Enabling Hydrogen Gas Production from Seawater Using Electrolytes Contained by Reverse Osmosis Membranes

The production of hydrogen gas is a significant component of global energy consumption and carbon emissions, accounting for 1% of global energy use. More than half this hydrogen is used to make fertilizer, and nearly all hydrogen gas is currently produced from fossil fuels. However, hydrogen gas can be produced from water using renewable electricity sources in a process called electrolysis, which splits water molecules into hydrogen and oxygen gases. The relative abundance of affordable wind energy, solar arrays, and seawater at offshore and coastal locations make them ideal sites for hydrogen gas production by this approach. However, the cost of hydrogen production by using a water electrolyzer must be reduced to make it economically competitive with other methods. Also, the production of toxic chemical byproducts from the chloride salts in seawater must be avoided. To meet these demands, the membranes typically used in electrolyzer systems will be replaced with the relatively inexpensive, salt-rejecting membranes commonly used for reverse osmosis (RO) seawater desalination. The use of RO membranes represents a fundamentally new approach to water electrolysis for hydrogen gas production. The RO membranes can be used to contain the seawater salts so that they do not react to form chemicals that are toxic or that could damage the membranes. This use of these ion-size selective RO membranes could have a large impact on methods for hydrogen gas production as well as other electrochemical separation technologies. This project, therefore, addresses a critical societal need for hydrogen gas production using a sustainable process. An educational platform will also be developed to engage the public in a conversation about energy use. The platform is expected to enhance general understanding of how our daily energy use can be modified to reduce fossil fuel use and carbon dioxide emissions.

This research project will develop a new seawater electrolysis approach to reduce the cost of water electrolyzers. The objective will be accomplished by eliminating the use of costly proton exchange membranes and containing the anolyte to avoid chlorine gas production from chloride salts in seawater. To accomplish these goals, the proton exchange membrane will be replaced with a reverse osmosis (RO) membrane that can exclude ions while allowing proton ion transport between the electrodes, balancing charge between the electrolytes. The anolyte is contained by the RO membrane so that only oxygen gas evolution occurs in that compartment, and hydrogen gas evolution from seawater occurs in the catholyte, enabled by proton transport through the RO membrane. This approach, therefore, uses RO membranes for simultaneous salt ion retention and charged ion (proton) transport. Gas transport is avoided between the chambers and the RO membrane enables direct pressurized production of hydrogen. Water replacement in the anolyte can be accomplished by balancing osmotic pressure to achieve forward osmosis or by intermittent pressure adjustments between the two chambers. Preliminary data support this claim that some RO membranes have sufficiently low internal resistance to support high current densities (>100 Amps per square centimeter). Methods are proposed to reduce crossover of salts and improve membrane performance through nanoscale engineering of the membrane surface and supporting structures. This RO membrane approach could make hydrogen gas production from water electrolysis using renewable energy cost-competitive with steam reforming using fossil fuels, which would have a great societal benefit. Another project goal with broad applications is to enhance energy literacy of the public by exploring energy use based in terms of a daily energy unit, D, which ranges from 1 (food for one person) to 106 (energy normalized per person in the USA per day). Materials will be developed for an undergraduate seminar class, and a website and videos will be developed aimed at assisting STEM students in understanding energy used based on D and the carbon dioxide emissions unit, C (daily carbon dioxide emissions from one person).

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.