Iron-based oxides for thermochemical splitting of water and carbon dioxide
- Approximately 40 Gt-CO2 is emitted from human activities per year globally, contributing to global warming. There are worldwide efforts to reduce the greenhouse gas (GHG) emissions and hold "the increase in global average temperature to well below 2°C above pre-industrial levels". One approach to achieve this goal is the synthetic transformation of CO2. The splitting of CO2 to carbon monoxide and oxygen initiates CO2 transformation. Another approach is to split water to produce hydrogen and oxygen using GHG-free energy, and hydrogen can be used for storing intermittent solar and wind electricity, as a transportation fuel, for converting CO2 into organics, for decarbonizing the existing petrochemical and fertilizer industries, and as a fuel for industrial heating. For these to make a difference to global warming, the processes need to be cost-competitive with current approaches to synthesize chemicals and fuels and compatible for scale-up in an infrastructure capable of handling Gt-scale CO2. The chemical infrastructure today at the Gt-scale relies almost exclusively on thermochemical processes. Hence, such dominance of thermochemistry warrants research in creating options for the thermochemical splitting of water and CO2. The main requirements of two-step thermochemical splitting of water and CO2 include high thermodynamic equilibrium gas splitting capacity of the oxide, fast reaction kinetics and long-term cyclability of materials and system. Motivated by these requirements, this dissertation focuses on identifying materials design strategies, the thermodynamic mechanisms, and cost reduction methods for the two-step cycle. At the materials level, the strategy of cation mixing was used to lower the reaction temperature of the two-step cycle. The discovered poly-cation oxide (PCO) demonstrates higher water splitting capacities than state-of-the-art materials, especially at a thermal reduction temperature as low as 1100°C. Additionally, the strategy of tuning two-phase ternary materials was applied to ferrites which have been long researched for the two-step cycle. Contrary to the conventional wisdom, it was discovered that when the ferrite is poor in iron and has a significant portion of the rocksalt phase, its gas splitting capacity can be several times higher than the traditional iron-rich ferrites. At the system level, for the two-step thermochemical pathway to be ultimately applicable in practice, the product cost ought to be competitive. The technoeconomic analysis of two-step thermochemical water splitting investigated systems using ceria and ferrites. Cost minimization was conducted to consider materials properties during system design. Also, the target properties of the oxide were recommended for a H2 cost to be $2/kg, and a series of cost reduction measures were discussed from the system design point of view..
|Type of resource
|electronic resource; remote; computer; online resource
|1 online resource.
|Goodson, Kenneth E, 1967-
|Degree committee member
|Goodson, Kenneth E, 1967-
|Stanford University, Department of Mechanical Engineering.
|Statement of responsibility
|Submitted to the Department of Mechanical Engineering
|Thesis Ph.D. Stanford University 2020.
- © 2020 by Shang Zhai
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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