Hydrogen is the next energy vector for a decarbonized society. Unfortunately, the H₂ mass production is methane-based. New technologies, such as waste-to-energy, electrolysis, chemical hydrogen in a loop or the steam iron process (SIP), are currently being developed to mass-produce hydrogen without CO₂ emissions, the so-called green hydrogen. The SIP technological principle operates in sequential reduction-reoxidation reactions of iron oxides by reductant gases and steam to produce purify and safely store hydrogen. SIP reactors operate in a fluidized bed using hematite pellets at 500-800 ºC, in which particle sintering reduces hydrogen production.
SIP units could be operating with renewable energy sources to generate and store green hydrogen. Firstly, the Fe₂O₃ is reduced to metallic Fe in a SIP reactor with H₂ from the unused streams generated by an electrolyser (made by photoactive composites), using biomass (biomethanol or bioethanol), or through the gasification of plastic waste. Subsequently, the metallic Fe can be reoxidized with steam to generate high-purity green hydrogen.
This green hydrogen could feed a fuel cell to produce electricity and heat delivered directly to final consumers. Also, the reduced metal can be sealed and transported to generate/store pure green H₂.
For the purpose of production and storage of H₂, our research group have proposed the use of Fe₂O₃/Fe porous structures. At present, doped Fe₂O₃ foams created by freeze-casting can withstand 10 redox cycles at different temperatures without a reduction in performance or pore size. The co-precipitation method was used to incorporate Al₂O₃ into Fe₂O₃ during nanopowder synthesis. The novelty of using stearic acid as a dispersant agent in camphene suspension proves to be much more efficient in reducing particle size, promoting pore enlargement, and an early reduction of the hematite phase during sintering. These results are relevant as demonstrate that freeze-casted foams improve long-term redox performances by combining a unique tailored interconnected pore structure with a specific chemical composition.
Here we show an improved version of a scaffolds structure combining direct ink writing within in-situ freeze-casting, using bioethanol as a reductant agent with promising results.