Study On Preparation And Properties Of Plasma Surface Modified Titanium Bipolar Plate

Traffic pollution has a great impact on environment,so clean and efficient fuel cell vehicles are studied to improve environment.A fuel cell is a device that converts chemical energy directly into electrical energy without burning it.Among them,proton exchange membrane fuel cell(PEMFC)is favored by researchers because of its high specific power,fast start-up speed at low temperature and long life,which has a broad commercial prospect.Bipolar plate is the key component of PEMFC,and the performance of PEMFC such as service life and output power are determined by bipolar plate's quality.In the working environment of PEMFC,the contact resistance of titanium bipolar plate is biggish and surface modification of the bipolar plate is one of the best ways to solve this problem.Zr coating and ZrC coating are prepared on the surface of titanium TA1 by double glow plasma surface modification.Firstly,the reasonable technological parameters for preparing Zr-TA1 and ZrC-TA1 bipoar plates are investigated by using the control variable method.After that,the surface morphology and element changes of Zr-TA1 and ZrC-TA1 are investigated,and the corrosion resistance,conductivity before and after polarization,hydrophobicity and long-term stability of the bipolar plate are analyzed and compared.The surface of Zr-TA1 and ZrC-TA1 bipolar plates is uniform,flat,dense and without obvious defects.The thickness of the modified layer is about 3?m,and that of the diffusion layer is about 1?m.The potential polarization and potentiostatic polarization tests of Zr-TA1 and ZrC-TA1 plates are tested in simulated PEMFC cathodic and anodic environments.In the dynamic potential polarization test,the corrosion potential of Zr-TA1 is 0.3V higher than that of uncoated TA1,and that of ZrC-TA1 is 0.15V higher than that of Zr-TA1.Moreover,the corrosion current density of ZrC-TA1 is the lowest,which is 1.03?A cm-2(cathode)and-0.29?A cm-2(anode),indicating that ZrC-TA1 bipolar plate has better corrosion resistance.In the simulation of potentiostatic polarization curves test under the simulated PEMFC cathodic environment,the corrosion current density of uncoated TA1,Zr-TA1 and ZrC-TA1 is 61.67?A cm-2,5.51?A cm-2 and 1.03?A cm-2.In the simulated PEMFC anodic environment,the corrosion current density of Zr-TA1 and ZrC-TA 1 plates are-4.89?A cm-2 and-0.29?A cm-2,indicating that Zr coating and ZrC coating have cathodic protection effect.After that,the surface morphology of the samples tested by potentiostatic polarization curves is observed and the surface corrosion of uncoated TA1 is serious while Zr-TA1 and ZrC-TA1 plates have fewer corrosion traces after surface modification.The above results show that among the compared bipolar plates,ZrC-TA1plate has the best long-term stability and corrosion resistance while Zr-TA1 plate has slightly poor performance and the uncoated TA1 bipolar plate has the worst performance.In the contact resistance test with a compressive strength of 1.4MPa,ZrC-TA1 plate has the lowest contact resistance(7.7m?cm~2),Zr-TA1plate has a slightly higher contact resistance(15.5m?cm~2)and uncoated TA1plate has the highest contact resistance(113.5m?cm~2).After potentiostatic polarization test under simulated PEMFC cathodic and anodic environment,the contact resistance of uncoated TA1 is 395.3mQ cm~2 and 323.5m? cm~2;the contact resistance of Zr-TA1 plate is 11.3m? cm~2 and 11.1m? cm~2;the contact resistance of ZrC-TA1 plate is 25.8m? cm~2 and 23.8m? cm~2,which illustrates that the long-term stability and corrosion resistance of ZrC-TA1 plate is better.In addition,the water contact angles of uncoated TA1,Zr-TA1 and ZrC-TA1plate increase successively:76°,94° and 105°,indicating that ZrC-TA1 bipolar plate has the most excellent hydrophobic performance.