E-fuels represent a crucial technology for transitioning to fossil-free energy systems, driven by the need to eliminate dependence on fossil fuels, which are major environmental pollutants. This study investigates the production of carbon-neutral synthetic fuels, focusing on e-hydrogen (e-H₂) generated from water electrolysis using renewable electricity and carbon dioxide (CO₂) captured from industrial sites or the air (CCUS, DAC). E-H₂ can be converted into various e-fuels (e-methane, e-methanol, e-DME/OME, e-diesel/kerosene/gasoline) or combined with nitrogen to produce e-ammonia. These e-fuels serve as efficient energy carriers that can be stored, transported, and utilized across different energy sectors, including transportation and industry. The first objective is to establish a clear framework encompassing the required feedstocks and production technologies, such as water electrolysis, carbon capture, and nitrogen production techniques, followed by an analysis of e-fuel synthesis technologies. The second objective is to evaluate these technologies’ technological maturity and sustainability, comparing energy conversion efficiency and greenhouse gas emissions with their electric counterparts. The sustainability of e-fuels hinges on using renewable electricity. Challenges and future prospects of an energy system based on e-fuels are discussed, aiming to inform the debate on e-fuels’ role in reducing fossil fuel dependency.

Cycling high temperature CO₂ capture using CaO–based solid sorbents, known as the calcium looping (CaL) process, is gaining considerable scientific and industrial interest due to the high theoretical sorbent capacity (0.78 gCO₂/gCaO), the low specific cost, and the negligible environmental impact of the employed materials. In this work, we investigated the self–combustion synthesis of CaO–CaZrO₃ sorbents with different CaO contents (40, 60, and 80 wt%) for use in the CaL process. CaZrO₃ was used as a spacer to avoid CaO grains sintering at high temperature and to reduce the diffusional resistances of CO₂ migrating towards the inner grains of the synthetic sorbent. Samples were characterized by X–ray diffraction (XRD), Brunauer–Emmett–Teller (BET), and scanning electron microscopy (SEM) analyses. The reaction between CO₂ and CaO (i.e., carbonation) was carried out in 20 vol% CO₂ at 650 °C and calcination (i.e., decomposition of CaCO₃ to CaO and CO₂) at 900 °C in pure Ar or with 85 vol% CO₂ using a thermogravimetric analyzer (thermogravimetric/differential thermal analysis (TG–DTA)). The most stable sorbent was with 40 wt% of CaO showing a CO₂ uptake of up to 0.31 g CO₂/g_sorbent and 0.26 g CO₂/g_sorbent operating under mild and severe conditions, respectively. The experimental data corroborated the prediction of the shrinking core spherical model in the first phase of the carbonation. A maximum reaction rate of 0.12–0.13 min⁻¹ was evaluated in the first cycle under mild and severe conditions of regeneration.