Internal macropores in silicon/graphene/graphene nanoribbon (Si/Gr/GNR) hybrid anodes by facile thermal removal of sacrificial polymer, polyvinyl alcohol (PVA), are incorporated, to mitigate the volume expansion of silicon and to increase the silicon utilization and rate capability of the anode. The resulting Si/Gr/GNR hybrid anodes give a high capacity of 1874 mAh g−1 at 0.1 C, based on total weight of the electrode including binder and carbon, as well as great capacity retention of above 800 mAh g−1 after 350 cycles at 0.3 C. The mitigation of volume expansion by carrying out in situ thickness change measurements of small pouch cells via a dilatometer is further demonstrated, exhibiting the saturation of volume expansion below 40% after 100 cycles due to the incorporation of the macropores. Moreover, Si/Gr/GNR anodes with pores exhibit superior rate capability, yielding 1,250 mAh g−1 at 2 C rate due to the effective network of graphene sheets and GNRs.

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Smart materials are versatile material systems which exhibit a measurable response to external stimuli. Recently, smart material systems have been developed which incorporate graphene in order to share on its various advantageous properties, such as mechanical strength, electrical conductivity, and thermal conductivity as well as to achieve unique stimuli‐dependent responses. Here, a graphene fiber‐based smart material that exhibits reversible electrical conductivity switching at a relatively low temperature (60 °C), is reported. Using molecular dynamics (MD) simulation and density functional theory‐based non‐equilibrium Green's function (DFT‐NEGF) approach, it is revealed that this thermo‐response behavior is due to the change in configuration of amphiphilic triblock dispersant molecules occurring in the graphene fiber during heating or cooling. These conformational changes alter the total number of graphene‐graphene contacts within the composite material system, and thus the electrical conductivity as well. Additionally, this graphene fiber fabrication approach uses a scalable, facile, water‐based method, that makes it easy to modify material composition ratios. In all, this work represents an important step forward to enable complete functional tuning of graphene‐based smart materials at the nanoscale while increasing commercialization viability.

Advanced lithium-ion batteries (LIB) and Fuel Cells demonstrate promise as the next generation energy storage and conversion (ESC) technology especially as it pertains to wearable technology and electric vehicles. Although LIB dominate the battery market (>90%) due its reliability, long cycle life, and market maturity, different and more innovative ways to improve the chemistry of the electrode structure must be discovered in order to reduce the cost of materials, dendritic issues at the solid-electrolyte interphase (SEI) layer, and improve upon the limited anode capacity (graphite theoretical capacity 372 mAh g-1). Fuel cells are also promising renewable energy sources due to their high energy densities and scalability. However, both LIB and Fuel Cells are limited by the 3D materials that enable their enhanced electrochemical and catalytic performance. We propose a platform methodology for the synthesis of 3D electrodes with carbon nanomaterials and noble metals. The enhanced electrical, thermal, chemical, and mechanical stability of graphene and carbon nanotubes (CNTs) offer an ideal platform for electrode design for energy storage applications. Here we utilize spontaneous galvanic displacement driven by reduction potential difference to produce three-dimensional (3D) graphene-CNT-noble metal nanoparticle 3D electrode without the use of any harsh chemical reducing agents. A graphene-CNT slurry with a poly(acrylic acid) (PAA) binder is air-controlled electrosprayed onto copper foil to create 3D composite thin film electrodes. Although noble metals are expensive materials to be used in LIB, we propose a new approach for synthesizing conductive electrochemically stable electrodes. We demonstrate a spontaneous technique to reduce the noble metal salts by galvanically displacement with the copper substrate to deposit noble metal nanoparticles onto the graphene-CNT electrode. The noble metal salt solutions (HAuCl4, K2PtCl4, and Na2PdCl4) are drop casted onto the resulting copper supported graphene-CNT electrodes to enable electroless noble metal nanoparticle deposition. Scanning electron microscopy (SEM) imaging confirms that the carbon nanomaterials are integrated with noble metal nanoparticles forming an overall 3D electrode structure. Raman spectroscopy verifies the characteristic D-band, G-band, and 2D-band peaks from the graphitic structure within the 3D carbon and noble metal nanostructure. Cyclic voltammetry and electrochemical impedance spectroscopy (EIS) are used to characterize the electrochemical properties of the electrodes. We demonstrate that the use of an energy-free and spontaneous process based on the difference in thermodynamic reduction potentials as the driving force for producing carbon nanomaterial/noble metal nanostructured electrodes for batteries and fuel cells. This process is a more simple, scalable, and cost-efficient alternative to current methods for developing lightweight and catalytic electrodes for energy storage applications, such as lithium-ion batteries, lithium-air batteries, and fuel cells. Raman Spectroscopy is used to confirm the presence defects on the oxidized carbon nanotube and graphene oxide surface. Scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX), and x-ray diffraction (XRD) were used to characterize the morphology of the 3D carbon-noble metal structure and the surface elemental composition. Electrochemical characterization techniques such as electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), performance testing for oxygen reduction reaction (ORR), hydrogen evolution reaction (HER), and potentiostatic measurements are used to characterize the areal specific resistance (ASR), areal capacitance, electrochemical surface area, initial Coulombic efficiency (ICE), rate capability and cycling performance, and electrochemical stability, respectively.

Silicon as anode material has been very promising to satisfy the high energy density demands for electric vehicle (EV) applications due its extraordinary theoretical capacity. However, silicon undergoes huge volume expansion (~ 300%) during lithiation. To accommodate the mechanical stress caused due to the volume expansion of silicon, graphene or reduced graphene oxide is frequently used. .Thus, silicon reduced graphene oxide(Si/rGO) composite electrodes have been extensively studied for the multiple benefits of rGO in providing mechanical integrity to buffer the silicon volume expansion, maintaining the electronic contact with Si to provide a Li-ion transport pathway and to form uniform solid electrolyte interface (SEI) layer. However, there is no systematic approach to discern the properties of rGO and isolate the desirable qualities. There are mainly three different routes to synthesize rGO from graphene oxide (GO) namely by thermal treatment (TrGO), by chemical treatment (CrGO) and by plasma treatment (PrGO). Each method of reduction of graphene oxide results in producing rGOs with very different properties. The quality of a particular rGO very much depends on how it is reduced and this quality of rGO is further linked with the electrochemical behavior of the widely used Si/rGO electrodes for Li-ion batteries.In this study, we extensively characterize various commercial grade rGOs which have been reduced by the three methods mentioned above and determine their morphology, chemical composition, and other properties such as defects, electrical resistivity and interlayer spacing of the graphene sheets and these are correlated to the electrochemical performance of Si/rGO composites. The studied rGOs also have distinctively different lateral dimensions. We found that reduction of structural and functional group defects in rGO led to a higher initial columbic efficiency (ICE) of 83% whereas a higher sphericity of rGO displayed stable cycle-life performance for Si/rGO electrodes with 70% capacity retention after 150 cycles. We also observed the important role of electrical conductivity of rGO in the electrochemical performance of Si/rGO at faster charging-discharging rates resulting in a capacity of 1000 mAh/g at 2C charge/discharge rates.Overall, plasma reduced graphene oxide (PrGO) were found to yield the best performance, and thusthe effect of the lateral dimension of the plasma reduced graphene oxide on rate capability was studied. Plasma reduced graphene oxide with an average lateral dimension of 25µm was found to be the most optimum rGO in our study to satisfy all the requirements expected of a Si/rGO electrode efficiently.