Caine Finnerty

Carbon formation on and deactivation of nickel-based/zirconia anodes in solid oxide fuel cells running on methane

Abstract Nickel/zirconia fuel reforming anodes in solid oxide fuel cells (SOFCs) running on methane have been studied using a test cell based on a tubular SOFC. The anodes have been characterised using temperature-programmed reduction (TPR) which reveals that two distinct types of nickel oxide are present in the anode prior to reduction. The steam reforming activity and surface chemistry of two different nickel/zirconia anode formulations and a molybdenum doped nickel/zirconia anode have been studied. All three show good activity towards methane steam reforming. It is found that the quantity of carbon deposited on the anode during methane reforming is strongly affected by the operating temperature and the methane/steam ratio. The addition of small quantities of molybdenum leads to a significant reduction in the amount of carbon deposited, whilst having little effect on the reforming activity or cell performance. Temperature-programmed oxidation (TPO) has revealed that three types of carbon are formed on the anodes during high temperature reaction of methane. As current is drawn from the cell, increased methane conversion occurs together with reduced carbon deposition, through reaction via partial oxidation and oxidative coupling with the flux of oxygen ions through the solid electrolyte.

Novel applications for micro-SOFCs

Abstract The application of micro-solid oxide fuels cells in small systems is discussed. Two types of application are examined, namely, leisure CHP systems and micro-hybrid vehicles. A unique triple layer catalyst–SOFC–catalyst system has been designed utilising propane/butane fuel. The system consists of a co-generating gas burner with a pre-reforming catalyst, a micro-SOFC stack and an oxidation catalyst. The pre-reforming catalyst comprising of Ru metal on Saffil® ceramic wool, was used to partially reform the propane/butane gas prior to entering the fuel cell, preventing carbon formation. The micro-SOFCs were YSZ tubes (Adelan, UK) with nickel/YSZ cermet anodes on the outside and strontium-doped lanthanum manganite cathodes on the inside. Final oxidation was provided by a cordierite honeycomb coated with platinum combustion catalyst producing most of the heat for the fuel cell operation. Initial performance results were obtained and it was shown that a co-generating system could be achieved using a propane/butane fuel supply, piezoelectric ignition system and air supply for the triple catalyst system. The application of this micro-SOFC system for leisure and micro-hybrid vehicles, such as golf trolleys and power-assisted bicycles, is described.

Internal reforming over nickel/zirconia anodes in SOFCS oparating on methane : influence of anode formulation, pre-treatment and operating conditions

Abstract Internal methane reforming over nickel/zirconia cermet anodes has been studied in detail using a thin-walled extruded zirconia tubular SOFC reactor. The influence of anode formulation, anode pre-treatment, operating temperature and methane/steam ratio on the reforming characteristics, resistance to carbon deposition and durability of the anode have been investigated under actual operating conditions. Post-reaction TPO has been used to determine the amount of carbon deposition and its strength of interaction with the anode. A 90-vol.% nickel/zirconia anode shows higher activity than a 50-vol.% Ni anode at higher reforming temperatures, and shows very good durability. Pre-reducing the anodes in H2 at 1173 K leads to a more active reforming catalyst. Carbon is removed from the anodes in two processes during TPO, suggesting two types of carbon species. As the reforming temperature increases both carbon types are removed at higher temperature, and there is an increase in the relative population of the more strongly bound form of carbon.

SOFC system with integrated catalytic fuel processing

Abstract In recent years, there has been much interest in the development of solid oxide fuel cell technology operating directly on hydrocarbon fuels. The development of a catalytic fuel processing system, which is integrated with the solid oxide fuel cell (SOFC) power source is outlined here. The catalytic device utilises a novel three-way catalytic system consisting of an in situ pre-reformer catalyst, the fuel cell anode catalyst and a platinum-based combustion catalyst. The three individual catalytic stages have been tested in a model catalytic microreactor. Both temperature-programmed and isothermal reaction techniques have been applied. Results from these experiments were used to design the demonstration SOFC unit. The apparatus used for catalytic characterisation can also perform in situ electrochemical measurements as described in previous papers [C.M. Finnerty, R.H. Cunningham, K. Kendall, R.M. Ormerod, Chem. Commun. (1998) 915–916; C.M. Finnerty, N.J. Coe, R.H. Cunningham, R.M. Ormerod, Catal. Today 46 (1998) 137–145]. This enabled the performance of the SOFC to be determined at a range of temperatures and reaction conditions, with current output of 290 mA cm −2 at 0.5 V, being recorded. Methane and butane have been evaluated as fuels. Thus, optimisation of the in situ partial oxidation pre-reforming catalyst was essential, with catalysts producing high H 2 /CO ratios at reaction temperatures between 873 K and 1173 K being chosen. These included Ru and Ni/Mo-based catalysts. Hydrocarbon fuels were directly injected into the catalytic SOFC system. Microreactor measurements revealed the reaction mechanisms as the fuel was transported through the three-catalyst device. The demonstration system showed that the fuel processing could be successfully integrated with the SOFC stack.

Thermal Stability of Portable Microtubular SOFCs and Stacks

Rapid start-up times are a big challenge for high-temperature fuel cells such as solid oxide fuel cells (SOFCs), especially large-sized stacks with high power outputs. This paper presents the development of tubular and microtubular anode-supported SOFCs and the design and testing of the thermal stability of such single cells and stacks. It was demonstrated that single cells with various sizes have very good thermal shock resistance. Preliminary results also showed that stacks can be started up within minutes and withstand more than 50 thermal cycles and that single cells can withstand temperature changes of 550 °C/min. Several factors that affect the thermal stability are discussed.

Development of a novel test system for in situ catalytic, electrocatalytic and electrochemical studies of internal fuel reforming in solid oxide fuel cells

A test system based around a thin‐walled extruded solid electrolyte tubular reactor has been developed, which enables the fuel reforming catalysis and surface chemistry occurring within solid oxide fuel cells and the electrochemical performance of the fuel cell to be studied under genuine operating conditions. It permits simultaneous monitoring of the catalytic chemistry and the cell performance, allowing direct correlation between the fuel cell performance and the reforming characteristics of the anode, as well as enabling the influence of drawing current on the catalysis and surface reaction pathways to be studied. Temperature‐programmed reaction measurements can be carried out on anodes in an actual SOFC, and have been used to investigate the reduction characteristics of different anode formulations, methane activation and methane steam reforming, and to evaluate the nature and level of carbon deposition on the anode during reforming.

A Review of the Implications of Silica in Solid Oxide Fuel Cells

Silica is a well-known impurity in solid oxide fuel cell raw materials, namely NiO and yttria-stabilized zirconia (YSZ). At elevated temperatures silica will migrate to the grain boundaries, form insulating siliceous phases, and lead to a decrease in the ionic conductivity of the electrolyte. Furthermore, silica impurities have been shown to damage the anode/electrolyte interface, such that an overall decrease in cell performance and long-term stability is observed. Despite the fact that silica is ubiquitous in commercial-grade raw materials and can be incorporated from several extrinsic sources, it has negative effects on the solid oxide fuel cell, such that any further contamination should be avoided to prevent performance degradation and eventual cell failure. This paper reviews and outlines the sources and effects of silica on the solid oxide fuel cell, and attempts to determine a guideline for acceptable levels of silica contamination.

Portable Propane Micro-Tubular SOFC System Development

NanoDynamics Energy Inc. is developing a family of compact, integrated micro-tubular SOFC systems with high volumetric power density and multiple fuel options including methane, propane, diesel and JP8. The development program aims to bring to the market highly efficient, clean, and cost competitive fuel cell systems with outputs above 50We for portable power generation applications. Balance-of-plant (BoP), electronic controls, and power management systems have been identified and integrated with a partial oxidation reformer and SOFC stack. A system test for the integrated process chain was performed with our proprietary cell and system technologies. The performance of a system developed using a micro-tubular SOFC stack is evaluated for different operating conditions. Results from these studies will be presented. System design, integration, and control methodologies are also discussed. Introduction The increase in demand for energy and concern for environmental impacts has created an increase in demand for low-emission energy sources. Fuel cell systems can provide clean energy and with higher efficiency than typical generators (1). To meet increasing power and longevity demands of remote applications, lightweight, man portable fuel cell systems are under development. Balance of Plant (BoP), electronic controls, and power management sub-systems have been designed and tested for use with a micro-tubular solid oxide fuel cell (SOFC) stack and integrated partial oxidation (POX) reformer. This process addressed stack and reformer requirements as well as system level requirements for run-time, fuel type, and typical output loads. Each sub-system was tested under actual conditions to prove functionality, and lastly integrated with the POX reformer and SOFC stack for final evaluation. Proprietary technology allows for subsystem designs that are modular and scalable to meet larger portable power requirements. Sub-System Development Partial Oxidation (POX) Reformer Experiments were conducted to identify and optimize the operating conditions for hydrogen generation via POX reforming of propane fuel using a 2-stage reforming process carried out on proprietary catalyst formulations. ECS Transactions, 7 (1) 483-492 (2007) 10.1149/1.2729127,

Geometric Effects on Tubular Solid Oxide Fuel Cells

Micro-tubular solid oxide fuel cell systems have many desirable characteristics compared with their planar counterparts; however, there are many obstacles and difficulties that must be met to achieve a successful and economically viable manufacturing process and stack design. One of the most important parameters is the cell size and geometries. Anode-supported tubes provide an excellent platform for individual cells. A thin electrolyte layer applied to the outside of the tube helps to minimize polarization losses thus avoiding the difficulty of coating the inside of electrolyte or cathode-supported tubes. The stack design with anode supported tubes also avoids using a fuel chamber on the outside of the tube. Various geometries of the cell support, in terms of diameter, length, cross-section shape and arrangement were investigated. Results of geometric effects on micro-tubular SOFCs will be discussed and presented in this paper.

Thermal Stability of Portable Micro-Tubular Solid Oxide Fuel Cell and Stack

Rapid start-up times are a big challenge for high temperature fuel cells such as solid oxide fuel cells (SOFCs), especially large-sized stacks with high power outputs. This paper presents the development of tubular and micro-tubular anode-supported SOFCs and the design and testing of the thermal stability of such single cells and stacks. It was demonstrated that single cells with various sizes have very good thermal shock resistance. Preliminary results also showed that stacks can be started up within minutes and withstand more than 50 thermal cycles and temperature changes of 550C/min. Several factors that affect the thermal stability are discussed.