(Invited, Digital Presentation) La-Sr-Co Oxide Catalysts for Oxygen Evolution Reaction in Anion Exchange Membrane Water Electrolyzers: The Role of Electrode Fabrication on Performance and Durability

The low temperature water electrolysis technology is essential to allow the production of “green” hydrogen at an affordable cost. Recently, successful development and commercialization of anion exchange membranes (AEMs) with improved performance and durability has accelerated progress in low-temperature water electrolyzers (LTWEs) with AEM acting as a solid polymer electrolyte.1 Although still at an R&D stage, AEM-LTWEs are attracting a lot of interest as a promising alternative to liquid-alkaline and proton exchange membrane (PEM) devices thanks to the promise of operating with pure water feed and using inexpensive platinum group metal-free (PGM-free) electrocatalysts.2 Among different catalysts for oxygen evolution reaction (OER), La-Co perovskite oxides have been extensively investigated in liquid alkaline electrolytes, showing promising OER activity and stability.3–6 A series of La-Sr-Co oxides were recently developed by a joint research effort of Los Alamos National Laboratory and Pajarito Powder LLC, showing promising performance in an AEM-LTWE.7 In this work, we investigated the application of a LaxSr1-xCoO3-δ oxide at the AEM-LTWE anode. As first step, we prepared and tested a series of membrane electrode assemblies (MEA) using different commercial AEMs and ionomers, as well as standard commercial PGM catalysts (PtRu/C on the cathode and IrO2 on the anode). This first set of experiments served to establish a performance baseline and to validate the MEA fabrication method and testing procedure. For testing the LaxSr1-xCoO3-δ PGM-free OER catalyst, we fabricated a series of three electrodes using the same procedure but varying the ink formulation. We demonstrated how the anode catalyst ink composition is improving the AEM-LTWE performance and durability when using a PGM-free catalyst. In particular, we investigated the electrolyzer operation with pure water and with 0.1 M KOH and 1% K2CO3 aqueous electrolyte solutions feed. The electrolyzer performance was much less sensitive to the electrode composition when operated with a supporting electrolyte than when operated on pure water. In the latter case, achieving an optimum interface between the AEM, ionomer, and catalyst particles is essential to ensure good OH- ionic conductivity within the electrode. On the other hand, when a supporting electrolyte solution is used, the abundance of OH- ions within the electrode volume enables a faster ionic OH- transport, making the electrolyzer operation less sensitive to electrode optimization parameters. References H. A. Miller et al., Sustain. Energy Fuels, 4, 2114–2133 (2020). G. A. Lindquist et al., ACS Appl. Mater. Interfaces (2021). C. E. Beall, E. Fabbri, and T. J. Schmidt, ACS Catal., 11, 3094–3114 (2021). J. Suntivich, K. J. May, H. A. Gasteiger, J. B. Goodenough, and Y. Shao-horn, Science (80-. )., 334, 2010–2012 (2011) http://www.sciencemag.org/cgi/doi/10.1126/science.1212858. J. Suntivich et al., Nat. Chem., 3, 546–550 (2011) http://www.nature.com/doifinder/10.1038/nchem.1069. J. Kim, X. Chen, P. C. Shih, and H. Yang, ACS Sustain. Chem. Eng., 5, 10910–10917 (2017). H. T. Chung, 2020 DOE Annu. Merit Rev. - Proj. ID p185 (2020).