## 1 Introduction
E-fuels are all fuels in gas or liquid form that are produced from renewable (solar or wind power, for example) or decarbonised electricity. These fuels are sometimes referred to as electrofuels because they involve the use of electricity (\"electro-\") to generate the necessary chemical transformations. E-fuels are synthetic fuels produced by using renewable energy to convert carbon dioxide (CO\({}_{2}\)) and hydrogen (often derived from water electrolysis) into liquid or gaseous hydrocarbons, which is also called the power-to-liquids (PLL) pathway. The synthesised hydrocarbon e-fuels can be created by combining hydrogen (often produced using renewable energy sources) with carbon dioxide directly captured from the atmosphere [28] or biomass/biogas. The proposition of e-fuels is truly transformative: they have the potential to deliver the high-energy demands of modern societies while ensuring a significantly lower carbon footprint [29]. In addition, their capacity to serve as a direct substitute for conventional fuels in existing infrastructures, without the need for extensive modifications, makes them especially attractive [30; 31]. E-fuels are not merely another alternative energy source. They represent a potential cornerstone in the next phase of our global energy transition, as illustrated in Figure 3. By harnessing the power of e-fuels, humanity could pave the way towards a more sustainable energy landscape for carbon-neutral or even carbon-negative solutions, which would drastically reduce our carbon emissions and mitigate the worst effects of climate change [32]. Historically, the concept of e-fuels is rooted in the Fischer-Tropsch process, a method developed in the 1920s to convert coal into liquid hydrocarbons [33]. While the principle of synthesising liquid fuels from non-petroleum sources is not new, the integration of modern renewable energy sources to power such processes is a relatively recent development [34]. Over the past two decades, a burgeoning body of research has investigated the potential of e-fuels [35]. Initial studies were primarily focused on the technical feasibility of producing e-fuels [36]. Advances in direct air capture (DAC) technologies, as investigated by [PERSON] et al. (2017), have opened up the possibility of sourcing carbon dioxide directly from the  
Figure 2: Comparison of the technological potential of renewable aviation fuels. atmosphere, providing a truly sustainable carbon source [37]. The economic viability of e-fuels has also been a topic of significant interest [38]. Cost analyses associated with the technologies employed, such as those conducted by [PERSON] et al. (2019), have aimed to benchmark the production costs of e-fuels against conventional fossil fuels and other renewable alternatives [39]. These studies highlight both the challenges and potential cost reduction pathways, emphasising the role of technological innovation and economies of scale [40]. Life cycle assessments (LCAs) have been paramount from an environmental perspective [41]. These comprehensive studies, exemplified by recent works like that of [PERSON] et al. (2022), evaluate not only the carbon footprint but also a broad spectrum of environmental impacts, from resource extraction to end-of-life considerations [42]. Such LCAs have provided nuanced insights into the genuine sustainability credentials of e-fuels, considering varied production pathways in methodologies and regional contexts [43]. However, despite these numerous and valuable individual research endeavours, there remains an evident gap: a holistic and integrated analysis that bridges techno-economic evaluations (TEAs) with life cycle assessments (LCAs), providing a comprehensive overview of e-fuel production [44; 45; 46]. Our study seeks to address this lacuna. By amalgamating insights from both a TEA and LCAs, we aim to provide an integrated perspective on e-fuels, offering a multifaceted understanding of their feasibility, costs, and environmental implications. Figure 3: Basic principle and energy, carbon flows of e-fuels.