Influence of Supporting Electrolyte on Hydroxide Exchange Membrane Water Electrolysis Performance: Anolyte

Aleksandr Kiessling,Andreas Gerstmayr,Nemanja Danilovic,Alexey Serov,Barr Zulevi,Xiong Peng,Samuel Mckinney,Julie C Fornaciari,Adam Z Weber,Grace Anderson,Michael R Gerhardt,Yu Seung Kim

doi:10.1149/1945-7111/ac1dcd

Abstract

Hydroxide-exchange-membrane water electrolysis (HEMWE) is an emerging hydrogen-production pathway that combines many advantages of incumbent alkaline water electrolysis (AWE) and proton-exchange-membrane water electrolysis (PEMWE). Advancement in HEMWE has been accelerated with the development of stable and conductive hydroxide exchange membranes (HEMs) and a more comprehensive understanding of alkaline gas-evolving kinetics. However, performance and durability without supporting electrolytes (SELs) remain inferior to PEMWE and AWE and little is known about the role and impact of the SELs. This study investigates the effects of SELs used as anolyte solutions in HEMWEs including cation-type, anion-type, SEL conductivity and pH, presence of carbonates and increased cation/OH− ratios on cell voltage and stability. We report our findings that (i) cell potential and high-frequency resistance did not correlate with anolyte SEL conductivity, (ii) cation-type influences cell voltage at low current densities (<50 mA cm−2) as predicted by half-cell measurements, (iii) increased cation/OH− ratio causes increased overpotentials, and (iv) carbonates are exchanged in the HEM but removed via self-purging at high current density. Overall, this study concludes that concentrated KOH is still the best SEL.

Highlights

To cite this article: Aleksandr Kiessling et al 2021 J
de-ionized water (DIW) operation.—Ideally, hydroxide-exchange-membrane water electrolysis (HEMWE) would operate on pure water
Operating with DIW solely utilizes catalyst sites covered with the hydroxide exchange membrane (HEM) ionomer, in our case AS-4

Summary

Introduction

To cite this article: Aleksandr Kiessling et al 2021 J. The performance of the 1 M KOH HEMWE is nearly equivalent to PEMWE operation on NafionTM 117 (N117), achieving roughly 2 A cm−2 below 2V.27 after adequate circulation of DIW as an anolyte, a polarization curve was obtained, there is a ∼150 mV penalty at 250 mA cm−2 and high current densities are not sustainable as with SELs. The inset in Fig. 2 shows that the kinetics of the reaction are severely affected, with a 150 mV overpotential increase, which can be attributed to a combination of reaction mechanisms (based on the slope change) and electrochemically active surface area changes.

Results

Conclusion