Electrochemical Response of 3D-Printed Free-Standing Reduced Graphene Oxide Electrode for Sodium Ion Batteries Using a Three-Electrode Glass Cell.

Graphene and its derivatives have been widely used to develop novel materials with applications in energy storage. Among them, reduced graphene oxide has shown great potential for more efficient storage of Na ions and is a current target in the design of electrodes for environmentally friendly Na ion batteries. The search for more sustainable and versatile manufacturing processes also motivates research into additive manufacturing electrodes. Here, the electrochemical responses of porous 3D-printed free-standing log-type structures fabricated using direct ink writing (DIW) with a graphene oxide (GO) gel ink are investigated after thermal reduction in a three-electrode cell configuration. The structures delivered capacities in the range of 50-80 mAh g-1 and showed high stability for more than 100 cycles. The reaction with the electrolyte/solvent system, which caused an initial capacity drop, was evidenced by the nucleation of various Na carbonates and Na2O. The incorporation of Na into the filaments of the structure was verified with transmission electron microscopy and Raman spectroscopy. This work is a proof of concept that structured reduced GO electrodes for Na ion batteries can be achieved from a simple, aqueous GO ink through DIW and that there is scope for improving their performance and capacity.

Remarkable Effects of an Electrodeposited Copper Skin on the Strength and the Electrical and Thermal Conductivities of Reduced Graphene Oxide-Printed Scaffolds.

Architected Cu/reduced graphene oxide (rGO) heterostructures are achieved by electrodepositing copper on filament-printed rGO scaffolds. The Cu coating perfectly contours the printed rGO structure, but isolated Cu particles also permeate inside the filaments. Although the Cu deposition conveys a certain mass augment, the three-dimensional (3D) structures remain reasonably light (bulk density ≅ 0.42 g·cm-3). The electrical conductivity (σe) of the Cu/rGO structure (∼8 × 104 S·m-1) shows a notable increment compared to σe of the rGO structure (∼2 × 102 S·m-1). The effect on the scaffold robustness is also notable with an increase of the compressive strength by nearly 10 times (from 20 kPa of the rGO scaffold to 150 kPa of the Cu/rGO structure) and cyclability as well. The improved thermal conductivity of the Cu-coated scaffolds (∼4 times higher), in addition to the σe and strength improvements, suggests that 3D Cu/rGO structures could be suitable assemblies for integration into thermal dissipation systems, particularly as thermal interface materials, for compact electronic devices.