Improved hydrogen-steam electrodes for solid oxide electrolysers

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Hydrogen is increasingly emerging as an attractive low carbon energy carrier to support the de-carbonisation of hard to address sectors such as industrial heat, chemicals, heavy duty vehicles, shipping, and trains. This is being increasingly recognised globally, along with the launch of a European hydrogen strategy, the inclusion of hydrogen at scale in the November 2020 UK Government Green plan, and the recent launch of the UK Hydrogen strategy. Much of the focus of these strategies is on the production of 'green' hydrogen using electrolysis, driven by renewable electricity. Today, 96% of hydrogen globally is produced from unabated fossil fuels, with 6% of global natural gas and 2% of coal consumption going to hydrogen production, primarily for petrochemicals. Currently green hydrogen is the most expensive form of hydrogen, with around 60-80% of the cost coming from the cost of the electrical power input. A critical factor that influences this is the efficiency of the electrolyser itself. Electrolysers fall into one of two categories: low-temperature (70-120C) and high temperature (600-850C). While low temperature electrolyser systems based around alkaline or polymer technology are already mature and commercially available, their relatively modest efficiency (around 65%) means that the solid oxide electrolyser (SOEC), which operates at much higher temperatures (600-900C) where both the thermodynamics and kinetics of water splitting are more favourable, is of growing interest. Indeed, high temperature steam electrolysis driven by renewable electricity is the most efficient way to produce hydrogen, with electrical efficiencies for steam electrolysis to hydrogen of over 90%, and with the possibility of integrating waste heat into the endothermic process to further reduce the electrical energy requirements.However, high temperature electrolysis using solid-oxide electrolyser cells (SOECs) is not yet a mature technology, with only one company (Sunfire) testing at any scale. A number of companies are now entering the race to develop SOEC stacks and systems, such as Fuel Cell Energy and Bloom in the USA, and Ceres Power in the UK. However, one of the major drawbacks of SOEC systems is that their lifetime is significantly lower than polymer electrolyte and alkaline electrode competitors. The degradation of nickel - a widely used electrode material on the hydrogen/steam side, is severe in the high steam contents found in electrolysers, and is a major source of degradation of the whole cell. While Ni is a vital component in a conventional SOEC fuel electrode, in which it acts as both catalyst and electron conductor, it would be beneficial to find a substitute with better thermal and redox stability to take over the roles of nickel.In this work we seek to build on our prior work on novel composite electrode structures, with a particular focus on utilising nickel exsolved ceria combined into both conventional composites and with our novel electrospun materials to create high performance and durable hydrogen-steam electrodes for solid oxide electrolysers, that will help accelerate their on-going development and deployment, leading to lower cost green hydrogen production.