PHOTO-INDUCED ELECTRON DYNAMICS AT THE TRANSITION-METAL OXIDE–WATER INTERFACE FROM TIME-RESOLVED LIQUID-JET PHOTOEMISSION

Introduction

Photocatalytic water splitting using transition metal oxides (TMOs) has the potential to play a key role in the sustainable large-scale production of hydrogen. Due to their activity, cost-effectiveness, and stability, TMOs are viewed as attractive materials to catalyze water splitting by harnessing solar energy.

Challenges in Water Splitting

A major challenge is effectively preventing the recombination of electrons and holes in the TMOs produced upon (solar) light absorption. While these charge recombination processes occur on the pico-to-nanosecond timescale, the whole water splitting process is almost 12 orders of magnitude slower!

This huge difference urgently demands a better understanding of the underlying mechanisms and charge-driven chemical reactions involving:

1. Electron transfer (reduction reaction)
2. Hole transfer (oxidation reaction)

These processes take place at the TMO semiconductor–liquid interface.

Research Objectives

In my WATER-X project, I will investigate these sub-10-picoseconds processes at the interface of TMO nanoparticles in bulk water by using time-resolved femtosecond laser photoelectron spectroscopy with a liquid microjet setup.

The objectives of this research include:

• Measuring the early-time molecular intermediates and their associated electronic structures
• Determining their lifetimes, energetics, photoelectron angular distributions, and decay mechanisms of the short-lived molecular intermediates

Expected Outcomes

With this knowledge, we can determine the exact mechanisms of light-induced water dissociation. This will pave the way to manipulating light-induced interactions at the solid-aqueous interface for improving the efficiency of light-to-energy conversion.

Experimental Focus

These novel experiments will be performed for four nanoparticle photocatalysts:

1. Hematite
2. Titanium dioxide
3. Cerium oxide
4. Nickel-iron-oxyhydroxide

These materials possess manifold electronic-structure properties (bandgap, charge carrier dynamics, and energetics), which make them attractive for future applications.