Electrolyte Supply Methods in Anion Exchange Membrane Water Electrolysis Cells with Custom Inkjet Printed Catalyst Layers
Creators: Eitzen, Jasper
Publisher: name: University of Alberta Library
Year: 2023

<p>This work was concerned with the construction and testing of anion exchange membrane water electrolysis (AEMWE) cells to study the effect of electrolyte feed method. Each cell used a catalyst-coated membrane (CCM) fabricated in-house by inkjet printing catalyst layers onto Aemion+ membranes using a Fujifilm Dimatix DMP-2850 printer. Inkjet printing allowed for precise control in the deposition of catalyst layer materials, but necessitated that printable inks containing catalyst nanopowder (platinum supported on carbon and iridium oxide) and ionomer (Aemion+ AP2-HNN5-00-X) be formulated. To develop ink formulae, a procedure was followed that began by selecting a base of propylene glycol and isopropanol with a dynamic viscosity and surface tension close to that required for printing. The ionomer solution was then added, and the mixture was re-characterized to ensure it still had the required rheology. Any necessary adjustments were made and the catalyst powder was finally added. This process resulted in inks that were successfully printed without the need to produce multiple complete inks, reducing the waste of expensive catalyst and ionomer.</p>

<p>Initial in-situ AEMWE cell tests were run to ensure that cell performance was repeatable. Five cells were tested, achieving this goal as the last four all performed similarly. Cell construction was altered between some of these cells, most notably the type of Aemion+ membrane was changed, i.e., increasing the thickness from 50 to 75 µm and altering the reinforcement type, the cathode porous transport layer (PTL) was changed from carbon to nickel, and the bipolar plate material was changed from titanium to nickel 400 alloy. These changes slightly improved cell performance by reducing the ohmic losses caused by resistance within the cells. Cells were tested by feeding 1 M potassium hydroxide (KOH) and compared to literature. The performance of the cells was similar to state of the art CCM cells using Aemion+, achieving a current density of 900 mA/cm2 at 2 V.<br>
Once good, repeatable cell performance was achieved, the same cell construction was used for the study on electrolyte feed method.</p>

<p>Four cells were used to study the effect of feeding aqueous 1 M potassium hydroxide solution to both electrodes, just the cathode, and just the anode was done for the first time in AEMWE cells. A reference electrode was also connected to the cell membrane using a strip of membrane passed out the side of the cell. Challenges were encountered with the experimental setup that resulted in some inconsistent measurements from the reference electrode, caused by cell operation. Despite this, it did allow for separate anode and cathode overpotentials to be measured. The cells tested in this work performed similarly with two-electrode and anode-only feed, resulting in 900 mA/cm2 at 2 V, whereas cathode-only feed achieve the lower 550 mA/cm2 at 2 V. Six hour constant-current stability tests also resulted in increased degradation for cathode-only feed. The change was due to poor anode performance, as the separate electrode potentials obtained using the reference electrode showed an increase in anode overpotential in this feed configuration. The lack of electrolyte in the anode catalyst layer possibly resulted in increased ionic resistance as the electrolyte normally supports this, or a loss of reactant hydroxide that would normally be supplied by the electrolyte.</p>