Ammonia Production Rate Research Articles

(Invited, Digital Presentation) Eco-Friendly and Sustainable Ammonia Production with Atmospheric Pressure Rotating Gliding Arc Discharge

Increasing fossil-free global energy demands have motivated the scientific community to investigate new clean and sustainable techniques that can meet global energy demands. The production of green and sustainable fuel, such as ammonia, from base molecules like water and nitrogen using electricity from renewable sources shows great potential to solve energy issues. Non-thermal atmospheric pressure plasma-based ammonia synthesis has great potential for carbon-free fertilizer production powered by renewable electricity. We developed an atmospheric pressure rotating gliding arc discharge reactor coupled with a catalyst for a higher ammonia production rate. Here we reported two-step ammonia production, including 1) facile production of NOx and hydrogen from nitrogen discharge in water, and 2) highly selective catalytic reduction of NOx to ammonia in the presence of hydrogen. The studied plasma technique offers ~0.84 % ammonia concentration with ~95 % selectivity and a 120 µmol/s production rate by integrating a catalytic reduction system with plasma. Compared with previous studies on ammonia synthesis from nitrogen, the remarkable ammonia yield (300–400-fold higher). These promising results provide a breakthrough in the transition toward sustainable and environmentally friendly ammonia production.

Activating nano-bulk interplays for sustainable ammonia electrosynthesis

Small changes in a catalyst’s composition, modification, and/or integration into a reactor can have significant yet often poorly understood effects on (electro)catalysis. Here we demonstrate the careful tailoring of Ru/La0.25Ce0.75O2−x catalysts through the post-synthesized hydrothermal treatment together with control over the Ru loadings to create hydroxyl groups and electronic restructuring for ammonia electrosynthesis. When integrated into a protonic ceramic electrolyzer, the in situ formed Ce3+−OH/Ru sites facilitate both the NN decoupling and NH formation at 400 °C and 1 bar of N2, boosting the ammonia production rate (2.92 mol h−1 m−2) up to 100-fold higher than the current state-of-the-art electrolyzers. Moreover, such catalysts and electrolyzer design concepts can be readily tuned to more complex applications such as coproducing ammonia and other chemicals with hydrocarbons as direct hydrogen sources. The creation of coordinated saturated support –OH/metal sites in the advanced electrolyzer offers an attractive approach for future clean-energy and green-chemical industries.

A bifunctional electrochemical flow cell integrating ammonia production and electricity generation for renewable energy conversion and storage

Renewable energy has rapidly advanced in the global energy system, triggering the visible development of energy storage technologies in recent decades. Among them, the electricity-fuel-electricity approach is an effective way for the storage and utilization of renewable power. In this work, a bifunctional electrochemical flow cell integrating both ammonia production and electricity generation modes is developed for renewable energy conversion and storage. Ammonia, a hydrogen carrier having a high hydrogen content of 17.6 wt %, is relatively easier to convert to liquid phase for large-scale storage. The long-distance ammonia transport can reliably depend on the established infrastructure. In addition, as a carbon-free fuel beneficial for achieving the goal of carbon-neutrality, ammonia is considered as an environmentally benign and cost-effective mediator fuel. This flow cell is able to operate via two modes, i.e., an ammonia-production mode for energy storage in the form of ammonia (via nitrogen reduction reaction) and an electricity-generation mode for energy conversion in the form of electricity (via ammonia oxidation reaction). This flow cell is constituted by a PtAu/C-coated nickel-foam electrode for nitrogen and oxygen reduction reactions, a Pt/C-coated nickel-foam electrode for water and ammonia oxidation reactions, and an alkaline anion exchange membrane for charge-carrier migration. Charging this flow cell with the supply of nitrogen results in a Faradaic efficiency of 2.70% and an ammonia production rate as high as 9.34 × 10−10 mol s−1 cm−2 at 23 °C. Moreover, energizing this flow cell with ammonia results in an open-circuit voltage of 0.59 V and a peak power density of 3.31 mW cm−2 at 23 °C. A round-trip efficiency of 25.7% is realized with the constant-electrode mode.

Electrochemical Generation of Catalytically Active Edge Sites in C2 N-Type Carbon Materials for Artificial Nitrogen Fixation.

The electrochemical nitrogen reduction reaction (NRR) to ammonia (NH3 ) is a potentially carbon-neutral and decentralized supplement to the established Haber-Bosch process. Catalytic activation of the highly stable dinitrogen molecules remains a great challenge. Especially metal-free nitrogen-doped carbon catalysts do not often reach the desired selectivity and ammonia production rates due to their low concentration of NRR active sites and possible instability of heteroatoms under electrochemical potential, which can even contribute to false positive results. In this context, the electrochemical activation of nitrogen-doped carbon electrocatalysts is an attractive, but not yet established method to create NRR catalytic sites. Herein, a metal-free C2 N material (HAT-700) is electrochemically etched prior to application in NRR to form active edge-sites originating from the removal of terminal nitrile groups. Resulting activated metal-free HAT-700-A shows remarkable catalytic activity in electrochemical nitrogen fixation with a maximum Faradaic efficiency of 11.4% and NH3 yield of 5.86µg mg-1 cat h-1 . Experimental results and theoretical calculations are combined, and it is proposed that carbon radicals formed during activation together with adjacent pyridinic nitrogen atoms play a crucial role in nitrogen adsorption and activation. The results demonstrate the possibility to create catalytically active sites on purpose by etching labile functional groups prior to NRR.

A‐Site Substitution Motivating the Phase Transformation of LaNiO3 Perovskite for High‐Performance Artificial N2 Fixation

AbstractElectrocatalytic N2 reduction reaction (NRR) to NH3 under ambient conditions is an attractive strategy compared to the traditional Haber‐Bosch process. However, there still remains a great challenge due to the high activation barrier of N2 and consequent sluggish kinetics. Herein, A‐site substitution of LaNiO3 perovskites by Sr‐doping is proposed which can lead to phase transformation and to the formation of oxygen vacancies, significantly improving the NRR performance of La1‐xSrxNiO3 (LSNO). The appropriate oxygen vacancy concentration can be modulated by changing the stoichiometric ratio of La and Sr elements. LSNO‐III (x=0.5) delivers the highest ammonia production rate of 55.9 μg h−1 mg−1cat. at −0.7 V and Faraday efficiency of 23.17 % at −0.5 V versus the reversible hydrogen electrode in 0.1 M Na2SO4. Density functional theory (DFT) calculations further demonstrate that introduction of oxygen vacancies decreases the distance of the d‐band center to the Fermi energy level, which not only facilitates adsorption and activation of N2 molecules and subsequent hydrogenation reactions, but also further optimizes reaction pathways in NRR.

Electrosynthesis of ammonia with high selectivity and high rates via engineering of the solid-electrolyte interphase.

SummaryAmmonia is a large-scale commodity essential to fertilizer production, but the Haber-Bosch process leads to massive emissions of carbon dioxide. Electrochemical ammonia synthesis is an attractive alternative pathway, but the process is still limited by low ammonia production rate and faradaic efficiency. Herein, guided by our theoretical model, we present a highly efficient lithium-mediated process enabled by using different lithium salts, leading to the formation of a uniform solid-electrolyte interphase (SEI) layer on a porous copper electrode. The uniform lithium-fluoride-enriched SEI layer provides an ammonia production rate of 2.5 ± 0.1 μmol s−1 cmgeo−2 at a current density of −1 A cmgeo−2 with 71% ± 3% faradaic efficiency under 20 bar nitrogen. Experimental X-ray analysis reveals that the lithium tetrafluoroborate electrolyte induces the formation of a compact and uniform SEI layer, which facilitates homogeneous lithium plating, suppresses the undesired hydrogen evolution as well as electrolyte decomposition, and enhances the nitrogen reduction.

Phase-separated CuAg alloy interfacial stress induced Cu defects for efficient N2 activation and electrocatalytic reduction

The electrochemical nitrogen reduction reaction (eN2RR) to produce ammonia represents a promising approach to substitute the traditional Haber-Bosch process. However, it remains challenging due to the low ammonia yield caused by low Faradic Efficiency over the target intermediates. Herein, the adjacent Cu defect formed at the interface of phase-separated CuAg alloy was successfully prepared by using the cation-exchange method and identified as the most active electrocatalytic center for efficient N2 reduction. The phase-separated CuAg alloy with rich interfacial Cu defective sites exhibited excellent eN2RR performance with an ammonia production rate (38.35 µg h−1 cm−2) and a Faradaic efficiency of 12.72 % at − 0.60 V versus reversible hydrogen electrode. Our work unravels fundamental principles for the rational design of electrocatalysts, and provides a strategy for fabricating the CuAg-PS alloy with rich interfacial Cu defective sites for eN2RR.

Z-scheme heterojunctions with double vacancies semiconductors MoO3−x and Fe-doped W18O49 for photocatalytic nitrogen fixation

Ammonia gas has important application value in many fields. However, a large amount of energy is consumed to prepare ammonia by the Haber-Bosch process. A cleaner catalytic way to prepare ammonia has become a common goal of human beings. In this paper, Z-scheme heterojunction MoO3−x/Fe-W18O49 was prepared by two-step solvothermal method. The prepared MoO3−x is a flower-like structure formed by the stacking of nanosheets, which can be applied as the attachment carrier of Fe-W18O49 nanowires to effectively inhibit the aggregation of nanowires. Therefore, Fe-W18O49 nanowires will have more oxygen vacancies (OVs) on the surface of the catalyst as the active center of the reaction. MoO3-x containing OVs has LPSR effect, which can enlarge the light absorption range of the heterojunction. In addition, the vacancies contained in MoO3−x can promote the recombination of weak reducing electrons and weak oxidation holes. The catalyst MoO3−x/Fe-W18O49 exhibits strong redox capacity, which is conducive to the occurrence of nitrogen fixation reaction. Under the simulated sunlight condition, the ammonia production rate reached 137.5 µmol g−1 h−1 without any sacrificial reagent. MoO3−x/Fe-W18O49 has good catalytic performance and stability. This work has a certain reference value for the construction of efficient heterojunction catalyst for photocatalytic nitrogen fixation.

Assembly of Hydrophobic ZIF-8 on CeO2 Nanorods as High-Efficiency Catalyst for Electrocatalytic Nitrogen Reduction Reaction.

The electrocatalytic nitrogen reduction reaction (NRR) can use renewable electricity to convert water and N2 into NH3 under normal temperature and pressure conditions. However, due to the competitiveness of the hydrogen evolution reaction (HER), the ammonia production rate (RNH3) and Faraday efficiency (FE) of NRR catalysts cannot meet the needs of large-scale industrialization. Herein, by assembling hydrophobic ZIF-8 on a cerium oxide (CeO2) nanorod, we designed an excellent electrocatalyst CeO2-ZIF-8 with intrinsic NRR activity. The hydrophobic ZIF-8 surface was conducive to the efficient three-phase contact point of N2 (gas), CeO2 (solid) and electrolyte (liquid). Therefore, N2 is concentrated and H+ is deconcentrated on the CeO2-ZIF-8 electrocatalyst surface, which improves NRR and suppresses HER and finally CeO2-ZIF-8 exhibits excellent NRR performance with an RNH3 of 2.12 μg h−1 cm−2 and FE of 8.41% at −0.50 V (vs. RHE). It is worth noting that CeO2-ZIF-8 showed excellent stability in the six-cycle test, and the RNH3 and FE variation were negligible. This study paves a route for inhibiting the competitive reaction to improve the NRR catalyst activity and may provide a new strategy for NRR catalyst design.

Transition-Metal-Free Barium Hydride Mediates Dinitrogen Fixation and Ammonia Synthesis.

Transition-metal-mediated dinitrogen fixation has been intensively investigated. The employment of main group elements for this vital reaction has recently sparked interest because of new dinitrogen reaction chemistry. We report ammonia synthesis via a chemical looping process mediated by a transition-metal-free barium hydride (BaH2 ). Experimental and computational studies reveal that the introduction of hydrogen vacancies is essential for creating multiple coordinatively unsaturated Ba sites for N2 activation. The adjacent lattice hydridic hydrogen (H- ) then undergoes both reductive elimination and reductive protonation to convert N2 to NHx . The ammonia production rate supports this hydride-vacancy mechanism via a chemical looping route that far exceeds that of a catalytic process. The BaH2 -mediated chemical looping process has prospects in future technologies for ammonia synthesis using transition-metal-free materials.

Transition‐Metal‐Free Barium Hydride Mediates Dinitrogen Fixation and Ammonia Synthesis

Transition-metal-mediated dinitrogen fixation has been intensively investigated. The employment of main group elements for this vital reaction has recently sparked interest because of new dinitrogen reaction chemistry. We report ammonia synthesis via a chemical looping process mediated by a transition-metal-free barium hydride (BaH2). Experimental and computational studies reveal that the introduction of hydrogen vacancies is essential for creating multiple coordinatively unsaturated Ba sites for N2 activation. The adjacent lattice hydridic hydrogen (H−) then undergoes both reductive elimination and reductive protonation to convert N2 to NHx. The ammonia production rate supports this hydride-vacancy mechanism via a chemical looping route that far exceeds that of a catalytic process. The BaH2-mediated chemical looping process has prospects in future technologies for ammonia synthesis using transition-metal-free materials.

Lewis acid–dominated aqueous electrolyte acting as co-catalyst and overcoming N2 activation issues on catalyst surface

The growing demands for ammonia in agriculture and transportation fuel stimulate researchers to develop sustainable electrochemical methods to synthesize ammonia ambiently, to get past the energy-intensive Haber-Bosch process. However, the conventionally used aqueous electrolytes limit N2 solubility, leading to insufficient reactant molecules in the vicinity of the catalyst during electrochemical nitrogen reduction reaction (NRR). This hampers the yield and production rate of ammonia, irrespective of how efficient the catalyst is. Herein, we introduce an aqueous electrolyte (NaBF4), which not only acts as an N2-carrier in the medium but also works as a full-fledged "co-catalyst" along with our active material MnN4 to deliver a high yield of NH3 (328.59 μg h-1 mgcat-1) at 0.0 V versus reversible hydrogen electrode. BF3-induced charge polarization shifts the metal d-band center of the MnN4 unit close to the Fermi level, inviting N2 adsorption facilely. The Lewis acidity of the free BF3 molecules further propagates their importance in polarizing the N≡N bond of the adsorbed N2 and its first protonation. This push-pull kind of electronic interaction has been confirmed from the change in d-band center values of the MnN4 site as well as charge density distribution over our active model units, which turned out to be effective enough to lower the energy barrier of the potential determining steps of NRR. Consequently, a high production rate of NH3 (2.45 × 10-9 mol s-1 cm-2) was achieved, approaching the industrial scale where the source of NH3 was thoroughly studied and confirmed to be chiefly from the electrochemical reduction of the purged N2 gas.

Coordination Symmetry Breaking of Single-Atom Catalysts for Robust and Efficient Nitrate Electroreduction to Ammonia.

Nitrate electrocatalytic reduction (NO3 RR) for ammonia production is a promising strategy to close the N-cycle from nitration contamination, as well as an alternative to the Haber-Bosch process with less energy consumption and carbon dioxide release. However, current long-term stability of NO3 RR catalysts is usually tens of hours, far from the requirements for industrialization. Here, symmetry-broken Cusingle-atom catalysts are designed, and the catalytic activity is retained after operation for more than 2000 h, while an average ammonia production rate of 27.84mg h-1 cm-2 at an industrial level current density of 366mA cm-2 is achieved, obtaining a good balance between catalytic activity and long-term stability. Coordination symmetry breaking is achieved by embedding one Cu atom in graphene nanosheets with two N and two O atoms in the cis-configuration, effectively lowering the coordination symmetry, rendering the active site more polar, and accumulating more NO3 - near the electrocatalyst surface. Additionally, the cis-coordination splits the Cu 3d orbitals, which generates an orbital-symmetry-matched π-complex of the key intermediate *ONH and reduces the energy barrier, compared with the σ-complex generated with other catalysts. These results reveal the critical role of coordination symmetry in single-atom catalysts, prompting the design of more coordination-symmetry-broken electrocatalysts toward possible industrialization.

Construction of a 2D/2D g-C3N5/NiCr-LDH Heterostructure to Boost the Green Ammonia Production Rate under Visible Light Illumination.

Photocatalytic N2 fixation has emerged as one of the most useful ways to produce NH3, a useful asset for chemical industries and a carbon-free energy source. Recently, significant progress has been made toward designing efficient photocatalysts to achieve this objective. Here, we introduce a highly active type-II heterojunction fabricated via integrating two-dimensional (2D) nanosheets of exfoliated g-C3N5 with nickel-chromium layered double hydroxide (NiCr-LDH). With an optimized loading of NiCr-LDH on exfoliated g-C3N5, excellent performance is realized for green ammonia synthesis under ambient conditions without any noble metal cocatalyst(s). Indeed, the g-C3N5/NiCr-LDH heterostructure with 2 wt % of NiCr-LDH (CN-NCL-2) exhibits an ammonia yield of about 2.523 mmol/g/h, which is about 7.51 and 2.86 times higher than that of solo catalysts, i.e., NiCr-LDH (NC-L) and exfoliated g-C3N5 (CN-5), respectively, where methanol is used as a sacrificial agent. The enhancement of NH3 evolution by the g-C3N5/NiCr-LDH heterostructure can be attributed to the efficient charge transfer, a key factor to the photocatalytic N2 fixation rate enhancement. Additionally, N2 vacancies present in the system help adsorb N2 on the surface, which improves the ammonia production rate further. The best-performing heterostructure also shows long-term stability with the NH3 production rate remaining nearly constant over 20 h, demonstrating the excellent robustness of the photocatalyst.

Analysis of the Ammonia Production Rates by Nitrogenase

Ammonia (NH3) is produced industrially by the Haber–Bosch process from dinitrogen (N2) and dihydrogen (H2) using high temperature and pressure with an iron catalyst. In contrast to the extreme conditions used in the Haber–Bosch process, biology has evolved nitrogenase enzymes, which operate at ambient temperature and pressure. In biological settings, nitrogenase requires large amounts of energy in the form of ATP, using at least 13 GJ ton−1 of ammonia. In 2016, Brown et al. reported ATP-free ammonia production by nitrogenase. This result led to optimism that the energy demands of nitrogenase could be reduced. More recent reports confirmed the ATP-free production of ammonia; however, the rates of reaction are at least an order of magnitude lower. A more detailed understanding of the role of ATP in nitrogenase catalysis is required to develop ATP-free catalytic systems with higher ammonia production rates. Finally, we calculated the theoretical maximal ammonia production rate by nitrogenase and compared it to currently used Haber–Bosch catalysts. Somewhat surprisingly, nitrogenase has a similar theoretical maximum rate to the Haber–Bosch catalysts; however, strategies need to be developed to allow the enzyme to maintain operation at its optimal rate.

Transition metal modified 3DOM WO3 with activated N N bond triggering high-efficiency nitrogen photoreduction

Photocatalytic nitrogen fixation is a promising green strategy for ammonia synthesis, yet the high activation energy for nitrogen is the significant limitation to its practical application. Herein, a novel Fe-doped WO3 photocatalyst with three dimensional macroporous (3DOM) structure was designed and prepared. This special photocatalyst not only provides effective adsorption active sites to enhance the chemisorption and activation of N2, but also promotes the charge separation and transfer from catalyst to nitrogen. As a result, the optimized 5% Fe-3DOM WO3 sample achieves excellent ammonia production rate of 60 μmol g−1h−1, ∼30 times higher than that of pure 3DOM WO3. The in-situ DRIFTS results show the existence of several intermediates containing NH bonds during nitrogen reduction. Meanwhile, the density functional theory calculation results show that the presence of Fe promotes the adsorption and activation of nitrogen, and the reaction pathway is biased towards the alternate hydrogenation mechanism.

Potential-Driven Restructuring of Cu Single Atoms to Nanoparticles for Boosting the Electrochemical Reduction of Nitrate to Ammonia

Restructuring is ubiquitous in thermocatalysis and of pivotal importance to identify the real active site, yet it is less explored in electrocatalysis. Herein, by using operando X-ray absorption spectroscopy in conjunction with advanced electron microscopy, we reveal the restructuring of the as-synthesized Cu-N4 single-atom site to the nanoparticles of ∼5 nm during the electrochemical reduction of nitrate to ammonia, a green ammonia production route upon combined with the plasma-assisted oxidation of nitrogen. The reduction of Cu2+ to Cu+ and Cu0 and the subsequent aggregation of Cu0 single atoms is found to occur concurrently with the enhancement of the NH3 production rate, both of them are driven by the applied potential switching from 0.00 to -1.00 V versus RHE. The maximum production rate of ammonia reaches 4.5 mg cm-2 h-1 (12.5 molNH3 gCu-1 h-1) with a Faradaic efficiency of 84.7% at -1.00 V versus RHE, outperforming most of the other Cu catalysts reported previously. After electrolysis, the aggregated Cu nanoparticles are reversibly disintegrated into single atoms and then restored to the Cu-N4 structure upon being exposed to an ambient atmosphere, which masks the potential-induced restructuring during the reaction. The synchronous changes of the Cu0 percentage and the ammonia Faradaic efficiency with the applied potential suggests that the Cu nanoparticles are the genuine active sites for nitrate reduction to ammonia, which is corroborated with both the post-deposited Cu NP catalyst and density functional theory calculations.

Investigation of the thermodynamic analysis of solar Energy-Based multigeneration plant for sustainable multigeneration

Renewable energy-based multigeneration plants are a huge potential to tackle environmental problems and also to the passing of the carbon-free future. The main goal of the present research is to design and examine the combined cycle motivated by solar energy for multigeneration which is power, hydrogen, ammonia, and freshwater generation. The innovative design multigeneration system is made up of a parabolic trough solar collector, a steam Rankine cycle with high and low-pressure turbines, a transcritical Rankine cycle with a carbon-dioxide fluid, a desalination part, a Proton Exchange Membrane electrolysis, and an ammonia reactor. A comprehensive thermodynamic analysis, environmental impact assessment, and exergo-environmental analysis are addressed to determine the performance and carbon dioxide emission reduction of the overall plant. Furthermore, in this planned research, a thorough parametric evaluation is performed to define how the variation of some significant parameters (e.g., ambient temperature, solar radiation, and collector outlet temperature) has an impact on the cycle’s efficiency and useful outputs. The findings of the research analysis indicated that the total net power and hydrogen production capacities are 1654 kW and 0.0025 kgs-1. The irreversibility rate is determined as 7047 kW and the parabolic trough solar collector has the uppermost rate among the components. Furthermore, energetic and exergetic performances of the modeled cycle are computed as 29.04% and 27.43%, respectively. Finally, freshwater and ammonia production rates are determined as 1.182 kgs-1 and 0.004842 kgs-1, respectively.

Enhanced photocatalytic ammonia generation from water and nitrogen by decorating BiOCl nanosheets with CoOOH oxygen evolution reaction cocatalyst

Photocatalytic synthesis of ammonia from N2 and water consists of N2 reduction and water oxidation, but most research is focused only on the N2 reduction. Here, we demonstrated a strategy to improve ammonia generation by enhancing water oxidation through an oxygen evolution reaction (OER) cocatalyst. We employed cobalt oxyhydroxide as an OER cocatalyst for a well-known nitrogen reduction photocatalyst bismuth oxychloride (BiOCl). A series of cobalt-doped BiOCl (Co–BiOCl) nanoplatelets were synthesized through a combination of coprecipitation and hydrothermal synthesis with systematic variation in the percentage of added cocatalyst. The formation of a few atom clusters of cobalt oxyhydroxide was verified via X-ray diffraction, X-ray photoelectron spectroscopy, electron microscopy, Raman, and infrared spectroscopy. A 4.6-fold improvement in the ammonia production rate was realized with 5% Co–BiOCl. OER from water using Co–BiOCl was performed and correlated well with the ammonia generation. Enhancing water oxidation by loading of an OER cocatalyst points a promising and applicable method for better N2 fixation photocatalyst design.

Controlled Growth of the Interface of CdWOx/GDY for Hydrogen Energy Conversion

AbstractDirectly extracting hydrogen energy from water in one device to achieve sustainable hydrogen energy generation‐conversion‐electricity storage system is an ideal major step forward for enabling a zero‐pollution, hydrogen‐fueled economy. The new concept of hydrogen energy conversion can be enabled by spontaneous reduction of nitrate to ammonia driven by potential differences between the well‐matched anode and cathode, leading to the full use of the electrochemical redox reactions to generate electric energy. The hydrogen energy in the acidic electrolyte can be transformed to electric energy with the rationally assembled primary battery, which can simultaneously power the electric devices and produce high value‐added ammonia. The new concept of hydrogen conversion device shows a record‐high specific capacity of 15 500 mA h g–1 and achieves the highest ammonia production rate (149 mmol gcat–1 h–1) and Faradaic Efficiency (99.2%) in acidic electrolytes. This work opens a new direction for hydrogen conversion and utilization which has obvious advantages over lithium and battery solutions.