Nickel Hydroxide Decorated Hydrogenated Zinc Oxide Nanorod Arrays with Enhanced Photoelectrochemical Performance

Synthesis of 2D layered transition metal (Ni, Co) hydroxides via edge-on condensation

Layered transition metal hydroxides (LTMHs) with transition metal centers sandwiched between layers of coordinating hydroxide anions have attracted considerable interest for their potential in developing clean energy sources and storage technologies. However, two-dimensional (2D) LTMHs remain largely understudied in terms of physical properties and applications in electronic devices. Here, for the first time we report > 20 μm α-Ni(OH)2 2D crystals, synthesized from hydrothermal reaction. And an edge-on condensation mechanism assisted with the crystal field geometry is proposed to understand the 2D intra-planar growth of the crystals, which is also testified through series of systematic comparative studies. We also report the successful synthesis of 2D Co(OH)2 crystals (> 40 μm) with more irregular shape due to the slightly distorted octahedral geometry of the crystal field. Moreover, the detailed structural characterization of synthesized α-Ni(OH)2 are performed. The optical band gap energy is extrapolated as 2.54 eV from optical absorption measurements and the electronic bandgap is measured as 2.52 eV from reflected electrons energy loss spectroscopy (REELS). We further demonstrate its potential as a wide bandgap (WBG) semiconductor for high voltage operation in 2D electronics with a high breakdown strength, 4.77 MV/cm with 4.9 nm thickness. The successful realization of the 2D LTMHs opens the door for future exploration of more fundamental physical properties and device applications.

Current progress in developing metal oxide nanoarrays-based photoanodes for photoelectrochemical water splitting

Solar energy driven photoelectrochemical (PEC) water splitting is a clean and powerful approach for renewable hydrogen production. The design and construction of metal oxide based nanoarray photoanodes is one of the promising strategies to make the continuous breakthroughs in solar to hydrogen conversion efficiency of PEC cells owing to their owned several advantages including enhanced reactive surface at the electrode/electrolyte interface, improved light absorption capability, increased charge separation efficiency and direct electron transport pathways. In this Review, we first introduce the structure, work principle and their relevant efficiency calculations of a PEC cell. We then give a summary of the state-of the-art research in the preparation strategies and growth mechanism for the metal oxide based nanoarrays, and some details about the performances of metal oxide based nanoarray photoanodes for PEC water splitting. Finally, we discuss key aspects which should be addressed in continued work on realizing high-efficiency metal oxide based nanoarray photoanodes for PEC solar water splitting systems.

The chemically reduced CuO–Co3O4 composite as a highly efficient electrocatalyst for oxygen evolution reaction in alkaline media

The fabrication of efficient, alkaline-stable and nonprecious electrocatalysts for the oxygen evolution reaction is highly needed; however, it is a challenging task.

Highly Enhanced Visible-Light-Driven Photoelectrochemical Performance of ZnO-Modified In2S3 Nanosheet Arrays by Atomic Layer Deposition

Photoanodes based on In₂S₃/ZnO heterojunction nanosheet arrays (NSAs) have been fabricated by atomic layer deposition of ZnO over In₂S₃ NSAs, which were in situ grown on fluorine-doped tin oxide glasses via a facile solvothermal process. The as-prepared photoanodes show dramatically enhanced performance for photoelectrochemical (PEC) water splitting, compared to single semiconductor counterparts. The optical and PEC properties of In₂S₃/ZnO NSAs have been optimized by modulating the thickness of the ZnO overlayer. After pairing with ZnO, the NSAs exhibit a broadened absorption range and an increased light absorptance over a wide wavelength region of 250-850 nm. The optimized sample of In₂S₃/ZnO-50 NSAs shows a photocurrent density of 1.642 mA cm^-2 (1.5 V vs. RHE) and an incident photon-to-current efficiency of 27.64% at 380 nm (1.23 V vs. RHE), which are 70 and 116 times higher than those of the pristine In₂S₃ NSAs, respectively. A detailed energy band edge analysis reveals the type-II band alignment of the In₂S₃/ZnO heterojunction, which enables efficient separation and collection of photogenerated carriers, especially with the assistance of positive bias potential, and then results in the significantly increased PEC activity.

Compound Homojunction:Heterojunction Reduces Bulk and Interface Recombination in ZnO Photoanodes for Water Splitting

Photoelectrochemical water splitting is far more efficient thanks to the novel ZnOSe/ZnO/BZO thin-film photoanodes fabricated in this work. A novel structure is developed for simultaneously suppressing the charge recombination in the ZnO bulk and at the semiconductor-electrolyte interface. This structure achieves a five-fold enhancement in water-splitting performance, compared to that of pristine ZnO photoanodes, when illuminated using visible light.

Nickel hydroxides and related materials: a review of their structures, synthesis and properties

This review article summarizes the last few decades of research on nickel hydroxide, an important material in physics and chemistry, that has many applications in engineering including, significantly, batteries. First, the structures of the two known polymorphs, denoted as α-Ni(OH)₂ and β-Ni(OH)₂, are described. The various types of disorder, which are frequently present in nickel hydroxide materials, are discussed including hydration, stacking fault disorder, mechanical stresses and the incorporation of ionic impurities. Several related materials are discussed, including intercalated α-derivatives and basic nickel salts. Next, a number of methods to prepare, or synthesize, nickel hydroxides are summarized, including chemical precipitation, electrochemical precipitation, sol-gel synthesis, chemical ageing, hydrothermal and solvothermal synthesis, electrochemical oxidation, microwave-assisted synthesis, and sonochemical methods. Finally, the known physical properties of the nickel hydroxides are reviewed, including their magnetic, vibrational, optical, electrical and mechanical properties. The last section in this paper is intended to serve as a summary of both the potentially useful properties of these materials and the methods for the identification and characterization of 'unknown' nickel hydroxide-based samples.