The Preparation Of Electrode Materials And The Research Of Performance In The Direct Peroxide-Peroxide Fuel Cell

Hydrogen peroxide?H₂O₂?is known as a compound composed of hydrogen and oxygen elements,and as an oxidant has been widely used.In recent years,H₂O₂ has been used as the oxidizer?H₂O₂+2H++2e-= 2H2O?,instead of O2 in the air,for some special fuel cells?such as metal-hydrogen peroxide fuel cells,direct boronhydride-hydrogen peroxide fuel cells,direct hydrazine-hydrogen peroxide fuel cells,etc.?,so that the fuel cells can operate in anaerobic environment?such as space and underwater power?.In fact,H₂O₂ can be used as both oxidant?electron acceptor?and fuel?H₂O₂=H2O+1/2O2,?G=-120 kJ·mol-1?,which can be also oxidated?H₂O₂=1/2O2+2H++2e-?in a fuel cell engine?electron donor?.Based on this theory,many researchers put forward using H₂O₂ as a fuel and oxidant in a new type of fuel cell,namely direct peroxide-peroxide fuel cell?DPPFC?.This dissertation aims at the performance and theory of the catalyzing electrode materials in this new type fuel cell.We have successfully prepared a series of noble and non-noble metal electrodes with three dimensional?3D?open structures,and have obviously improved the catalytic activity and stability of H₂O₂ reduction in acidic medium and H₂O₂ oxidation in alkaline solution.DPPFC with these electrodes as anode and cathode also displays exciting cell performance,and the mechanism of H₂O₂ reaction on the electrode surface is explored by electrochemical experiments.Firstly,the preparation of carbon fiber cloth supporting dendritic Pd?Pd/CFC?and Au electrode?Au/CFC?with 3D open structure by electrochemical method was studied.The as-prepared electrodes had special morphology and structure identified by using TEM and SEM technique.Electrochemical experiments have proved that Pd/CFC and Au/CFC electrodes exhibited high electrocatalytic activity and stability,and the current density towards H₂O₂ electroreduction and oxidation was far greater than the commercial catalyst.The high-performance two-compartment DPPFC with the Pd/CFC electrode both as the anode and cathode has also been demonstrated.The DPPFC displayed a stable OCP of?0.9 V.The peak power densities of 14.3 mW·cm^-2 at 20? and 58.4 mW·cm^-2 at 60?were achieved,indicating that DPPFC has a great development space.Meanwhile,we have also found that the polarization overpotential on the cathode?H₂O₂ electroreduction in acid?was significantly greater than that on the anode?H₂O₂ electrooxidation in base?,showing that H₂O₂ reduction had the slower kinetics than oxidation,namely the DPPFC performance is mainly determined by the cathode reaction.Secondly,we investigated CFC supporting Au-Pd bimetallic catalyst,and prepared the flower-like Au-Pd nanoparticles by the square wave potential electrodeposition.By changing electrodeposition conditions,a series of different morphology,composition and particle size of Au-Pd alloy nanoparticles was successfully synthesized.To test the electrochemical performance of alloy particles with different composition,we found that they had high catalytic activity towards H₂O₂ electroreduction in acidic medium,and higher than that on the precious metal Pd electrode as well as the commercial Pd/C electrode with the same loading.In addition,CFC supporting dendritic precious metal composite electrode?Au@Pd/CFC?was prepared by a two-step square wave potential electrodeposition and the DPPFC with Au@Pd/CFC electrode both as the anode and cathode also exhibited high performance.The peak power density of 20.7 mW·cm^-2 at 20? was obtained.H₂O₂ oxidation has a faster kinetics than reduction.Thus further reduce the cost of DPPFC,the anode can use non-noble metal materials.Therefore,we prepared CFC supporting Ni?Co nanofilm?Ni/CFC and Co/CFC?by the square wave potential electrodeposition and applied them as the anode matching with Pd/CFC cathode in a DPPFC,then systematically examined the stability and the influence of temperature,electrolyte concentration and the flow rate on the cell performance.We have assembled the DPPFC with Pd/CFC as the cathode and Ni/CFC?Co/CFC and Au/CFC as the anode,respectively.Notably,the DPPFC with Ni/CFC as the anode had the highest OCP,which could reach 0.87V?0.85V for Au/CFC,0.83V for Co/CFC?.For the discharge performance of fuel cell,the DPPFC with Ni/CFC as the anode also exhibited the highest performance,even higher than the previous anode?Au/CFC?.The peak power density was 21.6mW·cm^-2,corresponding to the cell voltage of 0.6V and current density of 36 mA cm^-2.Besides,we also prepared Ni foam supporting porous metal film electrode with high porosity?Ni/Ni-foam and Co/Ni-foam?using hydrogen bubbles as the template,and then decorated the surface of electrode with previous metals?Au-and Pd-modified Co/Ni foam?.The catalytic behavior of H₂O₂ oxidation reaction on the electrode surface was evaluated by cyclic voltammetry technique?CV?.Relevant research on mechanism indicated that a series of interaction of H₂O₂ with the surface already covered by low valance nickel species during H₂O₂ oxidation and Ni?OH?₂ was the real active sites.Experimental results revealed that porous Co film had low catalytic activity towards H₂O₂ reduction in alkaline medium.After decoration with precious metals,the electrode showed high catalytic performance and good stability.Due to the porous metal film with large specific surface area,it can provide a desired framework for noble metal deposition which could remarkably reduce the usage of precious metals.