基于有序中孔碳化钨/炭复合材料的低Pt无Ru甲醇氧化电催化剂的研究

The low activity, sensitivity to poison, low stability and high cost of the conventional PtRu/C electrocatalyst for methanol electrooxidation hinders the practical application of direct methanol fuel cells (DMFC). Tungsten carbide possesses the characteristics of Pt-like catalytic property, CO-resistance ability and high stability in acidic media at high potential, however its low surface area and undesirable pore structure for mass transfer limits its applications in catalysis. To address the above problems, based on the design and control of microscale pore structure of tungsten carbide/carbon composite materials, the present proposal aims to develop novel low-Pt non-Ru electrocatalyst supported on ordered and mesoporous tungsten carbide/carbon composite materials with high surface-area in order to enhance the electrocatalytic activity for methanol electrooxidation, increase the resistance to CO poison, prolong the stability and at the same time reduce the cost of the catalyst. The present project includes the following main research contents: (1) synthesizing ordered mesoporous tungsten carbide/carbon composite materials with high surface area and different pore sizes and pore structures by a template-in-situ-high-temperature-synthesis method, and (2) with them as the support, preparing low-Pt electrocatalyst by microwave technique, and then (3) characterizing their physico-chemical properties by the techniques of XRD、TEM etc and evaluating methanol electrooxidation activity, CO-resistance ability and stability by using the techniques of voltammetry, AC impedance, electrochemical accelerating method etc. Finally, exploring the relationship between the electrochemical performance and the composite, morphology and microstructure of tungsten carbide/carbon composite materials supported low-Pt non-Ru electrocatalysts and then clarifying the corresponding electrocatalytic mechanism. Through this project, it is expected that it is of vital importance because the activity towards methanol electrooxidation, the CO-tolerance ability and stability could be enhanced and thus accelerating the practical applicability of DMFCs.

传统的甲醇氧化PtRu/C电催化剂活性低、易毒化、稳定性差和成本高，限制了直接甲醇燃料电池（DMFC）的实用化。碳化钨具有类Pt催化特性、抗CO毒化和酸性高电位下稳定等优点，但其低的比表面积及不利于传质的孔结构，制约了它在催化中的应用。为此，本项目拟采用碳化钨/炭复合材料，在对其微观孔结构进行设计与调控的基础上，研制高比表面积有序中孔碳化钨/炭复合材料负载的新型低Pt无Ru电催化剂，以期提高甲醇氧化活性、抗毒化能力、稳定性和降低成本。研究内容包括采用模板-原位高温合成技术，合成不同孔径和孔结构的有序中孔碳化钨/炭复合材料；进而采用微波技术，制备其负载的低Pt催化剂。通过XRD、TEM等表征材料的物化性质；利用伏安法、交流阻抗、电化学老化等考察催化剂甲醇氧化性能，探索其性能和结构、组成之间的关系，阐明催化机理。本项目成果对提高甲醇氧化电催化剂的性能，降低成本，促进DMFC实用化，有重要意义。

传统的甲醇电氧化PtRu/C催化剂活性低、易毒化、稳定性差、成本高，尤其是Ru的溶解，不仅降低了PtRu催化剂的抗CO性，而且溶解的Ru离子能渗透到阴极，降低氧还原活性，且能加速Nafion电解质膜的降解，限制了直接甲醇燃料电池（DMFC）的实用化。本项目针对上述问题，利用碳化钨具有类Pt催化特性、抗CO毒化和酸性高电位下稳定等优点，联用水热技术、模板法和高温后处理技术，并借助脉冲微波助多元醇制备负载型电催化剂技术，微/纳尺度上构筑和合成了碳化钨/有序介孔炭（WC/OMC）负载的低Pt无Ru甲醇氧化电催化剂（Pt@WC/OMC），研究了其结构、组成和甲醇氧化活性、稳定性和抗CO性能之间的关系，探索了催化机理，完成了研究计划内容。同时，拓展采用本项目有序材料和炭基负载型催化剂的制备技术，开发了氧还原活性高、稳定的氮、硫（N、S）共掺杂有序介孔炭（NS-OMC）氧还原非金属电催化剂，及Pd基葡萄糖氧化非Pt催化剂，为低、非Pt电催化材料的研究提供了实验积累。研究成果已发表SCI期刊论文9篇、会议论文6篇；培养博士研究生1名、硕士研究生4名；国外专家来访1人次、项目组成员赴国外进行学术交流6人次。.执行项目中取得的主要代表性成果如下：1）首次采用硬模板-水热-高温碳化联合技术合成有序、中孔、碳化钨/炭（WC/OMC）复合功能性载体，以此负载Pt，提高了Pt对甲醇氧化的活性和稳定性。2）以WC/OMC为基体，采用浸渍-高温处理技术，利用有序介孔炭阵列的限域作用及高比表面积特性，可控制备了小粒径，高分散的碳化钨-钨铁矿（WC-FeWO4）纳米复合物，嵌于氮掺杂有序介孔炭（NOMC）中，成功合成WC-FeWO4@NOMC氧还原非贵金属电催化剂。无论在酸性还是碱性介质中，它们都具有与Pt/C相当、甚至更优的催化活性和稳定性及更优异的抗甲醇性。3）开发了一种简单易行的杂原子掺杂、且组分易调的有序炭复合材料制备途径，获得了高比表面积、高度有序的N/S共掺杂介孔炭材料（SN-OMC）。4）利用氨水络合技术和CeO2修饰载体功效，有效降低负载型Pd基催化剂的金属粒径，提高了其电催化葡萄糖氧化性能。