Electrochemical water splitting is a promising technology for sustainable conversion, storage, and transport of hydrogen energy. Searching for earth-abundant hydrogen/oxygen evolution reaction (HER/OER) electrocatalysts with high activity and durability to replace noble-metal-based catalysts plays paramount importance in the scalable application of water electrolysis. A freestanding electrode architecture is highly attractive as compared to the conventional coated powdery form because of enhanced kinetics and stability. Herein, recent progress in developing transition-metal-based HER/OER electrocatalytic materials is reviewed with selected examples of chalcogenides, phosphides, carbides, nitrides, alloys, phosphates, oxides, hydroxides, and oxyhydroxides. Focusing on self-supported electrodes, the latest advances in their structural design, controllable synthesis, mechanistic understanding, and strategies for performance enhancement are presented. Remaining challenges and future perspectives for the further development of self-supported electrocatalysts are also discussed.

Self-Supported Transition-Metal-Based Electrocatalysts for Hydrogen and Oxygen Evolution

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). Herein, it is described how researchers are working to improve the performance of TMS-based materials by manipulating their 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 are explained in order to delve into the various strategies being used to achieve higher electrocatalytic performance in the HER. Complementary strategies can be used to increase the OER performance of TMS, resulting in bifunctional water-splitting electrocatalysts for both the HER and the OER. Finally, the current challenges and future opportunities of TMS materials in the context of water splitting are summarized. The aim herein is 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.

https://espace.library.uq.edu.au/view/UQ:df1181f/UQdf1181f_OA.pdf

Nanoarchitectonics for Transition-Metal-Sulfide-Based Electrocatalysts for Water Splitting.

Recent years have witnessed an upsurge in the development of non-precious catalysts (NPCs) for alkaline water electrolysis (AWE), especially with the strides made in experimental and computational techniques. In this contribution, the most recent advances in NPCs for AWE were systematically reviewed, emphasizing the application of in situ/operando experimental methods and density functional theory (DFT) calculations in their understanding and development. First, we briefly introduced the fundamentals of the anode and cathode reaction for AWE, i.e., the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER), respectively. Next, the most popular in situ/operando approaches for characterizing AWE catalysts, including hard and soft XAS, ambient-pressure XPS, liquid and identical location TEM, electrochemical mass spectrometry, and Raman spectroscopy were thoroughly summarized. Subsequently, we carefully discussed the principles, computational methods, applications, and combinations of DFT with machine learning for modeling NPCs and predicting the alkaline OER and HER. With the improved understanding of the structure-property-performance relationship of NPCs for AWE, we proceeded to overview their current development, summarising state-of-the-art design strategies to boost their activity. In addition, advances in various extensively investigated NPCs for AWE were evaluated. By conveying these methods, progress, insights, and perspectives, this review will contribute to a better understanding and rational development of non-precious AWE electrocatalysts for hydrogen production.

Non-precious-metal catalysts for alkaline water electrolysis: operando characterizations, theoretical calculations, and recent advances

Transition metal dichalcogenides (TMDs) have attracted considerable attention in recent years due to their unique properties and promising applications in electrochemical energy storage and conversion. However, the limited number of active sites and blocked ion and mass transport severely impair the electrochemical performance of TMDs. Construction of three-dimensional (3D) architectures from TMD nanomaterials has been proven an effective strategy to solve the aforementioned problems due to their large specific surface area and short ion and mass transport distance. Here, we summarize the commonly used routes to build 3D TMD architectures and highlight their applications in electrochemical energy storage and conversion, including batteries, supercapacitors, and electrocatalytic hydrogen evolution. Moreover, the challenges and outlooks in this research area are also discussed.

Three-Dimensional Architectures Constructed from Transition-Metal Dichalcogenide Nanomaterials for Electrochemical Energy Storage and Conversion.

Molybdenum disulfide is naturally inert for alkaline hydrogen evolution catalysis, due to its unfavorable water adsorption and dissociation feature originated from the unsuitable orbital orientation. Herein, we successfully endow molybdenum disulfide with exceptional alkaline hydrogen evolution capability by carbon-induced orbital modulation. The prepared carbon doped molybdenum disulfide displays an unprecedented overpotential of 45 mV at 10 mA cm−2, which is substantially lower than 228 mV of the molybdenum disulfide and also represents the best alkaline hydrogen evolution catalytic activity among the ever-reported molybdenum disulfide catalysts. Fine structural analysis indicates the electronic and coordination structures of molybdenum disulfide have been significantly changed with carbon incorporation. Moreover, theoretical calculation further reveals carbon doping could create empty 2p orbitals perpendicular to the basal plane, enabling energetically favorable water adsorption and dissociation. The concept of orbital modulation could offer a unique approach for the rational design of hydrogen evolution catalysts and beyond. Technologies allowing for sustainable hydrogen production will contribute to the decarbonization of the future energy supply. Here the authors report that carbon induced orbital modulation can facilitate the otherwise inert MoS2 electrocatalyst superior alkaline hydrogen evolution reactivity.

/pdf/tuning-orbital-orientation-endows-molybdenum-disulfide-with-31ppw56hzx.pdf

Tuning orbital orientation endows molybdenum disulfide with exceptional alkaline hydrogen evolution capability.

The hydrogen evolution reaction in an alkaline environment using a non-precious catalyst with much greater efficiency represents a critical challenge in research. Here, a robust and highly active system for hydrogen evolution reaction in alkaline solution is reported by developing MoS2 nanosheet arrays vertically aligned on graphene-mediated 3D Ni networks. The catalytic activity of the 3D MoS2 nanostructures is found to increase by 2 orders of magnitude as compared to the Ni networks without MoS2. The MoS2 nanosheets vertically grow on the surface of graphene by employing tetrakis(diethylaminodithiocarbomato)molybdate(IV) as the molybdenum and sulfur source in a chemical vapor deposition process. The few-layer MoS2 nanosheets on 3D graphene/nickel structure can maximize the exposure of their edge sites at the atomic scale and present a superior catalysis activity for hydrogen production. In addition, the backbone structure facilitates as an excellent electrode for charge transport. This precious-metal-free and highly efficient active system enables prospective opportunities for using alkaline solution in industrial applications.

Three-Dimensional Structures of MoS2 Nanosheets with Ultrahigh Hydrogen Evolution Reaction in Water Reduction

Enhanced synthesis of cadmium sulfide by electrodeposition in dye-sensitized solar cells

The electrical transport properties of (110)-oriented PrBa2(Cu0.8Ga0.2)3O7 (PBCGO) thin films have been investigated. The electrical resistivity, ρ(T), of (110)-oriented PBCGO thin films is 8.91 × 105 Ω-cm at 77 K, about five orders of magnitude higher than that of the (110)-oriented PrBa2Cu3O7 thin films and follows Mott’s T−1/4 law up to room temperature. Our experimental results suggest filling and localization of holes in Cu-O chains of (110)-oriented PBCGO thin films. We observed very less proximity effect on YBa2Cu3O7 (YBCO)/PBCGO multilayers indicating that the (110)-oriented PBCGO thin films may serve as effective insulators in YBCO SIS tunneling Josephson junction.

Electrical transport properties of (110)-oriented PrBa2(Cu0.8Ga0.2)3O7 thin films

We have used electro-deposition, a simple and effective method, to fabricate a NiOx/graphene (PMS) bilayer Shottcky junction. An n-Si/graphene (NMS) Shottcky junction was then deposited on top of the NiOx/graphene bilayer Shottcky junction to form a double Shottcky solar cell. This double Shottcky combination thus contains an n-type Si/grphene (NMS) Shottcky junction and a p-type NiOx/graphene (PMS) Shottcky junction, an overall n-p junction. The thicknesses of the NiOx film are different for different junctions. The NiOx films performed excellently as the p-type substance for the solar cells. SEM, EDX, UV, XRD, and Raman techniques were used to study the physical properties of these solar cell materials and devices. I–V studies were also carried out on these samples. The I–V characteristic curves show that the power conversion efficiency improves when the thickness of NiOx thin film is increased.

Double Shottcky of NiOx/graphene/Si for enhance efficiency solar cells

A non-hydrazine solution followed by spin-coating has been used to produce Cu 2 ZnSnS 4 (CZTS) precursor. After annealed with sulfur or selenium powders in tube furnace at 530°C, Cu 2 ZnSn(S 1−x Se x ) 4 (CZTSSe) thin films were obtained. Both theoretical calculation and experimental results showed that band gap can be tuned from 1.48 to 1.04eV by replacing S with Se in CZTSSe. Solar cell devices were fabricated using nominally CZTS and CZTSe absorbers with thickness around 500 nm. The device based on CZTSSe shows better performance than the CZTS device owing to the larger grain size and better electronic transport.

Experimental and theoretical study on band gap tuning of Cu 2 ZnSn(S 1−x Se x ) 4 absorbers for thin-film solar cells

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