Electrolyte-supported solid oxide fuel cells for gas sensing applications

Solid Oxide Fuel Cells show an ability to generate voltage and current outputs proportional to the type and concentration of fuel being supplied, and hence show sensitivity to these measures. The single chamber concept of fuel cell sidesteps or simplifies many issues with present conventional SOFCs such as separation of fuel and air/oxygen streams, sealing requirements and thermal shock resistance. Fuel utilization and output is compromised, but this concept may be well suited to being used as a sensor, as maximum power density is not of prime importance. Thus far, sensor design and fabrication has focused on dedicated design and materials, whilst minimizing the electrolyte thickness for quick response. Electrolyte support still offers mechanical robustness, ready adaptability, handling and possible material stability. At present, these meritorious characteristics are often overlooked in favour of minimised ohmic resistance from other support structures. The electrolyte supported cell was chosen on this basis to be the evaluated platform in this study. Commercially-sourced planar electrolyte-supported cells were tested for two prospective sensing functions: (i) air-fuel ratio switching in single chamber and split-chamber configurations and (ii) hydrogen sensing in methane bulk gas, to anticipate the advent of Power-to-Gas hydrogen storage in the natural gas grid. The preliminary analysis concludes that the cell displays provisionally good sensitivity for gas species in both OCV and amperometric modes. Amperometric outputs under voltage bias produced better sensing performance, but overall results were either nonreproducible, subject to drift or are insufficiently responsive for the Air-fuel sensing case when compared to the state-of-the-art oxygen sensors. Deployment in split-chamber configuration showed more promise as a hydrogen content sensor in natural gas, especially operated in amperometric mode under voltage bias. Dedicated design, engineering and analysis is needed to maximize the sensitivity of non-specialized cells such as these to be employed as functional and reliable sensing devices. The research performed concludes that a promising route is towards a multi-channel or distributed gas flow arrangement to parse and disaggregate the sensor responses to individual gases, but the cell should be operated at a lower temperature and higher current draw to mitigate coking and degradation with the present material construction.