Graphene coatings for corrosion resistance of nickel and copper in acidic,alkaline and neutral environments

Graphene coatings have been reported to provide impressive corrosion resistance to nickel(Ni)and copper(Cu),because of remarkable characteristics of inertness and impermeablity of graphene.However,as the earlier investigations have generally been carried out in chloride environment,and it is important to understand the performance of graphene coating also in more aggressive environments such as acids and alkali.This study investigated the electrochemical corrosion behaviour of bare and graphene-coated(by chemical vapour deposition(CVD))Ni and Cu in 0.5 M H_(2)SO_(4),0.1 M NaCl and 0.5 M NaOH solutions.Electrochemical tests and post corrosion characterisation revealed the improvement in the corrosion resistance of Ni due to multilayer graphene coating to be similar in the three solutions,i.e.,the robustness of the barrier property of the multilayer graphene is largely unaffected by the aggressiveness of the corrosive environment.However,the improvement in corrosion resistance of bare Ni due to multilayer graphene is considerably greater(nearly 3 orders of magnitude)in the most aggressive of the test solutions(0.5 M H_(2)SO_(4)).The improvement is considerably less in 0.5 M NaOH because bare Ni develops a robust passive layer in highly alkaline solutions.The improvement in corrosion resistance of bare Cu is limited(within an order of magnitude)in the three solutions because Cu develops only 1-2 layers of graphene.

Graphene-calcium carbonate coating to improve the degradation resistance and mechanical integrity of a biodegradable implant

Biodegradable implants are critical for regenerative orthopaedic procedures,but they may suffer from too fast corrosion in human-body environment.This necessitates the synthesis of a suitable coating that may improve the corrosion resistance of these implants without compromising their mechanical integrity.In this study,an AZ91 magnesium alloy,as a representative for a biodegradable Mg implant material,was modified with a thin reduced graphene oxide(RGO)-calcium carbonate(CaCO_(3))composite coating.Detailed analytical and in-vitro electrochemical characterization reveals that this coating significantly improves the corrosion resistance and mechanical integrity,and thus has the potential to greatly extend the related application field.

Curing Kinetics, Mechanical Properties and Thermal Stability of Epoxy/Graphene Nanoplatelets(GNPs) Powder Coatings

Epoxy/graphene nanoplatelets（GNPs） powder coatings were fabricated using ultrasonic predispersion of GNPs and melt-blend extrusion method. The isothermal curing kinetics of epoxy/GNPs powder coating were monitored by means of real-time Fourier transform infrared spectroscopy（FT-IR） with a heating cell. The mechanical properties of the epoxy/GNPs cured coatings had been investigated, by evaluating their fracture surfaces with field-emission scanning electron microscopy（FE-SEM） after three-point-bending tests. The thermal stability of the epoxy/GNPs cured coatings was studied by thermo-gravimetric analysis（TGA）. The isothermal curing kinetics result showed that the GNPs would not affect the autocatalytic reaction mechanism, but the loading of GNPs below 1.0 wt % additive played a prompting role in the curing of the epoxy/GNPs powder coatings. The fracture strain, fracture toughness and impact resistance of the epoxy/GNPs cured coatings increased dramatically at low levels of GNPs loading（1 wt %）, indicating that the GNPs could improve the toughness of the epoxy/GNPs powder coatings. Furthermore, from FE-SEM studies of the fracture surfaces, the possible toughening mechanisms of the epoxy/GNPs cured coatings were proposed. TGA result showed that the incorporation of GNPs improved the thermal stability of the cured coatings. Hence, the GNPs modified epoxy can be an efficient approach to toughen epoxy powder coating along with improving their thermal stability.

Core@shell sulfur@polypyrrole nanoparticles sandwiched in graphene sheets as cathode for lithium–sulfur batteries

A nano sulfur-based composite cathode material featured by uniform core@shell-structured sulfur@polypyrrole nanoparticles sandwiched in three-dimensional graphene sheets conductive network（S@PPy/GS） is fabricated via a facile solution-based method. The S@PPy nanoparticles are synthesized by in situ chemical oxidative polymerization of pyrrole on the surface of sulfur particles,and then graphene sheets are covered outside the S@PPy nanoparticles,forming a three-dimensional conductive network. When evaluating the electrochemical performance of S@PPy/GS in a lithium–sulfur battery,it delivers large discharge capacity,excellent cycle stability,and good rate capability. The initial discharge capacity is up to 1040 m Ah/g at 0.1 C,the capacity can remain 537.8 m Ah/g at 0.2 C after 200 cycles,even at a higher rate of 1 C,the specific capacity still reaches 566.5 m Ah/g. The good electrochemical performance is attributed to the unique structure of S@PPy/GS,which can not only provide an excellent transport of lithium and electron ions within the electrodes,but also retard the shuttle effect of soluble lithium polysulfides effectively,thus plays a positive role in building better lithium-sulfur batteries.

Graphene quantum dots assisted photovoltage and efficiency enhancement in CdSe quantum dot sensitized solar cells

CdSe quantum dot sensitized solar cells （QDSCs） modified with graphene quantum dots （GQDs） have been successfully achieved in this work for the first time. Satisfactorily, the optimized photovoltage （Voc） of the modified QDSCs was approximately 0.04 V higher than that of plain CdSe QDSCs, consequently improving the photovoltaic performance of the resulting QDSCs. Served as a novel coating on the CdSe QD sensitized photoanode, GQDs played a vital role in improving Voc due to the suppressed charge recombination which has been confirmed by electron impedance spectroscopy as well as transient photovoltage decay measure- ments. Moreover, different adsorption sequences, concentration and deposition time of GQDs have also been systematically investigated to boost the power conversion efficiency （PCE） of CdSe QDSCs. After the coating of CdSe with GQDs, the resulting champion CdSe QDSCs exhibited an improved PCE of 6.59% under AM 1.5G full one sun illumination.

Corrosion Resistance of Graphene-Reinforced Waterborne Epoxy Coatings

Graphene （G） was dispersed uniformly in water and used as an inhibitor in waterborne epoxy coatings. The effect of dispersed G on anticorrosion performance of epoxy coatings was evaluated. The composite coatings displayed outstanding barrier properties against H20 molecule compared to the neat epoxy coating. Open circuit potential （OCP）, Tafel and electrochemical impedance spectroscopy （EIS） analysis confirmed that the corrosion rate exhibited by composite coatings with 0.5 wt% G was an order of magnitude lower than that of neat epoxy coating. Salt spray test results revealed superior corrosion resistance offered by the composite coating.

Insight into the effect of graphene coating on cycling stability of LiNi_(0.5)Mn_(1.5)O_(4):Integration of structure-stability and surface-stability

Graphene has presented promising features for application in lithium ion batteries(LIBs)due to its superior electronic conductivity and high surface area.It has been successfully used for modifying cathode materials to meet the increasing demand for LIBs with longer cycle life.However,the improving effect of graphene on cycling stability is still unclear,which restricts its further application in LIBs.Herein,graphene coated hollow sphere-like structure LiNi0.5Mn1.5O4(LNMO)wasdesigned and the improvement mechanism of graphene coating on LNMO’s cycling stability was investigated.The results show that graphene coating not only contributes to suppress structural deformation from mechanistic reaction and extend solid-solution reaction,but also helps protect electrode from corrosion by the products from electrolyte decomposition and suppress the generation of surface defects,especially at high temperature.Owing to graphene coating,graphene coated LNMO can deliver a discharge capacity of 91 mAh g1 with high capacity retention of 82.5%after 1000 cycles under 20C and 83.8 mAh g1 with 94.5%capacity retention after 100 cycles under 2C at 55C.This work deeply explores the effect of graphene coating on cycling stability from crystal stability and surface stability,which will help a wider application of graphene in energy storage field.

Lithiation-enhanced charge transfer and sliding strength at the silicon-graphene interface:A first-principles study

The application of silicon as ultrahigh capacity electrodes in lithiumion batteries has been limited by a number of mechanical degradation mechanisms including fracture, delamination and plastic ratcheting, as a result of its large volumetric change during lithiation and delithiation. Graphene coating is one feasible technique to mitigate the mechanical degradation of Si anode and improve its conductivity. In this paper, first-principles calculations are performed to study the atomic structure, charge transfer and sliding strength of the interface between lithiated silicon and graphene. Our results show that Li atoms segre- gate at the （lithiated） Si-graphene interface preferentially, donating electrons to graphene and enhancing the interfacial sliding resistance. Moreover, the interfacial cohesion and sliding strength can be further enhanced by introducing single-vacancy defects into graphene. These findings provide insights that can guide the design of stable and efficient anodes of silicon/graphene hybrids for energy storage applications.