Degradation in High-Temperature Co-Electrolysis Using Reversible Solid Oxide Fuel Cells: A Review

The need for cleaner and more efficient energy generation and storage is essential to cope with increasing energy demand and to reduce fossil fuel consumption. Solar, wind, hydroelectric, and other renewable energy sources are promising alternatives to fossil fuels, however, display considerable fluctuation in production due to their dependence on weather conditions. This is why supplementary alternative energy generation devices and storage are vital to progress towards a more feasible sustainable future, also including the options for more resilient energy systems, for instance with regards to grid reliability during natural disasters.

Reversible solid oxide fuel cells (rSOFC) have recently become a topic of interest in the energy industry due to their ability to produce fuel for storage in electrolysis mode and consume this fuel to produce electricity in fuel cell mode in one single unit when required. However, one of the primary issues hindering the widespread commercialisation of fuel cells is the lifetime on account of the effects of degradation on the cell. These effects, such as electrode poisoning, air electrode delamination, and fuel electrode redox stability, have been investigated extensively in the literature for solid oxide fuel cells (SOFC) and solid oxide electrolysers (SOE) [1–4] separately, yet there are limited papers available on the degradation of reversible fuel cells and how cycling between the two modes affects the lifetime [5]. Co-electrolysis of H2O and CO2 using high-temperature SOEs is another pathway to reducing CO2 emissions via energy storage and conversion devices with high-energy efficiencies and similarly, there is a gap in the understanding of degradation mechanisms with this mixed feed. This paper will present a review of the background, fundamental challenges and developments of SOFC, SOE and rSOFC, focusing on the different approaches to high-temperature co-electrolysis in terms of materials, fuel composition and how these influence the rate of degradation.