Electrochemical capacitors (best known as supercapacitors) are high‐performance energy storage devices featuring higher capacity than conventional capacitors and higher power densities than ...batteries, and are among the key enabling technologies of the clean energy future. This review focuses on performance enhancement of carbon‐based supercapacitors by doping other elements (heteroatoms) into the nanostructured carbon electrodes. The nanocarbon materials currently exist in all dimensionalities (from 0D quantum dots to 3D bulk materials) and show good stability and other properties in diverse electrode architectures. However, relatively low energy density and high manufacturing cost impede widespread commercial applications of nanocarbon‐based supercapacitors. Heteroatom doping into the carbon matrix is one of the most promising and versatile ways to enhance the device performance, yet the mechanisms of the doping effects still remain poorly understood. Here the effects of heteroatom doping by boron, nitrogen, sulfur, phosphorus, fluorine, chlorine, silicon, and functionalizing with oxygen on the elemental composition, structure, property, and performance relationships of nanocarbon electrodes are critically examined. The limitations of doping approaches are further discussed and guidelines for reporting the performance of heteroatom doped nanocarbon electrode‐based electrochemical capacitors are proposed. The current challenges and promising future directions for clean energy applications are discussed as well.
Heteroatom doping and oxygen functionalizations are a promising solution to improve the energy storage performance of nanocarbon materials. The fundamental effects of doping and oxygen functionalization on the physicochemical properties of nanocarbons leading to enhanced supercapacitor performance are reviewed. This article may serve as a reference for fundamental properties and practical applications of heteroatom doped and oxygen functionalized nanocarbons.
A comparable power conversion efficiency (PCE) to that of commercial Si solar cells (over 23%) has been achieved by organic–inorganic hybrid perovskite solar cells (OIH-PSCs) within several years. As ...OIH-PSC materials have hygroscopic organic cations that limit their thermal and long-term stability (i.e. operational lifetime of about 1 year, much shorter than commercial Si of 20–25 years), significant research efforts have been directed to the development of all-inorganic PSCs to overcome this limitation. These studies have demonstrated that cesium lead halide (CsPbX3) and Pb-free cesium tin halide (CsSnX3) perovskites are promising materials for the fabrication of thermally stable and efficient solar cells. This work reviews recent progress on versatile CsPbX3 and CsSnX3 inorganic PSCs. Remarkable PCE values over 17% and 4% have been achieved by employing CsPbX3 and CsSnX3 perovskites, respectively, in a short development time. In addition, we evaluate the materials engineering methods and film deposition techniques for producing such inorganic perovskite materials. Several strategies including surface and interfacial passivation are discussed to alleviate hysteresis and instability of inorganic PSCs. Furthermore, future research directions including device engineering using inorganic metal oxide charge transport layers are suggested to further reinforce this innovative advances in the inorganic PSCs.
Alkaline water electrolysis (AWE) systems offer a cost‐effective and scalable approach for large‐scale hydrogen production using renewable energy sources. However, their susceptibility to load ...fluctuations, particularly the reverse‐current (RC) phenomenon during shutdown events, poses a significant challenge to the long‐term stability and scalability of these systems. Herein, a catalytic approach for enhancing the RC tolerance in AWE systems by using Pb‐decorated Ni cathode catalysts (Pb/Ni) is introduced. The oxidation of Pb/Ni by repeated RC lowers the electromotive force for the reverse current operation, and consequently, imparts RC tolerance. Intriguingly, contrary to the expectation that the decoration with lead, an inert material for the hydrogen evolution reaction (HER), will interfere with the hydrogen generation of the Ni catalyst, the presence of Pb on the Ni cathode after the RC flow promotes both the proton desorption and water‐dissociation steps, improving the HER activity. Furthermore, the AWE stack testing with Pb/Ni catalysts is perfectly operated, demonstrating remarkably enhanced RC tolerance during startup/shut‐down (SU/SD) testing protocol. This paper presents a new strategy for mitigating the AWE performance degradation induced by RC flow and for achieving Pb/Ni catalysts with improved operational durability against RC flow in AWE systems.
The transient stability of the catalyst caused by the reverse‐current phenomenon during the shutdown of the AWE system by load fluctuations is one of the most challenging limitations to address. This study introduces a catalytic approach for enhancing the RC by decorating lead on Ni catalysts. The surface decoration of the Ni catalyst with Pb (Pb/Ni) catalyst exhibits improved HER activity as well as remarkable RC‐flow resistance.
Golden bristlegrass‐like unique nanostructures comprising reduced graphene oxide (rGO) matrixed nanofibers entangled with bamboo‐like N‐doped carbon nanotubes (CNTs) containing CoSe2 nanocrystals at ...each node (denoted as N‐CNT/rGO/CoSe2 NF) are designed as anodes for high‐rate sodium‐ion batteries (SIBs). Bamboo‐like N‐doped CNTs (N‐CNTs) are successfully generated on the rGO matrixed nanofiber surface, between rGO sheets and mesopores, and interconnected chemically with homogeneously distributed rGO sheets. The defects in the N‐CNTs formed by a simple etching process allow the complete phase conversion of Co into CoSe2 through the efficient penetration of H2Se gas inside the CNT walls. The N‐CNTs bridge the vertical defects for electron transfer in the rGO sheet layers and increase the distance between the rGO sheets during cycles. The discharge capacity of N‐CNT/rGO/CoSe2 NF after the 10 000th cycle at an extremely high current density of 10 A g−1 is 264 mA h g−1, and the capacity retention measured at the 100th cycle is 89%. N‐CNT/rGO/CoSe2 NF has final discharge capacities of 395, 363, 328, 304, 283, 263, 246, 223, 197, 171, and 151 mA h g−1 at current densities of 1, 2, 4, 6, 8, 10, 12, 14, 16, 18, and 20 A g−1, respectively.
As high‐performance anodes for sodium‐ion batteries, golden bristlegrass‐like graphene nanofibers entangled with N‐doped CNTs containing CoSe2 nanocrystals are designed and synthesized. The synthesized unique nanostructure exhibits high cycling and rate performances even at extremely high current densities. The synergistic effect of the golden bristlegrass‐like unique structure and the N‐doped CNTs/graphene composite results in efficient anode materials for sodium‐ion batteries.
The electrochemical reduction process has been used to reduce spent oxide fuel to a metallic form using pyroprocessing technology for a closed fuel cycle in combination with a metal-fuel fast ...reactor.In the electrochemical reduction process,oxides fuels are loaded at the cathode basket in molten Li2O–LiCl salt and electrochemically reduced to the metal form.Various approaches based on thermodynamic calculations and experimental studies have been used to understand the electrode reaction and efficiently treat spent fuels.The factors that affect the speed of the electrochemical reduction have been determined to optimize the process and scale-up the electrolysis cell.In addition,demonstrations of the integrated series of processes（electrorefining and salt distillation） with the electrochemical reduction have been conducted to realize the oxide fuel cycle.This overview provides insight into the current status of and issues related to the electrochemical processing of spent nuclear fuels.
Controlling the polarization state of light has been a significant issue for various integrated optical devices such as optical imaging, sensors, and communications. Recent advances in metamaterials ...enable the optical elements for controlling light to be miniaturized and to have various multi-functions in subwavelength scale. However, a conventional approach of a circular polarizer has an inherent limitation to eliminate the unwanted circular polarization, which means that the efficiency varies significantly depending on the polarization state of incident light. Here, we propose a novel concept of a circular polarizer by combining two functions of transmission and conversion for orthogonal circular polarizations with a total thickness of 440 nm. The proposed three-layer metasurface composed of rotating silver nanorods transmits the left-handed circularly polarized (LCP) light with maintaining its own polarization state, whereas the right-handed circularly polarized (RCP) light is converted into LCP light. Regardless of the polarization state of incoming light, the polarization of light in the last medium is LCP state in the broadband operating wavelength range from 800 nm to 1100 nm. The converted RCP and the transmitted LCP have efficiencies of up to 48.5% and 42.3%, respectively. Thus the proposed metasurface serves as a stable circular polarizer for a randomly polarized light. In addition, high-efficiency asymmetric transmission of about 0.47 is achieved at the same time due to the conversion characteristic of RCP component. The proposed metasurface has the significance as an ultra-thin optical element applicable to optical switching, sensors, and communications in unidirectional channel as well as a broadband circular polarizer for randomly polarized light.
In recent years, circulating fluidized bed combustor (CFBC) has been regarded as a viable alternative to the conventional pulverized coal combustor (PCC) for utility-scale coal power generation owing ...to its superior technology for fuel flexibility and supercritical (SC)/ultra supercritical (USC) steam circuit adaptability. The objective of this study is to analyze the economic feasibility of a 600MWe USC CFB boiler, in which coal or a mixture of coal and biomass would be used as fuel. After the demonstration and commercialization of SC CFBC units had succeeded up to 600MWe, USC CFBCs have been widely developed throughout the world. Although high capital costs, high auxiliary power use, and technology maturity have hindered the adoption of USC CFBC for utility power generation, the demand of cleaner environments and energy conversion have driven communities to develop and adopt USC CFBC. Its economic feasibility was evaluated in terms of net present value (NPV), benefit/cost ratio (B/C ratio), and internal rate of return (IRR). In particular, the effect of coal tax and domestic biomass co-combustion on economic efficiency was analyzed.
•The economic feasibility of 600MWe USC CFB power plant were investigated.•The economic efficiency of biomass co-combustion could be higher than that of coal combustion due to carbon trade exchange.•The 600MWe USC CFB power plant with biomass co-combustion could be feasible in spite of coal tax or carbon tax.
Electrode materials design is the most significant aspect in constructing a supercapacitor device. The evolution of metal nitrides/oxynitrides as supercapacitor electrode is strikingly noticeable ...today besides prevailing carbon or 2D materials, metal oxides/hydroxides and conducting polymers electrode materials. The theoretically estimated specific capacitance of a nitride-based supercapacitor is 1,560 F g
-1
. These nanostructures exhibit an excellent capacitive behavior with a specific capacitance of 15–951.3 mF cm
-2
or 82–990 F g
-1
, high energy density (16.5-162 Wh Kg
-1
) and power density (7.3-54,000 W Kg
-1
). On this account, supercapacitor performance of metal nitrides/oxynitrides is reviewed exclusively. The major focus of the present review is directed towards state-of-art progress in supercapacitor performance of nitrides/oxynitrides, underlying charge-storage mechanism, important outcomes and their limitations. Finally, we conclude with challenges and prospects of metal nitrides/oxynitrides for supercapacitor electrodes.
•Carbonization characteristics of biomass and coking coal blends were examined.•CH4 and H2 were the main gases of coal and biomass/coal blends during carbonization.•Calorific value of the bio-coke ...was higher than 7000 kcal/kg.•Ignition temperature of the bio-cokes was 400–600 °C, meeting coke standards.•Resultant bio-coke is a good substitute for coal, reducing CO2 emissions.
Carbonization is a low-temperature thermochemical process that converts organic matter in the absence of oxygen mainly into char, gas, and liquids. Bio-coke is a char prepared from a mixture of biomass/charcoal and a coal blend. It can reduce greenhouse gas emissions by replacing coke and reducing coal consumption in the ironmaking process. In this study, the carbonization characteristics such as char conversion, gas and tar composition of bio-coke were determined using a batch-type carbonization reactor. Yellow poplar wood used as a biomass was added to a coking coal in different ratios (0, 10, 15, 20, and 30 wt%) and the resulting raw bio-coke was carbonized at different final temperatures (500–800 °C). The calorific value of bio-coke was higher than 7000 kcal/kg, exceeding the standard value. Moreover, the initiation combustion temperature of the resultant bio-coke determined using TGA was in the range of 400–600 °C. It is concluded that bio-coke is a suitable substitute for conventional fossil fuels reducing CO2 emissions.
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•BEAD-SBRCu produced methanol from food waste increasing methylotrophic methanogens.•BEAD-SBRCu removed COD and produced methane with no pH decrease at high OLR.•Methanol is converted ...to methane by hydrogenotrophic and methylotrophic methanogens.
In this study, the metabolism of methanol and changes in an archaeal community were examined in a bioelectrochemical anaerobic digestion sequencing batch reactor with a copper-coated graphite cathode (BEAD-SBRCu). Copper-coated graphite cathode produced methanol from food waste. The BEAD-SBRCu showed higher methanol removal and methane production than those of the anaerobic digestion (AD)-SBR. The methane production and pH of the BEAD-SBRCu were stable even under a high organic loading rate (OLR). The hydrogenotrophic methanogens increased from 32.2 to 60.0%, and the hydrogen-dependent methylotrophic methanogens increased from 19.5 to 37.7% in the bulk of BEAD-SBRCu at high OLR. Where methanol was directly injected as a single substrate into the BEAD-SBRCu, the main metabolism of methane production was hydrogenotrophic methanogenesis using carbon dioxide and hydrogen released by the oxidation of methanol on the anode through bioelectrochemical reactions.
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