Strategy for Improving Oxygen Evolution Performance of Noble Metal Catalysts for Alkaline Water Electrolysis

Abstract

Among water splitting techniques, electrochemical water splitting is enhanced using efficient catalysts to complete hydrogen evolution (HER) and oxygen evolution (OER) reactions. However, when it comes to commercial level processing to create water electrolyzers including AEM and PEM electrolyzers, these catalysts mostly in powder state require to be immobilized onto a current collector using a suitable polymeric binder. This coating process is very important to maintain the catalyst strength, reducing the interfacial resistance between catalyst and current collector etc. However, peeling off of the catalysts and thereby catalyst aggregation is often confronted during long term operation causing large decrease in electrolyzer performance. In this scenario, self-supported catalysts which are directly grown or developed on conductive substrates or forming free-standing films are identified as a solution to overcome this problem while progressing to realize efficient water electrolyzers. Some major advantages of the self-supported catalysts include; direct use of catalysts as anode/cathode electrodes, excellent synergistic effect between the catalyst and substrate, reduced peeling off catalysts and more importantly greater charge transfer between catalyst layer and current collector. In the present work, we developed self-supporting multi metal catalysts over nickel foam which can be used as electrode materials for integrating water electrolyzers capable of high performance and durability in alkaline conditions. Oxygen evolution reaction (OER) studies under half cell conditions in 1 M KOH using the developed self-supported catalysts involving Fe and Ru over nickel foam displayed an over potential of 185 mV at 10 mA cm-2, while 111 mV was for observed during hydrogen evolution reaction (HER). The presentation will include water splitting performance data using the processed catalysts under alkaline conditions and also the detailed electrochemical and spectroscopic results during and post OER/HER. Further, the synergistic interactions among the metal species, creation of active species/sites and changes in electron charge transfer leading to the excellent activity and stability will also be discussed. Fig 1. HER and OER CV profiles in half cell conditions using the self-supported catalysts References Zhang et al, Homogeneously dispersed multimetal oxygen-evolving catalysts, Science 2016, 352,333-337 Kwon, H. Han, S. Choi, K. Park, S. Jo, U. Paik, T. Song, Current Status of Self-Supported Catalysts for Robust and Efficient Water Splitting for Commercial Electrolyzer, ChemCatChem 2019, 11, 5898–59 Miyanishi, T. Yamaguchi, Highly conductive mechanically robust high M wpolyfluorene anion exchange membrane for alkaline fuel cell and water electrolysis application, Polym. Chem. 2020, DOI: 10.1039/D0PY00334DA. Miller, K. Bouzek, J. Hnat, S. Loos, C. I. Bernacker, T. Weißgarber, L. Rontzsch, J. Meier-Haack, Green hydrogen from anion exchange membrane water electrolysis: a review of recent developments in critical materials and operating conditions, Sustainable Energy Fuels, 2020,4, 2114-2133 Acknowledgements: This presentation is based on results obtained from a project commissioned by the New Energy and Industrial Technology Development Organization (NEDO), Japan Figure 1