Elisadiki Joyce, Gabookolwe Mavis K, Onisuru Oluwatayo R, Meijboom Reinout, Muiva Cosmas, King'ondu Cecil K
Department of Chemical and Forensic Sciences, Botswana International University of Science and Technology Private Bag 16 Palapye Botswana
Department of Physics, University of Dodoma P. O. Box 338 Dodoma Tanzania.
RSC Adv. 2022 Apr 27;12(20):12631-12646. doi: 10.1039/d2ra01322c. eCollection 2022 Apr 22.
Two-electrode electrochemical tests provide a close performance approximation to that of an actual supercapacitor device. This study presents mesoporous carbon materials successfully derived from bark (Mexican fan palm) and their electrical performance in a 2-electrode supercapacitor device. The triad relationship among carbon materials "processing, properties, and performance" was comprehensively investigated. X-ray diffraction reveal that amorphousness increases with activating KOH ratio and decreases with both activation time and temperature. Raman spectroscopy shows an increase in structural defects and degree of graphitization with an increase in KOH ratio, temperature and time while transmission electron microscopy shows conversion of aggregated particles to materials with interconnected porosity and subsequent destruction of porosity with an increase in KOH ratio. A nitrogen-sorption study reveals varying trends between BET, micro and mesopore surface areas, however, pore size and volume and hysteresis loop size decreases with KOH ratio and temperature. Electrochemical studies on the other hand reveal that both the specific capacitance and charge-discharge time increase with KOH ratio, temperature and time while both charge transfer and Warburg resistances decrease and the phase angles increases towards the ideal -90° with an increase in KOH ratio, temperature and time. The device fabricated with the HHPB sample prepared at 700 °C, KOH ratio 3 for 60 min attained a specific capacitance of 179.3 and 169 F g at a scan rate of 5 mV s and current density of 0.5 A g, respectively, good cycling stability with 95% capacitance retention and 100% coulombic efficiency when cycled 5000 times at a current density of 2 A g. HHPB electrodes reveal perfect EDLC behavior with an energy density of 20 W h kg and power density of 2000 W kg when used in a symmetric coin supercapacitor cell with 6 M KOH solution. These findings show the potential of fan palm bark as electrode materials with good stability and high-rate capability for supercapacitor application.
双电极电化学测试能提供与实际超级电容器器件相近的性能近似值。本研究展示了成功由树皮（墨西哥蒲葵）衍生而来的介孔碳材料及其在双电极超级电容器器件中的电学性能。对碳材料“加工、性质和性能”之间的三元关系进行了全面研究。X射线衍射表明，非晶性随活化KOH比例增加而增加，随活化时间和温度降低而降低。拉曼光谱显示，随着KOH比例、温度和时间增加，结构缺陷和石墨化程度增加，而透射电子显微镜显示，聚集颗粒转变为具有相互连通孔隙的材料，随后随着KOH比例增加孔隙被破坏。氮吸附研究揭示了BET、微孔和介孔表面积之间的不同趋势，然而，孔径、孔体积和滞后回线尺寸随KOH比例和温度降低。另一方面，电化学研究表明，比电容和充放电时间均随KOH比例、温度和时间增加，而电荷转移电阻和Warburg电阻均降低，且随着KOH比例、温度和时间增加，相角向理想的-90°增加。在700℃、KOH比例为3、时间为60分钟条件下制备的HHPB样品制成的器件，在扫描速率为5 mV s和电流密度为0.5 A g时，比电容分别达到179.3和169 F g，在2 A g电流密度下循环5000次时具有良好的循环稳定性，电容保持率为95%，库仑效率为100%。当HHPB电极用于含6 M KOH溶液的对称硬币超级电容器电池时，展现出完美的双电层电容行为，能量密度为20 W h kg，功率密度为2000 W kg。这些发现表明蒲葵树皮作为超级电容器应用中具有良好稳定性和高倍率性能的电极材料的潜力。
