Conversion Of Chemical Energy Research Articles

Improved photosynthetic characteristics of Chlorella mutant MS700 induced by nuclear radiation

Chlorophyll a variable fluorescence and oxygen evolution were measured in microalgae Chlorella and its mutant MS700, which was mutated by nuclear radiation with an increased biomass yield. The mutant MS700 showed an improvement in photosynthetic characteristics under various CO2 concentrations. Results showed that chlorophyll-based flash oxygen yield was 104% higher in MS700 than in the wild type, indicating more available electron acceptors in the plastoquinone pool and a higher light to chemical energy conversion efficiency. The higher chlorophyll a variable fluorescence at the end of PQ pool-regulated phase implied a more robust mechanism for consumption of electrons generated in PSII, indicating a more efficient downstream process. Monitoring of CO2 fixation in the Calvin cycle showed that the mutant had a 27.7% higher capability of incorporating its dissolved inorganic carbon. The oxygen evolution rate was 31.4% higher in MS700, which also indicated a higher CO2 fixation rate. These results consistently demonstrated carbon fixation efficiency in the mutant MS700, resulting in the higher biomass yield.

Bioinspiration in light harvesting and catalysis

Capturing and converting solar energy into fuels and feedstocks is a global challenge that spans numerous disciplines and fields of research. Billions of years of evolution have allowed natural organisms to hone strategies for harvesting light from the sun and storing energy in the form of carbon–carbon and carbon–hydrogen bonds. Photosynthetic antenna proteins capture solar photons and funnel photoexcitations to reaction centres with high yields, and enzymes catalyze multi-electron reactions, facilitating chemical transformations not yet efficiently implemented using artificially engineered catalysts. Researchers in renewable energy often look to nature to understand the mechanisms at work and, if possible, to explore their translation into artificial systems. Here, we review advances in bioinspiration across the fields of biological light harvesting and chemical energy conversion. We examine how multi-photon and multi-electron reactions in biology can inspire new methods in photoredox chemistry to achieve novel, selective and complex organic transformations; how carbonic-dehydrogenase-inspired design principles enable catalytic reactions such as the conversion of CO2 into useful products such as fuels; and how concepts from photosynthetic antenna complexes and reaction centres can benefit artificial light-harvesting materials. We then consider areas in which bioinspiration could enable advances in the rational design of molecules and materials, the expansion of the synthetic capabilities of catalysts and the valorization of molecular building blocks. We highlight the challenges that must be overcome to realize these advances and propose new directions that may use bioinspiration to achieve them.

Microbial Fuel Cell-Based Biological Oxygen Demand Sensors for Monitoring Wastewater: State-of-the-Art and Practical Applications.

Environmental pollution has been a continuous threat to sustainable development and global well-being. It has become a significant concern worldwide to combat the ecological crisis using low-cost innovative technologies. Biological oxygen demand (BOD) is a key indicator to comprehend the quality of water to guarantee environmental safety and human health; however, none of the present technologies are capable of online monitoring of the water at the source. Microbial fuel cells (MFC) are a promising technology for simultaneous power generation and wastewater treatment. MFCs have also been shown in fascinating applications to measure and detect the toxic pollutants present in wastewater. These are the bioreactors where exoelectrogenic microorganisms catalyze the conversion of the inherent chemical energy stored in organic compounds to electrical energy. Sensors employ energy conversion to measure BOD, which is considered an international index for the detection of organic material load present in wastewater. The MFC-based BOD sensors have gone through a wide range of advancement from mediator to mediator-less, double chamber to single-chamber, and large size to miniature. There have been detailed studies to improve the accuracy and reproducibility of the sensors for commercial applications. Additionally, multistage MFC-based BOD biosensors and miniature MFC-BOD sensors have also been ubiquitous in recent years. A considerable amount of work has been carried out to improve the performance of these devices by fabricating the proton exchange membranes and altering catalysts at the cathode. However, there remains a dearth for the fabrication of the devices in aspects like suitable microbes, proton exchange membranes, and cheaper catalysts for cathodes for effective real-time monitoring of wastewater. In this review, an extensive study has been carried out on various MFC-based BOD sensors. The efficiency and drawbacks associated with the different MFC-based BOD sensors have been critically evaluated, and future perspectives for their development have been investigated. The breadth of work compiled in this review will accelerate further research in MFC-based BOD biosensors. It will be of great importance to broad ranges of scientific research and industry.

Blue Energy Collection toward All‐Hours Self‐Powered Chemical Energy Conversion

AbstractThe conversion and transmission of blue energy in the ocean are critical issues. By employing triboelectric nanogenerators (TENGs), blue energy can be harvested but the corresponding electricity transmission and storage are still great challenges. In this work, an automatic high‐efficiency self‐powered energy collection and conversion system is proposed that converts blue energy to chemical energy. A gear‐driven unidirectional acceleration TENG is designed to convert disordered and low‐frequency water wave energy to low voltage and high current DC output. The output bias from the TENG can be used to drive a Ti–Fe2O3/FeNiOOH based photoelectrochemical cell under sunlight to produce hydrogen. Moreover, under the situation without sunlight, the self‐powered system can be automatically switched to another working state to charge a Co3O4 based lithium‐ion battery. The hydrogen production rate reaches to 4.65 µL min‐1 under sunlight at the rotation speed of 120 rpm. The conversion efficiency of the whole system is calculated to be 2.29%. The system triggered by photoswitches can automatically switch between two working states with or without sunlight and convert the blue energy to either hydrogen energy or battery energy for easy storage and transmission, which widens the future applications for blue energy.

Graphene-Capped Liquid Thin Films for Electrochemical Operando X-ray Spectroscopy and Scanning Electron Microscopy.

Electrochemistry is a promising building block for the global transition to a sustainable energy market. Particularly the electroreduction of CO2 and the electrolysis of water might be strategic elements for chemical energy conversion. The reactions of interest are inner-sphere reactions, which occur on the surface of the electrode, and the biased interface between the electrode surface and the electrolyte is of central importance to the reactivity of an electrode. However, a potential-dependent observation of this buried interface is challenging, which slows the development of catalyst materials. Here we describe a sample architecture using a graphene blanket that allows surface sensitive studies of biased electrochemical interfaces. At the examples of near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and environmental scanning electron microscopy (ESEM), we show that the combination of a graphene blanket and a permeable membrane leads to the formation of a liquid thin film between them. This liquid thin film is stable against a water partial pressure below 1 mbar. These properties of the sample assembly extend the study of solid–liquid interfaces to highly surface sensitive techniques, such as electron spectroscopy/microscopy. In fact, photoelectrons with an effective attenuation length of only 10 Å can be detected, which is close to the absolute minimum possible in aqueous solutions. The in-situ cells and the sample preparation necessary to employ our method are comparatively simple. Transferring this approach to other surface sensitive measurement techniques should therefore be straightforward. We see our approach as a starting point for more studies on electrochemical interfaces and surface processes under applied potential. Such studies would be of high value for the rational design of electrocatalysts.

A photoactive process cascaded electrocatalysis for enhanced methanol oxidation over Pt-MXene-TiO2 composite

Highly efficient photo-assisted electrocatalysis for methanol oxidation reaction (MOR) realizes the conversion of solar and chemical energy into electric energy simultaneously. Here we report a Pt-MXene-TiO2 composite for highly efficient MOR via a photoactive cascaded electro-catalytic process. With light (UV and visible light) irradiation, MXene-TiO2 serves as the photo active centre (photoinduced hole) to activate the methanol molecules, while Pt particles are the active centre for the following electro-catalytic oxidation of those activated methanol molecules. Pt-MXene-TiO2 catalyst exhibits a lower onset potential (0.33 V) and an impressive mass activity of 2,750.42 mA·mg−1Pt under light illumination. It represents the highest MOR activity ever reported for photo-assisted electrocatalysts. Pt-MXene-TiO2 also shows excellent CO tolerance ability and stability, in which, after long-term (5,000 s) reaction, still keeps a high mass activity of 1,269.81 mA·mg−1Pt (62.66% of its initial activity). The photo-electro-catalytic system proposed in this work offers novel opportunities for exploiting photo-assisted enhancement of highly efficient and stable catalysts for MOR.

Electronic coupling strategy to boost water oxidation efficiency based on the modelling of trimetallic hydroxides Ni1-x-yFexCry(OH)2: From theory to experiment

Developing low-cost yet highly efficient earth-abundant electrocatalysts for oxygen evolution reaction (OER) is of great significance for industrial scale water splitting for clean hydrogen production, as well as for rechargeable metal-air batteries. In searching for advanced catalysts, it is equally important to fundamentally understand working mechanism and be able to rationally design and manipulate catalytic sites. Starting from the density functional theory (DFT) calculations as a guidance, our theoretical model revealed that chromium substitution in nickel–iron hydroxides (Ni1-xFex(OH)2) not only accelerated the charge transfer but also regulated the adsorption energy of OER intermediates to achieve optimal binding strength. Experimentally, chromium was doped into the laminate of Ni1-xFex(OH)2, resulting in the enhanced catalytic performance for oxygen evolution reaction, which confirmed the predictions from the theoretical data. The porous and ultra-thin ternary Ni1-x-yFexCry(OH)2 electrocatalysts were grown directly on a nickel foam (NF) substrate, with an optimum composition Ni0.66Fe0.27Cr0.07(OH)2/NF identified, which exhibited a superior OER performance, i.e., achieving a significant current density of 10 mA cm−2 at a low overpotential of 231 mV, a small Tafel slope (31 mV dec−1) and an excellent stability at a highly oxidative potential of 1.68 V vs RHE in alkaline electrolyte. The comprehensive study involving both theoretical and experimental results in this work provides an insightful guidance in designing efficient OER catalysts for chemical and electrical energy conversion and storage.

Exploitation of the far-offshore wind energy resource by fleets of energy ships – Part 1: Energy ship design and performance

Abstract. This paper deals with a new concept for the conversion of far-offshore wind energy into sustainable fuel. It relies on autonomously sailing energy ships and manned support tankers. Energy ships are wind-propelled. They generate electricity using water turbines attached underneath their hull. Since energy ships are not grid-connected, they include onboard power-to-X plants for storage of the produced energy. In the present work, the energy vector is methanol. The aim of the paper is to propose an energy ship design and to provide an estimate for its energy performance as function of the wind conditions. The energy performance assessment is based on a numerical model which is described in the paper. Results show that the wind energy-to-methanol (chemical energy) conversion efficiency is 24 % and that such an energy ship deployed in the North Atlantic Ocean could produce approximately 5 GWh per annum of chemical energy (900 t of methanol per annum).

Superprotonics: New Materials for Energy-Efficient Technologies

One of the most rapidly developing directions in the field of alternative energy sources is hydrogen energetics. Fuel cells, the main component of which is a proton-exchange membrane, facilitate the direct conversion of chemical energy into electrical energy. Superprotonic crystals are promising materials for the creation of proton-exchange membranes of fuel cells and other electrochemical. Multicomponent water–salt growth systems are studied in order to obtain new superprotonic crystals MmHn(AO4)(m + n)/2 ⋅ yH2O (M = K, Rb, Cs, NH4, AO4 = SO4, SeO4, HPO4) and modify the properties of known compounds. The conditions for the growth of a number of new superprotonics are found, and the relationships between their structure and properties are studied.

Інноваційні можливості газової детонації

Introduction. Explosive technologies are widely used in the extraction industries, in mechanical engineering for welding, hardening, etc. However, the use of solid explosives is limited, above all, by safety requirements. Therefore, the use of a safer and more convenient source of energy, gas detonation, is attracting much attention. Pressures, temperatures, and velocities in detonation waves or shock waves in gases close to them in terms of intensity, as well as the pulse nature of the influence of these factors determine a high potential of their technical and technological use. Problem Statement. In many technical systems, deflagration modes of burning prevail. However, a more thermodynamically advantageous method of combustion and conversion of chemical energy of fuel into useful work is the detonation mode of combustion. This ensures the feasibility of development, research and wider implementation of various technologies and devices using controlled gas detonation. Purpose. Systematization and analysis of the main trends in the development and design of detonation gas technologies and devices in Ukraine and throughout the world. Materials and Methods. Systematization and analysis of scholarly research publications and patents on the practical application of gas detonation in various sectors of the economy. Results. The tendencies of practical use of gas detonation in different branches of industry have been revealed and analyzed. Priority developments in the technological application of the method in mechanical engineering have been performed in Ukraine. However, in many technical areas Ukraine has fallen behind the world leaders in terms of the creation of detonation gas technologies and devices. Conclusions. For the practical use of the potential of gas detonation, it is necessary to develop fundamentally new devices that ensure reliable, safe, and controlable generation and propagation of detonation waves in gases and sprayed fuels. Gas detonation is promising for the creation of more advanced technologies and equipment.

Model of the Generation of Electron Excitations in a Crystal during Events of Chemical Interaction between Hydrogen Atoms on the Surface of a Semiconductor

The generation of excess electrons in semiconductor structures via the heterogeneous chemical reaction of the recombination of hydrogen atoms is investigated theoretically. The theoretically possible efficiency of the conversion of chemical energy to electrical energy using semiconductor heterostructures is determined. The micromechanism of the generation of chemocurrent is described in an approximation of a multiple-quantum vibrational electronic transition.

1701-P: The Role of UGT1a in Regulating Brown Adipose Tissue and Thermogenic Function

Increasing biological thermogenesis (the conversion of chemical energy to heat) has been proposed as an approach towards lowering blood glucose, improving insulin sensitivity and mitigating type 2 diabetes. Non-shivering thermogenesis occurs primarily in adipocytes that express uncoupling protein 1 (UCP1) including brown adipose tissue (BAT) and beige adipose tissue but does not substantially occur in white adipose tissue (WAT). To identify genes that regulate thermogenesis and BAT function, we recently compared genes expressed in paired human patient samples (n = 10) of the deep neck BAT located next to the carotid sheath and superficial subcutaneous WAT in the neck. We found UDP-glucuronide transferase 1A (UGT1A) is co-expressed in individuals with a high amount of the thermogenic protein uncoupling protein 1 (UCP1). This enzyme is known to glucuronidate metabolites, including bilirubin and xenobiotics, which increases their water solubility and excretion. Based on this function, we hypothesize UGT1A regulates BAT not through direct action of the enzyme but through modulating the availability of thermogenic molecules. Here, we characterized expression of different UGT1A isoforms in vivo and in vitro. Cold exposure is an effective method for activating BAT and increasing thermogenesis in mice. Interestingly, expression of multiple UGT1A isoforms, including UGT1A6a and UGT1A6b, are decreased in BAT of mice exposed to a cold environment (5°C) for 7 days. This finding is consistent with data in multiple publicly available datasets which have shown UGT1A6a/6b are decreased in cold exposure and other thermogenic stimuli. In vitro, most UGT1A isoforms were increased during the differentiation of murine brown adipocytes but only certain isoforms were differentially expressed during in vitro differentiation in human brown adipocytes. Based on these data, we propose that UGT1A may have a function related to thermogenesis and understanding its function could lead to novel approaches for activating BAT. Disclosure S. Kodani: None. M. Lynes: None. F. Shamsi: None. C. Wang: None. S. Sugimoto: None. R. Xue: None. T. Huang: None. A.P. White: None. A.M. Cypess: None. Y. Tseng: Consultant; Self; Boehringer Ingelheim International GmbH. Funding National Institutes of Health (R01DK07709, R01DK102898, T32DK007260)

Cobalt Colloid-derived Efficient and Durable Nanoscale Electrocatalytic Films for High-Activity Water Oxidation.

Oxygen evolution reaction is of immense importance and is vitally necessary for devices such as electrolyzers, fuel cells, and other solar and chemical energy conversion devices. The major challenges that remain in this quest are due to the lack of effective catalytic assemblages operating with optimum efficiency and obtainable following much simpler setups and easily accessible methods. Here, we demonstrate that the robust electrocatalytic activity toward water oxidation can be achieved employing straightforwardly obtainable nanoscale electrocatalysts derived from easily made colloidal-cobalt nanoparticles (Co-CNPs) prepared in clean carbonate systems. Thin-film non-noble metal nanoscale electrocatalysts such as simple Co-CNPs/FTO and annealed Co-CNPs/FTO250 and Co-CNPs/FTO500 obtained by depositing Co-CNPs on the FTO substrate are shown to initiate water oxidation at much lower overpotentials such as just 240 mV for Co-CNPs/FTO250 under mildly alkaline conditions while demonstrating an impressive Tafel slope of just 40 mV dec–1. Furthermore, the robust catalyst demonstrated a high electrochemical surface area of 91 cm2 and high turnover frequency and mass activity of 0.26 s–1 and 18.84 mA mg–1, respectively, just at 0.35 V, and superior durability during long-term electrolysis. These outstanding catalytic outcomes using easily prepared Co-CNPs/FTO250-type catalytic systems are comparable and even better than other noble and non-noble metal-based nanoscale catalytic assemblages obtained by much difficult methods. Most advantageously, the colloidal route also offers the easiest approach of incorporating carbon contents in the catalytic layer, which can ultimately increase mechanical stability and mass transfer capability of the system.

Evaluation of Transition Metals with Lanthanoid Series Elements for Water Electrolysis

Enhancing the electrochemical activity of different electrocatalysts for environmental sustainability is of significant importance for the effective conversion of electricity and chemical energy. Enhancement of transition metal-based (Ni) electrocatalysts with lanthanide series elements has recently grown exponentially, and elements of rare earth (RE) (Ce) due to their unique characteristics are of special concern among different elements. In the present work a bifunctional catalyst (Ni-Ce) will be tested for Oxygen Evoluation Reaction (OER) and Hydrogen Evolution Reaction (HER). Cyclic voltammetry, as well as chronoamperometry, is used to test these electrocatalysts from alkaline to acidic medium for the OER and HER under laboratory conditions typically used for water electrolysis. HER and OER performance is tested in 1 M NaOH. The experimental results will suggest the factors affecting the hydrogen and oxygen evolution process and the catalyst will further be improved with the right combination of different group elements. sample characterization will be performed using XPS. Lower overpotential with Tafel slope will reflect the material activity for oxygen evolution reaction. Alteration in the morphology of the electrocatalyst is analyzed with scanning electron microscope

CO2 Hydrogenation with Cu/ZnO/Al2O3: A Benchmark Study

AbstractThe suitability of a commercial and industrially applied Cu‐based catalyst for the synthesis of methanol by CO2 hydrogenation was investigated. Unexpectedly, this system showed high stability and well‐performance under conditions that may be relevant for chemical energy conversion using hydrogen and energy from renewable technologies. This Cu‐based catalyst demonstrated excellent suitability for dynamical process operation that may be essential for effective compensation of the volatility of renewable energy sources.

Synergy between thermal and nonthermal effects in plasmonic photocatalysis

Plasmonic photocatalysis represents the synergetic union of two active fields of research: plasmonic effects in illuminated metallic nanoparticles and catalytic effects in tailored metallic nanoparticles. Traditionally, metallic nanoparticles that excel for one application are limited for the other, but recent developments have shown that desirable catalytic behaviors, such as reduced activation barriers and improved product selectivity, derive from nonthermal behaviors uniquely produced by this synergy. After examining such findings, this review will address a specific debate that has recently surfaced: what is the relative degree of contributions of thermal and nonthermal effects in plasmonic photocatalysis? We demonstrate the importance of correctly accounting for thermal effects before characterizing nonthermal contributions. We show that another synergy occurs: these desirable nonthermal behaviors have a temperature dependence, and the resulting temperature-dependent reaction rates far exceed what can be explained from purely thermal effects alone. Thus, the synergy of plasmonic photocatalysis offers an exciting new contribution to the quest for efficient, selective, sustainable methods for chemical synthesis and energy conversion.

Fungal Light Emitter: Understanding Its Chemical Nature and pH-Dependent Emission in Water Solution.

Fungal bioluminescence is a fascinating natural process, standing out for the continuous conversion of chemical energy into light. The structure of fungal oxyluciferin (light emitter) was proposed in 2017, being different and more complex than other oxyluciferins. The complexity of fungal oxyluciferin arises from diverse equilibria such as keto/enol tautomerization or deprotonation equilibria of four titratable groups. For this reason, still some crucial details of its structure remain unexplored. To obtain further structural information, a combined experimental and computational study of natural and three synthetic fungal oxyluciferin analogues has been performed. Here, we state the most stable chemical form of fungal oxyluciferin regarding its keto and enol tautomers, in the ground and excited states. We propose the (3Z,5E)-6-(3,4-dihydroxyphenyl)-4-hydroxy-2-oxohexa-3,5-dienoic acid form as the light emitter (fluorescent state) in water solution. Moreover, we show that chemical modifications on fungal oxyluciferin can affect the relative stability of the conformers. Furthermore, we show the clear effect of pH on emission. General conclusions about the role of these titratable groups in emission modulation have been drawn, such as the key role of dihydroxyphenyl deprotonation. This study is key to further analyze the properties of fungal bioluminescence and propose novel synthetic analogues.

Розвиток світового ринку енергоустановок на паливних елементах. СтРозвиток світового ринку енергоустановок на паливних елементах. Створення нормативної бази водневої енергетикиворення нормативної бази водневої енергетики

We show the importance of development and implementation of new hydrogen power systems for different branches of the Ukrainian economy. It is determined that the key technologies for the creation of hydrogen power in Ukraine are the technologies of hydrogen production using own energy sources and the direct conversion of chemical energy of hydrogen fuels into electricity in fuel cells. We present the main characteristics and advantages of fuel cell power plants (FCPP) and the global volume of their application for different industries. The total electric capacity of FCPP working in 2019 became more than 11 times greater as compared with 2009 and reached 1,100 MW. It was established that the introduction of fuel cell technologies in industrialized countries is considered as a basis for the creation of a centralized world hydrogen economy with the presence and further development of extensive hydrogen infrastructure. The state of work on standardization in the field of hydrogen power at the international level is analyzed, and the complexity and multiplicity of such tasks are shown. It is substantiated that the appropriate base of normative documents is necessary for the practical implementation of energy-efficient and environmentally friendly hydrogen technologies in Ukraine, in particular, for the production or import of equipment with its subsequent certification. These normative documents should be harmonized with European and international ones in order to remove possible technical barriers in trade.

Modifying the Surface Structure of Perovskite-Based Catalysts by Nanoparticle Exsolution

In heterogeneous catalysis, surfaces decorated with uniformly dispersed, catalytically-active (nano)particles are a key requirement for excellent performance. Beside standard catalyst preparation routines—with limitations in controlling catalyst surface structure (i.e., particle size distribution or dispersion)—we present here a novel time efficient route to precisely tailor catalyst surface morphology and composition of perovskites. Perovskite-type oxides of nominal composition ABO3 with transition metal cations on the B-site can exsolve the B-site transition metal upon controlled reduction. In this exsolution process, the transition metal emerges from the oxide lattice and migrates to the surface where it forms catalytically active nanoparticles. Doping the B-site with reducible and catalytically highly active elements, offers the opportunity of tailoring properties of exsolution catalysts. Here, we present the synthesis of two novel perovskite catalysts Nd0.6Ca0.4FeO3-δ and Nd0.6Ca0.4Fe0.9Co0.1O3-δ with characterisation by (in situ) XRD, SEM/TEM and XPS, supported by theory (DFT+U). Fe nanoparticle formation was observed for Nd0.6Ca0.4FeO3-δ. In comparison, B site cobalt doping leads, already at lower reduction temperatures, to formation of finely dispersed Co nanoparticles on the surface. These novel perovskite-type catalysts are highly promising for applications in chemical energy conversion. First measurements revealed that exsolved Co nanoparticles significantly improve the catalytic activity for CO2 activation via reverse water gas shift reaction.

Photocatalytic Fuel Cell Based on Zinc Oxide Loaded Carbon Plate Photoanode for Simultaneous Photocatalytic Degradation of Azo Dyes and Electricity Generation

Photocatalytic fuel cell (PFC) is promising to own its synchronous degradation of organic pollutants with electricity generation under illumination of light. The oxidation and reduction process promote the conversion of chemical energy in the pollutants into electrical energy. In this study, PFC is driven by the electrode reactions between the zinc oxide loaded carbon plate (ZnO/C) photoanode and carbon plate cathode under irradiation of UVA light. The ZnO/C photoanode was successfully fabricated by using simple ultrasonication-annealed method and investigated by XRD, SEM and EDX. To investigate the capability of the PFC, reactive red 120 (RR120), congo red (CR) and acid orange 7 (AO7) are employed well compared among themselves. The results indicated that the molecular structure of azo dyes with different adsorption of light by dye itself, number of azo bonds and sulfonic groups can be the crucial factors of decolorization in the PFC. The photocatalytic fuel cell with AO7 as sacrificial agent was able to perform 82.43% of decolorization efficiency, a maximum short circuit current (JSC) of 0.0017 mA cm-2 and maximum power density (Pmax) of 0.0886 µW cm-2.