Yuanyuan Huang

Fast Photoelectron Transfer in (Cring)–C3N4 Plane Heterostructural Nanosheets for Overall Water Splitting

Direct and efficient photocatalytic water splitting is critical for sustainable conversion and storage of renewable solar energy. Here, we propose a conceptual design of two-dimensional C3N4-based in-plane heterostructure to achieve fast spatial transfer of photoexcited electrons for realizing highly efficient and spontaneous overall water splitting. This unique plane heterostructural carbon ring (Cring)-C3N4 nanosheet can synchronously expedite electron-hole pair separation and promote photoelectron transport through the local in-plane π-conjugated electric field, synergistically elongating the photocarrier diffusion length and lifetime by 10 times relative to those achieved with pristine g-C3N4. As a result, the in-plane (Cring)-C3N4 heterostructure could efficiently split pure water under light irradiation with prominent H2 production rate up to 371 μmol g-1 h-1 and a notable quantum yield of 5% at 420 nm.

Hexane-Driven Icosahedral to Cuboctahedral Structure Transformation of Gold Nanoclusters

Whether and how nanoclusters possessing a rich diversity of possible geometric configurations can transform from one structural type to another are critical issues in cluster science. Here we demonstrate an icosahedral-to-cuboctahedral structural transformation of Au nanoclusters driven by changing the chemical environment. For icosahedral Au(13) clusters protected by a mixture of dodecanethiol and triphenylphosphine ligands, solvent exchange of ethanol by hexane leads to quick selective desorption of the thiolate layers from the cluster surface. The surviving Au cores then undergo a much slower energy-minimization process via structural rearrangement, stabilized in the cuboctahedral structure and protected by triphenylphosphine in the hexane environment. In response to the dramatically changed atomic structure, the character of the electronic structure of the Au clusters is converted from semiconducting to metallic. This work addresses the structure-property correlation and its strong dependence on the chemical environment for metal nanoclusters.

Oxyhydroxide Nanosheets with Highly Efficient Electron-Hole Pair Separation for Hydrogen Evolution.

The facile electron-hole pair recombination in earth-abundant transition-metal oxides is a major limitation for the development of highly efficient hydrogen evolution photocatalysts. In this work, the thickness of a layered β-CoOOH semiconductor that contains metal/hydroxy groups was reduced to obtain an atomically thin, two-dimensional nanostructure. Analysis by ultrafast transient absorption spectroscopy revealed that electron-hole recombination is almost suppressed in the as-prepared 1.3u2005nm thick β-CoOOH nanosheet, which leads to prominent electron-hole separation efficiencies of 60-90u2009% upon irradiation at 350-450u2005nm, which are ten times higher than those of the bulk counterpart. X-ray absorption spectroscopy and first-principles calculations demonstrate that [HO-CoO6-x] species on the nanosheet surface promote H(+) adsorption and H2 desorption. An aqueous suspension of the β-CoOOH nanosheets exhibited a high hydrogen production rate of 160u2005μmolu2009g(-1) u2009h(-1) even when the system was operated for hundreds of hours.

Unidirectional Thermal Diffusion in Bimetallic Cu@Au Nanoparticles

Understanding the atomic diffusions at the nanoscale is important for controlling the synthesis and utilization of nanomaterials. Here, using in situ X-ray absorption spectroscopy coupled with theoretical calculations, we demonstrate a so far unexplored unidirectional diffusion from the Au shell to the Cu core in thermally alloying Cu@Au core@shell architecture of ca. 7.1 nm. The initial diffusion step at 423 K is found to be characterized by the formation of a diffusion layer composed of a Au-dilute substitutional CuAu-like intermetallic compound with short Cu-Au bond length (2.61 Å). The diffusion further happens by the migration of the Au atoms with large disorder into the interior Cu matrix at higher temperatures (453 and 553 K). These results suggest that the structural preference of a CuAu-like compound, along with the nanosized effect, plays a critical role in determining the atomic diffusion dynamics.

Adsorption kinetic process of thiol ligands on gold nanocrystals

Understanding the kinetic mechanism during ligand adsorption on gold nanocrystals is important for designing and fine-tuning their properties and implications. Here, we report a kinetic study on the adsorption process of dodecanethiol ligands on Au nanocrystals of 3.3 nm by an in situ time-resolved X-ray absorption fine structure technique. A two-step process of dodecanethiol adsorption on Au NC surfaces is proposed based on the obtained ligand coverage, which shows a quick increase from 0 to 0.40 within the first 20 min, followed by a much slower increase to the limiting value of 0.94. In-depth analysis suggests that the first stage involves the quick adsorption of dodecanethiol to the corner and edge sites of Au NCs surfaces, leading to remarkable surface Au-Au bond length relaxation (from 2.79 to 2.81 Å) and pronounced gold-to-ligand charge transfer. The second step that corresponds to the much slower adsorption process to the surface facets could be described by the Langmuir kinetics equation with an adsorption rate constant of 0.0132 min(-1) and an initial coverage of 0.41, in good agreement with the initially preferable adsorption of thiols to the most favorable sites.

Synergetic enhancement of plasmonic hot-electron injection in Au cluster-nanoparticle/C3N4 for photocatalytic hydrogen evolution

Photocatalytic hydrogen evolution driven by abundant sunlight is critical for the effective conversion of renewable energy. Here, we present a combination of Au clusters and nanoparticles (NPs) on a graphitic carbon nitride (g-C3N4) semiconductor to achieve efficient plasmonic hot electron injection for realizing high visible and near-infrared photocatalytic hydrogen evolution activity. Ultraviolet photoelectron and transient photovoltage spectroscopy demonstrate that the synergetic electron coupling between Au clusters and NPs via strong sp2 hybridization with the C3N4 host could effectively tune the semiconductor work function for reducing the metal/semiconductor interfacial Schottky barrier by 0.6 eV, which greatly shortens the injection time and prolongs the average lifetime of energetic hot electrons in C3N4 by one order of magnitude under visible and near-infrared irradiation. Hence, the as-obtained Au cluster-NP/C3N4 photocatalyst achieves a prominent photocatalytic H2 production rate of 230 μmol g−1 h−1 in the light absorption range of 400–900 nm, which is 6–20 times those of its Au NP/C3N4 and Au cluster/C3N4 counterparts.

Strongly electrophilic heteroatoms confined in atomic CoOOH nanosheets realizing efficient electrocatalytic water oxidation

Developing active and durable oxygen evolution reaction (OER) electrocatalysts is greatly desired for worldwide renewable energy applications. Here, via an efficient electrophilic extraction of local electrons in cobalt oxyhydroxide (CoOOH) nanosheets realized by confining high-valence transition-metal ions (Mn4+) in cation sites of the basal plane, we significantly facilitate the proton–electron transfer kinetics and reduce the charge transfer resistance by more than 50% for high-efficiency water oxidation. The as-synthesized Mn-doped CoOOH nanosheets exhibit an excellent OER performance with a quite low overpotential of 255 mV at 10 mA cm−2 and a small Tafel slope of ∼38 mV dec−1. X-ray absorption spectroscopy and first-principles calculations demonstrate that the high-valence Mn4+ ion with an unpaired 3d3 configuration extracts local electrons from Co active sites and reduces the adsorption free energy of OH by 0.7 eV for efficient oxygen evolution.

Strong Surface Hydrophilicity in Co-Based Electrocatalysts for Water Oxidation

Developing efficient and durable oxygen evolution electrocatalyst is of paramount importance for the large-scale supply of renewable energy sources. Herein, we report the design of significant surface hydrophilicity based on cobalt oxyhydroxide (CoOOH) nanosheets to greatly improve the surface hydroxyl species adsorption and reaction kinetics at the Helmholtz double layer for high-efficiency water oxidation activity. The as-designed CoOOH-graphene nanosheets achieve a small surface water contact angle of ∼23° and a large double-layer capacitance (Cdl) of 8.44 mF/cm2 and thus could evidently strengthen surface species adsorption and trigger electrochemical oxygen evolution reaction (OER) under a quite low onset potential of 200 mV with an excellent Tafel slope of 32 mV/dec. X-ray absorption spectroscopy and first-principles calculations demonstrate that the strong interface electron coupling between CoOOH and graphene extracts partial electrons from the active sties and increases the electron state density around the Fermi level and effectively promotes the surface intermediates formation for efficient OER.

XAFS studies of monodisperse Au nanoclusters formation in the etching process

Understanding the formation mechanism of gold nanoclusters is essential to the development of their synthetic chemistry. Here, by using x-ray absorption fine-structure (XAFS) spectroscopy, UV-Vis and MS spectra, the formation process of monodisperse Au13 nanoclusters is investigated. We find that a critical step involving the formation of smaller Au8-Au11 metastable intermediate clusters induced by the HCl + HSR etching of the polydisperse Aun precursor clusters occurs firstly. Then these intermediate species undergo a size-growth to Au13 cores, followed by a slow structure rearrangement to reach the final stable structure. This work enriches the understanding of cluster formation chemistry and may guide the way towards the design and the controllable synthesis of nanoclusters.

Combined spectroscopic study on the growth mechanism of Diphosphine-stabilized Gold Nanoclusters

The formation process of 1,5-Bis(diphenylphosphino) pentane (L5)-protected Au nanocluster through the reduction of precursor Au2L5Cl2 by borane-tert-butylamine (TBAB) is traced by a combination of time-dependent x-ray/UV-vis absorption spectroscopies and mass spectrometry. It is revealed that the initial generation of dual-core basic unit Au4L5 2Cl is a critical step, which allows for a subsequent size-growth process via incorporation of the existing Au monomer (Au(I)-Cl) or Au2L5 to form Au5L5 2, Au8L5 3Cl, Au10L5 4Cl and finally main Au11L5 4Cl2 This work advances one step further toward understanding the mechanism of formation and growth of diphosphine ligands-protected Au NCs.