Carbon-Nanodot Solar Cells from Renewable Precursors

It has recently been shown that waste biomass can be converted into a wide range of functional materials, including those with desirable optical and electronic properties, offering the opportunity to find new uses for these renewable resources. Photovoltaics is one area in which finding the combination of abundant, low‐cost and non‐toxic materials with the necessary functionality can be challenging. In this paper the performance of carbon nanodots derived from a wide range of biomaterials obtained from different biomass sources as sensitisers for TiO2‐based nanostructured solar cells was compared; polysaccharides (chitosan and chitin), monosaccharide (d‐glucose), amino acids (l‐arginine and l‐cysteine) and raw lobster shells were used to produce carbon nanodots through hydrothermal carbonisation. The highest solar power conversion efficiency (PCE) of 0.36 % was obtained by using l‐arginine carbon nanodots as sensitisers, whereas lobster shells, as a model source of chitin from actual food waste, showed a PCE of 0.22 %. By comparing this wide range of materials, the performance of the solar cells was correlated with the materials characteristics by carefully investigating the structural and optical properties of each family of carbon nanodots, and it was shown that the combination of amine and carboxylic acid functionalisation is particularly beneficial for the solar‐cell performance

Monitoring Hydrogen Evolution Reaction Intermediates of Transition Metal Dichalcogenides via Operando Raman Spectroscopy

© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim A deeper understanding of the water-splitting hydrogen evolution reaction (HER) mechanism during photocatalytic processes is crucial for the rational design of efficient photocatalysts. In particular, the HER mechanism promoted by multielement hybrid structures remains extremely challenging and elusive. Herein, an in situ photoelectrochemical/Raman measurement system is employed to monitor the HER mechanism of hybrid nanostructures under realistic working conditions via operando Raman spectra and linear-sweep voltammetry curves. As a proof of concept, tunable composition transition metal dichalcogenides MoS2xSe2(1−x) nanosheets are used as a model photocatalyst to unveil the corresponding photocatalytic mechanism. The spectroscopic studies reveal that hydrogen atoms can be adsorbed to active sulfur and selenium atoms via intermediate species formed during the photocatalytic process. More importantly, the studies demonstrate that an exponential relationship exists between the number of reactive electrons and the Raman intensity of intermediate species, which can serve as a guideline to directly evaluate the HER performance in photocatalysts by comparing the Raman intensities of the intermediate species. As a simple, intuitive, and general analytical method, the designed operando Raman measurement approach provides a new tool for elucidating catalytic reaction mechanisms in a realistic and complex environment; and strategically improving H2 production performance of multielement photocatalysts

Doping carbon electrodes with sulfur achieves reversible sodium ion storage

We present a combination of experiments and theory to study the effect of sulfur doping in hard carbons anodes for sodium-ion batteries. Hard carbons are synthesised through a two step process: hydrothermal carbonisation followed by pyrolysis of a biomass-derived carbon precursor. Subsequent sulfur doping is introduced via chemical-vapour deposition. The resulting sulfur-doped hard carbon shows enhanced sodium storage capacity with respect to the pristine material, with significantly improved cycling reversibility. Atomistic first principles simulations give insight into this behaviour, revealing that sulfur chemisorbed onto the hard carbon increases the sodium adsorption energies and facilitates sodium desorption. This mechanism would increase reversible Na storage, confirming our experimental observations and opening a pathway towards more efficient Na-ion batteries

Heat Diffusion-Induced Gradient Energy Level in Multishell Bisulfides for Highly Efficient Photocatalytic Hydrogen Production

© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Insufficient light absorption and low carrier separation/transfer efficiency constitute two key issues that hinder the development of efficient photocatalytic hydrogen production. Here, multishell ZnS/CoS2 bisulfide microspheres with gradient distribution of Zn based on the heat diffusion theory are designed. The Zn distribution can be adjusted by regulating the heating rate and manipulating the diffusion coefficients of the different elements conforming the multishell photocatalyst. Because of the unique structure, a gradient energy level is created from the core to the exterior of the multishell microspheres, which effectively facilitates the exciton separation and electron transfer. In addition, stronger light absorption and larger specific surface area have been achieved in the multishell ZnS/CoS2 photocatalysts. As a result, the multishell ZnS/CoS2 microspheres with gradient distribution of Zn exhibit a remarkable hydrogen production rate of 8001 µmol g−1 h−1, which is 3.5 times higher than that of the normal multishell ZnS/CoS2 particles with well-distributed Zn and 11.3 times higher than that of the mixed nonshell ZnS and CoS2 particles. This work demonstrates for the first time that controlling the diffusion rate of the different elements in the semiconductor is an effective route to simultaneously regulate morphology and structure to design highly efficient photocatalysts

Lignin-derived electrospun freestanding carbons as alternative electrodes for redox flow batteries

Based on information provided the embargo period/end date is 12 monthsBased on information provided the embargo period/end date is 12 month

Manipulating the Optical Properties of Carbon Dots by Fine-Tuning their Structural Features

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Microcellular Electrode Material for Microbial Bioelectrochemical Systems Synthesized by Hydrothermal Carbonization of Biomass Derived Precursors

V.F. acknowledges a UQ Postdoctoral Fellowship. This work was supported by the Australian Research Council Grant DP110100539. The authors acknowledge the facilities and the scientific and technical assistance of the Australian Microscopy & Microanalysis Research Facility at the Centre for Microscopy and Microanalysis (The University of Queensland). The Ghent University Special Research Fund (BOF) is acknowledged for the postdoctoral grant of M.N.B

Synthesis and Application of Carbon–Iron Oxide Microspheres’ Black Pigments in Electrophoretic Displays

Carbon–iron oxide microspheres’ black pigments (CIOMBs) had been prepared via ultrasonic spray pyrolysis of aqueous solutions containing ferrous chloride and glucose. Due to the presence of carbon, CIOMBs not only exhibited remarkably acid resistance, but also could be well dispersed in both polar solvents and nonpolar solvent. Finally, dispersions of hollow CIOMBs in tetrachloroethylene had successfully been applied in electrophoretic displays

Free-standing supercapacitors from Kraft lignin nanofibers with remarkable volumetric energy density

We have discovered a very simple method to address the challenge associated with the low volumetric energy density of free-standing carbon nanofiber electrodes for supercapacitors by electrospinning Kraft lignin in the presence of an oxidizing salt (NaNO₃) and subsequent carbonization in a reducing atmosphere. The presence of the oxidative salt decreases the diameter of the resulting carbon nanofibers doubling their packing density from 0.51 to 1.03 mg cm⁻² and hence doubling the volumetric energy density. At the same time, the oxidative NaNO₃ salt eletrospun and carbonized together with lignin dissolved in NaOH acts as a template to increase the microporosity, thus contributing to a good gravimetric energy density. By simply adjusting the process parameters (amount of oxidizing/reducing agent), the gravimetric and volumetric energy density of the resulting lignin free-standing carbon nanofiber electrodes can be carefully tailored to fit specific power to energy demands. The areal capacitance increased from 147 mF cm⁻² in the absence of NaNO₃ to 350 mF cm⁻² with NaNO₃ translating into a volumetric energy density increase from 949 μW h cm⁻³ without NaNO₃ to 2245 μW h cm⁻³ with NaNO₃. Meanwhile, the gravimetric capacitance also increased from 151 F g⁻¹ without to 192 F g⁻¹ with NaNO

A Two-Step Hydrothermal Synthesis Approach to Monodispersed Colloidal Carbon Spheres

This work reports a newly developed two-step hydrothermal method for the synthesis of monodispersed colloidal carbon spheres (CCS) under mild conditions. Using this approach, monodispersed CCS with diameters ranging from 160 to 400 nm were synthesized with a standard deviation around 8%. The monomer concentration ranging from 0.1 to 0.4 M is in favor of generation of narrower size distribution of CCS. The particle characteristics (e.g., shape, size, and distribution) and chemical stability were then characterized by using various techniques, including scanning electron microscopy (SEM), FT-IR spectrum analysis, and thermalgravity analysis (TGA). The possible nucleation and growth mechanism of colloidal carbon spheres were also discussed. The findings would be useful for the synthesis of more monodispersed nanoparticles and for the functional assembly