Stephanie Wolf

 

Boundaries of high-temperature co-electrolysis towards CO2-electrolysis

Schematic diagram of co-electrolysis in a SOC. Copyright: L.Dittrich Schematic diagram of co-electrolysis in a SOC.

Conventional processes in the chemical industry often rely on intermediate reactants produced by coal gasification or carbohydrate reforming to synthesize bulk chemicals. The continual reliance on fossil fuels counteracts efforts in environmental protection due to high exhaust of greenhouse gases like CO2 in the atmosphere. Forward-looking technologies, like the co-electrolysis of water and captured carbon dioxide in a solid-oxide electrolysis cell, avoid emissions in the atmosphere and even reuse CO2 to produce a mixture of carbon monoxide and hydrogen, called syngas. Co-electrolysis operated with regenerative energies generates "white syngas". The ratio of H2 to CO can be influenced by adjusting the system parameters. This is relevant for different industrial processes, which require different syngas ratios. The synthesis gas can then be used, for example, in the industrially established Fischer-Tropsch process as a starting material for basic chemical components such as methane or for the production of climate-neutral, synthetic fuels. This way, the dependency of the chemical industry on fossil resources (natural gas, coal, oil) can be significantly reduced by means of co-electrolysis. Extensive process studies are necessary in order to operate co-electrolysis in an optimal way. In particular, the transition between co-electrolysis and CO2-electrolysis has not been fully investigated yet.

In this work, the processes underlying the transition of high-temperature co-electrolysis towards CO2-electrolysis are investigated. In-depth information on the influence of parameter settings on the mechanisms at the triple phase boundary of a Ni-YSZ/YSZ/GDC/LSC based SOC are provided by impedance spectroscopy and current-voltage characteristics.