Oxygen Evolution Platinum Group Metal-Free Catalyst Loading Optimization for Anion Exchange Membrane Water Electrolysis with Low Concentration Electrolyte
Authors: Rossini Matteo , Koyuturk Burak , Khataee Amirreza , Lindbergh Göran , Cornell Ann 
Published: December 2024

Anion exchange membrane water electrolysis (AEMWE) is receiving tremendous attention by many researchers in the field of the electrochemistry as it shows the potential to make the electrolytic hydrogen production more cost-effective. This technological advance has been made possible by the progress in the polymer chemistry of anion exchange membranes (AEMs) [1]. These materials can conduct hydroxide anions without suffering from the chemical degradation induced by the hydroxide itself. Like alkaline water electrolysis (AWE), AEMWE can exploit low cost and abundant materials, for example nickel and its alloys, for plates and porous transport layers and as catalysts. Furthermore, catalyst coated membranes (CCMs) can be manufactured as in proton exchange membrane water electrolysis and higher current densities can be achieved compared to AWE [2].

However, nickel-based catalysts suffer from low mass activity as many other platinum-group metals-free (PGM-free) catalysts [3]. This downside could be mitigated by employing thick and high loading catalyst layers. However, as the catalyst is placed further from the membrane, the ohmic loss induced by the thickness of the electrode increases and reduces the utilization of the catalyst [4]. As the cost of PGM-free catalysts is orders of magnitude lower than traditional platinum and iridium catalysts, the fabrication of high loading catalyst seems a viable solution. Nevertheless, as the catalyst layer thickness continues to increase, the utilization of the catalyst decreases further and eventually it limits the performance improvement [3]. This applies especially to water or low concentration electrolyte fed systems, as concentrated KOH solution has been shown to greatly reduce catalyst layer ionic resistance [5]. Furthermore, mass transport issue can also play a significant role limiting performance as thick electrode have higher diffusion resistance.

To explore the fabrication and electrochemical behavior of high loading anode electrodes, catalyst coated membranes (CCMs) were manufactured via decal transfer method [6]. RaneyTM Nickel mixed with Co3O4and RaneyTM Nickel served as the anode and cathode catalyst and the anode catalyst layer thickness was adjusted to control the loading. Low concentration electrolyte (0.1 KOH) was fed to the anode and the cathode was left dry. As expected, the cell voltage decreased increasing the catalyst loading. Notably, the performance was improved even when the catalyst loading increased from 6 to 12 mg/cm2.

This work aims to study the performance limitations of high loading catalyst layer with PGM-free catalysts. It was found that even high catalyst loadings (12 mg/cm2) can deliver a sensible improvement of overall performance. We explain this with our systematic approach in this study.

References

[1] Henkensmeier, Dirk, Malikah Najibah, Corinna Harms, Jan Žitka, Jaromír Hnát, and Karel Bouzek. “Overview: State-of-the Art Commercial Membranes for Anion Exchange Membrane Water Electrolysis.” Journal of Electrochemical Energy Conversion and Storage 18, no. 2 (May 1, 2021): 024001.

[2] Chen, Binyu, Peter Mardle, and Steven Holdcroft. “Probing the Effect of Ionomer Swelling on the Stability of Anion Exchange Membrane Water Electrolyzers.” Journal of Power Sources 550 (December 2022): 232134.

[3] Damjanović, Ana Marija, Burak Koyutürk, Yan-Sheng Li, Davide Menga, Christian Eickes, Hany A. El-Sayed, Hubert A. Gasteiger, Tim-Patrick Fellinger, and Michele Piana. “Loading Impact of a PGM-Free Catalyst on the Mass Activity in Proton Exchange Membrane Fuel Cells.” Journal of The Electrochemical Society 168, no. 11 (November 1, 2021): 114518.

[4] Bernt, Maximilian, Armin Siebel, and Hubert A. Gasteiger. “Analysis of Voltage Losses in PEM Water Electrolyzers with Low Platinum Group Metal Loadings.” Journal of The Electrochemical Society 165, no. 5 (2018): F305–14.

[5] Liu, Jiangjin, Zhenye Kang, Dongguo Li, Magnolia Pak, Shaun M. Alia, Cy Fujimoto, Guido Bender, Yu Seung Kim, and Adam Z. Weber. “Elucidating the Role of Hydroxide Electrolyte on Anion-Exchange-Membrane Water Electrolyzer Performance.” Journal of The Electrochemical Society 168, no. 5 (May 1, 2021): 054522.

[6] Rossini, Matteo, Burak Koyuturk, Björn Eriksson, Amirreza Khataee, Göran Lindbergh, and Ann Cornell. “Rational Design of Membrane Electrode Assembly for Anion Exchange Water Electrolysis.” ECS Meeting Abstracts MA2023-01, no. 36 (August 28, 2023): 2059–2059.

Figure
1
Polarization curve of CCMs with different anode catalyst loadings. RaneyTM Nickel and CO3O4 are used in the anode. The cathode contains catalyst RaneyTM Nickel and Super PTM Carbon. The measurements are conducted at 60 °C feeding 0.1 M KOH to anode.

Figure 1