Techno-Economic Analysis of the Sabatier Electrolyzer: CO2-to-Methane Using Proton-Conducting Ceramics
Authors: Pritchard Tyler , Braun Robert J. , Sullivan Neal P 
Published: December 2020

As intermittent renewable-electricity generation achieves higher market penetration, the need for quick and efficient storage and dispatch of this energy becomes more pronounced. In this report, we present our techno-economic analysis of a Sabatier Electrolyzer based on proton-conducting ceramic materials. The Sabatier Electrolyzer technology is illustrated in the figure, and integrates steam electrolysis and hydrogen production with CO2 hydrogenation into a single reactor based on protonic-ceramic electrolysis cells (PCECs) and Sabatier catalysts. CO2 and H2O are fed to fuel and steam electrodes, respectively, of a protonic-ceramic electrolysis cell. An external power source drives H2O splitting at the steam electrode. The product O2 is exhausted from the cell. The product protons are driven across the protonic-ceramic membrane to the fuel electrode, where they react with CO2 to form CH4 and H2O. The combination of processes can match the exothermicity of CO2 hydrogenation with the endothermicity of H2O electrolysis to facilitate thermal balance and high efficiency.

When powered by solar and / or wind energy, the Sabatier Electrolyzer has the potential to store intermittent renewable electricity in the form of commodity chemicals while simultaneously reducing carbon dioxide emissions, thereby addressing two principle societal concerns in a single device. Methane presents an attractive energy-storage method; it is stable, integrates well with our existing infrastructure, and can be dispatched quickly for energy generation. In addition to our experimental demonstrations presented in another report, we explore the market potential of the Sabatier electrolyzer through techno-economic analysis (TEA) of a 1.3-MW PCEC electrolysis plant that methanates CO2 produced from a Greenfield coal-fired power plant with a three-ton-per-day coal feedstock. Preliminary models establish a levelized-cost of storage (LCOS) for synthesized methane produced by the PCEC plant. This LCOS represents the required sale price of 1 MWh of synthesized methane to enable “break-even” investment of the SOEC plant over a 30-year plant life. We estimate LCOS of just under 400 $/ MWhe of synthesized methane, less than that of lithium-ion batteries, lead-acid batteries, and advanced lead-acid batteries for commercial and industrial standalone applications.

The techno-economic model includes extensive cost estimates for PCEC balance of plant components taken from the literature, the Energy Information Administration, and the U.S. Department of Energy. Our sensitivity analyses show that PCEC Faradaic efficiency and methane selectivity have the largest impact on the Levelized Cost of Storage. A 20% reduction in methane selectivity raises LCOS of the plant by 258 $/MWh, or more than 50%. Further, a 20% decrease in Faradaic efficiency increases LCOS by nearly the same amount. Of the many model inputs, these two parameters prove most critical in estimating the Levelized Cost of Storage.

Building on this result, we are now developing a Life Cycle Assessment using the well-established CO2U analysis from the DOE National Energy Technology Laboratory. LCA results will also be presented as part of this talk.

Figure 1