Tailoring Microwave Frequencies for High-Efficiency Hydrogen Production from Biomass

Generating green hydrogen through biomass thermochemical conversion is pivotal for contributing to carbon neutrality. However, the efficiency of hydrogen production is hindered by the byproduct of tar formed during biomass depolymerization. This study employed a variable-frequency microwave ranging from 2430 to 6000 MHz to investigate the influence of microwave frequency on tar removal and hydrogen recovery over activated charcoal (AC). Experimental results indicated that microwave frequencies significantly impact the temperature distribution and heating rates of AC. Notably, at 4640 MHz the AC rapidly reached 1145 °C within seconds, with an instantaneous heating rate of 2022 °C/min. The ultra-fast heating rate crucially contributes to achieving 100% efficiency in tar cracking, resulting in a hydrogen yield of 32.8 mmol/g. With a hydrogen recovery rate surpassing 94%, the 4640 MHz frequency represents a 15.4-fold increase compared to the conventional 2450 MHz. This innovative approach holds significant promise for enhancing energy efficiency in the pursuit of carbon-neutral energy production.