RESUMO
Bimetallic oxides have significant attraction as supercapacitor electrode materials due to their highly reversible redox processes, which are commonly associated with their surface chemistry and morphological features. Here, we report the synthesis, characterization, and electrochemical evaluation of bimetallic oxides with different molar compositions of Co and V (Co0.6V0.4, Co0.64V0.36, Co0.68V0.32, and Co0.7V0.3 denoted as S1, S2, S3, and S4 samples, respectively). The materials were synthesized by a modified solvothermal method using glycerol as a stabilizing agent, characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, scanning electron microscopy-energy-dispersive X-ray spectroscopy, X-ray fluorescence spectroscopy, N2 adsorption isotherms, cyclic voltammetry, and galvanostatic charged/discharged in a three-electrode cell. The role of the CoV oxide compositions on the pseudocapacitive properties was studied through the analysis of the energy storage mechanism following the power law and Dunn's methodology to obtain the b values. An important finding of this work is that CoV oxides exhibited electrochemical characteristics of a pseudocapacitive electrode material even though the charge storage occurs in bulk. This behavior is consistent with the pseudocapacitance generated by redox processes, showing b values of 0.67, 0.53, 0.75, and 0.84, with a capacitive current contribution of 74, 74, 63, and 70% analyzed at a scan rate of 1 mV s-1, for S4, S3, S2, and S1 samples, respectively. Co0.7V0.3 (S4) oxide presented the highest specific capacitance of 299 F g-1 at 0.5 A g-1 with a Coulombic efficiency of 93% tested at 4 A g-1. The better electrochemical performance of this sample was attributed to the synergistic effect of the Co and V atoms since a minimum amount of V in the structure may distort the crystal lattice and improve the electrolyte diffusion, in addition to the formation of several oxidation states due to reduction of V5+, including V3+ and V4+ as well as to the formation of the metastable V4O9.
RESUMO
The confinement of small amounts of benzene in InOF-1 (Bz@InOF-1) shows a contradictory behavior in the capture of CO2 and SO2. While the capture of CO2 is increased 1.6 times, compared to the pristine material, the capture of SO2 shows a considerable decrease. To elucidate these behaviors, the interactions of CO2 and SO2 with Bz@InOF-1 were studied by DFT periodical calculations postulating a plausible explanation: (a) in the case of benzene and CO2, these molecules do not compete for the preferential adsorption sites within InOF-1, providing a cooperative CO2 capture enhancement and (b) benzene and SO2 strongly compete for these preferential adsorption sites inside the MOF material, reducing the total SO2 capture.
