Transition metal oxides (TMOs) are promising materials for supercapacitors (SCs) because of their high theoretical capacity. However, their finite active sites and poor electrical conductivity lead to reluctant electrochemical performance. Herein, we report a facile electrochemical activation (ECA) method to boost the electrochemical activity of Ni‐Co oxide nanosheet arrays (NiCoO NSA) for SCs. Specifically, honeycomb‐like NiCoO NSA that was made through a solvothermal method followed by air annealing was activated by simply exerting certain cyclic voltammetry scans (the activated sample is named ac‐NiCoO NSA). We have found this treatment results in dramatic surface structure change, forming numerous sub‐nanostructures (nanoparticles and nano‐leaves) on the NiCoO nanosheets. Rich antisite defects and oxygen vacancies in the NiCoO spinel phase were also created by the ECA treatment. Consequently, the ac‐NiCoO NSA delivered a maximum capacity of 206.5 mAh g−1 (0.5 A g−1), which is about three times of the NiCoO NSA without treatment. A hybrid SC based on the ac‐NiCoO NSA demonstrated excellent energy storage capacity (power density of 17.3 kW kg−1 and energy density of 45.4 Wh kg−1) and outstanding cyclability (>20,000 cycles, 77.4% retention rate). Our method provides a simple strategy for fabricating high performance TMOs for electrical energy storage devices like SCs.
Different sized Pt nanoparticles
supported on carbon nanotubes
were prepared and then applied in selective oxidation of glycerol
in a base-free condition to understand the size effects. It is shown
that the turnover frequency of glycerol increases with Pt particle
size to a maximum at the mean size of 2.5 nm followed by a decline
with a further increase in size, which may be due to strongly adsorbed
intermediates blocking Pt active sites for smaller sized Pt catalyst.
Moreover, compared with dihydroxyacetone, glyceraldehyde and subsequent
glyceric acid (GLYA) are dominating products. In particular, smaller
sized Pt catalyst favors the formation of GLYA, which could be related
to the stronger oxidation. Unexpectedly, the selectivity of C3 products
is insensitive to both Pt particle size and reaction time within 9
h.
Metal–organic frameworks (MOFs), known as porous coordination polymers, have attracted intense interest as electrode materials for supercapacitors (SCs) owing to their advantageous features including high surface area, tunable porous structure, structural diversity, etc. However, the insulating nature of most MOFs has impeded their further electrochemical applications. A common solution for this issue is to transform pristine MOFs into more stable and conductive metal compounds/porous carbon materials through pyrolysis, which however losses the inherent merits of MOFs. To find a consummate solution, recently a surge of research devoted to improving the electrical conductivity of pristine MOFs for SCs has been carried out. In this review, the most related research work on pristine MOF‐based materials is reviewed and three effective strategies (chemical structure design of conductive MOFs (c‐MOFs), composite design, and binder‐free structure design) which can significantly increase their conductivity and consequently the electrochemical performance in SCs are proposed. The conductivity enhancement mechanism in each approach is well analyzed. The representative research works on using pristine MOFs for SCs are also critically discussed. It is hoped that the new insights can provide guidance for developing high‐performance electrode materials based on pristine MOFs with high conductivity for SCs in the future.
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