Public Research Seminar by Advanced Materials Thrust, Function Hub, HKUST(GZ) - Photocatalytic and electrocatalytic pathways to sustainable fuels and chemicals: insights into reaction kinetics from optical spectroscopy

I will start by introducing the challenge of sustainably synthesising fuels and chemicals as part of our transition to a more sustainable energy system. I will introduce photocatalytic, photoelectrode and electrocatalytic pathways to sustainable fuels and chemicals.  I will then go on to discuss the use of transient optical spectroscopies to provide insight into both photocatalytic and electrocatalytic function, focusing in particular on the challenge of splitting water to synthesis green hydrogen, as well as the organic oxidations (e.g. photoreforming). I will highlight the particular kinetic challenge for photocatalysis resulting from the timescale mismatch between the picosecond to nanosecond lifetimes of photoexcitations in most light absorbing materials versus the microsecond to second timescales of chemical fuel synthesis, and contrast this with kinetic challenges in photovoltaic solar cells. I will give examples of photocatalytic approaches employing both organic and inorganic materials, including metal oxides and conjugated polymers and how transient optical spectroscopies can give insight into their function. I will move on to the challenge of water oxidation catalysis, the key kinetic and thermodynamic bottleneck for both photocatalytic and electrocatalytic water splitting.  I will again illustrate how transient optical spectroscopies to used to provide insight into catalyst function. In particular, I will show how operando optical spectroelectrochemistry can used to determine redox state population densities and catalysis kinetics in metal oxides electrocatalysts and photocatalysts during water oxidation. This spectroelectrochemical approach is based on the idea that the redox states of most transition metal oxides are coloured, allowing the specific concentrations of each state to be tracked by their optical absorption/reflection as a function of material, applied bias, time, electrolyte etc. I will show how such optical analyses can yield insights difficult to achieve from more widely employed electrochemical analyses. I will discuss examples of the insights gained from such operando spectroelectrochemistry into materials design and function, for example comparing water oxidation kinetics on heterogeneous and molecular iridium electrocatalysts, as well as on hematite photoelectrodes.