Synergetic effects of radio-frequency (RF) in-liquid plasma and ultrasonic vibration on hydrogen production from glucose

Abstract

Hydrogen is a very attractive source of highly efficient and environmentally friendly energy. Investigation into hydrogen production from glucose decomposition by 27.12 MHz radio-frequency in-liquid plasma with and without ultrasonic vibrations was carried out utilizing 29 kHz and 1.6 MHz ultrasonic transducers to determine the effects of agitation and acoustic streaming. In-liquid plasma is generated inside a bubble, resulting in a high temperature chemical reaction field within the liquid which is then irradiated by ultrasonic vibration. The dependence of hydrogen production rate, hydrogen yield, hydrogen purity and hydrogen production efficiency on the types of ultrasonic vibration applied was investigated. Higher intensities of active C atoms species were observed in the emission spectrum of RF in-liquid plasma when irradiated with ultrasonic vibration and it is believed that these species function as precursors or intermediaries for other components in the gas product. Hydrogen production rate was enhanced by 30% when RF in-liquid plasma was irradiated by the 1.6 MHz piezoelectric transducer. The highest hydrogen yield was 72% for RF in-liquid plasma with the 29 kHz ultrasonic transducer at an initial concentration 1.0%. The hydrogen purity was enhanced by 5% for the highest initial concentration when applying the 29 kHz ultrasonic transducer to the RF in-liquid plasma. Thus the acoustic streaming effect by 1.6 MHz piezoelectric vibration enhanced the hydrogen production rate, while on the other hand, the agitation effect by 29 kHz ultrasonic vibration enhanced hydrogen yield and hydrogen purity. Though the hydrogen production efficiency of RF in-liquid plasma with ultrasonic vibration applied was lower overall when compared to that without ultrasonic vibration except for decomposition of glucose 20 wt% by RF in-liquid plasma with 1.6 MHz ultrasonic transducer which was 7% higher than that without ultrasonic vibrations, this remains a process that could be considered as a promising future technique for hydrogen production.