The Secret to Man’s Red Fire… Electrochemistry! CPS Lecture 6

– Article by Belle Taylor

Last week’s CPS talk was given by UCL’s very own Dr. Daren Caruana whose research interests lie in the field of gas phase electrochemistry. We were eased into the talk with a demonstration showing that when two electrodes were placed in a flame (butane was used as an example) a potential can be measured, similar in magnitude to that over a salt solution electrolyte. Using this knowledge there are huge implications in using a flame as the electrolyte in electrochemistry experiments.

A brief history of flames was then given. Did you know that a flame is hollow? (It blew my mind!) This is because all the reactions occur where O₂ meets the fuel. Of course, no one is able to see the inside of a flame, (although we later learned that Dr. Caruana has tried…) Flames are dynamic and extremely complex. The simplest H₂ flame can be described by 11 reactions but different flames are much more complicated in character. A hydrocarbon flame for example, is thought to be made up of around 150 trace species /ions formed through thermal collisions and subsequent transfer of energy. Although not involved in the main combustion reactions, their presence is enough to change the properties of the flame. If a flame is made entirely of ions it is electrically conducting and is termed a plasma. These conductive properties mean that a plasma is considered analogous to a salt dissolved in liquid, the electrolyte medium used in liquid phase electrochemistry.

The gas phase is of huge interest in electrochemistry; and not just because it can provide a mechanistic understanding of the solid/gas interface. Reactions can be looked at without the restrictions of the potential window defined by solution phase, with boundaries coinciding with the oxidation and reduction of water.  A larger potential window means that a much wider breadth of redox reactions can be studied. Previous studies have involved doping a flame with different oxide additives. It was found that the different oxides produced different fingerprints and showed a concentration dependence. This method of detecting different species is currently being taken further (as below).

Dr. Caruana talked about some of his current research in the field; that of bio-detection. This involves using gas phase electrochemistry to detect the presence of (and to distinguish between) biological species present in a gas. It was found that burning pollen spores in an H₂ flame led to the formation of plumes (amplification) which could be detected with electrodes positioned in the gas. The voltage of plumes passing the electrolytes varied significantly between different pollen spores and so the species were able to be distinguished. The addition of more electrodes meant that a 3D picture of the plumes was able to be formed, giving a more complete view of the electrochemistry.

This work has been built on by examining the presence of amino acids in gas. It is hoped that systematic addition of functional groups to an amino acid will allow similarities and differences in the cyclic voltammetry scan to be seen. Although in the early stages, it is looking promising that certain peaks may correspond to certain breakdown products of the amino acids (which attach to the electrode allowing detection). Spectroscopic techniques will soon be brought in to identify the breakdown products and thus make more concrete assignments of peaks. This work has application in industries where air purity is of importance; for example the medical industry, where the detection of biological species (e.g. viruses) in air could ultimately save lives.

Questions were answered regarding the potential window (it can be extended as far as the instruments will allow), the sun (electrochemistry on the surface of interstellar particles can drive redox reactions), the prospects of detection in ‘normal’ air (filtering out the rubbish and introducing a trickle of sample allows for readings – improvements needed for detection of non-introduced samples) and thermally stable coatings on the electrode (could use a zeolitic material)

All in all, it was an extremely interesting and well-presented talk (Dr. Caruana is a phenomenal public speaker). It was great to hear current research being discussed in an exciting field that most of us have been taught the basics of (so it wasn’t completely over our heads..!) It was made all the better as the research is taking place in our own department!