Thermally-Integrated Water Desalination—Electrolysis System for Clean Hydrogen Generation

Description

The Hong Kong government is gradually pursuing decarbonization in support of its Climate Action Plan 2050 by replacing fossil fuels with low- or zero-carbon energy sources. Given this, hydrogen (H2), regarded as a zero-carbon-emitting energy carrier, is one of the most promising clean and sustainable energy sources with a minimum carbon footprint that can support Hong Kong in reaching its carbon neutrality goal. One common method for producing hydrogen is water electrolysis; however, this process requires enormous amounts of ultrapure water and expensive proton-exchange- membranes (PEM) for electrolyzers, making it economically and environmentally challenging. It is estimated that approximately 9 L of ultrapure water (UPW) is needed to produce 1 kg of hydrogen. Due to the growing scarcity of freshwater and high costs, widespread applications of water electrolysis for H2generation are still in their infancy. In view of the inherent limitations of water electrolysis systems, this project focuses on developing a highly efficient, thermally integrated desalination—electrolysis system for hydrogen (H2) generation. The proposed integrated system will use a state-of-the-art membrane distillation (MD) system integrated with waste-heat recovery as an energy- efficient alternative desalination technology to produce UPW, which will be utilized as H2feedstock in an anion exchange membrane electrolyzer (AEMEL) containing an ether- free, highly-conductive hydroxide exchange membrane for high-efficiency H2 production. The overarching goal of this project is to reduce the cost of green H2production through electrolysis by significantly reducing the capital and operational costs of the thermally integrated MD-AEMEL technology. In this project, first, we will overcome the intrinsic limitations associated with MD and electrolyzers by developing stable and high-performing membranes. Then, we will subsequently design and operate a system model for their practical and optimized thermal integration for green H2generation. Specifically, for uninterrupted long-term MD operations, we will fabricate a superhydrophobic membrane with hierarchical polydimethylsiloxane (PDMS) spherical microstructures. The engineered membrane with the ability to produce high quality permeate and anti-scaling and anti-wetting properties will be employed in the MD system for UPW production for the electrolysis in the next step. Secondly, a highly conductive ether-free, polyphenylene-based AEM with superior anion transfer efficiency will be synthesized, and subsequently, the membrane electrode assembly with Ag as a catalyst will be modularized for high-efficiency water electrolysis for H2generation. With the optimized MD and AEMEL system, next, we will aim to design and build a waste heat recovery system to capture and utilize excess waste heat generated from the AEMEL in the MD system for UPW production. Lasty, the thermal performance of the integrated system will be validated experimentally using a prototype MD-AEMEL system. This thermal integration of MD and AEMEL for waste heat recovery will significantly alleviate MD’s operational cost for producing UPW and the associated cost of cooling down the electrolyzers. A prototype MD-electrolyzer integrated system for practical demonstration will be designed and engineered, and the technical performance and economic feasibility of the proposed system will be determined.