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Splitting water to produce hydrogen requires the development of non-noble-metal catalysts that are able to make this reaction feasible and energy efficient. Herein, we show that cobalt pentlandite (Co9S8) nanoparticles can serve as an electrochemically active, noble-metal-free material toward hydrogen evolution reaction, and they work stably in neutral solution (pH 7) but not in acidic (pH 0) and basic (pH 14) media. We, therefore, further present a carbon-armoring strategy to increase the durability and activity of Co9S8over a wider pH range. In particular, carbon-armored Co9S8nanoparticles (Co9S8@C) are prepared by direct thermal treatment of a mixture of cobalt nitrate and trithiocyanuric acid at 700 °C in N2atmosphere. Trithiocyanuric acid functions as both sulfur and carbon sources in the reaction system. The resulting Co9S8@C material operates well with high activity over a broad pH range, from pH 0 to 14, and gives nearly 100% Faradaic yield during hydrogen evolution reaction under acidic (pH 0), neutral (pH 7), and basic (pH 14) media. To the best of our knowledge, this is the first time that a transition-metal chalcogenide material is shown to have all-pH efficient and durable electrocatalytic activity. Identifying Co9S8as the catalytically active phase and developing carbon-armoring as the improvement strategy are anticipated to give a fresh impetus to rational design of high-performance noble-metal-free water splitting catalysts.

A series of Bi2O3/BaTiO3composite photocatalysts with different mass ratios of Bi2O3vs BaTiO3were prepared by an impregnating-annealing method. X-ray diffraction (XRD), high-resolution transmission electron microscopic (HRTEM), and UV–vis diffuse reflection spectroscopy (DRS) confirmed that Bi2O3and BaTiO3coexisted in the composites. The results of surface photovoltage (SPV) experiments showed enhancements of photovoltaic response in composites, which indicated a higher separation efficiency of photoinduced charges due to the establishment of an efficient interfacial electric field between Bi2O3and BaTiO3in the composites. The consistency of phtocatalytic activity and photovoltaic response intensity of photocatalysts showed that the efficiency interfacial electric field between Bi2O3and BaTiO3played an important role in improving the degradation efficiency of Rhodamine B (RhB). The 60%-Bi2O3/BaTiO3sample with the best activity was found by optimizing the mass ratios of Bi2O3vs. BaTiO3. On the basis of the work function (WF) measurements, a reasonable energy band diagram was proposed for BaTiO3/Bi2O3composite. It would be helpful in designing and constructing high efficiency heterogeneous semiconductor photocatalyst.

Bi2WO6/ZnWO4composite photocatalysts have been successfully synthesized by a facile hydrothermal process. The catalysts were characterized by powder X-ray diffraction (XRD), transmission electron microcopy (TEM), and UV–vis diffuse reflectance spectrum (DRS). The results show that Bi2WO6nanoparticles grow on the primary ZnWO4nanorods. The Bi2WO6/ZnWO4composites have better UV light photocatalytic activities compared to single ZnWO4nanorods. Furthermore, the photoinduced charge transfer properties of Bi2WO6/ZnWO4composites were investigated by means of transient photovoltage (TPV) technique in detail. The interconnected interface of Bi2WO6/ZnWO4composites led to the low recombination ratios of photoinduced electron–hole pairs and enhanced photocatalytic activities.