Effect of SiO2/Al2O3 ratio on the electrochemical performance of amorphous zeolite loaded with cobalt oxide grown via steam-assisted crystallization method

Abstract

Improving the performance of a supercapacitor is one of the main approaches to solve the energy shortage problem. Electrode material is one of the key components limiting the efficiency of a supercapacitor. Discovering, tuning, and improving electrode materials are very important. This work reports the effect of SiO₂/Al₂O₃ ratio on electrochemical performances of amorphous zeolites ZSM5 (AZ) and H-ZSM5 (H-AZ) loaded with cobalt oxide. Two SiO₂/Al₂O₃ ratios (1 = 6.2 and 2 = 8.3) of AZ₁, AZ₂ and H-AZ₁, H-AZ₂ were synthesized by a facile impregnation method. Then, controlled masses of cobalt oxide were introduced to enhance the supercapacitive performances of the amorphous zeolite. Investigation of the SiO₂/Al₂O₃ ratio in the cobalt oxide/zeolite composite (Co/AZ and Co/H-AZ) was carried out to unveil its effect on the electrochemical properties. Worthy of note is the fact that the resulting electrode materials exhibited supercapacitive behavior that is effective over a potential window ranging from 0 to 0.5 V in potassium hydroxide (1 M KOH) aqueous electrolyte. Results from Galvanometry Charging and Discharging (GCD) analyses show that the modified Ni-foam electrodes loaded with Co/H-AZ₁ and Co/H-AZ₂ are capable of delivering a relatively high specific capacity from 45.97 mA h g⁻¹ to a high value of 72.5 mA h g⁻¹ at 1 A g⁻¹ and Ni-foam electrodes loaded with Co/AZ₁ and Co/AZ₂ exhibited values from 26 mA h g⁻¹ to 52.83 mA h g⁻¹ respectively. It is clearly shown that, when the mass ratio SiO₂/Al₂O₃ increases, the specific capacity increases as well. It was also noticed that after 2000 cycles, Co/H-AZ₁ and Co/AZ₁ have a poor coulombic efficiency while Co/H-AZ₂ and Co/AZ₂ exhibited 98% for coulombic efficiency. Finally, this study shows that to fabricate high performance supercapacitors with amorphous zeolite loaded with cobalt oxide, one should keep the ratio of SiO₂/Al₂O₃ as high as possible during synthesis.