Abstract
The continuous increase of energy demand with the subsequent huge fossil fuel consumption is provoking dramatic environmental consequences. The main challenge of this century is to develop and promote alternative, more eco-friendly energy production routes. In this framework, Solid Oxide Cells (SOCs) are a quite attractive technology which could satisfy the users’ energy request working in reversible operation. Two operating modes are alternated: from “Gas to Power”, when SOCs work as fuel cells fed with hydrogen-rich mixture to provide both electricity and heat, to “Power to Gas”, when SOCs work as electrolysers and energy is supplied to produce hydrogen. If solid oxide fuel cells are an already mature technology with several stationary and mobile applications, the use of solid oxide electrolyser cells and even more reversible cells are still under investigation due to their insufficient lifetime. Aiming at providing a better understanding of this new technological approach, the study presents a detailed description of cell operation in terms of electrochemical behaviour and possible degradation, highlighting which are the most commonly used performance indicators. A thermodynamic analysis of system efficiency is proposed, followed by a comparison with other available electrochemical devices in order to underline specific solid oxide cell advantages and limitations.
Highlights
One of the main global challenges is the reduction of greenhouse gas emissions in order to decrease climate changes and environmental pollution, having as a goal the achievement of carbon neutrality by 2050 [1]
A new road was opened by high-temperature Solid Oxide Cells (SOCs), which allow for a single bifunctional unit characterised by a superior round-trip energy efficiency
Solid oxide cells are promising technologies due to better performance compared to low-temperature designs: high efficiency, lower requested electricity consumption in electrolysis mode and flexible feeding to fuel cell are only some main advantages. One of their strong points is the possibility to work in reversible operation so that a single unit allows for both energy storage and generation
Summary
One of the main global challenges is the reduction of greenhouse gas emissions in order to decrease climate changes and environmental pollution, having as a goal the achievement of carbon neutrality by 2050 [1]. Protonic exchange membrane cells are quite well-known devices, the reversible operation of the same unit is not possible since the common catalysts used for the oxygen reduction in fuel cell mode have a low performance for the oxygen production in electrolysis mode [13] Due to these limits, a new road was opened by high-temperature Solid Oxide Cells (SOCs), which allow for a single bifunctional unit characterised by a superior round-trip energy efficiency. Using renewable energies paired with the reversible cell operation, the household electric consumption, heating and hot water would be satisfied, and a part of stored hydrogen could be directly used as transport fuel [20] At this scale application, the proposed integration allows for the cost reduction saving on electricity grid extension. The rSOC state-of-the-art is discussed in terms of Technology Readiness Level (TRL) and through the comparison with other available power systems, showing that SOFCs are already a mature system with initial commercial stationary applications, whereas SOECs and, above all, reversible cells request further studies and improvements to become reliable and affordable systems, in spite of different tested prototypes at the industrial level
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