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In situ decoration of laser-scribed graphene with TiO2 nanoparticles for scalable high-performance micro-supercapacitors

Graphene-based miniaturized supercapacitors, obtained via laser conversion of suitable precursors, have been attracting recent attention for the production of energy storage small-scale devices. In this work, a one-pot synthesis of TiO2 nanoparticles embedded in porous graphene-based electrodes has been obtained with the LightScribe® technology, by converting the precursor materials through the absorption of a DVD burner infrared laser light. Enhanced electrochemical performance of devices has been achieved thanks to the combination of faradic surface reactions, arising from metal oxide nanoparticles, with the conventional electrochemical double layer capacitance, arising from porous graphene. Micro-supercapacitors, consisting of TiO2-graphene electrodes, have been tested by investigating two hydrogel polymer electrolytes, based on polyvinyl alcohol/H3PO4 and polyvinyl alcohol/H2SO4, respectively. Specific areal capacitance up to 9.9 mF/cm2 are obtained in TiO2-graphene devices, corresponding to a volumetric capacitance of 13 F/cm3 and doubling the pristine graphene-based device results. The micro-supercapacitors achieved specific areal energy and specific areal power of 0.22 μWh/cm2 and 39 μW/cm2, along with a cyclability greater than 3000 cycles. These high-performance results suggest laser-scribed TiO2-graphene nanostructures as remarkable candidates in micro-supercapacitors for environment-friendly, large-scale and low-cost applications.

Reproduced with permission. Copyright 2021, Elsevier

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Nickel addition to optimize the hydrogen storage performance of lithium intercalated fullerides

The addition of transition metals to alkali intercalated fullerides proved to enhance their already good hydrogen absorption properties. Herein we present a study based on two different synthetic strategies, allowing the addition of nickel as aggregates with different size to the lithium fulleride Li6C60: the former is based on the metathesis of nickel chloride, while the latter on the thermal decomposition of nickel carbonyl clusters. The hydrogen-storage properties of the obtained materials have been investigated with manometric and calorimetric measurements, which indicated a clear enhancement of the final absorption value and kinetics with respect to pristine Li6C60, as a consequence of nickel surface catalytic activity towards hydrogen molecules dissociation. We found up to 10 % increase of the total H2 weight % absorbed (5.5 wt% H2) in presence of Ni aggregates. Furthermore, the control of the transition metal particles size distribution allowed reducing the hydrogen desorption enthalpy of the systems.

Reproduced with permission. Copyright 2020, Elsevier

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Neutron scattering study of nickel decorated thermally exfoliated graphite oxide

Surface decoration of graphene-based nanostructures with metals has been predicted to be an efficient way towards the development of resistant catalysts and novel materials for energy applications, such as hydrogen production and storage. We report on an extensive neutron scattering study of a defective graphene-based material decorated with nickel nanoparticles, obtained via the chemical decoration of thermally exfoliated graphite oxide. The combination of neutron diffraction and inelastic neutron scattering measurements has been used to characterize the low-dimensional carbon backbone and the presence of the nickel nanoparticles, organized at the nanometer scale on the graphene plane. The structural features of this system, along with the nickel capability of dissociating the hydrogen molecule upon hydrogen treatment, are herein discussed.

Reproduced with permission. Copyright 2020, Elsevier

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Platinum carbonyl clusters decomposition on defective graphene surface

Having single atoms or small clusters docked onto a single layer graphene represents a charming feature for energy-storage and catalysis. Unfortunately, the large cohesion energy of transition metals often prevents the isolation of nanoscopic clusters, which invariably tend to aggregate. The decoration of defective graphene layers with single Pt atoms and sub-nanometric clusters is herein achieved by exploiting metal carbonyl clusters, as precursor, and investigated by means of transmission electron microscopy and X-ray photoemission spectroscopy. Unexpectedly, the process of aggregation of Pt into larger clusters is inhibited onto the surface of defective graphene, where the Pt-clusters are found to fragment even into single metal atoms.

Reproduced with permission. Copyright 2019, Elsevier

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Super-activated biochar from poultry litter for high-performance supercapacitors

We report on the preparation of a novel hierarchically-porous super-activated carbon originating from organic waste with specific surface area exceeding 3000 m2/g, obtained starting from biochar derived by the pyrolysis of poultry litter. The chemical activation process proved to be efficient to remove the majority of impurities other than carbon, stabilizing a highly porous hierarchical structure with local graphene-like morphology. The presence of P and S with concentration below 0.1 wt% distinguishes this activated carbon from the usual ones obtained from vegetal sources. Thanks to these features, the obtained porous compound demonstrated to behave as an excellent electrode material for high-performance symmetric supercapacitors, reaching high specific capacitance up to 229 (13) F/g. Remarkably, the devices also supply high current density of 10 A/g without using any conducting additives and display high power density and reliability. Moreover, these optimal performances have been obtained operating by using simple eco-friendly electrolytes, like KOH and Na2SO4 aqueous solutions. The availability, the biocompatibility and the inexpensiveness of the starting materials, together with the low environmental impact of the electrolyte, suggest possible large-scale applications for such devices, for example in the field of transportation or in renewable energy-grids, but also in the field of bio-medicine.

Reproduced with permission. Copyright 2019, Elsevier.

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Electrochemical intercalation of fullerene and hydrofullerene with sodium

We report on the ability of fullerene C60 and hydrogenated fullerene C60Hx (x∼39) to operate as negative electrodes in novel Na-ion batteries. Building upon the known solubility of C60 in common organic electrolytes used in batteries, we developed a suitably optimized solid-state Na-(polyethylene oxide) electrolyte for this application. Electrochemical and structural properties of the fullerene electrodes were investigated through cyclic voltammetry, fixed-current charge/discharge of the electrodes, impedance spectroscopy and powder X-ray diffraction. Both C60 and hydrogenated C60 have been electrochemically intercalated with sodium. Specific capacities after the first cycle are 250 mAh g−1 and 230 mAh g−1 for C60 and C60Hx respectively. However, C60 electrode shows a strong irreversible character after the first discharge, probably due to the formation of stable polymeric NaxC60 phases, where Na+ ions diffusion is hindered. On the contrary, C60Hx displays better reversibility, suggesting that hydrogenation of the buckyball could be effective to preserve sufficiently large interstitial pathways for Na+ diffusion upon intercalation.

Reproduced with permission. Copyright 2018, Elsevier

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Mechanisms of Sodium Insertion/Extraction on the Surface of Defective Graphenes

Two chemically synthesized defective graphene materials with distinctly contrasting extended structures and surface chemistry are used to prepare sodium-ion battery electrodes. The difference in electrode performance between the chemically prepared graphene materials is qualified based on correlations with intrinsic structural and chemical dissimilarities. The overall effects of the materials physical and chemical discrepancies are quantified by measuring the electrode capacities after repeated charge/discharge cycles. Solvothermal synthesized graphene (STSG) electrodes produce capacities of 92 mAh/g in sodium-ion batteries after 50 cycles at 10 mA/g, while thermally exfoliated graphite oxide (TEGO) electrodes produce capacities of 248 mAh/g after 50 cycles at 100 mA/g. Solid-state 23Na nuclear magnetic resonance spectroscopy is employed to locally probe distinct sodium environments on and between the surface of the graphene layers after charge/discharge cycles that are responsible for the variations in electrode capacities. Multiple distinct sodium environments of which at least 3 are mobile during the charge–discharge cycle are found in both cases, but the majority of Na is predominantly located in an immobile site, assigned to the solid electrolyte interface (SEI) layer. Mechanisms of sodium insertion and extraction on and between the defective graphene surfaces are proposed and discussed in relation to electrode performance. This work provides a direct account of the chemical and structural environments on the surface of graphene that govern the feasibility of graphene materials for use as sodium-ion battery electrodes.

Reproduced with permission. Copyright 2016, American Chemical Society