Abstract
In recent years, the high cost and availability of energy sources have boosted the implementation of strategies to obtain different types of renewable energy. Among them, methane contained in biogas from anaerobic digestion has gained special relevance, since it also permits the management of a big amount of organic waste and the capture and long-term storage of carbon. However, methane from biogas presents some problems as energy source: 1) it is a gas, so its storage is costly and complex, 2) it is not pure, being carbon dioxide the main by-product of anaerobic digestion (30%–50%), 3) it is explosive with oxygen under some conditions and 4) it has a high global warming potential (27–30 times that of carbon dioxide). Consequently, the conversion of biogas to methanol is as an attractive way to overcome these problems. This process implies the conversion of both methane and carbon dioxide into methanol in one oxidation and one reduction reaction, respectively. In this dual system, the use of effective and selective catalysts for both reactions is a critical issue. In this regard, nanomaterials embedded in metal organic frameworks have been recently tested for both reactions, with very satisfactory results when compared to traditional materials. In this review paper, the recent configurations of catalysts including nanoparticles as active catalysts and metal organic frameworks as support materials are reviewed and discussed. The main challenges for the future development of this technology are also highlighted, that is, its cost in environmental and economic terms for its development at commercial scale.
Introduction
In last years, the recent increase in the cost and scarcity of traditional energy sources has boosted the interest in renewable energy sources. Among them, anaerobic digestion of organic waste has gained especially interest among researchers, public administrations, and private companies (Lora Granado et al., 2017). The main advantages of anaerobic digestion are the worldwide availability of organic wastes and the low environmental impact of this technology when compared with other management strategies such as landfill (Mondello et al., 2017) and even composting, especially in energy terms (Colón et al., 2012).
Anaerobic digestion is a natural process that results in the production of biogas that can be a useful source of renewable energy. The production of methane from biogas has been reviewed from the point of view of operational strategies (Komilis et al., 2017) and the use of additives to increase the amount of biogas and its content in methane (Barrena et al., 2022). Methane, being the major component of natural gas, is a useful renewable source of energy when it comes from biogas. However, methane, to be used, presents several challenges: 1) being a gas, its storage requires high volumes, 2) it is not pure, being carbon dioxide the main by-product of anaerobic digestion (30%–50%), with other tracer gases like nitrogen or hydrogen, which are not a problem for biogas uses, being the most dangerous and undesirable hydrogen sulphide (Yuan Chen et al., 2015; Wang et al., 2019; Vu et al., 2022) 3) it is explosive and flammable with oxygen under some specific conditions, which are relatively low concentrations of methane (within 9%–15%), although other factors such as the geometry of pipelines is crucial (Kundu et al., 2016) and 4) it has a high global warming potential (27–30 times of that of carbon dioxide, approximately) (USEPA, 2022). Another point important to mention is that the contents of biogas and the relative percentage of its main gases (methane and carbon dioxide) can change as a result of the waste composition (Herout et al., 2011), the conditions of anaerobic digestion (Sołowski, 2022) and the use of some additives (Cerrillo et al., 2021). All these factors must be carefully considered when methane and carbon dioxide are intended to be transformed into methanol.
To overcome these problems, several strategies have been proposed, but the only one that can give a positive solution to all these challenges in the full conversion of biogas (including methane and carbon dioxide) into methanol (Figure 1). Methanol is liquid at ambient conditions, easy to transport and use as source of energy and a starting chemical for the synthesis of other more complex organic materials (Zhang et al., 2019; Pawelczyk et al., 2022).
FIGURE 1
However, the conversion of the main compounds of biogas into methanol is not straightforward. On one hand, it implies the oxidation of methane to methanol, an exothermic oxidation reaction that needs very selective catalysts to avoid the formation of typical undesirable by-products from the combustion of methane: carbon dioxide and carbon monoxide (Zacaria and Kamarudin, 2016). One the other hand, the conversion of carbon dioxide to methanol is a hydrogen consuming reduction that needs effective catalysts that provide mild conditions in terms of temperature and pressure to be profitable in terms of economic cost and environmental impact, although the reaction is thermodynamically favourable (Zain and Mohamed, 2018). Finally, biogas is not pure, as it contains some compounds that could harm the catalyst, especially hydrogen sulphide (Wang et al., 2019).
The main objective of this paper is to give a general perspective of the overall conversion of biogas to methanol. Methanol can be used as a source of renewable energy that can be easily stored, transported and used, which gives it important advantages when compared to biogas. However, there are several shortcomings and challenges that hampers the implementation of this conversion, especially at full scale. This paper compiles the main advances and challenges in the development of new catalysts based on nanoparticles (NP) immobilized in metal organic frameworks (MOF) to improve the conversion of biogas to methanol.
Chemical reactions
Oxidation of methane to methanol
Conversion of methane into methanol can be achieved through two different routes. The indirect route is a two-step process: 1) partial oxidation or steam reforming of methane to syngas (CO + H2) and 2) catalytic conversion of syngas to methanol. It is known that the steam reforming step is an endothermic reaction (∆H298K0 = +206.2 kJ·mol−1), therefore, this process is extremely energy demanding. To overcome this problem, the direct route based on the conversion of methane to methanol at low temperature has been recently explored (Xie et al., 2018).
Partial oxidation of methane is an energy-saving process that converts methane to partially oxidized compounds such as methanol, formic acid or formaldehyde. This route is thermodynamically favorable and uses oxygen as oxidant (Eq. 1). Although oxygen is the oxidant used in practically all the cases, water vapor at high temperature and pressure has been also explored (Khirsariya and Mewada, 2013).
Regarding this direct route, different works have been published regarding its main drawback: overoxidation of methane to carbon monoxide and/or carbon dioxide. The main strategies involve the use of selective catalysts such as different types of zeolites working at low temperature resulting in moderate conversions (Tomkins et al., 2017) and the activation of methane in a liquid phase using H2O and H2O2 as oxidants (Hammond et al., 2012; Sushkevich et al., 2017). However, as explained later, selected NP and MOF offer a promising alternative for the direct route to convert methane into methanol, with high selectivity.
Reduction of carbon dioxide to methanol
Carbon capture and utilisation has the objective to transform carbon dioxide into useful products such as chemical feedstock and renewable fuels (Saeidi et al., 2021). Specifically, this paper focuses on the catalytic hydrogenation of carbon dioxide, since it is considered as the most used and simplest process (Li and Tsang, 2018). Several chemical products can be obtained from carbon dioxide hydrogenation, being methanol the most common. In the past decades, several routes have been proposed and industrially exploited for the synthesis of methanol using heterogeneous catalysts such as Cu, Cr, and Zn oxides, which typically need high pressure and low temperature (Ertl et al., 2008), Currently, the Cu/ZnO/Al2O3 catalyst is the most used material for the conversion of carbon dioxide to methanol.
The hydrogenation of carbon dioxide to methanol consists of two main competing reactions. The first is the methanol synthesis from carbon dioxide and hydrogen (Eq. 2):
The second reaction is the reverse water-gas shift reaction that produces carbon monoxide (Eq. 3):
Furthermore, catalytic hydrogenation of carbon dioxide to methanol can also occur indirectly from carbon monoxide formed through the previous reaction (Eq. 4).
As observed, the increase of pressure and the decrease of temperature will shift the reaction towards the products.
Among the different options of catalyst, copper is economically favourable. For the methanol synthesis through the hydrogenation of carbon monoxide and carbon dioxide, special emphasis on copper metal acting as the active phase and zinc oxide as the active promoter has been reported (Álvarez et al., 2017). This catalyst reduces the pressure up to 50–100 bar, while methanol selectivity is around 50%. In fact, bimetallic catalysts permit a change in the adsorption properties of metal surfaces, leading to an improved catalytic yield (Li and Tsang, 2018). Other examples of catalysts such as Pd-Zn and Pd-Ga (Collins et al., 2012) or Cu-Ni and Ga-Ni (Studt et al., 2014) have been proposed. Among them, Pd-Zn based catalysts can act as an unusually high kinetic barrier for Eq. 2 under low pressure conditions (20 bar). Another important issue in this conversion is the catalytic yield. To obtain acceptable values, several types of supports are used to increase the adsorption capacity of the active surfaces and to increase the surface area. Regarding supports, capping agents are probably the most used (Javed et al., 2020) with abundant examples of zeolite, activated carbon and alumina (Choi et al., 2009; Alonso et al., 2017; Carrasco-García, 2022).
At the same time, carbon dioxide presents two points that make its conversion into methanol less favourable than that of methane: 1) it has a much lower global warming potential, 2) biogas contents more methane than carbon dioxide and 3) chemically, its conversion presents less favourable conditions and needs hydrogen. Therefore, a rigorous sustainable assessment (environmental and economic) should be performed to consider the entire conversion of biogas into methanol or the sole conversion of methane.
Integration of both reactions
Figure 2 explains a proposal for the integrated conversion of biogas to methanol, including all the required steps. Although the core of Figure 2 is the conversion of biogas into methanol using NP and MOF and will be discussed in the next point, two other pretreatment steps should be highlighted.
FIGURE 2
The first one is not represented and Figure 2 and may be optional, but it is critical for the next catalytic steps. A problem often not considered is the presence of water vapour in biogas. Although not being a product of anaerobic digestion of organic waste, biogas can be easily water-saturated (Petersson and WellinGer, 2018). The removal of water from the biogas stream can be easily achieved by cooling, compression, absorption or adsorption. This removal is critical because of several reasons: water may condensate in gas pipelines and cause corrosion, it causes damage to the catalysts and supports, it participates in some secondary reactions, thus altering kinetics and possible equilibria, and it hampers some biogas upgrading strategies (Duran et al., 2018).
Removal of biogas contaminants
The second important pretreatment is the removal of hydrogen sulphide from biogas. Hydrogen sulphide is inherently produced in the anaerobic digestion of organic waste (Vu et al., 2022) and it is a problematic impurity that can inhibit methanogenesis and cause equipment corrosion. Regarding the catalytic conversion of biogas to methanol, hydrogen sulphide and, in general, sulphur compounds, are one of the main chemicals provoking the poisoning of heterogeneous catalysts (Wachter et al., 2021). Traditionally, the use of iron-based formulations have been used for the total and partial removal of hydrogen sulphide in biogas (Magnone et al., 2018; Persson et al., 2021). However, emerging strategies using other approaches have been recently published. They are summarized in Table 1, where adsorption and biological treatments are predominant. It also worthwhile to mention that studies from various groups are focused on other detrimental gases found in biogas such as siloxanes (Yang and Corsolini, 2019; Piechota, 2021).
TABLE 1
| References | Strategy | H2S removal |
|---|---|---|
| Su and Hong (2020) | Photocatalytic UV module with TiO2 coated light-expanded clay | ≥99% |
| Gasquet et al. (2021) | Sewage sludge ash with activated carbon | 10%–50% |
| Okonkwo et al. (2020) | Sterically hindered amine adsorbents | ≥99% |
| Bahraminia et al. (2020) | Ion-exchanged nanostructured zeolite for fueling solid oxide fuel cells | ≥90% |
| Thanakunpaisit et al. (2017) | Laterite materials as adsorbent | ≥90% |
| Díaz et al. (2010) | Pure oxygen, air and nitrate as oxidant reactives directly supplied to the biodigester | ≥99% |
| Das et al. (2022) | Simultaneous removal of H2S and NH3 in hollow fibre membrane bioreactors | ≥99% |
| López et al. (2016) | Aerobic biotrickling filter through a multi-step oxidation mechanism | ≥90% (at very high concentrations of 2000–10000 ppmv) |
| Andreides et al. (2021) | Microaerobic sequencing batch reactor | ≥90% |
| Montebelo et al. (2022) | Aerobic and anoxic biotrickling filters | ≥90% (depending on the loading) |
| Kumar Gupta et al. (2022) | Metal-organic framework-derived NaMnxOy hexagonal microsheets | Practically 100% at high concentrations |
Compilation of some recent strategies for the removal of hydrogen sulphide from biogas.
In general, all these strategies presented need to be carefully considered, as the effect of hydrogen sulphide on sophisticated high-cost catalyst based on NPs and MOF can limit the implementation of the entire process (Figure 2).
New catalysts: Nanoparticles and metal-organic frameworks
Traditional catalysts
Zeolite, in its different configurations, has been the traditional catalyst used in the conversion of methane and carbon dioxide to methanol. In 1997, Kudo and Ono investigated the catalytic activity of ZSM-5 as the first zeolites used for the partial oxidation of methane (Kudo and Ono, 1997). The maximum selectivity for methanol was not more than 10% and the major product of the catalysis was carbon dioxide with a selectivity of more than 80% at 0.01 bar methane partial pressure and 600°C–700°C after 1 h. Afterwards, over the last decade, copper-exchanged zeolites are the ones that have been more extensively studied (Zhu et al., 2020; Yu et al., 2021). In this case, and although better results have been obtained in terms of conversion and selectivity (more than 90% in both parameters), a major issue is the use of high temperatures up to 600°C (Michalkiewicz, 2004).
Methane to methanol
It is important to mention that, in this reaction, the use of nanomaterials has been widely reported without using MOF as support material. In this sense, zeolite and graphene have been the most widely used supports, apart from MOF (Lewis et al., 2019; Wang et al., 2022). With these supports, some excellent results in terms of conversion and selectivity have been obtained, although graphene and graphene oxide are the most promising ones (Impeng et al., 2014; Impeng et al., 2015; Shan et al., 2017; Sahoo et al., 2018; Yuan et al., 2018; Chang et al., 2020; Sirijaraensre and Limtrakul, 2022).
The hypothesis on which these results rely is the fact that these supports can mimic methane monooxygenases, which is also the case of MOF. Methane monooxygenases from methanotrophic bacteria convert methane to methanol under ambient conditions due to their ability to control the transport of oxygen and methane to the active site. In fact, hydrophobic cavities in methane monooxygenases act as an access gate to oxygen and methane in their way to the active site via a hydrophobic passage. Then, the activation of the oxygen in the metal centre of the monooxygenase proteins leads to the formation of an oxidative intermediate being able to perform the cleavage of the strong C-H bonds of methane (Sirajuddin and Rosenzweig, 2015). When these enzymes rearrange their conformation, cavities dissociate from each other resulting in the blockage of the hydrophobic passage and consequently restricting back diffusion and overoxidation of methanol while simultaneously opening separated hydrophilic pores for methanol to be released. This biological system has an extraordinary high selectivity to methanol and permit the control of mass transfer to and from the active sites. Therefore, it can be concluded that the presence of a hydrophobic cavity in the proximity of catalytic sites could lead to a higher affinity towards methane than methanol (Ikbal et al., 2019).
In
Table 2, a summary of some representative studies recently reported with the combined use of NP and MOF for the conversion of methane into methanol is presented.
Table 2is not an exhaustive compilation of the totality of papers published on this topic, since each month new materials appear. However, it is useful for the reader to have a general perspective about the main materials used and their main challenges for a full implementation:
1) There is a wide diversity of materials used, both for NP and MOF. In the case of NP, it is important to note that noble metals can be substituted by low-cost metals such as Cu and Fe, an important issue when comparing with traditional catalysts. In the case of MOF, these are complex structures, which requires laborious synthesis protocols and a rigorous MOF characterization to have reproducible and reliable materials (Rogge et al., 2021).
2) Apart from the products coming from the overoxidation of methane, other side products can be obtained, such as ethanol or acid acetic (Xia et al., 2022), Obviously, the formation of these compounds decreases the selectivity towards methanol; however, they can also be considered products of interest.
3) Reactions conditions are variable, but generally in the mild range: temperature ranges between 50°C and 200°C and there are some works performed at atmospheric pressure. The maximum pressure is around 20 bar. This presumes an important economic issue, with some research focused on it. For instance, Hall and Bollini (2020) performed the reaction using tri-iron nodes in a MOF material at low temperatures (between 100°C–200°C) and even sub-ambient pressures. Room temperature has been also successfully checked with the help of photocatalysis (An et al., 2022).
4) MOF can catalyst the reaction without NP, which is an unexpected result that needs further research (Imyen et al., 2020). Apart from the obvious role of MOF as a support of NP to anchor the active site and to permit the diffusion of reactants and products, the conclusion is that a control with only MOF is necessary. However, no information about the mechanisms of this effect of MOF has been found in literature.
5) Mechanisms are not often clear, but the hypothesis of hydrophobic cavities are suggested in some studies.
TABLE 2
| References | Nanoparticle and metal-organic framework | Conversion/selectivity (%) |
|---|---|---|
| Osadchii et al. (2018) | Fe atoms in Al-based MOF | Both very high (>90%) |
| Ren et al. (2021) | Cu oxides clusters in UiO-bpy channels | Both very high (>90%) |
| Xia el al. (2022) | Pt and polyoxometalate in UiO-67 MOF | High (>90%)/low (17%) |
| Yang el al. (2019) | Ir in Cu-BTC MOF | Both very high (>90%) |
| Xu et al. (2021) | Au-Pd nanoparticles in ZIF-8, Zn (2-methylimidazole) | Both high (>80%) |
| Baek et al. (2018) | Cu in MOF-808 using different ligands | Both high (>90%) depending on the ligand |
| Ikuno et al. (2017) | Cu-Oxo dimers in NU-1000 MOF | High (>90%)/medium (47%) |
| Hall and Bollini (2020) | Fe2+ active sites in MIL-100 MOF | Both very high (>90%) |
| Imyen et al. (2020) | No NP, simultaneous MOF and zeolites (Fe-ZSM-5@ZIF-8) | Both very high (>90%) |
Methane to methanol processes using nanoparticles and MOF.
In summary, catalysts based on NP and MOF seem to be a very promising option when compared to traditional ones in terms of conversion and selectivity. However, all the studies consulted are carried out at lab scale, with some milligrams of MOF (Table 2). It is mandatory to scale-up the synthesis of MOF. Another important point that is not often considered is the long-term operation of these novel catalysts and their reuse, two critical points that also needs further research.
Carbon dioxide to methanol
In this case, the number of studies is more limited. It is evident that, thermodynamically, this reaction is not favourable unless high pressures of hydrogen are used. Moreover, in kinetic terms, the possibilities of other secondary reactions is highly-dependent on the conditions used. In
Table 3, some works reported for the conversion of carbon dioxide into methanol with the combined use of NP and MOF are presented. Again, the main conclusions that can be extracted from
Table 3are:
1) In general, the number of works published is much lower than those related to conversion to methane to methanol, which implies that the diversity of materials used for both NP and MOF synthesis in relatively scarce. Among them, Pt, Cu, and TiO2 are the main NP used, whereas most of the MOF are based on Zr.
2) There are some important variations of the catalyst process. For instance, not all the studies are carried out in gas phase, having aqueous solution and dissolved products a relative presence. Moreover, photocatalytic processes (visible light) are practically the half of the recent studies.
3) Efficiency is typically high but selectivity presents a feature that is worthy to mention. In some works, selectivity does not reach values higher than 90%, but the cause is that other products of interest apart from methanol are also the objectives of the study. This is the case of formic acid, formaldehyde, ethanol, and methane, among others in less proportion.
4) Contrarily to the conversion of methane to methanol, there are scarce references on the mechanisms of these reactions, especially in the case of gas-phase conditions. For instance, Duma et al. (2022) reports the results using copper-zinc bimetallic catalysts supported on a Zirconium-based MOF, where using advanced techniques they revealed the presence of copper active sites after impregnation and thermal activation. In general, research is clearly focused on having highly active sites to destabilize the molecules of carbon dioxide and hydrogen, where Ni, Co, Ru, Rh, and Pd are the most used materials (Cheng et al., 2021). To my knowledge, the most complete mechanism to date for the conversion of carbon dioxide to methanol/ethanol mixtures is presented by An et al. (2019) using Cu NP on a zirconium-based MOF. In this case, a complete mechanism is presented: the catalytic cycle is likely to proceed via bimetallic oxidative addition to activate hydrogen followed by hydrogenating carbon dioxide to methanol, and then coupling of methanol and formyl species to form C2 oxygenates. In other different conditions, MOF can be employed for the electrochemical reduction of carbon dioxide to methanol, where redox electrocatalysts is used to lower the kinetic barriers and give the higher reaction efficiency. In this case, MOF are hybrid materials that are made up of three components: a metallic component, pore space and the organic linker, which are the sites attributed to the catalytic activity of the MOF (Fayez Nasir et al., 2018).
5) Working conditions are mild. Temperature from 80°C to 200°C are reported, whereas pressure is around 5–10 bars.
TABLE 3
| References | Nanoparticle and metal-organic framework | Conversion/selectivity (%) |
|---|---|---|
| Olsbye et al. (2020) | Pt in UiO Zr-MOF | High (>90%)/medium (around 50%) |
| Gutterød et al. (2020) | Pt embedded in Zr-based UiO-67 MOF | Both high (>90%) |
| Zhao et al. (2019) | Cu/Zn/Al derived from layered double hydroxide/MOF composites | Both high (>90%) |
| Han et al. (2022) | Cu@ZrO2 derived from Zr-MOF | Both high (>90%) |
| Aadil et al. (2022) | Several NP in TiO2– and MOF–based nanocomposites | Wide range of results |
| Alqarni et al. (2022) | Zr-MOF metallated with Ru, Rh, Pd, and In | Wide range of results |
| Nagababu et al. (2021) | TiO2 on synthesized MOFs (Cu-BTC-MOF and Ni-BTC-MOF) | Both high (>90%) |
| Rayder et al. (2021) | Ru complex encapsulated in MOF UiO-66 | Both high (>90%) |
| Cardoso et al. (2018) | MOFs based on ZIF-8 deposited on TiO2 nanotubes | High (>90%)/medium (around 50%) |
| Mangal et al. (2016) | TiO2 in copper-based MOF Cu3BTC2 | Both high (>90%) |
| Maina et al. (2017) | TiO2 and Cu-TiO2 in zeolitic imidazolate framework (ZIF-8) | Both high (>90%) |
| An et al. (2017) | Cu/ZnOx ultrasmall NP in UiO-bpy MOFs | Both high (>90%) |
Carbon dioxide to methanol processes using nanoparticles and MOF.
To sum up, the use of NP and MOF for the conversion of carbon dioxide to methanol is still in an embryonic stage of research, and some questions about mechanisms and production of several compounds needs to be assessed. Again, most of the studies reported are carried out at lab scale or with small quantity of catalyst (Table 2) and the process scale-up is an important challenge to develop this technology. Long-term operation and reuse should be also considered in new publications, as they are very scarce in literature. Very recently, Lu et al. (2022) have used the term “reusable MOF” in scientific literature. Although it is not applied for the reactions discussed in this study, they appear as a very flexible and low-cost material for a lot of organic reactions.
A critical issue that can be applied to both reactions is the absence of economic data of the catalysts cost and its potential benefits to transform biogas into methanol. This is especially important as it hampers the implementation of this strategy at full-scale. Recently, some preliminary works have presented some techniques to synthetize these catalyst in a low-cost protocol (Duan et al., 2020; Ghorbani-Choghamarani et al., 2021; Kumari et al., 2021), but it is evident that other essential data are still unavailable to present a preliminary economic assessment.
Conclusion
In the current situation of energy scarcity and availability, it is evident that biogas from the anaerobic digestion of organic waste will have a key role in the development of easily and locally available low-impact renewable energy sources. Biogas can be used directly in cogeneration units, upgraded to methane and injected in the existing natural gas network or, taking a step forwards on that point, converted into methanol. Using this strategy, several problems of methane are overcome, but the need of effective and selective catalysts for all the chemical reactions involved is a critical issue. In this sense, nanomaterials embedded in metal organic frameworks provide very satisfactory results. It is evident that this field needs further research, but the results are promising. On the things-to-do side, the main challenges for the future development of this technology is its full-scale implementation and a complete economic assessment, which considers both the catalysts cost and the benefits of the conversion of biogas into methanol.
Statements
Author contributions
All authors listed have made a substantial, direct, and intellectual contribution to the work and approved it for publication.
Funding
This research was funded by Fundación Ramón Areces, in the hallmark of the META2NOL project granted in the XIX national call of life and matter sciences projects, grant number CIVP19A5952.
Conflict of interest
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Publisher’s note
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Summary
Keywords
biogas, metal organic framework, methanol, nanoparticles, carbon dioxide, carbon storage, energy storage
Citation
Sánchez A (2022) Biogas improvement as renewable energy through conversion into methanol: A perspective of new catalysts based on nanomaterials and metal organic frameworks. Front. Nanotechnol. 4:1012384. doi: 10.3389/fnano.2022.1012384
Received
05 August 2022
Accepted
26 September 2022
Published
11 October 2022
Volume
4 - 2022
Edited by
Dr. Surender Kumar, Advanced Materials and Processes Research Institute (CSIR), India
Reviewed by
Dr. Swati Dubey, Samrat Ashok Technological Institute, India
Viplov Chauhan, Jawahar Navodaya Vidyalaya, Aurangabad, India
Archana Charanpahari,India
Divyaratan Kumar, Linköping University, Sweden
Updates
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© 2022 Sánchez.
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*Correspondence: Antoni Sánchez, antoni.sanchez@uab.cat
This article was submitted to Nanotechnology for Energy Applications, a section of the journal Frontiers in Nanotechnology
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