Electride Materials Chemistry

Lead Research Organisation: University of Glasgow
Department Name: School of Chemistry

Abstract

New phenomena and properties are critical in launching advanced materials beyond the current state-of-the-art. This is explicit in the EPSRC ambition to "Introduce the next generation of innovative and disruptive technologies". Electrides are a group of solids that are extraordinary phenomenologically and have the potential to transform the materials landscape.

In fact, electrides have been regarded as rare and fascinating curiosities born from solution state inorganic chemistry and lauded in condensed matter physics. Alkali metals such as sodium (Na) were first shown to exist as positively charged cations (e.g. Na+) with solvated negatively charged electrons in solutions with liquid ammonia at the turn of the 20th century. Over six decades later, it was demonstrated that certain types of ring-like organic molecules (crown ethers or crytpands) could bind to these species and stabilise them (to form organometallic complexes). It was possible to crystallise these complex molecules and these crystals were the first examples of so-called electrides and alkalides. Research progressed gradually in the field in the following decades but ground-breaking discoveries made since the turn of the millennium have changed the rules for electrides in the solid state and revealed chemical & physical properties that are both exotic and practically useful. The new examples of electrides are inorganic and relatively physically robust, although chemically they can be extremely reactive. The electrons in electrides can be thought of as the smallest possible negatively charged anions that occupy discrete spaces in the structure around the metal cations (rather like chloride in sodium chloride, for example). The physical properties of electrides can be very different from conventional metals, for example, as a result. They also exhibit intriguing crystal structures, often containing channels or spaces between layers that can be populated by other atoms. The examples of such electrides known to date however, number only a handful. This exploratory project argues from the premise that electrides should be classified collectively, synthesised by design principles and scrutinised as cutting edge materials with applications in electronics, energy storage and catalysis.

The research programme will be driven the by the synthesis of new solid state electrides. This exploratory project will focus on electrides formed containing (other) anions from groups 14 and 15; tetrelides (such as carbon or silicon) and pnictides (such as nitrogen or phosphorus). The programme consists of 3 scientific themes:

1. Locating new electrides.
Driven both by chemical analogy/intuition and by computational prediction, the aim is to characterise emerging electrides (in terms of structure, bonding, composition and physical properties) and to pick targets for the synthesis of new electride materials.

2. Materials design; doping, substitution and (de)intercalation.
By either (partially) replacing the electride electrons with other anions, by replacing metals within the cation framework and/or by inserting other species between layers or within channels, it should be possible to engender modified or new physical properties in the materials that we synthesise.

3. Exfoliation, functionalisation and nanocomposites
By analogy to graphene, we will test the feasibility of forming "electrenes" from layered electrides. We also attempt to fashion electride nanowires using templating procedures. We will measure the changes in electronic properties and evaluate the suitability of the nanomaterials for energy storage and catalysis.

Publications

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