Recently, binary transition metal oxides, phosphates, and sulfides have attracted wide attention due to their potential applications in supercapacitors. The emergence of metal-organic frameworks (MOFs) provides new opportunities for the synthesis and investigation of porous binary metal compounds with similar microstructures. Herein, binary metal oxide (NiCo-O) tubular structures are derived from NiCo-MOF-74 via a facile annealing process, and then phosphate (NiCo-P) and sulfide (NiCo-S) structures are obtained from NiCo-O by heat treatment and solvothermal process, respectively. Among the three derivatives, NiCo-S with nanosheet structures has the highest specific capacitance of 930.4 F g −1 at a current density of 1 A g −1 and an excellent rate capability with a retention of ≈80% at 10 A g −1 . The long-term cycling performance of NiCo-S is superior with 70.5% retention after 10 000 cycles. The hybrid supercapacitor device with NiCo-S and activated carbon as positive and negative electrodes delivers a high energy density of 22.6 W h kg −1 at a power density of 800 W kg −1 . The excellent performance of NiCo-S can be attributed to its nanosheet structure, which increases the specific surface area and electroactive sites.
Jie Hu,Lei Li,Hao Li,Ying Zhai,Fushun Tang,Zhe Zhang,Banglin Chen
The mixed bimetal metal–organic framework Ni0.37Co0.63-MOF-74 has been constructed by the solvothermal method for NO adsorption. The results showed that bimetal Ni0.37Co0.63-MOF-74 takes up NO with a capacity of up to 174.3 cc g−1 under ambient conditions, which is 16.3% higher than that of the best single metal Co-MOF-74. The IAST adsorption selectivity for a NO/CO2 binary mixture can reach a maximum of 710 at low adsorption partial pressure, while the regeneration performance can be retained even after five cyclic adsorption–desorption experiments. Its separation performance was further confirmed by breakthrough experiments, indicating this new bimetal Ni0.37Co0.63-MOF-74 as one of the best materials for NO adsorption and separation in flue gas.
Yujuan Cao,Ning Wu,Fan Yang,Meng Yang,Tingting Zhang,Hao Guo,Wu Yang
Due to the insufficient performance, it is still a challenge to combine conventionally synthesized metal-organic framework (MOF-74) with other materials to fabricate composite electrodes for high-performance supercapacitors . Herein, we synthesized a series of NiCo-MOF-74 composite materials with different amounts of polypyrrole nanotubes (T-PPy) denoted as NiCo-MOF-74/T-PPy-m (m = 2.5, 5, 10, 15 and 20) through in situ growth of the bimetallic MOF around the PPy nanotubes by a simple solvothermal method . By comparison, the NiCo-MOF-74(1)/T-PPy-10 composite, with a Ni/Co molar ratio of 1:1 obtained in the presence of 10 mg of T-PPy, possessed the highest specific capacitance of 849 C·g −1 at 1 A·g −1 and excellent cyclic stability with a capacitance retention rate of 90.0% after 10,000 cycles as well as good rate performance. Moreover, the assembled asymmetric supercapacitor respectively using NiCo-MOF-74(1)/T-PPy-10 and active carbon as positive electrode and negative electrode achieved a superior energy density of 58.4 Wh kg −1 at the power density of 747.6 W kg −1 and high cyclic lifespan (91.4% capacitance retention after 10,000 cycles). The mechanism of capacitance increase was studied in detail, influences of metal molar ratios, morphology and addition amounts of PPy on electrochemical performances of the formed composition materials were systematically discussed, and it was found that the interpenetrating network structure assembled by “string of candied haws”-like T-PPy-interweaved NiCo-MOF-74(1) polyhedrons possessed the best capacitive performance for enhanced conductivity of the resulted composite, improved dispersity of the bimetallic MOF and more exposed active sites. And the interwoven structure alleviated the stress change-induced structure or phase variation caused by repeated volumetric swelling and shrinking during charge/discharge cycle and enhanced the rate capability and cycling stability.
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