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In recent years, there has been huge advancements in 3D printing technologies, graphene research and energy storage. Graphene has many properties that make it an ideal material for many applications and 3D printers provide a quick and unique method of manufacturing material and or/device prototypes, across various applications. Now, a team of researchers from the UK and China have developed a unique range of 3D disc electrode (3DE) configurations, through 3D printing graphene-based polylactic acid (graphene/PLA) filaments for multiple electrochemical applications.

The last decade has seen the advancement of 2D materials, such as graphene, reach new heights and are now present in many applications across a range of scientific fields. Scientists are always trying to find new ways to efficiently fabricate graphene and exploit its many beneficial properties.

3D printing has also gained popularity in recent years due to its ability to easily fabricate complex and intricate structures at low cost. 3D printing in electronic applications is a relatively new research area and metallic-based battery structures have recently been printed using lithium-based composites. However, in many applications graphene has been show to outperform lithium (and other metals), especially in voltaics, and is now been tested against its metallic counterparts in 3D fabrication technologies.

Graphene-based electrodes have previously been fabricated using 3D printers, using a graphene oxide ink and graphene nanoplatelets. However, in many applications, the in-situ curing stages have been rendered far from ideal, when compared with freestanding 3D printed electrochemical systems.

The development of these new electrodes created by this researcher tean has come about from a culmination of indirect 3D printed carbon research. Previous to this undertaking, both carbon black and graphite-PLA electrodes have been 3D printed for use in electrochemical cells. The discovery of 3D printed electrodes from other carbon allotropes is what prompted the researchers to attempt a graphene-based electrode, whilst attempting to solve the issues of the curing stage.

For the first time, the researchers have developed a 3D printed version of graphene with geometries suitable for electrochemical systems.

The 3D Printed Device

The 3D printed designs were fabricated a RepRap fused deposition moulding (FDM) 3D printer, using a graphene-based PLA filament into a circular disc electrode. The designs were produced using Solidworks, and the experimental procedures were carried out using three-electrode setup with a printed 3D electrode- where the graphene/PLA printed electrodes are fabricated as freestanding lithium-ion anodes and solid-state graphene supercapacitors.

Many different techniques were utilised to measure the performance and the structure of the graphene-based electrodes, including voltammetric measurements (Metrohm Autolab PGSTAT100), charge-discharge measurements (Arbin battery test system-BT2000), scanning electron microsopy-SEM (JEOL JSM-5600LV), Raman spectroscopy (Renishaw InVia spectrometer), thermogravimetric analysis (PerkinElmer TGA 4000) and X-ray photoelectron spectroscopy-XPS (Specs GmbH Focus 500, Specs GmbH Phoibos, Specs GmbH FG20, CasaXPS software v2.3.16)

This method, unlike other 3D printed graphene electrodes, requires no in-situ curing stage- allowing them to be freestanding. The freestanding anodes do not require a current collector and offer a simple and cheaper alternative to conventional lithium-ion systems. The PLA molecules within the composite also allow for an infinite amount of geometries and sizes to be fabricated without the need for any extra modifications. A highly tuneable process indeed.

As a by-property, these devices can also produce hydrogen, through a hydrogen evolution reaction (HER). This has the potential to be utilised as an alternative to current methods involving platinum electrodes (and electrolysers), as the graphene/PLA electrodes exceeded expectations by possessing a higher onset potential than platinum electrodes. The 2DE electrodes showed a high HER catalytic activity of -0.46 on the 1000th cycle.

The performance of these electrodes has not yet been optimised and there is the potential for a much-increased performance. These electrodes, in both the anode and supercapacitor, currently exhibit tremendous values considering the composite is composed of only 8% graphene. More research is currently being undertaken to increase the graphene concentration within the electrode, to improve the performance and take the electrode to commercially viable levels. It is expected, that in the future, these graphene-based filaments will allow for the simple fabrication of energy storage devices with bespoke designs.

Source:

Foster C. W., Down M. P., Zhang Y., Ji X., Rowley-Neale S. J., Smith G. C., Kelly P. J., Banks C. E., 3D Printed Graphene Based Energy Storage Devices, Scientific Reports, 7, 42233

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