Hydrogen Production from Seawater electrolysis using Highly Selective Earth-Abundant Catalysts and Membraneless Electrolyzer

Qatar is committed to lowering its carbon footprint and making a smooth transition to a knowledge-based and post-carbon economy. Diversifying energy resources, maximizing utilization of the abundant solar energy, and investing in advanced technologies for carbon-free renewable energy production is the key to achieve this goal. Electric power from renewable solar energy presents opportunities for the country to enhance its future energy mix and reduce carbon emissions. Yet, industry and transport will still require combustible fuels for many purposes. Such needs could be met with hydrogen (H2), which itself can be produced by water electrolysis using renewable electricity. H2 is of central importance in key industrial processes such as oil refining, and is widely used as a feedstock in the production of various chemicals such as ammonia and methanol. In addition, its compelling properties as an energy carrier make H2 a promising candidate for future energy storage and transportation. Water electrolysis offers an attractive approach for the renewable production of carbon-free H2 because it needs only water and electricity as inputs. H2 production from water electrolysis is emission-free as long as renewable energy is used. It is also a promising approach for storing intermittent renewable energy such as solar or wind power. Alkaline and polymer electrolyte membrane (PEM) electrolyzers are the two main technologies for splitting water into H2 and oxygen (O2). Both technologies are sensitive to water impurities and thus require purified water, which is usually obtained by purification of fresh water resources. However, fresh water is very limited in Qatar and the costly energy-intensive seawater desalination plants provide the main water supply for domestic and industrial uses. Therefore, using fresh water is not a viable option for water electrolysis in Qatar and many countries worldwide that face increasing fresh water shortage. Thus, if seawater or reject brine from desalination plants can be used directly as water source, it would provide a nearly unlimited water supply for H2 production. Seawater is a natural electrolyte solution due to its high ionic conductivity. Brine would be more desirable because it has higher ionic conductivity since it is a concentrated product of seawater. However, several major challenges must be overcome in order for H2 production from direct seawater or brine splitting to become economical. First, the presence of chloride ions in seawater and brine introduces an undesired side reaction, the chlorine evolution reaction (CER), which competes with the desired O2 evolution reaction (OER) during the water splitting process. Second, the use of seawater or brine as the electrolyte creates challenges for electrolyzer operation due to incompatibility with conventional membranes resulting from biofouling and/or pH gradients that would rapidly develop across the membrane from Na+ transport. Another challenge in seawater electrolysis is the presence of magnesium (Mg) and calcium (Ca) ions, which can form solid precipitates on electrode surfaces and cell dividers due to the alkaline nature at the electrolyzer cathode. This normally requires removal of Mg and Ca from the water prior to the electrolysis process but this is costly and produces solid waste. A solution to eliminate solids precipitation without the need to remove these ions is to operate the electrolyzer at or near neutral pH. However, the kinetics for the H2 evolution and O2 evolution reactions are sluggish at neutral pH due to the requirement of an additional water dissociation step. Current state-of-the art electrolyzers and their main components were designed and optimized for operation in acidic and alkaline environments, making them highly unsuitable for operation in pH-neutral seawater. Membraneless electrolyzers offer an ideal platform for redesigning low-cost electrolyzers that can operate with high efficiency and durability in seawater without concern for degradation and fouling of a membrane. To the best of our knowledge, there is no commercially available electrolyzer that can split seawater or brine into H2 and O2. We propose to overcome the challenges associated with electrolysis of seawater or brine (thereafter, saline water) by exploiting novel encapsulated electrocatalysts and innovative membrane-free electrolyzer designs tailored for pH-neutral saline water environment. Our proposal will be based on three pillars: 1) Development of an active and stable electrocatalyst for H2 evolution from saline water in pH-neutral environment, 2) Development of an active, selective, and stable electrocatalyst for O2 evolution from saline water, and 3) Design of a membrane-free electrolyzer device for efficient saline water splitting at near neutral pH. We will use the following approaches throughout the project: 1) Perform computational screening for efficient H2 and O2 evolution electrocatalysts using machine learning and density functional theory calculations. 2) Fabricate and characterize multicomponent nanostructured electrocatalysts for selective H2 and O2 evolutions from saline water. 3) Develop ultrathin nanomembrane coatings that will enable selective O2 evolution at the anode by suppressing the undesired chlorine evolution reaction. 4) Characterize and optimize performance of electrocatalysts in three-electrode cell at different operating conditions and buffers. 5) Develop a low-cost, membrane-free electrolyzer that is optimized for efficient and durable saline water electrolysis. 6) Conduct techno-economic and life cycle analysis of the electrolyzer system to establish the foundation for construction of a pilot-scale plant.