Efficient Valorization of Biomass Waste to Green Hydrogen over Flash Joule Heating-Engineered High-Entropy Alloy Catalysts

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In the context of global energy transition and carbon neutrality goals, developing sustainable technologies for converting biomass waste into high-value green hydrogen (H2) is critical for advancing cleaner production and a circular economy. This study presents a novel approach to synthesizing carbon-supported ultrasmall FeCoNiCuZn high-entropy alloy (HEA) nanoparticles via flash Joule heating (FJH) carbothermal shock, enabling efficient catalytic valorization of poplar sawdust waste into H2. The FJH process at 1000 °C suppresses volatile metal (e.g., Zn) loss and promotes rapid reduction, yielding high-density active sites with enhanced metallic states. Structural characterizations confirm the formation of a single-phase face-centered cubic HEA structure, uniformly dispersed on nitric acid-modified biochar with strong metal-support interactions, stabilized by oxygen-containing functional groups. The synergistic effects of ultrasmall particle size (<5 nm), high specific surface area (1636 m2/g), and graphitized carbon framework significantly boost catalytic efficiency in ex situ biomass pyrolysis. The optimized catalyst (FeCoNiCuZn/C-8-HNO3) achieves a H2 yield of 23.56 mmol/gbiomass-daf (48.66 vol %), which is 37-fold higher than noncatalytic pyrolysis and 1.3-fold higher than conventional tube furnace-synthesized catalysts. This work establishes a sustainable pathway for converting low-value biomass waste into green H2 using cost-effective, high-performance HEA catalysts, addressing key challenges in cleaner production, resource utilization, and carbon-neutral energy systems.