Redox Stable Cathodes for CO 2 -Steam Co-Electrolysis Process in Solid Oxide Electrolyzers for Syn-Gas Generation

Penetration of renewable energy (RE) in the consumable energy mix is expected to grow substantially in near future from its current share of 6.6 % of the total energy consumed globally.[i] In parallel, an allied energy conversion and storage technologies are also being developed and deployed globally. The batteries can provide short to medium term energy storage solution, however long term energy storage as well as transport of RE from the regions with high RE generation capacity to the regions with low RE capacity need innovative solutions. The conversion of RE into storable and transportable fuels is one of such approaches. The technologies such as electrolytic hydrogen production have already entered commercial space, however large scale storage and transport of hydrogen is energy intensive with about $15/kg cost just for the storage of compressed H 2 at 700 bar.[ii] Further, the infrastructure for hydrogen transport is almost non-existent. Hence, the alternative electrochemical technologies which can produce transportable liquid fuels like blended hydrocarbons and methanol are being explored. These fuels are ready to use in the existing technologies like IC engines and diesel generators. As CO 2 from industrial sources is used in the synthesis of these fuels, there is no net addition of CO 2 in the cycle. It is worth noting that even with increased penetration of RE, there would be numerous industrial processes which generate vast amount of CO 2 amounting to about 21 % of total CO 2 emissions.[iii] The solid oxide electrolyser (SOE) is an electrochemical membrane reactor based upon oxygen ion conducting ceramic electrolyte which can efficiently produce syn-gas (mixture of H 2 and CO) as a feedstock for synthesis of liquid fuels. SOEs can be thermally integrated to liquid fuel synthesis reactors which boosts the overall efficiency of the system with heat input from an exothermic fuel synthesis reaction used in the SOE. The total synthesis and transport efficiencies of such integrated system can be above 75 % with cost in the range of US$ 0.8 to 0.9 per litre of the fuel using well established existing fuel transportation infrastructure.[iv] Traditionally, yttria stabilised zirconia (YSZ) electrolytes are used in SOE with Ni-YSZ cermet electrodes for splitting of CO 2 and H 2 O on cathode side (negative electrode) and a perovskite La 0.80 Sr 0.20 MnO 3 (LSM) is used to facilitate oxygen evolution reaction on the anode side (positive electrode). While Ni-