NHEMOE: Nanoparticulate high entropy materials as low-loading Ir/Ru oxygen evolution catalysts in acid media

Jonathan Ruiz Esquius (Terrassa, 1990) holds a bachelor’s and a master’s degree in chemistry from the Autonomous University of Barcelona (Spain). He then moved to the Cardiff Catalysis Institute (United Kingdom), where he received his PhD in 2019 for his work on iridium-based catalysts for the electrochemical oxygen evolution reaction (OER) and on PdZn alloys for the thermal CO2 hydrogenation to methanol.

He remained at the Cardiff Catalysis Institute for a post-doctoral position where he worked on the thermal synthesis of synthetic fuels over hybrid catalysts. In 2021, he joined the International Iberian Nanotechnology Laboratory (Portugal) to work on the design of electrocatalysts with reduced iridium-loading for OER. In April 2023, he joined the Instituto de Ciencia y Tecnología del Carbono (INCAR, CSIC) in Oviedo (Spain) as a ComFuturo fellow to develop his project NHEMOE.


El hidrógeno es un combustible perfecto ya que su combustión no emite gases de efecto invernadero, como el CO2, sino solo vapor de agua. Cuando su producción se lleva a cabo mediante un proceso electroquímico (electrólisis) capaz de descomponer las moléculas de agua en hidrógeno y oxígeno (que sería el único subproducto) usando electricidad procedente de fuentes renovables, entonces hablamos del hidrógeno verde, una pieza clave en la descarbonización de la economía. Sin embargo, aún es necesario el desarrollo de electrolizadores capaces de operar en condiciones ventajosas desde el punto de vista industrial, especialmente en medio ácidos, y que no requieran un elevado uso de metales nobles y escasos como el platino y el iridio. El proyecto NHEMOE busca identificar nuevos materiales, concretamente los llamados de alta entropía, más estables y económicos al reducir su concentración de metales nobles, que puedan ser usados en electrolizadores a escala industrial.
Hydrogen is a perfect fuel as its combustion does not emit greenhouse gases, such as CO2 , but only water vapour. When its production is carried out by means of an electrochemical process (electrolysis) capable of breaking down water molecules into hydrogen and oxygen (which would be the only by-product) using electricity from renewable sources, then we are talking about green hydrogen, a key element in the decarbonisation of the economy. However, there is still a need to develop electrolysers capable of operating in industrially advantageous conditions, especially in acidic environments, and which do not require a high use of scarce noble metals such as platinum and iridium. The NHEMOE project seeks to identify new materials, namely high entropy materials, which are more stable and economical by reducing their noble metal concentration, and which can be used in industrial-scale electrolysers.

Extended project summary:

The generation of energy has historically relied on fossil fuels, with the associated environmental costs. To reduce the greenhouse gases emissions associated with the production of energy, such as CO2. Energy must be obtained from renewables. Nevertheless, parallel systems that enable the storage of such electricity needs to be also developed. For example, this could be achieved by producing hydrogen (and oxygen) from the electrolysis of water (H2O ⇌ H2 + ½ O2). Hydrogen can then be used as a “green fuel”. At present, research on the development of electrocatalysts that can withstand relevant operating conditions is still needed, specially under acidic conditions. In addition, a major bottleneck for acidic water electrolysis is that it employs scarce and expensive noble metal-based catalysts. For instance, Pt and Ir are employed as catalysts for the hydrogen and the oxygen evolution reaction, respectively.

To ensure the widespread implementation of acidic water electrolysers the concentration of noble metals on electrocatalysts must be reduced, or ultimately eliminated. High entropy materials (HEMs), containing five or more metal components, have higher stability due to the high lattice distortion and slow atomic diffusion compared to the mono, bi- o trimetallic counterparts. In addition, synergy between elements is commonly observed due to the wide variety of absorption sites. HEMs have been widely studied for alkaline water electrolysis, but it is still not clear if improved stability can translate to acidic conditions.

This project seeks to develop and optimise an easy and rapid method for the synthesis of low-content noble metal HEMs electrocatalysts; as well as characterise and assess such materials under acidic conditions, and determine whether there is a significant improvement in the stability compared to standard catalysts. Ultimately, developed materials are to be tested on a water electrolyser under industrially relevant conditions.