Layer-controlled Pt-Ni porous nanobowls with enhanced electrocatalytic performance

Hollow and porous Pt-based nanomaterials are promising catalysts with applications in many sustainable energy technologies such as fuel cells. Economical and green synthetic routes are highly desirable. Here, we report a facile approach to prepare double- and single-layered Pt-Ni nanobowls （DLNBs and SLNBs） with porous shells. Microstructural analysis revealed that the shells were constructed of alloyed Pt-Ni nanocrystals and small amounts of Ni compounds. X-ray photoelectron spectra showed that their Pt 4f binding energies shifted in the negative direction compared to those of the commercial Pt/C catalyst. Furthermore, the DLNBs contained greater contents of oxidized Ni species than the SLNBs. The layer-controlled growth processes were confirmed by microscopy, and a formation mechanism was proposed based on the assistance of citrate and poly（vinylpyrrolidone） （PVP）. For the methanol oxidation reaction, the DLNBs and SLNBs exhibited 2.9 and 2.5 times higher mass activities than that of the commercial Pt/C catalyst, respectively. The activity enhancements were attributed to electronic effects and a bifunctional mechanism. Chronoamperometry and prolonged cyclic voltammetry indicated that the Pt-Ni bowl-like structures had better electrochemical properties and structural stability than the commercial Pt/C catalyst, thus making the Pt-Ni nanobowls excellent electrocatalysts for use in direct methanol fuel cells.

Conformal BiVO_(4)/WO_(3) nanobowl array photoanode for efficient photoelectrochemical water splitting

As one of the most promising photoanode candidates for photoelectrochemical(PEC)water splitting,the photocurrent density of BiVO_(4) still needs to be further improved in order to meet the practical application.In this work,a highly‐matched BiVO_(4)/WO_(3) nanobowl(NB)photoanode was constructed to enhance charge separation at the interface of the junction.Upon further modification of the BiVO_(4)/WO_(3)NB surface by NiOOH/FeOOH as an oxygen evolution cocatalyst(OEC)layer,a high photocurrent density of 3.05 mA cm^(−2) at 1.23 V vs.RHE has been achieved,which is about 5‐fold higher than pristine BiVO_(4) in neutral medium under AM 1.5 G illumination.5 times higher IPCE at 450 nm is also achieved compared with the BiVO_(4) photoanode,leading to about 95%faradaic efficiency for both H_(2) and O_(2) gas production.Systematic studies attribute the significantly enhanced PEC performance to the smaller BiVO_(4) particle size(<90 nm)than its hole diffusion length(~100 nm),the improved charge separation of BiVO_(4) by the single layer WO_(3) nanobowl array and the function of OEC layers.Such WO_(3)NB possesses much smaller interface resistance with the substrate FTO glass and larger contact area with BiVO_(4) nanoparticles.This approach provides new insights to design and fabricate BiVO_(4)‐based heterojunction photoanode for higher PEC water splitting performance.

High-efficiency colorful perovskite solar cells using TiO2 nanobowl arrays as a structured electron transport layer

The rapid development of perovskite solar cells(PSCs) has stimulated great interest in the fabrication of colorful PSCs to meet the needs of aesthetic purposes in varied applications including building integrated photovoltaics and wearable electronics. However, it remains challenging to prepare high-efficiency PSCs with attractive colors using perovskites with broad optical absorption and large absorption coefficients. Here we show that high-efficiency PSCs exhibiting distinct structural colors can be readily fabricated by employing Ti O2 nanobowl(NB) arrays as a nanostructured electron transport layer to integrate with a thin overlayer of perovskite on the NB arrays. A new crystalline precursor film based on lead acetate was prepared through a Lewis acid-base adduct approach, which allowed for the formation of a uniform overlayer of high-quality CH3 NH3 Pb I3 crystals on the inner walls of the NBs. The PSCs fabricated using the Ti O2 NB arrays showed angle-dependent vivid colors under light illumination. The resultant colorful PSCs exhibited a remarkable photovoltaic performance with a champion efficiency up to16.94% and an average efficiency of 15.47%, which are recordbreaking among the reported colorful PSCs.

Substrate-based galvanic replacement reactions carried out on heteroepitaxially formed silver templates

Galvanic replacement reactions have been widely used to transform solution dispersed silver template structures into intricate nanoshell geometries. Here, we report on the use of these same reactions to form hollow substrate-supported Au-Ag nanoshells from silver templates having a heteroepitaxial relationship with the underlying single crystal substrate. The structures obtained exhibit a nanohut geometry, show highly tunable plasmonic properties and are formed as periodic arrays using a lithography-free technique. When removed from the substrate the inverted nanohuts appear as nanobowls with a notch in the rim. The study lays the groundwork for wafer-based devices utilizing nanoshells located at site-specific locations.

Oriented electron tunneling transport in hierarchical Ag/SiO_(2)/TiO_(2) nanobowl arrays for plasmonic solar water splitting

Hierarchical Ag/SiO_(2)/TiO_(2) nanobowl(NB)arrays were fabricated for use as plasmonic photoanodes for solar-hydrogen conversion.The nanobowls had large pore size and were composed of an upper TiO_(2) nanoring and a lower TiO_(2) nanohole.A thin SiO_(2) inter-layer was introduced as an electron transmission channel to change the mechanism of hot electron transport.Simulations were performed to characterize the variation of electron concentration in Ag/SiO_(2)/TiO_(2) NB arrays,taking into account both the optical transition of photogenerated electrons,and electron tunneling.The multiphysics coupling function of COMSOL software provided the light source for optical transition of photogenerated electrons,and a Wentzel-Kramers-Brillouin model was employed to represent the tunneling.The results demonstrate that the TiO_(2) nanoring was a transporter,which transmitted electrons downward to the nanohole.The SiO_(2) layer replaces the Schottky barrier to become a bridge for tunneling of hot electrons in high-and low-energy states into TiO_(2).Moreover,the coverage of the SiO_(2) layer helped increase the light absorption of TiO_(2),it also reduced the near electric field coupling between Ag and TiO_(2).Accordingly,under AM 1.5 light irradiation,the photocurrent density and average hydrogen evolution rate of Ag/SiO_(2)/TiO_(2) were 1.8 and 2.2 times higher,respectively,than those of pure TiO_(2),implying far more efficient migration of carriers.