Function Of Polymer Microencapsulation And Its Effect On The Electrochemical Properties Of Hydrogen Storage Alloys

In order to improve the electrochemical kinetic properties of the rare earth-basedAB₅-type and La–Mg–Ni-based AB₃-type hydrogen storing alloy, conductive polymerfilms are fabricated on the alloy powder surface. This study investigated the conditionsand methods of various conducting macromolecule modifications such as chemicalmodified PANI, electrodeposited PANI, chemical modified PPy, chemical modified PSand Ni/PANI. FE-SEM, FT-IR and UV-vis methods were used to thoroughly characterizemorphology. The electrochemical properties of the alloy electrodes are invesgated bygalvanostatic method and exchange current density, limiting current density and hydrogendiffusion coefficient. Effects mechanism of conductive polymer on microstructure andelectrochemical properties of alloys were studied.Owing to the chemical modified PANI coating, PANI is uniformly coated on thesurface of the AB₅-type alloy La_0.64Ce_0.25Pr_0.03Nd_0.08Ni_4.19Mn_0.31Co_0.42Al_0.23)and the AB₃-type alloy La_0.80Mg_0.20Ni_2.70Mn_0.10Co_0.55Al_0.10 powders. Through the chemicalmodified PANI-coating the maximum discharge capacity and the high rate dischargeability （HRD） of the alloy electrode all increase and then decrease. In case of treating timet=10min, the alloy electrode shows better kinetic properties. Through the chemicalmodified PANI-coating, the HRD of the AB₅-type alloy increases from18.5%to45.0%and the AB₃-type alloy increases from12.5%to30.4%at a discharge current density of1500mA g–1.To improve the treatment efficiency, we electrodeposit PANI onto the AB₅-type alloyLa_0.64Ce_0.25Pr_0.03Nd_0.08Ni_4.20Mn_0.30Co_0.42Al_0.23and the AB₃-type alloy La_0.80Mg_0.20Ni_2.70Mn_0.10Co_0.55Al_0.10powders using electroplating facility manufactured by ourselves.Owing to the electrodeposit PANI coating, the PANI is coated on the alloy surfaceuniformly more than chemical modified PANI coating through FE-SEM observation. Themaximum discharge capacity and the HRD of the alloy electrode all increase and thendecrease. In case of the treating voltage U=2V and treating time t=1min, the alloyelectrode shows better kinetic properties. Through the electrodeposit PANI-coating, theHRD of the AB₅-type alloy increases from27.4%to42.0%at a discharge current density of1500mA g^-1and the the discharge capacity at the200th cycle of the AB₃-type alloyincreases from281mAh g^-1to295mAh g^-1.For purpose of reduce environment pollution through the conductive polymermodification process, the chemical modification of PPy is used with the AB₅-type alloyLa_0.65Ce_0.25Pr_0.02Nd_0.08Ni_3.85Mn_0.39Co_0.73Al_0.31. Owing to the chemical modified PPycoating, the spongy PPy is coated on the surface of the AB₅-type alloy. The rate ofcapacity retention and the HRD of the alloy electrode all increase and then decrease, andthe alloy electrode shows better electrochemical properties after doping. In case of treatingtime t=8min, Na₂SO₄as the dopant, the alloy electrode shows better kinetic properties.After the chemical modification of PS coating, the net and slices characterized PS iscoated on the surface of the AB₅-type alloy La_0.65Ce_0.25Pr_0.02Nd_0.08Ni_3.85Mn_0.39Co_0.73Al_0.31.In case of treating time t=1min, the coated alloy electrodes exhibited a higher exchangecurrent density, a higher limiting current density, a higher hydrogen diffusion coefficient,and lower charge transfer resistance. Through the chemical modified PS-coating, the alloyelectrode shows better HRD and cycling stability.For the sake of treatment efficiency with polymer microencapsulation, theNi/PANI-coated is used with the hydrogen storing alloy for expand researches. Owing tothe chemical modified Ni/PANI coating, the double characterized Ni and PANI are coatedon the surface of the AB₅-type alloy La_0.65Ce_0.25Pr_0.02Nd_0.08Ni_3.85Mn_0.39Co_0.73Al_0.31. Through the Ni/PANI-coating, the alloy electrode shows better HRD, cycling stability andkinetic properties.