In this work, a two-step calcination method to fabricate Co 3 O 4 @CoP hollow nanoparticles embedded in N, S-codoped reduced graphene oxide substrates is reported. The electrocatalyst is synthesized through a hydrothermal-calcination method of adding graphene oxide using ZIF-67 as a template followed by an annealing process in the presence of NaH 2 PO 4 • H 2 O. In the designed electrocatalyst, the formed hollow nanoparticles had an average diameter of 100 nm. The synthesized electrocatalyst displays a hydrogen evolution reaction overpotential of 54 mV at 10 mA cm −2 current density in 0.5 mol L −1 H 2 SO 4 solution at room temperature, comparable to Pt/C catalysts. The oxygen evolution reaction overpotential in 1 mol L −1 KOH electrolyte is 288 mV, which is almost equivalent to that of IrO 2 . Stated thus, the as-prepared composite catalysts are promising candidates for bifunctional catalysts for water splitting technology, relieving the limitation of commercial catalysts caused by their single catalytic performance.
The SiO x /C composite, as a form of silicon-based materials, has been considered as an attractive alternative anode for next-generation lithium-ion batteries. The porous SiO 0.71 C 1.95 N 0.47 anode material exhibiting robust Si−O skeletons wrapped by carbon layers is successfully prepared and delivers an initial capacity of over 1700 mAh g −1 with an initial coulombic efficiency of 69.4% and favorable cycle life. Both Si (2p) X-ray photoelectron spectroscopy (XPS) and 29 Si nuclear magnetic resonance (NMR) demonstrate the existence of SiO 4 and SiO 3 C units as main lithium storage sites in the original state. The XPS curve moved toward the direction of the binding energy decreasing with NMR spectra shifting to a high field after the first lithiation process. The massive capacity loss during the first discharge and charge cycle results from the formation of irreversible Li silicate (Li 2 SiO 4 ). The fluctuation of the charge and discharge capacity, including a persistent decline during the first 30 cycles and a continuous elevation in the following 400 cycles, could be attributed to the participated degree of reversible Li silicate (Li 2 SiO 3 and Li 2 Si 2 O 5 ) in the delithiation process. The Si−O skeletons are gradually corroded and ultimately destroyed in the final 400 cycles, leading to the sharp drop of the cycling performance of the half-cell.
Si/C materials have attracted much attention as anode materials for lithium-ion batteries. Here, nitrogen-doped silica carbon composites with a carbon-coated structure were synthesized using poly(1-vinylimidazole) in the presence of octavinyl-silsesquioxane followed by annealing and magnesium thermal reduction processes of the polymer precursor (PPVIm). Benefiting from the moderate Si–O–C bonds, the prepared NSiOC possesses a high first discharge capacity of 1862.3 mAh·g–1 at 0.2 A·g–1 and an initial Coulombic efficiency of 70.0% at 30 °C. When the temperature rises to 60 °C, the first discharge and charge specific capacities of the synthesized anode material at 0.2 A·g–1 increase to 2103.0 and 1528.7 mAh·g–1 with an ultralong lifespan of more than 1000 cycles. Moreover, the results show that the degradation of performance during the initial phase of cycles can be ascribed to the formation of an SEI layer and insufficient electrolyte penetration. The battery maintains a steady state (nearly 600 consecutive cycles) for a long time afterward as the activation of the anode material increases, attributed to the low expansion coefficient originating from the porous structure of the carbon capping layer and silicon oxide. In addition, the electrochemical attenuation process of the electrode material with a unique inorganic silica skeleton and exceptional electrochemical performance was also investigated for the assistance of future design in high-performance electrode materials.
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