As the international community is focused on the development of low (or net zero) carbon technologies it is imperative that efficient and effective routes to produce alternative fuels are developed. Leading governments worldwide have made significant commitments to the use of hydrogen as a future fuel, and proposed several renewable routes to produce significant volumes of hydrogen for use in transport and in both domestic and industrial settings. However transport and storage of hydrogen are issues that need to be addressed before widespread adoption of hydrogen can be envisaged. As an energy carrier ammonia, with significant hydrogen content, has been considered attractive as this hydrogen carrier is produced industrially at volume and has an international transport infrastructure. The current disadvantage with ammonia is that the synthesis of this has a large carbon footprint, relying on steam methane reforming to produce the hydrogen required to synthesis ammonia. Assuming that green ammonia can be produced, the remaining issue is the availability of effective earth abundant materials for the catalytic decomposition of ammonia, and the separation of the resultant gas streams. In this project we will develop new catalysts for ammonia decomposition and couple these with separation technologies: direct electrolysis and permeation membranes. These two solutions will offer complementary devices that are scalable and that can be deployed easily at locations where hydrogen is required.

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.

The use of fossil fuels and resulting CO2 emissions are exacerbating global climate change. The alternative use of hydrogen could cut CO2 emissions and improve air quality of urban areas, since burning hydrogen generates harmless water. To realise this potential we need to find clean ways to produce hydrogen fuel. Water splitting into hydrogen (and oxygen) can be achieved cleanly with electrolysers running on electricity from renewable sources such as solar, wind or hydropower. In a more direct manner, water can also be cleanly split using sunlight and semiconductor absorbing layers integrated in photoelectrodes of photoelectrochemical (PEC) cells. PEC solar water splitting is limited by both poor lifetime of photo-induced charges and poor catalytic properties of semiconductor surfaces to split water at the electrolyte interface. This fellowship aims to develop novel approaches to engineer the interface between semiconductors and electrolytes, in order to optimise the performance of the semiconductors and achieve efficient solar energy devices. We will develop fabrication methods to tune those interfaces and boost their PEC final performance. Photoelectrodes will be prepared oriented and with exposed active crystal facets, or with extra layers on their surface to mediate with aqueous electrolytes. A systematic approach involving novel syntheses, advanced electrochemical characterisation and solar water splitting performance tests will be carried out to establish the optimal conditions for the formation of photoelectrodes and the characteristics which make them better performing. Finally, best photoelectrodes will be integrated in tandem cells for more efficient solar water splitting. Preparing semiconductors with engineered interface will have a considerable impact on the research of (photo)electrochemistry, photocatalysis, photovoltaics and on their energy application. This will ensure important advances towards a more sustainable energy mix of clean energy for current and future generations.

'Energy materials' encompass a wide range of technologies, ranging from thermoelectrics to fuel cells, batteries, photovoltaics and magnetocalorics, among others. Many of these energy materials are developed as multi-component solid state devices and these devices inherently possess a number of electrochemically active interfaces. It is these interfaces, e.g. solid/solid, liquid/solid or gas/solid, that control the function of the device, and are typically the source of degradation. Many current techniques used to analyse these devices and their components rely on idealised systems in high vacuum environments to gain information on the near surface chemistry. This necessitates the use of post-mortem operation analysis and clearly represents a significant mismatch from the conditions under which devices operate. Increasingly it is acknowledged that in-operando measurements are required, but that the measurements are themselves difficult and demanding. It is our intention to develop expertise with in-operando characterisation of energy materials. This will build on our existing expertise and capability in surface analysis and in-situ measurements. As an example, a fuel cell operating at 823K will be subjected to temperature gradients, cation segregation, potential gradients, poisoning and chemical changes induced by these conditions, all of which are inter-related, but separating the individual contributions has so far proved impossible. Similar issues involving the interface and surface chemistry of solid state batteries, permeation membranes and co-electrolysers will also be addressed using these techniques. By developing in-operando correlative characterisation we aim to deconvolute these processes and provide detailed mechanistic understating of the critical processes in a range of energy systems.

The electrode, and the electrolyte-electrode interface, plays a critical role in the performance of all cells. In Solid Oxide Fuel Cells (SOFCs) the microstructures of the porous composite anode and cathode are particularly critical as they determine the electrochemical, electrical, mechanical and transport properties of the electrode, and of current distribution to/from the electrode/electrolyte interface. Current state of the art SOFC electrodes rely on a largely empirical understanding to establish the electrode microstructure, and its influence on key performance characteristics, including long term durability. But recent work by the proposers has established a new suite of tools and techniques that offer the prospect of moving towards a design led approach to manufacture of improved electrodes, based on our ability to image, model, simulate and fabricate new electrode structures with controlled properties. This proposal seeks to develop and demonstrate this, further improving and validating our analysis and modelling tools, using these design optimum structures, fabricating these using three novel processing techniques established by the proposers, and then measuring device performance to feedback into the design process.