Chaveanghong Suwilai, Nakamura Takahiro, Takagi Yasumasa, Cagnon Benjamin, Uruga Tomoya, Tada Mizuki, Iwasawa Yasuhiro, Yokoyama Toshihiko
Department of Materials Molecular Science, Institute for Molecular Science, Okazaki, Aichi 444-8585, Japan.
Phys Chem Chem Phys. 2021 Feb 14;23(6):3866-3873. doi: 10.1039/d0cp06020h. Epub 2021 Feb 4.
We have investigated the S adsorption behaviours on Pt (average particle diameter of ∼2.6 nm) and PtCo (∼3.0 nm) anode and cathode electrode catalysts in polymer electrolyte fuel cells (PEFCs) under working conditions for the fresh state just after the aging process and also the degraded state after accelerated degradation tests (ADT), by studying near ambient pressure hard X-ray photoelectron spectroscopy (HAXPES). S 1s HAXPES of both the anode and cathode electrodes shows not only the principal S species from the sulfonic acid group (-SOH) in the Nafion electrolyte but also other characteristic S species such as zero-valent S (S) adsorbed on the carbon support and anionic S (S) adsorbed on the Pt electrode. The S species on Pt should be ascribed to S contamination poisoning the Pt catalyst electrode. The S species on the cathode can be oxidatively removed by applying a high cathode-anode bias voltage (≥0.8 V) to form SO, while at the anode the S species cannot be eliminated because of reductive environment in hydrogen gas. The important finding is the difference in S adsorption behaviours between the Pt/C and PtCo/C electrodes after ADT. After ADT, the Pt/C anode electrode exhibits much larger S adsorption than the PtCo/C anode electrode. This indicates that the PtCo/C anode is more desirable than the Pt/C one from the viewpoint of S poisoning. The reason for more tolerance of the PtCo/C anode catalyst against S poisoning after ADT can be ascribed to the more negative charge of the surface Pt atoms in the PtCo/C catalyst than those in the Pt/C one, thus yielding a weaker interaction between the surface Pt and the anionic S species as S, SO, and SO. A similar behaviour was observed also in the cathode catalyst. The present findings will nevertheless provide important information to design novel Pt-based PEFC electrodes with higher performance and longer durability.
我们通过研究近常压硬X射线光电子能谱（HAXPES），考察了聚合物电解质燃料电池（PEFC）中，新鲜状态（老化过程刚结束后）以及加速降解试验（ADT）后的降解状态下，S在Pt（平均粒径约2.6 nm）和PtCo（约3.0 nm）阳极和阴极电极催化剂上的吸附行为。阳极和阴极电极的S 1s HAXPES不仅显示了来自Nafion电解质中磺酸基团（-SOH）的主要S物种，还显示了其他特征S物种，如吸附在碳载体上的零价S（S）和吸附在Pt电极上的阴离子S（S）。Pt上的S物种应归因于使Pt催化剂电极中毒的S污染。通过施加高的阴极-阳极偏置电压（≥0.8 V）形成SO，可以氧化去除阴极上的S物种，而在阳极，由于氢气中的还原环境，S物种无法消除。重要的发现是ADT后Pt/C和PtCo/C电极之间S吸附行为的差异。ADT后，Pt/C阳极电极比PtCo/C阳极电极表现出更大的S吸附。这表明从S中毒的角度来看，PtCo/C阳极比Pt/C阳极更可取。ADT后PtCo/C阳极催化剂对S中毒具有更高耐受性的原因可归因于PtCo/C催化剂中表面Pt原子的电荷比Pt/C催化剂中的表面Pt原子更负，从而使表面Pt与作为S、SO和SO的阴离子S物种之间的相互作用更弱。在阴极催化剂中也观察到了类似的行为。然而，本研究结果将为设计具有更高性能和更长耐久性的新型Pt基PEFC电极提供重要信息。
