Compositional Tuning of Nickel Sulfoselenides for Use As Bifunctional Oxygen Electrocatalysts in Aqueous Electrochemical Energy Storage

Abstract

Increasing grid-scale deployment of intermittent energy sources necessitates the development of advanced energy storage technologies. Electrochemical energy storage technologies using alkaline electrolytes, especially secondary Zn-air batteries, are uniquely suitable, using inexpensive, non-flammable aqueous electrolytes and making extensive use of earth abundant elements (C, Zn, Mn, etc.). Unfortunately, development of Zn-air batteries is currently limited by electrochemical challenges at both the Zn anode and the air cathode, with the limitations at the air cathode being particularly complex. An ideal cathode would use a bifunctional oxygen electrocatalyst (BOE) capable of efficiently and sequentially catalyzing both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). Precious metal-containing materials (Pt, RuO2, etc.) are currently the most efficient BOEs, but their high cost makes them unideal for commercialization. Transition metal chalcogenides (e.g., NiS2, Ni3Se2) have previously been used as BOEs, but are still relatively underdeveloped alternatives to precious metal electrocatalysts.In this presentation, we report the electrocatalytic performance of a series of compositionally-tunable nickel sulfoselenides (Ni3(S,Se)2, NiSSe) for use as BOEs in Zn-air batteries in place of existing precious metal electrocatalysts. These materials have previously shown promise as OER electrocatalysts, but their ORR and BOE performance has not yet been explored. We demonstrate the synthesis of a range of NiSSe materials with variable S/Se composition, and subsequently use multiple characterization techniques, including cyclic voltammetry, X-ray diffraction spectroscopy (XRD), X-ray photoelectron spectroscopy (XPS), and others, to explore the performance of these materials as BOE electrocatalysts. The nanoscale NiSSe materials show homogeneous mixing of S/Se over a wide compositional range (10-90% Se), and electrocatalytic testing shows that this S/Se composition has an observable impact on the OER/ORR performance. Roughly 50/50 mixtures showed the best OER performance, while pure Ni3Se2 showed the best ORR performance. As a result, optimum BOE performance of the mixed NiSSe materials was observed near a composition of Ni3S0.4Se1.6; the (electro)chemical stability of this mixed NiSSe was subsequently evaluated using chronoamperometry and XPS. Compared with the binary Ni3S2 and Ni3Se2 compounds, NiSSe was found to be reasonably stable after testing and is therefore a promising candidate for use in air cathodes. As a demonstration, we then tested this NiSSe electrocatalyst in a Zn-air battery and found good agreement with the results from previous the Zn-free experiments. Together, our results show that nickel sulfoselenides are a promising class of tunable electrocatalysts with applications in oxygen electrocatalysis for energy storage.This work was supported by the U.S. Department of Energy, Office of Electricity, and the Laboratory Directed Research and Development program at Sandia National Laboratories, a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA-0003525. This work was performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science. Dr. Imre Gyuk, Director of Energy Storage Research, Office of Electricity is thanked for his financial support. The views expressed herein do not necessarily represent the views of the U.S. Department of Energy or the United States Government.