CH4 and CH3OH by co-electrolysis of CO2 and H2O at intermediate temperatures using bifunctional catalysts

Title : CH4 and CH3OH by co-electrolysis of CO2 and H2O at intermediate temperatures using bifunctional catalysts

Abstract:

A setup for steam electrolysis as well as steam electrolysis combined with CO₂ reduction at “Intermediate temperature” (240 -300^oC) and elevated pressures (up to 30 bar) was constructed. This temperature range is placed in between the temperature range for proton exchange membrane (PEM) electrolysis and alkaline electrolysis (up to 90^oC), and the solid oxide electrolysis (SOEC) range 700-900^oC. This range is particularly Interesting for CO₂-H₂O co-electrolysis for synthesis of organic compounds (Power-to-X), as it is the range where such compounds are prepared by classical methods.  The desired compounds are thermally stable, and low overvoltages for electrochemical reactions may be obtained. The special characteristics of the process are:

• A solid electrolyte based on a proton conducting phosphate (CsH₂PO₄) – allowing for use at the temperature range mentioned.
• The capability of applying a water vapor pressure above 1 bar, up to at least 10 bar, which is necessary to prevent the CsH₂PO₄ from dehydrating and thereby loose its conductivity.
• By this setup we have demonstrated direct synthesis of methane from co-electrolysis of CO₂ and water in a one-step process at more than 90% current efficiency and a low cell voltage, starting from a value as low as 1.3V for small current densities . The cathode material was nickel, which has been demonstrated to produce hydrogen both by a direct electrochemical reduction and by a chemical reaction between CO₂ and H₂ generated by the electrolysis.  Recently we demonstrated production of methanol in a one-step process, using a bifunctional cathode consisting of a combination of platinum or nickel and a classical copper methanol catalyst. The system was operated with current densities of up to ca. 100 mA/cm² with a voltage of less than 2 volts producing methanol with a Faradaic efficiency of up to ca. 7 %. As this is a new type of process, all components are under re-developmenet  (Electrodes, electrolytes, bipolar plates, gasket materials, cell design, stack design).

Audience Take Away: 

• A completely new concept for CO₂-H₂O co-electrolysis and water electrolysis (Power-to-X) have been demonstrated, so far in lab scale. It has led to the introduction of bifunctional catalysts/electrodes for formation of simple organic products at 240 to 300 ^oC.
• The chance to find sufficiently active alternatives to Pt and IrO₂ in acidic electrolysis are improved compared to the possibilities for PEM electrolysers.
• It opens new opportunities for research in electro-catalysts, as the data for the new temperature range so far are very limited.
• In a similar way it opens new opportunities for research in bifunctional catalytic-electrocatalytic materials and processes.
• The results indicate that it is possible to store electrical energy as organic fuels in a one-step process instead of a two step process, i.e. first making hydrogen by electrolysis, and then react it with CO₂ in a separate reactor

Biography:

Dr. Erik Christensen studied at the Technical University of Denmark (DTU), and graduated in 1983. He joined the Material Science Group of Prof. Niels J. Bjerrum at the Department of Chemistry, DTU, and received his PhD degree here in 1987. He continued to work there as assistant professor, but was then employed by the Danish company Danfoss, but still working at DTU on various collaboration projects until 2007. He then went back to DTU employment, now as a Senior Researcher to change his field to water electrolysis using various types of proton conducting solid electrolytes.