Recently, a research team led by Dr. Lu Zhiyi, a researcher at the Hydrogen and Energy Storage Materials Technology Laboratory of the Institute of Materials Technology and Engineering, Chinese Academy of Sciences in Ningbo, has made new progress in the direct electrolysis of seawater for hydrogen production by introducing a dense hydration layer between two solids, giving the cathode used for in-situ seawater electrolysis hydrophobic properties. This achievement was recently published in the "Nano Express" journal.
Effective Seawater Electrolysis
Developing renewable energy electrolysis technology for hydrogen production is one of the key pathways to achieving the goals of "carbon peak and carbon neutrality."
The global development of marine renewable energy is rapid, with the total installed capacity of offshore wind power expected to reach about 100GW by 2025.
Seawater electrolysis, with a low cost of $2-3 per kilogram of hydrogen, offers a promising solution for the utilization of deep-sea renewable energy. In this regard, in-situ direct seawater electrolysis, which eliminates the need for loading, storage, and transportation by not requiring treatment of seawater, is poised to become one of the most effective seawater electrolysis technologies.
However, compared to gray and blue hydrogen produced as byproducts, the cost of electrolyzing seawater to produce green hydrogen remains high. Gray hydrogen is produced from carbon-based energy sources, emitting carbon dioxide during production; blue hydrogen is derived from gray hydrogen, with the carbon dioxide generated during its production being captured and stored using capture technology; green hydrogen is produced through water electrolysis and renewable energy but is limited by renewable energy and water electrolysis technology.
Effectively utilizing the abundant mineral resources in seawater for green hydrogen production while extracting minerals is expected to significantly reduce the cost of green hydrogen production.
Dense Water Molecule Layer
Nevertheless, there is an unavoidable issue in in-situ seawater hydrogen production.
The large amount of magnesium and calcium ions in seawater not only hinder the extraction of hydroxides but also attach to the cathode surface, impeding electrode contact with reactants, leading to electrode damage and increased energy consumption.
Based on this, the electrochemical environmental catalysis team at the Institute of Materials Technology and Engineering in Ningbo, inspired by previous research on alkaline seawater electrolysis, proposed a hydrophobic strategy. By increasing the surface energy of the electrode material to enhance water adsorption on the electrode surface, a more complete water layer (hydrogen bond network) makes it difficult for magnesium ions to cross to the electrode surface for nucleation and growth, giving the electrode surface hydrophobic properties and effectively alleviating scaling issues.
Dr. Lu Zhiyi, the corresponding author of the paper, explained to "Chinese Science Bulletin" that to weaken the interaction between solid products of seawater electrolysis and the electrode surface, they proposed introducing a dense layer composed of water molecules between two solids to generate specific additional repulsive forces specific to water, thereby achieving hydrophobic properties of the cathode for in-situ seawater electrolysis.
Accelerating the Industrial Process of Seawater Magnesium Extraction for Hydrogen Production
Researchers chose nickel mesh, widely used in industrial applications, as the research subject because nickel metal exhibits excellent hydrogen evolution activity in neutral and alkaline environments. In experiments, by adjusting electrodeposition and subsequent heat treatment parameters, they were able to synthesize nickel-copper alloy electrodes with high surface disorder and high surface energy.
Direct Sea Water Electrolysis Cathode Schematic. Image provided by the research team.
Experimental results indicate that a nickel-copper alloy electrode with high surface energy can stably operate for over 1000 hours in a solution with magnesium-calcium ion concentration 10 times that of seawater, continuously producing small-grain, high-purity magnesium hydroxide exceeding 99%.
Researchers have confirmed through theoretical simulations and experimental validation that the adsorbed water on the electrode surface effectively hinders magnesium ions from nucleating and growing on the electrode surface.
Furthermore, based on the economic advantages of hydrogen and magnesium hydroxide dual products, this technological approach can enhance economic benefits by approximately 10 times compared to traditional seawater electrolysis for hydrogen production.
Lu Zhiyi stated that this research addresses significant issues in direct seawater electrolysis for hydrogen production, proposing a new route for direct seawater electrolysis hydrogen production that will significantly simplify existing seawater electrolysis technologies. Considering the high economic benefits brought by the dual products, this route will greatly accelerate the industrial-scale commercialization process of seawater magnesium extraction for hydrogen production.
Related paper information: https://doi.org/10.1021/acs.nanolett.4c01484
