Fabrication of Co3O4@ZnIn2S4 for photocatalytic hydrogen evolution: Insights into the synergistic mechanism of photothermal effect and heterojunction.

Integration of photothermal materials and photocatalysts can effectively improve photocatalytic hydrogen production. However, the synergistic mechanism of photothermal effect and heterojunction still need to be deeply investigated. Herein, Co3O4@ZnIn2S4 (ZIS) core-shell heterojunction was constructed as a photothermal/ photocatalytic integrated system for photocatalytic hydrogen production. The photothermal effect induced by Co3O4 boosts the surface reaction kinetic of hydrogen evolution with an apparent activation energy decrease from 42.0 kJ⋅mol-1 to 33.5 kJ⋅mol-1. The photothermal effect also increases the charge concentrations of Co3O4@ZIS, which ameliorates the conductivity of Co3O4@ZIS and thus benefits to charge transfer. In addition, a p-n junction forms between Co3O4 and ZIS and provides a built-in electric field to enhance charge separate and prolong charge life time. Benefiting from the synergy of photothermal effect and heterojunction, the photocatalytic performance of Co3O4@ZIS is significantly improved with a highest hydrogen evolution rate of 4515 µmol⋅g-1⋅h-1, which is about 3.5 times higher than that of pure ZIS. This work offers a full perspective to understand the photothermal/photocatalytic integrated conception for solar hydrogen production.

Spatially Separating Redox Centers and Photothermal Effect Synergistically Boosting the Photocatalytic Hydrogen Evolution of ZnIn2 S4 Nanosheets.

Spatially separated loading of reductive and oxidative cocatalysts is a useful strategy for expediting charge separation and surface reaction kinetics, which are two key factors for determining the photocatalytic efficiency. However, loading the spatial separation of dual cocatalysts on a 2D photocatalyst is still a great challenge. Herein, decorating the spatial separation of oxidative and reductive cocatalysts on ZnIn2 S4 nanosheets is realized by designing a ternary Co9 S8 @ZnIn2 S4 @PdS (CS@ZIS@PS) hollow tubular core-shell structure. Particularly, Co9 S8 and PdS functionally serve as the reduction and oxidation cocatalysts, respectively. Experimental results confirm that the spatial separation of Co9 S8 and PdS cocatalysts not only efficiently improve charge separation and accelerate surface reduction-oxidation kinetics, but also generate a photothermal effect to further enhance charge transfer and surface reaction kinetics. As a result, the optimized CS@ZIS@PS yields a remarkable H2 evolution rate of 11407 µmol g-1 h-1 , and the apparent quantum efficiency reaches 71.2% at 420 nm, which is one of the highest values among ZnIn2 S4 so far. The synergistic effect of spatially separated dual cocatalysts and photothermal effect may be applied to other 2D materials for efficient solar energy conversion.

Constructing a ZnIn2S4 nanoparticle/MoS2-RGO nanosheet 0D/2D heterojunction for significantly enhanced visible-light photocatalytic H2 production.

A zero-dimensional (0D)/two-dimensional (2D) heterojunction has an excellent advantage of boosting the photo-generated carrier separation and obtaining enhanced photocatalytic activities. Here, a ZnIn2S4 nanoparticle/MoS2-RGO nanosheet 0D/2D heterojunction was prepared by a rapid and low temperature hydrothermal method. TEM characterization results reveal that ZnIn2S4 nanoparticles are uniformly dispersed on the surface of MoS2-RGO nanosheets, which can provide abundant active sites and shorten the charge-migration distance, while the MoS2-RGO nanosheet acts as a support to avoid the aggregation of 0D ZnIn2S4 nanoparticles and also serves as a low-cost cocatalyst for effective hydrogen evolution. Through optimizing the MoS2-RGO composition and content, the highest hydrogen evolution rate of 425.1 µmol g-1 h-1 was obtained over the ZnIn2S4/MoS2-RGO 0D/2D heterojunction photocatalyst under visible light irradiation (λ > 420 nm), which is about 34.6 times higher than that of pure ZnIn2S4. Efficient charge separation can be attributed to the significantly enhanced photocatalytic performance, which originates from the favorable properties of the ZnIn2S4/MoS2-RGO 0D/2D heterojunction. This study provides an effective method to improve the photocatalytic performance of the ZnIn2S4 photocatalyst based on the 0D/2D heterojunction.

PtNi Alloy Cocatalyst Modification of Eosin Y-Sensitized g-C3N4/GO Hybrid for Efficient Visible-Light Photocatalytic Hydrogen Evolution.

An economic and effective Pt-based alloy cocatalyst has attracted considerable attention due to their excellent catalytic activity and reducing Pt usage. In this study, PtNi alloy cocatalyst was successfully decorated on the g-C3N4/GO hybrid photocatalyst via a facile chemical reduction method. The Eosin Y-sensitized g-C3N4/PtNi/GO-0.5% composite photocatalyst yields about 1.54 and 1178 times higher hydrogen evolution rate than the Eosin Y-sensitized g-C3N4/Pt/GO-0.5% and g-C3N4/Ni/GO-0.5% samples, respectively. Mechanism of enhanced performance for the g-C3N4/PtNi/GO composite was also investigated by different characterization, such as photoluminescence, transient photocurrent response, and TEM. These results indicated that enhanced charge separation efficiency and more reactive sites are responsible for the improved hydrogen evolution performance due to the positive synergetic effect between Pt and Ni. This study suggests that PtNi alloy can be used as an economic and effective cocatalyst for hydrogen evolution reaction. Graphical abstract A significant enhancement of photocatalytic H2 evolution is realized over the Eosin Y-sensitized g-C3N4/PtNi/GO composite with PtNi alloy as an efficient cocatalyst.

MoS2 Nanosheet-Modified CuInS2 Photocatalyst for Visible-Light-Driven Hydrogen Production from Water.

Exploiting photocatalysts respond to visible light is of huge challenge for photocatalytic H2 production. Here, we synthesize a new composite material consisting of few-layer MoS2 nanosheets grown on CuInS2 surface as an efficient photocatalyst for solar H2 generation. The photocatalytic results demonstrate that the 3 wt % MoS2 /CuInS2 photocatalyst exhibits the highest H2 generation rate of 316 µmol h(-1) g(-1) under visible light irradiation, which is almost 28 times higher than that of CuInS2 . Importantly, the MoS2 /CuInS2 photocatalyst shows a much higher photocatalytic activity than that of Pt-loaded CuInS2 photocatalyst. The enhanced photocatalytic activities of MoS2 /CuInS2 photocatalysts can be attributed to the improved charge separation at the interface of MoS2 and CuInS2, which is demonstrated by the significant enhancement of photocurrent responses in MoS2 /CuInS2 photoelectrodes. This work presents a noble-metal-free photocatalyst that responds to visible light for solar H2 generation.

Aging Precursor Solution in High Humidity Remarkably Promoted Grain Growth in Cu2ZnSnS4 Films.

Earth-abundant Cu2ZnSnS4 (CZTS) is a promising material for thin film solar cells or solar water splitting cells. Generally, large grain size and vertical penetration are highly desirable microstructures to high-efficiency solar conversion devices. Up to date, some kinds of vacuum methods have been used to prepare large grain-sized CZTS, which are expensive and limit their applications on a large scale. It is still a key challenge to prepare large-grained and vertical-penetration CZTS by a low-cost solution method. In this study, we obtained vertical-penetration CZTS thin film with 1.3 µm grain sizes by a faclie solution method. Different from previous studies, precursor solution was aged in high-humidity air before it was used to prepare CZTS films. The grain size prepared with aging precursor solution was one of the largest among the samples prepared by a solution method after sulfurizing. Moreover, the large-grained CZTS films were used as photocathodes for solar water splitting, which exhibited a much higher photocurrent than those of the samples without aging. To the best of our knowledge, this is the first demonstration to promote grain growth in CZTS by aging precursor solution in high-humidity air. This aging method can offer a reference to prepare other high-performance films.

Hydrogen photogeneration promoted by efficient electron transfer from iridium sensitizers to colloidal MoS2 catalysts.

We report the utilization of colloidal MoS2 nanoparticles (NPs) for multicomponent photocatalytic water reduction systems in cooperation with a series of cyclometalated Ir(III) sensitizers. The effects of the particle size and particle dispersion of MoS2 NPs catalyst, reaction solvent and the concentration of the components on hydrogen evolution efficiency were investigated. The MoS2 NPs exhibited higher catalytic performance than did other commonly used water reduction catalysts under identical experiment conditions. The introduction of the carboxylate anchoring groups in the iridium complexes allows the species to be favorably chem-adsorbed onto the MoS2 NPs surface to increase the electron transfer, resulting in enhancement of hydrogen evolution relative to the non-attached systems. The highest apparent quantum yield, which was as high as 12.4%, for hydrogen evolution, was obtained (λ = 400 nm).