Characterization methods for electrochemically active materials used in alkaline water electrolysis and lithium-ion batteries

Materials used in electrochemical reactions can be designed to increase the rate of a chemical reaction occurring in an electrochemical system but can suffer from inefficiencies (e.g., bubble accumulation, charge transfer resistance, poor durability) and require improvement for widespread use of clean energy technologies. Many researchers are investigating low-cost alternatives to address concerns such as durability and efficiency. An improved understanding of the underlying processes of these electrochemically active materials is essential to address these concerns while designing more efficient and durable materials for electrochemical processes. Characterization of these interfaces and an improved understanding of the transformations taking place thereupon can assist in guiding the development of more robust and cost-effective materials. Nickel is incorporated into electrocatalysts that are used for a variety of electrocatalytic reactions due to the low-cost and natural abundance of nickel. For alkaline water electrolysis, nickel-based (Ni-based) catalysts are conventionally used but the long-term stability of these catalysts is not well understood. A freeze-drying workflow was developed along with an accelerated stop-go aging procedure, based on potential cycling techniques, to characterize these Ni-based catalysts in their hydrated state. This workflow enabled the observation of a gel-like state with inclusions of nanocrystalline domains that were composed of Ni(OH)2/NiOOH. This gel-like material had a higher degree of hydration than predicted from other measurements such as hydrous oxide materials, which have been reported to have thicknesses related to the charge passes (i.e., electrochemically active surface area). The observation of the gel-like layer could account for some of the variability between the techniques used to assess the electrochemically active surface area. Further, the evolution of materials between the electrochemically active phases (Ni(OH)2/NiOOH) and the electrolyte can be modified with coatings that seek to improve the material's stability. The work pursued herein included the addition of an alumina coating to nickel-based electrocatalysts that enhanced their durability to prolonged cycling of the applied potential. In addition to water electrolysis, Ni-based materials are also used as electrochemically active materials in lithium-ion battery cathodes. Atomic-to-nanoscale microscopy-based analyses of these cathode materials is challenging as they are often prepared from microscale diameter particles. A focused ion beam (FIB) milling procedure was developed to enable a higher throughput workflow (~5× improvement) compared to conventional FIB lift-out procedures. This FIB workflow was used to study commercially available lithium nickel cobalt aluminum oxide and irregularly shaped lithium manganese nickel oxide cathode microparticles but can be readily extended to the study of many other types of microscale materials.