An electrode material with high performance as a key part is highly desirable for supercapacitors. Herein, NiO/Ni metal−organic framework (Ni-MOF) composites were successfully synthesized via the first preparation of NiO nanoflakes and then in situ formation of Ni-MOF over NiO. Particularly, the conversion degree of Ni-MOF from NiO was conveniently tuned by altering the amount of terephthalic acid added in the hydrothermal process. NiO/Ni-MOF-25 with 25% of the conversion ratio of NiO to Ni-MOF possessed superior electrochemical performance with a specific capacity of 163.4 mA h g −1 (1176.6 F g −1 ) at a current density of 1 A g −1 , higher than Ni-MOF (79.3 mA h g −1 ) and NiO (79.8 mA h g −1 ). The boosted electrochemical performance of NiO/Ni-MOF-25 was attributed to its core-shell configuration, relatively high specific surface area, and enhanced electrical conductivity. The assembled NiO/Ni-MOF-25//activated carbon asymmetrical supercapacitor achieved a maximum energy density of 31.3 W h kg −1 at a power density of 374.2 W kg −1 and decent cyclic durability with 88.7% of incipient capacitance after 2000 cycles. Moreover, two asymmetric devices in series constructed 3 months ago could efficiently illuminate a green light-emitting diode (LED) lamp. This work offers a facile way to rationally design and synthesize composite electrode materials for powerful supercapacitors.
Integrating electrolytic hydrogen production from water with thermodynamically more favorable aqueous organic oxidation reactions is highly desired, because it can enhance the energy conversion efficiency in relation to traditional water electrolysis, and produce value‐added chemicals instead of oxygen at the anode. In this Minireview, we introduce some key considerations for anodic auxiliary electrosynthesis and outline three types of electrocatalytic organic reactions including biomass derivative, alcohol and amine oxidation reactions, which can boost cathodic hydrogen generation. Furthermore, frequently used noble‐metal‐free electrocatalysts are classified into nickel‐based, cobalt‐based, other transition‐metal‐based and bimetallic electrocatalysts. The preparation methods of these catalysts and their performance towards electrochemical oxidation reactions are also discussed in detail. We specifically highlight the importance of redox active sites on the surface of the electrocatalysts, which act as electron mediators to promote oxidation reactions. Finally, the current challenges and future developments in this emerging field are also discussed.
Indoor environmental quality directly affects the life
quality
and health of human beings, and therefore, it is highly vital to eliminate
the volatile organic compounds especially formaldehyde (HCHO), which
is regarded as one of the most common harmful pollutants in indoor
air. Hydroxyapatite (HAP)-supported Pt (Pt/HAP) catalysts with a low
content of Pt (0.2 wt %) obtained via hydrothermal and chemical reduction
processes could effectively remove gaseous HCHO from the indoor environment
at room temperature. The influence of modifier in the preparation
on the catalyst activity was investigated. The HAP and HAP modified
by sodium citrate and hexamethylenetetramine-supported 0.2 wt % Pt
could completely decompose HCHO into CO2 and water, while
HAP modified by sodium dodecyl-sulfate-supported Pt removed HCHO primarily
via adsorption. The HAP modified by the sodium citrate catalyst exhibited
superior catalytic performance of HCHO compared to the HAP and HAP
modified by hexamethylenetetramine and sodium dodecyl-sulfate-supported
Pt catalysts, which was mainly because of its higher surface Ca/P
ratio providing more Lewis acidic sites (Ca2+) for co-operational
capture of HCHO molecules and a larger amount of active oxygen species.
Our results indicate that an optimized combination of functional supports
and low-content noble metal nanoparticles could be a route to fabricate
effective room-temperature catalysts for potential application in
indoor air purification.
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