Preparation Of Ionic Compound Doped Alkaline PVA Membrane And Its Application In Fuel Cell

Fuel cell is an energy conversion device,which can directly convert chemical energy stored in fuel and oxidant to electrical energy through electrochemical reaction,and has the advantages of high energy conversion efficiency,low noise,no pollution and long life.Direct borohydride fuel cell（DBFC）which is developed on the basis of proton exchange membrane fuel cell（PEMFC）,has attracted much attention as a potential candidate of power supplier due to its high open circuit voltage（1.64 V）,theoretical energy density（5.67 Ah/g）,high theoretic energy conversion rate（91%）,storage convenience and non-pollution to the environment.However,the use of expensive solid electrolyte membrane limits its commercialization.Therefore,in recent years,one of the hot spots of DBFC technology research is to develop a cheap and efficient solid electrolyte membrane.In this paper,ionic compound doped alkaline polyvinyl alcohol（PVA）membrane has been developed as a cheap and efficient solid electrolyte membrane and applied in DBFC.Ionic compound doped alkaline PVA-AER membrane was prepared by using these raw materials:PVA,anion-exchange resins（AER）and ionic compound inorganic salts such as CoCl₂·6H₂O,CoSO₄·7H₂O and KCl.X ray diffraction（XRD）,X ray absorption near edge structure spectroscopy（XANES）,micro X X-ray fluorescence spectroscopy（m-XRF）and scanning electron microscopy（SEM）were applied to characterize the micro structure of the membrances.The membrane ion exchange capacity,water content and swelling rate,thermal stability,power performance and fuel utilization werealso studied,the relationship between the microstructure and electrochemical properties of the membrane were studied thoroughly.Firstly,the CoCl₂doped PVA-AER composite membrane with cobalt ion concentration of 0.4%（CoCl₂-PVA-AER）was studied.The results show that cobalt ions exist in the form of+3 valence and distribute in the membrane homogeneously.The ion exchange capacity is 1.32mmol/g,the ion conduction rate is 31.7 mS/cm at 20°C,which is 1.2 times of N117membrane（25.8 m S/cm）and 1.5 times of PVA-AER membrane（21.6 mS/cm）at the same condition.The DBFC with CoCl₂ doped alkaline PVA-AER membraneachieves a maximum power density of 155.4 mW/cm² at 30°C and 216.9 mW/cm² at 60°C.And DBFC usingthis membrane exhibited good stability at room temperature.After discharging for 2400 min,the cell voltage dropped by 8%.When DBFC uses CoCl₂-PVA-AER membrane as the electrolyte membrane,the anodic reaction impedance and the cathode reaction impedance are improved.Then the influence of doping concentration of ionic compound on the composite membrane is studied.The results show that the different cobalt ion doping concentration does not affect the existence of cobalt ions in the composite membrane.The composite membrane possesses the best thermal stability when the cobalt doping concentration is 0.4%,and the fuel cell using this membrane exhibits the best electrochemical performance.The coulombic efficiency of the composite membrane shows a parabolic curve with the increase of cobalt doping concentration.The composite membrane has the highest fuel utilization rate when the cobalt ion concentration is 2%.Finally,the effects of the types of anion of the compounds on the electrochemical performance of the alkaline anion exchange membrane were investigated.For different anions,the DBFC using membrane with 0.4%CoCl₂ exhibits the highest power density at 30°C,while the DBFC using membrane with 0.4%CoSO₄ exhibits the highest power density at60°C.This shows that the improvement by the SO₄^2-anion is more obvious than the Cl^-anion as the increase of working temperature.For different cations,the electrochemical performances of the composite membranes at both 30°C and 60°C follow the sequence:CoCl₂-PVA-AER>FeCl₃-PVA-AER>KCl-PVA-AER>PVA-AER.