Reactive Deposition Versus Strong Electrostatic Adsorption (SEA): A Key to Highly Active Single Atom Co‐Catalysts in Photocatalytic H₂ Generation

Abstract

In recent years, the use of single atoms (SAs) has become of a rapidly increasing significance in photocatalytic H2 generation; here SA noble metals (mainly Pt SAs) can act as highly effective co‐catalysts. The classic strategy to decorate oxide semiconductor surfaces with maximally dispersed SAs relies on “strong electrostatic adsorption” (SEA) of suitable noble metal complexes. In the case of TiO2 – the classic benchmark photocatalyst – SEA calls for adsorption of cationic Pt complexes such as [(NH3)4Pt]2+ which then are thermally reacted to surface‐bound SAs. While SEA is widely used in literature, in the present work it is shown by a direct comparison that reactive attachment based on the reductive anchoring of SAs, e.g., from hexachloroplatinic(IV) acid (H2PtCl6) leads directly to SAs in a configuration with a significantly higher specific activity than SAs deposited with SEA – and this at a significantly lower Pt loading and without any thermal post‐deposition treatments. Overall, the work demonstrates that the reactive deposition strategy is superior to the classic SEA concept as it provides a direct electronically well‐connected SA‐anchoring and thus leads to highly active single‐atom sites in photocatalysis.

Photocatalytic H2 Generation: Controlled and Optimized Dispersion of Single Atom Co‐Catalysts Based on Pt‐TCPP Planar Adsorption on TiO2

“…Moreover, in the case of porphyrin attachment, the resulting SAs are also significantly more stable against photoinduced agglomeration in photocatalytic tests (as confirmed by little to no agglomeration observed after 4 h of H 2 evolution-Figure S20 and Figure S21), than using "reactive" or "SEA" as a deposition method. [14,22] That is, the deposition and annealing process described here lead to a SA anchoring (placement) that is remarkably more stable against "light-induced" agglomeration than obtained by other treatments.…”

“…HAADF‐STEM in Figure 4e shows indeed that after air annealing at 350 °C exclusively SAs are present on the surface, i.e., this treatment provides a controlled conversion of adsorbed Pt‐TCPP to SA Pt adsorbed on the TiO 2 surface—this species is sufficiently anchored on the surface to prevent thermal agglomeration and this configuration shows the highest co‐catalytic activity. In comparison to conventional Pt SA deposition methods via the “reactive” deposition or SEA, [8,14] planar adsorption of Pt‐TCPP followed by a thermal treatment leads to a comparable activity in H 2 evolution, as depicted in Figure S19.…”

“…SA-deficient areas and/or aggregated SAs to rafts or clusters. [10,14,21] Such irregularities in co-catalyst dispersion contribute to poor utilization of either photoexcited carriers (due to limited electron diffusion length and turnover frequency at each site [8] ) or noble metal atoms (due to irregular spacing or size-dependent activity of co-catalytic sites [22] ) in photocatalytic reactions.…”

“…However, due to inherently limited control over the preferential reaction or adsorption sites via these methods, the resulting SA‐decorated surfaces often show inhomogeneous SA deposition i.e. SA‐deficient areas and/or aggregated SAs to rafts or clusters [10,14,21] . Such irregularities in co‐catalyst dispersion contribute to poor utilization of either photoexcited carriers (due to limited electron diffusion length and turnover frequency at each site [8] ) or noble metal atoms (due to irregular spacing or size‐dependent activity of co‐catalytic sites [22] ) in photocatalytic reactions.…”

Charge Separation to Facilitate The Conversion of Copper‐Phenylacetylide from Aggregation‐Induced Emission to Efficient Photocatalysis

“…[1] In general, the DOI: 10.1002/adfm.202311591 photocatalytic activity is primarily determined by its light absorption efficiency (𝜂 absorption ), carrier separation and transfer efficiency (𝜂 separation ), and interfacial reaction efficiency (𝜂 reaction ). [2,3] Among them, the robust light-harvesting and photoexcitation ability are the basic premise to trigger the highly efficient photocatalytic process. [4] Essentially, this is consistent with the requirements of an excellent photoluminescence (PL) material, except that the application of its photogenerated carriers is different.…”