NSF-DFG Echem:Elucidating Surface Structure Contribution of Facets, Steps and Kinks in Electrocatalysis of the Oxygen Evolution and Reduction Reactions

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Electrolysis as a key technology to generate green hydrogen uses the excess of renewable energies while fuel cells are crucial for the efficient conversion of stored chemical into electrical energy. Both technologies require oxygen electrocatalysis as counter reaction, namely the oxygen evolution reaction (OER) in electrolysis and the oxygen reduction reaction (ORR) in fuel cells. Unfortunately, their sluggish kinetics cause high overpotentials of the oxygen half-cells limiting the efficiencies and thus requiring the development of improved electrocatalysts.The overarching goal of this project is to create higher performing, more durable non-precious metal catalysts for the OER. Our central hypothesis is that controlling the surface termination and facet exposure of a catalyst can alter the coordination and bonding environments at the surface thus changing the reactant-catalyst interaction and the electrocatalytic OER/ORR activity. Therefore, the connection between synthesis, surface morphology and electrochemical performance is crucial for the design of a catalyst. The proposed work program targets following goals: (i) Synthesis of electrocatalysts with defined local active sites, (ii) Synthesis of electrocatalysts with defined morphology (pores, facets, steps and kinks) and (iii) Structural characterization and determination of the activity of the developed electrocatalysts. The rock salt structure enables synthesis of shape-controlled NiO particles with (111) or (100) surfaces allowing elucidation of their role in oxygen electrocatalysis. Further, these materials offer ideal platforms to systematically study the effects of tailoring the surfaces with steps and kinks and making multi-metal oxides with elements of similar ionic radii (e.g. Co, Mn, Fe). The Richards group will develop nanoscale faceted mixed metal oxide electrocatalysts including Fe, Mn and Co by cation exchange starting from NiO. Furthermore, a series of multi-metal oxides (e.g. nickel ferrite) will be synthesized based on a modified aerogel method developed for NiO(111). The Wark group will employ electrochemical deposition as well as (microwave-assisted) hydro- and solvothermal routes to form highly porous (with ordered mesoporosity), faceted mixed metal oxides with similar stoichiometry. The electrocatalysts will be structurally characterized using e.g. advanced operando techniques like AFM or environmental X-ray photoelectron spectroscopy (E-XPS). Evaluation of the ORR and OER under operation conditions will be addressed by tests in GDE half-cells and in MEAs in test benches in the Harms group.