Structure-Directing and High-Efficiency Photocatalytic Hydrogen Production by Ag Clusters

Abstract

H2 production by water splitting is hindered mainly by the lack of low-cost and efficient photocatalysts. Here we show that sub-nanometric silver clusters can catalyze the anisotropic growth of gold nanostructures by preferential adsorption at certain crystal planes of Au seeds, with the result that the final nanostructure can be tuned via the cluster/seed ratio. Such semiconducting Ag clusters are extremely stable and retain their electronic structure even after adsorption at the tips of Au nanorods, enabling various photocatalytic experiments, such as oxygen evolution from basic solutions. In the absence of electron scavengers, UV irradiation generates photoelectrons, which are stored within the nanorods, increasing their Au Fermi level up to the redox pinning limit at 0 V (RHE), where hydrogen evolution occurs with an estimated high efficiency of 10%. This illustrates the considerable potential of very small zerovalent, nonmetallic clusters as novel atomic-level photocatalysts.

Thermal Stability and Hot Carrier Dynamics of Gold Nanoparticles of Different Shapes

“…For the preparation of different shapes of gold nanoparticles, seeds and growth solutions were made as described below [34]- [36]:…”

“…The objectives of this study are twofold that are continuation to our previous results [34]- [36]; 1) to investigate the role of shape and capping material on the thermal decomposition of gold nanoparticles as the stability enhancement is of interest for practical applications and 2) to investigate the dynamics of the hot carriers in the gold nanoparticles of different shapes, induced by femtosecond laser pulses.…”

“…Recently a new proposed mechanism for the formation of anisotropic gold nanoparticles was published that takes into account the reduction of Ag ions by ascorbic acid forming intermediate small Ag clusters, which can then act as a catalyst for the formation of gold nanoparticles by their adsorption onto the surface of the gold seeds [34] [36]- [38]. By controlling the concentration of silver ions that reduced to silver clusters and adjust the ratio with seeds concentration, gold spheres are formed as this ratio equal zero, rods as the ratio equal 1 and prisms are formed as the ratio equal 3 [34]. After controlling the shapes of gold nanostructures, the thermal stability of the formed particles was studied.…”

“…The prepared gold nanoparticles are capped with only one surfactant (CTAB), and the anisotropic shape resulted by adding Ag + ions or clusters during particle growth [34]. It is important to understand the effect of surfactant structure on the stability of the formed micelles which represent the capping material of the gold particles.…”

Metallic Clusters: Theoretical Background, Properties and Synthesis in Microemulsions

“…Recently, the catalytic activity of Ag clusters for the formation of different Au anisotropic structures has been reported [51] to depend on the amount of added clusters. In Figure 11, one can see a schematic representation of the proposed mechanism for the structure-directing catalysis by Ag clusters.…”