Fe plays a critical, but not yet understood, role in enhancing the activity of the Ni-based oxygen evolution reaction (OER) electrocatalysts. We report electrochemical, in situ electrical, photoelectron spectroscopy, and X-ray diffraction measurements on Ni1–xFex(OH)2/Ni1–xFexOOH thin films to investigate the changes in electronic properties, OER activity, and structure as a result of Fe inclusion. We developed a simple method for purification of KOH electrolyte that uses precipitated bulk Ni(OH)2 to absorb Fe impurities. Cyclic voltammetry on rigorously Fe-free Ni(OH)2/NiOOH reveals new Ni redox features and no significant OER current until >400 mV overpotential, different from previous reports which were likely affected by Fe impurities. We show through controlled crystallization that β-NiOOH is less active for OER than the disordered γ-NiOOH starting material and that previous reports of increased activity for β-NiOOH are due to incorporation of Fe-impurities during the crystallization process. Through...

Nickel–Iron Oxyhydroxide Oxygen-Evolution Electrocatalysts: The Role of Intentional and Incidental Iron Incorporation

Discrete particle simulation of particulate systems: A review of major applications and findings

Chem. Pharm. Bull.(オピニオン)

Mixed Ni–Fe oxides are attractive anode catalysts for efficient water splitting in solar fuels reactors. Because of conflicting past reports, the catalytically active metal redox state of the catalyst has remained under debate. Here, we report an in operando quantitative deconvolution of the charge injected into the nanostructured Ni–Fe oxyhydroxide OER catalysts or into reaction product molecules. To achieve this, we explore the oxygen evolution reaction dynamics and the individual faradaic charge efficiencies using operando differential electrochemical mass spectrometry (DEMS). We further use X-ray absorption spectroscopy (XAS) under OER conditions at the Ni and Fe K-edges of the electrocatalysts to evaluate oxidation states and local atomic structure motifs. DEMS and XAS data consistently reveal that up to 75% of the Ni centers increase their oxidation state from +2 to +3, while up to 25% arrive in the +4 state for the NiOOH catalyst under OER catalysis. The Fe centers consistently remain in the +3 sta...

Oxygen Evolution Reaction Dynamics, Faradaic Charge Efficiency, and the Active Metal Redox States of Ni–Fe Oxide Water Splitting Electrocatalysts

All-solid-state batteries (ASSBs) have attracted enormous attention as one of the critical future technologies for safe and high energy batteries. With the emergence of several highly conductive solid electrolytes in recent years, the bottleneck is no longer Li-ion diffusion within the electrolyte. Instead, many ASSBs are limited by their low Coulombic efficiency, poor power performance, and short cycling life due to the high resistance at the interfaces within ASSBs. Because of the diverse chemical/physical/mechanical properties of various solid components in ASSBs as well as the nature of solid-solid contact, many types of interfaces are present in ASSBs. These include loose physical contact, grain boundaries, and chemical and electrochemical reactions to name a few. All of these contribute to increasing resistance at the interface. Here, we present the distinctive features of the typical interfaces and interphases in ASSBs and summarize the recent work on identifying, probing, understanding, and engineering them. We highlight the complicated, but important, characteristics of interphases, namely the composition, distribution, and electronic and ionic properties of the cathode-electrolyte and electrolyte-anode interfaces; understanding these properties is the key to designing a stable interface. In addition, conformal coatings to prevent side reactions and their selection criteria are reviewed. We emphasize the significant role of the mechanical behavior of the interfaces as well as the mechanical properties of all ASSB components, especially when the soft Li metal anode is used under constant stack pressure. Finally, we provide full-scale (energy, spatial, and temporal) characterization methods to explore, diagnose, and understand the dynamic and buried interfaces and interphases. Thorough and in-depth understanding on the complex interfaces and interphases is essential to make a practical high-energy ASSB.

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Interfaces and Interphases in All-Solid-State Batteries with Inorganic Solid Electrolytes.

Fine particle coating by a novel rotating fluidized bed coater

Agglomerates of nanoparticles were fluidized in a rotating fluidized bed (RFB) system at different rotating speeds corresponding to 10, 20, 30 and 40 times the gravity force (9.8 m/s2). The powders, fumed silica Aerosil® R974, Aerosil® R972 and Aeroxide® TiO2 P25, with a primary particle size of 12, 16 and 21 nm, respectively, form micron sized nanoagglomerates having a very low bulk density of around 30 kg/m3 for the fumed silicas, and a somewhat higher bulk density of about 90 kg/m3 for Aeroxide® TiO2 P25. Their fluidization behaviors are described by the fluidized bed expansion, pressure drop and minimum fluidization velocity (Umf). It was found that the fumed silica agglomerates expanded considerably while the TiO2 agglomerates showed very little bed expansion. The minimum fluidization velocities for Aerosil® R974 and R972 ranged from 0.02 to 0.07 m/s and from 0.13 to 0.20 m/s for Aeroxide® TiO2 P25; Umf increased at higher rotating speeds for all powders. At gas velocities above Umf, the fluidized bed pressure drop of fumed silica agglomerates was higher than theoretically estimated by mathematical models found in the literature. Thus, it is believed that for these light particles additional tangential momentum effects may increase the bed pressure drop and a revised model is proposed. In addition, the agglomerate size and external void fraction of the bed are predicted by using a fractal analysis coupled with a modified Richardson-Zaki equation for data obtained with Aerosil® R972. © 2006 American Institute of Chemical Engineers AIChE J, 2006

Hideya Nakamura

Papers

Fine particle coating by a novel rotating fluidized bed coater

Fluidization of nanoagglomerates in a rotating fluidized bed

Scale-up of high shear mixer-granulator based on discrete element analysis

Fundamental particle fluidization behavior and handling of nano-particles in a rotating fluidized bed

Numerical modeling of particle fluidization behavior in a rotating fluidized bed