Size and Coverage Effects of Ni and Pt Co-Catalysts in the Photocatalytic Hydrogen Evolution from Methanol on TiO₂(110)

Abstract

In the past decade, hydrogen evolution from photocatalytic alcohol oxidation on metal-loaded TiO2 has emerged as an active research field. While the presence of a metal cluster co-catalyst is crucial as a H2 recombination center, size and coverage effects on the catalyst performance are not yet comprehensively understood. To some extent, this is due to the fact that common deposition methods do not allow for an independent change in size and coverage, which can be overcome by the use of cluster sources and the deposition of size-selected clusters. This study compares size-selected Ni and Pt clusters as co-catalysts on a TiO2(110) single crystal and the resulting size- and coverage-dependent effects in the photocatalytic hydrogen evolution from alcohols in ultrahigh vacuum (UHV). Larger clusters and higher coverages of Ni enhance the product formation rate, although deactivation over time occurs. In contrast, Pt co-catalysts exhibit a stable and higher activity and size-specific effects have to be taken into account. While H2 evolution is improved by a higher concentration of Pt clusters, an increase in the metal content by the deposition of larger particles can even be detrimental to the performance of the photocatalyst. The acquired overall mechanistic picture is corroborated by H2 formation kinetics from mass spectrometric data. Consequently, for some metals, size effects are relevant for improving the catalytic performance, while for other co-catalyst materials, merely the coverage is decisive. The elucidation of different size and coverage dependencies represents an important step toward a rational catalyst design for photocatalytic hydrogen evolution.

Ni loaded SnS2 hexagonal nanosheets for photocatalytic hydrogen generation via water splitting

“…Many researchers have reported that noble metal NPs, such as Au, Pt, Ag, Rh, Ni-Pt, Pd, Cu-Pd, and Au-Pd have been reported resulting in enhanced overall photocatalytic activity by enhancing the electron-hole charge separation. [61][62][63][64][65][66][67][68][69][70][71] In this regard, SnS 2 nanostructures were synthesized by hydrothermal method and were in situ decorated with Ni as a cocatalyst having different concentrations of Ni i.e., 1 mol%, 2.5 mol%, 5 mol%, and 10 mol% through a simple thermal reduction method. The detailed physico-chemical characterisation and inuence of Ni loading on SnS 2 towards its photocatalytic performance were investigated.…”

“…Many researchers have reported that noble metal NPs, such as Au, Pt, Ag, Rh, Ni-Pt, Pd, Cu-Pd, and Au-Pd have been reported resulting in enhanced overall photocatalytic activity by enhancing the electron–hole charge separation. 61–71…”

Hydrogen Evolution on Electrode‐Supported Ptn Clusters: Ensemble of Hydride States Governs the Size Dependent Reactivity

“…[17] Finally, in a recent non-electrochemical study, specific Pt clusters (most notably Pt 10 ) on titania (TiO 2 ) were reported to show high and stable catalytic activity toward the photo-induced production of H 2 compared to Pt 1 /TiO 2 . [18] Herein, we present a joint experimental and theoretical study of the activity and stability of size-selected Pt 1,4,7,8 clusters deposited fluorine-doped tin oxide (FTO) electrode supports, towards the electrocatalytic hydrogen evolution reaction (HER). Mass-selected deposition in ultra-high vacuum (UHV) was used to prepare electrodes with identical Pt loadings, differing only in cluster size.…”

Hydrogen Evolution on Electrode‐Supported Ptn Clusters: Ensemble of Hydride States Governs the Size Dependent Reactivity

“…[17] Finally, in a recent non-electrochemical study, specific Pt clusters (most notably Pt10) on titania (TiO2) were reported to show high and stable catalytic activity toward the photo-induced production of H2 compared to Pt1/TiO2. [18] Herein, we present a joint experimental and theoretical study of the activity and stability of size-selected Pt1,4,7,8 clusters deposited fluorine-doped tin oxide (FTO) electrode supports, towards the electrocatalytic hydrogen evolution reaction (HER). Mass-selected deposition in ultra-high vacuum (UHV) was used to prepare electrodes with identical Pt loadings, differing only in the size of clusters deposited.…”