Yu Hang Li

Unidirectional suppression of hydrogen oxidation on oxidized platinum clusters

Solar-driven water splitting to produce hydrogen may be an ideal solution for global energy and environment issues. Among the various photocatalytic systems, platinum has been widely used to co-catalyse the reduction of protons in water for hydrogen evolution. However, the undesirable hydrogen oxidation reaction can also be readily catalysed by metallic platinum, which limits the solar energy conversion efficiency in artificial photosynthesis. Here we report that the unidirectional suppression of hydrogen oxidation in photocatalytic water splitting can be fulfilled by controlling the valence state of platinum; this platinum-based cocatalyst in a higher oxidation state can act as an efficient hydrogen evolution site while suppressing the undesirable hydrogen back-oxidation. The findings in this work may pave the way for developing other high-efficientcy platinum-based catalysts for photocatalysis, photoelectrochemistry, fuel cells and water-gas shift reactions.

Stable Isolated Metal Atoms as Active Sites for Photocatalytic Hydrogen Evolution

The process of using solar energy to split water to produce hydrogen assisted by an inorganic semiconductor is crucial for solving our energy crisis and environmental problems in the future. However, most semiconductor photocatalysts would not exhibit excellent photocatalytic activity without loading suitable co-catalysts. Generally, the noble metals have been widely applied as co-catalysts, but always agglomerate during the loading process or photocatalytic reaction. Therefore, the utilization efficiency of the noble co-catalysts is still very low on a per metal atom basis if no obvious size effect exists, because heterogeneous catalytic reactions occur on the surface active atoms. Here, for the first time, we have synthesized isolated metal atoms (Pt, Pd, Rh, or Ru) stably by anchoring on TiO2 , a model photocatalystic system, by a facile one-step method. The isolated metal atom based photocatalysts show excellent stability for H2 evolution and can lead to a 6-13-fold increase in photocatalytic activity over the metal clusters loaded on TiO2 by the traditional method. Furthermore, the configurations of isolated atoms as well as the originality of their unusual stability were analyzed by a collaborative work from both experiments and theoretical calculations.

Titania single crystals with a curved surface

Owing to its scientific and technological importance, crystallization as a ubiquitous phenomenon has been widely studied over centuries. Well-developed single crystals are generally enclosed by regular flat facets spontaneously to form polyhedral morphologies because of the well-known self-confinement principle for crystal growth. However, in nature, complex single crystalline calcitic skeleton of biological organisms generally has a curved external surface formed by specific interactions between organic moieties and biocompatible minerals. Here we show a new class of crystal surface of TiO₂, which is enclosed by quasi continuous high-index microfacets and thus has a unique truncated biconic morphology. Such single crystals may open a new direction for crystal growth study since, in principle, crystal growth rates of all facets between two normal {101} and {011} crystal surfaces are almost identical. In other words, the facet with continuous Miller index can exist because of the continuous curvature on the crystal surface.

Mn3O4 nano-octahedrons on Ni foam as an efficient three-dimensional oxygen evolution electrocatalyst

Large-scale electrolysis of water for hydrogen production requires efficient and earth-abundant oxygen evolution catalysts. Here, we demonstrate a facile method to prepare catalytically active Mn3O4 octahedral crystals on Ni foam as a composite electrode, which exhibits outstanding activity and stability for electrocatalytic oxygen evolution.

One-step fabrication of porous oxygen-doped g-C3N4 with feeble nitrogen vacancies for enhanced photocatalytic performance

Porous oxygen-doped graphitic carbon nitride (g-C3N4) with feeble nitrogen vacancies was fabricated through thermal polycondensation of melamine with an appropriate amount of polyvinylpyrrolidone. After optimization, the bandgap of g-C3N4 can be narrowed by 0.2 eV and the specific surface area expanded, which contribute to increasing the utilization of solar energy. Consequently, the optimized g-C3N4 exhibits impressive enhancement in photocatalytic hydrogen evolution performance, by nearly 5 times compared with the pristine one under the irradiation of visible light.

In situ growth of mirror-like platinum as highly-efficient counter electrode with light harvesting function for dye-sensitized solar cells

In this work, we prepared a continuous nanostructured Pt-mirror film with metallic lustre and good adhesion to the F-doped tin oxide conducting glass (FTO) substrate through a simple in situ growth method, which retains a good catalytic activity and more importantly, exhibits significant light reflection for light-harvesting. The dye-sensitized solar cells (DSCs) fabricated with Pt-M CE exhibited superior photovoltaic performance compared with the conventional Pt CE. The enhancements of the short-circuit current density and energy conversion efficiency are 15.3% and 18.5%, respectively. Such significant enhancement of the short-circuit current density was found to be related to the excellent light reflection and high catalytic activity of the Pt-M CE. This has been proved by ultraviolet and visible reflection spectra (UV/Vis), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV).

Direct insight into crystallization and stability of hybrid perovskite CH3NH3PbI3via solvothermal synthesis

Here we report a one-pot solvothermal approach to synthesize cuboid shaped CH3NH3PbI3 single crystals and study the stability of crystallographic planes in a solvothermal system. Furthermore, the dissolution phenomenon from specific facets was discovered for the first time. Through careful control of the crystallization and dissolution processes, we found that reaction factors including temperature and time play critical roles in the crystallization process of perovskite crystals.

Orange Zinc Germanate with Metallic Ge-Ge Bonds as a Chromophore-Like Center for Visible-Light-Driven Water Splitting

The efficiency of solar-energy-conversion devices depends on the absorption region and intensity of the photon collectors. Organic chromophores, which have been widely stabilized on inorganic semiconductors for light trapping, are limited by the interface between the chromophore and semiconductor. Herein we report a novel orange zinc germanate (Zn-Ge-O) with a chromophore-like structure, by which the absorption region can be dramatically expanded. Structural characterizations and theoretical calculations together reveal that the origin of visible-light response can be attributed to the unusual metallic Ge-Ge bonds which act in a similar way to organic chromophores. Benefiting from the enhanced light harvest, the orange Zn-Ge-O demonstrates superior capacity for solar-driven hydrogen production.

Platinum@regular indium oxide nanooctahedra as difunctional counter electrodes for dye-sensitized solar cells

Platinum (Pt) nanoparticles below 2 nm loaded on In2O3 nanooctahedra were prepared with the assistance of polymer ligands, and applied as efficient difunctional counter electrode (CE) materials for dye-sensitized solar cells (DSCs). Owing to the excellent light scattering performance of regular nanooctahedra, the light harvesting efficiency was significantly increased, resulting in the noticeable 19.5% enhancement of energy conversion efficiency.

Cluster Size Effects of Platinum Oxide as Active Sites in Hydrogen Evolution Reactions

The successful design of photocatalytic hydrogen generation from water relies on a thorough understanding of the role of cocatalyst. The photoreactivity was studied as a function of the cluster size of the oxidized platinum cocatalyst. The maximum turnover frequency is found on the smallest-sized cocatalyst. This effect can be attributed to the size-dependent proton adsorption.