A Cocatalyst that Stabilizes a Hydride Intermediate during Photocatalytic Hydrogen Evolution over a Rhodium‐Doped TiO₂ Nanosheet

Abstract

The hydrogen evolution reaction using semiconductor photocatalysts has been significantly improved by cocatalyst loading. However, there are still many speculations regarding the actual role of the cocatalyst. Now a photocatalytic hydrogen evolution reaction pathway is reported on a cocatalyst site using TiO2 nanosheets doped with Rh at Ti sites as one‐atom cocatalysts. A hydride species adsorbed on the one‐atom Rh dopant cocatalyst site was confirmed experimentally as the intermediate state for hydrogen evolution, which was consistent with the results of density functional theory (DFT) calculations. In this system, the role of the cocatalyst in photocatalytic hydrogen evolution is related to the withdrawal of photo‐excited electrons and stabilization of the hydride intermediate species; the presence of oxygen vacancies induced by Rh facilitate the withdrawal of electrons and stabilization of the hydride.

Proton-assisted electron transfer and hydrogen-atom diffusion in a model system for photocatalytic hydrogen production

“…However, the actual role of noble metal co-catalysts in the proton reduction reaction remains elusive. Metal co-catalysts (e.g., Pt, Pd, Ni, Cu) (i) trap electrons and facilitate the proton reduction reaction 25 ; (ii) provide catalytic sites for the recombination of H-atoms 26 ; and (iii) accelerate the formation of gaseous molecular hydrogen 27,28 . Furthermore, Pt-decorated materials are also thought to assist during interfacial proton transfer 12,[29][30][31] .…”

“…This is mainly due to the fact that not all atoms in the particle co-catalyst have catalytic activity, which limits to elucidate the relationship between the active center and their catalytic performance. With recent advances in the study of single-atom catalysts, the mechanistic understanding the nature of heterogeneous catalysis at an atomic level is improving 28,32 .…”

Mn0.4In1.6S3 Nanoflower Solid Solutions for Visible-Light Photocatalytic Hydrogen Evolution

“…Then two such reduced protons evolve from the surface in the form of hydrogen molecules (2H ad → H 2 ; Tafel step). 55 Therefore, for the sake of explaining the significantly enhanced photocatalytic hydrogen evolution of the Mn 0.4 In 1.6 S 3 NSS over pure In 2 S 3 , we performed DFT-based first-principles calculations for In 2 S 3 and Mn 0.4 In 1.6 S 3 NSS and calculate the Gibbs free energies of H* adsorbed at two different active sites, Mn and In, respectively, based on the crystal structure models of In 2 S 3 and Mn 0.4 In 1.6 S 3 NSS with 20% Mn substituting In site on the (311) surface (Figure 7a−c). The calculation shows an unsatisfactory ΔG H* of −4.29 eV for pure In 2 S 3 (Figure 7d).…”

Two‐Dimensional Transition Metal Oxides and Chalcogenides for Advanced Photocatalysis: Progress, Challenges, and Opportunities

“…Ida et al found that the interaction of H + with active sites, a rate‐determining step in photocatalytic H 2 evolution, differed between pure TiO 2 NSs and Rh‐doped TiO 2 NSs. [ 247 ] On pure TiO 2 NSs, two H + are anchored on the surface O atoms with Δ E ab = 0 eV. On Rh‐doped TiO 2 NSs, one H + is anchored on the surface Rh atom in Rh‐doped TiO 2 NSs and forms a Rh–H species, whereas another H + is attached on the surface O atom bound to the Rh atom, hence giving a lower Δ E ab of about −1.31 eV.…”