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Three-Dimensional Graphene Architectures as Templates for Electrochemical Devices

Periodic Reporting for period 1 - 3D-GATED (Three-Dimensional Graphene Architectures as Templates for Electrochemical Devices)

Reporting period: 2015-05-15 to 2017-05-14

Electrochemical energy devices, such as super-capacitors, batteries, fuel cells, and water-splitting catalysts, are already a multi-billion dollar industry globally. These devices permeate our everyday life from powering our consumer electronics, providing power storage for renewable energy generation systems, and generating pure H2 or O2. The materials that power these devices rely on having a high conductivity, surface area, and a defined pore structure, along with the commercial focus of having a small footprint and being lightweight.

3-Dimensional Graphene Architectures as Templates for Electrochemical Devices (3D-GATED), targeted providing new materials platforms for the continuing miniaturization of these electrochemical energy devices. The increasing power demands along with the focus on weight reduction of consumer electronics such as smartphones, portable gaming consoles, and smartwatches, leads to a constant need for better utilization of the volume and weight available for the electronics powering these devices. Additive manufacturing, or 3D printing, has been developing in capabilities exceptionally rapidly over the past decade, and now provides a tool for the production of scaffolds on the macro- to nano- scale with customisable densities and structures. 3D-GATED aimed to take one of the most promising energy storage materials in graphene and grow this extremely light weight material on designer, 3D printed architectures. These 3D, freestanding, graphene architectures then allow for the incorporation of materials to add device specificity (super-capacitor, battery, or water splitting catalyst). Layered transition metal dichalcogenides (LTMDs) are an ideal material for coupling to these graphene architectures as they strongly interact and bind with graphene along the basal plane, have a high surface area, can be highly conductive or catalytically active (depending on their crystal structure), and are both environmentally abundant and friendly.

Through the combination of additive manufacturing, graphene synthesis, LTMD synthesis, and electrochemical device fabrication, 3D-GATED aimed to provide a new materials platform for the formation of high power and energy electrochemical devices that can be tailored, either through structural design or LTMD additive type for specific application requirements. Throughout 3D-GATED there was significant transfer of knowledge, with training gained in LTMD synthesis and characterisation, and photo- and electro-catalytic electrochemistry, and training given in graphene synthesis, super-capacitance device building and characterisation, and carbon composite formation.

The Mattevi Research Group and Imperial College London was an ideal place to conduct 3D-GATED as it provided excellent support for this multidisciplinary project, whilst also providing excellent personal and career development opportunities. The Postdoctoral development Centre at Imperial College London further facilitated these development opportunities with an array of courses to develop research and management skills.

At the conclusion of 3D-GATED, 3D tailorable graphene architectures, 3D LTMD architecutres, and 3D graphene/LTMD architectures have been grown directly on additive manufactured scaffolds. The produced materials have shown great promise as super-capacitor devices and as water-splitting catalyst electrodes. Full device testing and optimisation is currently ongoing to test these materials in real world scenarios.
"Graphene growth via chemical vapour deposition was developed and optimised on a vertical furnace system, allowing for homogenisation of carbon concentration over the substrate during growth. This optimisation allowed for successful growth of graphene on copper or nickel, foils, foams, meshes, fibres, and nickel selective laser melted 3D scaffolds. Direct laser writing (DLW) was successfully used to fabricate 3D scaffolds with nanometer scale features. These DLW scaffolds, made from a photoresist could be coated with gold, nickel, or copper via sputtering, and etched away via plasma treatment resulting in 3D metal structures that used for CVD growth of graphene or transition metal dichalcogenides. Growth of vertical, few-layered WS2 on gold coated DLW scaffolds was highly successful resulting in a dense coverage in the semi-conducting, catalytically active, 2H state. Few layered MoS2 and WS2 were produced via exfoliation and were used as produced, or with conductive carbons to test their catalytic and electrochemical properties. Both 3D LTMDs produced via CVD and exfoliated LTMDs were studied for both hydrogen evolution and water oxidation. These 3D structures showed high on/off ratio for photocatalysis, large photocurrent, and stability. 3D graphene architectures produced on SLM nickel architectures were tested as super-capacitor electrodes. The materials showed an exceptionally low time constant and high power density, with cycling up to 100V/s showing square wave behaviour. The addition of LTMDs to the graphene materials via dip coating resulted in an increase in energy density but a decrease in power density.

In Summary, 3D-GATED has developed new protocols for the growth of Graphene and LTMDs directly on additive manufacture architectures, probed the electro- and photo-catalytic properties of the composites, build supercapacitor devices, and established strong collaborations to build and continue to exploit these results.

Throughout 3D-GATED the outcomes have been disseminated through social media (@3DGATED), conference attendance, and journal publications. Specifically, 3 peer reviewed journal publications have been disseminated based on the work carried out during 3D-GATED. Further to this, publications on 3D printing LTMDs, 3D Graphene growth, and 3D LTMD growth are all in preparation or submitted for dissemination. Further publications on collaborations build through 3D-GATED are also forthcoming. I have presented 3D-GATED at the EMRS meeting in Lille 2016 with a presentation entitled ""3D CVD graphene monoliths by additive manufacturing"" which was well recieved. Dissemination will continue at upcoming conferences, Carbon 2017 (Melbourne, Australia), and Chem2DMater (Strasbourg, France)"
3D GATED has progressed beyond the state of the art in 3D synthesis of graphene (previously done on poorly controlled metal structures) and LTMDs via the incorporation of additive manufactured architectures as templates into the growth process. This has opened up a plethora of potential applications which are currently being explored including electrochemical energy devices, sensing, tissue engineering, and photo-thermal therapy. Research into heterostructures between graphene and LTMDs has opened will continue to be a research focus into the future, with the potential to realise opto-electronic, energy, and healthcare applications. Continued development of LTMD composite materials had both progressed fundamental science and application driven research. Ongoing research using the diverse heterostructures of 2D materials within the Mattevi research group using the information provided in 3D GATED will allow for further progress in energy storage and conversion devices.
Schematic showing the processes used in 3D-GATED to produce energy devices