Porous two-dimensional layered materials for high-capacity energy storage

Supervisors

Nuno Bimbo (Department of Engineering, Lancaster)
Sarah Haigh (School of Materials, Manchester)
Harry Hoster (Department of Chemistry, Lancaster)

Project Overview

The goal of this PhD project is to synthesise and characterise new porous two-dimensional materials layered materials that have the potential to deliver high-impact technological solutions in electrochemical energy storage applications. For energy storage in high-power applications, including in power tools, and components in portable electronics, electric buses and hybrid vehicles, supercapacitors are becoming the technology of choice, due to their high-power densities, short response times and sustained performance over a large number of cycles. Materials are key for electrochemical energy storage in supercapacitors, and research on electrode materials research will underpin advances in supercapacitor technology. This project will focus on MXenes, recently discovered two-dimensional materials that have so far shown fascinating and unusual properties [1]. MXenes are alkaline earth metal carbides and nitrides that result from the exfoliation of MAX phases, and they have so far displayed outstanding performance for energy applications, particularly as supercapacitor materials [2]. For electrochemical energy storage applications, and specifically as supercapacitor materials, performance is intrinsically connected to porosity and accessible surface area. Exfoliation of stacked layers has led to increases in accessible surface area from 20 m^2 g^-1 to 100 m^2 g^-1 [2,3], resulting in some of the highest capacitances seen for any material – 900 F cm^-3 and 245 F g^-1 for volumetric and gravimetric capacitances, respectively, whereas more common porous carbon capacitors typically have 60-100 F cm^-3. In addition to improved performance, MXene synthesis is easily scalable and uses inexpensive, non-toxic materials, as opposed to other high performing electrodes made from metal oxides, which rely on elements such as ruthenium or indium. A promising strategy to improve on what is already a top-of-the-range electrochemical performance is to create porosity between the layers. Electric charge storage is surface-area dependent, and increasing surface areas will lead to higher specific capacitances, which can be done by inserting pillaring agents between the layers. This approach would give birth to a new family of porous solids, which would have a combination of thermal, electrical and mechanical properties no other porous material possesses. The different pillaring agents also allow for the porosity to be tailored, which facilitates correlations between pore size distributions and electrochemical performance.

The PhD project will consist on synthesising porous MXenes from parent MAX phases, adopting strategies used in catalysis to increase surface areas and accessible porosity. The resulting porous MXenes will be characterised using a suite of techniques, including SEM and TEM, X-ray diffraction and thermal gravimetry. The tailored porosity will be confirmed using a combination of gas sorption and electron tomography, for a full characterisation of the pore sizes and distributions. Finally, porous MXenes will be tested for electrochemical performance, calculating their capacitances and correlating these with chemical and structural composition and pore morphology. The project is a collaboration between Engineering (Dr Nuno Bimbo) and Chemistry (Prof Harry Hoster) in Lancaster and the School of Materials in Manchester (Dr Sarah Haigh) and would be very well suited for an enthusiastic student with laboratory experience interested in energy and materials.

References

  1. ACS Nano, 6(2), 1322-1331 (2012).
  2. Science, 341(6153), 1502-1505 (2013).
  3. Nature, 516(7529), 78-81 (2014).
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