Electrosynthesis of organic molecules offers a viable pathway for the green manufacturing of chemicals. Electroorganic synthesis reactions can be applied in fields such as biomass conversion, hydrogen cycling, fossil fuel waste valorization and waste water treatment. Conventional thermochemical processes for organic synthesis typically operate at elevated temperatures, relying on fossil fuels and generating carbon emissions. In contrast, electrocatalytic process run at ambient temperatures and are powered by electricity, omitting the need for fossil fuel heating for the reactions and minimizing the carbon footprint. However, a comprehensive carbon footprint analysis must account for the entire system, including product purification, rather than focusing solely on the reaction process. In this work, we conducted a comparative carbon footprint assessment of thermochemical, electrochemical, and hybrid systems for liquid organic hydrogen carrier (LOHC) cycling applications using the acetone/isopropanol (IPA) LOHC pair as a model system. The carbon footprint for thermochemical cycling was 5.2 and 74.3 kgCO₂/kg H₂ when powered by renewable and non-renewable electricity, respectively. The primary contributors to the thermochemical carbon footprint were the endothermic dehydrogenation of IPA and upstream hydrogen production. In electrochemical LOHC cycling, the carbon footprint was highly dependent on the electricity source and downstream separation method. Without product purification, the carbon footprint was 0.8 and 28.3 kgCO₂/kg H₂ when using renewable and non-renewable electricity, respectively. However, distillation-based product purification significantly increased the footprint due to its high energy demand that is powered by fossil fuel. Sensitivity analysis revealed that the carbon footprint was concentration-dependent, with diluted organic mixtures producing a larger carbon footprint due to needing more energy for separation by distillation. Additionally, the use of KOH in the electrolyte increased the footprint due to its upstream production footprint. Hybrid LOHC cycling exhibited a lower carbon footprint only when electrochemical processes operated at concentrations greater than 4M LOHC in water. Overall, this study highlights how the carbon footprint of LOHC cycling systems is influenced not only by the reactions themselves but also by the entire system factors. Utilizing renewable electricity and minimizing the product separation process in electrochemical systems will enable a more greener and sustainable LOHC cycling system.
