Disordering and electronic state of cobalt ions in mechanochemically synthesized LiCoO2
Mechanical activation (MA) combined with heat treatment at moderate temperatures was used to prepare disordered and highly dispersed LiCoO2 starting from the mixtures of various cobalt precursors (CoOOH, Co(OH)2, and Co) and LiOH. X-ray powder diffraction and IR spectroscopy were used to investigate the phase composition and the crystal structure of as-prepared samples, while the electronic state of cobalt ions was characterized by diffuse reflectance electron spectroscopy. MA of the LiOH+CoOOH mixture led to the formation of LT-LiCoO2 with a cubic spinel-related structure. Heat treatment at 600°C of the latter resulted in the formation of HT-LiCoO2 with a hexagonal layered structure similar to ceramic LiCoO2. However, as-prepared HT-LiCoO2 is characterized by Co3+ O6 octahedra less perfect than those of ceramic LiCoO2. All MA-LiCoO2 samples are exclusively described by localized d electrons.
Facile Access to an Active γ-NiOOH Electrocatalyst for Durable Water Oxidation Derived From an Intermetallic Nickel Germanide Precursor
Identifying novel classes of precatalysts for the oxygen evolution reaction (OER by water oxidation) with enhanced catalytic activity and stability is a key strategy to enable chemical energy conversion. The vast chemical space of intermetallic phases offers plenty of opportunities to discover OER electrocatalysts with improved performance. Herein we report intermetallic nickel germanide (NiGe) acting as a superior activity and durable Ni-based electro(pre)catalyst for OER. It is produced from a molecular bis(germylene)-Ni precursor. The ultra-small NiGe nanocrystals deposited on both nickel foam and fluorinated tin oxide (FTO) electrodes showed lower overpotentials and a durability of over three weeks (505 h) in comparison to the state-of-the-art Ni-, Co-, Fe-, and benchmark NiFe-based electrocatalysts under identical alkaline OER conditions. In contrast to other Ni-based intermetallic precatalysts under alkaline OER conditions, an unexpected electroconversion of NiGe into γ-NiIIIOOH with intercalated OH?/CO32? transpired that served as a highly active structure as shown by various ex situ methods and quasi in situ Raman spectroscopy.
Menezes, Prashanth W.,Yao, Shenglai,Beltrán-Suito, Rodrigo,Hausmann, J. Niklas,Menezes, Pramod V.,Driess, Matthias