Yu-Zhu Zhou

Freestanding Ultrathin Metallic Nanosheets: Materials, Synthesis, and Applications.

Freestanding ultrathin metallic nanosheets (FUMNSs) with atomic thickness attract extensive attention because they display remarkable advantages over their bulk counterparts by virtue of their large specific area, high aspect ratio, and unsaturated surface coordination. The state of the art of research on FUMNSs is reviewed here, wherein the important progress from the aspects of material category, synthetic strategy, and practical application are introduced, and it is demonstrated that FUMNSs will play an important role in the fields of optoelectrics, catalysis, and magnetism.

Single crystalline Cu2ZnSnS4 nanosheet arrays for efficient photochemical hydrogen generation

Cu2ZnSnS4 (CZTS) is promising for application in photoelectrochemical (PEC) water splitting systems, owing to its high absorption coefficient, abundance, non-toxicity and direct band gap suitable for solar conversion. Here we present a scalable route for the preparation of single crystalline CZTS nanosheet arrays (NSAs) on a conductive glass substrate by using CuS nanosheets (NSs) as a sacrificial template. When employed as a photocathode for PEC solar hydrogen production, the CZTS NSAs yield a photocurrent density of −1.32 mA cm−2 at 0 V versus the reversible hydrogen electrode under illumination of AM 1.5. This is the highest value ever reported for a CZTS-based electrode without a co-catalyst and protective layer. The CZTS NSAs photocathode remains active after 3.5 h of testing and maintains 60% of its initial photocurrent. This work demonstrates the reality of using earth-abundant CZTS for efficient hydrogen production.

A stable inverse opal structure of cadmium chalcogenide for efficient water splitting

Cadmium chalcogenide nanocrystals (CCNCs) are regarded as promising materials for photoelectrochemical (PEC) water splitting. However, the relatively low PEC response and poor stability restrict their practical applications. In the present work, we demonstrate that a well-designed inverse opal structure (IOS) composed of CCNCs can achieve an unprecedentedly high photocurrent and hydrogen production rate. In particular, the IOS electrode remains stable during 3 h of continuous illumination, which is even superior to those photoanodes with surface passivation and/or co-catalysts. Quantitative investigation reveals that the IOS possesses high charge-separation efficiency and light-absorption capacity, which eventually result in excellent PEC performance.

Arrays of Ultrathin CdS Nanoflakes with High-Energy Surface for Efficient Gas Detection

It is fascinating and challenging to endow conventional materials with unprecedented properties. For instance, cadmium sulfide (CdS) is an important semiconductor with excellent light response; however, its potential in gas-sensing was underestimated owing to relatively low chemical activity and poor electrical conductivity. Herein, we demonstrate that an ideal architecture, ultrathin nanoflake arrays (NFAs), can improve significantly gas-sensing properties of CdS material. The CdS NFAs are grown directly on the interdigitated electrode to expose large surface area. Their thickness is reduced below the double Debye length of CdS, permitting to achieve a full depletion of carriers. Particularly, the prepared CdS nanoflakes are enclosed with high-energy {0001} facets exposed, which provides more active sites for gas adsorption. Moreover, the NFAs exhibit the light-trapping effect, which further enhances their gas sensitivity. As a result, the as-prepared CdS NFAs demonstrate excellent gas-sensing and light-response properties, thus being capable of dual gas and light detection.

Localized Defects on Copper Sulfide Surface for Enhanced Plasmon Resonance and Water Splitting

Surficial defects in semiconductor can induce high density of carriers and cause localized surface plasmon resonance which is prone to light harvesting and energy conversion, while internal defects may cause serious recombination of electrons and holes. Thus, it is significant to precisely control the distribution of defects, although there are few successful examples. Herein, an effective strategy to confine abundant defects within the surface layer of Cu1.94 S nanoflake arrays (NFAs) is reported, leaving a perfect internal structure. The Cu1.94 S NFAs are then applied in photoelectrochemical (PEC) water splitting. As expected, the surficial defects give rise to strong LSPR effect and quick charge separation near the surface; meanwhile, they provide active sites for catalyzing hydrogen evolution. As a result, the NFAs achieve the top PEC properties ever reported for Cux S-based photocathodes.

Laser-driven absorption/desorption of catalysts for producing nanowire arrays in solution

We report the synthesis of CdTe nanowire arrays (NWAs) in solution by laser driven absorption and desorption of gold catalysts. The process can be conducted under ambient conditions and completes in several minutes. The obtained NWAs possess a monocrystal structure, high density and uniform distribution, showing promise for device construction.

Engineering hollow electrodes for hybrid solar cells for efficient light harvesting and carrier collection

The organic–inorganic hybrid solar cell (HSC) is regarded as a promising candidate for third-generation solar cells. Currently, their performance hovers at a low level due to the contradiction between the exciton diffusion and light absorption of the organic layer. In the present work, we provide an efficient solution by designing a hollow electrode for the HSC, which contains CdS nanoflake arrays (NFAs) coated with a thin organic active layer and a roof-like metallic electrode. The hollow electrode facilitates light absorption, charge separation, and hole transportation simultaneously, and as a result, the novel HSC outperforms traditional solid and core–shell HSCs. Our work demonstrates that the reasonable design of the electrode structure is of great importance for improving the power conversion efficiency of HSCs.

ZnO nanosheets with atomically thin ZnS overlayers for photocatalytic water splitting

Zinc oxide is a cost-efficient and eco-friendly material for solar-to-chemical energy conversion. However, the relatively wide band gap and poor stability restrict its practical applications. Herein, we report on the modification of ZnO nanosheets with a porous atomically thin ZnS overlayer. The as-prepared ZnS/ZnO/ZnS sandwich nanosheets exhibit a reduced band gap (2.72 eV) and yet a slightly elevated conduction band minimum, which remarkably broadens the wavelength range for light absorption and generates electrons with enough reducing capability. At the same time, the newly-prepared sandwich nanosheets possess alternatively exposed ZnS and ZnO surface patches, which attract and accommodate photo-generated holes and electrons, respectively. In addition, the ZnS overlayer catalyzes and accelerates hole-consumption reactions, thus preserving electrons for efficient water splitting. As a result, the ZnS/ZnO/ZnS sandwich nanosheets demonstrate intensive light absorption, fast charge separation, long electron lifetime, and eventually the highest hydrogen production rate reported for oxide catalysts so far. This work proves that passivation with an ultrathin layer is a potent approach for energy-band engineering, and semiconductor sandwich nanostructures are promising for highly efficient water splitting under sunlight.