Theoretical prediction and design for chalcogenide-quantum-dot/TiO2 heterojunctions for solar cell applications.

Quantum dot sensitized solar cells have attracted much attention due to their high efficiency of photoelectric conversion and low manufacturing cost. In this study, a series of heterojunction structures with cubic (MA)4 chalcogenide quantum dots adsorbing on the (001) surface of TiO2 were investigated, in order to explore new quantum dot sensitizers for solar cell applications. Our study revealed that sulfide and selenide quantum dots are more suitable for solar energy harvesting, compared to their oxide counterparts, due to their smaller ionization potentials and smaller HOMO-LUMO (highest occupied molecular orbital-lowest unoccupied molecular orbital) gaps, but in general exhibit weaker adsorption on TiO2. M4A3B and M4A2B2 quantum dots were designed in combination with the advantage of higher adsorption stability and photoelectric conversion capability. Our theoretical predictions for the structurally precise chalcogenide systems suggest a possible direction for the design of quantum-dot sensitized solar cells.

Efficient Catalytic Conversion of Polysulfides by Biomimetic Design of "Branch-Leaf" Electrode for High-Energy Sodium-Sulfur Batteries.

Rechargeable room temperature sodium-sulfur (RT Na-S) batteries are seriously limited by low sulfur utilization and sluggish electrochemical reaction activity of polysulfide intermediates. Herein, a 3D "branch-leaf" biomimetic design proposed for high performance Na-S batteries, where the leaves constructed from Co nanoparticles on carbon nanofibers (CNF) are fully to expose the active sites of Co. The CNF network acts as conductive "branches" to ensure adequate electron and electrolyte supply for the Co leaves. As an effective electrocatalytic battery system, the 3D "branch-leaf" conductive network with abundant active sites and voids can effectively trap polysulfides and provide plentiful electron/ions pathways for electrochemical reaction. DFT calculation reveals that the Co nanoparticles can induce the formation of a unique Co-S-Na molecular layer on the Co surface, which can enable a fast reduction reaction of the polysulfides. Therefore, the prepared "branch-leaf" CNF-L@Co/S electrode exhibits a high initial specific capacity of 1201 mAh g-1 at 0.1 C and superior rate performance.

One-core-atom loss in a gold nanocluster promotes hydroamination reaction of alkynes.

It has been well-established that surface atoms play a vital role in catalysis; however, it is still unclear whether the catalytic performance can be tuned by a core atom away from the surface. The investigation into this issue is complicated, as it is challenging to abstract a core atom from a conventional catalyst. The successful synthesis of atomically precise Au25 and Au24 nanoclusters, where a core atom can be extracted from Au25 to form Au24, provides a new opportunity for unravelling the catalytic properties of a single core-atom. Herein, a distinction has been made between the catalytic activities of Au25 and Au24 in that the Au24 nanocluster exhibits superior activity in the intramolecular hydroamination of alkynes when compared to the Au25 nanocluster.

Reversible Switching of Catalytic Activity by Shuttling an Atom into and out of Gold Nanoclusters.

It is challenging to control the catalyst activation and deactivation by removal and addition of only one central atom, as it is almost impossible to precisely abstract an atom from a conventional catalyst and analyze its catalysis. Here we report that the loss of one central atom in Au25 (resulting in Au24 ) enhances the catalytic activity in the oxidation of methane compared to the original Au25 . More importantly, the activity can be readily switched through shuttling the central atom into Au24 and out of Au25 . This work will serve as a starting point for design rules on how to control catalytic performance of a catalyst by an atom alteration.