Effect of different solvents on hydrogen production from hydrolysis of potassium borohydride with a new and active Ni-based catalyst synthesized by green synthesis

Abstract

In this study, a novel Ni-based catalyst supported on carbon quantum dots (CQDs), synthesized from caffeine via a green hydrothermal method was developed to enhance hydrogen generation. The effects of different solvents, including water, and ethanol, on the catalyst's performance were explored. The results demonstrate that the Ni@CQDs catalyst prepared in ethanol exhibited superior hydrogen production rates due to improved nickel dispersion and higher surface area, as confirmed by BET, XPS, and XRD analyses. Ethanol was found to effectively modify the catalyst, resulting in faster H₂ conversion compared to water. The HGR values obtained with catalysts synthesized in water and ethanol were 4662, and 12262 mL min−1g−1, respectively. The study also investigated the impact of KOH concentration, catalyst loading, KBH4 concentration, and temperature on the hydrolysis process. The Ni@CQDs catalyst synthesized in ethanol achieved optimal performance at higher KBH₄ and KOH concentrations, producing 100% H2 yield over six reusability cycles with minimal loss of catalytic efficiency. Thermodynamic analysis using the Arrhenius and Eyring-Polanyi equations indicated that the catalyst in ethanol had a lower activation energy, enhancing the hydrolysis reaction rate. The Ni@CQDs (ethanol) catalyst exhibited a significantly higher TOF of 1696 h⁻1 at 4% KBH4 concentration and a lower activation energy (Ea) of 33.78 kJ mol−1 compared to the Ni@CQDs (water) catalyst, which had a TOF of 601.5 h⁻1 at 2% KBH4 concentration and an Ea of 38.93 kJ mol−1, indicating superior catalytic efficiency with ethanol as the solvent.