Salinity-gradient based osmotic energy conversion enhanced by waste heat generated from proton exchange membrane electrolyzer

Abstract

Proton exchange membrane electrolyzer is an essential device to generate hydrogen from water. However, a huge amount of low-grade waste thermal energy is generated during hydrogen production process of proton exchange membrane electrolyzer. Furthermore, osmotic energy conversion is capable of harnessing salinity-gradient energy in natural water sources to produce electricity. Nevertheless, salinity-gradient osmotic energy conversion suffers from an issue of relatively low power density. The current work reports a hybrid system that integrates a proton exchange membrane electrolyzer with an osmotic energy conversion module, harnessing the waste heat produced by the electrolyzer to improve both osmotic power density and overall systematic energy efficiency. A one-dimensional finite difference model is firstly developed to analyze performance of proton exchange membrane electrolyzer. Then, a three-branch bipolar plate of proton exchange membrane electrolyzer is designed to enhance heat transfer between water and its electrodes for waste heat utilization. When the waste heat generated during water electrolysis is used to raise up freshwater pumped into osmotic energy conversion device from 20 °C to 40.3 ℃, 43.9 ℃, and 47.5 ℃, the corresponding osmotic power density using graphene oxide membrane is elevated from 6.32 W/m² to 9.82 W/m², 10.67 W/m², and 11.54 W/m² by 55.4 %, 68.8 %, and 82.6 %, respectively. The current work introduces a promising strategy for enhancing salinity-gradient osmotic power generation performance by effectively harnessing waste thermal energy produced within proton exchange membrane electrolyzer during hydrogen production, which shows great potential for industrial renewable energy applications.