The Study Of Anode Electrocatalyst And Single Cell In Ascorbic Acid Fuel Cell

Due to the environmental pollution and source shortage,there is a trend of exploring the new energy resource,in which fuel cell has attracted attention because of its low pollution and high energy conversion efficiency.For fuel used in fuel cel,safety,transport,and price problems exist in hydrogen;crossover and toxicity problems exist in methanol.As one of solutions for these problems,biomass fuel including ascorbic acid（AA）may be the substitute.Advantages of AA contain strong reducibility,nontoxicity,and low price,so it is of high potential in application.Direct ascorbic acid fuel cell（DAAFC）is a device conversing chemical energy of AA to electric energy,which still needs improvement in power density and cost.In this thesis,acid treated carbon（ATC）is used as anodic electrocatalyst for DAAFC in alkaline working condition,and chemical oxidation energy(Ea_Chem)and electrochemical oxidation(Ea_Elec)of AA are analyzed.Details are discussed as follow:（1）To prepare ATC,commercial carbon BP2000 is acidic treated with 4 M HNO₃.A large amount of oxygen containing groups were produced on carbon surface,which improved the electrocatalytic activity and hydrophilicity of carbon.Next,ATC was firstly used as anodic electrocatalyst in alkaline membrane DAAFC,and a series of parameters of single cell were optimized.When the fuel was 0.5 M AA and 1 M NaOH,DAAFC of the CCM（Catalyst coated membrane）assembly method with the ATC loading of 0.5 mg·cm^-2 and 25 wt% ionomer reached the highest power density of 18.5 mW·cm^-2.Stability test at 25 and 75°C both showed a stable working state of DAAFC in 25 min with 30 mL fuel solution in circulation.（2）Ea_Chem and Ea_Elec of AA were evaluated.Ultraviolet-visible light spectroscopy was used and the fitting result calculated Ea_Chem of AA in alkaline condition as 37.095 kJ·mol^-1;Electrochemical impedance spectroscopy was used,and the fitting result calculated EaElec of AA in DAAFC without and with ATC as 34.507 and 26.462 kJ·mol^-1.The catalytic activity of ATC accounted for the decrease of activation energy.When the potential in test was 50,100,150,200 mV lower than open circuit potential,Ea_Elec was 23.328,22.794,19.015,18.125 kJ·mol^-1.Ea_Elec was decreased with potential decrease,reflecting the dominating factor of AA chemical oxidation transformed from activation into mass transfer.（3）Some initial exploratory work was made.N-doping carbon materials was prepared and the catalytic activity for AA oxidation in acidic condition was evaluated.PdAg alloy was prepared in water phase synthesis method and the catalytic activity for AA oxidation in alkaline condition was evaluated,in which Pd₃Ag₁ was of the best activity and high application potential.Firstly,citric acid served as the fuel of fuel cell in which ATC served as anodic electrocatalyst,obtaining a power density of 0.76 mW·cm^-2.