conduction and/or optical properties play a critical role, like in microelectronics, [17] sensing, [18,19] biosensing. [20] The possibility of exploring nanoarchi tectures for MOx (such as 0D, 1D, 2D, 3D) structures and extended networks [21,22] ) with electronic features different from their bulk counterpart [23,24] enabled their exploitation in a variety of new fields, in which networking in 3D is critical for a series of physical/chemical processes like light absorption and confinement, [25] sur face reactivity, [18,26] charge exchange/col lection. [27,28] For this reason, the possibility of extending MOx geometry from standard thin films to 3D architectures (including nanowires, nanorods, nanowalls, nano networks, and hierarchical structures), induced a renaissance for these materials, which are considered good candidates for successful application in the real life.The synthesis of composite MOx archi tectures experienced a strong and fast development in the last 15 years, now being a mature branch of Science, able to offer a diversified series of morphologies, shapes, and crystal line assemblies. [22,29] Scheme 1 illustrates the most commonly produced 0D to 2D structures (nanoparticles (NPs), nanowires (NWs), nanotubes (NTs), nanorods (NRs), nanosheets (NSs)) reported in the literature as building blocks to fabricated hier archically assembled geometries and/or nano/microarrays. In their work, [30] Umar and Hahn offer a comprehensive summary of MOx nanostructures, covering the synthesis and application, from both an experimental and theoretical point of view. Chem ical and physical preparation routes are described, including vapor transport and condensation techniques, hydrothermal and electrochemical synthesis, vacuum and nonvacuumbased techniques.While in the past focus was given on the development of new architectures and shapes through a series of physical and chemical routes, [21,22,29,31] now the research is much more focused on the investigation of the functional properties these new structures can offer, such functionalities being tailored for specific enduser applications.The research of new materials for renewable energy sources is one of the fields most benefitting of the outstanding proper ties of MOx. MOx find application in, for instance, solar cells, [32] electrochemical water splitting (WS), photoelectrochemical WS, photocatalysis. [33] In most of the cases, MOx are chosen for the possibility of having 3D networks with maximized specific sur face area, tunable bandgap allowing light absorption in a broad Metal oxide (MOx) semiconducting nanostructures hold the potential for playing a critical role in the development of a new platform for renewable energies, including energy conversion and storage through photovoltaic effect, solar fuels, and water splitting. Earth-abundant MOx nanostructures can be prepared through simple and scalable routes and integrated in operating devices, which enable exploitation of their outstanding optical, electronic, and catalytic properties. In this review, the ...

The design of the earth-abundant, nonprecious, efficient, and stable electrocatalysts for efficient hydrogen evolution reaction (HER) in alkaline media is a hot research topic in the field of renewable energies. A heterostructured system composed of MoS x deposited on NiO nanostructures (MoS x @NiO) as a robust catalyst for water splitting is proposed here. NiO nanosponges are applied as cocatalyst for MoS 2 in alkaline media. Both NiO and MoS 2 @NiO composites are prepared by a hydrothermal method. The NiO nanostructures exhibit sponge-like morphology and are completely covered by the sheet-like MoS 2 . The NiO and MoS 2 exhibit cubic and hexagonal phases, respectively. In the MoS x @NiO composite, the HER experiment in 1 m KOH electrolyte results in a low overpotential (406 mV) to produce 10 mA cm −2 current density. The Tafel slope for that case is 43 mV per decade, which is the lowest ever achieved for MoS 2 -based electrocatalyst in alkaline media. The catalyst is highly stable for at least 13 h, with no decrease in the current density. This simple, cost-effective, and environmentally friendly methodology can pave the way for exploitation of MoS x @NiO composite catalysts not only for water splitting, but also for other applications such as lithium ion batteries, and fuel cells.

Hydrogen production as alternative energy source is still a challenge due to the lack of efficient and inexpensive catalysts, alternative to platinum. Thus, stable, earth abundant, and inexpensive catalysts are of prime need for hydrogen production via hydrogen evolution reaction (HER). Herein, we present an efficient and stable electrocatalyst composed of earth abundant TiO2 nanorods decorated with molybdenum disulfide thin nanosheets, a few nanometers thick. We grew rutile TiO2 nanorods via the hydrothermal method on conducting glass substrate, and then we nucleated the molybdenum disulfide nanosheets as the top layer. This composite possesses excellent hydrogen evolution activity in both acidic and alkaline media at considerably low overpotentials (350 mV and 700 mV in acidic and alkaline media, respectively) and small Tafel slopes (48 and 60 mV/dec in acidic and alkaline conditions, respectively), which are better than several transition metal dichalcogenides, such as pure molybdenum disulfide and cobalt diselenide. A good stability in acidic and alkaline media is reported here for the new MoS2/TiO2 electrocatalyst. These results demonstrate the potential of composite electrocatalysts for HER based on earth abundant, cost-effective, and environmentally friendly materials, which can also be of interest for a broader range of scalable applications in renewable energies, such as lithium sulfur batteries, solar cells, and fuel cells.