Galvanically Displaced Noble Metal Nanoparticles Onto Electrosprayed Graphene-CNT Electrodes for Lithium-Ion and Fuel Cell Applications

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.