Energy Efficiency

NEW PARADIGMS FOR ENERGY EFFICIENT MATERIALS

We live in an era of remarkable technological innovations that have profoundly impacted our lifestyles. The unprecedented advances in medicine, communications, energy, transportation, computers and national security have been enabled by a global information and energy revolution. As a case in point, the transfer of enormous quantities of information over large distances in a short time using light (photons) has successfully been enabled by high-speed optical fibre networks (represented in Australia by our National Broadband Network (NBN)).

The efficiencies of information and energy transfer systems are governed in large part by the materials upon which they are based. Our research focuses on hybrid materials that lie at the interface between traditional metal-based materials (eg. alloys) and organics. These Metal-Organic Framework (MOF) materials combine the 'best of both worlds'. At the present time however, their development for electronics and optics is relatively more limited than applications in gas adsorption and separations. Our research directly addresses this knowledge gap.

CONDUCTING AND SUPERCONDUCTING MOFS

The development of multifunctional electroactive, magnetic and conducting microporous materials is a highly sought-after goal: at a fundamental level these materials offer unprecedented insights into electron delocalisation in three-dimensional coordination space; at an applied level, they have enormous potential in applications ranging from electrocatalysis to solar energy conversion. Our research in this area has involved the design and synthesis of MOFs that integrate molecular components for electron transfer including radical ligands, metal centres and mixed-valence clusters. Exploiting the different redox states offers exciting prospects for controlling host-guest chemistry – an aspect that was largely unexplored prior to our work.

Recently, we have become interested in prospects for potentially superconducting MOFs - that is, materials that can transmit electrons without any electrical resistance. The discovery of this phenomenon in new classes of materials is highly sought-after, with MOFs offering a powerful platform for structure-function relationships that may enable a unification of the existing theories of superconductivity.

This project involves strong collaborations with Theoretical Physicist Prof. Ben Powell (UQ) and Experimental Physicist Prof. Adam Micolich (UNSW).

PROJECTS AVAILABLE IN CONDUCTING AND SUPERCONDUCTING MOFS:

(1) Electronic and magnetic phenomena in MOFs with topologies conducive to superconducting phenomena

(2) The development of 2nd and 3rd row ruthenium- and osmium-based Metal-Organic Frameworks

Each sub-project requires students to develop a broad range of skills and techniques from the synthesis and structural characterisation of MOFs, to the detailed analysis of their optical and electrochemical properties.

PHOTONIC MOFS FOR LIGHT-TO-LIGHT CONVERSION AND ALL-OPTICAL DEVICES

The photonics-based industry sector in Australia contributed $4.3 billion to economic activity in 2018 and continues to grow on the back of enormous investments in fibre optic technology for long-range information transfer (represented locally by our National Broadband Network (NBN)). While data is encoded in photons for transmission, signals are converted into the electronic domain for processing and storage. These photon-electron interconversions present a significant bottleneck in our telecommunications networks, drastically increasing energy consumption and reducing signal speed.

All-Optical devices are regarded as a potentially ‘breakthrough’ technology that can be integrated with existing fibre-optic infrastructure, offering the ability to manipulate photons with photons at ultrafast speeds (> 500 GB s^-1/in terahertz range) without passing into the electrical domain. Despite the inherent advantages of All-Optical devices over their electronic counterparts, there exists a serious ‘materials bottleneck’ in traditional nonlinear media such as lithium niobate, conjugated organic polymers and liquid crystals investigated to date. Specifically, the energy required to access the All-Optical operation regime is high and the response time is too slow, reducing bandwidth and limiting device performance. The lack of efficient means to achieve photon-photon interactions has fueled research into alternate strategies to surmount these barriers. A technological breakthrough urgently requires the development of active, controllable, nonlinear materials for understanding and ultimately controlling All-Optical phenomena.

This project aims to harness chiral Metal-Organic Frameworks (MOFs) as a powerful new nonlinear optical materials platform to investigate and exploit All-Optical phenomena to achieve ultrafast and energy-efficient photon-photon interactions. The champion second order nonlinear MOFs must exhibit (a) non-centrosymmetry, (b) stability under the irradiative conditions, (c) ultrafast switching times (ideally fs), and (d) high energy efficiency.

In this project with A/Prof. Girish Lakhwani (USyd), Dr Akshay Rao and Prof. Sir Richard Friend (UCambridge), we are developing chiral MOFs as novel nonlinear optical mateirals for next generation All-Optical devices.

PROJECTS AVAILABLE IN PHOTONIC MOFS:

(1) Design and synthesis of nonlinear optical MOFs (e.g. chiral MOFs) using either macro- or microcopic methods for chirality.

(2) Exploiting donor-acceptor interactions in MOFs to enhance nonlinear optical responses.

(3) Development of thin film and device fabrication techniques for photonic MOFs.

MULTIFUNCTIONAL PHOTO-MECHANO-ELECTROACTIVE MOFS

The cofacially arranged Py₂TTF moieties of (a) 1, (b) 2 and (c) 3 experience an unprecedented double [2 + 2] photocyclisation reaction. The view down the c-axis of (d) 1, (e) 2 and (f) 3. The two independent nets have been highlighted in orange and blue. The coloured spheres represent C (black), N (light blue), O (red), S (yellow) and Cd (violet). Hydrogen atoms and solvent molecules in each of the frameworks have been omitted for clarity.

Reversible structural transformations of porous coordination frameworks in response to external stimuli such as light, electrical potential, guest inclusion or pressure, amongst others, have been the subject of intense interest for applications in sensing, switching and molecular separations. In this project, we build on our recent discovery reported recently in Nature Communications of a coordination framework based on an electroactive tetrathiafulvalene exhibiting a reversible single crystal-to-single crystal double [2 + 2] photocyclisation, leading to profound differences in the electrochemical, optical and mechanical properties of the material upon light irradiation. Electrochemical and in situ spectroelectrochemical measurements, in combination with in situ light-irradiated Raman spectroscopy and atomic force microscopy, shed light on the variable mechanical properties of the framework that were supported using Density Functional Theory (DFT) calculations. The reversible structural transformation points towards a plethora of potential applications for coordination frameworks in photo-mechanical and photoelectrochemical devices, such as light-driven actuators and photo-valves for targeted drug delivery.

"Cofacial MOFs"

The aforementioned MOF is an example of a "cofacial" structure where the ligands are arranged in a "double-up" fashion. We have found that this structural feature gives rise to interesting phenomena including through-space Intervalence Charge Transfer (IVCT) which represented, at the time, a new mechanism for charge transfer in MOFs.

We have established structure-function relationships for these MOFs based on ligands including napthalenediimides, tetrathiafulvalenes and thiadiazoloes.

We have also shown that these interactions can be exploited to produce a "super-reductant" state of some MOFs. The latter are "high-energy" states that we have shown can be used, for example, as photocathodes to reduce carbon dioxide.

PROJECTS AVAILABLE IN MULTIFUNCTIONAL MOFS:

(1) Expanding the library of cofacial MOFs with novel multifunctional behaviour

(2) The development of novel solid state spectroelectrochemical technqiues

(3) The development of electrochemical methods (DC and AC) to understand the fundamental aspects of electron transport in crystalline MOFs

RESEARCH HIGHLIGHTS FROM ELECTROACTIVE & RADICAL MOFS (2010-2021)

Our team's research has made inroads into elucidating fundamental charge transfer processes within extended 2D and 3D systems including MOFs and Porous Organic Polymers (POPs). In addition to a number of presentations on this topic, highlights of our research achievements include:

We have published a number of critical invited reviews and perspective articles on the exciting field of conducting MOFs which has the potential to revolutionise a wide range of technological and industrial applications including clean energy technologies, electrocatalysts, sensors and solar cell devices, amongst numerous others.
Quantifications of through-space donor-acceptor charge transfer and Intervalence Charge Transfer in a MOF, the latter representing a new mechanism for charge transfer in a MOF. These findings demonstrated a fundamental link between the low energy absorption bands in MOFs (known as Intervalence Charge Transfer bands) and their conductivities, representing an important strategy for achieving long-range conductivity in nanoporous materials.
The observation and elucidation of through-bond charge transfer mediated via a mixed-valence interaction between redox-active triarylamine cores in a series of POPs. Subtle and systematic modifications to the backbone of the material (including the introduction of heteroatoms to the linkers, light-active units such as viologens, and redox-active units such as thiazolothiazoles) could be used to modulate the inherent electronic and spectroscopic properties. Classical electron transfer theory was applied for the first time to these porous conjugated polymers to comprehend the extent of charge delocalisation. In addition to the fundamental insights gained, their multiple accessible redox states lend these materials to potential applications in solid state electronics systems including electrochromic devices for ‘smart windows’.
Recent work from our group has revealed that radical MOFs (i.e., those incorporating ligands that possess stable radical states) can exhibit electronic delocalisation in concert with magnetic properties. These results provide a basis for exploring the interplay between electron delocalisation and spin which is key to metalloenzyme function in nature, and can be exploited for applications in information storage and spin-based molecular electronics .
Owing to our team's strong experience in experimental and theoretical methods for assessing electron delocalisation in a variety of inorganic and organic systems, we have made important contributions to collaborative research on a wide-range of systems including vanadium-oxo clusters, molecular squares and porphyrin-based systems for molecular electronics applications. One very important result has been the rare observation of the double-exchange phenomenon in discrete mixed-valence complexes of vanadium due to the interplay between electron delocalisation and magnetism (with Professor Jeff Long, UC Berkeley).
Discovery of rare charge separation phenomena in microporous MOF systems. The coexistence of porosity and charge transfer paves the way towards highly sought-after multifunctional properties that can be attained and fine-tuned by exploiting donor-acceptor interactions.
Discovery of a new mechanism known as double [2+2] photocyclisation in multifunctional electroactive MOFs based on tetrathiafulvalene.
Novel ligands have been developed which are based on components including triarylamines that can be reversibly switched between their neutral and radical states. A vast array of new MOF structures incorporating these ligands have been synthesised, and interesting functional behaviours have been demonstrated including switchable electronic properties and ‘on’/‘off’ fluorescence.
A series of POPscontaining redox-active triarylamines have been shown to possess important gas separations properties. The facile electrochemical or chemical oxidation of POPs generates mixed-valence radical cation states with markedly enhanced adsorption properties relative to their neutral analogues, including a 3-fold improvement in the H₂ uptake and CO₂/N₂ selectivity. The properties of these materials are particularly advantageous for industrial separation of flue streams containing water vapour, and the materials have been integrated into mixed-matrix membranes for testing in pilot-scale gas separations processes.