How can plasma be used as a source of energy

In this paper, the present study focuses on the direct energy conversion systems such as magnetohydrodynamics MHD and plasmadynamic PDC. In these systems, a plasma source is directly converted into electrical energy without the use of any mechanical energy.

Furthermore, the electrical power generated from these systems is very efficient and large loss of energy is greatly minimised. The objective of the present study is to develop an improved MHD energy conversion system based on the principle of Faraday's Law of electromagnetism and plasma physics.

Scientific evidence suggests that plasma is actually the most common state of matter in the universe, and plasmas are even present on earth. The distinguishing factor between plasma and gas is that plasma has become energized to the point where some electrons break free from and continue to travel with their nucleus. Bright celestial objects, like the sun and stars, are powered by plasma fusion.

Hydrogen fusion in the core of the sun takes place at a temperature of 14 million kelvin. Recent research at universities and labs around the world indicates that this process can be replicated, and the power generated may be harnessed as a clean and renewable source of energy.

This method of generating power is sometimes referred to as capturing a star in a jar. Fusion energy involving plasma is an attractive renewable source because fossil fuels and other unsustainable energy sources will become exhausted over time.

Other renewable methods that are growing in popularity, such as solar power or wind, cannot presently produce power at a comparable concentration.

To generate energy through plasma fusion, scientists must build containers in which intense conditions that resemble the energy-generating qualities of the sun can be produced and maintained. The demands on container and wall materials are high, making the composition of the plasma and container materials and the design of the vessel essential matters. To produce energy using plasma, a vessel must remain intact during the fusion process, and the plasma must remain clean.

Creating a powerful magnetic field is an integral part of the construction of containers suitable for fusion experiments. One of the most common designs is a tokamak, a magnetized toroidal-shaped chamber.

Fusion reactors are designed using different materials and ingredients to alter the ultimate power output from plasma by controlling interactions between the plasma, wall, and container. Most of the major challenges that researchers have encountered in recent years involve plasma-surface interactions.

PSIs describe the interaction between plasma, walls, and other materials within a confined and magnetized environment. At this time, short pulse magnetic confinement machines such as TFTR or JET have already proven that it is feasible to measure fusion taking place in plasma. Plasma energy has not yet generated enough power to offset the amount consumed in producing the conditions that are necessary for fusion to take place. Plasma power is only beginning to reach the point where it can be operated for a short period of time — approximately a minute or a slightly longer — at an efficient level of performance.

Plasma research presently centers around the International Thermonuclear Experimental Reactor located in southern France. The energy efficiency can sometimes be enhanced by introducing packing of dielectric material in the gap between the electrodes, creating a so-called packed-bed DBD reactor. The reason for the improved energy efficiency is the polarization of the dielectric packing beads as a result of the applied potential difference, enhancing the electric field near the contact points of the packing beads, and thus the electron energy.

Furthermore, the packing beads can have catalytic properties or be covered by a catalytic material to enable the selective production of targeted compounds by so-called plasma catalysis. Plasma catalysis combines the high reactivity of a plasma with the selectivity of a catalyst, so that targeted compounds can be formed with high product yield and selectivity.

Microwave MW Plasmas. A MW plasma is created by applying MWs, i. There are different types of MW plasmas, such as cavity-induced plasmas, free expanding atmospheric plasma torches, electron cyclotron resonance plasmas, and surface wave discharges.

The latter type are most frequently used for gas conversion applications. The gas flows through a quartz tube, which is transparent to MW radiation, intersecting with a rectangular waveguide, to initiate the discharge see Figure 1 b.

The MWs propagate along the interface between the quartz tube and the plasma column, and the wave energy is absorbed by the plasma. MW plasmas can operate from reduced pressure e. Gliding Arc GA Discharges. A GA discharge is a transient type of arc discharge. A classical GA discharge is formed between two flat diverging electrodes see Figure 1 c.

This type of two-dimensional GA discharge yields only limited gas conversion because a large fraction of the gas does not pass through the arc discharge. Therefore, other types of three-dimensional GA discharges have been designed, such as a gliding arc plasmatron GAP and a rotating GA, operating between cylindrical electrodes. The GAP is schematically illustrated in Figure 1 d. The cylindrical reactor body operates as a cathode powered electrode , while the reactor outlet acts as an anode and is grounded.

The gas enters tangentially between the two cylindrical electrodes. When the outlet diameter is significantly smaller than the diameter of the reactor body, the gas flows in an outer vortex toward the upper part of the reactor body, and subsequently, it will flow back in a reverse inner vortex with smaller diameter because it has lost some speed, and thus, it can leave the reactor through the outlet.

The arc is again initiated at the shortest interelectrode distance and expands until the upper part of the reactor, rotating around the axis of the reactor until it more or less stabilizes in the center after about 1 ms.

In the ideal scenario, the inner gas vortex passes through this stabilized arc, allowing a larger fraction of the gas to be converted than in a classical two-dimensional GA discharge. The GA discharge operates at atmospheric pressure, making it also suitable for industrial implementation.

However, the gas temperature is also fairly high typically a few K , limiting the energy efficiency, like in a MW plasma, because the plasma approaches thermal equilibrium see below. Highlights of Ongoing Research. CO 2 conversion into value-added chemicals and fuels is considered one of the great challenges of the 21st century. Due to limitations of the traditional thermal approaches, several novel technologies are being developed, such as electrochemical, solar thermochemical, photochemical, and biochemical pathways, either with or without catalysts, and all of their possible combinations.

Plasma chemical conversion can be seen as an additional novel technology, but it has received less attention up to now than the other upcoming technologies. Research on plasma-based CO 2 splitting into CO and O 2 started already in the s, when a lot of experiments were performed in the former Soviet Union, in various types of plasma reactors. In the past decade, there has been renewed interest in plasma-based CO 2 conversion, with various groups around the world actively searching for optimized conditions in various types of plasma reactors and trying to understand the underlying mechanisms.

All results obtained up to now in the literature are summarized in Figure 2 , in terms of energy efficiency vs CO 2 conversion, indicated per plasma type. This figure is adopted from the recent review paper on CO 2 conversion by plasma technology, published by Snoeckx and Bogaerts.

Therefore, we refer to ref 2 for a complete overview of the state-of-the-art. Figure 2. Comparison of all data collected from the literature for CO 2 splitting in the different plasma types, showing the energy efficiency as a function of conversion.

Adopted from ref 2 with kind permission; published by The Royal Society of Chemistry. Here, we present some characteristic examples for the three different plasma types discussed previously to illustrate their capabilities and limitations. Van Laer et al. However, it should be stressed that a packed-bed DBD does not always yield better performance.

Indeed, introducing the packing reduces the residence time at constant flow rate due to a reduced plasma volume, and this will negatively affect the conversion. Thus, depending on the conditions i. Indeed, when compared at the same flow rate cf. When compared with the unpacked reactor at the same residence time and thus much higher flow rate, cf.

Figure 3. CO 2 conversion a and energy efficiency b in a DBD, with and without dielectric packing, for four different packing materials legend and three different bead sizes x -axis , in the case of a DBD reactor with an Al 2 O 3 dielectric barrier, 4. Note that the results of Figure 3 do not represent the best performance found in the literature for packed-bed DBD reactors, but they illustrate that inserting a packing does not always lead to better performance and that the results greatly depend on the packing material and geometry, as well as the rector geometry.

At atmospheric pressure, Spencer et al. Figure 4. Summary of the best results published in the literature for energy efficiency vs CO 2 conversion in a MW plasma, at both reduced pressure open symbols and atmospheric pressure full symbols.

As explained previously, in a GAP, the gas enters tangentially, and when the anode outlet diameter is smaller than the cathode reactor diameter, it flows in an outer vortex toward the upper end of the reactor, followed by a reverse vortex with smaller diameter toward the outlet see Figure 1 d. This reverse vortex gas flow passes through the active arc in the middle of the reactor, yielding better conversion and energy efficiency than in the case of an anode outlet with larger diameter, comparable to the reactor diameter.

This is indeed obvious from Figure 5. We believe that this gas fraction could be enhanced by smart design of the GAP reactor or the gas inlet. Likewise, in a classical GA, this gas fraction might be enhanced by modifying the reactor setup and hence the gas flow configuration to realize a higher relative velocity between the arc and gas flow, as demonstrated by model calculations.

Figure 5. Energy efficiency vs CO 2 conversion in a GAP for three different configurations with different anode diameters cf.

In general, it is clear that a MW when operating at reduced pressure and a GA provide much better energy efficiency than a DBD, and this is attributed to the role of vibrational kinetics. This yields electron energies around 1 eV, which are most beneficial for vibrational excitation of CO 2. Subsequently, these levels collide with each other in so-called vibrational—vibrational VV relaxation, gradually populating the higher levels. On the other hand, electronic excitation to a dissociative level, which is the main process in a DBD reactor, would require 7—10 eV.

It should be mentioned, however, that the vibrational levels can also get lost by vibrational—translational VT relaxation. This becomes especially important at high gas temperature, as revealed by computer simulations, 27 where it results in a vibrational distribution function VDF that is nearly in thermal equilibrium with the gas temperature.

Unfortunately, a GA and MW plasma operating at atmospheric pressure exhibit a quite high gas temperature on the order of several K, resulting in a VDF that is indeed close to thermal.

At atmospheric pressure, realizing a lower gas temperature is not so straightforward. One option is to use a supersonic gas flow, as demonstrated by Asisov et al. A possible alternative could be to apply a pulsed power, so that the gas can cool down in between the applied pulses.

A higher power density can be obtained by reducing the dimensions, i. An alternative to improve the conversion and energy efficiency, as revealed by model predictions, 23,24 is to remove O 2 from the gas mixture to avoid the back-reaction, i. To remove O 2 from the gas mixture, scavenging materials or chemicals 28 or membranes could be applied, as demonstrated by Mori et al.

Most research in the literature has been performed up to now with CH 4 as the H-source, i. Figure 6 presents an overview of all results obtained up to now in the literature for DRM, plotting the energy cost vs total conversion.

Figure 6. Comparison of all data collected from the literature for DRM in the different plasma types, showing the energy cost as a function of the conversion. The thermal equilibrium limit and an target energy cost of 4. The y -axis is reversed to allow comparison with Figure 2. Figure 6 also indicates the thermal equilibrium limit, as well as the efficiency target. When directly forming liquids such as methanol , the energy efficiency requirements would be drastically reduced because the energy-intensive step of further processing syngas into the desired liquid products can be circumvented.

For instance, a solar-to-methanol conversion efficiency of 7. Although DRM indeed mainly yields syngas, when combined with a suitable catalyst, it is also possible to selectively produce oxygenates. Scapinello et al.

The selectivity for formic acid was found to be four and three times higher with nickel and copper, respectively, than that with stainless steel.

This was attributed to a chemical catalytic effect of the metals, more specifically, hydrogenation of chemisorbed CO 2 , which has a rather high barrier in the gas phase, and seems to play a key role in the synthesis of these carboxylic acids. Plasma catalysis yields a slightly lower conversion of CO 2 and CH 4 than plasma alone, which might be attributed to the change in discharge behavior due to the full packing of the catalysts in the plasma reactor.

Consequently, also the total energy efficiency for conversion slightly drops, from Figure 7. The results of plasma alone and plasma catalysis were found to be similar in terms of selectivity of the gaseous products, with H 2 , CO, and C 2 H 6 being the major ones.

The combination of plasma with catalyst yields the same products but with some potential to tune the distribution of the different liquid products due to the presence of both gas-phase reactions and plasma-assisted surface reactions. It will be crucial to specifically and rationally design catalysts tailored for the plasma environment with high selectivity toward desired liquid chemicals. Just like for pure CO 2 splitting cf. Furthermore, as indicated in Figure 6 , only a few experiments have been reported for DRM with a MW plasma, which is a bit surprising in view of the good results obtained for pure CO 2 splitting cf.

On the other hand, Figure 6 illustrates quite promising results for GA plasma reactors. Note that the absolute conversions i. The corresponding energy cost is then ca. Figure 8. Figure 8 c also depicts the product selectivity, obtained without catalyst. The CO selectivity slightly drops upon higher CH 4 fraction due to the formation of some C 2 hydrocarbons mainly C 2 H 2 , as also revealed from plasma chemistry modeling 32 and probably higher hydrocarbons or other carbon-based products not detected by the gas chromatograph.

The H-based selectivity of H 2 increases with increasing CH 4 fraction; the remaining H atoms give rise to higher hydrocarbons and H 2 O. In general, CO and H 2 or syngas are the major compounds formed in the absence of a catalyst.

Finally, also other plasma reactors have been investigated for DRM, and especially ns-pulsed discharges, spark discharges, and atmospheric pressure glow discharges APGDs showed quite promising results see Figure 6. Figure 7 , middle panel. However, only limited results have been reported in the literature for this type of discharge, and more research is needed to better understand their underlying mechanisms and to further exploit their possibilities.

The conversions reported in CO 2 hydrogenation and the corresponding energy efficiency are, however, a factor of 2—3 lower and thus the energy cost is the same factor higher than those for DRM and pure CO 2 splitting. This mixture could in principle be very interesting as H 2 O is the cheapest H-source available, and this process could mimic the natural photosynthesis process.

Therefore, plasma chemistry modeling reveals that H 2 O might not be a suitable H-source for the direct formation of oxygenated hydrocarbons from CO 2 because of the abundance of O atoms, O 2 molecules, and OH radicals in the plasma, trapping the H atoms. This was indeed confirmed in a GA discharge at atmospheric pressure. N 2 Fixation. Besides CO 2 conversion, plasma also has great potential for N 2 fixation.

It forms an essential part of amino acids and nucleotides, which lead to the formation of proteins, DNA, and RNA, the building blocks of all life on Earth. Therefore, atmospheric N 2 is hardly accessible to most living beings. The process to convert N 2 into small molecules like NH 3 or NO x that can be more easily used as building blocks for life on Earth is called N 2 fixation.

N 2 fixation by chemical processes started in the beginning of the 20th century. In , Birkeland and Eyde successfully developed thermal arc furnaces to convert air into nitrogen oxides. It suffered from a low NO x yield and a low energy efficiency due to the high temperature. In , the Haber—Bosch H—B process was successfully developed as an alternative N 2 fixation technique. The H—B process was commercialized in and gradually took over the Birkeland—Eyde process because of its lower energy consumption and high NH 3 production.

This process has been significantly optimized over the last century to reduce its environmental footprint and increase its energy efficiency, and currently, it almost reaches its theoretical limits. The changing social and environmental conditions worldwide create significant challenges for more environmentally friendly NH 3 synthesis based, e.

Plasma-based N 2 fixation is a very promising alternative because of its thermal nonequilibrium between the light electrons and the gas molecules, as explained in the introduction, which allows one to perform N 2 fixation at lower temperature and relatively low energy consumption.

Indeed, the theoretical limit of the energy consumption of plasma-based N 2 fixation is more than 2. Two processes are mainly investigated in plasma-based N 2 fixation, i. A detailed overview of plasma-based N 2 fixation can be found in the very interesting review papers by Hessel and co-workers.

NH 3 synthesis from N 2 and H 2 is an exothermic reaction and therefore favored at low temperature, making nonthermal plasma very attractive. However, the dissociation of N 2 is a strongly endothermic reaction, which requires high energy input. To our knowledge, no plasma-based NH 3 synthesis process has been developed and implemented on the industrial or pilot scale, but numerous efforts have been reported on the lab scale.

Similar trends can be observed at higher temperatures. Table 1. It must be mentioned, however, that the value reported by Kim et al. Figure 9. In some references, only the NH 3 yield or maximum NH 3 concentration or N 2 or H 2 conversion or energy consumption was mentioned.

Table 1 illustrates the measured values for NH 3 yield and energy consumption for various plasma types. This is not a complete overview of all literature results because the latter is not in the spirit of this Perspective article; it only gives an indication of typical values obtained by different groups. Note that the energy consumption values reported are only for the reactors and not for the overall process. The maximum H 2 or N 2 conversions are mentioned per pass; therefore, they can be further improved in a recirculating reactor.

Furthermore, we believe that plasma-based NH 3 synthesis still has room for improvement as this application is recently gaining significant interest for sustainable energy storage and several research groups are starting activities in this field.

Especially plasma catalysis seems to be promising in this respect, as is clear from Table 1. Finally, we should perhaps not use the H—B process as a benchmark as plasma-based N 2 fixation has potential for distributed production plants, as discussed below.

For plasma-based NO x formation, a larger number of different plasma types have been investigated, including various thermal and nonthermal discharges. Again, the energy consumption values reported are only for the reactors and not for the overall process, except for the Birkeland—Eyde process first row in the table.

Quite some work was performed several decades ago cf. In some references, only the energy consumption was mentioned, and not the NO x yield.

Again, the results reported in the literature vary a lot among different plasma types see Table 2. Thermal plasmas, such as arc discharges as also used in the Birkeland—Eyde process but also laser-produced plasmas, RF discharges, and arc jets, provide reasonable NO x yields but typically at fairly high energy costs because the energy in a thermal system is distributed over all degrees of freedom, including those not effective for the NO x synthesis see below.

The best results are obtained in MW plasmas operating at reduced pressure. Pulsed MW plasmas yield a low energy cost of 0. Furthermore, the low-pressure operation of these MW plasmas requires vacuum equipment, which makes it more difficult to be applied in industrial-scale processes, and the energy requirements of this vacuum equipment should in fact also be included when calculating the energy consumption. DBDs have not been investigated so often as for NH 3 synthesis see Table 1 , and the yields reported are relatively low, with higher energy costs than for MW and GA discharges, even when combined with catalysts.

This is illustrated in Figure 10 region between the dashed lines. This means that GA and MW discharges contain large amounts of vibrationally excited N 2 molecules, which provide the most energy-efficient N 2 dissociation pathway, just like for CO 2.

DBDs are characterized by reduced electric fields above — Td and are expected to be less efficient in N 2 vibrational excitation, as can be seen in Figure Indeed, the mechanism of NO x synthesis in a DBD involves charged and electronically excited species, and thus, it is limited by the high energy cost for the formation of these species, just like for CO 2 conversion cf. Nevertheless, DBDs are interesting to further exploit because they can easily be combined with catalysts, operate at atmospheric pressure, and are easy to scale up.

Figure Fraction of electron energy transferred to different channels of excitation, as well as ionization and dissociation of N 2 , as a function of the reduced electric field bottom x -axis and electron energy top x -axis.

The region between the two vertical dashed lines, i. As mentioned above, the H—B process for NH 3 synthesis still has a lower energy consumption, i. Computer simulations 81 can help to improve the process as they elucidate the limiting factors for energy-efficient NO x synthesis, and thus, they can help to provide solutions to overcome these limitations. On the other hand, it might be difficult to compete with the H—B process, which has been well established for so many years and benefits from its large scale.

However, we believe that plasma-based N 2 fixation has great potential for modular, small-scale reactors, e. This could, for instance, be of great interest for local farmers in regions where a wealth of under-used wind and solar resources exists.

In general, we believe that plasma technology opens new windows of opportunities for small-scale NH 3 and NO x production cf. Critical Analysis of the Performance of Plasma Technology.

This is attributed to the important role of vibrational excitation for energy-efficient dissociation of CO 2 in this type of plasmas. On the other hand, in combination with suitable catalysts, plasma also allows the direct production of higher-value compounds, such as higher hydrocarbons or oxygenates. This is a clear advantage, and it would significantly reduce the energy efficiency target to be competitive with other technologies if the latter would need a two-step process for this purpose.

In this sense, even DBD plasmas could become suitable, especially because they have a simple design, allowing easy upscaling and straightforward implementation of catalysts. However, more research is needed to search for the precise mechanisms at play which may differ from the thermal mechanisms 82 and, based on this knowledge, to specifically and rationally design catalysts to be implemented in plasma reactors.

For N 2 fixation, the same types of plasmas appear to be most promising as those for CO 2 conversion, i. This is most apparent for NO x synthesis, while for NH 3 synthesis nearly all results obtained in the literature are for DBD plasmas, mostly in combination with catalysts. However, there are indications that the higher gas temperatures in MW and GA reactors might be advantageous for NH 3 production, based on the kinetic modeling of Hong et al.

In order to provide available active surface sites for N 2 and other NH x intermediate species, the authors suggested increasing the surface temperature, which will accelerate the recombination of surface-adsorbed H s.

Because the surface temperature equilibrates with the plasma gas or heavy species temperature, this can be achieved by increasing the gas temperature of the plasma, as is the case for MW and GA plasmas. On the other hand, although MW and GA plasmas yield higher N 2 vibrational populations, it was recently demonstrated that even in DBD plasmas N 2 dissociation at catalyst surfaces is enhanced by the N 2 vibrational levels, which enables one to overcome typical classical NH 3 synthesis scaling relations.

In general, an industrial process for plasma-based NO x synthesis might be more successful in the end than for plasma-based NH 3 synthesis as it can utilize air as feed gas, while NH 3 synthesis requires H 2 as co-feed, and the cost for H 2 production is still quite high. In this respect, it would be interesting to perhaps use CH 4 or H 2 O as the H-source, just like for CO 2 conversion, and maybe this would give rise to other value-added chemicals, such as amines. Clearly more research is needed to exploit these possibilities.

When comparing the energy efficiencies or energy costs reported in the literature for both NH 3 and NO x synthesis with those for the H—B process, it is clear that plasma-based N 2 fixation is not yet competitive. However, we should probably not compare with the H—B process as one cannot fight against the economy of scale at thermodynamic equilibrium.

However, as the world is changing and creates new economies, we should follow new business models, and we believe that, in this respect, plasma-based N 2 fixation, in contrast to the H—B process, has great potential for distributed production plants based on renewable energy sources, including fertilizer production in underdeveloped countries.

Snoeckx and Bogaerts 2 recently made a detailed comparison with other emerging technologies, such as electrochemical, solar thermochemical, photochemical, biochemical, and catalytic conversion, for the application of CO 2 conversion, but similar arguments apply to N 2 fixation as well.

It was concluded that plasma technology is quite promising, for the following reasons: 1 Process versatility , allowing different types of reactions to be carried out. For CO 2 conversion, this includes pure CO 2 splitting, as well as CO 2 conversion in the presence of a H-source, such as CH 4 , H 2 , or H 2 O, although the latter two seem only viable if suitable catalysts can be found.

However, clearly more research is needed to specifically and rationally design catalysts tailored for the plasma environment. Moreover, if the appropriate catalysts can be designed, other N-containing compounds could be targeted as well e. This process versatility allows plasma technology to be used at a wide variety of locations, independent of the available feed gas composition and even adjustable to a variable-feed gas composition. Indeed, for instance, in the case of CO 2 conversion, large amounts of N 2 , as present in CO 2 effluent gases, can even be beneficial to enhance the CO 2 conversion.

No use of rare earth metals , which is currently a limiting factor and thus the subject of many investigations for various other technologies. Turnkey process : plasma can be turned on and off very quickly as it requires no preheating or long stabilization times and no cool-down times. In fact, the gas conversion starts immediately after plasma ignition, i. This makes plasma technology very suitable for converting intermittent renewable energy into fuels or chemical building blocks.

Low investment and operating costs. Furthermore, plasma technology can be applied in a very modular setting as there is almost no economy of scale. Indeed, plasma tubes scale up linearly with the plant output. Thus, plasma technology allows for local on-demand production schemes. This can be of special interest for fertilizer production from air N 2 fixation and renewable energy, even by local farmers, e. Finally, plasma allows the use of various types of renewable energy and is thus not limited only to solar energy, like other emerging technologies solar thermochemical, photochemical and biochemical.

The advantage of the latter technologies is that they directly use renewable energy solar radiation , thus skipping an energy conversion step, which always leads to energy losses.

In contrast, plasma technology only employs indirect renewable electricity, but this allows use also of other renewable energy sources, such as wind, hydro, wave, and tidal power. This increases its application versatility as it can be installed and operated independent of the availability of solar radiation although it needs to be noted that photochemical and biochemical technologies may also rely on indirect renewable energy when used in combination with artificial lighting.

Van Rooij et al. It should be realized, however, that in the case of direct production of liquid fuels or higher-value chemicals, for which the reference price is much higher, the business case would be much more optimistic, also because product separation would be easier. This again stresses the need for rational design of catalysts tailored for the plasma environment to selectively produce these target compounds.

Conclusions and Future Directions. In this Perspective article, we discussed the possibilities of plasma technology for storage of renewable electricity, showing two examples, i. For further improvement, more research efforts are needed, especially to design catalysts tailored to the plasma environment. When applying this to storage of renewable electricity, it should still be electricity when it is retrieved. This definition does not apply to all of the examples given in this article.

On the other hand, while we refer in this article to fertilizer production from N 2 , it should be realized that NH 3 produced from N 2 fixation clearly has more potential than only for fertilizer purposes. Indeed, it is also widely viewed as an energy storage and transportation medium, where it is transformed back into H 2 for fuel cell vehicles or alternatively utilized directly in solid oxide fuel cells in an internal combustion engine or a gas turbine.

The general advantage of plasma technology for renewable electricity storage or use is its overall flexibility. This includes flexibility in terms of feed gas i. However, further research is needed to improve the capabilities of this application. Major efforts should go to improving the energy efficiency. The latter largely depends on the type of plasma reactor and operating conditions.

In summary, what is needed for energy-efficient CO 2 conversion or N 2 fixation is i a reduced electric field of 5— Td but still high enough plasma power, yielding sufficient vibrational excitation of the gas molecules, as this provides the most energy-efficient dissociation pathway, ii in combination with a low gas temperature to minimize vibrational losses upon collision with other gas molecules so-called VT relaxation or, in other words, a strong thermal nonequilibrium.

Besides further improving the energy efficiency, research should also focus on enhancing the conversion e. Operating at conditions that promote the vibrational kinetics cf. In the case of CO 2 splitting, the separation of CO and O 2 is rather energy-intensive and provides the largest energy cost, as demonstrated by van Rooij et al. The syngas mixture does not really pose a problem when it is subsequently used for Fischer—Tropsch or methanol synthesis.

Moreover, plasma technology is able to deliver a wide variety of syngas ratios, depending on the initial feed gas mixing ratio. Furthermore, when the plasma conversion would enable direct production of liquid compounds e. However, as discussed above, clearly more research is needed toward specific and rational design of catalysts tailored for the plasma environment.

To conclude, we can identify three specific areas where advances are needed for further improvement, i. We want to stress that when plasma converts CO 2 into renewable fuels, the CO 2 will later be emitted again. Hence, the whole process can at most be carbon-neutral, which is certainly better than using fossil fuels, but it does not realize negative CO 2 emissions, which is crucially needed to stop global warming.

However, as mentioned above, much more research will be needed for this to design the right catalysts, yielding the selective production of such value-added chemicals. In general, we believe that plasma technology can play an important role in the future energy infrastructure as it has great potential in combination with renewable energies for storage or use of peak energies and stabilization of the energy grid, and in this way, it contributes indirectly to CO 2 emission reductions.

Finally, this is of interest not only for the production of renewable fuels so-called solar fuels but also for the production of chemicals. Indeed, we hope that the concepts of modular plants and decentralized chemical production facilities will soon gain acceptance in the chemical industry. Annemie Bogaerts is full professor of physical chemistry at the University of Antwerp.

She is head of the research group PLASMANT, with research activities on modelling of plasma chemistry, plasma reactor design, and plasma—surface interactions, as well as plasma experiments for various applications, with major emphasis on environmental and medical applications.

His expertise is in atomic-scale simulations of nanomaterials and plasma catalysis, with emphasis on nanotechnological and environmental applications. Furthermore, we would like to thank V. Hessel, H. Kim, R. Snoeckx, and W. Wang for the interesting discussions and providing feedback. More by Annemie Bogaerts. More by Erik C. Article Views Altmetric -.

Citations Abstract High Resolution Image. High Resolution Image. Table 2. Author Information. Erik C. The authors declare no competing financial interest. Plasma technology — a novel solution for CO 2 conversion? Royal Society of Chemistry. A review. CO2 conversion into value-added chems. Due to the limitations of the traditional thermal approaches, several novel technologies are being developed. One promising approach in this field, which has received little attention to date, is plasma technol.

Its advantages include mild operating conditions, easy upscaling, and gas activation by energetic electrons instead of heat. This allows thermodynamically difficult reactions, such as CO2 splitting and the dry reformation of methane, to occur with reasonable energy cost.

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A prominent feature is the simple scalability from small lab. Efficient and cost-effective all-solid-state power supplies are available. The preferred frequency range lies between 1 kHz and 10 MHz, the preferred pressure range between 10 kPa and kPa.

Industrial applications include ozone generation, pollution control, surface treatment, high power CO2 lasers, UV excimer lamps, excimer based mercury-free fluorescent lamps, and flat large-area plasma displays. Depending on the application and the operating conditions, the discharge can have pronounced filamentary structure or fairly diffuse appearance.

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American Chemical Society. Thermal-catalytic gas processing is integral to many current industrial processes. Ever-increasing demands on conversion and energy efficiencies are a strong driving force for the development of alternative approaches.

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By means of an in-depth elec. Improving the conversion and energy efficiency of carbon dioxide splitting in a zirconia-packed dielectric barrier discharge reactor. Energy Technol. The use of plasma technol. We demonstrate that the introduction of a packing of dielec. We obtained a max. However, it is the ability of the packing to almost double both the conversion and the energy efficiency simultaneously at certain input parameters that makes it very promising.

The improved conversion and energy efficiency can be explained by the higher values of the local elec. Plasma-photocatalytic conversion of CO2 at low temperatures: Understanding the synergistic effect of plasma-catalysis. Elsevier B.

A coaxial dielec. The effect of specific energy d. SED on plasma process performance was examd. In the absence of a catalyst in the plasma, max. CO2 conversion is UV intensity generated by CO2 discharge was significantly lower than that emitted from UV lamps used to activate photocatalysts in conventional photocatalytic reactions, suggesting the UV emissions generated by CO2 DBD only play a very minor role in the BaTiO3 and TiO2 catalysts activation in the plasma-photocatalytic conversion of CO2.

The synergy of plasma-catalysis for CO2 conversion is mainly attributed to the phys. Effect of dielectric packing materials on the decomposition of carbon dioxide using DBD microplasma reactor.

AIChE J. Carbon dioxide CO2 decompn. The conversions of CO2 in dielec. Particle size, dielec. The conversion of CO2 and energy efficiency achieved the highest values of Quartz wool was also an excellent dielec.

CO 2 dissociation in a packed bed DBD reactor: First steps towards a better understanding of plasma catalysis. Michielsen, I.