水热碳化制备榴莲壳复合焦及其电化学性能

为研究水热碳化处理对榴莲壳复合改性焦性能的影响,将榴莲壳原料及250℃、10 h制备的水热焦分别与层状氢氧化镁铝(Mg/Al Layered Double Hydroxide,MgAl-LDH)复合,获得榴莲壳与MgAl-LDH复合焦MgAl-LDH@DP和榴莲壳水热焦与MgAl-LDH复合焦MgAl-LDH@HC,分...

Durian shell composite biochar prepared by hydrothermal carbonization and its electrochemical properties

Abstract: Hydrothermal Carbonization (HTC) can widely be used to convert the dry/wet biomass (green and renewable materials) directly into the hydrochar with a rich oxygenated functional group (a high value-added carbonaceous material). There is a promising potential application of hydrochar in energy storage in recent years. Nevertheless, a relatively low capacitance of hydrochar has limited to serve as electrode materials. Recently, Layered Double Hydroxide (LDH) has also been considered as one of the most promising electrode materials, due to the high energy density, dispersed active sites, and cheap raw materials. However, the LDH extension has been confined to a relatively weak electrical conductivity and mechanical stability. Therefore, combing the LDH and hydrochar may be a promising trade-off to develop high-efficient electrode materials. Herein, the hydrochar (HC) was prepared through HTC using durian shell (DP) at 250℃ and 10h. Then magnesium aluminum Layer Double Hydroxides (MgAl-LDH) were decorated on the surface of HC, in order to obtain the MgAl-LDH@HC composite. MgAl-LDH was also decorated on the surface of DP raw materials to explore the effect of HTC process on the performance of the composite. The microstructure of MgAl-LDH@DP and MgAl-LDH@HC were characterized using X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), and scanning electron microscopy (SEM). An electrochemical test was also carried out for the properties of the composite. The results show that the cellulose crystal structure of the durian shell was destroyed after HTC treatment, where the carbon content of HC was 70.29%. The XRD pattern of MgAl-LDH@HC presented the sharp peaks at 11.23°, 22.64°, 33.98°, and 60.11° of 2θ, being assigned to the (003), (006), (012), and (110) planes, respectively, indicating a typical hydrotalcite-like structure. The XRD spectra also illustrated that the MgAl-LDH was successfully decorated on the surface of HC. In MgAl-LDH@DP, there were strong peaks of cellulose crystallinity structure at 22.37° and 34.39°, in spite of the characteristic peaks of LDH in the XRD spectra. There were much stronger active oxygenated functional groups, while much higher dispersion for the LDH nanosheets in the MgAl-LDH@HC, compared with the MgAl-LDH@DP. In MgAl-LDH@HC, a strong polymer characteristic peak at 1622 cm-1 contributed to the activity and hydrophilicity of the composite as electrode materials. The XPS spectra of MgAl-LDH@HC presented the strong C 1s, O 1s peaks at 284.80 and 532.14 eV, while the weak Mg 2p, Al 2p peaks at 50.31 and 74.71 eV, respectively. In the C 1s spectra, three peaks centered at 284.53, 285.73, and 288.18 eV corresponding to the C=C, C=O chemical bonding. In the O 1s spectra, three peaks centered at 531.08, 531.93, and 532.78 eV identifying as Al2O3,-OH and -O-, C=O, respectively. These functional groups significantly increased the hydrophilicity, wettability and activity of composite in the electrode solution. SEM images showed that the MgAl-LDH@DP contained a lot of needle-like structures, whereas, the MgAl-LDH@HC presented irregular lamellar structures with porous surfaces. In MgAl-LDH@HC electrochemical test, the Brunauer-Emmett-Teller (BET) surface area was 62.96m2/g, the average pore diameter was 14.81 nm, and the Barrett-Joyner-Halenda (BJH) cumulative pore volume was 0.24 cm3/g, indicating higher properties than those of MgAl-LDH@DP. It inferred that the structure of MgAl-LDH@HC was more conducive to charge storage and electron transmission. Three electrode systems were constructed, with the composite as working electrode and the KOH solution as electrolyte. They were close to rectangle and triangle in the cyclic voltammetry and galvanostatic charge-discharge curve. Higher capacitive property and rate performance were achieved in the MgAl-LDH@HC, compared with the MgAl-LDH@DP. The slope of impedance curve was much larger for the MgAl-LDH@HC at the low frequency, indicating a relatively smaller ion diffusion resistance. Therefore, the MgAl-LDH@HC can be expected to serve as potential electrode materials for supercapacitors.