From the simulation results, calculations were performed to determine the carbon footprint of the overall TCH process. The CO2 emission coefficient of natural gas combustion fuel was obtained from the Energy Information Administration (EIA) and reported to be 5.02Χ10 -5 kgCO2/kJ. Consequently, the acetone TCH process had a carbon footprint of 2.2 kgCO2/kg H2 stored when electricity is from a renewable source as shown in Table . Further details and calculations for the carbon footprint of TCH with different sources of energy are provided in Table and supplementary information. The carbon footprint significantly increased when hydrogen was sourced from non-renewable sources such as steam methane reforming or fossil fuel electricity.