Protonic ceramic electrochemical cells (including fuel cells (PCFCs) and electrolysis cells (PCECs)) are positioned as an eco-friendly means for realizing energy/chemical conversion at low (below 500 °C) and intermediate (500–800 °C) temperatures; as a result, R&D of PCFCs and PCECs are compatible with hydrogen energy and CO2 utilization programs that play an increasing role in global environmental practice. However, along with ionic transport, the majority of proton-conducting ceramic materials also exhibit electronic transport under oxidizing conditions and elevated temperatures. This feature negatively affects the performance of cells due to the short-circuit effect leading to a reduction in faradaic and energy efficiencies. In response, in order to achieve a compromise between high performance and high efficiency, the present review article aims at revealing the main factors contributing to undesirable electronic transport of materials used in PCFCs and PCECs, as well as possible solutions leading to its suppression for improving their efficiency.

Electrochemistry and energy conversion features of protonic ceramic cells with mixed ionic-electronic electrolytes

The current review highlights features of electron transport in proton-conducting electrolytes and possible ways of its eliminating to increase performance and efficiency of the related protonic ceramic electrochemical cells. 

Protonic ceramic fuel cells (PCFCs) or proton-conducting solid oxide fuel cells (SOFCs) are a class of electrochemical devices with high proton conductivity at the intermediate, even low operating temperatures (450–750 °C), which directly convert the chemical energy of hydrogen or hydrogen-containing fuels into electricity in a clean and efficient manner. In comparison to oxygen-ion conducting SOFCs , the operation at lower operating temperature overcomes the incompatibility and cathode delamination issues in high-temperature operated SOFCs. More attractively, the fuel is not diluted owing to the production of water at the cathode side . However, lowing working temperature weakens the electrode reaction kinetics and the ion migration, therefore the rational design of high-performance cathode materials is highly desired for PCFCs. Herein, we provide a review on the design criteria and state-of-art materials of PCFC composite cathodes including proton-conducting composite, proton-blocking composite and other types of composite cathodes, and discuss the underlying rationales and mechanisms. In particular, we discuss the feasibility of self-assembled composite cathodes used in PCFCs, and point out the future development directions of composite cathodes. 

Composite cathodes for protonic ceramic fuel cells: Rationales and materials

Solid oxide fuel cells (SOFC) are promising, environmentally friendly energy sources. Many works are devoted to the study of materials, individual aspects of SOFC operation, and the development of devices based on them. However, there is no work covering the entire spectrum of SOFC concepts and designs. In the present review, an attempt is made to collect and structure all types of SOFC that exist today. Structural features of each type of SOFC have been described, and their advantages and disadvantages have been identified. A comparison of the designs showed that among the well-studied dual-chamber SOFC with oxygen-ion conducting electrolyte, the anode-supported design is the most suitable for operation at temperatures below 800 °C. Other SOFC types that are promising for low-temperature operation are SOFC with proton-conducting electrolyte and electrolyte-free fuel cells. However, these recently developed technologies are still far from commercialization and require further research and development.

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Classification of Solid Oxide Fuel Cells

A review on mathematical modelling of Direct Internal Reforming- Solid Oxide Fuel Cells

Scientometric review of proton-conducting solid oxide fuel cells

A highly efficient Ruddlesden‐Popper structure anode material with a formula of Sr3Fe1.3Mo0.5Ni0.2O7‐δ (RP‐SFMN) has been developed for hydrocarbon fueled solid oxide fuel cells (HF‐SOFC) application. It is demonstrated that a nanostructured RP‐SFMN anode decorated with in‐situ exsolved Ni nanoparticles (Ni@RP‐SFMN) has been successfully prepared by annealing the anode in reducing atmosphere similar to the operating conditions. The phase compositions, valence states, morphologies, and electrocatalytic activities of RP‐SFMN material have been characterized in detail. In addition, the in‐situ exsolution mechanism of the metallic Ni phase from the parent oxide is clearly explained by using density function theory calculation. The peak output power density at 800°C is significantly enhanced from 0.163 to 0.409 W/cm2 while the electrode polarization resistance is effectively lowered from 0.96 to 0.30 Ω cm2 by the substitution of B‐site Fe by Ni, which is attributed to the improved electrocatalytic activities induced by the in‐situ exsolved Ni nanocatalysts. Moreover, the single cell with RP‐SFMN anode exhibits good stability in 3% H2O humidified H2 and syngas for 110 and 60 h at 800°C, respectively. Our findings indicate that RP‐SFMN is a greatly promising anode candidate of HF‐SOFCs due to its good electrochemical performance and stability during the operation.

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/sus2.58

Robust Ruddlesden‐Popper phase Sr3Fe1.3Mo0.5Ni0.2O7‐δ decorated with in‐situ exsolved Ni nanoparticles as an efficient anode for hydrocarbon fueled solid oxide fuel cells

Na Yu

Papers

Scientometric review of proton-conducting solid oxide fuel cells

Robust Ruddlesden‐Popper phase Sr3Fe1.3Mo0.5Ni0.2O7‐δ decorated with in‐situ exsolved Ni nanoparticles as an efficient anode for hydrocarbon fueled solid oxide fuel cells

Evaluation of the electrocatalytic performance of a novel nanocomposite cathode material for ceramic fuel cells

A robust direct-propane solid oxide fuel cell with hierarchically oriented full ceramic anode consisting with in-situ exsolved metallic nano-catalysts

Direct ammonia protonic ceramic fuel cell: A modelling study based on elementary reaction kinetics