【摘要】 质子交换膜燃料电池(proton exchange membrane fuel cells, PEMFCs)作为高效清洁的电化学能源转换装置,是目前应用最广泛、研究最热门的氢燃料电池之一.基于PEMFCs的低成本与高性能需求, Pt合金催化剂极具研究前景.电化学活性面积(electrochemical active surface area, ECSA)是筛选燃料电池高效催化剂以及研究催化动力学基础理论的重要参数,其评价的准确性至关重要.对于Pt/C催化剂ECSA的表征方法已经成熟,然而Pt合金因其不同于Pt/C催化剂的化学组成和结构,直接将传统Pt/C催化剂ECSA表征方法移植到Pt合金催化剂,将不再满足表征准确性需求.本文对Pt合金催化剂ECSA的表征方法及其表征ECSA偏差的来源进行综述.更多还原

【Abstract】 Proton exchange membrane fuel cells(PEMFCs) are one of the most promising technologies for clean energy. However,some fundamental challenges remain to be addressed before PEMFCs with low Pt usage become the top contender. To achieve high-performance and cost-effective in PEMFCs, Pt-alloy catalysts are currently one of the bright catalyst candidates. Electrochemical active surface area(ECSA) is a key indicator to gauge the performance of Pt catalysts and an important parameter in studying catalytic kinetic issues in PEMFCs. Therefore, the accurate estimation on the ECSA is exceptionally critical. Known and mature ECSA characterization methods for Pt/C catalysts have been established, which have been widely available for many decades. However, there are issues remaining for ECSA characterization of Pt-alloy catalysts due to the significant difference in properties, such as composition, particle size, shape compared with Pt catalysts. Therefore, the ECSA characterization approaches for Pt/C catalysts cannot be transplanted to Pt-alloy catalysts since the characterization accuracy will no longer meet the requirement.In this review, the present characterization methods of ECSA for Pt-alloy catalysts and their inaccuracy sources are described and explained, including physical methods and electrochemical methods. The physical methods cover X-ray diffraction(XRD) and transmission electron microscopy(TEM), while hydrogen underpotential deposition(H-upd),carbon monoxide stripping(CO-stripping) and underpotential deposition of metals are classified as electrochemical methods. The ECSA obtained from XRD and TEM is considered to be theoretical ECSA to evaluate the catalyst utilization.Therefore, the ECSA calculated from XRD and TEM is usually used as a reference. Owing to the differences in surface adsorption properties after alloying, it will be underestimated the ECSA of Pt-alloy catalysts by H-upd and CO-stripping,which lead to exaggerate specific activity compared with Pt/C catalysts. Generally, it is accepted that the surface area from electrochemical methods is active, but in fact it is still controversial. The surface area of different metal components of Ptalloy catalysts could be quantified by metal underpotential deposition method. Since the contribution of different metal components to the catalytic activity is different, the actual ECSA cannot be simply calculated by adding the respective metal surface area.The active surface area of Pt-alloy catalysts is affected by many factors, making it hard to develop a universal method to characterize the ECSA accurately. To evaluate the performance of Pt-alloy catalysts more objectively, it is necessary to clarify the relationship between the surface structure of Pt-alloys catalysts and adsorption energy as well as the coverage of adsorbed species. It is essential to develop an innovative electrochemical method with high accuracy which is also important and urgent for the research on new Pt-alloy catalysts with high-performance.更多还原