A review of high temperature co-electrolysis of H₂O and CO₂to produce sustainable fuels using solid oxide electrolysis cells (SOECs): advanced materials and technology

Abstract

High-temperature solid oxide electrolysis cells (SOECs) are advanced electrochemical energy storage and conversion devices with high conversion/energy efficiencies. They offer attractive high-temperature co-electrolysis routes that reduce extra CO emissions, enable large-scale energy storage/conversion and facilitate the integration of renewable energies into the electric grid. Exciting new research has focused on CO electrochemical activation/conversion through a co-electrolysis process based on the assumption that difficult C[double bond, length as m-dash]O double bonds can be activated effectively through this electrochemical method. Based on existing investigations, this paper puts forth a comprehensive overview of recent and past developments in co-electrolysis with SOECs for CO conversion and utilization. Here, we discuss in detail the approaches of CO conversion, the developmental history, the basic principles, the economic feasibility of CO/HO co-electrolysis, and the diverse range of fuel electrodes as well as oxygen electrode materials. SOEC performance measurements, characterization and simulations are classified and presented in this paper. SOEC cell and stack designs, fabrications and scale-ups are also summarized and described. In particular, insights into CO electrochemical conversions, solid oxide cell material behaviors and degradation mechanisms are highlighted to obtain a better understanding of the high temperature electrolysis process in SOECs. Proposed research directions are also outlined to provide guidelines for future research.

Electrochemical Performance and Preliminary Post-Mortem Analysis of a Solid Oxide Cell Stack with 20,000 h of Operation

“…Possible explanations of the continuous increase in the ohmic resistance include grain growth in the electrolyte, pore formation near the 8YSZ/GDC (gadolinium doped ceria) interface, as reported by Schefold et al 17 and Tietz et al, 18 and depletion of nickel near the boundary of the electrolyte and fuel electrode as observed by different groups. [19][20][21][22] The effective ionic conductivity of the composite electrodes is usually below 10% of that of the bulk electrolyte depending on the porosity and volume fraction of the composites according to Zheng et al 23 Therefore, the increase of ohmic resistance can be one of the consequences of Ni depletion in Ni/YSZ electrode, which shifts the working electrode area outwards and increases the electrolyte thickness. Note that the polarization and total resistance of layer 2 from the last measurement are not presented in Figure 5.…”

Direct Electrolysis of CO2 in a Symmetrical Solid Oxide Electrolysis Cell with Spinel MnCo2O4 as Electrode

“…[1,2] More and more attentions have been paid to develop new energy technologies reducing CO 2 emission and utilizing CO 2 . [1,2] More and more attentions have been paid to develop new energy technologies reducing CO 2 emission and utilizing CO 2 .…”

CO2 Reduction by Hydrogen Pre‐Reduced Acceptor‐Doped Ceria

“…One approach is based on thermally reducing CeO 2 (solar driven) and then splitting CO 2 (and/or water) on the pre‐reduced oxide . Another viable way to access CO (or CO/H 2 mixtures) is the high‐temperature (co‐)electrolysis of CO 2 (and H 2 O) . Using in‐situ X‐ray photoelectron spectroscopy, the coupling between Ce 3+ /surface oxygen vacancy centers and carbonate intermediates has been shown .…”

“…In order to derive general features of the influence of the doping level on the CO 2 reactivity we focused on Gd‐ and Sm‐acceptor‐doped ceria, as these materials have been in the focus of basic research and electrode development. Properties such as a high oxygen ion conductivity, as well as electronic conductivity in their reduced state, make them interesting materials for the use in solid oxide cells . Activation of CO 2 – which is mediated by oxygen vacancies – is mandatory for high temperature electrolysis of CO 2 and the dry reforming reaction of hydrocarbons.…”