The development of flexible near-infrared (NIR) photovoltaic (PV) devices containing silicon meets the strong demands for solar utilization, portability, and sustainable manufacture; however, improvements in the NIR light absorption and conversion efficiencies in ultrathin crystalline Si are required. We have developed an approach to improve the quantum efficiency of flexible PV devices in the NIR spectral region by integrating Si nanowire arrays with plasmonic Ag nanoplates. The Ag nanoplates can directly harvest and convert NIR light into plasmonic hot electrons for injection into Si, while the Si nanowire arrays offer light trapping. Taking the wavelength of 800 nm as an example, the external quantum efficiency has been improved by 59 % by the integration Ag nanoplates. This work provides an alternative strategy for the design and fabrication of flexible NIR PVs.

The development of flexible near-infrared (NIR) photovoltaic (PV) devices containing silicon meets the strong demands for solar utilization, portability, and sustainable manufacture; however, improvements in the NIR light absorption and conversion efficiencies in ultrathin crystalline Si are required. We have developed an approach to improve the quantum efficiency of flexible PV devices in the NIR spectral region by integrating Si nanowire arrays with plasmonic Ag nanoplates. The Ag nanoplates can directly harvest and convert NIR light into plasmonic hot electrons for injection into Si, while the Si nanowire arrays offer light trapping. Taking the wavelength of 800 nm as an example, the external quantum efficiency has been improved by 59 % by the integration Ag nanoplates. This work provides an alternative strategy for the design and fabrication of flexible NIR PVs.

Oxidation reactions by molecular oxygen (O₂) over palladium (Pd)-based nanomaterials are a series of processes crucial to the synthesis of fine chemicals. In the past decades, investigations of related catalytic materials have mainly been focused on the synthesis of Pd-based nanomaterials from the angle of tailoring their surface structures, compositions and supporting materials, in efforts to improve their activities in organic reactions. From the perspective of rational materials design, it is imperative to address the fundamental issues associated with catalyst performance, one of which should be oxygen activation by Pd-based nanomaterials. Here, the fundamentals that account for the transformation from O₂ to reactive oxygen species over Pd, with a focus on singlet O₂ and its analogue, are introduced. Methods for detecting and differentiating species are also presented to facilitate future fundamental research. Key factors for tuning the oxygen activation efficiencies of catalytic materials are then outlined, and recent developments in Pd-catalyzed oxygen-related organic reactions are summarized in alignment with each key factor. To close, we discuss the challenges and opportunities for photocatalysis research at this unique intersection as well as the potential impact on other research fields.

A Ru³⁺-mediated synthesis for the unique Pd concave nanostructures, which can directly harvest UV-to-visible light for styrene hydrogenation, is described. The catalytic efficiency under 100 mW cm⁻² full-spectrum irradiation at room temperature turns out to be comparable to that of thermally (70 °C) driven reactions. The yields obtained with other Pd nanocrystals, such as nanocubes and octahedrons, are lower. The nanostructures reported here have sufficient plasmonic cross-sections for light harvesting in a broad spectral range owing to the reduced shape symmetry, which increases the solution temperature for the reaction by the photothermal effect. They possess a large quantity of atoms at corners and edges where local heat is more efficiently generated, thus providing active sites for the reaction. Taken together, these factors drastically enhance the hydrogenation reaction by light illumination.

Silicon should be an ideal semiconductor material if it can be proven usable for photocatalytic water splitting, given its high natural abundance. Thus it is imperative to explore the possibility of water splitting by running photocatalysis on a silicon surface and to decode the mechanism behind it. It is reported that hydrogen gas can indeed be produced from Si nanowires when illuminated in water, but the reactions are not a real water-splitting process. Instead, the production of hydrogen gas on the Si nanowires occurs through the cleavage of SiH bonds and the formation of SiOH bonds, resulting in the low probability of generating oxygen. On the other hand, these two types of surface dangling bonds both extract photoexcited electrons, whose competition greatly impacts on carrier lifetime and reaction efficiency. Thus surface chemistry holds the key to achieving high efficiency in such a photocatalytic system.

Pt(100) facets are generally considered less active for the oxygen reduction reaction (ORR). Reported herein is a unique Pt-branched structure, a multicube, whose surface is mostly enclosed by {100} facets but contains high-index facets at the small junction area between the adjacent cubic components. The synthesis is accomplished by a Ni²⁺-mediated facet evolution from high-index {311} to {100} facets on the frameworks of multipods. Despite the high {100} facet coverage, the Pt multicubes exhibit impressive ORR activity in terms of half-wave potential and current density nearly to the level of the most active Pt-based catalysts, while the durability of catalysts is well retained. The facet evolution creates a set of samples with tunable ratios of high-index to low-index facets. The results reveal that the excellent ORR performance of Pt multicubes is a combined result of active sites by high-index facets and low resistance by flat surface. It is anticipated that this work will offer a new approach to facet-controlled synthesis and ORR catalysts design.

A Ru³⁺-mediated synthesis for the unique Pd concave nanostructures, which can directly harvest UV-to-visible light for styrene hydrogenation, is described. The catalytic efficiency under 100 mW cm⁻² full-spectrum irradiation at room temperature turns out to be comparable to that of thermally (70 °C) driven reactions. The yields obtained with other Pd nanocrystals, such as nanocubes and octahedrons, are lower. The nanostructures reported here have sufficient plasmonic cross-sections for light harvesting in a broad spectral range owing to the reduced shape symmetry, which increases the solution temperature for the reaction by the photothermal effect. They possess a large quantity of atoms at corners and edges where local heat is more efficiently generated, thus providing active sites for the reaction. Taken together, these factors drastically enhance the hydrogenation reaction by light illumination.

Silicon should be an ideal semiconductor material if it can be proven usable for photocatalytic water splitting, given its high natural abundance. Thus it is imperative to explore the possibility of water splitting by running photocatalysis on a silicon surface and to decode the mechanism behind it. It is reported that hydrogen gas can indeed be produced from Si nanowires when illuminated in water, but the reactions are not a real water-splitting process. Instead, the production of hydrogen gas on the Si nanowires occurs through the cleavage of SiH bonds and the formation of SiOH bonds, resulting in the low probability of generating oxygen. On the other hand, these two types of surface dangling bonds both extract photoexcited electrons, whose competition greatly impacts on carrier lifetime and reaction efficiency. Thus surface chemistry holds the key to achieving high efficiency in such a photocatalytic system.

Pt(100) facets are generally considered less active for the oxygen reduction reaction (ORR). Reported herein is a unique Pt-branched structure, a multicube, whose surface is mostly enclosed by {100} facets but contains high-index facets at the small junction area between the adjacent cubic components. The synthesis is accomplished by a Ni²⁺-mediated facet evolution from high-index {311} to {100} facets on the frameworks of multipods. Despite the high {100} facet coverage, the Pt multicubes exhibit impressive ORR activity in terms of half-wave potential and current density nearly to the level of the most active Pt-based catalysts, while the durability of catalysts is well retained. The facet evolution creates a set of samples with tunable ratios of high-index to low-index facets. The results reveal that the excellent ORR performance of Pt multicubes is a combined result of active sites by high-index facets and low resistance by flat surface. It is anticipated that this work will offer a new approach to facet-controlled synthesis and ORR catalysts design.

Surfaces and interfaces are two key parameters to maneuver the performance of photocatalytic materials, particularly for hybrid structures, in various reaction systems. In this Focus Review, we highlight the recent progress on surface and interface engineering toward designing highly efficient photocatalysts, and elucidate the fundamental principles behind the designs. We first introduce the roles of surfaces and interfaces in different models of charge kinetics—a key process determining the quantum efficiency of photocatalysis—followed by the definitions of surface and interface in basic photocatalytic architectural structures. We then outline the design rules and important parameters for surface and interface engineering, respectively. As an interplay effect, the relationships between surface and interface parameters in photocatalyst design are also presented. We further summarize the synthetic methods for surface and interface control. Finally, we discuss the challenges and opportunities for photocatalysis research in terms of surface and interface engineering.

Platinum is a commonly used cocatalyst for improved charge separation and surface reactions in photocatalytic water splitting. It is envisioned that its practical applications can be facilitated by further reducing the material cost and improving the efficacy of Pt cocatalysts. In this direction, the use of atomically controlled Pd@Pt quasi-core–shell cocatalysts in combination with TiO₂ as a model semiconductor is described. As demonstrated experimentally, the electron trapping necessary for charge separation is substantially promoted by combining a Schottky junction with interfacial charge polarization, enabled by the three-atom-thick Pt shell. Meanwhile, the increase in electron density and lattice strain would significantly enhance the adsorption of H₂O onto Pt surface. Taken together, the improved charge separation and molecular activation dramatically boost the overall efficiency of photocatalytic water splitting.

Platinum is a commonly used cocatalyst for improved charge separation and surface reactions in photocatalytic water splitting. It is envisioned that its practical applications can be facilitated by further reducing the material cost and improving the efficacy of Pt cocatalysts. In this direction, the use of atomically controlled Pd@Pt quasi-core–shell cocatalysts in combination with TiO₂ as a model semiconductor is described. As demonstrated experimentally, the electron trapping necessary for charge separation is substantially promoted by combining a Schottky junction with interfacial charge polarization, enabled by the three-atom-thick Pt shell. Meanwhile, the increase in electron density and lattice strain would significantly enhance the adsorption of H₂O onto Pt surface. Taken together, the improved charge separation and molecular activation dramatically boost the overall efficiency of photocatalytic water splitting.

The charge state of the Pd surface is a critical parameter in terms of the ability of Pd nanocrystals to activate O₂ to generate a species that behaves like singlet O₂ both chemically and physically. Motivated by this finding, we designed a metal–semiconductor hybrid system in which Pd nanocrystals enclosed by {100} facets are deposited on TiO₂ supports. Driven by the Schottky junction, the TiO₂ supports can provide electrons for metal catalysts under illumination by appropriate light. Further examination by ultrafast spectroscopy revealed that the plasmonics of Pd may force a large number of electrons to undergo reverse migration from Pd to the conduction band of TiO₂ under strong illumination, thus lowering the electron density of the Pd surface as a side effect. We were therefore able to rationally tailor the charge state of the metal surface and thus modulate the function of Pd nanocrystals in O₂ activation and organic oxidation reactions by simply altering the intensity of light shed on Pd–TiO₂ hybrid structures.

A practical strategy is proposed to facilitate the migration of holes in semiconductor (the low rate of which limits photocatalytic efficiency) by taking advantage of the Schottky barrier between p-type semiconductor and metal. A high work function is found to serve as an important selection rule for building such desirable Schottky junction between semiconductor surface facets and metal. The intrinsic charge spatial distribution has to be taken into account when selecting the facets, as it results in accumulation of photoexcited electrons and holes on certain semiconductor facets. Importantly, the facets have a high work function, the same characteristic required for the formation of Schottky junction in a p-type semiconductor–metal hybrid structure. As a result, the semiconductor crystals in the hybrid design may be better enclosed by single facets with high work function, so as to synergize the two effects: Schottky barrier versus charge spatial separation.

Surface charge state plays an important role in tuning the catalytic performance of nanocrystals in various reactions. Herein, we report a synthetic approach to unique Pt–Pd–graphene stack structures with controllable Pt shell thickness. These unique hybrid structures allow us to correlate the Pt thickness with performance in the hydrogen-evolution reaction (HER). The HER activity increases with a decrease in the Pt thickness, which is well explained by surface polarization mechanism as suggested by first-principles simulations. In this hybrid system, the difference in work functions of Pt and Pd results in surface polarization on the Pt surface, tuning its charge state for hydrogen reduction. Meanwhile, the supporting graphene provides two-dimensional channels for efficient charge transport, improving the HER activities. This work opens up possibilities of reducing Pt usage while achieving high HER performance.

Surface charge state plays an important role in tuning the catalytic performance of nanocrystals in various reactions. Herein, we report a synthetic approach to unique Pt–Pd–graphene stack structures with controllable Pt shell thickness. These unique hybrid structures allow us to correlate the Pt thickness with performance in the hydrogen-evolution reaction (HER). The HER activity increases with a decrease in the Pt thickness, which is well explained by surface polarization mechanism as suggested by first-principles simulations. In this hybrid system, the difference in work functions of Pt and Pd results in surface polarization on the Pt surface, tuning its charge state for hydrogen reduction. Meanwhile, the supporting graphene provides two-dimensional channels for efficient charge transport, improving the HER activities. This work opens up possibilities of reducing Pt usage while achieving high HER performance.