Wang Li, Lettenmeier Philipp, Golla-Schindler Ute, Gazdzicki Pawel, Cañas Natalia A, Morawietz Tobias, Hiesgen Renate, Hosseiny S Schwan, Gago Aldo S, Friedrich K Andreas
Institute of Engineering Thermodynamics, German Aerospace Center, Pfaffenwaldring 38-40, Stuttgart, 70569, Germany.
Group of Electron Microscopy of Materials Science, Central Facility for Electron Microscopy, University of Ulm, 89081 Ulm, Germany.
Phys Chem Chem Phys. 2016 Feb 14;18(6):4487-95. doi: 10.1039/c5cp05296c.
PEM water electrolysis has recently emerged as one of the most promising technologies for large H2 production from a temporal surplus of renewable electricity; yet it is expensive, partly due to the use of large amounts of Ir present in the anode. Here we report the development and characterization of a cost-effective catalyst, which consists of metallic Ir nanoparticles supported on commercial Ti4O7. The catalyst is synthesized by reducing IrCl3 with NaBH4 in a suspension containing Ti4O7, cetyltrimethylammonium bromide (CTAB) and anhydrous ethanol. No thermal treatment was applied afterwards in order to preserve the high conductivity of Ti4O7 and the metallic properties of Ir. Electron microscopy images show an uniform distribution of mostly single Ir particles covering the electro-ceramic support, although some agglomerates are still present. X-ray diffraction (XRD) analysis reveals a cubic face centered structure of Ir nanoparticles with a crystallite size of ca. 1.8 nm. According to X-ray photoelectron spectroscopy (XPS), the ratio of metallic Ir and Ir-oxide, identified as Ir(3+), is 3 : 1 after the removal of surface contamination. Other surface properties such as primary particle size distribution and surface potential were determined by atomic force microscopy (AFM). Cyclic and linear voltammetric measurements were conducted to study the electrochemical surface and kinetics of Ir-black and Ir/Ti4O7. The developed catalyst outperforms the commercial Ir-black in terms of mass activity for the oxygen evolution reaction (OER) in acid medium by a factor of four, measured at 0.25 V overpotential and room temperature. In general, the Ir/Ti4O7 catalyst exhibits improved kinetics and higher turnover frequency (TOF) compared to Ir-black. The developed Ir/Ti4O7 catalyst allows reducing the precious metal loading in the anode of a PEM electrolyzer by taking advantage of the use of an electro-ceramic support.
质子交换膜水电解最近已成为利用可再生电力的暂时过剩大量生产氢气最具前景的技术之一；然而，它成本高昂，部分原因是阳极中使用了大量铱。在此，我们报告一种具有成本效益的催化剂的开发与表征，该催化剂由负载在商用Ti4O7上的金属铱纳米颗粒组成。通过在含有Ti4O7、十六烷基三甲基溴化铵（CTAB）和无水乙醇的悬浮液中用硼氢化钠还原IrCl3来合成该催化剂。之后未进行热处理，以保持Ti4O7的高导电性和铱的金属特性。电子显微镜图像显示，尽管仍存在一些团聚体，但大多为单个的铱颗粒均匀分布在电陶瓷载体上。X射线衍射（XRD）分析表明铱纳米颗粒具有立方面心结构，微晶尺寸约为1.8纳米。根据X射线光电子能谱（XPS），去除表面污染物后，金属铱与被鉴定为Ir(3+)的氧化铱的比例为3∶1。通过原子力显微镜（AFM）测定了其他表面性质，如一次粒径分布和表面电位。进行了循环伏安和线性伏安测量，以研究Ir黑和Ir/Ti4O7的电化学表面和动力学。在0.25 V过电位和室温下测量，所开发的催化剂在酸性介质中析氧反应（OER）的质量活性方面比商用Ir黑高出四倍。总体而言，与Ir黑相比，Ir/Ti4O7催化剂表现出更好的动力学和更高的周转频率（TOF）。所开发的Ir/Ti4O7催化剂通过利用电陶瓷载体，能够减少质子交换膜电解槽阳极中的贵金属负载量。
