Ultrasmall MoO_x Clusters as a Novel Cocatalyst for Photocatalytic Hydrogen Evolution

Abstract

of semiconductor photocatalysts to retard the recombination of charge carriers and enhance surface reaction rates. [13][14][15] Among various kinds of cocatalysts, Pt often shows the best performance. However, practical application of Pt-based cocatalysts is limited by their scarcity and high cost. [16] Therefore, development of highly active and cost-efficient alternatives to Pt is urgently needed. A large number of transition metals (e.g., iron, cobalt, nickel, molybdenum, and tungsten) and their derivative compounds have been studied. Fu and colleagues have integrated CdS with MoS 2 and obtained much improved hydrogen evolution activity. [17] However, the performances of which are still far from satisfactory because of the low active surface areas and sluggish separation of electron-hole pairs. [18][19][20] Thus, designing novel materials which can address these problems may lead to the discovery of non-noble metal cocatalysts with enhanced performance. Metal oxide clusters, constructed by a small number of atoms, can largely expose active metal sites. [21] Moreover, when loaded onto semiconductor photocatalysts, metal oxide clusters can induce discrete energy bands to trap charge carriers and promote the separation of electrons and holes. Regarding such unique properties, cluster cocatalysts show the potential to boost the activity of semiconductor photocatalysts for solar water splitting.The performance of cluster cocatalysts is significantly influenced by the number and coordination environment of the active atoms. [22][23][24] Therefore, it is essential to establish a synthetic method to precisely control the configuration of clusters decorated on the surface of semiconductor photocatalysts at atomic level. [25,26] Herein, a bottom-up strategy is developed to decorate ultrasmall molybdenum-oxygen (MoO x ) clusters onto the surface of CdS nanowires (NWs). The decorated clusters with finely controlled size and configuration greatly enhance the photocatalytic H 2 evolution efficiency of CdS NWs.CdS NWs are first synthesized through a solvothermal approach. [27] X-ray diffraction (XRD) pattern of as-prepared sample shows characteristic peaks of CdS with hexagonal wurtzite crystal structure ( Figure S1, Supporting Information). Field-emission scanning electron microscope (FESEM), transmission electron microscope (TEM), and high-resolution TEM (HRTEM) images indicate the successful synthesis of CdS NWs with good crystallinity (Figure S2, Supporting Information). The average diameter of the CdS NWs is about 75 nm (Figure S3, Supporting Information). MoO x clusters are then decorated To enhance the performance of semiconductor photocatalysts, cocatalysts are used to accelerate surface reactions. Herein, ultrasmall molybdenumoxygen (MoO x ) clusters are developed as a novel non-noble cocatalyst, which significantly promotes the photocatalytic hydrogen generation rate of CdS nanowires (NWs). As indicated by extended X-ray absorption fine structure analysis, direct bonds are formed between CdS NWs and MoO x clusters,...

Boosting Oxygen Evolution Kinetics by Mn–N–C Motifs with Tunable Spin State for Highly Efficient Solar‐Driven Water Splitting

“…[5][6][7][8][9] The improved activity is generally attributed to enhanced light absorption, increased number of reaction sites or accelerated carrier transportation, but little has been done to enhance the intrinsic surface redox kinetics. Integrating semiconductor with earthabundant, low-cost, and high-catalytic-active transition metal compound (including elemental doping or cocatalyst deposition) is an effective strategy to promote solar conversion efficiency.…”

Design of Heterostructured Hollow Photocatalysts for Solar‐to‐Chemical Energy Conversion

“…Novel experimental designs such as isotope labeling and probe–molecule‐involved experiments are helpful for understanding the reaction pathways and the behaviors of photogenerated charge carriers. On the other hand, novel characterization methods such as in situ attenuated total reflectance infrared spectroscopy and X‐ray absorption spectroscopy can provide detailed information about the surface and bulk properties of the photocatalysts during the reactions . Besides, time‐resolved spectroscopies, such as time‐resolved transient absorption spectroscopy, time‐resolved photoluminescence and time‐resolved X‐ray spectroscopy, would be useful tools for the study of the charge trapping behaviors and reaction mechanisms .…”

Effect of Fluorination on the Photovoltaic Properties of Medium Bandgap Polymers for Polymer Solar Cells

“…[24][25][26][27][28][29][30][31][32] Among several strategies for designing conjugated polymers, the substitution of fluorine atoms on the conjugated polymer backbone has attracted much attention for the last few years due to their unique advantages, including energy level lowering without sacrifice of the bandgap, enhancement of molecular orientation by an induced dipole along the C-F bond, and no steric hindrance due to the small size of fluorine atoms. [33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] In our previous work, a series of polymers (PBT-0F, PBT-1F, PBT-2F and PBT-3F) with or without fluorine atoms were synthesized and applied in PSCs. With the increase of the fluorine atom number, the V oc exhibits a growth spurt from 0.56 to 0.78 V, which leads to a sharp increase of PCE from 4.5% to 8.6%.…”