# The Development of Current Collection in Micro-Tubular Solid Oxide Fuel Cells--A Review
## 9 Conclusions and Perspective  
This paper presented an overview of current collection issues in \(\upmu\)T-SOFC. The key bottlenecks in \(\upmu\)T-SOFC technology were discussed with a particular focus on current collection. The metrics of current collector performance were detailed as well as the overall requirements of an optimal design. The effect of current collector size, spacing and positioning on cell performance was studied and the key design trade-offs identified. The nickel mesh internal anode current collector and coated Crofer mesh cathode current collector configuration presented by [PERSON] et al. [118] was highlighted as a low-cost, high performing design that did not sacrifice durability. In order to achieve high cell performance (with a low ASR) and high stability/ durability over the cell lifetime, research into \(\upmu\)T-SOFCs needs to place greater focus on current collection issues. Divergence should be made from the use of the state-of-the-art silver current collectors to low-cost alternatives given the widely reported durability concerns surrounding mechanical integrity at typical SOFC operating temperatures. Mechanically durable metallic current collectors are available and reduce bulk conductivity and contact resistance while adhering to delivering chemical and CTE compatibility. For a given current collector material, the minimisation of contact resistance between the current collector and the electrode is essential for a low ohmic polarisation. Brazing offers a commercially viable pathway to provide physical joints at multiple current collector-electrode interfaces, reducing contact resistance while also significantly improving durability. Minimisation of contact resistance through the coating of low-cost current collectors with thin layers of highly conductive materials and corrosion-proof material must be explored in more detail. Combining coated low-cost current collectors with physical contacting through brazing would favour a durable and high performing design and present a viable route for progression in the field. Facile manufacturing and contacting a larger and well-distributed surface area of the inner electrode, thus minimising current conduction pathways, is a key element of \(\upmu\)T-SOFC stack design. Care must be given when matching the current collector material with the current collector design. Both internal and embedded current collectors allow for a higher cell active area and thus a higher total cell power as they do not require any space to be positioned on the cell exterior (where the cathode is located in the typical anode-supported cell configuration). Current collector designs must be reproducible and must consider manufacture and assembly in the design phase. Researchers working in cell testing may have results masked by variation in the current collector design as opposed to their study parameters, for example, in materials development. In addition, researchers must also be aware that long conduction pathways in tubular cells can necessitate multiple  
Figure 19: Wall thickness versus area-specific resistance for 12 mm long 0.8 mm OD tube [52]. current collectors per cell for a low ohmic polarisation, particularly for cells with high length to diameter ratios. Conceptualization, O.H.-P., A.D., R.S.-W.; investigation, O.H.-P.; resources, O.H.-P., A.D., R.S.-W.; data curation, O.H.-P.; writing--original draft preparation, O.H.-P.; writing--review and editing, O.H.-P., A.D., R.S.-W.; visualization, O.H.-P.; supervision, A.D., R.S.-W.; project administration, A.D., R.S.-W.; funding acquisition, R.S.-W. All authors have read and agreed to the published version of the manuscript. This research was funded by the EPSRC, grant number EP/L015749/1, through the CDT in Fuel Cells and their Fuels, led by the University of Birmingham.