Sensor technology for in situ monitoring of the surface temperature distribution of SOFC

Solid oxide fuel cell (SOFC) is the most efficient energy conversion technology of alltime in producing electricity from fuels. However, temperature-driven premature degradation is one of the biggest problems that impedes the widespread use of this technology. Understanding the temperature distribution of an operating SOFC is central to mitigate such degradations as well as to further enhance the performance. The published efforts on SOFC temperature sensing, except small button cells, are mainly confined to measure temperature only from the gas channels (fuel/ air) with relatively low spatial resolution. However, the electrodes’ temperature distribution measured with an adequate spatial resolution is more desirable than the gas temperature to investigate a cells’ behaviour and its correlation to a stack’s performance. The insufficiency of technology to in situ monitor the cell surface temperature distribution with an adequate spatial resolution was identified as a crucial research gap in the SOFC development cycle. Therefore, this research is aimed at developing a sensing technology to monitor in situ the cell surface temperature distribution of an operating SOFC with an adequately high spatial resolution and applying that technology to get a better insight into SOFC operation. [Continues.

SOFC temperature sensing during anode reductions and cell operations

SOFC temperature sensing during anode reductions and cell operation

THERMONO: cell integrated thin-film sensor array for in-situ monitoring of SOFC temperature

In-situ temperature monitoring from a working SOFC stack indicates the overall health of the system. It also helps detecting variety of cell problems[1] while providing information to understand degradation and to develop better stack designs. Current efforts on simulating temperature distributions involve a great deal of assumptions[2]~[8], which may not present in a working stack. Existing temperature sensing technology does not qualify for in-situ temperature monitoring of a SOFC stack as it causes a significant disturbance to normal stack operation when inserted into a stack[9]. Therefore, Novel temperature sensor architecture was developed to in-situ monitor SOFC running temperature while causing only a minimum disturbance to the normal stack operation. This architecture, named as THERMONO, enables to reduce the number of external wires required: only {N+1} number of external wires for N number of independent temperature sensing points. A thin-film THERMONO having 4 independent sensing points was fabricated on the cathode of a cell (Φ52mm, Kerafol Ltd, KeraCell II). Standard K-type thermocouple materials, Alumel (Ni 95%, Mn 2%, Al 2%, Si 1%) and Chromel (Ni 90%, Cr 10%) of 99.99% purity were chosen as the THERMONO materials. THERMONO was successfully tested in a furnace up to 10500C. A commercial K-type thermocouple was placed adjacent to THERMONO as a reference. Transient response of THERMONO was in very good agreement with the thermocouple validating the sensor concept and proving its robustness on commercial cells. THERMONO is being tested in a specially designed fuel cell test rig to sense the temperature from a working SOFC. Integration of THERMONO into commercial fuel cells and short stacks is also covered in this study and the results will be useful to understand various degradation mechanisms and for advancement of SOFC stack operation conditions

Thin-film multi-junction thermocouple array for in-situ temperature monitoring of SOFC

Thin-film multi-junction thermocouple array for in-situ temperature monitoring of SOF

Cell integrated thin-film multi-junction thermocouple array for in-situ temperature monitoring of Solid Oxide Fuel Cells

A thin-film multi-junction thermocouple array was developed and tested for multi-point simultaneous temperature measurements from an operating SOFC stack. The array requires only {N+1} number of wires/ thermo-elements for N number of independent temperature measuring points. Hence, it requires less number of lead wires than any available contact-temperature sensors require for the same number of measurements. Because the multi-junction thermocouple array operates on the same principle of a conventional thermocouple, the Seebeck effect, it shares all the merits of a thermocouple. A thin-film multi-junction thermocouple array was sputter deposited on the cathode of a SOFC test cell and tested and evaluated up to 10500C from 200C. Temperature measured from the thermocouple array was compared with that from a commercial thermocouple placed adjacent to it during the test; they were in very good agreement within the entire temperature range that a SOFC stack generally operates

Cell integrated thin-film multi-junction thermocouple array for in-situ temperature monitoring of solid oxide fuel cells

A thin-film multi-junction thermocouple array was developed and tested for multi-point simultaneous temperature measurements from an operating SOFC stack. The array requires only {N+1} number of wires/ thermo-elements for N number of independent temperature measuring points. Hence, it requires less number of lead wires than any available contact-temperature sensors require for the same number of measurements. Because the multi-junction thermocouple array operates on the same principle of a conventional thermocouple, the Seebeck effect, it shares all the merits of a thermocouple. A thin-film multi-junction thermocouple array was sputter deposited on the cathode of a SOFC test cell and tested and evaluated up to 10500C from 200C. Temperature measured from the thermocouple array was compared with that from a commercial thermocouple placed adjacent to it during the test; they were in very good agreement within the entire temperature range that a SOFC stack generally operates

Fabrication and evaluation of a novel wavy Single Chamber Solid Oxide Fuel Cell via in-situ monitoring of curvature evolution

Wavy type Single Chamber Solid Oxide Fuel Cells (SC-SOFCs) are beneficial for improved triple phase boundary conditions contributing to higher performance, compared with planar type SC-SOFCs of the same diameter. This study presents a fabrication process for wavy-type, cathode-supported SC-SOFCs with a single fabrication step via co-sintering of a triple-layer structure consisting of NiO/CGO-CGO-LSCF, with a thickness ratio of 1:3:9 respectively. Curvature evolution occurs due to different sintering behaviour of each layer during the co-sintering process. In-situ observation of each layer during the co-sintering process allows for minimisation of mismatched stresses to avoid unnecessary warping and cracking. Bilayers, consisting of NiO/CGO-CGO and CGO-LSCF, are co-sintered at 1200°C. In-situ observation, to monitor the shrinkage of each material and the curvature evolution of the structures, is performed using a long focus microscope (Infinity K-2). Monitoring curvature behaviour in real time minimised the development of undesired curvature in the triple-layer structure. Performance testing of wavy cell is carried out in a methane-air mixture (CH4:O2 =1:1). The wavy SC-SOFC generated 0.39 V and 9.7 mWcm-2 at 600°C, which produced 260% and 540% increments in OCV and in maximum power density, respectively, over the planar SC-SOFC under the same operational conditions

High spatial resolution monitoring of the temperature distribution from an operating SOFC

High spatial resolution monitoring of the temperature distribution from an operating SOF

Thin film THERMONO for cathode temperature gradient of SOFC

High thermal gradient is considered as the main reason for cell degradation and failure. A sizeable number of the available scientific work related to the problem in the literature is focused on using simulation or modelling to predict temperature distribution in the cell. THERMONO, a novel temperature monitoring sensor, has been developed by the authors’ group. THERMONO is capable of monitor {N2} temperature reading by using {2N} number of external wires, e.g. temperature measurement at 400 multiple points simultaneously can be done only use around 20 wires, whilst commercial thermocouple using 800 wires. However, there are still difficulties in accurate and real time temperature measurement from a cell stack for practical implementations and desired resolution. Wiring based sensors, which are normally large in size, that are mounted on the cell electrode surface can make significant disturbance to gas flow and operating conditions. In this study, an innovative method is developed to overcome these limitations associated with implementing the large sized wire sensors. Nano-scale thin film THERMONO (FT-THERMONO) will be fabricated on the cell electrode surface to provide enabling technique for in-situ temperature monitoring of the cell with higher spatial and temporal resolution compared to wire sensors. The novel TF-THERMONO architecture will be directly deposited on a test cell’s (50mmx50mm, NextCell-5) electrode surface via sputtering technique. As a result, the test cells’ cathode in-situ temperature distribution will be monitored during the normal operation. TF-THERMONO has a great potential for in-situ temperature monitoring by minimizing the unnecessary impact to the cell’s operation thus its performance

In-situ monitoring of temperature distribution in operating solid oxide fuel cell cathode using proprietary sensory techniques versus commercial thermocouples

Real time surface temperature distribution monitoring of Solid Oxide Fuel Cell (SOFC) systems is important to identify temperature related degradation and understand cell performance. This type of monitoring is limited due to the harsh operating environment of SOFC. Therefore, the temperature variation of an operating SOFC is generally predicted by applying modelling tools which take into account the conventional I-V (current (I)-voltage (V)) curve. However, experimentally obtained temperature data is vital for management of high temperature related degradation and for more reliable modelling of the SOFC. In this study, the temperature distribution of the SOFC is in-situ monitored along the entire cell cathode simultaneously, using commercial TCs on the gas flow channel (the present conventional method) alongside the in-house-developed sensor sensing points (SSPs) directly from the cell cathode surface under both open circuit voltage (OCV) and loading conditions. A considerable difference is observed, especially under the loading condition, between the temperature obtained from the TCs and SSPs even from the same locations. Furthermore, the contribution(s) of different parameters on the temperature variation are investigated, including fuel/air amount under OCV, gas cooling effect, contact area effect and flow direction effect under the loading condition for the given SOFC. There is a fivefold increase in spatial resolution, alongside higher temporal resolution, being observed with the implemented sensor compared to the resolution obtained from the conventional TCs, which yields promise for further development and investigation into test cells and stacks