The Alkaline Thermal Treatment (ATT) reaction presented in this study utilizes wet and salty biomass (e.g., food and agricultural wastes, and seaweeds), which are often ignored resources. This particular biomass conversion reaction is unique, since it integrates in-situ CO2 capture and co-generate biochar, and solid carbonates such as CaCO3. Our study has shown that high purity hydrogen can be produced in a single step ATT reaction under mild reaction conditions (ambient pressure and reaction temperature less than 600 °C, 1 atm) in the presence of gas reforming Ni-based catalysts. The placement of catalysts and the type of hydroxides are investigated in order to probe the mechanisms of the ATT reaction. Some of these marine biomasses can be cultivated with deep sea water which contains significantly higher metal concentrations. The ATT of these seaweeds can further concentrate metals into solid phase, while producing bio-hydrogen. The extraction and separation of the energy-relevant critical minerals/metals such as rare earth elements, Ni, Co, Li, Ce, and Cu, would provide a sustainable pathway to resource recovery required for our clean energy transition.Recently, Hatton group has developed a technology where carbonate salts can be electrochemically converted to high purity carbon nanotubes (CNTs) using renewable energy (e.g., offshore wind energy). Park and Hatton groups integrated these two unique technologies in the context of a novel tandem thermo-electrochemical (elecATT) process to treat and upcycle marine wastes. Our study showed that our novel elecATT of polyethylene and salty brown seaweed performed at 500-600 oC can produce hydrogen at high purity (85%), and these reactions can be enhanced by the presence of both heterogeneous in-situ and ex-situ y-zeolite and Ni/ZrO2 catalysts. The majority of carbon from seaweed and plastics was converted to carbonate ions in a molten electrolyte composed of Li2CO3/K2CO3/LiOH and converted to carbon nanotubes via electrosplitting of carbonate ions with near 100% Coulombic efficiency. Carbon analysis was performed to analyze the fate of carbon throughout the elecATT reactions, and to evaluate the recyclability of LiOH/KOH electrolytes for the ATT reaction. Overall, this study presented an innovative method for the treatment and upgrading of marine plastic pollutants by producing high purity H2 and purified polymer intermediates for upcycling,and capturing carbon via a molten salt which can then be electrochemically converted to produce high-value CNTs using renewable energy.
