Investigation of hydrogen production and energy storage capacities of supported catalysts produced from walnut shell wastes by Taguchi method

In this study, catalysts were synthesized for the methanolysis of sodium borohydride (NaBH4) using walnut shell (WS), one of the organic waste types. The Taguchi method was employed to determine the most efficient catalyst, aiming to save time, materials, and labor. Then, methanolysis experiments were conducted with the catalyst that showed the highest catalytic activity, in order to achieve the highest hydrogen production under various catalyst amounts, NaBH4 concentrations, and reaction temperatures. Additionally, the effect of using a methanol/propylene glycol mixture as the solvent in hydrogen production reactions was evaluated in terms of hydrogen production rate (HGR). To this end, the influence of experimental parameters was investigated, and experiments were carried out at various catalyst amounts, NaBH4 concentrations, and reaction temperatures. The maximum HGR obtained in methanolysis reactions using the WS catalyst was calculated to be 5013.9 ml min-1 g-1. Moreover, the activation energy of this catalyst was found to be 9.80 kJ/mol. In the reaction where methanol+propylene glycol was used as the solvent, the HGR was 49800 ml min-1 g-1, and the activation energy was determined to be 45.47 kJ/mol. Characterization of the WS catalyst was performed using XPS, XRD, FTIR, and SEM-EDX analyses. Furthermore, the WS catalyst with the highest catalytic activity was used as an electrode material in supercapacitor design, and its electrochemical performance was investigated. Electrochemical measurements were conducted to determine the energy storage capacity of the catalyst. For this purpose, Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS), Galvanostatic Charge- Discharge (GCD), and stability cycle analyses were performed.