UK scientists have used x-ray photoelectron spectroscopy (XPS) to follow an electrochemical reaction in situ.

Spectroscopic techniques such as infrared and ultraviolet-visible absorption are routinely used to investigate electrochemical reactions, giving important mechanistic and structural information. However, these methods are limited to probing the outer electrons of species and cannot be used to monitor core electronic changes. XPS could fulfil this need but its requirement for ultra-high vacuum (UHV) conditions introduces a critical obstacle: solvent evaporation.

 

The reduction of iron(III) to iron(II) is monitored using X-ray photoelectron spectroscopy

 

Peter Licence at the University of Nottingham, UK, has overcome this problem using ionic liquids, exploiting both their low volatility and inherent conduction properties. By specifically employing an iron(III)-containing ionic liquid, Licence and his colleagues were able to monitor iron(III)-iron(II) reduction using XPS. Simple though it sounds, the work has been far from easy. 'We had phenomenal problems,' admits Licence, 'we could do the electrochemistry in UHV and we've been able to [measure the XP spectra] of the ionic liquids, but to do both at the same time has been a real uphill struggle.' Given the difficulties, Licence is clearly pleased with his team's success. 'This is the first time that anyone has been able to monitor a real chemical reaction in a high vacuum environment,' he says.

Gregory Wildgoose, an expert in electrochemistry at the University of Oxford, is similarly enthusiastic. 'This is an important step forward; actually being able to do the electrochemistry inside the spectrometer is a very desirable tool for developing sensors and catalysts.' Wildgoose also praises the team's ingenuity in improving the technique's sensitivity. 'Incorporating the redox probe into the ionic liquid is very clever, enabling a sharp XPS signal, which would be difficult in a normal solute-solvent system,' he adds. 

Licence is now eager to apply the technique, and test its limits. 'We're interested in designing more efficient catalysts, new probes, sensors, functionalised electrodes,' he explains, 'we really want to push this technology to see how far we can take it.'

Philip Robinson

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