Investigation on Oxidation and Reduction of H2O2 Over Pd,Au,Ni and Co Electrodes on Nanometer Arrays

Author:Wang Zuo

Supervisor:cao dian xue

Database:Doctor

Degree Year:2018

Download:95

Pages:128

Size:8896K

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Energy and environmental issues are two of the most serious problems facing mankind in the 21st century,so the development of safe and clean new energy has become the focus of international research.Fuel cells are electrochemical devices that use electrochemical reactions to convert the high efficiency and low-pollution chemical energy stored in fuel into electrical energy.Fuel cell technology is of great importance to solve the problems such as shortage of fossil energy,low utilization efficiency and environmental degradation,so as to realize energy conservation and emission reduction and development of environmentally friendly low-carbon economy.Direct hydrogen peroxide fuel cell(DPFCs)is a new type of liquid fuel cell that uses both H2O2 as a fuel and H2O2 as an oxidant.Since H2O2 is nontoxic,recyclable,easy to store and transport(liquid),highly electrochemically active,independent of the characteristics of fossil fuels,direct hydrogen peroxide fuel cell becomes an international research hotspot in the field of fuel cells.n this thesis,a series of noble metal cathodes and base metal anodes with three-dimensional open structure were designed and synthesized for the direct hydrogen peroxide fuel cell.The catalytic activities of H2O2 in electro-reduction(cathodic reaction)and electro-oxidation in alkali anode reaction)activity and stability,assembly and examination of the performance of DPFCs.The main research contents are as follows:Firstly,the C@TiC nanowire arrays were successfully grown on Ti6Al4V alloy by chemical vapor deposition.Then Pd and Ni were directly deposited on the C@TiC nanowire array substrate by electrochemical coprecipitation to prepare Pd-Ni/C@TiC electrode.Finally,the NP-Pd/C@TiC nanowire electrode with porous structure was obtained by chemical de-alloying to remove Ni element.FESEM test results show that the surface of titanium alloy is completely covered by C@TiC nanowires(length 7μm and diameter 150 nm)of the array structure.After Pd-Ni co-deposition on the surface of nanocrystalline nanostructures,when the metal Ni is removed by etching,a uniform and porous noble metal Pd catalyst is formed on the nanowires.The catalytic performance of NP-Pd/C@TiC electrodes under different concentrations of H2SO4 and H2O2 was studied by linear sweep voltammetry and chronoamperometry.The results show that NP-Pd/C@TiC electrode exhibits the best electrochemical catalytic performance(0.2 V vs.Ag/AgCl potential)when the concentration of hydrogen peroxide is 2.0 mol L-1 and the concentration of sulfuric acid is 2.0 mol L-1 Under the reduction of current density reached 3.47 A mg-1).The NP-Pd/C@TiC nanowire array electrode with porous structure was obtained by electrochemical deposition of noble metal(Pd)-base metal(Ni)method and then by chemical dealkylation to remove base metal(Ni)With a large electrochemical activity of specific surface area,reducing the amount of precious metals,very suitable for direct hydrogen peroxide fuel cell cathode catalyst.The cell performance of DPFCs with porous Ni/Ni foam as the anode and NP-Pd/C@TiC nanowire electrodes as the cathode was assembled and investigated.At room temperature,when the flow rate was 10 cm3min-1,the anolyte was 4.0 mol dm-3KOH+1.0 mol dm-3H2O2 and the catholyte was 2.0 mol dm-3 H2SO4+2.0 mol dm-3 H2O2,The maximum output power of the battery is 44.2 mW cm-2.Pd-Au/TiC NAs catalytic electrodes were deposited directly on TiC nanowire arrays using square-wave potential electrodeposition without any conductive agent and binder.SEM analysis showed that the obtained Pd-Au/TiC NAs catalytic electrodes had different microstructures(pineapple root,haze and feather).The morphology of the Pd-Au cathode catalyst can be easily adjusted and controlled by changing the electrochemical deposition conditions.In H2O2+H2SO4 electrolyte system,the relationship between the relative content of Pd-Au and the electrochemical performance of the catalytic reduction of hydrogen peroxide was studied by linear sweep voltammetry.As the Pd content increased,the catalytic electrode The catalytic activity of Pd5Au1/TiC NAs electrode has the best catalytic hydrogen peroxide reduction activity.Then,the catalytic performance and stability of Pd5Au1/TiC NAs electrode under different concentrations of H2SO4 and H2O2 were systematically investigated by linear sweep voltammetry and chronoamperometry.The results showed that the current density of Pd5Au1/TiC NAs electrode was 0.480 A cm-2when the electrode potential was 0.2V in 2.0 mol dm-3 H2O2 and 2.0 mol dm-3 H2SO4 electrolyte.mg-1,divided by the total loading of noble metal catalyst).The cell performance of DPFCs with porous Ni/Ni foam as anode and Pd5Au1/TiC NAs electrode as cathode was assembled and investigated.At room temperature,when the flow rate was 10 cm3 min-1,the anolyte was 4.0 mol dm-3 KOH+1.0mol dm-3 H2O2 and the catholyte was 2.0 mol dm-3 H2SO4+2.0 mol dm-3 H2O2,The maximum output power of the battery is 56.5 mW cm-2.Ni/TiC NAs and Co@TiC NAs nanowire array electrodes with large specific surface area were prepared by depositing transition metal Ni and Co directly on TiC nanowire array substrate by electrochemical deposition.SEM analysis shows that the diameter of a single Ni@TiC NAs nanowire is 470 nm and shows a spine structure,while the Co catalyst exhibits an ultrathin nanosheet structure with a single Co@TiC NAs diameter of 405 nm.Cyclic voltammetry and chronoamperometry were used to study the catalytic activity and stability of the prickly Ni@TiC NAs and Co@TiC NAs electrodes in KOH+H2O2 electrolyte solution respectively.Studies have shown that the prickly Ni@TiC NAs electrode catalyzed hydrogen peroxide electrooxidation has better catalytic activity and stability than the sheet-like Co@TiC NAs electrode.The cell performance with Ni@TiC NAs as the anode and Au-Pd/CFC as the cathode DPFCs was assembled and investigated.The open circuit voltage of the battery was 0.90 V at room temperature.When the flow rate was 10 cm3 min-1,the anolyte was 4.0 mol dm-3KOH+1.0 mol dm-3H2O2 and the catholyte was 2.0 mol dm-3H2SO4+2.0 mol dm-3 H2O2,the maximum output power of the battery reached 30.2 mW cm-2,and its battery performance was significantly higher than that of the reported battery performance of the noble metal Au-Pd/CFC anode,indicating that the use of the base metal Ni@TiC NAs The anode not only reduces the cost of the fuel cell but also improves the performance of the DPFCs.