Nanomaterials for Energy Conversion

The increasing demands for sustainable catalysis and carbon neutrality are driving the need for the development of green, scalable, and multifunctional reaction platforms. This review establishes the conceptual framework for wood as a structurally preserved monolithic microreactor for catalysis and reaction-based processes. The relationships between wood architecture, physicochemical properties (porosity, channel size, tortuosity, thickness, tailored surface chemistry), as well as catalytic performance (mass transport efficiency, directional electron transfer, catalyst immobilization, and confinement-modulated reaction pathways) are summarized to elucidate the structure-function correlations governing reactivity and durability. This review represents the first example to systematically analyze wood as a monolithic, structurally preserved, reaction-governing scaffold for catalysis and reaction-based processes. Applications in catalytic conversion, solar steam generation, environmental energy harvesting (e.g., moisture-electric generators for wearable electronics), and gas-phase reactions demonstrate the versatility of these systems. Especially, we deeply analyze how the wood structure governs the catalytic performance in these advanced applications. Besides, we compare the cost, sustainability, and some other factors of wooden microreactors with other monolithic platforms (e.g., ceramic foams, metallic structures, polymeric scaffolds). Finally, current challenges for rational design and scalable implementation are proposed in perspective of sustainable catalysis and energy conversion.

Development of porous heteroatom‐doped carbon materials from plant biomass is of great significance for various applications in environment, energy conversion and catalysis process. However, the different natures of carbon materials derived from the leaf, stem and root of the same plant biomass are rarely reported. Herein, we synthesized porous carbon materials from the leaf, stem and root of amaranth respectively by pyrolysis without any activation treatment. Detailed characterizations indicated that these three carbon materials all had nitrogen, sulfur doped atoms and similar degree of graphitization, but showed distinct differences in the pore structures and surface compositions. We suggested these differences were contributed by the different contents of ashes, vascular bundles and proteins in different parts. When used as metal‐free carbocatalysts for the oxidation of aromatic hydrocarbons, stem‐derived carbon (SDC‐A) exhibited the highest catalytic performance due to its high surface area, profitable pore volume and rich doped heteroatoms. Moreover, the carbocatalysts derived from the leaf, stem and root of pumpkin vine and coriander showed similar activity differences in oxidation of aromatic alkanes, implying the present results have a certain extent generality, and provide a new guidance for preparing carbon materials from plant biomass.

Solar energy induced catalytic reactions allow solar energy to be used directly in sunlight-to-chemical energy conversions. Many scientific progress have been made in solar energy utilization and conversions, whereas, scientists from all over the world claimed that there are still many problems need to be further addressed including how to further enhance the solar energy utilization & conversion efficiency etc. The detail micro-interface process, redox mechanism, charge-carrier transfer behavior and active species actions need to be further studied. Following all of these concerns, series of multifunctional complex oxides with hetero-junctions have been well designed in our group towards solar energy utilization and conversion process via photo-induced chemical process, and different transient physical techniques including in situ EPR, in situ SPV and transient laser flash photolysis etc. have also been used to elucidate the interfacial photo-induced redox process and charge-carrier behaviors. We found that hierarchical nanostructured assemblies can be engineered to tailor the properties of external fields modulated and/or light harvesting assemblies. The crystal-, micro- and surface-interface structure could be tailored by utilizing various synthesis strategies, which would incur the nanomaterials with novel PEC/PC properties. Furthermore, combined in - situ spectroscopic characterization could provide more detail structural information and redox process over micro-interface, which would be beneficial for design efficient solar and energy conversion based materials at molecular utilization and/or atomic level. The tailored hierarchical nanomaterials may find novel applications in multidisciplinary fields.

Advanced nano-structured materials have emerged as key elements in enhancing the acting of strength storage devices in the way that fuel cells, solar cells, Li-ion batteries, super-capacitors, and capacitors. These matters offer superior characteristics including high surface area, enhanced electrical conductivity, and improved mechanical strength, enabling efficient energy storage and conversion processes. In fuel cells and solar cells, nano-structured materials like graphene, quantum dots, and alloy oxides facilitate rapid charge transfer and increase design efficiency. In Li-ion batteries, nano-structured electrodes reinforce ion diffusion and provide higher energy densities. Super-capacitors benefit from nano-structured carbon materials with increased capacitance and faster charge/discharge rates. Capacitors with nano-structured dielectrics exhibit enhanced energy storage capabilities and prolonged lifespan.

Heterogeneous based functionalized nanocomposite materials have attracted considerable attention in both energy storage and conversion process, due to their fast electron transfer process and their ling-life cycles. Herein, the review briefly discussed different kinds of techniques, which are used for the fabrication of carbon based nanocomposites like sol-gel, hydrothermal (HT), in situ polymerization and electrochemical methods, etc In particularly, functionalized carbon decorated nanocomposites have been focused on the designing and development of rational candidate for future energy technologies. Especially, the highlighted nanocomposites have become more attention in the area of energy technologies mainly caused by their larger electrode surface area, high mechanical strength, excellent electrochemical properties, and rapid electrochemical redox behaviour. Considerable advancements in the combinations of nanoscale based composite devices have the platforms to develop new energy storage technology to fulfill the global energy demands. Finally, it summarizes the recent advantages of carbon supported composite, which significantly enhanced their electrochemical energy storage devices properties like high capacitance and boosted specific capacitive values.

Carbon and silicon materials are two of the most important materials involved in the history of the science and technology development. In the last two decades, C and Si nanoscale materials, e.g., carbon nanotubes, graphene, and silicon nanowires, and quantum dots, have also emerged as the most interesting nanomaterials in nanoscience and nanotechnology for their myriad promising applications such as for electronics, sensors, biotechnology, etc. In particular, carbon and silicon nanostructures are being utilized in energy-related applications such as catalysis, batteries, solar cells, etc., with significant advances. Understanding of the nature of surface and electronic structures of nanostructures plays a key role in the development and improvement of energy conversion and storage nanosystems. Synchrotron soft X-ray absorption spectroscopy (XAS) and related techniques, such as X-ray emission spectroscopy (XES) and scanning transmission X-ray microscopy (STXM), show unique capability in revealing the surface and electronic structures of C and Si nanomaterials. In this review, XAS is demonstrated as a powerful technique for probing chemical bonding, the electronic structure, and the surface chemistry of carbon and silicon nanomaterials, which can greatly enhance the fundamental understanding and also applicability of these nanomaterials in energy applications. The focus is on the unique advantages of XAS as a complementary tool to conventional microscopy and spectroscopy for effectively providing chemical and structural information about carbon and silicon nanostructures. The employment of XAS for in situ, real-time study of property evolution of C and Si nanostructures to elucidate the mechanisms in energy conversion or storage processes is also discussed.

Energy generation and storage are perhaps two of the most imperative, ongoing, and challenging issues facing the world to date. The rapidly growing global energy demand is placing increasingly greater burdens on the incumbent fossilfuel based infrastructure necessitating the development and mobilization of alternative technologies, particularly those focused on exploiting or scavenging new and clean energy sources alongside the development of highly efficient energy storage devices. Though advanced energy storage concepts and regenerative energy systems have been the focus of considerable attention over the past decade, the advent of the nanoage added traction to field by promising the potential to fabricate, for the first time, a wide range of truly novel devices that will enable this paradigm shift in energy applications. However, breakthroughs are needed to synthesize, engineer, and manufacture, en masse, nanomaterials and microand macrostructures based thereon. Central to this is a new understanding of the atomistic assembly of such materials in order to study energy transduction at nanoscale and to elucidate the underlying chemical and physical mechanism involved in high efficient energy conversion and storage. This special issue—which focuses on the science and engineering of nanomaterials and nanodevices used in all forms of energy harvesting, conversion, storage, and utilization—consists of 13 papers spanning topics detailing the empirical exploitation of nanowires for enhanced supercapacitors to thermoelectric generators, photocatalytic nanoparticles, and small molecule based organic solar cells. L. Chen et al. discuss the use of scanning force microscopy to investigate frictional images of newly cleaved surface domains of single crystal BaTiO 3 under ambipolar biases, providing a new method to determine domain polarization direction, whereas H.-S. Tsai et al. synthesized novel onedimensional SiO 2 /Ta 2 O 5 core-shell nanostructures, proposing a Ta-O diffusion-controlled growth process. P. Hiralal et al. report on the tailored growth of carbon nanostructures for application in high-frequency supercapacitors formed from engineered vertically aligned nanocarbon electrodes which are shown to enhance the porosity and electrolyte permeability within the device, resulting in a novel fabrication route to realise a functionally advanced compact energy storage platform. In a similar approach, H. Xu et al. summarise their work towards the preparation of Co 3 O 4 nanoparticles which facilitate long-lifetime and electrochemically superior supercapacitors by undertaking detailed studies of the electrode metrology. Z. Ma et al. report on energy recovery of coolant heat for internal combustion engines using thermoelectric generation technology. They showed that cooling improved with increased fan speeds and that the Seebeck coefficient was reduced with an increase in temperature difference between the two ends of thermoelectric generator.

Fuel cells, supercapacitors and lithium-ion batteries are the typical energy conversion and storage devices of great significance in which carbon-based nanostructures could play irreplaceable role. The functionalized carbon-based nanotubes/nanocages (CNTs/CNCs) could be applied to fuel cells to lower Pt loading by highly dispersing and immobilizing Pt-based nanoparticles, or to totally get rid of Pt with the metal-free electrocatalytic ability themselves. The abundant nanostructures and morphologies, tunable compositions, high surface area, good conductivity, small volume expansion, as well as the low cost and environmental benignity make the CNTs/CNCs have great potential as electrode materials of supercapacitors and lithium-ion batteries. In this talk I will give a brief introduction to the progressive advancements in our group about the synthesis, performance and mechanism of the CNTs/CNCs for this kind of energy conversion and storage. Special attention will be paid to the materials design by doping the CNTs/CNCs with electron-rich N, electron-deficient B, and the both to elucidate the correlation of the performance with the doping microstructures, which is a general interesting issue in developing the advanced carbon-based energy materials.

As a very attractive approach to energy conversion and storage, electrocatalytic, photocatalytic, and photoelectrocatalytic strategies have gained increasing attention in the past decades. Numerous modification methods have been used to boost the performances of electrocatalytic, photocatalytic, and photoelectrocatalytic reactions, including morphology optimization, element doping, and heterostructure construction. In addition to these traditional technologies, the introduction of thermal field emerges as a unique and robust technology for enabling highly efficient electrocatalytic, photocatalytic, and photoelectrocatalytic processes. This review focuses on the recent developments in the application of thermal field to enhance the electrocatalytic, photocatalytic, and photoelectrocatalytic energy conversion and storage. First, the mechanisms of thermal field–assisted enhancement in charge transfer, reaction kinetics, and mass transport are presented. Then, the heating methods (i.e., traditional heating, photothermal heating, and magnetic heating) used to increase the temperature of electrocatalytic, photocatalytic, and photoelectrocatalytic materials are summarized. Highlights are put on the photothermal conversion materials for thermal field–enhanced catalytic reactions. The applications of thermal field–enhanced catalytic processes are discussed, including water splitting, value‐added chemical production, and pollutant degradation. Finally, a proper discussion of the remaining challenges and further outlook for coupling thermal field with catalytic energy conversion and storage processes is provided.

Evaporative electrical energy generation via diffusion-driven ion-electron-coupled transport in semiconducting nanoporous channel

Developing transition metal nitrides with unique nanomorphology is important for many energy storage and conversion processes. Here, a facile and novel one-step approach of growing 3D hierarchical nickel nitride (hNi3 N) on Ni foam via nitrogen plasma is reported. Different from most conventional chemical synthesis, the hNi3 N is obtained in much shorter growth duration (≤15 min) without any hazardous or reactive sources and oxide precursors at a moderate reaction zone temperature of ≤450 °C. Among possible multifunctionalities of the obtained nanocoral hNi3 N, herein the performance in reversible lithium ion storage and electrocatalytic oxygen evolution reaction (OER) is demonstrated. The as-obtained hNi3 N delivers a considerable cycling performance and rate stability as a lithium ion battery anode, and its property can be further enhanced by coating the hNi3 N surface with graphene quantum dots. The hNi3 N also serves as an active OER catalyst with high activity and stability. Additionally, on the basis of controlled growth under different nitrogen plasma treatment time, the formation mechanism of the nanocoralline hNi3 N is outlined for further extension to other materials. The results on time- and energy-efficient nitrogen-plasma-based preparation of hNi3 N pave the way for the development of high-performance metal nitride electrodes for energy storage and conversion.

In the becoming years, energy demand is expected to grow faster than current needs. Thermoelectric technology works through conversion process from heat energy into electricity directly and vice versa. Thermoelectric device that use for energy conversion from heat into electrical is known as thermoelectric generator (TEG). TEG is made of Bismuth Telluride, Lead Telluride and Silicon Germanium compound which contains figure of merit (ZT). In term of applications, TEG is possible to be applied in extreme condition such as a power supply in the space mission, harvesting heat from transportation vehicle, and getting waste heat from industrial sector. Furthermore thermoelectric generation is possible also to be applied as a micro power generation system which is very useful for electrical source for residential installation. In this paper, a brief review of above applications is presented. Early developed research investigation is carried out for application of thermoelectric generator in residential installation by using biomass wooden-fuel stove. The early result shows that there are amount of heat emitted from the side cylinder cook stove as energy waste. There is a chance and possibility to harvest energy waste in the stove to become electric source and finally this related research effort will increase the efficiency of the electric stove in energy conversion.

Heterogeneous nanostructure array for electrochemical energy conversion and storage

The conversion of thermal energy to electricity and vice versa by means of solid state thermoelectric devices is extremely appealing. However, its cost-effectiveness is seriously hampered by the relatively high production cost and low efficiency of current thermoelectric materials and devices. To overcome present challenges and enable a successful deployment of thermoelectric systems in their wide application range, materials with significantly improved performance need to be developed. Nanostructuration can help in several ways to reach the very particular group of properties required to achieve high thermoelectric performances. Nanodomains inserted within a crystalline matrix can provide large charge carrier concentrations without strongly influencing their mobility, thus allowing to reach very high electrical conductivities. Nanostructured materials contain numerous grain boundaries that efficiently scatter mid- and long-wavelength phonons thus reducing the thermal conductivity. Furthermore, nanocrystalline domains can enhance the Seebeck coefficient by modifying the density of states and/or providing type- and energy-dependent charge carrier scattering. All these advantages can only be reached when engineering a complex type of material, nanocomposites, with exquisite control over structural and chemical parameters at multiple length scales. Since current conventional nanomaterial production technologies lack such level of control, alternative strategies need to be developed and adjusted to the specifics of the field. A particularly suitable approach to produce nanocomposites with unique level of control over their structural and compositional parameters is their bottom-up engineering from solution-processed nanoparticles. In this work, we review the state-of-the-art of this technology applied to the thermoelectric field, including the synthesis of nanoparticles of suitable materials with precisely engineered composition and surface chemistry, their combination and consolidation into nanostructured materials, the strategies to electronically dope such materials and the attempts to fabricate thermoelectric devices using nanoparticle-based nanopowders and inks.

Study on photochemistry and component transport coupling processes of azobenzene molecular solar thermal system