Microwave-assisted pyrolysis of biomass and plastic wastes for hydrogen production

The development of hydrogen energy is a key path to achieving carbon neutrality, providing zero-carbon and efficient clean energy solutions. Moreover, it can enhance energy security, promote green transformation in industry, transportation and other fields, and form new economic growth points. Microwave-assisted pyrolysis is an emerging thermochemical technology that has gained significant attention for efficiently converting hydrogen-rich resources to H₂ and high-value carbon materials. Microwave heating enhances the uniformity of heat distribution. Electromagnetic energy is converted to molecular kinetic energy in microwave heating. Dielectric loss is the phenomenon in which a dielectric material dissipates its electromagnetic energy in the form of heat or other forms. Dielectric loss is inherent to all materials and occurs naturally. This paper summarizes the research advances and key challenges in the microwave-assisted pyrolysis of biomass and plastic wastes for H₂ production. In general, microwave pyrolysis is the selective heating of feedstocks. The parameters of microwave pyrolysis include the reaction temperature, the reaction time, the supply of microwave power, the origin of the microwave feedstock, the particle size of the feedstock, the mixing ratios of feedstock, the dielectric constant of the feedstock, the feedstock pretreatment, and the use of catalysts and microwave absorbers. The effects of these parameters on H₂ production from microwave-assisted pyrolysis are clarified. H₂ production through microwave-assisted catalytic pyrolysis of waste plastic and biomass has advantages in terms of lower energy consumption and potential for reducing tar formation, thus increasing the yield and selectivity of H₂ compared with conventional pyrolysis. Key challenges include achieving uniform heating in large reactors due to variable dielectric properties of feedstocks and limited microwave penetration, which risks hot spots and inconsistent product quality. Feedstock variability in composition, moisture, and size complicates stable material flow and continuous feeding systems. Microwave generation demands costly equipment and optimized energy use to ensure economic viability. Maintaining consistent product quality is difficult due to uneven heating and feedstock diversity, alongside managing the carbon byproducts. Furthermore, the future directions in the microwave-assisted pyrolysis of each resource are discussed, thus promoting H₂ production toward high-efficiency, energy-saving and low-carbon development.