Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - NEIL (Nanoscale Electrochemistry in Ionic Liquids)

Teaser

Recent years have seen the emergence of a diverse range of electrochemical technologies (devices) capable of reliably generating (e.g., solar cells), converting (e.g., fuel cells) and storing (e.g., batteries) energy from renewable sources. These devices are comprised of one...

Summary

Recent years have seen the emergence of a diverse range of electrochemical technologies (devices) capable of reliably generating (e.g., solar cells), converting (e.g., fuel cells) and storing (e.g., batteries) energy from renewable sources. These devices are comprised of one or more electrochemical cells, which, in their simplest form, are made up of two electronic conductors (electrodes) separated by an ionic conductor (electrolyte). One particularly important class of electrode are “electrocatalysts”, which are materials that promote or “catalyse” a number of technologically important electrochemical reactions (water splitting, fuel oxidation etc.). Electrocatalysts are crucial in the operation of many salient electrochemical technologies, where they lower the energy barriers associated with electrochemical transformation, maximising overall device efficiency.

The characteristics of the electrodes (e.g., electrocatalysts) and electrolyte are critically important as they ultimately dictate properties of the electrochemical device, including the lifetime, performance and safety. It follows that in order to “rationally” design new materials that are cheaper, safer and/or more efficient in these applications, one must understand the functional properties of said materials in minute detail. In this project, we present a new tool that makes use of a special probe (known as a “scanning probe”) to measure the functional properties of (electrode) materials, which can be related to microscopic structure in order to guide the development of more effective renewable energy technologies (i.e., devices).

In essence, we have developed and implemented a suite of “scanning probe” techniques to measure functional (electrochemical) information with unprecedented spatial-resolution, which, when taken with complementary information on microscopic structure, allowed the features that comprise a “functional” or “active” electrode (i.e., the “active sites”) to be unambiguously revealed. We effectively showed that this novel approach to relating “structure” and “function” (i.e., activity) is generally applicable to any type of electrode material by applying it to study a number of promising electrocatalysts, including metal nanoparticles, molybdenum disulfide and pentlandite. In addition, we adapted the “scanning probe” technology to explore the use of novel electrolytes in these applications, notably ionic liquids, which possess a number of favourable properties including high conductivity and non-flammability.

Work performed

\"The first body of work to be explored in this project focussed on two electrode materials, molybdenum disulfide and pentlandite, which are both electrocatalysts for the hydrogen evolution reaction, the process that occurs at the cathode of electrolysers, producing hydrogen fuel from water. “Scanning probe” techniques were used to reveal the “active sites” of both materials, which allowed us to optimize their performance for water splitting (hydrogen fuel generation). These works were disseminated via publication:

(1) Bentley, C. L., et al., \"\"Electrochemical Maps and Movies of the Hydrogen Evolution Reaction on Natural Crystals of Molybdenite (MoS2): Basal vs. Edge Plane Activity\"\", Chemical Science 2017, 8 (9), 6583-6593.
(2) Bentley, C. L., et al., \"\"Local Surface Structure and Composition Control the Hydrogen Evolution Reaction on Iron Nickel Sulfides\"\", Angewandte Chemie International Edition 2018, 57 (15), 4093-4097.

The latter piece of work was also featured in Science Daily:

“Robust and inexpensive catalysts for hydrogen production”, April 10 2018, https://www.sciencedaily.com/releases/2018/04/180410103512.htm

After completing these works, significant focus was given to improving the “scanning probe” techniques, specifically the spatial-resolution, which allowed us to interrogate more minute structural features of electrodes, further facilitating rational electrode design. Again, these works were disseminated via publication:

(3) Kang, M., et al., \"\"Simultaneous Topography and Reaction Flux Mapping at and around Electrocatalytic Nanoparticles\"\", ACS Nano 2017, 11 (9), 9525-9535.
(4) Bentley, C. L., et al., \"\"Nanoscale Structure Dynamics within Electrocatalytic Materials\"\", Journal of the American Chemical Society 2017, 139 (46), 16813-16821.

The latter study produced a lot of interest, with presentations given at a number of internationally-leading conferences, including Electrochem 2017 (Birmingham, U.K.), Gordon Research Conference on Electrochemistry (Ventura, U.S.A.) and 69th Annual Meeting of the International Society of Electrochemistry (Bologna, Italy).

After completing these works, we further developed some of the technical aspects of the “scanning probe”, specifically, how to implement these techniques for renewable energy materials (e.g., electrocatalyst) research. Again, these works were disseminated via publication:

(5) Bentley, C. L., et al., \"\"Stability and Placement of Ag/AgCl Quasi-Reference Counter Electrodes in Confined Electrochemical Cells\"\", Analytical Chemistry 2018, 90 (12), 7700-7707.
(6) Bentley, C. L., et al., \"\"Nanoscale electrochemical movies and synchronous topographical mapping of electrocatalytic materials\"\", Faraday Discussions 2018, 210, 365-379.

Over the project period, two review articles addressing various aspects of the use of the “scanning probe”, as well as implementation of ionic liquids as electrolytes were also published:

(7) Bentley, C. L., et al., \"\"Scanning electrochemical cell microscopy: New perspectives on electrode processes in action\"\", Current Opinion in Electrochemistry 2017, 6 (1), 23-30.
(8) Bentley, C. L., et al., \"\"Voltammetric Perspectives on the Acidity Scale and H+/H2 Process in Ionic Liquid Media\"\", Annual Review of Analytical Chemistry 2018, 11 (1), 397-419.

Finally, since finalizing the above publications, the optimized “scanning probe” techniques have been used to investigate a range of phenomena in electrocatalysis and beyond (e.g., ionic liquid electrolytes).
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Final results

The work performed during this project was entirely original and innovative, effectively pushing the state-of-the-art in terms of “scanning probe” resolution and speed, meaning these techniques can now be used to interrogate more minute structural features of electrodes in a fraction of the time that was previously required. We predominantly used these techniques to interrogate electrocatalysts, directly revealing the “active” sites that drive catalytic reactions at materials such as molybdenum disulfide and pentlandite, which are cheap, earth-abundant water splitting (hydrogen evolution) catalysts, a critically important process for the so-called “hydrogen economy”. This information, taken with complementary information on microscopic structure, can be used to guide the development of the next generation of highly efficient renewable energy technologies, which is the heart of “rational materials design/synthesis”. Additionally, outside of energy research, the “scanning probe” techniques developed herein have shown to be powerful in sensing, cell biology, corrosion, etc. where “structure-activity problems” are ubiquitous and where higher resolution techniques have the potential for developing considerable new knowledge. Overall, there is no doubt that this project was highly successful, having given rise to a number of high-impact publications, as well as multiple (ongoing) international collaborations within Europe and beyond.

Website & more info

More info: https://warwick.ac.uk/fac/sci/chemistry/research/unwin/electrochemistry/home/.