The question of whether
the metal chalcogenides (phosphides) that
have been acknowledged to be efficient materials for bifunctional
electrocatalysts really perform as the active species or just “pre-catalysts”
has been debated. Herein, a series of operando measurements, including
in situ X-ray absorption spectroscopy, liquid-phase transmission electron
microscopy, and in situ Raman spectroscopy, were conducted to unravel
in real time the structural and chemical stability of P-substituted
CoSe2 electrocatalysts under both hydrogen and oxygen evolution
reactions (HER and OER, respectively) in an alkaline electrolyte.
It can be conclusively revealed that, in an alkaline electrolyte,
the P-substituted CoSe2 electrocatalyst was acting as the
“pre-catalyst” rather than the real reactive species.
The introduction of phosphorus is speculated to generate more vacancies
or defects around Co cations in the initial CoSe2 and considerably
facilitates the structural transformation into the “real reactive
species”, such as metallic cobalt (for HER) and cobalt oxyhydroxide
(for OER).
In this study, ordered mesoporous carbons (OMCs) with different pore structures, namely 2D hexagonal CMK-3 and 3D cubic CMK-8 prepared by the nanocasting method using mesoporous silicas SBA-15 and KIT-6 as hard templates, respectively, in their pure forms are used as anode materials in lithium ion batteries (LIBs) to evaluate the role of mesoporous structures in their electrochemical performances. The results demonstrate that the CMK-8 electrode exhibits a higher reversible capacity and better cycling stability and rate capability, as compared to the CMK-3 electrode, due to its unique 3D cubic mesostructure. The initial capacities of 1884 and 964 mA h g À1 are obtained for the CMK-8 and CMK-3 electrodes, respectively. The CMK-8 electrode exhibits a higher capacity value (around 37.4% higher) than the CMK-3 electrode at the 100 th cycle. The enhanced electrochemical performance of CMK-8 is mainly attributable to its unique 3D channel networks, which are beneficial for efficient Li storage and volume change. Although CMK-3 is the most investigated OMCs used in LIBs, herein we demonstrate that CMK-8 is a better carbon matrix for the fabrication of the electrode materials composed of mesoporous carbons.
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