Metal Chalcogenide Nanostructures for Renewable Energy Applications E-Book

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 458

Veröffentlichungsjahr: 2014

Beschreibung

This first ever reference book that focuses on metal chalcogenide semiconductor nanostructures for renewable energy applications encapsulates the state-of-the-art in multidisciplinary research on the metal chalcogenide semiconductor nanostructures (nanocrystals, nanoparticles, nanorods, nanowires, nanobelts, nanoflowers, nanoribbons and more). The properties and synthesis of a class of nanomaterials is essential to renewable energy manufacturing and this book focuses on the synthesis of metal chalcogendie nanostructures, their growth mechanism, optical, electrical, and other important properties and their applications in different diverging fields like photovoltaics, hydrogen production, theromelectrics, lithium battery, energy storage, photocatalysis, sensors. An important reference source for students, scientists, engineers, researchers and industrialists working on nanomaterials-based energy aspects associated with chemistry, physics, materials science, electrical engineering, energy science and technology, and environmental science.

Leseprobe

Contents

Cover

Half Title page

Title page

Copyright page

Preface

Part 1: Renewable Energy Conversion Systems

Chapter 1: Introduction: An Overview of Metal Chalcogenide Nanostructures for Renewable Energy Applications

1.1 Introduction

1.2 Metal Chalcogenide Nanostructures

1.3 Growth of Metal Chalcogenide Nanostructures

1.4 Applications of Metal Chalcogenide Nanostructures

1.5 Summary and Future Perspective

References

Chapter 2: Renewable Energy and Materials

2.1 Global Energy Scenario

2.2 Role of Renewable Energy in Sustainable Energy Future

2.3 Importance of Materials Role in Renewable Energy

References

Chapter 3: Sustainable Feed Stock and Energy Futures

3.1 Introduction

3.2 Discussion

References

Part 2: Synthesis of Metal Chalcogenide Nanostructures

Chapter 4: Metal-Selenide Nanostructures: Growth and Properties

4.1 Introduction

4.2 Growth and Properties of Different Groups of Metal-Selenide Nanostructures

4.3 Metal Selenides from III–VI Semiconductors

4.4 Metal Selenides from IV–VI Semiconductors

4.5 Metal Selenides from V–VI Semiconductors

4.6 Metal Selenides from Transition Metal (TM)

4.7 Ternary Metal-Selenide Compounds

4.8 Summary and Future Outlook

Acknowledgment

References

Chapter 5: Growth Mechanism and Surface Functionalization of Metal Chalcogenides Nanostructures

5.1 Introduction

5.2 Synthetic Methods for Layered Metal Chalcogenides

5.3 Surface Functionalization of Layered Metal Dichalcogenide Nanostructures

5.4 Applications of Inorganic Nanotubes and Fullerenes

References

Chapter 6: Optical and Structural Properties of Metal Chalcogenide Semiconductor Nanostructures

6.1 Optical Properties of Metal Chalcogenides Semiconductor Nanostructures

6.2 Structural Properties and Defects of Metal Chalcogenide Semiconductor Nanostructures

References

Chapter 7: Structural and Optical Properties of CdS Nanostructures

7.1 Introduction

7.2 Nanomaterials

7.3 II–VI Semiconductors

7.4 Sol-Gel Process

7.5 Structural and Surface Characterization of Nanostructured CdS

7.6 Optical Properties

7.7 Conclusion

References

Part 3: Applications of Metal Chalcogenides Nanostructures

Chapter 8: Metal Sulfide Photocatalysts for Hydrogen Generation by Water Splitting under Illumination of Solar Light

8.1 Introduction

8.2 Photocatalytic Water Splitting on Single Metal Sulfide

8.3 Photocatalytic Water Splitting on Multi-metal Sulfide

8.4 Metal Sulfides Solid-Solution Photocatalysts

8.5 Summary and Future Outlook

References

Chapter 9: Metal Chalcogenide Hierarchical Nanostructures for Energy Conversion Devices

9.1 Introduction

9.3 Different Methods to Grow Cd-Chalcogenide Nanocrystals

9.4 Solar Energy Conversion

9.5 Cd-Chalcogenide Nanocrystals as Solar Energy Conversion

9.6 Summary and Future Outlook

References

Chapter 10: Metal Chalcogenide Quantum Dots for Hybrid Solar Cell Applications

10.1 Introduction

10.2 Chemical Synthesis of Quantum Dots

10.3 Quantum Dots Solar cell

10.4 Summary and Future Prospects

References

Chapter 11: Solar Cell Application of Metal Chalcogenide Semiconductor Nanostructures

11.1 Introduction

11.2 Chalcogenide-Based Thin-Film Solar Cells

11.3 CdTe-Based Solar Cells

11.4 Cu(In,Ga)(S,Se)2 (CIGS)-Based Solar Cells

11.5 Metal Chalcogenides-Based Quantum-Dots-Sensitized Solar Cells (QDSSCs)

11.6 Hybrid Metal Chalcogenides Nanostructure-Conductive Polymer Composite Solar Cells

11.7 Conclusions

References

Chapter 12: Chalcogenide-Based Nanodevices for Renewable Energy

12.1 Introduction

12.2 Renewable Energy

12.3 Nanodevices

12.4 Density Functional Theory

12.5 Analytical Studies

12.6 Conclusion

References

Chapter 13: Metal Tellurides Nanostructures for Thermoelectric Applications

13.1 Introduction

13.2 Thermoelectric Microdevice Fabricated by a MEMS-Like Electrochemical Process

13.3 Bi2Te3-Based Flexible Micro Thermoelectric Generator

13.4 High-Thermoelectric Performance of Nanostructured Bismuth Antimony Telluride Bulk Alloys

13.5 Nano-manufactured Thermoelectric Glass Windows for Energy Efficient Building Technologies

13.6 Conclusion

References

Index

Metal Chalcogenide Nanostructures for Renewable Energy Applications

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Publishers at Scrivener Martin Scrivener([email protected]) Phillip Carmical ([email protected])

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Library of Congress Cataloging-in-Publication Data:

ISBN 978-1-118-23791-5

Preface

Meeting impending energy requirements by an ecologically benign approach entails scientific innovations to proficiently produce, store, transfer, and utilize enormous amounts of energy. The critical requirement to attain this goal demands to develop cost-effective materials by imparting novel intriguing features to convert maximum energy from sun and other renewable means.

Metal chalcogenide semiconductor nanostructures present the most important class of nanomaterial that provides highly anisotropic diverse morphologies, described by the efficient transport of electrons and excitons, and has been regarded as the most promising building block for nanoscale renewable energy nanodevices and nanosystems. The growth, characterization, and applications of nanostructures entreat various disciplines of science and engineering. The objective of this book is to illuminate the essentials, underlying science related to semiconductor metal chalcogenide nanostructures fabrication for potential renewable energy applications. The effect is an illustrative snapshot of the latest developments from diverse perspectives in a series of chapters based on synthesis, properties, characterization, and applications of metal sulfide, selenide, and telluride nanostructures from distinguished betrothed researchers.

This book contents are divided into three main sections.

Chapters 1–3 present an overview of increasing greenhouse emissions, recent research and substantial progress reported in the literature, covering formation of 0, 1, 2, and 3 dimensional metal sulfide, selenide, and telluride nanostructures. The application of chalcogenide materials for renewable energy conversion, which includes photovoltaics, hydrogen production, thermoelectrics, fuel cell, supercapacitors, and lithium-ion batteries and their future projections are covered in Chapter 1. The potential impact of materials for alternative energy conversion systems and various important renewable energy alternatives is anticipated in Chapters 2 and 3.

Chapters 4–7 are devoted to comprehensive synthesis of metal chalcogenide (sulfide, selenide, and telluride) nanostructures including inorganic graphenes (layered structures) by various important methods, their characterization and growth mechanism for the formation of enthralling morphologies, and various important protocols for surface functionalization of chalcogenides to improve the processability in technological applications are included in Chapters 4 and 5. The potential to engineer semiconductor nanostructures properties during and after fabrication presents an exciting realms and extensive prospect to simply improve the performance of renewable energy conversion systems. Chapters 6 and 7 provide detailed account of structural and optical properties of semiconductor chalcogenides.

Chapters 8–13 are typically covering applications of metal chalcogenides nanostructures in diverse renewable energy conversion devices. Chapter 8 presents updated works metal sulfide nanostructures for solar-driven hydrogen production through water splitting. Chapter 9 gives brief account on hierarchical chalcogenide nanostructures, their properties and applications in energy conversion devices. Chapters 10 and 11 are based on metal chalcogenides in photovoltaic applications. Chapter 12 focuses on theoretical work including indirect band gap calculations results and density functional theory. Chapter 13 focuses on metal telluride nanostructures for thermoelectric devices operating around room temperature.

Ahsanulhaq QurashiDhahran, Saudi ArabiaAugust 2014

Part 1

RENEWABLE ENERGY CONVERSION SYSTEMS

Chapter 1

Introduction: An Overview of Metal Chalcogenide Nanostructures for Renewable Energy Applications

Ahsanulhaq Qurashi

Center of Research Excellence in Nanotechnology and Chemistry Department, King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia

*Corresponding author: [email protected]

Abstract

In this chapter in the beginning global fossil fuel resources their current status and future anticipation and CO2 emissions its direct and indirect consequences are presented. Also significance of materials for renewable energy conversion systems as an alternative energy source is discussed. An overview of different metal chalcogenide semiconductors and their fascinating properties is reviewed. Various important (0-, 1-, 2-, and 3-dimensional) morphologies of chalcogenide nanostructures developed by different intriguing methods are illustrated followed by their important applications in renewable energy devices and their future outlook are discussed. The new class of metal chalcogenide nanostructures and their heterostructures offer outstanding prospect for the development of cost-effective, high-performance, smart, robust, and efficient energy conversion devices.

Keywords: Metal chalcogenide nanostructures, semiconductors, renewable enregy, metal sulphide, metal telluride, metal selenide nanostructures

1.1 Introduction

Sustainable energy supply is essential for the profitable and societal structure of nations, and for the comfort of human lives. In the times when the demand of traditionally subjugated natural resources is surpassing supply, industrial growth has resulted in unwanted climatic changes and developing regions are contending for bigger share of restricted fuel stocks, the exploration for new methods to meet these supplies becomes more imperative. At present, more than 80% energy use is based on oil gas and coal. Figure 1.1 shows world energy usage from different sources including oil gas and coal [1]. International energy agency (IEA) data from 1990 to 2008 reveal that the average energy use per person increased 10% whereas world population increased 27% [2, 3]. In the year 2008, total worldwide energy consumption was 474 exajoules (132,000 TWh) [4]. This is equivalent to an average power use of 15 terawatts (TW) (2.0×1010 hp) [4].

Figure 1.1 Rates of energy usage (Ref. [1]).

Presently, the world uses energy at a rate of approximately 4.1 × 1020 joules/yr, which is equivalent to a continuous power consumption of 13 trillion watts, or 13 TW [5]. With insistent conservation and advancement of energy efficiency measures, an increase in the Earth’s population to 9 billion people escorted by fast technology expansion and economic growth worldwide, is anticipated to generate more than double the requirement for energy (to 30 TW) by 2050 [5]. Sunlight is the largest source of all carbon-neutral energy. It is estimated that more energy from sunlight strikes the Earth in one hour (4.3 × 1020 J) than all the energy being consumed on the planet in a year (4.1 × 1020J) [5].

On the other hand, fossils fuel a major source of present energy will start depleting in coming decades. According to recent studies, anticipation of fossil fuel depletion by 2050 is shown in the figure (which is carried out by peak oil and gas 2007) [6]. On the basis of these studies, it is important to understand that without viable options for supplying double or triple of today’s energy use, the speedily developing world’s economic, industrial, and technological prospects will be relentlessly restricted.

According to the recent report World Energy Outlook published by the IEA, world primary energy use will raise from 12 Gtoe (metric gigatons oil equivalent) in 2007 to 17 Gtoe in 2030, for typical yearly growth of 1.5% [6].

On the basis of IEA reports, which uses an energy production mix that comprises 80% fossil fuels, CO2emissions will increase nearly 50% between 2007 and 2030 [6]. The Intergovernmental Panel on Climate Change (IPCC) has shown that this increase could result in a 6°C elevation in temperature by the end of the century [6, 7]. Figure 1.3 shows photo-graphic image of a CO2 emission at site of an industrial plant [8].

Figure 1.2

Source: Association for the Study of Peak Oil and Gas, 2007 (Ref. [6]).

Figure 1.3 Photographic image for CO2 emission at an industrial plant (Ref. [8]).

Carbon dioxide emissions resulting from energy production are an environmental predicament. Recent efforts to resolve the CO2 emission include the famous summit (Kyoto Protocol) which is a UN agreement that intends to decrease harmful climate impacts signed by many countries [9]. The main deliberation of this debate was to reduce green house gases (GHGs) emission in a time framework to be monitored by United Nations Framework Convention on Climate Change (UNFCCC) [9]. Due to continuous unregulated industrial growth of developing and under-developed nations and struggle to attain technological progression by developed nations, air quality standards are decreasing tremendously. Figure 1.4 shows continuous CO2 production by 2050 and effect of alternative policy scenario (APS) if the IPCC policies are implemented apolitically and meritoriously [10, 11]. Very recent studies include dangerous effect of air pollution including size-dependent particulate matters (PMs) on lung cancer and cardiac diseases [12, 13]. There are apparent policies adopted by developed nations as a result of tight environmental regulations to transfer substantial production of their products to under-developed and developing nations due to low manufacturing cost and high-profit margin which also enormously contribute in CO2 emissions.

Figure 1.4 Global CO2 emissions based on IEA scenarios. Black line: the Reference Scenario (RS). Blue line: the APS from 2005 to 2030 and extrapolation to the ACT Map scenario in 2050. Red line: extrapolation from APS in 2030 to the TECH Plus scenario in 2050. Green line indicates CO2 emissions reduced by 2/3 in 2050 compared to emissions today. As such, the green line represents the IPCC target of 50–80% reduction in global CO2 emissions by 2050 (Ref. [10]).

Consequently, a paramount responsibility for IEA and other international institutions arises to sternly implement global standard with respect to increasing industrial growth and regulate physically the climate changes, which can minimize its harmful effects on humans in particular and living organism in general. Considering all these important prospective of fossil fuels’ depletion, increasing pollution by the massive production of energy by various conventional sources, it is essential to explore the sources of renewable energy and more efficient strategies for energy storage and conversion into electrical or mechanical powers. The performance of conversion and storage devices strongly depends on the properties of their materials. Inventive materials chemistry predominantly new materials hold the key to indispensable advances in energy conversion and storage, both of which are essential in order to meet the challenge of global warming [14]. The purpose of materials science is to endow with key solutions for the sustainable development of renewable energy. New and engineered materials science can meet the intimidating challenges, to harvest renewable energy from natural resources. It nevertheless has an essential part to play in attaining the ambitious target. In the past, material science has contributed drastically to progress in the safe, consistent and proficient use of energy and existing natural resources. The overall efficiency, effectiveness, and expediency of potential future energy sources or systems are directly related to many imperative materials factors. These important factors include nature of the materials, cost, availability and improvement in optical, chemical, mechanical, electrical, and thermal properties as well as capability to produce materials in different forms and shapes that work effectively in areas of energy generation storage and conversion. There is a significant relationship between energy efficiency, new avenues of energy, and materials science.

The worldwide market for advanced materials and devices used in renewable energy system was $18.2 billions in 2010; it is projected to approach 31.8 billion in 2016 increasing at compound annual growth rate (CAGR) of 7.4% which includes electromechanical and electronic devices, photovoltaic materials and devices, composite and reflective materials, and so on [15]. Consequently, the need of materials study for energy conversion systems is a field of incredible opportunities for pragmatic and socially momentous applications.

1.2 Metal Chalcogenide Nanostructures

Systematic choice is a paramount for the material of a particular application which begins with desired properties and costs of candidate materials. Various organic and inorganic materials till now have been profoundly investigated for renewable energy conversion devices. Among them, semiconductor metal chalcogenides (sulfide, selenide, and telluride) received remarkable attention due to their intriguing chemical, optical, thermal, electrical, mechanical properties and optimal combination of decent conversion efficiency, ability to grow and deposit in ambient conditions, low band gap, band gap engineering, diverse crystal structures, nature to grow in layer forms, and so on [16]. A chalcogenide is a chemical compound comprises of at least one chalcogen anion and at least one more electropositive element. Even though all group 16 elements of the periodic table are defined as chalcogens, the term chalcogenide is more frequently used for sulfides, selenides, and tellurides, rather than oxides [17]. Some of the most indispensable semiconductor metal chalcogenides are shown in table 1.1.

Table 1.1 Shows properties of some of the promising metal chalcogenide semiconductors.

1.3 Growth of Metal Chalcogenide Nanostructures

Transition metal chalcogenides nanostructures, exceptional to their chemical composition and nanometer dimension, demonstrate a variety of fascinating properties and offer a solution of diversity of issues for research of both fundamental and practical interests. The purpose of this book is to encapsulate the state-of-the-art multidisciplinary research on the metal chalcogenide semiconductor nanostructures and their applications in energy conversion devices. Fundamental properties of nanomaterials are powerful function of their size and shapes. The major difference between nanomaterials and bulk materials is high surface area and large surface-to-volume ratio. Atoms at the surface have smaller number of neighbors than the chunk and have higher average binding energy per atoms. Various interesting properties like melting, phase transition conform the scaling laws. Atoms at the edges and corners have yet lower coordination and bind with foreign atoms or molecules firmly [18]. Intrinsic properties of metal chalcogenide can be further explored to utilize them in energy-harvesting devices. The properties of chalcogenide nanostructures are sturdily reliant on method of synthesis, shape, size, crystallinity, nature of surface, presence of defects, etc. For instance, it is very well documented that by changing size of quantum dots (quantum confinement effect) their color changes [18]. Considering all essential feature of metal chalcogenide nanostructures, here we review few imperative metal chalcogenide nanostructures engineered by different fascinating synthetic technique.

Manna et al. synthesized shape-dependent CdSe nanostructures [19]. Figure 1.5 shows solution processed CdSe nanorods, quantum dots, and nanostars. The shape of these nanocrystals was tailored by hexylphosphonic acid and trioctylphosphine oxide (HPA and TOPO, respectively) surfactants in inert atmosphere. ZnSe nanowires were synthesized by gold-catalyzed vapor liquid solid (VLS) mechanism from ZnSe (Aldrich 99.99%) powder sources by Wu et al. [20]. The diameter of these ZnSe nanowires varies widely from 30 nm to several microns, and can have lengths up to a few millimeters as shown in Figure 1.6. These tremendous lengths (ultra-high aspect ratio) lead to impressive nanowires growth that is visible to the naked eyes. The temperature of furnace was kept 1050°C in argon atmosphere. The XRD spectrum showed high crystallinity.

Figure 1.5 TEMs of the single-injection experiments. All of the surfactant ratio experiments (a–c) used an injection volume of 2.0 mL of stock solution. The surfactant ratio was increased from (a) 8 to (b) 20 to (c) 60% HPA in TOPO. For the injection volume experiments (d–f), 20% HPA in TOPO was used, as it was found to provide optimal rod growth conditions. The injection volumes used were (d) 1.0, (e) 1.5, and (f) 2.0 mL. Greater injection volume favors rod growth (df).

Reprinted with permission from Ref. [19]. Copyright 2013 ACS.

Figure 1.6 (a) Scanning electron microscopy (SEM) image of ZnSe nanowires as grown. (b) XRD pattern obtained from nanowires on the as-grown substrate, indexed to zinc blende ZnSe. (c) TEM image of a ZnSe nanowire with associated SAED (inset). (d) Photograph of growth substrate, where the mm-long nanowires were grown on the up-stream edge. (e) SEM image of a highly uniform ZnSe nanowire transferred onto an Au/Si substrate. The wire was broken during transfer, and is therefore shorter than as-grown structures. (Insets) SEM images of the endpoints and two middle segments.

Reprinted with permission from Ref. [20]. Copyright 2013 Springer.

Among all metal chalcogenide semiconductor nanostructures, ZnS and CdS nanostructures are popularly studied in terms of their synthesis by different fascinating methods; intriguing structural, optical, and electrical properties; and diverse applications in nanodevices. Recently, Moore et al. demonstrated the anisotropic growth of one-dimensional ZnS nanobelts as shown in Figure 1.7 [21]. The growth of nanobelts was controlled by the use of Au as catalyst. Interestingly, phase change from wurtzite metal stable to zinc blend structure is observed in this study.

Figure 1.7 (a) SEM images of ZnS nanobelts; (b) ZnS nanobelts exhibiting the weed-like growth that is typically present when no catalyst is used; (c) a deposition substrate partially covered with Au nanoparticles shows the effect of catalyst on encouraging growth on specific areas of the substrate. (Inset) The Au catalyst particle is evident at the end of the ZnS nanostructure.

Reprinted with permission from Ref. [21]. Copyright 2013 RSC.

Ye at al. synthesized CdS nanosheets on Au-coated silicon substrate by VLS method at 850°C in argon atmosphere. The surfaces of nanosheets were smooth and interestingly their diameters were in micron size. The thickness of each nanosheet ranges from 40 to 100 nm as shown in Figure 1.9. These two-dimensional nanosheets were grown using CdS powder as source materials.

Figure 1.8 (a)–(d) FESEM images of as-synthesized CdS nanosheets of different sizes.

Reprinted with permission from Ref. [22]. Copyright 2013 IOP.

Figure 1.9 (A and B) SEM images of the typical caved cuboctahedral crystals, synthesized by the solvothermal process at 140°C for 24 h.

Reprinted with permission from Ref. [23]. Copyright 2013 ACS.

Wu et al. synthesized copper sulfide (CuS) three-dimensional Concaved Cuboctahedrons by simple hydrothermal method as shown in Figure 1.9 [22]. The large-scale highly shape-tailored synthesis was carried out in the presence of ethylene glycol. These multifaceted superstructures can offer manifold preference for the renewable energy conversion devices.

We produced SnS nanoboxes by simple aqueous solution on SnS-seeded glass substrates [23]. The as-grown SnS nanostructures have an apparent stoichiometry between their constituent elements with excellent nanoboxes morphology. FESEM investigation demonstrated the SnS nanocrystals produced by the low-temperature solution method with regular orthorhombic shape and a well-defined morphology as shown in Figure 1.10. We have also developed highly crystalline SnS nanolayers by simple thermal evaporation method on different substrates [25].

Figure 1.10 (a) Low-magnification FESEM image of SnS nanobox structures (the inset shows the FESEM image of a single SnS nanobox), (b) schematic image of an orthorhombic SnS nanobox with its lattice planes, (c and d) highly magnified HRTEM images taken at the corner and center of the nanobox (the inset shows the low- and high-magnification HRTEM images of a nanobox), and (e) the SAED image of the nanobox taken at its center.

Reprinted with permission from Ref. [24]. Copyright 2013 ACS.

Au-catalyzed CdTe nanowires have been developed by Dubrovskii et al. via sublimation on Mo foils via the vapor–liquid–solid method [26]. CdTe nanowire lengthens up to 25 μm and increased as a function of growth temperature and time. The average diameter of CdTe nanowires ranges between 150 and 550 nm. These nanowires were grown at low temperature 550 and 520°C at 25 torr pressure in nitrogen atmosphere.

A significant advancement has been made for the fabrication of 1D nanostructures in the past several years [27–29]. We have developed ZnO-aligned nanostructures on different substrates [30, 31]. The development of suitable methodologies to align and position these nanostructures of various metals, metal oxides, sulfides, selenides, telluride, etc., is still at a very premature stage. One-dimensional nanostructures can be easily prepared through low-temperature solution, chemical vapor deposition, physical vapor deposition, anodization, etc. However, they still exhibit a disordered alignment with random positions and orientations apart from molecular beam epitaxy (MBE) and metal organic chemical vapor deposition (MOCVD) techniques. To assimilate 1D nanostructures into device applications, a striking challenge still remains in the hierarchical organization of these architectures into functional nanosystems and nanodevices. Well-aligned 1D nanostructures demonstrate better properties compared to their disordered counterparts. Electrons can straightly transport from one end to the other along aligned 1D nanostructures axis, whereas they might move circularly then be wasted through dispersive disordered nanowires networks. Recently, Utama et al. demonstrated the successful growth of well-aligned oriented and ordered metal chalcogenide (CdS, CdSe, and CdTe nanoarrays) on (001) muscovite Mica substrate [32]. Figure 1.12 shows FESEM and XRD analyses of CdS, CdSe, and CdTe nanoarrays. These nanowire arrays were grown by vapor transport method, and exhibited uniform diameter throughout their length, and sharp interface to the substrate. These arrays are grown with preferential growth direction of [0001] for the monocrystalline wurtzite CdS and CdSe and [111] for zinc blende CdTe nanowires, which also attributed copious twinning precincts.

Figure 1.11 Back-scattered electron image of a typical CdTe NW array grown on Mo foil.

Reprinted with permission from Ref. [26]. Copyright 2013 IOP.

Figure 1.12 SEM images with 45_ inclined view and XRD spectra of the as-grown vertically aligned cadmium chalcogenide nanostructures on mica. Low-magnification images of (a) CdS nanowire and belts, (b) CdSe nanowires, and (c) CdTe nanorods are shown (scale bar represents 1 μm) along with the higher-magnification ones which are provided as insets (scale bar represents 500 nm). In (d), the XRD spectrum from pure muscovite mica is also displayed. The spectra have been offset accordingly and scaled to show weaker peaks for the sake of clarity.

Reprinted with permission from Ref. [32]. Copyright 2013 ACS.

Multifarious nanostructures, both in the shape of hierarchically branching/hyperbranching nanowire and multi-component nanowire heterostructures, are probably even more fascinating for renewable energy harvesting and transfer. Several diverse customized bottom-up synthetic techniques are used to catalyze branching in nanowires to structure hierarchical nanowires. Figure 1.13 shows dislocation-driven growth of hierarchical PbS nanostructures by Song Jin group [33]. The growths of these complex nanostructures were controlled by hydrogen atmosphere in the furnace, pressure, temperature, and substrate, respectively. The hierarchical and hyperbranched nanostructures and their heterostructures with different chemical compositions can be potential future candidates for improved solar conversion efficiencies in photovoltaic and photoelectrochemical devices.

Figure 1.13 Global effects of hydrogen flow on the morphology of PbS nanowires or other CVD products. (a) Clusters of hyperbranched nanowires formed with 1-min initial hydrogen flow at 1.0 sccm. (b) Exclusively tree morphology resulting from 1.0 to 2.5 sccm constant flow of hydrogen. (c) Mixtures of trees, hyperbranched clusters, and small cubes from 9.0 to 20 sccm of hydrogen flow.

Reprinted with permission from Ref. [33]. Copyright 2013 ACS.

1.4 Applications of Metal Chalcogenide Nanostructures

Tailoring of size, shape, surface area, architecture, and assembly properties of nanostructured materials are fundamental steps toward their behavior and their applications in advanced and miniatured nanodevices and nanosystems [34–36]. Predominantly, semiconductor metal chalcogenide nanostructures are promising materials due to their narrow emission spectra for renewable energy conversion devices such as solar cell, electrochemical water splitting, thermoelectrics, lithium ion batteries, supercapacitors, energy storage, fuel cells, and piezoelectrics [37–59]. Figure 1.14 shows 0-, 1-, 2- and 3-dimensional semiconductor metal chalcogenide nanostructures and their potential applications in renewable energy conversion applications. The biggest impact of metal chalcogenides may have, however, in solar power thermoelectric and hydrogen production [60–64].

Figure 1.14 Schematic diagram of metal chalcogenide nanostructures for different renewable energy conversions devices systems.

This particular book is divided into three parts. First part is typically focused on an introduction of metal-chalcogenide nanostructures, current status of renewable energy and its future perspectives, and need of nanomaterials for renewable energy applications. In the second part of the book, attention is paid to different methods of synthesis, growth mechanism, and structural and optical properties of metal sulfide, selenide, and telluride nanostructures. Third part is mostly based on the applications of chalcogenide nanostructures in different emerging fields which include solar cells, hydrogen production, and thermoelectrics.

1.5 Summary and Future Perspective

It is anticipated that the world will entail virtually about 30 TW of new power by 2050 [5]. The enormous energy requisite and fossil-fuel-stimulated environmental pollution will produce colossal strain for scientists to develop clean and sustainable technologies to offer abundant energy in an economically feasible approach. Energy conversions devices such as solar cell, fuel cells, thermoelectric devices, photoelectrochemical water splitting cells, piezoelectric nanogenerators, Li-ion batteries and supercapacitors, etc., have the immense potential to power the energy challenging fields that range from portable devices to transportation and stationary sources. These renewable energy conversion devices predominantly depend upon synthesis techniques of functional materials and their intrinsic properties. Nanomaterials offer unique and attractive features: high surface area, better conductivity, improved catalytic activities, smooth electron transport, less quantity, economical synthetic methods, etc. Among different types of nanomaterials, metal chalcogenide semiconductor nanostructures exhibit unique electronic, chemical, and physical properties. The inherent properties of metal chalcogenide nanostructures can be further tuned depending upon their application to particular energy conversion device applications. The new class of metal chalcogenide nanostructures and their heterostructures offer magnificent prospect for the development of cost-effective, high-performance, smart, robust, and efficient energy conversion devices. Metal doping of metal chalcogenide nanostructures with particular dopant can engineer the band gap of materials which can enhance the efficiency of energy conversion devices. There is colossal opportunity for metal chalcogenide heterostructures formation (binary, ternary, and quaternary chalcogenides) depending upon the nature of applications and requisite. These new type of materials with multiple chalcogens can provide better efficiency of solar energy conversion systems and other renewable energy device applications.

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Chapter 2

Renewable Energy and Materials

Muhammad Asif1,2

1Department of Architectural Engineering, King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia

2School of Engineering and Built Environment, Glasgow Caledonian University, Glasgow, UK

*Corresponding author: [email protected]

Abstract

Renewable energy is playing an active role in addressing the energy and environmental problems across the world. Its contribution at the global level is set become more important in future. Development of advanced and high performance materials has played a pivotal role in the success of renewable energy technologies. The last couple of decades, for example, have shown development of a wide variety of solar photovoltaic cells and an exponential growth in the capacity of wind turbines, thanks to improved and innovative materials. The chapter discusses the significance of materials in the advancement of renewable energy technologies. It also briefly reflects upon the impact of modern materials on the development of hydrogen and fuel cell technologies.

Keywords: Renewable energy, solar photovoltaic, wind turbine, hydrogen, fuel cell

2.1 Global Energy Scenario

Energy is the backbone of modern societies. Human dependency on energy is ever increasing across the world. It has become vital in almost every aspect of modern life including agriculture and farming, transportation, education, and manufacturing of goods. The accomplishments of civilization have largely been achieved through the increasingly efficient and extensive harnessing of various forms of energy to extend human capabilities and ingenuity. One of the most significant transitions in global energy systems is that of decarbonization, an increase in energy quality. Considering the case of fossil fuels, the dominating energy resource over the course of human history, each successive transition from one source to another – from wood to coal, from coal to oil – has entailed a shift to fuels that were not only harnessed and transported more economically, but also had a lower carbon content and higher hydrogen content. It is also evident that at each step greater energy density is being achieved. The third wave of decarbonization is now at its threshold, with natural gas use growing fastest, in terms of use, among the fossil fuels. The fourth wave, the production and use of pure hydrogen, is on the horizon. Its major drivers are technological advances, renewed concern about the security and price of oil and gasoline, and growing pressure to address local air pollution and climate change.

Energy security – provision of sufficient, affordable, and consistent energy – is essential for eradicating poverty, improving human welfare, and raising living standards worldwide. The current international energy scenario faces a string of serious challenges in terms of long-term sustainability. These include rapidly surging demands, depletion of conventional fossil fuels reserves, global warming and other energy-related environmental concerns, geopolitical and military conflicts surrounding oil-rich countries, insecurity of energy supplies, and fluctuating energy prices [1]. The world heavily relies on fossil fuels to meet its energy requirements – fossil fuels such as oil, gas, and coal – which are providing almost 80% of the global energy demands. Fossil fuel reserves, however, are diminishing rapidly in most parts of the world and stress on existing reserves is increasing day by day due to increased demand as also highlighted in Table 2.1 [2]. The existing global oil reserves are reported to have a reserve to production ration of 54 years [3]. While the global energy demands are set to rise in future due to growing population, urbanization, and modernization, the enormous amount of energy already being consumed across the world is having adverse implications on the ecosystem of the planet. Fossil fuels are regarded to be inflicting enormous impacts on the environment. Global warming and climatic changes driven by human activities, in particular, the production of greenhouse gas emissions (GHG), directly impact the environment.

Table 2.1 Growth in global oil demand.

The world faces an unprecedented challenge not only in terms of availability of resources but also affordability of resources. The age of abundant and cheap resources is drawing to an end. The average cost of drilling for oil, for example, has doubled over the past decade. Similarly, rising food prices drove nearly forty-four million people below the poverty line in the latter half of 2010 alone [4].

2.2 Role of Renewable Energy in Sustainable Energy Future

Renewable energy as the name implies is the energy obtained from natural sources such as solar energy, wind power, hydropower, biomass energy, geothermal energy, and wave and tidal power. Renewable energy resources that use indigenous sources have the potential to provide energy services with zero or almost zero emissions of both air pollutants and greenhouse gases. They are presently meeting almost 13.5% of the global primary energy demands and are acknowledged as a vital and plentiful source of energy that can indeed meet entire world’s energy demand.

Renewable energy sources have enormous potential towards meeting the present and future world energy demands. Solar energy, for example, is the most widely and evenly distributed energy resource in the world; the noon sunshine delivers about 1 kW/m2 of solar energy. The amount of solar radiation received by our planet is far more than our needs – according to some estimates, 10,000 times more than the global requirements. Estimates also suggest that the world’s total electricity needs can be met from a photovoltaic system covering 1.5% of the European landmass, 380 km × 380 km as shown in Figure 2.1 [5].

Figure 2.1 EU land mass needed to generate electricity for entire world from solar PV.

Renewable energy adds a great value to the sustainable development in general and sustainability of the energy scenario in particular. It can enhance diversity in energy supply markets, secure long-term sustainable energy supplies, and reduce local and global atmospheric emissions. It can also provide commercially attractive options to meet specific needs for energy services (particularly in developing countries and rural areas), create new employment opportunities, and offer possibilities for local manufacturing of equipment. The use of renewables can also reduce the reliance on fossil fuel imports and to a certain extent insulate the economies from fluctuating fossil fuel prices.

Renewable energy has come of age to play a significant role in national energy supplies across the world. Over the last decade, and despite the recent economic crisis, renewable energy has experienced a rapid and sustained development in terms of policy frameworks, technologies markets, and industries. Estimates as of 2011 (the latest year to have the comprehensive data) suggest that renewable energy supplied 19% of global final energy consumption. While the substantial contribution comes from traditional biomass, modern renewable sources accounted for an estimated 4.1% of total final energy consumption. Estimates suggest that the worldwide installed capacity of renewable energy exceeded 1470 GW in 2012, up about 8.5% from 2011. Wind power is the fastest growing form of renewable energy as it represented around 39% of the renewable power capacity added worldwide in 2012, followed by hydropower and solar PV, each accounting for approximately 26% increment in installed capacity [6]. Offshore wind power is expected to play a significant role in the future growth of wind power. Forecasts suggest that the global offshore wind investment will grow nine-fold between 2011 and 2025, rising from US$6 billion to US$52 billion. The total installed capacity of offshore wind is expected to reach around 95 GW by 2025 up from the current capacity of 4.2 GW [7].

2.3 Importance of Materials Role in Renewable Energy

Advancements in materials have greatly contributed to the evolution of the energy sector. Oil and gas drilling bits, power generation turbines (i.e., hydro turbines, steam turbines, and gas turbines) and corrosion-resistant materials and coating are some of the vivid examples of technologies that have seen substantial performance enhancement both in terms of efficiency and durability as a result of improvements in materials. Similarly, the modern era of renewable energy technologies dawned in 1970s owe its success to improvements in their constituent materials and the involved manufacturing techniques. Solar cells, for example, have not only experienced efficiency enhancement for the traditional silicon-based systems but have also seen a wide variety of new materials providing the photovoltaic effect. The lab efficiency of PV cells has now increased from 6% in 1950s to over 20%. In terms of composition, PV cells have seen a wide range of diversity; the mono- and poly-crystalline silicon PV cells are now being commercially accompanied by PV cells made of materials like gallium-arsenide, gallium-antimony, copper-indium-diselenide, and cadmium-telluride. While the plastic and organic PV cells are in the research and development (R&D) phase, multi-junction tandem PV cells with efficiency of over 40% are already in market. When it comes to wind power, the phenomenal growth of wind turbines both in capacity and application could not have been possible without the development of more robust materials. Commercially available wind turbines have seen a jump in capacity from less than 100 kW in 1980s to 7.5 MW in 2010s as shown in Figure 2.2.

Figure 2.2 Growth in size of wind turbines over the last three decades.

In view of the enormous amount of structural and mechanical stresses faced by multi-MW range wind turbines, the production of tower and blades – which for a 7.5 MW turbine can be 140 m high and over 65 m long respectively – has truly tested the scientific and engineering skills of materials scientists. Modern wind turbine blades are being made from composite materials such as glass fiber and carbon fiber reinforced plastic and lightweight cores. Onshore wind turbines are now being paralleled by offshore and completely floating wind turbines. The offshore application of wind turbines, being regarded as the future of wind power, poses its own set of challenges, primarily due to exposure to harsher weather conditions, the solutions of which require rigorous contribution from material science.

While huge developments have been made at various stages of the energy equation including extraction, production and processing of resources, transformation of energy, and utilization options, effective storage of energy especially in electric form remains to be a challenge. Storage capacity remains to be the main issue with electric batteries.

Given the intermittency of renewable energy and storage issues with batteries, hydrogen, and fuel cells are being deemed as a potential solution for future. Fundamental research is vital for developing novel materials that can meet the challenges of on-board hydrogen storage production, fuel cell, and other renewable energy conversion devices and systems. Predominantly nanostructured materials with exceptionally high surface areas and abundant catalytically active sites open new avenues for improved catalytic performance and selectivity. Shape-controlled nanostructures need attention of researchers since nanomaterials provide great potential for improved hydrogen storage due to short diffiusion distances, diverse phases with good capacity, less heats of adsorption/desorption, swift kinetics, and surface states able to catalyze hydrogen dissociation. Proficient conversion of sunlight to hydrogen by water splitting via photovoltaic cells or through direct photocatalysis or photoelectrochemical cells is an imperative landmark for hydrogen production and economy, which completely depends on catalytic materials [8–15]. Therefore, the process of energy conversion through charge collection, separation and transport in solar cells, photocatalytic and photoelectrochemical devices requires nanoarchitectured materials with very-well-tuned properties and tailored morphology [16–22]. As there is an immense need for new strategies to proficiently harvest light and utilize the entire solar spectrum. Thus, catalytic materials are highly significant to realize the improved energy conversion devices.

Similarly, enormous progress has been made for the development of high-performance fuel cell [23–30]. Presently, huge research efforts have been devoted to the development of high-performance, high-efficiency, low-cost environmental benign fuel cells, which significantly depend on the intrinsic properties of the analogous catalyst materials. Currently, the best and most commonly used catalysts for polymer electrolyte membrane (PEM) fuel cells are still the carbon nanomaterial-supported noble metal (Pt) nanocomposites, which, nevertheless, undergo severe limitations such as high costs (Pt), slow ORR kinetics, time-dependent flow and CO deactivation. Fortunately, the persistent evolution of material science reveals that transition metal chalcogenides are very efficient substitute to the Pt/C electrocatalysts and for high-efficiency solar energy conversion devices and their comparable catalytic performance is at much lower cost. [6, 31, 32–35]. In this book, we focused our attentions on the synthesis, properties and applications of transition metal chalcogenide semiconductor nanostructures for high-performance renewable energy conversion devices.

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Chapter 3

Sustainable Feed Stock and Energy Futures

H. Idriss

SABIC T&I CTS Riyadh and CRI KAUST, Saudi Arabia Department of Chemistry, University of Aberdeen, Aberdeen, UK

*Corresponding author: [email protected]

Abstract

The 21st