Dissertation
Cost and environmental impact of photoelectrochemical hydrogen production from waste brine
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Summer 2024
DOI: 10.25820/etd.007692
Abstract
Since the Industrial Revolution, the world’s primary energy source has been fossil fuels such as coal, oil, and natural gas. While fossil fuels have been crucial in advancing society to its current state, they come with important challenges including contribution to global warming, air pollution, and the depletion of fossil fuel reservoirs. Consequently, achieving greater energy sustainability has become a paramount societal goal, necessitating a heightened reliance on renewable energy sources such as solar. Sunlight can be a primary energy source, whether for generating electricity or to produce usable fuels and valuable chemicals that are currently derived from fossil fuels such as hydrogen. In this context, extensive research efforts have been dedicated to the pursuit of low-carbon hydrogen, however, current solar pathways for hydrogen production have not yet proven economically viable. This thesis analyzes the economic and environmental viability of an emerging solar hydrogen production pathway.
The production of hydrogen using a photoelectrochemical (PEC) cell offers a unique production pathway for hydrogen generation through the solar-driven electrolysis of brine. When brine is used as feedstock, it leads to the cogeneration of hydrogen with sodium hydroxide and chlorine as by-products. Sodium hydroxide and chlorine are commodity chemicals with numerous industrial applications and societal uses. The objective of this work is to investigate how the generation of marketable by-products can influence the cost-efficiency of hydrogen. To do this, a technoeconomic analysis (TEA) for PEC hydrogen production using a high-efficiency light-absorbing material is implemented. A conceptual triple-junction gallium arsenide (3-J GaAs) based photoelectrochemical (PEC) reactor at high solar concentrations (50-500x) is used. The base case of 200x solar concentration results in a solar-to-chemical (SCE) efficiency of 15% and a levelized cost of hydrogen (LCOH) production of $15.76/kgH2. The sensitivity analysis showed that under favorable combinations of the key variables (sodium hydroxide price, waste brine pretreatment price, and PEC replacement lifetime) PEC hydrogen generation from waste brine would be viable and have prices reaching $0.78/kgH2.
Analyzing the environmental burdens of this alternative pathway is the second part of the current work. To investigate this metric, an environmental impact analysis using life cycle assessment (LCA) methodology following the International Organization Standards, ISO 14040 and ISO 14044 is implemented. It is found that the process results in an overall global warming potential (GWP) of 75kgCO2eq/kgH2 when allocating all emissions to hydrogen. Using mass allocation, the GWP for hydrogen production is found to be 0.98 kgCO2eq/kgH2. While molar allocation results in the largest GWP, 18.9 kgCO2eq/kgH2. These results highlight the importance of considering the allocation method for PEC hydrogen generation. Separate research has found alternative hydrogen production methods, SMR and PV+electrolyzer, to have a GWP of approximately 9 kgCO2eq/kgH2 and 2 kgCO2eq/kgH2, respectively. PEC hydrogen production has a favorable outcome when mass allocation is considered compared to current hydrogen production methods.
PEC cell area requirements determine the cost of hydrogen production and the regional land area that must be occupied by the reactors. This thesis further carries out a comparison of the hydrogen production cost and land area of PEC cells when using 3-J Si and 3-J GaAs light-absorbing materials. The aim is to understand the trade-offs between using a high-efficiency light-absorbing material, 3-JGaAs, and a low-efficiency and cheaper material, 3-J Si. This results in a 3-J Si solar cell area of 2.3x10^6 m2 under no solar concentration. On the other hand, a 3-J GaAs solar cell provides sufficient voltage to drive the reaction, and therefore, the solar cell area is much lower, 8.9x10^5 m2. Despite the significantly larger area requirement, the cost of the 3-J Si PEC configuration is considerably cheaper, $2.06x10^8, than that of 3-J GaAs PEC, $2.07x10^10 USD.
Details
- Title: Subtitle
- Cost and environmental impact of photoelectrochemical hydrogen production from waste brine
- Creators
- Marisol Contreras
- Contributors
- Syed Mubeen (Advisor)Charles O. Stanier (Advisor)Jennifer Fiegel (Committee Member)Eric Nuxoll (Committee Member)Mark Mba-Wright (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Chemical and Biochemical Engineering
- Date degree season
- Summer 2024
- Publisher
- University of Iowa
- DOI
- 10.25820/etd.007692
- Number of pages
- xiv, 114 pages
- Copyright
- Copyright 2024 Marisol Contreras
- Language
- English
- Date submitted
- 07/23/2024
- Description illustrations
- Illustrations, tables, graphs, charts
- Description bibliographic
- Includes bibliographical references.
- Public Abstract (ETD)
Hydrogen holds significant potential as a fuel, especially in efforts to reduce greenhouse gas emissions. When hydrogen is reacted with oxygen in a fuel cell, it produces electricity with water being its only by-product and waste heat being released. This contrasts sharply with the emissions produced from burning fossil fuels, which, in addition to releasing atmospheric pollutants, also emit greenhouse gases (GHGs), which contribute to global warming. However, the primary method for hydrogen production in the U.S. is via steam methane reforming, which relies on fossil fuels as feedstock. A promising alternative involves extracting hydrogen from hydrogen-containing molecules using solar energy.
This thesis implements a cost analysis to determine the economic viability of solar hydrogen production using a high-efficiency solar cell and wastewater from the desalination industry as feedstock in a stand-alone design. The results are compared to current methods of hydrogen production and the cost goal set by the Department of Energy (DOE), $1 per kgH2. This work found that under favorable conditions, hydrogen can reach a production cost of $0.78 per kgH2. However, major improvements to the technology are needed to reach such a cost. Additionally, an environmental impact analysis is conducted to determine the environmental burdens of this hydrogen production pathway. The analysis is for solar hydrogen production using two distinct solar cells of different materials, a silicon-based and a gallium-based solar cell. The results indicate that that due to less material needs, the gallium-based solar system is more environmentally favorable compared to the silicon-based system. The emissions range from 0.98-18.9 kg CO2e/kgH2 depending on how emissions are allocated among the process coproducts. The insights gained through the environmental and cost analysis can guide research toward cost-effective and environmentally friendly hydrogen production.
- Academic Unit
- Chemical and Biochemical Engineering
- Record Identifier
- 9984698352102771
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