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

氢气生产是全球能源消耗和碳排放的重要组成部分，占全球能源使用量的1%。超过一半的氢气被用来制造肥料，目前几乎所有的氢气都是从化石燃料中生产出来的。然而，可以使用可再生能源从水中生产氢气，这一过程称为电解法，将水分子分解为氢气和氧气。近海和沿海地区相对丰富的负担得起的风能、太阳能电池板和海水使它们成为通过这种方法生产氢气的理想地点。然而，使用水电解槽生产氢气的成本必须降低，才能使其在经济上与其他方法相比具有竞争力。此外，必须避免从海水中的氯盐中产生有毒的化学副产品。为了满足这些需求，通常用于电解槽系统的膜将被相对便宜的、通常用于反渗透(RO)海水淡化的抗盐膜所取代。反渗透膜的使用代表了一种用水电解生产氢气的全新方法。反渗透膜可以用来容纳海水盐，这样它们就不会反应形成有毒或可能损害膜的化学物质。这些离子尺寸选择性反渗透膜的使用可能会对氢气生产方法以及其他电化学分离技术产生重大影响。因此，该项目解决了使用可持续工艺生产氢气的关键社会需求。还将开发一个教育平台，让公众参与关于能源使用的对话。该平台有望增强对如何改变我们的日常能源使用以减少化石燃料使用和二氧化碳排放的总体了解。这项研究项目将开发一种新的海水电解方法，以降低电解水器的成本。这一目标将通过取消使用昂贵的质子交换膜和含有阳极液来实现，以避免海水中的氯盐产生氯气。为了实现这些目标，质子交换膜将被反渗透(RO)膜取代，该膜可以排除离子，同时允许质子离子在电极之间传输，平衡电解液之间的电荷。阳极液包含在反渗透膜中，因此在该隔室中只有氧气析出，而在质子通过反渗透膜的传输下，从海水中析出氢气在阴极液中发生。因此，这种方法使用反渗透膜来同时保留盐离子和传输带电离子(质子)。避免了气室之间的气体传输，反渗透膜可以直接加压生产氢气。阳极液中的水替换可以通过平衡渗透压力来实现正向渗透，或者通过两个腔室之间的间歇压力调整来完成。初步数据支持这一说法，即一些反渗透膜具有足够低的内阻，足以支持高电流密度(每平方厘米100安培)。提出了通过膜表面和支撑结构的纳米工程来减少盐的渗透，提高膜性能的方法。这种反渗透膜法可以使可再生能源电解水生产氢气的成本与使用化石燃料的水蒸气重整相比具有成本竞争力，具有很大的社会效益。另一个具有广泛应用的项目目标是通过探索以每日能源单位D为基础的能源使用来提高公众的能源素养，D的范围从1(一个人的食物)到106(美国每人每天标准化的能源)。将为本科生研讨会课程开发材料，并将开发一个网站和视频，旨在帮助STEM学生了解基于D和二氧化碳排放单位C(个人每日二氧化碳排放量)所使用的能源。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.