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Strengthening the separation of photogenerated charge carriers is crucial for improving the efficiency of photocatalytic hydrogen evolution. Herein, t-Mn0.5Cd0.5S/Ov-WO3 (t-MCSW) triple-phase junctions with rich oxygen vacancies were developed using the calcination-hydrothermal method. The corresponding morphology and structure of the samples were examined by XRD, TEM and XPS. The formation of the S-scheme heterostructure in t-MCSW has also been confirmed with in situ XPS, work function analysis and free radical capture tests. The experimental results demonstrate that t-MCSW-7 exhibited optimal activity (194.2 mmol g−1 h−1), which was about 4 times higher than that of the individual Mn0.5Cd0.5S (t-MCS, 48.8 mmol g−1 h−1). The apparent quantum yield of t-MCSW-7 is 29.14% at 420 nm, and the material exhibits excellent stability after seven cycles of photocatalytic reaction. The excellent photocatalytic activity of t-MCSW-7 is attributed to more efficient separation of charge carriers by triple-phase junctions connected by homojunctions and heterojunctions. Moreover, the existence of oxygen vacancies broadens absorption spectra and accelerates surface charge transfer. The synergistic effect of phase junctions and oxygen vacancies leads to an enhancement of hydrogen evolution activity. This work provides a new idea for preparing efficient photocatalysts. [ABSTRACT FROM AUTHOR]

The development of high-efficiency, precious-metal-free electrical catalysts for hydrogen evolution reactions is expected to facilitate the production of hydrolytic hydrogen fuels. Heterogeneous structures with a one-dimensional (1D) morphology exhibit efficient electrocatalytic effects owing to their abundance of active centers in the radial direction and convenient axial charge transfer in interconnected networks. Hence, a 1D MoS2/NiCoP heterogeneous junction for highly efficient hydrogen evolution performance was developed. As expected, the optimized MoS2/NiCoP/NF showed a low overpotential of 148 mV for hydrogen evolution with a current density of 10 mA cm−2 in 1.0 M KOH. Meanwhile, the developed heterogeneous structure exhibited high stability within 50 hours of continuous testing. [ABSTRACT FROM AUTHOR]

As a narrow bandgap semiconductor, transition metal selenides are promising as excellent electrocatalysts for hydrogen evolution reactions (HERs). Herein, using an ultra-thin MOF as the precursor, a Co-doped core–shell shaped NiSe2 based catalyst is successfully constructed by a two-step calcination method as an efficient HER catalyst. Experiments and theoretical calculations indicate that the introduction of Co adjusts the electronic structure of Ni and Se, promoting charge transfer and reducing the energy barrier of the rate-limiting step to accelerate the hydrogen precipitation reaction. In addition, the core–shell structure contributes to mass transport, and the outer carbon layer improves the stability of the catalyst. The optimal catalyst (Ni0.75Co0.25Se2@NC) exhibited satisfactory electrocatalytic activity as evidenced by a low overpotential of −143 mV at a current density of −10 mA cm−2 and a small Tafel slope of 37.5 mV dec−1. This work provides a valuable strategy for fabricating efficient NiSe2 based electrocatalysts for the HER. [ABSTRACT FROM AUTHOR]

As a research hotspot, 2D-MoS2 has been regarded as a low-cost substitute for platinum, and has fascinated researchers worldwide. Two crystalline phases of MoS2, i.e. the metallic octahedral 1T phase and semiconducting trigonal prismatic 2H phase, have been extensively analysed. In comparison to 2H-MoS2, the 1T phase exhibits enhanced and unique physicochemical properties. Designing a structure with two-dimensional mixed-phase MoS2, i.e. 1T/2H-MoS2 nanosheets, via phase engineering for effective charge separation and migration has received growing interest in the field of photocatalytic hydrogen generation. In this study, by varying the wt% of ammonium bicarbonate via a facile hydrothermal technique, a series of 1T/2H-MoS2 nanosheets have been fabricated. The presence of the corresponding elements, the electronic environment, phase purity, morphology and phase distinction were confirmed by Raman, XPS, XRD and HRTEM analyses. Additionally, the impedance data and the photocurrent density of the photocatalysts verify the efficient charge separation and transfer phenomenon. In accordance with the electrochemical measurements, the developed mixed-phase MoS2 nanosheets exhibit a six times greater current density than 2H-MoS2. Furthermore, the highest response of photocatalytic hydrogen production is observed with the photocatalyst with 79% 1T phase, which is about 17 times greater than that of pristine 2H-MoS2 due to the enrichment of active sites on both the edges and basal plane as well as the enhanced electronic conductivity due to the 1T phase. This study indicates that with the construction of a heterophase, i.e. 1T/2H-MoS2 nanosheets, the photocatalytic hydrogen evolution capability can be boosted, providing new insights regarding these materials. [ABSTRACT FROM AUTHOR]

The separation efficiency of photogenerated carriers is a key factor affecting photocatalytic hydrogen evolution activity. However, loading precious metals is a cost problem, so in this work cheap carbon rods are introduced into the S-scheme heterojunction of CeO2/MoO2 as electron transfer channels. The construction of the S-scheme heterojunction greatly improves the reduction activity of a single catalyst and effectively inhibits the recombination of photogenerated electrons and holes. The carbon rods at the interface between CeO2 and MoO2 can ensure the rapid transfer of space charge, thus significantly improving the separation efficiency of photogenerated carriers. The synergistic effect of these two promotes the composite catalyst's photocatalytic hydrogen evolution activity. After optimization, the photocatalytic hydrogen evolution amount of 30% CeO2/MoO2–C (6725 μmol g−1) is 18.6 and 2.43 times those of CeO2 (373 μmol g−1) and MoO2–C (2771 μmol g−1), respectively. 30% CeO2/MoO2–C showed good stability in the photocatalytic cycle experiment. Simultaneously, steady-state fluorescence and electrochemical characterization showed that the introduction of carbon rods promoted the spatial transfer of electrons. This work provides a new design idea and method for applying and developing the S-scheme heterojunction. [ABSTRACT FROM AUTHOR]