Javed Hassan, Knop-Gericke Axel, Mom Rik V
Leiden Institute of Chemistry, Leiden University, PO Box 9502, Leiden 2300 RA, The Netherlands.
Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, Berlin 14195, Germany.
ACS Appl Mater Interfaces. 2022 Aug 10;14(31):36238-36245. doi: 10.1021/acsami.2c09249. Epub 2022 Jul 29.
Potential spikes during the start-up and shutdown of fuel cells are a major cause of platinum electrocatalyst degradation, which limits the lifetime of the device. The electrochemical oxidation of platinum (Pt) that occurs on the cathode during the potential spikes plays a key role in this degradation process. However, the composition of the oxide species formed as well as their role in catalyst dissolution remains unclear. In this study, we employ a special arrangement of XPS (X-ray photoelectron spectroscopy), in which the platinum electrocatalyst is covered by a graphene spectroscopy window, making the in situ examination of the oxidation/reduction reaction under wet conditions possible. We use this assembly to investigate the change in the oxidation states of Pt within the potential window relevant to fuel cell operation. We show that above 1.1 V (potential vs reversible hydrogen electrode), a mixed Pt/Pt/Pt surface oxide is formed, with an average oxidation state that gradually increases as the potential is increased. By comparing a model based on the XPS data to the oxidation charge measured during potential spikes, we show that our description of Pt oxidation is also valid during the transient conditions of fuel cell start-up and shutdown. This is due to the rapid Pt oxidation kinetics during the pulses. As a result of the irreversibility of Pt oxidation, some remnants of oxidized Pt remain at typical fuel cell operating potentials after a pulse.
燃料电池启动和关闭过程中的潜在尖峰是铂电催化剂降解的主要原因，这限制了设备的使用寿命。在电位尖峰期间阴极上发生的铂（Pt）的电化学氧化在这一降解过程中起关键作用。然而，所形成的氧化物物种的组成及其在催化剂溶解中的作用仍不清楚。在本研究中，我们采用了一种特殊的X射线光电子能谱（XPS）装置，其中铂电催化剂被石墨烯光谱窗口覆盖，使得在潮湿条件下原位检查氧化/还原反应成为可能。我们使用这个组件来研究与燃料电池运行相关的电位窗口内Pt氧化态的变化。我们表明，在高于1.1 V（相对于可逆氢电极的电位）时，形成了混合的Pt/Pt/Pt表面氧化物，其平均氧化态随着电位的增加而逐渐增加。通过将基于XPS数据的模型与电位尖峰期间测量的氧化电荷进行比较，我们表明我们对Pt氧化的描述在燃料电池启动和关闭的瞬态条件下也是有效的。这是由于脉冲期间Pt快速的氧化动力学。由于Pt氧化的不可逆性，脉冲后一些氧化Pt的残余物在典型的燃料电池工作电位下仍然存在。
