Electrochemical techniques for photoelectrode characterisation

Photoelectrodes enable simultaneous light absorption and catalysis of water splitting reactions. Their performance is established using electrochemical characterisation methods. Besides basic characterisation techniques such as voltammetry and chronoamperometry, employed in the dark or under illumination, more advanced techniques, including (photo-) electrochemical impedance spectroscopy, intensity-modulated impedance spectroscopy and transient absorption spectroscopy, can be used to evaluate key parameters and processes. For some of these techniques, data is often interpreted using over-simplified models, leading to the calculation of unreliable parameters. The values of the flat band potential and charge transfer efficiency depend heavily on the methods used to determine them, and it is recommended that the values are corroborated using multiple techniques. Lastly, certain 'efficiencies' defined in the literature for electrically biased systems should be revised.