Newcastle University

Solid Oxide Fuel Cells and Hydrogen Storage

 Solid Oxide Fuel Cells (SOFCs) are electrochemical devices that convert chemical energy to electrical energy via a redox reaction. In SOFCs a ceramic solid electrolyte (oxygen ion or proton conducting membrane) such as yttria-stabilised-zirconia is used.  Materials with electronic conductivity and catalytic activity are used as the anode and cathode electrodes. SOFCs typically operate at temperatures in the range of 700-900°C (ideal for energy integration as part of a complete energy generation system). Hydrogen is most commonly used as the fuel with air as the oxidant. Our work in SOFCs investigates the improvement of their performance and durability. We are also interested in the development of novel devices that can co-generate power and useful products through methane reforming.  In addition, we are investigating the integration of SOCFs with the MCH H2 transport system.

 

In situ characterisation of SOFCs

		Fuel cells are one of the key technologies to be used for energy generation in a low carbon economy. To facilitate their widespread deployment a thorough understanding of the basic science behind the complex processes occurring under operating conditions is required.  This collaborative project aims to develop new techniques for the in-situ characterisation of fuel cells under realistic operating conditions. In Newcastle focus will be placed in the study and performance of cathode materials.
The function of the cathode is known to include the catalytic reduction of oxygen and the subsequent adsorption and incorporation of the ionic species. A novel gas phase pulsed 18O method capable of determining in-situ surface exchange rates will be developed as part of this project. The determination of the surface exchange rate can be achieved by pulsing an aliquot of labelled gaseous oxygen (18O-18O) on to an oxide sample which may be either in powder form or in the form of a working cathode.

Mixed oxygen ion and protonic conducting SOFC for in situ methane reforming

 

 

It would be desirable if natural gas could be fed directly to a working solid oxide fuel cell without the need for the complication of external reforming.  However, the nickel anodes currently used in a fuel cell would undergo severe carbon deposition if a dry hydrocarbon feed was actually employed.  This has resulted in numerous studies of feeding hydrocarbon-water mixtures to the anode in an attempt to internally reform the hydrocarbon.

The problem with this approach is that the endothermic reforming reaction has rapid kinetics and results in a cold spot at the fuel cell inlet while the oxidation kinetics happen more slowly resulting in a hot spot further into the fuel cell.  Complex fuel cell geometries have been proposed to improve heat transfer and get around this thermal mismatch. Recently yttrium-doped barium cerate has been shown to be both an oxygen-ion conductor and proton conductor simultaneously. Oxygen vacancies can react with water on the high water partial pressure side to create lattice oxygen and protonic defects. Protons can then hop from one lattice oxygen to another.  The reverse reaction takes place on the low partial pressure side of the membrane. The level of hydration of the membrane will affect the ratio of protonic to oxygen-ion defects. Hence, water permeation is favoured at an optimal level of membrane hydration. The aim of this project is to control the level of hydration of the membrane and achieve sufficient water permeation to e.g. oxygen-ion or proton transport.  The benefit of this would be a gradual introduction of water.  This could avoid the need, in the case of internal reforming, to introduce water with fuel in the fuel inlet stream leading to better thermal management of the system

Hydrogen storage using the MTH system

Hydrogen is widely billed as the fuel of the future. However, it is also a buoyant and flammable gas, and so if we are to utilise hydrogen on a global scale, then a safe and practical way of storing and distributing hydrogen must be in place. This work studies one such solution. Liquid Organic Hydrides (LOHs) are organic chemicals which can reversibly bind to hydrogen. This means that effectively hydrogen can be transported as a stable liquid, using pipelines and tankers which already exist for transporting fossil fuels, and then liberated wherever it is needed. We study the MTH system (illustrated here). MTH stands for Methylcyclohexane-Toluene-Hydrogen.

In this case, the LOH is toluene, which chemically binds to hydrogen to form methylcyclohexane (MCH), which can be safely and easily stored and transported. When the hydrogen is needed, it is liberated from the MCH, leaving behind the toluene which we started with. Toluene can then be recharged and used again. In this project, we aim to perform a technical assessment of the MTH system for use on a vehicle, provide solutions to problems or difficulties which stop the system from being practical, and eventually to provide a suggested system strategy for commercialising this technology.