Techno-Economic Analysis of CO2-to-Fuel with a Proton-Conducting Ceramic Sabatier Electrolyzer

Abstract

As intermittent renewable electricity generation achieves higher market penetration, the need for robust storage and dispatch capabilities become more pronounced. In this report, we present a techno-economic analysis based around a levelized cost of storage (LCOS) calculation for a Sabatier Electrolyzer to illustrate the value proposition of electrolyzer technology. The Sabatier Electrolyzer is illustrated in Figure 1A; the CO2 feed to the fuel electrode is upgraded to CH4 through heterogeneous catalysis with hydrogen. The hydrogen is produced through water electrolysis at the steam electrode. When driven by surplus electricity, the Sabatier Electrolyzer presents an energy-storage option with CO2-to-fuels.The electrolyzer features a proton-conducting ceramic electrolyte (BaCe0.4Zr0.4Y0.1Yb0.1O3-d) that has shown encouraging performance under fuel-cell and H2O-electrolysis applications. The Sabatier chemistry (CO2 + 4 H2 = CH4 + 2 H2O) occurs within the porous fuel electrode, a nickel-ceramic composite, where protons emerging from the ceramic phase react with CO2 or recombine to form H2 over the nickel phase. The exothermic Sabatier reaction can be balanced by the endothermicity of H2O electrolysis improving plant-level thermal balance and higher efficiency.This report explores the economic potential of a commercial-scale Sabatier electrolyzer plant from the perspective of levelized cost of storage (LCOS). This LCOS is based on similar analyses conducted for lithium-ion batteries, flow batteries, flywheels, and pumped-hydro facilities. The model combines plant-level round-trip efficiency (RTE), overnight capital costs, variable operations and maintenance (O&M) costs, and charging costs into a time value of money (TVM) financial model. The model is exercised to estimate the lifetime cost of energy storage for the plant.The protonic-ceramic electrolyzer presents a perhaps unusual materials set. While protonic-ceramic fuel cells have demonstrated high performance and encouraging durability at the lab scale, the materials have also shown undesirable electronic conduction that can substantially decrease electrolysis efficiency, boosting costs. The electrochemical model captures the substantial impact of protonic-ceramic electrochemical performance on LCOS, and is validated by lab-scale experimental measurements of protonic-ceramic Sabatier Electrolyzer cells. Results were scaled to yield the commercial-scale LCOS.Sensitivity analyses demonstrate the primary cost drivers behind the commercial-scale Sabatier Electrolyzer plant. Key cost drivers include Faradaic efficiency, methane yield, utility cost of electricity, and cost of sequestered CO2. Depending on operational parameters, the LCOS of the commercial-scale Sabatier Electrolyzer plant ranges from $4,319 down to $348 per MWh of storage potential. Figure 1