Preparation And Hydrogen Sensitivity Of Pd/PAn/PTFE Composition Membranes

The key technology of hydrogen sensor is the fabrication of hydrogen sensitive material. Palladium has been well known for its hydrogen-selective adsorption and unique hydrogen-selectivity. Palladium/polymer composite membrane not only has traits of both of pure palladium and polymer membrane, but also has series of unique characters. Compared to palladium membrane, it has many advantages, such as longer life time, better hydrogen permeation and lower cost. Furthermore, polymer membrane is helpful to against the volume change inα- toβ-phase transition and then avoid distortion. So, palladium/polymer composite membrane can be widely used as hydrogen sensitive material for hydrogen sensor.Polyaniline, one of the conductive polymer, shows favorable properties with environmental stability, high conductivity, structure diversity, low-production cost. Polyaniline modified with metal microparticles shows high conductivity, and have electrocatalytic function for some electrochemical reaction. It can save a lot of noble metals. So, polyaniline modified with metal microparticles have become the new research field.In this paper, the composite membrane which was made up of palladium, polyaniline (PAn) and polytetraflouroethylene (PTFE) was studied. A conducting composite membrane of polyaniline with commercial microporous PTFE (PAn/PTFE) was made by permeating chemical polymerization. Ammonium persulfate was used as oxidants. Two methods were applied to introduce Pd particle into the above composite membranes and pure PTFE membrane: chemical deposition and electrodeposition method. The effects of electrodepositon conditions, which include PdCl2 concentration, hydrochloric acid concentration and deposition time, on the resulted membranes I-V performances were investigated. The optimum electrodepositon conditions in which PdCl2 concentration was 2 mmol·L-1, HCl concentration was 0.5 mol·L-1 and deposition time was 6 min were obtained.From the results of membranes I-V performances, we could conclude that the palladium made ohmic contact with PAn/PTFE composite membrane. The hydrogen sensitivity of the Pd composite membranes was tested by observing the change of current after imputting the voltage. The results showed that Pd/PTFE membrane and Pd/PAn/PTFE membrane made by chemical deposition delaminated and blistered exposed to 2% of H2 four times, and Pd/PAn/PTFE composite membrane made by electrodeposition did not delaminate and blister. So, Pd/PAn/PTFE composite membrane made by electrodeposition had better sensitivity and stability to hydrogen. Moreover, It can respond in 0.5% of H2(in N2).XRD results show oberviously the fine crystal structure of palladiums on the PAn/PTFE composite membrane. By SEM and AFM, surface morphology of the Pd/PAn/PTFE composite membrane made by electrodeposition was studied. The deposited palladium was in a spheric ship, and the amount of palladium was much less than that on the Pd/PAn/PTFE composite membrane made by chemical deposition.The hydrogen responsibility of Pd/PAn/PTFE was deduced to be mainly resulted from the conductivity changes of PAn upon to the dissociation of hydrogen catalyzed by high dispersed palladium and then simultaneously transfer from palladium to polyaniline chain.