Fabrication of wavy type porous triple-layer SC-SOFC via in-situ observation of curvature evolution during co-sintering

Wavy type Single Chamber Solid Oxide Fuel Cells (SC-SOFCs) have been shown to be conducive to improving the effective electrochemical reaction area contributing to higher performance, compared with planar type SC-SOFCs of the same diameter. This study presents a fabrication process for wavy type SC-SOFCs with a single fabrication step via co-sintering of a triple-layer structure. The monitoring and observation of the curvature evolution of bi- and triple-layer structures during co-sintering has resulted in an improved process with reduced manufacturing time and effort, as regards the co-sintering process for multi-layer structures. Investigation using in-situ monitoring helps different shrinkage behaviours of each porous layer to minimise mismatched stresses along with avoidance of severe warping and cracking. In the co-sintering of the multi-layer structures, the induced in-plane stresses contribute to curvature evolution in the structure, which can be utilised in the design of a curved multi-layer structure via the co-sintering process. For intermediate temperature SOFCs, the materials used are NiO/CGO for anode; CGO for electrolyte; and LSCF for cathode. These materials are tape-casted with 20µm thickness and assembled for bi- and triple-layer structures by hot pressing. Sintering mismatch stresses have been analysed in bi-layer structures, consisting of NiO/CGO-CGO and CGO-LSCF. The maximum sintering mismatch stress was calculated at interface of bi-layer structure in the top layer. In order to achieve the desired wavy type triple-layer structure, flexible green layers of each component were stacked up and laid on alumina rods to support the curvature during the process. In-situ observation, to monitor the shrinkage of each material and the curvature evolution of the structures, was performed using a long focus microscope (Infinity K-2). With these values, the main factors such as viscosity, shrinkage rate of each material, and curvature rate are investigated to determine the sintering mismatch stresses. This enables the prediction of curvature for triple-layer structure and the prediction is validated by in-situ monitoring of the triple-layer structure co-sintering process. Zero-deflection condition is confirmed to maintain initial shape during co-sintering and helps to minimise the development of undesired curvature in the triple-layer structure. Performance testing of the wavy cell was carried out in a methane-air mixture (CH4:O2 =1:1). In comparison with a planar SC-SOFC, it showed higher OCV which might be attributed to not only macro deformation, but also microstructural distribution affecting the effective gas diffusion paths and electrochemical active sites

Experimental observations of the co-sintering of porous triple-layer SOFCs including curvature evolution

Triple-layer co-sintering of SOFCs results in an improved production process via reduced time and effort. Understanding the sintering shrinkage behaviour of each porous layer during the co-sintering process leads to the minimisation of mismatched stresses along with avoidance of severe warping and cracking. In multilayer structure, sintering behaviour is mainly characterised by the in-plane properties rather than the thickness properties. The induced in-plane stresses contribute to curvature evolution in the structure, which can be utilised in the design of a SOFC

Multi-junction thermocouple array for in-situ temperature monitoring of SOFC: simulation

Novel multi-junction thermocouple architecture was developed and simulated to in-situ monitor the temperature distribution over a Solid Oxide Fuel Cell (SOFC). This thermocouple architecture requires only {N+1} number of wires for N number of independent temperature measuring points. Therefore, N+1 architecture can independently measure temperature at multiple points simultaneously with much less number of wires than a set of thermocouples require for the same number of independent temperature measurements. Requiring less number of external wires is a distinct advantage, particularly, in constrained environments such as those within SOFC stacks. A thermocouple array having 4 independent temperature measuring points with 5 thermo-elements was simulated in MATLAB. Alumel (Ni:Al:Mn:Si – 95:2:2:1 wt) and Chromel (Ni:Cr – 90:10 wt) were chosen as thermo-element materials because of their wide applicability in the industry as K-type thermocouples. The junctions were considered to be spot welded. Three sets of simulations were performed to investigate two aspects: validation of the multi-junction thermocouple concept and investigation of the effect of the heat affected zone created in spot welding to the temperature measurement. Simulation code generates random temperature values for each junction within a pre-defined range. Temperatures at the boundaries of heat affected zones were also generated randomly according to a pre-defined criterion. The change of Seebeck coefficients within the heat affected zone was set as a percentage change of their corresponding materials Seebeck coefficient. The temperature gradient induced emf values for each sensing point were calculated from Seebeck coefficients. The calculated emf was then mapped back to temperature using ASTM approved inverse conversion function. These mapped temperatures were then compared with the set temperatures for each junction and they were in very good agreement

Fabrication of three-dimensional wavy single chamber solid oxide fuel cell by in situ observation of curvature evolution

This study presents a fabrication process via experimental observations for curved porous multi-layer structures during co-sintering. Analysis of curvature evolution using in-situ monitoring of the structure was used in the design of a curved multi-layer structure. Materials used are NiO/gadolinium-doped cerium oxide (NiO/CGO) for anode; CGO for electrolyte; and lanthanum strontium manganite (LSCF) for cathode. In-situ observation, to monitor the shrinkage of each material and the evolution of the bi- and triple-layer structures, was performed using a long focus microscope (Infinity K-2). The results contribute to develop a novel design curved three dimensional multi-layer structures during co-sintering

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

In situ investigation of curvature change induced by stress in multilayer structure during co-sintering for wavy type SOFC

In situ investigation of curvature change induced by stress in multilayer structure during co-sintering for wavy type SOF

Performance testing of novel Wavy-type single chamber solid oxide fuel cell

Performance testing of novel Wavy-type single chamber solid oxide fuel cel