Facile Synthesis of Microsphere-like Co0.85Se Structures on Nickel Foam for a Highly Efficient Hydrogen Evolution Reaction.

Microsphere-shaped cobalt selenide (Co0.85Se) structures were efficiently synthesized via a two-step hydrothermal process. Initially, cobalt hydroxide fluoride (Co(OH)F) microcrystals were prepared using a hydrothermal method. Subsequently, Co0.85Se microsphere-like structures were obtained through selenization. Compared to Co(OH)F, the microsphere-like Co0.85Se structure exhibited outstanding catalytic activity for the hydrogen evolution reaction (HER) in a 1.0 M KOH solution. Electrocatalytic experiments demonstrated an exceptional HER performance by the Co0.85Se microspheres, characterized by a low overpotential of 148 mV and a Tafel slope of 55.7 mV dec-1. Furthermore, the Co0.85Se electrocatalyst displayed remarkable long-term stability, maintaining its activity for over 24 h. This remarkable performance is attributed to the excellent electrical conductivity of selenides and the highly electroactive sites present in the Co0.85Se structure compared to Co(OH)F, emphasizing its promise for advanced electrocatalytic applications.

Rationally Designed Bimetallic Co-Ni Sulfide Microspheres as High-Performance Battery-Type Electrode for Hybrid Supercapacitors.

Rational designing of electrode materials is of great interest for improving the performance of battery-type supercapacitors. The bimetallic NiCo2S4 (NCS) and CoNi2S4 (CNS) electrode materials have received much attention for supercapacitors due to their rich electrochemical characteristics. However, the comparative electrochemical performances of NCS and CNS electrodes were never studied for supercapacitor application. In this work, microsphere-like bimetallic NCS and CNS structures were synthesized via a facile one-step hydrothermal method by controlling the molar ratio of Ni and Co precursors. The physico-chemical results confirmed that microsphere-like structures with cubic spinel-type NCS and CNS materials were successfully fabricated by this method. When tested as the supercapacitor electrode materials, both NCS and CNS electrodes exhibited battery-type behavior in a three-electrode configuration with outstanding electrochemical performances such as specific capacity, rate performance and cycle stability. Impressively, the CNS electrode delivered a high specific capacity of 430.1 C g-1 at 1 A g-1, which is higher than 345.9 C g-1 of the NCS electrode. Furthermore, the NCS and CNS electrodes showed a decent cycling stability with 75.70 and 84.70% capacity retention after 10,000 cycles. Benefiting from the electrochemical advantage of CNS microspheres, we fabricated a hybrid supercapacitor (HSC) device based on CNS microspheres (positive electrode) and activated carbon (AC, negative electrode), which is named as CNS//AC. The assembled CNS//AC HSC device showed a large energy density of 41.98 Wh kg-1 at a power density of 800.04 W kg-1 and displayed a remarkable cycling stability with a capacity retention of 91.79% after 15,000 cycles. These excellent electrochemical performances demonstrate that both bimetallic NCS and CNS microspheres may provide potential electrode materials for high performance battery-type supercapacitors.

Extended vapor-liquid-solid growth of silicon carbide nanowires.

We developed an alloy catalytic method to explain extended vapor-liquid-solid (VLS) growth of silicon carbide nanowires (SiC NWs) by a simple thermal evaporation of silicon and activated carbon mixture using lanthanum nickel (LaNi5) alloy as catalyst in a chemical vapor deposition process. The LaNi5 alloy binary phase diagram and the phase relationships in the La-Ni-Si ternary system were play a key role to determine the growth parameters in this VLS mechanism. Different reaction temperatures (1300, 1350 and 1400 degrees C) were applied to prove the established growth process by experimentally. Scanning electron microscopy and transmission electron microscopy studies show that the crystalline quality of the SiC NWs increases with the temperature at which they have been synthesized. La-Ni alloyed catalyst particles observed on the top of the SiC NWs confirms that the growth process follows this extended VLS mechanism. The X-ray diffraction and confocal Raman spectroscopy analyses demonstrate that the crystalline structure of the SiC NWs was zinc blende 3C-SiC. Optical property of the SiC NWs was investigated by photoluminescence technique at room temperature. Such a new alloy catalytic method may be extended to synthesis other one-dimensional nanostructures.