# The Development of Current Collection in Micro-Tubular Solid Oxide Fuel Cells--A Review
## 6 Current Collector Shape and Structure
### Meshes  
For nearly 15 years, metallic meshes have been successfully used for electrode contacting both \(\upmu\)T-SOFC electrodes [115; 116]. Meshes can be made by hatching wire into a network or bought preformed with a range of thicknesses and mesh aperture sizes available. Meshes achieve a high cross-sectional contacting area without considerably increasing the diameter of the cell. This is particularly important on the outer electrode, allowing more  
Figure 11: Nickel anode current collecting layer with a porous support cell adapted from [110]. Figure 12: (**a**) Electrical conductivity as a function of current collector thickness [114]. (**b**) Cross-section schematic of dual-layer hollow fibre cell with mesh/finger-like protrusions for enhanced mass transport [114]. compact spacing for cells in stacks. Bore side meshes must be selected carefully so as not to block the flow of gas through the tube to the electrode surface. Problems can occur on the anode side in anode-supported cells due to the metal sagging as a result of a reduction in elasticity with an increase in temperature. The sagging results in loss of contact with the anode wall at high temperatures leading to a decrease in electrochemical performance, durability and reliability of the cell. Contact force, controlled by mechanical compression in planar devices, is known to be a key factor in optimising interconnect performance and is crucial for minimising contact resistance. To overcome these issues, slide pins and other mesh supports are in development. Meshes can also be secured with conductive pastes and better integrated into the electrode surface itself with the likes of a metal oxide slurry, such as NiO on the anode, or with current collecting layers such as lanthanum strontium cobalt ferrite (LSCF) [117] on the cathode side. In 2017, [PERSON] et al. [118] used a nickel mesh secured by a nickel paste on the anode side with a Crofer 22 mesh secured with an LSC paste on the cathode side. They compared the performance of the bare mesh with a 1.2 \(\upmu\)m electrodeposited dual-layered coating. The mesh, with fine wires of 100 \(\upmu\)m in diameter, was first applied with a Co\({}_{3}\)O\({}_{4}\) spinel layer followed by a LaMnO\({}_{3}\) perovskite layer. The bare mesh achieved a current density at 0.7 V of 0.5 and 0.52 A\(\cdot\)cm\({}^{-2}\) for the virgin and coated mesh, respectively, at 800 \({}^{\circ}\)C. The ohmic polarisation and ASR at OCV were 0.26 and 0.79 \(\Omega\cdot\)cm\({}^{2}\) for the coated Crofer and 0.34 and 0.81 \(\Omega\cdot\)cm\({}^{2}\) for the uncoated. The authors measured the increase in ohmic resistance over 1000 h of the bare versus coated Crofer mesh via impedance spectroscopy. Relative to a virgin sample, the ohmic degradation was reduced nearly 5-fold from 6.7 \(\times\) 10\({}^{-2}\) %\(\cdot\)h\({}^{-1}\) to 1.4 %\(\cdot\)h\({}^{-1}\). In 2015, [PERSON] et al. [119] achieved the highest current density of a tubular cell with a nickel, bore side anode mesh. The design achieved a current density at 0.7 V of 0.6, 0.99 and 1.15 A\(\cdot\)cm\({}^{-2}\) at 750, 800 and 850 \({}^{\circ}\)C, respectively. Platinum wire and paste were used on the cathode. The fuel and fuel flow rate were not disclosed. At 750 \({}^{\circ}\)C, the ohmic polarisation and ASR at OCV were 0.12 and 1.10 \(\Omega\cdot\)cm\({}^{2}\), respectively. A recent study where a nickel anode side mesh and a silver cathode mesh were used as current collectors was reported by [PERSON] et al. [116] in 2020. Operating on H\({}_{2}\), the current density at 0.7 V was 0.52 A\(\cdot\)cm\({}^{-2}\) at 850 \({}^{\circ}\)C. The ASR of the cell was 0.1 \(\Omega\cdot\)cm\({}^{2}\). In 2020, [PERSON] et al. [120] used silver mesh on both the anode and cathode sides for a flattened-tube cell design. On the anode side, silver mesh, silver wire and a silver-glass contact/sealing paste were used. On the cathode side, silver mesh, silver wire and LSC contact/sealing paste were used.