In situ time-resolved dynamic surface events on the Pt/C cathode in a fuel cell under operando conditions
In situ time-resolved dynamic surface events on the Pt/C cathode in a fuel cell under operando conditions
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DOI：
10.1002/anie.200604732
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发表时间：
2007-01-01
影响因子：
16.6
通讯作者：
Iwasawa, Yasuhiro
中科院分区：
文献类型：
--
作者：
Tada, Mizuki;Murata, Shigeaki;Iwasawa, Yasuhiro
环境友好型质子交换膜燃料电池（PEMFC）被认为是解决环境和能源问题的一种可能的方法。[1-8]为了使燃料电池汽车成为现实，必须提高Pt/C阴极催化剂的活性和寿命。为此，我们已经开发了一种新的时间门控快速XAFS（QXAFS）技术与1秒的时间分辨率和能量色散XAFS（DXAFS）系统与4毫秒的时间分辨率。使用这些技术，我们已经观察到的电化学反应机制，并发现证据的动态表面事件，涉及Pt溶解在Pt/C阴极，电子转移过程的反应动力学，氧化还原结构的变化（8个基本步骤），和一个显着的时间滞后这些事件之间的第一次在operando燃料电池条件下。对质子交换膜燃料电池中电流的真实的测量表明，从开路到工作状态的通电过程在其电极表面上引起快速的电化学反应，该反应在几秒钟内完成。这种具有巨大能量传递的通电和断电过程（电压从开路电压（OCV=例如1.0 V）变化到工作电压（例如0.4 V））对于燃料电池系统的商业应用是不可或缺的。然而，活性金属颗粒的表面原子倾向于稍微溶解到与阴极催化剂层接触的电解质中，并且不期望的Pt颗粒（或层）沉积在电解质中。[9，10]这种效应是一个问题，因为特别是汽车，需要在电池电压快速变化的情况下连续重复开/关过程以改变汽车的速度。为了克服这些严重的问题，必须在真实的时间内在电压步进过程中原位研究电极表面上的反应机理。然而，据我们所知，还没有报道已经充分探索和确定的反应动力学的金属催化剂的结构变化和电极表面上的电化学反应在PEMFC。我们研究了Pt/C催化剂上快速电压控制过程中涉及的电化学过程的机理。从Pt催化剂中的带电和结构变化的观点出发，使用原位时间分辨快速X射线吸收精细结构（QXAFS）光谱直接监测作为催化剂的Pt纳米颗粒中的化学键和电子状态。
Environment-friendly proton-exchange-membrane fuel cells (PEMFC) are considered a possible answer to environmental and energy problems.[1–8] To make fuel-cell automobiles a reality, the activity and life of the Pt/C cathode catalyst must be improved. Towards this goal, we have developed a novel time-gating quick XAFS (QXAFS) technique with 1-s time resolution and an energy-dispersive XAFS (DXAFS) system with 4-ms time resolution. Using these techniques, we have observed the electrochemical reaction mechanism and found evidence for dynamic surface events involving Pt dissolution at the Pt/C cathode, the reaction kinetics of the electrontransfer processes, redox structural changes (eight elementary steps), and a significant time lag among those events for the first time under operando fuel-cell conditions. Measurement of the current in a PEMFC in real time shows that a power-on process from open circuit to an operating state brings about rapid electrochemical reactions on its electrode surfaces, which are completed within a few seconds. Such power-on and-off processes (voltage change from open-circuit voltage (OCV= eg 1.0 V) to operating voltage (eg 0.4 V)) with huge energy transfer are indispensable for commercial applications of fuel-cell systems. However, surface atoms of the active metal particles tend to dissolve slightly into the electrolyte that is in contact with the cathode catalyst layer, and an undesired Pt particle (or layer) deposits in the electrolyte.[9, 10] This effect is a problem because automobiles, in particular, require continual repetition of the on/off processes with rapid changes in cell voltages to alter the car s speed.To overcome these serious problems, reaction mechanisms on the electrode surfaces must be investigated in situ during voltage-stepping processes in real time. However, to the best of our knowledge, there are no reports that have fully explored and determined the reaction kinetics of both the structural changes of the metal catalysts and the electrochemical reactions on the electrode surfaces in PEMFCs. We have investigated the mechanism of the electrochemical processes involved in rapid voltage-controlled processes on a Pt/C catalyst. From the viewpoints of electrification and structural changes in the Pt catalyst, in situ time-resolved quick X-ray absorption fine structure (QXAFS) spectroscopy was used to monitor directly the chemical bonding and electronic states in the Ptnanoparticles that act as the