Toward lightweight and integrated designs: A comprehensive review of the development in tubular solid oxide fuel cells

Tubular solid oxide fuel cells (T-SOFCs) hold great promise in the portable power supply sector due to their structural advantages, including simple sealing and uniform thermal stress distribution. This paper reviews the configuration of T-SOFCs and advances in stack integration from a structural design perspective. At the level of cell structure, the design characteristics, fabrication processes and performance of tubular cells in various configurations, including circular, flat, corrugated, hollow-fiber, and multi-channel micro-monolithic tubular types. At the stack level, flat-tubular stacks utilize internal ribs to perform dual functions of current distribution and collection, with a 60-cell stack delivering 921 W at 750 °C. Micro-tubular dual-conductor nickel pads shorten the current path through multi-point contact, with a 160-cell stack delivering over 1 kW at 700 °C. A series-segmented single-row sub-stack employs a single-row tubular bundle to achieve quasi-two-dimensional flow control, and when combined with optimized sieve plates, reduces the variation coefficient of gas distribution from 96% to 5.83%. Flat-tubular internal reforming stacks use multi-channel reforming reactors and suppress thermal gradients through internal thermal coupling, enabling stable operation over 400 h at S/C = 1. These structural innovations collectively have propelled tubular SOFCs from single cells to engineered stacks, offering broad application prospects in the future for drone propulsion, emergency power supply and renewable energy integration.