This Small Business Innovation Research (SBIR) Phase I project will determine the feasibility of operating innovative metal-supported SOFCs (solid oxide fuel cells) on direct natural gas fuel at high efficiency and without excessive carbon deposition. SOFCs are not successfully commercialized because they are too expensive and prone to failure. Point Source Power is pursuing Metal-Supported SOFCs that will overcome these issues by radically improving cost, performance, durability, and manufacturing. This project aims to enable metal-supported SOFCs for the genset market, providing a high-efficiency alternative to small internal combustion engines (ICEs) for power generation. Metal-supported cells with various anode catalysts will be tested with natural gas fuel.
The broader/commercial impacts of this research are that natural-gas fueled genset systems based on metal-supported SOFCs are expected to successfully address the needs of the small generator market, which comprises 74% of the total market based on units sold. In 2009, 9.3M genset units were sold globally for residential applications, and the US residential market is expected to approach $1.2B by 2014. Small ICE-based gensets are reliable and relatively inexpensive, but suffer from extremely low efficiency. Small gensets operate at <15% efficiency, whereas small fuel cell systems provide 35-45% efficiency. This large efficiency gain results in reduced operating/fuel costs and lower CO2, particulate, SOx and NOx emissions per kWh. For example, a 1kW gasoline powered generator running for 1500h at 15% efficiency consumes ~$1100 (273gal) of gasoline, whereas a fuel cell system running at 40% efficiency would consume ~$125 (5000 cu.ft.) of natural gas.
The use of solid oxide fuel cells (SOFCs) in a small natural gas-fueled genset would enable a system with much higher efficiency than current ~1kW internal combustion engine models on the market. Metal-supported solid oxide fuel cells offer significant advantages over conventional anode-supported cells, including: low materials cost; tolerance to rapid thermal cycling and anode oxidation; and, mechanical ruggedness. The main goal of this award project is to determine the feasibility of fueling metal-supported SOFCs directly with natural gas (NG), without the need for the conventional pre-reforming subsystem (that converts NG to electrochemically-active fuel species including H2 and CO) used with anode-supported cells. Metal-supported cells were fabricated with a variety of anode catalyst compositions, and tested with pure NG, NG/air and NG/steam mixtures in the range 650-800°C required for long metal support lifetime. High performance (>200mW/cm2) was only obtained in the range 750-800°C, for pure NG, and for catalysts with 20-50wt% Nickel content. These high-Ni content cells enabled conversion of some of the NG into electrochemically-active fuel species within the cell, however, this was accompanied by deposition of solid carbon on the cell. For all long-term testing with pure NG, the fuel inlet lines clogged up with deposited coke (solid carbon) within a few hours of operation. Addition of air or steam was sufficient to alleviate this coking condition, however, high power was not achieved for any anode catalyst operating directly on diluted NG. Unfortunately, the metal support was not sufficiently catalytic to convert NG to electrochemically-active fuel species without additional Ni. If those species were present, however, Ni was not necessary to convert them to electricity. A Ni-free cell with pure YDC catalyst coating the metal support obtained high power when fed with CO fuel. These results suggest that internal reforming of pure NG fuel on a metal-supported cell is not feasible in the range 650-800°C with the selected catalysts. We therefore conclude that the use of metal-supported cells will not enable a greatly simplified SOFC system (with no prereformer subsystem) at this time. However, if prereformed NG is provided to a metal-supported cell from a reforming subsystem, high power is expected even if there is no additional Ni catalyst in the cell. A metal-supported Ni-free cell is expected to offer significant cell-level cost, ruggedness, and fuel contaminant tolerance advantages over conventional SOFC cells. Preliminary cost analysis indicates that a system competitive with existing internal combustion engine gensets could be manufactured with high gross margins if the manufacturing volume is on the order of 50,000 units per year.
