Solid-State Electrochemistry and Solid Oxide Fuel Cells: Status and Future Prospects

Abstract

Solid-state electrochemistry (SSE) is an interdisciplinary field bridging electrochemistry and solid-state ionics and deals primarily with the properties of solids that conduct ions in the case of ionic conducting solid electrolytes and electrons and/or electron holes in the case of mixed ionic and electronic conducting materials. However, in solid-state devices such as solid oxide fuel cells (SOFCs), there are unique electrochemical features due to the high operating temperature (600–1 000 °C) and solid electrolytes and electrodes. The solid-to-solid contact at the electrode/electrolyte interface is one of the most distinguished features of SOFCs and is one of the fundamental reasons for the occurance of most importance phenomena such as shift of the equipotential lines, the constriction effect, polarization-induced interface formation, etc. in SOFCs. The restriction in placing the reference electrode in solid electrolyte cells further complicates the SSE in SOFCs. In addition, the migration species at the solid electrode/electrolyte interface is oxygen ions, while in the case of the liquid electrolyte system, the migration species is electrons. The increased knowledge and understanding of SSE phenomena have guided the development of SOFC technologies in the last 30–40 years, but thus far, no up-to-date reviews on this important topic have appeared. The purpose of the current article is to review and update the progress and achievements in the SSE in SOFCs, largely based on the author’s past few decades of research and understanding in the field, and to serve as an introduction to the basics of the SSE in solid electrolyte devices such as SOFCs. Graphical abstract

A critical review of key materials and issues in solid oxide cells

“…For fundamental issues related to the solidstate ionics and solid-state electrochemistry in SOCs, readers are encouraged to refer to a recent review on this important topic. [24] 2.2 | Thermodynamics of SOCs For a closed system, the change in internal energy (ΔU) equals to the heat transferred to the system (Q) minus the work (W) done by the system. Under the constant pressure (P) and general operation conditions of SOCs, the total work can be composed of mechanical work (PΔV) and electrical work (W′), and we can have [25] ∆…”

“…For fundamental issues related to the solid‐state ionics and solid‐state electrochemistry in SOCs, readers are encouraged to refer to a recent review on this important topic. [ 24 ]…”

Proton conductor NASICON-structure Li1+xCdx/2Zr2−x/2(PO4)3 as solid electrolyte for intermediate-temperature fuel cells

“…[1][2][3] The fuel cell system has been utilized in a variety of energy applications. 4,5 The attractive characteristics make them quite tting for addressing the energy crisis in the present situation of international energy development. Unfortunately, the large-scale commercialization of SOFCs is still challenging because of low ionic conductivity at high operating temperatures.…”

A Synergistic Three-Phase, Triple-Conducting Air Electrode for Reversible Proton-Conducting Solid Oxide Cells

“…Reversible solid oxide electrochemical cells (R-SOCs) are highly efficient electrochemical devices that can operate in both the fuel cell mode to generate electricity and the electrolysis mode to produce hydrogen or other cleaner fuels (by electrolyzing water and carbon dioxide). 1,2 Compared to other energy storage and conversion technologies, R-SOCs have the advantages of high efficiency, low cost, and good durability. 3 Compared to R-SOCs based on oxygen-ion-conducting electrolytes, 4,5 the R-SOCs based on proton-conducting electrolytes (or reversible proton-conducting solid oxide cells, R-PSOCs) have the potential to be more efficient and durable.…”

“…The growing energy consumption and environmental concerns have stimulated the development of efficient and reliable technologies for the storage and conversion of renewable energies (e.g., wind and solar) due to their intermittent nature. Reversible solid oxide electrochemical cells (R-SOCs) are highly efficient electrochemical devices that can operate in both the fuel cell mode to generate electricity and the electrolysis mode to produce hydrogen or other cleaner fuels (by electrolyzing water and carbon dioxide). , Compared to other energy storage and conversion technologies, R-SOCs have the advantages of high efficiency, low cost, and good durability …”