Abstract
Platinum nanoparticles (Pt NPs) are one of the most efficient cocatalysts in photocatalysis, and their size determines the activity and the selectivity of the catalytic reaction. Nevertheless, an in-depth understanding of the platinum’s size effect in the carbon dioxide photocatalytic reduction is still lacking. Through analyses of the geometric features and electronic properties with variable-sized Pt NPs, here we show a prominent size effect of Pt NPs in both the activity and selectivity of carbon dioxide photocatalytic reduction. Decreasing the size of Pt NPs promotes the charge transfer efficiency, and thus enhances both the carbon dioxide photocatalytic reduction and hydrogen evolution reaction (HER) activity, but leads to higher selectivity towards hydrogen over methane. Combining experimental results and theoretical calculations, in Pt NPs, the terrace sites are revealed as the active sites for methane generation; meanwhile, the low-coordinated sites are more favorable in the competing HER.
Highlights
Platinum nanoparticles (Pt NPs) are one of the most efficient cocatalysts in photocatalysis, and their size determines the activity and the selectivity of the catalytic reaction
The dissociated PtCl26À anions were absorbed on the surface of hierarchically ordered TiO2–SiO2 porous materials (HTSO) due to the electrostatic force, and this was followed by the ligand-exchange process with H2O or OH− within acidic or basic media, respectively (Eqs. 1 and 2), generating the Pt complex species[28, 29]; the Pt complex was reduced to Pt nuclei in the heated ethylene glycol (EG) or methanol (MeOH) solvent and grows into larger platinum nanoparticles (Pt NPs) according to the Ostwald ripening theory[30]
To exclude the possibility that the size of Pt NPs is affected by the concentration of Cl− instead of the H+ in the acidic environment, we replace the hydrochloride acid (HCl)–EG solution with the NaCl–EG solution with the same Cl− concentration in the 7.0PHTSO synthesis process
Summary
Platinum nanoparticles (Pt NPs) are one of the most efficient cocatalysts in photocatalysis, and their size determines the activity and the selectivity of the catalytic reaction. Size-dependent activity and selectivity in the CO2 electrocatalytic reduction reaction (CO2RR) have been reported for metal NPs, such as Pd, Au and Cu, due to the intrinsic free energy of key intermediate evolutions on different surface sites[19,20,21] Inspired by these works, we attempt to explore the size effect of Pt NPs in CO2PR by studying the diversity of electronic features and geometric properties of Pt NPs. Traditional size control methods of Pt NPs often involve variation of the amount of the Pt precursor or post deposition of presynthesized colloidal Pt NPs with controllable size on the support[12, 14, 22, 23]. The changes in the active sites of Pt NPs for the CO2PR and the competing HER with the size variation are discussed in detail
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