Abstract
The rational synthesis of semiconducting materials with enhanced photoelectrocatalytic efficiency under visible light illumination is a long-standing issue. ZnO has been systematically explored in this field, as it offers the feasibility to grow a wide range of nanocrystal morphology; however, its wide band gap precludes visible light absorption. We report on a novel method for the controlled growth of semiconductor heterostructures and, in particular, core/sheath ZnO/MoS2 nanowire arrays and the evaluation of their photoelectrochemical efficiency in oxygen evolution reaction. ZnO nanowire arrays, with a narrow distribution of nanowire diameters, were grown on FTO substrates by chemical bath deposition. Layers of Mo metal at various thicknesses were sputtered on the nanowire surface, and the Mo layers were sulfurized at low temperature, providing in a controlled way few layers of MoS2, in the range from one to three monolayers. The heterostructures were characterized by electron microscopy (SEM, TEM) and spectroscopy (XPS, Raman, PL). The photoelectrochemical properties of the heterostructures were found to depend on the thickness of the pre-deposited Mo film, exhibiting maximum efficiency for moderate values of Mo film thickness. Long-term stability, in relation to similar heterostructures in the literature, has been observed.
Highlights
The quick depletion of natural resources and moderation of carbon dioxide emissions are currently pursued by developing low-cost alternatives of electricity supply using renewable energy sources, such as solar light
Hybrid core/sheath nanostructures consisting of a metal oxide semiconductor core (ZnO) covered by transition metal di-chalcogenides layers (MX2, M: Mo, W, etc., and X: Se, S2, Te) and other chalcogenides, such as ZnSe [13,14], CdS [15] and CdSe [16,17], have been explored as potential efficient PEC anode materials stimulated by visible light benefiting from a more effective separation of photo-generated charges
Well-aligned ZnO/MoS2 core/sheath heterostructures have been grown on FTO/glass substrate by a sequence of synthesis methods, comprising chemical bath deposition of the ZnO nanowire arrays and Mo sputtering followed by low-temperature sulfurization
Summary
The quick depletion of natural resources and moderation of carbon dioxide emissions are currently pursued by developing low-cost alternatives of electricity supply using renewable energy sources, such as solar light. Hybrid core/sheath nanostructures consisting of a metal oxide semiconductor core (ZnO) covered by transition metal di-chalcogenides layers (MX2, M: Mo, W, etc., and X: Se, S2, Te) and other chalcogenides, such as ZnSe [13,14], CdS [15] and CdSe [16,17], have been explored as potential efficient PEC anode materials stimulated by visible light benefiting from a more effective separation of photo-generated charges. ZnO nanowire (NW) arrays prepared on FTO/glass substrates by chemical bath deposition stand as the scaffolds onto which the few-layer MoS2 thin films are grown. MoS2 sheath is prepared by low-temperature sulfurization of pre-deposited ultrathin Mo films on the ZnO surface. Controlling Mo film deposition and sulfurization conditions, heterostructures with varying thickness of MoS2 layers down to the monolayer, are prepared. For the formation of the MoS2 layer, the Mo-sputtered ZnO samples were placed into a triple temperature zone furnace to sulfurize the Mo films by exposing them to sulfur vapors. The electrochemical characterization and the evaluation of the heterostructures were observed by performing linear sweep voltammetry (LSV) and cyclic voltammetry (CV) with a scan rate of 50 mV s−1
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