Tuning the Electronic Properties of Platinum in Hybrid-Nanoparticle Assemblies for use in Hydrogen Evolution Reaction.

Platinum is the best electrocatalyst for the hydrogen evolution reaction (HER). Here, we demonstrate that by contact electrification of Pt nanoparticle satellites on a gold or silver core, the Fermi level of Pt can be tuned. The electronic properties of Pt in such hybrid nanocatalysts were experimentally characterized by X-ray photoelectron spectroscopy (XPS) and surface-enhanced Raman scattering (SERS) with the probe molecule 2,6-dimethyl phenyl isocyanide (2,6-DMPI). Our experimental findings are corroborated by a hybridization model and density functional theory (DFT) calculations. Finally, we demonstrate that tuning of the Fermi level of Pt results in reduced or increased overpotentials in water splitting.

Interfacial Evolution on Co-based Oxygen Evolution Reaction Electrocatalysts Probed by Using In Situ Surface-Enhanced Raman Spectroscopy.

Disclosing the roles of reactive sites at catalytic interfaces is of paramount importance for understanding the reaction mechanism. However, due to the difficulties in the detection of reaction intermediates in the complex heterophase reaction system, disentangling the highly convolved roles of different surface atoms remains challenging. Herein, we used CoOx as a model catalyst to study the synergy of CoTd2+ and CoOh3+ active sites in the electrocatalytic oxygen evolution reaction (OER). The formation and evolution of reaction intermediates on the catalyst surface during the OER process were investigated by in situ surface-enhanced Raman spectroscopy (SERS). According to the SERS results in ion-substitution experiments, CoOh3+ is the catalytic site for the conversion of OH- to O-O- intermediate species (1140-1180 cm-1). CoOOH (503 cm-1) and CoO2 (560 cm-1) active centers generated during the OER, at the original CoTd2+ sites of CoOx, eventually serve as the O2 release sites (conversion of O-O- intermediate to O2). The mechanism was further confirmed on Co2+-Co3+ layered double hydroxides (LDHs), where an optimal ratio of 1:1.2 (Co2+/Co3+) is required to balance O-O- generation and O2 release. This work highlights the synergistic role of metal atoms at different valence statuses in water oxidation and sheds light on surface component engineering for the rational design of high-performance heterogeneous catalysts.

Symmetry-breaking synthesis of Janus Au/CeO2 nanostructures for visible-light nitrogen photofixation.

Precise manipulation of the reactive site spatial distribution in plasmonic metal/semiconductor photocatalysts is crucial to their photocatalytic performance, but the construction of Janus nanostructures through symmetry-breaking synthesis remains a significant challenge. Here we demonstrate a synthetic strategy for the selective growth of a CeO2 semi-shell on Au nanospheres (NSs) to fabricate Janus Au NS/CeO2 nanostructures with the assistance of a SiO2 hard template and autoredox reaction between Ag+ ions and a ceria precursor. The obtained Janus nanostructures possess a spatially separated architecture and exhibit excellent photocatalytic performance toward N2 photofixation under visible-light illumination. In this scenario, N2 molecules are reduced by hot electrons on the CeO2 semi-shell, while hole scavengers are consumed by hot holes on the exposed Au NS surface, greatly promoting the charge carrier separation. Moreover, the exposed Au NS surface in the Janus structures offers an additional opportunity for the fabrication of ternary Janus noble metal/Au NS/CeO2 nanostructures. This work highlights the genuine superiority of the spatially separated nanoarchitectures in the photocatalytic reaction, offering instructive guidance for the design and construction of novel plasmonic photocatalysts.

Quantifying Hot Electron Energy Contributions in Plasmonic Photocatalysis Using Electrochemical Surface-Enhanced Raman Spectroscopy.

Due to the challenge in measuring hot electron energy under reaction conditions, very few studies focus on experimental determination of hot carrier energy. Here, we adjust the energy state of free electrons in Au nanoparticles to quantify the hot electron energy in plasmonic photocatalysis. Reactant molecules with different reduction potentials such as 4-nitrothiophenol (4-NTP), 4-iodothiophenol (4-ITP), etc. are chosen as molecular probes to investigate the reducing ability of hot electrons. By comparing the voltage required to achieve the same conversion of photo- and electro-reaction pathways, we calibrate the maximum energy efficiency of hot electrons in 4-NTP reduction to be 0.32 eV, which is much lower than the excitation photon energy of 1.96 eV. Our work provides insight into the energy distribution of hot electrons and will be helpful for rational design of highly efficient plasmon-mediated chemical reactions.

Site-Selective Growth of Crystalline Ceria with Oxygen Vacancies on Gold Nanocrystals for Near-Infrared Nitrogen Photofixation.

Site-selective growth of crystalline semiconductors on gold nanocrystals remains a great challenge because of the difficult control of both nucleation and growth dynamics as well as the easy agglomeration and deformation of gold nanocrystals at high temperatures of 400-1000 °C. Here we report a facile wet-chemistry route for the selective growth of crystalline ceria at the ends of gold nanorods (Au NRs) in the presence of a small amount of bifunctional K2PtCl4. Due to the smaller steric hindrance at the ends than at the side surface, K2PtCl4 may preferentially adsorb at the ends of Au NRs, triggering the autoredox reaction with the ceria precursor to obtain crystalline CeO2 at the ends. Notably, the surface of grown ceria is rich in oxygen vacancies (OVs) that facilitate the adsorption and activation of N2 molecules. The unique structure, the plasmon-induced hot carriers and the OVs make the obtained Au/end-CeO2 an excellent catalyst for nitrogen photofixation under near-infrared (NIR) illumination.