In recent years, platinum single atoms (SAs) have emerged as exceptionally efficient co-catalysts for photocatalytic hydrogen (H2) evolution. In the present work, we systematically investigate the solution parameters that govern the deposition of Pt SAs from dilute H2PtCl6 precursors onto well-defined sputtered anatase TiO2 thin films and evaluate the effect on photocatalytic H2 evolution. We show that both precursor concentration and solution composition critically determine the oxidation state, dispersion, and reactivity of surface-bound Pt species. Ultra-dilute, additive-free solutions (0.001–0.005 mM) enable strong electrostatic adsorption (SEA) and aquation-assisted anchoring of isolated Pt2+ atoms, leading to atomically dispersed Pt–O–Ti surface motifs with maximal H2 evolution per Pt. In contrast, increased ionic strength or unfavorable speciation caused by higher concentration or pH adjustment induces non-selective uptake, formation of Pt(IV)-rich 2D rafts, and diminished catalytic performance. Overall, we show that the placement and photocatalytic activity of Pt SAs are dictated by the pre-reaction deposition chemistry. From a practical view, this study defines a narrow yet actionable parameter window for scalable, efficient SA co-catalyst decoration and establishes the mechanistic basis for performance optimization via precursor-chemistry design.
Metal-Assisted Chemical Etching (MACE) using Ag as the catalyst lets prepare vertically aligned crystalline silicon nanopillars (SiNPs), a highly promising system for thermoelectric applications, with high aspect ratios in a wide doping range. MACE may be implemented either by using Ag both as the catalyst and the oxidant (so-called one-pot MACE) or by using another chemical (typically H2O2) as the oxidant (two-pot MACE). This study investigates how the localized etching rate depends upon Si doping in both MACE implementations, accounting for the concurrent non-catalyzed etching. The latter, which shortens SiNPs, is found to become more significant in p-type Si at higher doping levels due to the narrower space-charge regions at the bare Si-solution interface. We demonstrated that in both one- and two-pot MACE the etching rate is controlled by the band bending at silicon–silver interface. In p-type silicon, it decreases with doping due to faster hole diffusion, while the Schottky barrier at the interface hinders hole injection in n-type silicon at any doping level. Overall, we highlight that MACE may be effectively implemented in its one-pot version, facilitating MACE scale-up toward SiNP large-scale manufacturing.
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