potentiodynamic polarisation testing in simulated PEMFC environment,the 316L SS bipolar plate modified by tantalum still maintains good corrosion resistance and surface electrical conductivity.On the basis of tantalum modified 316L SS process,acetone gas was purged into the furnace,and a tantalum carbide alloy layer(Ta-C 316L SS)was prepared on the 316L SS substrate.The tantalum carbide modified layer is mainly composed of tantalum carbide surface layer and diffusion sub-surface layer.The surface morphology is dense and the metallurgical bonding performance with the substrate is good.In the simulated PEMFC environment,tantalum carbide layer has significantly improved the corrosion resistance and surface conductivity of 316L SS.The tantalum carbide diffusion modified layer reduced the self-corrosion current from 0.51 ?A cm-2 and 0.63 ?A cm-2 to 0.09 ?A cm-2 and 0.08 ?A cm-2 in simulated cathode and anode PEMFC environment,respectively,the self-corrosion current density of 316L SS was reduced by an order of magnitude.The contact resistance of 316L SS modified by tantalum carbide decreased from 83.42 m? cm2 to 13.93 m? cm2.The corrosion current density of the 316L SS modified by tantalum carbide which tested after constant potential polarization of 14400 s was reduced from 2.1 ?A cm-2 to 0.13 ?A cm-2 in cathode environment,from 1.8?A cm-2 decreased to-0.08 ?A cm-2 in anode environment.It shows slight increasing of Ta-C 316L SS ICR values.The Ta-C 316L SS bipolar plate maintains lower ICR values in simulated PEMFC environment.