Electrospun IrOx-Based Nanofiber Catalyst Materials in Acidic Water Electrolysis

The need for electricity conversion and energy storage from sustainable resources has fostered a climate of innovation, prompting diverse approaches to address the requirements of the energy transition. Therein, hydrogen has received a central role as energy carrier in transportation and storage, and has been known as feedstock material of the chemical industry. Water electrolysis has become a key technology to converting excess electrical energy into hydrogen. Proton exchange membrane water electrolysis (PEMWE) has attracted a lot of attention lately, and is considered a promising technology for industrial-scale hydrogen production. Despite the use of scarce and expensive noble metals, this technology has been thoroughly investigated worldwide, as it can be operated with renewable energy resources of intermittent nature. Enhanced utilization of noble metal catalysts is of core interest for the commercialization of PEMWE. We aim to synthesize catalyst materials of nanofibrous structure with high conductivity and high specific surface area, providing an alternative IrOx-based catalyst library to conventional nanoparticles. The most promising structures involve an increased aspect ratio, which denotes the relationship between the shortest and longest dimensions of the catalyst particles. Particles with the highest aspect ratios are called one-dimensional (1D) nanowires or nanofibers (NFs), attracting increasing attention in catalyst research of acidic water electrolysis. Electrospinning is the most favorable technique for nanofiber production due to its scalability and ease of operation. A calcination study at various temperatures from 400 °C to 800 °C is employed to optimize the synthesis for both electrocatalytic activity and stability. Morphology, structure, phase, and chemical composition are investigated using a scale-bridging approach to shed light on the structure–function relationship of the thermally prepared nanofibers. Furthermore, powder conductivity and chemical stability data are described in this work. Activity and stability are monitored by a scanning flow cell (SFC) coupled with an inductively-coupled plasma mass spectrometer (ICP-MS). Despite the opposite trend of performance and stability, the present study demonstrates that an optimum between these two aspects can be achieved. The impact of metal contaminations such as Fe and Al on activity and degradation is also discussed as a potential source of catalyst poisoning resulting from either the synthesis path, the feed water or PEM cell components. This work fills a gap for high-aspect-ratio OER electrocatalysts in the field of acidic water electrolysis as a material library and alternative to nanoparticles. A stable and continuous electrospinning process along with controlled calcination results in enhanced catalyst utilization of IrOx-based nanofibers. Further strategies are demonstrated here to produce nanofibers with outstanding activity and/or good stability applied as PEMWE electrocatalysts. All in all, this work extensively characterizes the materials, the provided properties of which can help guide future applications in PEM water electrolysis.