Evidencing the formation of Pt nano-islands on Cr2O3/Ag(111)

The present work reports on a comprehensive surface atomic structure investigation on the Pt/Cr2O3/Ag(111) model catalyst. Molecular beam epitaxy (MBE) was applied to achieve the Pt/Cr2O3 model system and in...

Ab initio simulations of water splitting on hematite

In recent years, hematite has attracted great interest as a photocatalyst for water splitting, but many questions remain unanswered about the mechanisms and the main limiting factors. For this reason, density functional theory has been used to understand the optical, electronic and chemical properties of this material at an atomistic level. Bulk doping can be used to reduce the band gap, and to increase photoabsorption and charge mobility. Charge transport takes place through adiabatic polaron hopping. The stable (0 0 0 1) surface has a stoichiometric termination when exposed to oxygen, it becomes hydroxylated in water, and it has an oxygen-rich termination under illumination in a photoelectrochemical setup. On the oxygen-rich termination, surface states are present that might act as recombination centres for electrons and holes. On the contrary, on the hydroxylated termination surface states appear only on reaction intermediates. The intrinsic surface states disappear in the presence of an overlayer of gallium oxide. The reaction of water oxidation is assumed to proceed by four proton-coupled electron transfers and it is shown to involve a nucleophilic attack with the formation of an OOH group. Calculated overpotentials are in the range of 0.5-0.6 V. Open questions and future research directions are briefly discussed.

Play the heavy: An effective mass study for α-Fe2O3 and corundum oxides

Iron(iii) oxide (α-Fe2O3) is a known water splitting catalyst commonly used in photoelectrochemical cells. These cells are severely impaired by poor conductivity in α-Fe2O3, and resolving the conductivity issue is therefore crucial. One of the most intrinsic properties of matter, which governs conductivity, is the carrier effective masses. In this work, we investigate the carrier effective masses in α-Fe2O3 and other corundum oxides, including Al2O3, Cr2O3, Ga2O3, and In2O3 with different theoretical constructs: density functional theory (DFT), DFT+U, hybrid DFT, and G0W0. We find DFT sufficiently describes the carrier masses and a quasi-particle theory is only required for accuracies better than 30% for the conduction band effective mass. Additionally, we compare the density of states (DOS) and band effective mass approximations and conclude the DOS effective mass provides poor results whenever the band structure is anisotropic. We find that the charge carriers in Fe2O3 "play the heavy" since they have large effective masses that reduce conductivity and device efficiency. Finally, we conclude that the less heavy electron effective masses of other corundum oxides studied relative to Fe2O3 could contribute to efficiency improvements in Fe2O3 upon Al2O3, Ga2O3, and In2O3 coverage.

Enhanced electrochemical water oxidation: the impact of nanoclusters and nanocavities

Hematite surfaces with a nanocavity are more active for OER than surfaces with nanoclusters.

Modeling and Simulations in Photoelectrochemical Water Oxidation: From Single Level to Multiscale Modeling

This review summarizes recent developments, challenges, and strategies in the field of modeling and simulations of photoelectrochemical (PEC) water oxidation. We focus on water splitting by metal-oxide semiconductors and discuss topics such as theoretical calculations of light absorption, band gap/band edge, charge transport, and electrochemical reactions at the electrode-electrolyte interface. In particular, we review the mechanisms of the oxygen evolution reaction, strategies to lower overpotential, and computational methods applied to PEC systems with particular focus on multiscale modeling. The current challenges in modeling PEC interfaces and their processes are summarized. At the end, we propose a new multiscale modeling approach to simulate the PEC interface under conditions most similar to those of experiments. This approach will contribute to identifying the limitations at PEC interfaces. Its generic nature allows its application to a number of electrochemical systems.