A Theoretical Study on Reversible Solid Oxide Cells as Key Enablers of Cyclic Conversion between Electrical Energy and Fuel

Saheli Biswas,Sarbjit Giddey,Sankar Bhattacharya,Aniruddha Kulkarni,Shambhu Rathore

doi:10.3390/en14154517

Saheli Biswas, Sarbjit Giddey + Show 3 more

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https://doi.org/10.3390/en14154517

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Abstract

Reversible solid oxide cells (rSOC) enable the efficient cyclic conversion between electrical and chemical energy in the form of fuels and chemicals, thereby providing a pathway for long-term and high-capacity energy storage. Amongst the different fuels under investigation, hydrogen, methane, and ammonia have gained immense attention as carbon-neutral energy vectors. Here we have compared the energy efficiency and the energy demand of rSOC based on these three fuels. In the fuel cell mode of operation (energy generation), two different routes have been considered for both methane and ammonia; Routes 1 and 2 involve internal reforming (in the case of methane) or cracking (in the case of ammonia) and external reforming or cracking, respectively. The use of hydrogen as fuel provides the highest round-trip efficiency (62.1%) followed by methane by Route 1 (43.4%), ammonia by Route 2 (41.1%), methane by Route 2 (40.4%), and ammonia by Route 1 (39.2%). The lower efficiency of internal ammonia cracking as opposed to its external counterpart can be attributed to the insufficient catalytic activity and stability of the state-of-the-art fuel electrode materials, which is a major hindrance to the scale-up of this technology. A preliminary cost estimate showed that the price of hydrogen, methane and ammonia produced in SOEC mode would be ~1.91, 3.63, and 0.48 $/kg, respectively. In SOFC mode, the cost of electricity generation using hydrogen, internally reformed methane, and internally cracked ammonia would be ~52.34, 46.30, and 47.11 $/MWh, respectively.

Highlights

Issues related to fossil fuel depletion and global warming continue to be the decade’s greatest concern
Giglio et al [63] reported ηX of 76% for synthetic natural gas production using a SOEC stack coupled with a methanator. Another recent study [64] on fuel gas (CH4, CO, CO2, H2 ) fed Reversible solid oxide cells (rSOC) reported ηRTE in the range of 55 to 60% depending on cell temperature and pressure
For the SOFC mode operations, two different routes have been considered for both methane and ammonia; Routes 1 and 2 involve internal reforming or cracking and external reforming or cracking, respectively

Summary

Introduction

Issues related to fossil fuel depletion and global warming continue to be the decade’s greatest concern. In spite of limited reserves [1], fossil fuel still dominates the energy sector [1,2] resulting in massive greenhouse gas (GHG) emission that leads to global warming. 1.5% as compared to 2019, and the share of renewables in global electricity generation jumped to nearly 28% in 2020 from 26% in 2019 In spite of these impressive numbers, RE is still faced with the problems of intermittency, storage, and transportation that have restricted its large-scale commercial application, causing an imbalance in the energy supply-demand. This has led to the emergence of power-to-X technology [6,7], whereby renewable energy can be converted into storable and transportable fuels and chemicals (denoted here as X) like hydrogen, methane, ammonia, syngas, formic acid, and methanol (Figure 1). The current cost for direct air capture is high ($0.094–$0.232 per kg of CO2 ), further R&D is expected to drive down the same [8]

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