Publication

The oxidation of water at surfaces requires reactive and metastable intermediates such as surface adsorbed and often electron deficient oxygen. An outstanding question is whether forming these intermediates depends primarily on the energetics of adsorption associated with the reorganization of bonds at a vacuum interface, or whether it must include contributions from the re-orientation of water dipoles and ions within the aqueous electrolyte that could lower the free energy.

Ruthenium oxides are essential catalysts and charge storage materials whose performance across reactions, from the oxygen evolution reaction to the chlor-alkali process, depends critically on reversible Ru redox cycling and the associated electronic structure changes. Although the Ru K-edge X-ray absorption spectroscopy (XAS) is routinely used for in situ studies, it provides limited information due to the low spectral resolution.

Hole transport and localization through small polarons are essential to the performance of TiO2 in photocatalysis applications. The existence of small hole polarons in bulk rutile TiO2 has been, however, controversial with contradicting evidence from theory and experiments. Here, we use first-principles computations and more specifically a Koopmans’ compliant hybrid functional and charge correction to study small hole polarons in bulk rutile.

Semiconductor photoelectrochemistry is a dynamic and interdisciplinary field at the forefront of research in solar fuels, energy conversion, and catalysis. This Perspective captures the collective insights from the second Gerischer Electrochemistry Today Symposium, held at Colorado State University in Fort Collins, CO, in August 2024, which convened leading researchers, early-career scientists, and industry partners to define the critical next steps for the field.

The present paper reports on the fabrication, detailed structural characterizations, and theoretical modeling of titanium nitride (TiN) and its isostructural oxide derivative, titanium oxynitride (TiNO) thin films that have excellent plasmonic properties and that also have the potential to overcome the limitation of noble metal and refractory metals.

While the protonation of homogeneous metal-oxide catalysts is quite relevant for mechanisms in aqueous solution, the relevance of surface acidity to catalytic mechanisms of heterogeneous metal oxides is far less understood. Without a distinguishing metric ascribed to transient intermediates, invoking surface acidity is limited to rationalizing pH-dependent product evolution. Recently, the emissive population associated with intermediates of electron and proton transfer at a titanium oxide surface demonstrated an isotherm with pH whose half-rise occurred at pH = 11.8. As detected by a time-resolved visible broadband probe, the intermediates formed within <2 ps upon photoexcitation of the oxygen evolution reaction (OER) at an electron-doped (0.1% Nb) SrTiO3/aqueous interface. Here, we demonstrate how the pH dependence of the <2 ps population is preserved such that when the intermediate population finally decays with a time constant of 10 μs, it does so with a pH onset at 11.4.

For water splitting, a comprehensive understanding of the underlying reaction intermediates and pathways is crucial for optimizing catalyst design. Among the most well-known active photoanodes for the oxygen evolution half-reaction are TiO2-based materials. A hole polaron, which consists of a metal-oxide distortion around trapped holes, has been suggested as a local reactive oxygen configuration. While first-principles calculations identify new electronic states in the middle of the band gap and the influence of trapped hole dynamics on transport, an assignment of hole polaron configurations to a measured spectrum has been challenging due to broad optical transitions in the visible regime. Here, we compare the excited-state absorption (ESA) for two titanium oxide materials with a similar electronic structure but differing crystal structure.

The oxygen evolution reaction is crucial to sustainable electro- and photo-electrochemical approaches to chemical energy production (for example, H2). Although mechanistic descriptions of the oxygen evolution reaction have been proposed, the frontier challenge is to extract the molecular details of its elementary steps. Here we discuss how advances in spectroscopy and theory are allowing for configurations of reaction intermediates to be elucidated, distinguishing between experimental approaches (static and dynamic) across a range of surface oxygen binding energies on catalysts (from ruthenium to titanium oxides).

Reaction intermediates buried within a solid-liquid interface are difficult targets for physiochemical measurements. They are inherently molecular and locally dynamic, while their surroundings are extended by a periodic lattice on one side and the solvent dielectric on the other. Challenges compound on a metal-oxide surface of varied sites and especially so at its aqueous interface of many prominent reactions. Recently, phenomenological theory coupled with optical spectroscopy has become a more prominent tool for isolating the intermediates and their molecular dynamics.

Oxygen evolution catalysis fuels the planet through photosynthesis and is a primary means for hydrogen storage in energy technologies. Yet the detection of intermediates of the oxygen evolution reaction (OER) central to the catalytic mechanism has been an ongoing challenge. This tutorial and minireview covers the relevance of ultrafast electronic and vibrational spectroscopy of the electrochemical transformations of a metal-oxide surface undergoing OER. Here, we highlight the ultrafast trigger and probes of the electron-doped SrTiO3/electrolyte as the primary example in which light probes across the electromagnetic spectrum have detected intermediate forms.