Heterogenous electrocatalysts based on transition metal sulfides (TMS) are being actively explored in renewable energy research because nanostructured forms support high intrinsic activities for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In this review article, the authors describe how researchers are working to improve the This article is protected by copyright. All rights reserved. 2 performance of TMS-based materials by manipulating its internal and external nanoarchitectures. A general introduction to the water splitting reaction is initially provided to explain the most important parameters in accessing the catalytic performance of nanomaterials catalysts. Later, the general synthetic methods used to prepare TMS-based materials is explained in order to delve into the various strategies being used to achieve higher electrocatalytic performance in HER. Complementary strategies can be used to increase the OER performance of TMS, resulting in bifunctional water-splitting electrocatalysts for both HER and OER. Finally, the current challenges and future opportunities of TMS materials in the context of water splitting are summarized. The authors aim to provide insights gathered in the process of studying TMS, and describe valuable guidelines for engineering other kinds of nanomaterial catalysts for energy conversion and storage technologies.

Triethoxy(alkyl)silanes containing 12—18 carbon atoms in the alkyl groups were hydrolyzed and polycondensed to form ordered structured materials. The XRD pattern of each condensed product showed sharp diffraction peaks with higher orders. The basal spacings approximately corresponded to twice the extended molecular length of the alkyl groups, and increased linearly as a function of the alkyl chain length. The SEM images of the products exhibited a platy morphology, and the 29Si CP/MAS NMR spectra revealed the formation of siloxane bonds with various silicon sites from T1 to T3 environments. All of these results indicated the formation of highly-organized inorganic–organic layered materials.

Two-dimensional monoclinic WO(3) nanoplates with high specific surface areas are synthesized through a novel conversion process using tungstate-based inorganic-organic hybrid micro/nanobelts as precursors. The process developed involves a topochemical transformation of tungstate-based inorganic-organic hybrid belts into WO(3) nanoplates via an intermediate product of H(2)WO(4) nanoplates, utilizing the similarity of the W-O octahedral layers in both H(2)WO(4) and WO(3). The as-obtained WO(3) nanoplates show a single-crystalline nanostructure with the smallest side along the [001] direction. The WO(3) nanoplates are 200-500 nm x 200-500 nm x 10-30 nm in size, and their specific surface areas are up to 180 m(2) g(-1). Photocatalytic measurements of visible-light-driven oxidation of water for O(2) generation in the presence of Ag(+) ions indicate that the activity of the as-obtained WO(3) nanoplates is one order of magnitude higher than that of commercially available WO(3) powders.

Highly efficient earth‐abundant electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are of great importance for renewable energy conversion systems. Herein, hollow porous heterometallic phosphide nanocubes are developed as a highly active and robust catalyst for electrochemical water splitting via one‐step phosphidation of a NiCoFe Prussian blue analogue. Through modulation of the composition of metals in the precursors, the optimal NiCoFeP exhibiting increased electrical conductivity and abundant electrochemically active sites, leading to high electrocatalytic activities and outstanding kinetics for both HER and OER, is successfully obtained. NiCoFeP shows low overpotentials of 273 mV for OER and 131 mV for HER at a current density of 10 mA cm−2 and quite low Tafel slopes of 35 mV dec−1 for OER and 56 mV dec−1 for HER.

Metal−organic frameworks (MOFs) can serve as high-surface-area templates to generate hierarchically ordered nanoporous carbon electrodes for high-performance supercapacitor devices. Here we describe a simple chemical approach to synthesize dense three-dimensional (3D) arrays of core−shell ZnO@ZIF-8 and Co(CO 3 ) 0.5 (OH)•0.11H 2 O@ZIF-67 nanowires on a conductive carbon cloth. Annealing the core−shell structures at high temperatures converted the MOF shell into a composite of nanoporous carbon (NC) mixed with conductive metal oxides. The conformal nature of the MOF-coating process generates a NC film with continuous conductive paths from the outer surfaces of the nanowires down to the flexible carbon electrode. Carbonization of ZIF-67 transforms the material into conductive sp 2 type carbon mixed with Co 3 O 4 nanostructures. Because Co 3 O 4 is a faradic metal oxide with a high theoretical capacitance, these Co 3 O 4 /NC hybrid heterostructure arrays are a promising candidate material for use in an electrochemical supercapacitor device. The Co 3 O 4 /NC hybrid electrodes had good performance and exhibited a high areal capacitance of 1.22 F• cm −2 at 0.5 mA•cm −2 . Conformal deposition of MOFs via the chemical vapor method offers a promising new platform to design conductive, ultrahigh surface area electrodes that preserve the 3D morphology for applications in supercapacitors and electrocatalysis.