The effect of water density on alkaline water electrolysis performance in superheated, subcritical, and supercritical phases

Abstract

Abstract

Abstract This work explores the potential of using high temperature and pressure water for alkaline water electrolysis systems. Specifically, we investigated the relationship of electrolyte conductivity vs alkaline salt concentration and water density at temperatures above 100°C using electrochemical impedance spectroscopy, linear sweep voltammetry, and tafel analysis. LSV results and redox kinetic investigation confirmed poorer electrolysis performance (higher solution resistance) at 380°C as compared to 350°C. This performance decrease was for all solvent densities with the drop-off larger for the lower density tests. A final set of experiments demonstrated better electrolyte performance at 200°C than 350°C. The production of H2 at elevated temperatures reduces the Nernst potential and may have benefits for other overpotentials such as electrode activity, bubble formation, and iR associated losses. High pressure production would mean less energy requirement for H2 pressurisation which for a normal electrolysis cell system equates to roughly 11% of the total energy contained in the product gas. We show that the solution density has a large effect on the observed ionic conductivity as well as the kinetics, and that subcritical and super heated steam outperform the supercritical phase for the densities investigated.