# Techno-Economic Potential of Plasma-Based CO\({}_{2}\) Splitting in Power-to-Liquid Plants
## 2 State of the Art
### Plasma-Based CO\({}_{2}\) Splitting--A Short Review  
Plasma technologies are promising in power-to-liquid processes due to their simple operating conditions and flexible use as renewable electrical energy. The term plasma describes an ionized gas in which at least one electron is not bound. Plasma can be achieved from the gaseous third state of matter by heat input, electric fields, and radiation. In non-thermal plasma, the temperatures of the individual plasma parts differ significantly. The electron temperature of about 10,000 K is significantly higher than all other temperatures (neutral particles, oscillating particles, ions). As a result, reactions operate in non-thermal plasmas that could not occur from a thermal point of view. Warm plasma represents a middle ground between thermal and non-thermal plasma. It contains properties of both types of plasma and is characterized by both high electron density and a high degree of non-equilibrium. [PERSON] and [PERSON] describe this type of plasma as very promising for CO\({}_{2}\) conversion due to its high process flexibility, which allows different types of reactions to be carried out (e.g., pure CO\({}_{2}\) splitting, as well as CO\({}_{2}\) conversion in the presence of CH\({}_{4}\), H\({}_{2}\), or H\({}_{2}\)O [15; 16; 17]). In addition, the investment and operating costs are very low, and rare earth metal-based catalysts are not necessarily required for the reactions. Another advantage is its possible application in a modular environment, since plasma reactors are linearly scaled with the plant capacity, allowing production according to demand. One of the most important advantages is the very simple linkage with renewable electricity. When plasma generation is combined with an additionally introduced catalyst, this is referred to as plasma catalysis. A distinction is made between in-plasma catalysis (catalyst in the plasma) and post-plasma catalysis (catalyst after the plasma). Compared to thermal processes, significantly smaller amounts of catalysts are required, and reactions can be carried out at much milder operating conditions (low pressures, low temperatures) due to the properties of non-thermal plasmas. In addition, interactions occur between the plasma and the catalyst (e.g., changes in the electric field or changes in the catalyst surface), which positively affectsboth. The applications of plasma catalysis are versatile, and Table 1 shows some processes, their reactants, and products, as well as their technology readiness levels (TRL) [15]. The challenges in applying plasma catalysis are the optimization and control of processes in terms of conversion, selectivity, and efficiency. Since the vibrational excitations triggered in the plasma significantly reduce the activation energy of reactions, plasma-based processes and plasma catalysis have very high potential in terms of energy efficiency. Moreover, the interactions between plasma and the catalyst are still not clear due to their complexity and require real-time studies directly at the interaction sites. In addition to a better understanding of plasma-catalyst interactions, [PERSON] et al. mentioned the further engineering development of plasma processes regarding new reactor designs and further process engineering adaptations as an important step toward the optimal exploitation of this potential [26]. To compare different plasma processes in the field of CO\({}_{2}\) splitting--conversion and efficiency must be considered. The efficiency \(\eta_{CO_{2}}\) of the plasma-based CO\({}_{2}\) splitting can be assumed to consist of the effective conversion of CO\({}_{2}\)\(\chi_{CO_{2}}\), and the specific energy input \(SEI\) is related to the standard reaction enthalpy of the CO\({}_{2}\) splitting reaction of \(\Delta H^{298.15K}=283\frac{\mathrm{kJ}}{\mathrm{mol}}\)[18].