Sustainable Energy Production Research Articles

Group-IV Pentaoctite: A New 2D Material Family

Abstract This study investigates the structural, mechanical, and electronic properties of novel two-
dimensional (2D) pentaoctite (PO) monolayers composed of group-IV elements (PO-C, PO-Si, PO-
Ge, and PO-Sn) using first-principles calculations. Stability is explored through phonon spectra and
ab initio molecular dynamics simulations, confirming that all proposed structures are dynamically
and thermally stable. Mechanical analysis shows that PO-C monolayers exhibit exceptional rigidity,
while the others demonstrate greater flexibility, making them suitable for applications in foldable
materials. The electronic properties show semimetallic behavior for PO-C and metallic behavior for
PO-Si, while PO-Ge and PO-Sn possess narrow band gaps, positioning them as promising candi-
dates for semiconductor applications. Additionally, PO-C exhibits potential as an efficient catalyst
for the hydrogen evolution reaction (HER), with strain engineering further enhancing its catalytic
performance. These findings suggest a wide range of technological applications, from nanoelectronics
and nanomechanics to metal-free catalysis in sustainable energy production.

Predicting the Electrical Behavior of Colored Photovoltaic Modules Integrating Absorptive or Diffusive Layers or PMMA Films Doped with Organic Chromophores

The advancement of photovoltaic (PV) technology is critical for sustainable energy production, with silicon‐based solar cells being the most prevalent due to their efficiency and cost‐effectiveness. In recent years, the use of materials to change the color of conventional silicon‐based PV cells, materials that can be laminated or not during the construction of the PV module, has become widespread. Colored PV cells offer aesthetic versatility, making them suitable for integrated architectural applications. However, these materials affect the performance of the final product. This study focuses on developing a predictive model for the performance of colored silicon PV cells. A comprehensive approach combining experimental data and computational simulations is employed to understand the impact of various colors on the electrical performance of colored PV modules, based on the optical properties of the colored layers. The model demonstrates high accuracy across a range of coloring technologies, including selective absorbers, diffusive layers, and fluorescent materials. The developed model accurately predicts the performance metrics of colored PV cells, providing valuable insights for optimizing design and material selection.

Novel Single Perovskite Material for Visible-Light Photocatalytic CO2 Reduction via Joint Experimental and DFT Study.

Developing advanced and economically viable technologies for the capture and utilization of carbon dioxide (CO2) is crucial for sustainable energy production from fossil fuels. Converting CO2 into valuable chemicals and fuels is a promising approach to mitigate atmospheric CO2 levels. Among various methods, photocatalytic reduction stands out for its potential to reduce emissions and produce useful products. Here, novel perovskite ZnMoFeO3 (ZMFO) nanosheets are presented as promising semiconductor photocatalysts for CO2 reduction. Experimental results show that ZMFO has a narrow bandgap, exceptional visible light response, large specific surface area, high crystallinity, and various surface-active sites, leading to an impressive photocatalytic CO2 reduction activity of 24.87 µmolg-1h-1 and strong stability. Theoretical calculations reveal that CO2 conversion into CO and CH4 on the ZMFO surface follows formaldehyde and carbine pathways. This study provides significant insights into designing innovative perovskite oxide-based photocatalysts for economical and efficient CO2 reduction systems.

Fostering regional intelligence from the ground up: a selection of case studies from EU projects

This paper argues that sustainable development and regional intelligence can be markedly advanced through the strategic application of bottom-up initiatives, emphasizing participatory vision setting, collaborative production, and resource acquisition via crowdfunding and cooperatives. The study explores how these components are practically implemented within the context of three HORIZON2020 EU projects spanning the period from 2019 to 2024: citizen science hubs, makerspaces, and community bioenergy initiatives. By examining these projects, the paper identifies and analyzes the key elements of regional intelligence that are strengthened through bottom-up approaches. Qualitative analysis reveals that community-based initiatives grounded in citizen science principles play a pivotal role in enhancing citizen trust, transparency, and public engagement. The establishment of citizen science hubs facilitates inclusive decision-making processes and empowers local communities to actively participate in scientific endeavors, thereby fostering a deeper integration of local knowledge into regional development strategies. Moreover, makerspaces, as platforms for collaborative production, promote principles of the circular economy by encouraging resource reuse and promoting sustainable manufacturing practices. They also serve as catalysts for user-driven innovation, facilitating the creation of customized solutions tailored to local needs. Finally, community-driven bioenergy initiatives contribute to sustainable energy production, diversify energy sources, reduce fossil fuel dependency, and enhance regional resilience. Cooperatives play a crucial role in improving organizational efficiency and sustainability, enabling local stakeholders to scale initiatives, maximize impact, and promote equitable distribution of benefits, fostering social cohesion and inclusivity. The findings underscore the critical importance of bottom-up strategies in advancing sustainable development goals through increased regional intelligence. By integrating these initiatives into regional policies and practices, policymakers can leverage local knowledge and resources to address complex challenges, promote innovation, and build resilient, inclusive communities capable of navigating future challenges.

ZIF-67 derived N doped carbon embedded CoxP for superior hydrogen evolution

Abstract Developing a sustainable non-noble hybrid electrocatalyst for effective electrocatalysis is the most crucial task; particularly in sustainable hydrogen energy production in the realm of energy conversion. In this work, effective thermal pyrolysis process followed by phosphorization strategy was employed to prepare and fabricate ZIF-67 (Zeolitic imidazole) assisted Co2P/N doped carbon electrocatalyst for hydrogen evolution reaction (HER). The optimized Co2P/N–C electrocatalyst exhibited hollow porous nanostructures as confirmed from the scanning electron microscopy. The achieved porous nanostructure improved the efficiency of the charge and mass transportation which is confirmed by the BET analysis, has high surface area value of 94.731 m2/g. In addition, a transition metal atom can regulate reactants adsorption and desorption capacity by modulating Co and P electronic configuration. The electrochemical studies of fabricated ZIF-67 derived Co2P/N–C electrode were analyzed using 1.0 M alkaline potassium hydroxide (KOH) medium in 3 electrode system process. Whilst, optimizing the pyrolysis temperature during the phosphorization will remarkably enhance the favourable characteristics of the hydrogen generation. Notably, the optimized ZIF-67 derived Co2P/NC at 350 °C electrode exhibited low overpotential (135 mV) at minimum 10 mA/cm2 and low 120.3 mV/dec Tafel slope. Besides, electrode stability at 10 mA/cm2 current density was verified by chronoamperometry test. Hence, this study furnishes the potential technique for the development of advanced hybrid MOF electrocatalyst as a successful alternative on large scale.

Bioenergy products sequestration proportions among three mixotrophically cultivated microalgae by remediating two organic waste resources

In this study, three microalgae species were cultivated using dairy and fish wastewater: Haematococcus pluvialis, Coelastrella saipanensis, and Chlorella sp. The process involved manipulating various physicochemical conditions, to determine optimal growth parameters. Our evaluation considered cell count, biomass productivity, specific growth rate, pigments, carbohydrates, proteins, lipid compositions, and cellulose stored in microalgae. A significant observation of highest cellulose accumulation was recorded in C. saipanensis cultivated in dairy waste (DW) medium (2.54 ± 0.042 µg/mg). In contrast, the species grown in fish waste (FW) media recorded a lower level (0.9405 ± 0.06 µg/mg) of cellulose. In DW, H. pluvialis and C. saipanensis accumulated substantial amounts of astaxanthin and carotenoid, respectively. Carbohydrate, protein, and lipid accumulation was maximized in DW culture, with H. pluvialis exhibiting a more incredible carbohydrate content. Lipid analysis showed as Chlorella sp. was capable of accumulating alpha-linolenic acid. The disparity may be attributed to DW’s nutritional and mineral content, which encourages cellulose deposition. The FTIR analysis confirmed the accumulation of cellulose. These findings underscore the potential of DW and FW media as valuable resources for microalgal biofuel and ethanol production, offering a hopeful future for sustainable energy production.

Amorphous silica production from Colombian rice husk: demonstration in scaled-up process Products

Introduction: the agroindustry generates significant waste, posing environmental, health, and economic challenges. Among these, rice husk, a byproduct of the food industry, stands out due to its potential as a source of silicon. Due to its silicon content, rice husk offers a unique opportunity for sustainable energy production and the extraction of high-value products, such as amorphous silicon dioxide (SiO2). However, optimizing processes for its efficient conversion remains a challenge.Objective: the aim of this study was to optimize the nitric acid concentration for the pretreatment of Colombian rice husk in order to produce high-purity amorphous SiO2 and demonstrate the feasibility of scaling up the process.Methods: a two-stage process was developed, which involved treating rice husk with nitric acid, followed by calcination at 620 °C. The nitric acid concentration was optimized to achieve the highest SiO2 purity. Material characterization was performed using thermogravimetric analysis (TGA), X-ray diffraction (XRD), X-ray fluorescence (XRF), and nitrogen adsorption-desorption. To assess the scalability of the process, the treatment was replicated on a larger scale using the optimized acid concentration.Results: the optimized process using a nitric acid concentration of 0.2 M yielded amorphous SiO2 with a purity of 94.9% and a surface area of 298 m²/g. When scaled up, the process achieved SiO2 with a purity of 95.5%, confirming the feasibility of the methodology for industrial applications. Conclusions: the treatment of rice husk with nitric acid followed by calcination proves to be an effective and scalable approach for producing high-purity amorphous SiO2. This process not only holds potential for industrial applications but also provides a sustainable solution for valorizing agroindustrial waste, contributing to the circular economy.

A De Novo Auto-Activated Solar-Driven Biohybrid System for Hydrogen Production in Methanotrophic Cells.

Climate change driving by greenhouse gas emissions from petroleum-based energy has garnered significant attention. Renewable energy production via a sustainable system that integrates the cell factory and visible-light-driven photocatalysts offers a novel approach for upcycling methane and addressing global energy challenges. Here, an auto-activated biohybrid system driven by solar energy is developed for converting methane into hydrogen fuel, which incorporated thienoviologen (S-MV2+) and genetically engineered methanotrophic bacteria. In this system, S-MV2+ functioned as photosensitizer and electron mediator, capturing solar energy and supplying electrons for an enzyme-catalyzed bioprocess. The genetically modified Methylomicrobium buryatense 5GB1 mutant, lacking methanol dehydrogenase but overexpressing hydrogenase, is able to convert methane into methanol that maintains the electron flow cycle by quenching photogenerated holes for both hydrogen biosynthesis and methane oxidation. Finally, the highest H2 production of 272.96 µM from this biohybrid system was achieved with methanol as a sacrificial agent generated by the H2-producing mutant, resulting in a 140-fold enhancement. This innovative method showcases the potential of coupling photocatalysis with methanotrophic biocatalysis for sustainable energy production. Additionally, the system introduces a new strategy for self-regeneration of sacrificial agents, offering a promising avenue for hydrogen production using greenhouse gases in an eco-friendly manner.

In situ formation of oxygen-deficient WO3-x nanosheets for enhanced photocatalytic activity in water splitting and plastic reforming

Photocatalytic pathways are essential for the sustainable production of chemicals and fuels, pivotal for achieving a pollution-free planet. Electron-hole recombination is a critical problem that has, so far, limited the efficiency of the photocatalytic materials. Here, oxygen-deficient WO3-x nanosheets were in situ grown in a polymeric carbon nitride (PCN) support during the thermal polycondensation of melamine. The introduction of defect in WO3-x, accompanied by spin polarization and the formed WO3-x/PCN heterostructure, greatly accelerated the charge separation and transfer. The synthesized WO3-x/PCN composite exhibited a tenfold increase in hydrogen generation activity than pure PCN under visible-light (420 ≤ λ ≤ 780 nm). The WO3-x/PCN also demonstrated consecutive 24 h and stable photocatalytic H2 production in the aqueous plastic-containing [poly(vinyl alcohol) (PVA), poly(ethylene terephthalate) (PET) and the PET bottle] solutions under visible light. The hydrogen production rates were determined to be 111.2, 50.5, and 7.8 μmol·h−1·g−1 in PVA, PET and PET bottle, respectively. In addition, the oxygen vacancies WO3 with their localized surface plasmon resonance effect, facilitated efficient utilization of NIR photon and the hydrogen evolution rate over WO3-x/PCN reached to 120 μmol h−1·g−1 under NIR light (700 ≤ λ ≤ 780 nm). This research not only advances the potential applications of WO3-x/PCN in sustainable energy production but also provides insights into environmental remediation through the conversion of plastic wastes.

Photothermal-assisted S-scheme heterojunction of NiPS3 nanosheets modified ZnIn2S4 microspheres for promoting photocatalytic hydrogen evolution

Exploring high-efficiency photocatalysts for solar hydrogen (H2) generation through water splitting is of great significance for addressing both energy shortage and environmental contamination. In this work, a facile self-assembly strategy was developed to couple NiPS3 nanosheets (NPS NSs) with ZnIn2S4 (ZIS) microspheres to synthesize NPS NSs/ZIS (NPS/ZIS) composites, featuring a characteristic of S-scheme charge transfer mechanism. The NPS/ZIS composites possess broad-spectrum light absorption property, improved photothermal effect and efficient charge transfer, showcasing exceptional solar-to-chemical energy conversion capability for visible-light-driven photocatalytic hydrogen evolution (PHE). The photothermal effect derived from NPS NSs loading can facilitate charge carrier transfer across the interfaces and surface reaction kinetics. By carefully adjusting the mass ratio of NPS NSs, the optimized 4-NPS/ZIS exhibits excellent stability and significantly improved PHE activity (1827.6 μmol⋅g−1⋅h−1) in water, which is 18.4 times higher than that of bare ZIS (99.4 μmol⋅g−1⋅h−1). Furthermore, the 4-NPS/ZIS also shows the high PHE efficiency of 312.2 μmol⋅g−1⋅h−1 in seawater. Diverse characterization results reveal that the remarkably enhanced PHE performance primarily arises from the synergistic effect of S-scheme heterostructure, heightened light harvesting capacity, and enhanced photothermal effect. On the basis of density functional theory (DFT) simulations and experimental verifications, a possible PHE mechanism via the S-scheme heterojunction with photothermal assistance in NPS/ZIS is proposed. This study serves as inspiration for the development of novel photothermal-assisted S-scheme photocatalysts, paving the way for efficient and sustainable green energy production.

Influence of impurities on the use of Fe-based powder as sustainable fuel.

Sustainable energy production, inherently transient and non-uniformly distributed around the world, requires the rapid development of sustainable energy storage technologies. Recently, pure iron powder was proposed as a high-energy density carrier. While promising, challenges are faced, such as nanoparticle emissions, micro-explosions or cavitation. In this work, a screening of the impact of the most common impurities in iron sources on these mechanisms was conducted through purely thermodynamic simulations. Two idealized models were considered to obtain a range of plausible flame temperatures and emitted gases when considering a purely diffusive regime in standard conditions and stoichiometric air-fuel mixture. The flame temperature and iron evaporation are increasing with the specific energy. A strong evaporation of C, S, Mo, Cu and P is also expected. Most impurities are predicted to decrease cavitation, except for Mn and MnO. The regeneration process by hydrogen-based direct reduction in fluidized bed reactors is also discussed. MgO and CaO are the most promising additions in terms of reducing nanoparticles and porosities, as well as to improve the fluidization and reduction kinetics of the combusted products. The potential of Fe powder as sustainable fuel, already very promising, could be further improved by the addition of selectively chosen impurities.This article is part of the discussion meeting issue 'Sustainable metals: science and systems'.

Efficient Production of Platform Chemicals from Lignocellulosic Biomass by Using Nanocatalysts: A Review

This paper discusses significant advancements in using lignocellulosic biomass for the sustainable production of biofuels and chemicals. As fossil-based resources decline and environmental concerns rise, the paper emphasizes the role of integrated biorefineries in producing renewable liquid fuels and high-value chemicals from biomass. It highlights exploring various green pathways for biomass conversion, with a particular focus on nanocatalysis. Due to their large surface area-to-volume ratio, nanocatalysts provide enhanced catalytic activity and efficiency in biomass transformation processes. The review delves into the synthesis of value-added and furfural platform chemicals alongside the hydrogenolysis of 5-hydroxymethylfurfural (5-HMF) into biofuels like 2,5-dimethylfuran (DMF) and 2,5-dimethyltetrahydrofuran (DMTHF). The paper ultimately underscores the importance of nanotechnology in achieving high yield and selectivity in the biomass conversion process, positioning it as a promising approach for future sustainable energy and chemical production.

DOWN DRAFT GASIFIER TO PRODUCE SYNGAS BY BIO WASTE

Biowaste is a valuable resource for sustainable energy production. Through combustion, it generates thermal energy, while gasification a thermo chemical process which transforms solid fuel into gaseous fuel. This process, specifically through a downdraft gasifier, converts biowaste into a combustible gas known as producer gas. Utilizing biowaste as a fuel source plays a crucial role in reducing dependency on fossil fuels, providing a renewable, low-carbon energy alternative. Combining biowaste with other renewable sources like wind and solar power is an effective solution for small-scale, decentralized power generation. This approach not only meets local electricity needs but also supplies heat for rural development. Optimizing operating conditions and methodologies for maximum syngas production in biomass gasification is essential. The gasification system designed here includes a downdraft biomass thermo chemical conversion gasifier, a gas transport line with tar removal, and a fully enclosed combustion chamber—together, forming a robust setup for efficient, clean energy production. KEY WORD: Downdraft gasifier, biowaste, gasification, pyrolysis, syngas

Converting lignocellulosic biomass into valuable end products for decentralized energy solutions: A comprehensive overview

This review manuscript delves into lignocellulosic biomass (LCB) as a sustainable energy source, addressing the global demand for renewable alternatives amidst increasing oil and gas consumption and solid waste production. LCB, consisting of lignin, cellulose, and hemicellulose, is versatile for biochemical and thermochemical conversions like anaerobic digestion, fermentation, gasification, and pyrolysis. Recent advancements have led to a 25 % increase in bioethanol yields through alkali pre-treatment and optimized fermentation, a 20 % enhancement in microbial delignification efficiency, and a 35 % improvement in enzyme efficiency via nanobiotechnology. These innovations enhance biofuel production sustainability and cost-effectiveness. Decentralized energy systems utilizing locally produced biomass can reduce transmission losses and greenhouse gas emissions by up to 30 %, fostering community energy independence. These developments significantly contribute to global sustainability and socio-economic development by converting waste into valuable energy, promoting environmental stewardship, and supporting economic resilience. Furthermore, this review also discusses innovative strategies to address technological, economic, and environmental challenges and highlights the role of decentralized solutions in promoting sustainable energy production.

Atmosphere-driven metal-support synergy in ZnO/Au catalysts for efficient piezo-catalytic hydrogen evolution

Piezo-catalysis, which leverages mechanical energy to drive chemical reactions, is emerging as a promising method for sustainable energy production. While the enhancement of piezo-catalytic performance through metal-support interactions is well-documented, the critical influence of the synthesis atmosphere during metal-loaded piezo-catalyst preparation has been a notable gap in the field. To this end, we systematically investigate how different atmospheric conditions during the synthesis of catalysts—without gas flow or with Ar, N2 and O2—affect metal dispersion, oxidation states, piezo-carrier dynamics, and electronic structure, and subsequently shape the metal-support interactions and piezo-catalytic activity. ZnO/Au, with Au deposited on ZnO, is selected as the model system, and hydrogen evolution reaction is used as the probe reaction. Our results demonstrate that an oxygen-enriched atmosphere significantly enhances the metal-support interactions, achieving an ultrahigh net hydrogen yield of 16.5 mmol·g–1·h–1 on ZnO/Au, a 3.58-fold increase over pristine ZnO. Specifically, the performance improvements substantially surpass those synthesized under other atmospheric conditions. Conversely, exposure to CO2 transforms the ZnO support into ZnCO3, adversely affecting its catalytic activity. These findings reveal the crucial impact of synthesis conditions on piezo-catalyst performance and thereby open new avenues for optimizing catalyst systems for enhanced sustainability.

AI-driven predictive maintenance and optimization of renewable energy systems for enhanced operational efficiency and longevity

The rapid growth of renewable energy systems necessitates advanced strategies for maintenance and optimization to ensure long-term operational efficiency and sustainability. Traditional approaches often fall short in predicting failures and optimizing performance across diverse and dynamic renewable energy infrastructures. This study investigates the application of artificial intelligence (AI) techniques for predictive maintenance and optimization of renewable energy systems, with the aim of enhancing operational efficiency and extending system longevity. We employ a combination of machine learning algorithms, including deep neural networks and reinforcement learning, to develop predictive models and optimization strategies. These models are trained on large-scale datasets collected from operational wind farms, solar installations, and hydroelectric plants. Our results demonstrate that AI-driven approaches can predict equipment failures with 92% accuracy, reducing unplanned downtime by 35% compared to traditional methods. Moreover, AI-optimized operational parameters improved overall energy output by 8.5% across the studied systems. The proposed framework also showed adaptability to various environmental conditions and system configurations, suggesting broad applicability across the renewable energy sector. This research underscores the significant potential of AI in revolutionizing maintenance practices and operational strategies in renewable energy systems, paving the way for more reliable, efficient, and sustainable clean energy production.

Mitochondrial Dysfunction and Metabolic Disturbances Induced by Viral Infections.

Viruses are intracellular parasites that utilize organelles, signaling pathways, and the bioenergetics machinery of the cell to replicate the genome and synthesize proteins to build up new viral particles. Mitochondria are key to supporting the virus life cycle by sustaining energy production, metabolism, and synthesis of macromolecules. Mitochondria also contribute to the antiviral innate immune response. Here, we describe the different mechanisms involved in virus-mitochondria interactions. We analyze the effects of viral infections on the metabolism of glucose in the Warburg phenotype, glutamine, and fatty acids. We also describe how viruses directly regulate mitochondrial function through modulation of the activity of the electron transport chain, the generation of reactive oxygen species, the balance between fission and fusion, and the regulation of voltage-dependent anion channels. In addition, we discuss the evasion strategies used to avoid mitochondrial-associated mechanisms that inhibit viral replication. Overall, this review aims to provide a comprehensive view of how viruses modulate mitochondrial function to maintain their replicative capabilities.

Performance Evaluation and Economic Sustainability of the PAU Model Batch Type Paddy Straw Biogas Plant

This study evaluates the performance and economic viability of the Punjab Agricultural University (PAU) Model Batch Type Paddy Straw Biogas Plant in rural India, addressing critical challenges in agricultural residue management and sustainable energy production. Data collected from two plants over four months showed an average daily biogas production of 1.46 to 3.13 m3 per day, with a total gas production of 284.8 m3 in a period of four months. Plant performance correlated moderately with ambient temperature. Economic analysis revealed annual savings of Rs. 47,600 through reduced LPG use and biogas slurry sales. The study concludes that the PAU Model is technically efficient and economically viable, offering a sustainable solution for paddy straw management and rural energy security. These findings have significant implications for policymakers and rural development practitioners in promoting sustainable agriculture and renewable energy adoption in developing regions.

New Approach for Tracking, Monitoring, and Diagnosing Faults in a Photovoltaic System in Real Time: An Experimental and Case Study

Photovoltaic installations have emerged as a cornerstone of sustainable energy production, playing a pivotal role in the global transition towards renewable sources of electricity. As the demand for clean energy surges, so too does the need for robust monitoring and diagnostic strategies to ensure the efficient operation of these systems. This study presents a novel methodology for the real-time tracking, monitoring, and diagnosing of faults in photovoltaic systems (PVSs), emphasizing their crucial role in sustainable energy production amid the global shift to renewable energy. The study was conducted in Guelma, Algeria, during the spring and summer seasons. The investigation utilized WatchPower simulation software over a 24-hour performance analysis of the photovoltaic system. On June 19, 2024, with a high temperature of 32°C, the system achieved a peak output power of 600W under optimal conditions, validating its efficiency in energy generation. The study also analyzed the effects of shading on energy output by comparing data from a shaded day on May 14, 2024, at 25°C, to an unshaded day on June 21, 2024, at 32°C, during peak sunlight hours from 9:00 AM to 2:15 PM, the period when sunlight is at its strongest. The results showed a significant drop in output power from 600W to 450W due to shading, underscoring the importance of real-time monitoring to detect performance inefficiencies. This research not only enhances operational reliability and maintenance strategies for PV systems but also demonstrates the effectiveness of integrating real-time data analytics to support decision-making in similar environments.

Microbial electrochemical snorkels: principle, structure, and applications in environmental amelioration

Microbial electrochemical technology (MET) represents a novel approach demonstrating promising application prospects in emerging strategic industries such as environment protection, energy saving, and sustainable energy production. Among different METs, microbial electrochemical snorkels (MES) are praised for the simple design, high flexibility, and low costs. Several pilot MESs have been employed to mitigate environmental issues in European and American countries. Despite the rapid development, only one review article on MES has been published so far. Here we review the latest achievements in this field and introduce the principles, structures, functions, and applications of MESs. Moreover, we summarize the key challenges and the future research areas in this field, aiming to give insights into the research on MESs and other METs and improve the applications of such technologies.