John Z. Staniforth

Biogas powering a small tubular solid oxide fuel cell

Abstract Biogas has been used to power a small tubular solid oxide fuel cell (SOFC). It was demonstrated that biogas could provide power equivalent to hydrogen, even when the methane content was reduced below the value at which normal combustion could occur. The carbon dioxide content of biogas was especially beneficial because it aided the internal reforming process. But carbon deposition was a problem unless air was added to the biogas before it entered the cell. When air was premixed, the biogas was comparable with than hydrogen in the power produced. However, a problem was the variability of biogas samples. Of the three types tested, only one produced a consistent power output.

Cannock landfill gas powering a small tubular solid oxide fuel cell — a case study

Abstract Cannock landfill gas — mainly a mixture of methane and carbon dioxide — can successfully power a small tubular solid oxide fuel cell. Initial experiments showed a relatively rapid falling off in power due to poisoning with hydrogen sulphide. A simple de-sulphurisation system alleviated this problem. Even greater performance was achieved by the pre-addition of air to help in the reforming of the gas, giving little loss of power over the lifetime of the experiment.

Implications for Using Biogas as a Fuel Source for Solid Oxide Fuel Cells: Internal Dry Reforming in a Small Tubular Solid Oxide Fuel Cell

The feasibility of operating a solid oxide fuel cell (SOFC) on biogas has been studied over a wide compositional range of biogas, using a small tubular solid oxide fuel cell system operating at 850 °C. It is possible to run the SOFC on biogas, even at remarkably low levels of methane, at which conventional heat engines would not work. The power output varies with methane content, with maximum power production occurring at 45% methane, corresponding to maximal production of H2 and CO through internal dry reforming. Direct electrocatalytic oxidation of methane does not contribute to the power output of the cell. At higher methane contents methane decomposition becomes significant, leading to increased H2 production, and hence transiently higher power production, and deleterious carbon deposition and thus eventual cell deactivation.

Mechanical properties and electrochemical characterisation of extruded doped cerium oxide for use as an electrolyte for solid oxide fuel cells

Doped cerium oxide is a promising electrolyte for use in a medium-temperature solid oxide fuel cell (SOFC), due to its high ionic conductivity at low temperatures. A colloidal processing route has been undertaken to prepare slurries from very fine doped-cerium oxide. The dried slurry is extruded into rods and tubes and the room temperature modulus of rupture is then measured. It is shown that the material could attain a modulus in excess of 220 MPa for (CeO2)0.8(GdO1.5)0.2, which is considerably greater than values obtained using traditional routes. A preliminary investigation is made of the electrochemical properties of single cells fabricated from the extruded doped-ceria tubes. At 600°C, a maximum power output of approximately 38 mW cm−2 is realised.

Running solid oxide fuel cells on biogas

The feasibility of operating a solid oxide fuel cell on biogas has been studied over a wide compositional range of biogas, using a small tubular solid oxide fuel cell system operating at 850 °C. In addition the response of the SOFC towards waste ammonia has been studied. It is possible to run the SOFC on biogas, even at remarkably low levels of methane, at which conventional heat engines would not work, thus offering a valuable and environmentally friendly use for poor-quality biogas that is currently wasted by detrimental venting to the atmosphere. The power output varies with methane content of the biogas, with maximum power production occurring at 45% methane, corresponding to maximal production of H2 and CO through internal dry reforming. Direct electrocatalytic oxidation of methane does not contribute to the power output of the cell. For biogas with higher methane contents methane decomposition becomes significant, leading to increased H2 production, and hence transiently higher power production, and deleterious carbon deposition and thus eventual cell deactivation. SOFCs are tolerant to ammonia, actually utilising the ammonia present in biogas to produce electrical power, at the same time acting as an environmental clean-up device breaking down the ammonia pollutant to N2 and water, with no formation of any undesirable nitrogen oxides.

Clean destruction of waste ammonia with consummate production of electrical power within a solid oxide fuel cell system

The response of a solid oxide fuel cell towards waste ammonia has been studied using a small tubular solid oxide fuel cell system, since ammonia is present in certain biogas in large quantities as a breakdown product of biological waste. SOFCs are not only tolerant to ammonia, but can actually utilise the ammonia present in biogas to produce electrical power, at the same time acting as an environmental clean-up device breaking down the ammonia pollutant to nitrogen and water. Ammonia is catalytically decomposed over the nickel cermet anode to N2 and H2, and the H2 is then electrochemically oxidised to water. Direct electrochemical oxidation of the ammonia does not occur, and no undesirable nitrogen oxides are formed.

A nickel doped perovskite catalyst for reforming methane rich biogas with minimal carbon deposition

A novel nickel-doped strontium zirconate perovskite catalyst for biogas reforming has been synthesised using a green, low temperature hydrothermal synthesis. The catalyst has been shown to be very efficient towards the conversion of methane-rich biogas at relatively low temperatures with high selectivity towards synthesis gas formation and extremely good resistance to carbon deposition in carbon-rich reaction mixtures. The catalyst displays very low carbon deposition which does not increase over time, and as a result shows excellent stability. The use of a catalyst produced by a low temperature hydrothermal route provides a potentially very attractive and sustainable source of useful chemicals from biogas that otherwise might be vented wastefully and detrimentally into the atmosphere.

Overcoming carbon deactivation in biogas reforming using a hydrothermally synthesised nickel perovskite catalyst

A hydrothermally synthesised nickel-strontium zirconate perovskite is shown to have excellent selectivity towards biogas reforming without suffering from deactivation due to carbon formation. Experiments reveal that this material is capable of very efficiently converting methane and carbon dioxide to synthesis gas, a mixture of hydrogen and carbon monoxide, at relatively low temperatures and, particularly importantly, high methane contents. Under these conditions we find that carbon production is extremely low and more importantly shows no increase over time, even after 10 days of continuous reforming activity. This conversion of a renewable product, using a catalyst prepared by low temperature hydrothermal methods, provides a route to future sustainable hydrogen, and oxygenate and higher hydrocarbon, production whilst lowering some greenhouse gas emissions.

Improving the Sulphur Tolerance of Nickel Catalysts for Running Solid Oxide Fuel Cells on Waste Biogas

Nickel dispersed on yttria-doped zirconia (YSZ) is the most commonly used anode material in solid oxide fuel cells (SOFC) because of its excellent electrochemical performance and desirable physical properties. It is relatively cheap and simple to fabricate, and also shows good catalytic activity towards reforming methane into synthesis gas, a property exploited in internally reforming SOFCs [1]. Biogas, a variable mixture of methane and carbon dioxide, can be reformed when passed over Ni/YSZ by the following reaction [2]: