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Solid‐state dewetting is the heat‐induced agglomeration of thin metal films into defined nanoparticles (NPs). Dewetted Pt nanoparticles are investigated on F‐doped SnO2 (FTO) substrates as model binder‐free electrodes for the hydrogen evolution reaction (HER). Dewetting of Pt films into particles exposes the FTO substrate and the metal/support (Pt‐FTO) contact line. Despite the decrease in Pt electrochemical surface area (ECSA) upon dewetting, dewetted NPs show a >3‐fold increase in ECSA‐normalized HER activity compared to as‐deposited nanocrystalline Pt films. Electrodes designed with dewetted Pt NPs of different sizes show that the HER activity does not only correlate with the ECSA but also increases with increasing the Pt‐FTO contact line length. The smaller the NPs, the larger the Pt‐FTO contact line, and the higher the activity. This effect is ascribed to electronic metal‐support interaction (EMSI), due to electron transfer from FTO to Pt. It is proposed that EMSI effects alter the electronic structure of Pt sites near the Pt‐FTO contact line, facilitating the H2 evolution kinetics. When NPs are a few nm‐sized, a large mass fraction of Pt is affected by EMSI, resulting in a further increase of HER activity compared to NPs ≥10 nm despite the lower ECSA. [ABSTRACT FROM AUTHOR]

In the present work, it is shown that anodic TiO2 nanotubes (NTs) can be decorated with Pt, Pd, Rh, and Au single atoms (SAs) by a simple "dark deposition" approach. Such TiO2 NTs with surface trapped noble metal SAs provide a high activity for photocatalytic H2 generation from pure water, i.e., in absence of a sacrificial agent. However, noble metals also act as active centers in the undesired hydrogen back‐oxidation (H2 + O2 → H2O), leading to a decrease in the overall photocatalytic H2 production efficiency. Here it is reported that the use of noble metal co‐catalysts, in the form of single atoms, can inhibit this recombination. From the different noble‐metal SAs investigated, Pd SAs yield the highest H2 production rate of 0.381 µmol h−1 cm−1 at a density of 0.41 × 105 Pd atoms µm−2. Overall, the results provide a path to a highly efficient photocatalytic performance for water splitting by the suppression of the H2/O2 recombination, which can be effectively achieved using Pd in the form of SAs as photocatalytic co‐catalysts. [ABSTRACT FROM AUTHOR]