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Direct Hydrogen Production from Sunlight and Water



OBJECTIVE: Develop a system that produces hydrogen from water and exposure to sunlight without any additional energy input that is ready to use in fuel cell or storage applications. 

DESCRIPTION: The Army has been investigating hydrogen fuel cells for vehicle power applications (both primary and non-primary) due to their reduced acoustic and thermal signatures as well as high power density and unlimited run time (provided fuel is supplied). Unlike current logistic fuels, hydrogen needs to be extracted from a source before it can be used, as it is not abundantly available in a usable form naturally. Numerous methods for hydrogen generation have been investigated in the past few decades, most usually requiring external energy to produce the hydrogen and treatment to remove compounds that could damage a fuel cell if passed through. Recent advances in technology have suggested that producing hydrogen from water with direct exposure to sunlight may be an attractive path for hydrogen generation. A system is desired to produce hydrogen from water and exposure to sunlight with no external energy input, just sunlight. The system should produce hydrogen that is of sufficient purity for proton exchange membrane (PEM) fuel cell use (99.999% pure). The hydrogen produced by the system should be ready to use in a fuel cell application or passed to a compressor/hydrogen storage system. The system should also be able use greywater or wastewater as a hydrogen source. The system should maximize hydrogen production per unit area, minimizing the total area of the system. 

PHASE I: The desired results of Phase I work are a preliminary design of the system and a small-scale demonstration of the underlying technologies and design. Specifically, the efficiency of the water splitting process, the hydrogen separation and collection, and proposed operations and control of the system should be demonstrated. These demonstrations do not need to be performed in concert with each other but should be performed at a small scale to demonstrate the feasibility of the design. The system should minimize both area and weight while providing the desired flow rate of hydrogen. 

PHASE II: The desired result of Phase II is a system that produces 1 kg of hydrogen per day assuming 6 hours of sun exposure per day. The system should be optimized for continuous operation and provide hydrogen that can be used in a PEM fuel cell system or compressed and stored for later use in such a system. A demonstration of the system will be performed in conjunction with a fuel cell system and/or a hydrogen storage apparatus. Hydrogen purity will be measured as well as overall system efficiency. A study should be undertaken to develop a plan to scale up the system to a higher production rate. Key difficulties in production and scale up should be identified and mitigations proposed and examined, when possible. 

PHASE III: Phase III would result in a portable, self-powered, high output hydrogen generation system. A scaled up system could support operational refueling of future hydrogen vehicles, enabling enhanced silent watch and mobility capabilities along with increasing lethality and survivability. Potentially larger systems could be developed for larger facilities and staging areas, further enhancing the capability. Commercially, this system could be used to augment the hydrogen economy infrastructure and lead to clean, potentially remote hydrogen generation and refueling stations. This technology would contribute to energy security and reduce pollution via increased zero emissions vehicles. 


1: Sheng Chu, Wei Li, Yanfa Yan, Thomas Hamann, Ishiang Shih, Dunwei Wang, Zetian Mi, Roadmap on solar water splitting: current status and future prospects, Nano Futures 1, 022001, September 2017.

2:  Faqrul A. Chowdhury, Michel L. Trudeau, Hong Guo, Zetian Mi, A photochemical diode artificial photosynthesis system for unassisted high efficiency overall pure water splitting, Nature Communications 9, 1707, April 2018.

KEYWORDS: Hydrogen, Hydrogen Production, Solar, Water Splitting 

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