Improved hydrogen-steam electrodes for solid oxide electrolysers

氢气正日益成为一种有吸引力的低碳能源载体，以支持工业供热、化工、重型汽车、航运和火车等难以解决的行业的去碳化。随着欧洲氢能战略的启动、2020年11月英国政府绿色计划中的大规模氢能利用，以及最近英国氢能战略的启动，这一点正日益得到全球的认可。这些战略的大部分重点是利用可再生电力驱动的电解法生产“绿色”氢气。今天，全球96%的氢气来自有增无减的化石燃料，全球6%的天然气和2%的煤炭消耗用于氢气生产，主要用于石化。目前，绿色氢气是最昂贵的氢气形式，大约60%-80%的成本来自电力输入的成本。影响这一点的一个关键因素是电解槽本身的效率。电解槽分为两类：低温(70-120摄氏度)和高温(600-850摄氏度)。虽然基于碱性或聚合物技术的低温电解槽系统已经成熟并可用于商业用途，但其相对较低的效率(约65%)意味着固体氧化物电解槽(SOEC)在更高的温度(600-900℃)下运行，在那里分解水的热力学和动力学都更有利，因此受到越来越多的关注。事实上，由可再生电力驱动的高温蒸汽电解是最有效的制氢方法，将蒸汽电解为氢气的电效率超过90%，并有可能将废热整合到吸热过程中，进一步降低电能需求。然而，使用固体氧化物电解槽(SOECs)的高温电解技术还不成熟，只有一家公司(Sunfire)进行了任何规模的测试。许多公司现在都在竞相开发SOEC电堆和系统，例如美国的燃料电池能源和Bloom，以及英国的Ceres Power。然而，SOEC系统的主要缺点之一是其寿命明显低于聚合物电解质和碱性电极竞争对手。镍是氢气/水蒸气侧广泛使用的电极材料，在电解槽中发现的高水蒸气含量下，镍的降解非常严重，是整个电池降解的主要来源。虽然镍是传统SOEC燃料电极的重要组成部分，在传统的SOEC燃料电极中，它既是催化剂又是电子导体，但寻找一种具有更好的热稳定性和氧化还原稳定性的替代品来取代镍的作用将是有益的。在这项工作中，我们寻求建立在我们之前对新型复合电极结构的基础上，特别关注将镍溶解的CeO结合到传统复合材料和我们的新型电纺材料中来创建高性能和耐用的固体氧化物电解槽的氢气电极，这将有助于加速其持续的开发和部署，从而导致更低的成本绿色氢气生产。

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.