Advanced Nanostructured Textile Catalysts for Enhanced Hydrogen Production in PEM Water Electrolysis: An Overview and Recent Developments
Authors: Nielson Kevin Von , Higashi Shougo 
Published: August 2024

As the global focus shifts towards a zero-emission society, hydrogen has emerged as a critical element in various industries, particularly in green hydrogen production. A promising method for this is Polymer Electrolyte Membrane Water Electrolysis (PEMWE), which uses pure water and electricity to produce high-purity hydrogen. However, the efficiency of PEMWE is highly dependent on the effectiveness of its catalysts, particularly in the context of the catalyst-coated membranes (CCMs) employed in these systems. Conventional preparation of these CCMs involves multiple steps, including synthesis and application of a catalyst ink, which often leads to catalyst agglomeration and requires high Ir (Iridium) loadings to maintain uniformity and performance.

In our latest study, we have developed a novel approach using ultralight conductive IrO2 nanostructured textiles (NST) as a catalyst layer for PEMWE. This innovative method successfully circumvents the issue of electrically isolated inactive catalysts, a common problem with lower Ir amounts in traditional catalyst layers. By employing a process of sputtering IrO2 onto water-soluble polymer nanofibers, we have achieved facile CCM preparation and demonstrated unprecedented long-term hydrogen evolution with ultra-low Ir mass loadings at high rates. Our study revealed that the high performance of these CCMs is derived from their low resistivity and unique porous three-dimensional structure.

The preparation of NST involves dissolving polyvinylpyrrolidone (PVP) in methanol, followed by electrospinning this solution onto a metal-foil collector. The resulting PVP nanofibers then undergo a sputtering process to deposit IrO2, forming the nanostructured textiles. This method eliminates the need for wet chemical routes and labor-intensive processes typically associated with conventional catalyst layer preparations, thus offering a more environmentally friendly and scalable alternative.

Our performance evaluations of these NST CCMs, with varying Ir mass loadings, have shown significant advancements. The operational cell voltages of CCMs containing as little as 0.05 mg-Ir cm−2 were suppressed across all investigated current densities compared to conventional CCMs. Notably, operational voltages remained below 2 V even at the highest current density of 7 A cm−2. This level of performance is unprecedented for CCMs with such low catalyst amounts. Additionally, the long-term stability of these CCMs was remarkable, with operational times exceeding 1500 hours without significant increases in voltage, showcasing their potential for practical applications.

An essential aspect of our study was the analysis of the electrical properties and the surface structure of the IrO2 NSTs. We observed that the electrical conductivity of these textiles was significantly higher than that of conventional catalyst layers. This high conductivity, coupled with the unique interconnected structure of the textiles, ensures efficient electrical contact between nano catalysts and the current collector, thus avoiding the formation of isolated catalysts. Our analyses revealed that the IrO2 NSTs have unique surface terminations and a high number of undercoordinated surface Ir atoms, contributing to their high intrinsic catalytic activity.

Further insights were gained through operando X-ray absorption spectroscopy (XAS) measurements, which showed that the IrO2-nanostructured textiles possess a large number of D-band holes and are intrinsically highly active. This finding is crucial as it links the unique chemical state of the textiles to their high activity in oxygen evolution reactions (OER), a key process in PEMWE.

Our recent developments in nanostructured textile catalysts for PEMWE mark a significant leap in hydrogen production technology. By demonstrating high-rate hydrogen production at low operational voltages and with significantly lower Ir mass loadings compared to conventional CCMs, we have addressed major challenges in the field. These advancements not only enhance the efficiency and sustainability of hydrogen production but also open avenues for applying this technology to other electrochemical conversion cells, paving the way for broader applications and further research. In this talk, we discuss the latest activity on NST, and highlight the challenges and opportunities for hydrogen production.