The electrochemical CO2 reduction reaction (CO2RR) towards CO allows to turn CO2 and renewable energy into feedstock for the chemical industry. Previously shown electrolyzers are capable of continuous operation for more than 1000 h at high faradaic efficiencies and industrially relevant current densities. However, the crossover of educt CO2 into the anode gas has not been investigated in current cell designs: Carbonates (HCO3− and CO32−) are formed at the cathode during CO2RR and are subsequently neutralized at the anode. Thus, CO2 mixes into the anodically evolved O2, which is undesired from commercial perspectives. In this work this chemical transport was suppressed by using a carbonate-free electrolyte. However, a second transport mechanism via physically dissolved gases became apparent. A transport model based on chemical and physical absorption of CO2 and O2 will be proposed and two solutions were experimentally investigated: the use of an anode GDL (A-GDL) and degassing the anolyte with a membrane contactor (MC). Both solutions further reduce the CO2 crossover to the anode below 0.1 CO2 for each cathodically formed CO while still operating at industrially relevant current densities of 200 mA/cm2.

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Based on the planar SOFC and SOE technology, a high temperature metal – air battery was operated at temperatures between 700°C and 800°C. It reached charging and discharging capacities of about 2 hours at power densities of more than 250mW/cm². A Siemens stack concept was developed and validated in numerous lab experiments as well as in several stack demonstrators of more than 1kW power output. The storage material is a proprietary development consisting of a iron/iron oxide combination which can be produced economically. It showed very low degradation rates of 1 - 2% in 1,000 charging / discharging cycles. More than 10,000 cycles were reached in 10x10 cm² short stacks. System efficiencies for the upper MW range of > 60% and a cycle life of about 10,000 cycles will be achieved.

A novel rechargeable high temperature metal -air battery based on the planar solid oxide fuel cell technology has been developed [H.

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