Hydrogen Production from Efficient Two-Step Water Splitting
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The demand for renewable energy sources such as hydrogen is projected to increase in the next few decades as the world turns its sights towards reducing the effects of climate change. Hydrogen has recently been considered for use in the automobile industry as a power source for fuel cell vehicles because of its high energy density by mass. The greenest form of hydrogen production is through water electrolysis. Traditional water electrolysis, however, requires a membrane, which lowers efficiency and raises costs and safety risks. In this report, we design a process for two-step splitting of water by rotating cycles of electrochemical production of hydrogen and thermochemical production of oxygen without the use of a membrane. The process produces 28,000 U.S. tons of hydrogen per year with a co-product of 222,000 U.S. tons of oxygen per year. The electricity to power the electrolysis and other process units is sourced from solar energy. With a selling price of $1.02/lb of hydrogen - based on current prices for grey hydrogen, a selling price of $0.04/lb of oxygen, and a tax credit of $1.46/lb for the production of green hydrogen, the plant would achieve a return on investment of -1.87%, an internal rate of return of 34%, and a net present value of $152 million. In the best-case scenario where oxygen can be sold at a higher price of $0.30 for medical uses, the plant becomes much more profitable with an IRR of 67% and an ROI of 44%. The process’ voltage efficiency of 91.0% and HHV efficiency of 81.3% make it competitive with the best electrolysis technologies used in industry. Overall, the process provides one pathway towards a large-scale hydrogen economy.