【作者】 杨帆；

【导师】 曹殿学；

【作者基本信息】 哈尔滨工程大学 ， 材料学， 2014， 博士

【摘要】 过氧化氢（H₂O₂）是人们熟知的一种由氢和氧元素构成的化合物,作为一种氧化剂而广泛使用。近年来,H₂O₂被用做一些特殊燃料电池（如金属半燃料电池、直接硼氢化物燃料电池、直接肼燃料电池等）的氧化剂（H₂O₂+2H++2e-=2H2O）,替代空气中的氧气,从而使得这些燃料电池可于无氧环境下工作（作为空间和水下电源）。实际上,H₂O₂既是氧化剂（电子受体）,还是储能物质（H₂O₂=H2O+1/2O2,△G=-120 kJ·mol-1）,能够发生电氧化反应（H₂O₂=1/2O2+2H++2e-）,因而可以作为燃料电池的燃料（电子供体）。基于此,人们提出利用H₂O₂即作为燃料又作为氧化剂的新型燃料电池-直接过氧化氢燃料电池（DPPFC）。本论文正是针对这一新型燃料电池的催化电极开展性能和理论的研究。成功制备了一系列具有三维立体开放结构的贵金属及非贵金属电极,显著地提高了H₂O₂在酸性和碱性溶液中的电催化活性和稳定性,以它们作为阴阳极的DPPFC具有较高的电池性能。通过电化学测试初步探究了 H₂O₂在电极表面发生电化学反应的机理。研究了碳布（CFC）负载的Pd、Au单金属催化电极,通过电化学方法制备具有三维立体开放结构的碳布负载的树枝状Pd电极（Pd/CFC）和Au电极（Au/CFC）,经TEM和SEM等表征,所制备的电极具有特殊的形貌和结构。电化学实验证明树枝状的Pd/CFC电极和Au/CFC电极具有很高的电催化活性和稳定性,对H₂O₂电还原和电氧化的催化电流密度远远大于商业催化剂。以Pd/CFC电极作为电池的阴阳极构成的双室DPPFC的开路电压稳定在0.9 V以上,20℃下峰值功率密度达14.3 mW·cm^-2,60℃下则高达58.4 mW·cm^-2,展现了 DPPFC具有极大的发展空间。H₂O₂在酸中电还原反应（阴极反应）的极化过电势显著大于H₂O₂在碱中电氧化反应（阳极反应）的极化过电势,表明H₂O₂电还原动力学慢于电氧化反应,即DPPFC性能主要由阴极决定。研究了碳布（CFC）负载的Pd-Au等双组分复合催化电极。运用方波电势电沉积法制备出CFC负载的具有花状的Au-Pd贵金属合金纳米粒子（Au-Pd/CFC）。通过改变电沉积条件,制备出一系列不同形貌、组成和粒径的Au-Pd合金纳米粒子。对不同组成的合金粒子进行电化学性能测试,发现它们对H₂O₂在酸性介质中的电还原反应具有很高的催化活性,且高于同样载量的贵金属Pd电极以及商业Pd/C电极。此外,还运用两步方波电势电沉积法制备出具有树枝状结构的碳布负载的贵金属复合电极（Au@Pd/CFC）,以其为阴阳极的DPPFC具有很高的电池性能。在20℃下,电池的峰值功率密度高达20.7mW·cm^-2。由于DPPFC阳极的反应动力学速度明显快于阴极,为了进一步降低电池成本,阳极催化剂可以采用非贵金属材料。因此,运用方波电流电沉积法制备了碳布负载的Ni、Co纳米薄膜电极（Ni/CFC和Co/CFC）,并将它们分别作为阳极与Pd/CFC阴极组成DPPFC,系统地研究了电池的稳定性和不同温度、不同电解液浓度以及流速对电池性能的影响。结果表明,非贵金属材料对H₂O₂电氧化反应表现出非常理想的催化性能。以Pd/CFC电极为阴极,分别以Ni/CFC、Co/CFC和Au/CFC为阳极构成双室DPPFC,其中以Ni/CFC为阳极的电池开路电压最高,达到了 0.87 V（Au/CFC为0.85 V,Co/CFC为0.83 V）,而对于电池的放电性能而言,此电池也显示出最高的性能,甚至超过了贵金属阳极Au/CFC,其最大输出功率为21.6 mW·cm^-2,对应的放电电流密度为36 mA·cm^-2,电压为0.6V。这些结果充分表明,非贵金属材料完全可以取代贵金属作为DPPFC的阳极。此外,利用氢气泡模板辅助电沉积法制备了泡沫镍负载的高孔隙率的多孔金属薄膜电极（Ni/Ni-foam和Co/Nifoam）,并对其表面进行贵金属修饰（Au-和Pd-modified Co/Nifoam）。运用循环伏安（CV）等技术研究了其对H₂O₂电氧化反应的催化行为。相关的机理研究指出,过氧化氢在Ni表面发生电氧化反应过程中会与表面低价态的Ni离子发生一系列的反应,Ni（OH）₂是真正的催化活性中心。检测到多孔Co金属薄膜对H₂O₂在碱性溶液中的电还原反应的催化活性很低,经过贵金属修饰后的电极具有很高的催化活性和良好的稳定性。由于多孔金属薄膜具有很大的比表面积,为贵金属提供了良好的沉积骨架,大大降低了贵金属的使用量。更多还原

【Abstract】 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.更多还原