A Spray-Drying Approach for Highly Active Amorphous NiFe2O4 for AEM Water Electrolysis

Water electrolysis, a key process for hydrogen production, holds immense potential in mitigating carbon dioxide emissions when powered by renewable energy sources, thereby contributing to a sustainable and clean energy future. Commercially available and widely recognized technologies for water electrolysis include the proton exchange membrane water electrolysis (PEMWE) and the traditional alkaline water electrolysis (AWE). In order to use the benefits of both systems, the anion exchange membrane water electrolysis (AEMWE) method is proposed, enabling the utilization of non-noble catalyst materials and achieving high current densities at low cell voltages [1]. In the present work, the influence of a spray-drying approach compared to a co-precipitation method on the bimetallic non-noble NiFe 2 O 4 catalysts on the oxygen evolution reaction (OER) activity is systematically investigated. State of the art catalyst for OER is Iridium oxide and so far, the best non-noble catalyst has not been found yet. A widely used non-noble catalyst is NiFe- layered double hydroxide but it suffers from low electric conductivity [2]. Another promising catalyst is the NiFe 2 O 4 , which also provides low OER overvoltage. However, amorphous oxides are said to have a higher activity than crystalline [3]. Furthermore, the use of a spray drying approach is highly reproducible, with which the crystallinity can be set very easily [4, 5]. The experimental study of the catalysts was carried out in a commercial Baltic-Fuel Cell with a geometrical area of 25 cm² at 60 °C in 1 M KOH electrolyte and a contact pressure of 1.25 MPa. The electrodes were prepared by directly spray coating the desired amount of catalyst onto the anode and cathode substrates. A Bekipor® 2NI 18-0.25 nickel felt was used as the substrate for the anode, while AvCarb MGL370 carbon paper was employed for the cathode. As cathode catalyst Pt/C from Tanaka (TEC10E40E, 37.2 % Pt) was used, while a loading of 0.5 mg cm -2 Pt was targeted during the spraying procedure. On the anode, the NiFe 2 O 4 loading was set to 2 mg cm -2 . Both electrodes were separated by a Sustainion® X37-50 Grade T membrane. For determination of relevant catalyst activity data chronopotentiometry (CP) and electrochemical impedance spectroscopy (EIS) were carried out. Figure 1 reveals that the spray-dried NiFe 2 O 4 (amorphous, red curve) has a superior performance compared to the precipitated NiFe 2 O 4 (green curve) , which is partly crystalline. With the spray-dried catalyst, a reduction in overvoltage of approx. 60 mV at 1 A cm -2 can be achieved. With a cell voltage of less than 1.7 V at a current density of 1 A cm -2 , our recently developed catalyst ranks among the most outstandingly described in the literature to date [6]. These findings can contribute to a further development of amorphous catalysts with even higher activity. [1] Cossar, E., Murphy, F. and Baranova, E.A. (2022), Nickel-based anodes in anion exchange membrane water electrolysis: a review. J Chem Technol Biotechnol, 97: 1611-1624. [2] Jeon, S.S., Lim, J. Kang, P.W., Lee, J.W., Kang, G., Lee, H. (2021), Design Principles of NiFe-Layered Double Hydroxide Anode Catalysts for Anion Exchange Membrane Water Electrolyzers. ACS Appl Mater Interfaces,13 (31): 37179-37186. [3] Shi, G., Arata, C., Tryk, D., Tano, T., Yamaguchi, M., Iiyama, A., Uchia, M., Iida, K., Watanabe, S., Kakinuma, K. (2023), NiFe Alloy Integrated with Amorphous/Crystalline NiFe Oxide as an Electrocatalyst for Alkaline Hydrogen and Oxygen Evolution Reactions. ACS Omega, 8: 13068−13077. [4] Kreitz, B., Arias, A. M., Martin, J., Weber, A. P., Turek, T. (2020), Spray-Dried Ni Catalysts with Tailored Properties for CO 2 Methanation, Catalysts, 10 (12): 1410. [5] Arias, A. M., Weber, A. P. (2019), Aerosol synthesis of porous SiO 2 -cobalt-catalyst with tailored pores and tunable metal particle size for Fischer-Tropsch synthesis (FTS), J Aerosol Sci, 131: 1-12. [6] Du, N., Roy, C. Peach, R., Turnbull, M., Thiele, S. and Bock, C. (2022), Anion-Exchange Membrane Water Electrolyzers. Chem Rev, 122: 11830-11895. Figure 1