Plasma Technology: An Emerging Technology for Energy Storage

Abstract

Plasma technology is gaining increasing interest for gas conversion applications, such as CO2 conversion into value-added chemicals or renewable fuels, and N2 fixation from the air, to be used for the production of small building blocks for, e.g., mineral fertilizers. Plasma is generated by electric power and can easily be switched on/off, making it, in principle, suitable for using intermittent renewable electricity. In this Perspective article, we explain why plasma might be promising for this application. We briefly present the most common types of plasma reactors with their characteristic features, illustrating why some plasma types exhibit better energy efficiency than others. We also highlight current research in the fields of CO2 conversion (including the combined conversion of CO2 with CH4, H2O, or H2) as well as N2 fixation (for NH3 or NO x synthesis). Finally, we discuss the major limitations and steps to be taken for further improvement.

CO2 Decomposition in CO2 and CO2/H2 Spark‐like Plasma Discharges at Atmospheric Pressure

“…This ranged between 54 and 14 depending on the gas residence time. [5,8] The upper range of efficiencies here is found to be comparable to the well optimised and larger volume glidinga rc plasma reactors [9] where both thermal and non-thermalp lasma modes exist as at ransient arc movesb etween aw idening discharge spacing. [5] The gas residence time in DBD reactors is, however,t ypically on the order of several seconds.…”

“…[5] The gas residence time in DBD reactors is, however,t ypically on the order of several seconds. [5,9] The relativelyh igh efficiencies recorded here suggest" spark-like" discharges can exploit this optimal chemistry,m otivating further study.T his should be taken into consideration for scalingt his technology or construction of multiple spark electrodes for larger scale devices. [5,8] The upper range of efficiencies here is found to be comparable to the well optimised and larger volume glidinga rc plasma reactors [9] where both thermal and non-thermalp lasma modes exist as at ransient arc movesb etween aw idening discharge spacing.…”

“…[5,9] Prior to use of this CO, the produced O 2 mustb e separated (e.g.,b yc ryogenic distillation) or consumed by the introduction of co-reactants such as hydrogen or methane. [5,9] Prior to use of this CO, the produced O 2 mustb e separated (e.g.,b yc ryogenic distillation) or consumed by the introduction of co-reactants such as hydrogen or methane.…”

“…Separation is currently ac onsiderable energy hurdle to generate O 2 -free syngas mixtures.C ommon techniques based on cryogenic distillation, membrane separation and chemical absorption( e.g.,a mines)a pproaches currently suffer from large energy expense exacerbated by the similarity in size and shape of CO compared with O 2 . [5,9,24] This estimate includes CO formation;t herefore, any dilution with ac o-reactant resulting in O 2 removal would be af raction of this energy range. [24] Here, estimates of energy costs range on the order of 200-450 kJ mol À1 [31] (with membrane technology coming at the lower end of this range) for varying degrees of purity.E nergyc osts associated with atmospheric plasma CO 2 conversion and co-reaction on the other hand are estimated as 10-50 kJ mol À1 .…”

“…[12] Pointed electrode geometries are typically employed to "pinch" the electric field by introducing curvature in the voltage applied. Such properties are of interest in gas conversion applications.I nvestigationo f spark and hybrid spark-glow ('spark-like')d ischarges in the context of CO 2 conversion has been limited to date [5,9] particularly in the context of ap ulsed kHz AC applied voltage as discussed here. [12] This strategy maintains the non-equilibrium charactero ft he plasma while enabling an intense discharge to be generated in ac onfined volume.…”