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摘 要随着固体碱性电解质膜的出现，直接碱性乙醇燃料电池日益受到广泛关注。在碱性环境中，Pd基催化剂具有较高催化活性，且成本比Pt低。本文利用在传统化工领域具有较高加/脱氢催化活性，被称为“类贵金属”的WC对不同的碳载体进行修饰制备不同WC含量的复合载体，进而负载Pd合成二元催化剂，并考察其在碱性环境中对乙醇的电氧化催化活性。
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本论文采用钨酸钠为前驱体，结合溶胶凝胶法和微波技术在碳载体上沉积WO3颗粒，在还原性气氛下进行程序升温碳化制备不同WC含量的碳载碳化钨复合载体，并利用微波法沉积上Pd纳米颗粒，获得二元催化剂。通过物理吸脱附、X射线衍射和电化学分析技术研究不同合成工艺、不同载体对其物相、结构、电化学性能的影响，并进一步分析其电化学反应机理。
通过研究不同还原性气氛（1.3%H2+4%CH4+Ar和25%H2+75%CH4）、不同气体流速（29~120 ml/min）和不同保温时间的影响，发现在100ml/min的1.3%H2+4%CH4+Ar气氛下975℃保温1小时条件下所获得20WC/XC复合载体中WC粒径最小，为13.1 nm。比较不同WC含量Pd/nWC/XC催化剂在1M KOH+1MEtOH溶液中的循环伏安性能发现，WC含量为20%时，乙醇电催化氧化峰值电流最高。进一步对比Pd/20WC/XC和Pd/20WC/MH1的循环伏安曲线，发现以VulcanXC-72R为碳载体所获得的Pd/20WC/XC催化剂对乙醇电氧化峰值电流(3.83mA)，为Pd/20WC/MH1催化剂(2.18mA)的近两倍。这可能与XC孔径集中分布在30.3nm处，较有利于Pd和WC负载有关，Pd/20WC/XC中Pd粒径为6.8nm，约为Pd/20WC/MH1中(12.7nm)的一半。
通过对Pd/20WC/XC催化剂在不同浓度KOH+1M乙醇溶液中的线性伏安扫描曲线和Tafel曲线分析其乙醇电化学反应动力学，发现：随着KOH浓度升高，乙醇电氧化峰值电流增加，但当KOH大于等于2M时，乙醇电氧化峰值电流反而下降；根据Temkin-type等温方程，OH-的反应级数近似为0.3；根据Butler-Volmer方程，求得乙醇氧化反应传递系数α为0.13；乙醇在Pd/20WC/XC电催化氧化反应总方程式为 。利用Pd/20WC/XC催化剂在1M KOH+1M乙醇溶液中不同扫速下的循环伏安扫描曲线分析乙醇电催化氧化峰值电流与扫速之间的关系，求得乙醇扩散系数为D=0.000059 cm2/s。
关键词：WC；碳纳米管；乙醇氧化；动力学；溶胶凝胶法10553
Abstract
With the appearance of a solid alkaline electrolyte membrane, direct alkaline ethanol fuel cells have attracted widespread attention. In an alkaline environment, Pd-based catalysts show high catalytic activity with lower cost than Pt. WC, the traditional industry catalyst for hydrogenation/ dehydrogenation reactions, referred to be "noble-liked" catalyst. In this paper, WC is used to decorate different carbon supports with varied percentage to prepare composite carriers. Then Pd is loaded on the composite carriers to obtain binary catalysts with varied WC content. The catalytic activity of the binary catalysts for ethanol electro-oxidation in an alkaline environment is studied.
In this paper, sodium tungstate is used as a precursor to deposite WO3 particles on carbon support by sol-gel method combined with microwave technology. Then it is carbonized in a reducing atmosphere by temperature-programmed method. Then nano-sized Pd is loaded by microwave method to obtain carbon supported binary catalysts. The catalysts are characterized by physical ad/desorption and XRD. The properties of the catalysts and the mechanism of ethanol electrooxidation are measured by electrochemical technology, such as cyclic voltammograms, linear sweep voltammograms and Tafel.
By studying the influence of processing conditions, such as reducing atmosphere (1.3% H2 +4% CH4 + Ar and 25% H2 +75% CH4), gas flow rate (29 ~ 120 ml / min) and holding times, it is found that 20WC/XC with the smallest WC particle size, 13.1nm, is synthesized in 100ml/min 1.3% H2 +4% CH4 + Ar atmosphere at 975 ℃ for 1 hour. According to the peak current of ethanol electrooxidation, Pd/20WC/XC catalyst shows the highest catalytic activity in 1M KOH +1 M EtOH. Both of Carbon nanotubes (MH1) and VulcanXC-72R carbon black (XC) are used as support. The ethanol electrooxidation peak current on Pd/20WC/XC (3.83mA) is higher than that on Pd/20WC/MH1 (2.18mA). It may because of the smaller Pd particle size (6.8nm) on Pd/20WC/XC, which can be contributed to the concentrated pore size distribution (30.3nm) of XC.