Nanoporous metal enhanced catalytic activities of amorphous molybdenum sulfide for high-efficiency hydrogen production

NiFe-layered double hydroxide/CoP2@MnP heterostructures of clustered flower nanowires on MXene-modified nickel foam for overall water-splitting

Exploiting efficient and economical electrocatalysts is indispensable to promoting the sluggish kinetics of overall water-splitting. Herein, we designed a phosphate reaction and two-step hydrothermal method to construct a 3D porous clustered flower-like heterogeneous structure of NiFe-layered double hydroxide (NiFe) and CoP2@MnP (CMP) grown in-situ on MXene-modified nickel foam (NF) substrate (denoted as NiFe/CMP/MX), with favorable kinetics. Density functional theory calculations (DFT) demonstrate that the self-driven transfer of heterojunction charges causes electron redistribution of the catalyst, and optimizes the electron transfer rate of the active site and the d-band center near the Fermi level, thereby reducing the adsorption energy of H and O reaction intermediates (H*, OH*, OOH*). As expected, the combination of CMP and NiFe with naturally conductive MXene forms a strong chemical and electron synergistic effect, which enables the synthesized NiFe/CMP/MX heterogeneous structure exhibits good activity for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) with a low overpotential of 200 mV and 126 mV at 10 mA cm-2, respectively. Furthermore, the overpotential of 1.58 V is enough to drive a current density of 10 mA cm-2 in a two-electrode configuration, which is better than noble metals (RuO2(+)//Pt/C(-)) (1.68 V).

Application of Oxygen-Group-Based Amorphous Nanomaterials in Electrocatalytic Water Splitting

Environmentally friendly energy sources (e.g., hydrogen) require an urgent development targeting to address the problem of energy scarcity. Electrocatalytic water splitting is being explored as a convenient catalytic reaction in this context, and promising amorphous nanomaterials (ANMs) are receiving increasing attention due to their excellent catalytic properties.Oxygen group-based amorphous nanomaterials (O-ANMs) are an important component of the broad family of ANMs due to their unique amorphous structure, large number of defects, and abundant randomly oriented bonds, O-ANMs induce the generation of a larger number of active sites, which favors a better catalytic activity. Meanwhile, amorphous materials can disrupt the inherent features of conventional crystalline materials regarding electron transfer paths, resulting in higher flexibility. O-ANMs mainly include VIA elements such as oxygen, sulfur, selenium, tellurium, and other transition metals, most of which are reported to be free of noble metals and have comparable performance to commercial catalysts Pt/C or IrO2 and RuO2 in electrocatalysis. This review covers the features and reaction mechanism of O-ANMs, the synthesis strategies to prepare O-ANMs, as well as the application of O-ANMs in electrocatalytic water splitting. Last, the challenges and prospective remarks for future development in O-ANMs for electrocatalytic water splitting are concluded.

Facile Synthesis of Nitrogen-Rich Porous Carbon/NiMn Hybrids Using Efficient Water-Splitting Reaction

Proper design of multifunctional electrocatalyst that are abundantly available on earth, cost-effective and possess excellent activity and electrochemical stability towards oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are required for effective hydrogen generation from water-splitting reaction. In this context, the work herein reports the fabrication of nitrogen-rich porous carbon (NRPC) along with the inclusion of non-noble metal-based catalyst, adopting a simple and scalable methodology. NRPC containing nitrogen and oxygen atoms were synthesized from polybenzoxazine (Pbz) source, and non-noble metal(s) are inserted into the porous carbon surface using hydrothermal process. The structure formation and electrocatalytic activity of neat NRPC and monometallic and bimetallic inclusions (NRPC/Mn, NRPC/Ni and NRPC/NiMn) were analyzed using XRD, Raman, XPS, BET, SEM, TEM and electrochemical measurements. The formation of hierarchical 3D flower-like morphology for NRPC/NiMn was observed in SEM and TEM analyses. Especially, NRPC/NiMn proves to be an efficient electrocatalyst providing an overpotential of 370 mV towards OER and an overpotential of 136 mV towards HER. Moreover, it also shows a lowest Tafel slope of 64 mV dec^-1 and exhibits excellent electrochemical stability up to 20 h. The synergistic effect produced by NRPC and bimetallic compounds increases the number of active sites at the electrode/electrolyte interface and thus speeds up the OER process.

Enhancing the catalytic OER performance of MoS2via Fe and Co doping

Enhancing the sluggish kinetics of the electrochemical oxygen evolution reaction (OER) is crucial for many clean-energy production technologies. Although much progress has been made in recent years, developing active, stable, and cost-effective OER electrocatalysts is still challenging. The layered MoS₂, based on Earth-abundant elements, is widely explored as a promising hydrogen evolution electrocatalyst but exhibits poor OER activity. Here, we report a facile strategy to improve the sluggish OER of MoS₂ through co-doping MoS₂ nanosheets with Fe and Co atoms. The synergistic effect obtained by adjusting the Co/Fe ratio in the Fe-Co doped MoS₂ induces electronic and structural modifications and a richer active surface area morphology resulting in a relatively low OER overpotential of 380 mV (at 10 mA cm^-2). The electronic modulation upon doping was further supported by DFT calculations that show favorable interaction with the OER intermediate species, thus reducing the energy barrier for the OER. This work paves the way for future strategies for tailoring the electronic properties of transition-metal dichalcogenides (TMDCs) to activate the structure for the sluggish OER with the assistance of non-noble-metal materials.

Surface engineering strategies for MoS2 towards electrochemical hydrogen evolution

Water splitting driven by renewable energy sources is an environmentally friendly and sustainable way to produce hydrogen as an ideal energy source in the future. Electrocatalysts can promote the water splitting performance at the both ends. Therefore, the development of cost-effective, high-performance electrocatalysis is a key factor in promoting water decomposition and renewable energy conversion. Among candidates, layered molybdenum disulfide (MoS 2 ) is considered as a most promising electrocatalyst to replace Pt for hydrogen evolution reaction (HER). Surface atomic engineering and interface engineering can induce new physicochemical properties for MoS 2 to greatly enhance HER activity. In this report, we summarize the latest improvement strategies and research progress to improve the catalytic activity of MoS 2 -based material catalysts through the surface and interface atomic and molecular engineering, thus effectively improving HER process. In addition, some unsolved problems in the large-scale application of modified MoS 2 catalyst are also discussed.

Local electrochemical activity of transition metal dichalcogenides and their heterojunctions on 3D-printed nanocarbon surfaces

Transition metal dichalcogenides (TMDs) have shown to be promising catalysts for the electrochemical hydrogen evolution reaction (HER) and 3D-printing enables fast prototyping and manufacturing of water splitting devices. However, the merging of TMDs with complex 3D-printed surfaces and nanostructures as well as their localized characterization remains challenging. In this work, electrodeposition of MoS2 and WS2 and their heterojunctions are used to modify thermally activated 3D-printed nanocarbon structures. Their electrochemical performance for the HER is investigated macroscopically by linear sweep voltammetry and microscopically by scanning electrochemical microscopy. This study demonstrates different local HER active sites of MoS2 and WS2 within the 3D-printed nanocarbon structure that are not solely located at the outer surface, but also in the interior up to ∼150 μm for MoS2 and ∼300 μm for WS2.

Regulating Crystal Structure and Atomic Arrangement in Single-Component Metal Oxides through Electrochemical Conversion for Efficient Overall Water Splitting

Single-component transition-metal oxide (TMO: FeO_x, NiO_x, or CoO_x) nanosheets grown on nickel foam (NF) were electrochemically optimized with Li ion (Na ion)-induced conversion reaction for bifunctional electrocatalysis. The optimum FeO_x/NF-Li electrocatalyst exhibits low overpotentials of 239 mV for hydrogen evolution reaction and 276 mV for oxygen evolution reaction at a current density of 100 mA cm^-2. A two-electrode water splitting cell using FeO_x/NF-Li as both anode and cathode requires only 1.60 V to achieve a current density of 10 mA cm^-2. The impressive water splitting performance of the FeO_x/NF-Li electrode is revealed to be attributed to Li-induced electrochemical conversion, which alters the crystal structure, creating more active sites for electrocatalytic reactions, as well as introduces O vacancies increasing the electron density and the intrinsic conductivity. More importantly, the atomic arrangement is regulated from tetrahedral Fe(Td) to octahedral Fe(Oh) coordination, which acts as catalytically active sites with reduced Gibbs free energy for the rate-determining steps. This electrochemical conversion reaction can be extended to other TMOs (i.e., NiO_x/NF and CoO_x/NF) for promoted electrocatalytic water splitting performances. This study provides an in-depth understanding on the nature of atomic and electronic structure evolution to promote the electrocatalytic activity.

Earlier diagnoses of acute leukemia by a sandwich type of electrochemical aptasensor based on copper sulfide-graphene composite

Due to high affinity and specificity of aptamers, they are widely considered for construction of aptasensor to specific recognizing of analytes in biological complex matrix. So, in this work we design a high selective and sensitive aptasensor for leukemia cancer cells (CCRF-CEM) via superior catalytic effect of copper sulfide-graphene (CuS-GR) nanocomposite as label and Au-GR nanocomposite as sensing platform. The CuS-GR nano-composite (label component) is CuS nanoparticles that wrapping on graphene sheets. Its catalytic activity (CuS-GR) increases the current of sensor in parallel with adding of CCRF-CEM and provide sensitive detection of analytes. The detailed of signal amplification and effect on the aptasensor performance completely discussed. This sensor has a linear range of 50-1 × 10⁶ cell mL^-1, with a limit of detection of 18 cell mL^-1. Also, the developed aptasensor has a significance specificity, high sensitivity and accuracy. It was used for the identification of CCRF-CEM cells in blood samples.

Defect Engineering of Molybdenum-Based Materials for Electrocatalysis

Molybdenum-based electrocatalysts have been widely applied in electrochemical energy conversion reactions. The essential roles of defects, including doping, vacancies, grain boundaries, and dislocations in improving various electrocatalytic performances have been reported. This review describes the latest development of defect engineering in molybdenum-based materials for hydrogen evolution, oxygen reduction, oxygen evolution, and nitrogen reduction reactions. The types of defects, preparation methods, characterization techniques, and applications of molybdenum-based defect materials are elucidated. Finally, challenges and future research directions for these types of materials are also discussed.

Intermetallic Cu5Zr Clusters Anchored on Hierarchical Nanoporous Copper as Efficient Catalysts for Hydrogen Evolution Reaction

Designing highly active and robust platinum-free electrocatalysts for hydrogen evolution reaction is vital for large-scale and efficient production of hydrogen through electrochemical water splitting. Here, we report nonprecious intermetallic Cu₅Zr clusters that are in situ anchored on hierarchical nanoporous copper (NP Cu/Cu₅Zr) for efficient hydrogen evolution in alkaline medium. By virtue of hydroxygenated zirconium atoms activating their nearby Cu-Cu bridge sites with appropriate hydrogen-binding energy, the Cu₅Zr clusters have a high electrocatalytic activity toward the hydrogen evolution reaction. Associated with unique architecture featured with steady and bicontinuous nanoporous copper skeleton that facilitates electron transfer and electrolyte accessibility, the self-supported monolithic NP Cu/Cu₅Zr electrodes boost violent hydrogen gas release, realizing ultrahigh current density of 500 mA cm⁻² at a low potential of -280 mV versus reversible hydrogen electrode, with exceptional stability in 1 M KOH solution. The electrochemical properties outperform those of state-of-the-art nonprecious metal electrocatalysts and make them promising candidates as electrodes in water splitting devices.

Recycled Utilization of a Nanoporous Au Electrode for Reduced Fabrication Cost of Perovskite Solar Cells

Perovskite solar cells (PSCs) using metal electrodes have been regarded as promising candidates for next-generation photovoltaic devices because of their high efficiency, low fabrication temperature, and low cost potential. However, the complicated and rigorous thermal deposition process of metal contact electrodes remains a challenging issue for reducing the energy pay-back period in commercial PSCs, as the ubiquitous one-time use of a contact electrode wastes limited resources and pollutes the environment. Here, a nanoporous Au film electrode fabricated by a simple dry transfer process is introduced to replace the thermally evaporated Au electrode in PSCs. A high power conversion efficiency (PCE) of 19.0% is demonstrated in PSCs with the nanoporous Au film electrode. Moreover, the electrode is recycled more than 12 times to realize a further reduced fabrication cost of PSCs and noble metal materials consumption and to prevent environmental pollution. When the nanoporous Au electrode is applied to flexible PSCs, a PCE of 17.3% and superior bending durability of ≈98.5% after 1000 cycles of harsh bending tests are achieved. The nanoscale pores and the capability of the porous structure to impede crack generation and propagation enable the nanoporous Au electrode to be recycled and result in excellent bending durability.

Improved charge injection of edge aligned MoS2/MoO2 hybrid nanosheets for highly robust and efficient electrocatalysis of H2 production

Molybdenum disulfide (MoS2) can be an efficient electro-catalyst for the hydrogen evolution reaction (HER) as an alternative to precious metals, but significant efforts are still needed to further improve its efficiency. Among various approaches, the formation of edge aligned MoS2 on an electrically conductive support is highly promising for cost-effective H2 production. Nevertheless, catalysis is highly impeded by the poor charge transport between the electrode materials and also between the multilayers of MoS2. This research presents a strategy to improve the HER catalysis by binding layers of metallic molybdenum dioxide (MoO2) and MoS2 to form hybrid MoS2/MoO2 nanosheets (attached and cross-linked to each other). Taking advantage of the hybrid structure and the mechanical strength of the carbon cloth, a catalyst with outstanding catalytic performance in the HER is demonstrated. This work shows not only a strategy to efficiently improve the electrochemical process, but also the preparation of a highly efficient catalyst for constant and robust H2 production.

An in situ grown lanthanum sulfide/molybdenum sulfide hybrid catalyst for electrochemical hydrogen evolution

An La₂S₃–MoS₂ catalyst with expanded interlayer spacing and engineered nano-interfaces was facilely synthesized, demonstrating enhanced catalytic activity for electrochemical hydrogen evolution.

Amorphous Catalysts and Electrochemical Water Splitting: An Untold Story of Harmony

In the near future, sustainable energy conversion and storage will largely depend on the electrochemical splitting of water into hydrogen and oxygen. Perceiving this, countless research works focussing on the fundamentals of electrocatalysis of water splitting and on performance improvements are being reported everyday around the globe. Electrocatalysts of high activity, selectivity, and stability are anticipated as they directly determine energy- and cost efficiency of water electrolyzers. Amorphous electrocatalysts with several advantages over crystalline counterparts are found to perform better in electrocatalytic water splitting. There are plenty of studies witnessing performance enhancements in electrocatalysis of water splitting while employing amorphous materials as catalysts. The harmony between the flexibility of amorphous electrocatalysts and electrocatalysis of water splitting (both the oxygen evolution reaction [OER] and the hydrogen evolution reaction [HER]) is one of the untold and unsummarized stories in the field of electrocatalytic water splitting. This Review is devoted to comprehensively discussing the upsurge of amorphous electrocatalysts in electrochemical water splitting. In addition to that, the basics of electrocatalysis of water splitting are also elaborately introduced and the characteristics of a good electrocatalyst for OER and HER are discussed.

Plasmonic-induced overgrowth of amorphous molybdenum sulfide on nanoporous gold: An ambient synthesis method of hybrid nanoparticles with enhanced electrocatalytic activity

Hybrid materials of earth abundant transition metal dichalcogenides and noble metal nanoparticles, such as molybdenum sulfide (MoS_x) and gold nanoparticles, exhibit synergistic effects that can enhance electrocatalytic reactions. However, most current hybrid MoS_x-gold synthesis requires an energy intensive heat source of >500 °C or chemical plating to achieve deposition of MoS_x on the gold surface. Herein, we demonstrate the direct overgrowth of MoS_x over colloidal nanoporous gold (NPG), conducted feasibly under ambient conditions, to form hybrid particles with enhanced electrocatalytic performance toward hydrogen evolution reaction. Our strategy exploits the localized surface plasmon resonance-mediated photothermal heating of NPG to achieve >230 °C surface temperature, which induces the decomposition of the (NH₄)₂MoS₄ precursor and direct overgrowth of MoS_x over NPG. By tuning the concentration ratio between the precursor and NPG, the amount of MoS_x particles deposited can be systematically controlled from 0.5% to 2% of the Mo/(Au + Mo) ratio. Importantly, we find that the hybrid particles exhibit higher bridging and an apical S to terminal S atomic ratio than pure molybdenum sulfide, which gives rise to their enhanced electrocatalytic performance for hydrogen evolution reaction. We demonstrate that hybrid MoS_x-NPG exhibits >30 mV lower onset potential and a 1.7-fold lower Tafel slope as compared to pure MoS_x. Our methodology provides an energy- and cost-efficient synthesis pathway, which can be extended to the synthesis of various functional hybrid structures with unique properties for catalysis and sensing applications.

A General Method for the Synthesis of Hybrid Nanostructures Using MoSe2 Nanosheet-Assembled Nanospheres as Templates

The layered transition metal dichalcogenides (TMDs) and transition metal phosphides are low-cost, earth-abundant, and robust electrocatalysts for hydrogen evolution reaction (HER). Integrating them into hybrid nanostructures is potentially promising to further boost the catalytic activity toward HER based on their synergistic effects. Herein, we report a general method for the synthesis of a series of MoSe₂-based hybrid nanostructures, including MoSe₂-Ni₂P, MoSe₂-Co₂P, MoSe₂-Ni, MoSe₂-Co, and MoSe₂-NiS, by postgrowth of Ni₂P, Co₂P, Ni, Co, and NiS nanostructures on the presynthesized MoSe₂ nanosheet-assembled nanospheres, respectively, via a colloidal synthesis method. As a proof-of-concept application, the as-synthesized hybrid nanostructures are used as electrocatalysts for HER, exhibiting high activity and stability in acidic media. Among them, the MoSe₂-Co₂P composite shows the highest HER activity with an overpotential of 167 mV at 10 mA cm^-2.

Electrodeposition of amorphous molybdenum sulfide thin film for electrochemical hydrogen evolution reaction

Amorphous molybdenum sulfide (MoS_x) is a highly active noble-metal-free electrocatalysts for the hydrogen evolution reaction (HER). The MoS_x was prepared by electrochemical deposition at room temperature. Low-cost precursors of Mo and S were adopted to synthesize thiomolybdates solution as the electrolyte. It replaces the expensive (NH)₂MoS₄ and avoid the poison gas (H₂S) to generate or employ. The (MoO₂S₂)²⁻, (MoOS₃)²⁻ and (MoS₄)²⁻ ions were determined by UV–VIS spectroscopy. The electrodeposition of MoS_x was confirmed with XRD, XPS and SEM. The electrocatalyst activity was measured by polarization curve. The electrolyte contained (MoO₂S₂)²⁻ ion and (MoOS₃)²⁻ ion electrodeposit the MoS_x thin film displays a relatively high activity for HER with low overpotential of 211 mV at a current density of 10 mA cm⁻², a relatively high current density of 21.03 mA cm⁻² at η = 250 mV, a small Tafel slope of 55 mV dec⁻¹. The added sodium dodecyl sulfate (SDS) can efficient improve the stability of the MoS_x film catalyst.

Synthesis and characterization of size controlled bimetallic nanosponges

Metallic and bimetallic nanosponges with well-defined size and form have attracted increasing attention due to their unique structural properties and their potential for many applications. In this chapter, the recently developed methods for the synthesis and preparation of metallic and bimetallic nanosponges are presented. These methods can be mainly cataloged in two groups: dealloying-based methods and reduction reaction-based methods. Different topographical reconstruction methods for the investigation of their structural properties are then reviewed briefly. The optical properties of the metallic nanosponges are clearly different from those of the solid counterparts due to the tailored disordered structure. The recent advances in the exploration of the distinct linear and non-linear optical properties of the nanosponges are summarized.

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

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.

Nanoporous Quasi-High-Entropy Alloy Microspheres

High-entropy alloys (HEAs) present excellent mechanical properties. However, the exploitation of chemical properties of HEAs is far less than that of mechanical properties, which is mainly limited by the low specific surface area of HEAs synthesized by traditional methods. Thus, it is vital to develop new routes to fabricate HEAs with novel three-dimensional structures and a high specific surface area. Herein, we develop a facile approach to fabricate nanoporous noble metal quasi-HEA microspheres by melt-spinning and dealloying. The as-obtained nanoporous Cu30Au23Pt22Pd25 quasi-HEA microspheres present a hierarchical porous structure with a high specific surface area of 69.5 m2/g and a multiphase approximatively componential solid solution characteristic with a broad single-group face-centered cubic XRD pattern, which is different from the traditional single-phase or two-phase solid solution HEAs. To differentiate, these are named quasi-HEAs. The synthetic strategy proposed in this paper opens the door for the synthesis of porous quasi-HEAs related materials, and is expected to promote further applications of quasi-HEAs in various chemical fields.

Textile-based high-performance hydrogen evolution of low-temperature atomic layer deposition of cobalt sulfide

Hydrogen is an appealing green energy resource to meet increasing energy demands. To produce hydrogen using the hydrogen evolution reaction (HER), platinum, an expensive and scarce metal, is commonly used and plays a crucial role in maximizing catalytic performance. Transition metal chalcogenides, especially cobalt sulfides (CoSx), are considered an alternative to platinum because of their electrochemical properties, for example, low Tafel slopes and overpotentials. Here, we report a light weight, flexible textile-based HER catalyst through a low-temperature process using the atomic layer deposition (ALD) of CoSx. The electrochemical properties of HER catalysts were investigated and found to be impressive, with a low Tafel slope of 41 mV dec-1 and high exchange current density, demonstrating that these are one of the best characteristics among textile-based HER catalysts. The superb catalytic performances were attributed to the amorphous CoSx phase, confirmed by DFT calculations. This study demonstrates that the integration of HER catalysts with textiles allows the development of highly efficient hydrogen energy production systems.

Robust hydrogen evolution reaction catalysis by ultrasmall amorphous ruthenium phosphide nanoparticles

Here, we report a facile method to synthesize ruthenium phosphides with diameter 1 nm and an amorphous structure at room temperature.

Ni/NiM2O4 (M = Mn or Fe) supported on N-doped carbon nanotubes as trifunctional electrocatalysts for ORR, OER and HER

The NCNT/Ni–NiM₂O₄ (M = Mn or Fe) exhibit excellent trifunctional electrocatalytic performance for ORR, OER and HER.

Molybdenum Sulfide Electrocatalysis is Dramatically Influenced by Solvents Used for Its Dispersions

Transition metal dichalcogenides, especially MoS₂ and related MoS₃, have attracted attention as potential replacement of platinum for electrochemical energy applications. These materials are typically treated before the use in solvents. It is assumed that these solvents do not influence follow-up electrochemistry. Here, we show that the oxygen reduction overpotentials as well as inherent electrochemistry of MoS₃ is dramatically influenced by solvents used, them being water, acetonitrile, dimethylformamide, or ethanol. This has a profound impact on the interpretation of the electrochemical studies and the choice of MoS _x solvent treatment.

One-step electrodeposition of a hierarchically structured S-doped NiCo film as a highly-efficient electrocatalyst for the hydrogen evolution reaction

An enormous challenge in the development of renewable hydrogen sources for electricity-driven water-splitting systems has been the limitation of the earth-abundant and robust highly-active cathode electrocatalysts. In this work, we developed a simple sulfur-anion doping strategy to obtain the S-doped NiCo composite (S-NiCo@50) on Ni foam (NF) via a one-step electrochemical deposition. It was found that doped sulfur plays a crucial role in reducing the overpotential of hydrogen evolution by providing abundant active sites as identified by the XPS spectrum. The formed metallic Ni and Co effectively promoted electron transportation. The synergistic effects between the amorphous CoxNiyS(x+y) substance and crystalline Ni and Co metal seemed to result in enhanced HER activity. In particular, the S-NiCo@50 electrode, featuring a hierarchical morphology, showed an ultralow overpotential of 28 and 125 mV at 10 and 100 mA cm-2, respectively, in 1.0 M NaOH with a large exchange current density (j0) of 4.8 mA cm-2 as well as high conductivity and stability; its catalytic properties are superior to most of the reported alkaline electrocatalysts and are on par with commercial Pt/C. Assembled with the counter electrode (Ni-Fe/NF), the overall water splitting was proved with a low 1.55 V at 10 mA cm-2. Moreover, we built the Ni24Co6S6 cluster as the S-NiCo@50 model and revealed its intrinsic activity by density functional theory (DFT) calculations. This study shows that S-doping and component control can be an exquisite strategy for realizing high-efficiency electrochemical water reduction.

PbTe quantum dots as electron transfer intermediates for the enhanced hydrogen evolution reaction of amorphous MoSx/TiO2 nanotube arrays

Amorphous molybdenum sulfides (a-MoSx) have been demonstrated as economic and efficient hydrogen evolution catalysts for water splitting. Further improvements of their hydrogen evolution reaction (HER) activities could be achieved by coupling them with appropriate electron transfer intermediates via interfacial engineering. In this study, a novel ternary composite electrode comprising PbTe quantum dots (QDs), a-MoSx and TiO2 nanotube arrays (TNAs) was successfully fabricated by a facile combination of successive ionic layer adsorption and reaction (SILAR) and electrodeposition routes. Investigation of the microstructures and electrocatalytic properties of the a-MoSx/PbTe QD/TNA hybrid material show that PbTe QDs can work as electron temporary storage and electron transfer intermediates between the electrocatalyst a-MoSx and electrode-based material TiO2 that significantly lower the impedance of electrode process, enhance the energy band bending at the interface between the electrolyte and electrode surface, and increase the electrochemically active surface area. The electron interphase crossing from a-MoSx to electrolyte and electron transport inside the electrode are greatly strengthened. The ternary PbTe@MoSx/TNA electrode demonstrates lowered onset potential and Tafel slope and superior electrocatalytic activity and cyclic stability towards HER.

Facile Synthesis of Molybdenum Diselenide Layers for High-Performance Hydrogen Evolution Electrocatalysts

A cost-effective solution-based synthesis route to grow MoSe₂ thin films with vertically aligned atomic layers, thereby maximally exposing the edge sites on the film surface as well as enhancing charge transport to the electrode, is demonstrated for hydrogen evolution reaction. The surface morphologies of thin films are investigated by scanning electron microscopy and atomic force microscopy, and transmission electron microscopy analyses confirm the formation of the vertically aligned layered structure of MoSe₂ in those films, with supporting evidences obtained by Raman. Additionally, their optical and compositional properties are investigated by photoluminescence and X-ray photoelectron spectroscopy, and their electrical properties are evaluated using bottom-gate field-effect transistors. The resultant pristine MoSe₂ thin film exhibited low overpotential of 88 mV (at 10 mA·cm^-2) and a noticeably high exchange current density of 0.845 mA·cm^-2 with excellent stability, which is superior to most of other reported MoS₂ or MoSe₂-based catalysts, even without any other strategies such as doping, phase transformation, and integration with other materials.

Template-Free Synthesis of Nanoporous Nickel and Alloys as Binder-Free Current Collectors of Li Ion Batteries

This paper reports a versatile template-free method based on the hydrogen reduction of metallic salts for the synthesis of nanoporous Ni and alloys. The approach involves thermal decomposition and reduction of metallic precursors followed with metal cluster nucleation and ligament growth. Topological disordered porous architectures of metals with a controllable distribution of pore size and ligament size ranging from tens of nanometers to micrometers are synthesized. The reduction processes are scrutinized through X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The formation mechanism of the nanoporous metal is qualitatively explained. The as-prepared nanoporous Ni was tested as binder-free current collectors for nickel oxalate anodes of lithium ion batteries. The nanoporous Ni electrodes deliver enhanced reversible capacities and cyclic performances compared with commercial Ni foam. It is confirmed that this synthesis method has versatility not only because it is suitable for different types of metallic salts precursors but also for various other metals and alloys.

An electrochemical anodization strategy towards high-activity porous MoS2 electrodes for the hydrogen evolution reaction

An electrochemical anodization strategy was developed for the formation of MoS₂ electrodes for the hydrogen evolution reaction.

One-step synthesis of cobalt-doped MoS2 nanosheets as bifunctional electrocatalysts for overall water splitting under both acidic and alkaline conditions

Cobalt covalent doping in MoS₂ effectively regulates its electronic structure to decrease the hydrogen adsorption free energy for high HER and simultaneously contributes additional catalytic active sites for the OER.

In situ synthesis of MoS2/graphene nanosheets as free-standing and flexible electrode paper for high-efficiency hydrogen evolution reaction

In this article, an exquisite flexible hybrid MoS₂/graphene free-standing electrocatalyst paper was fabricated by a one-step in situ solvothermal process. The assembled MoS₂/graphene catalysts exhibit significantly enhanced electrocatalytic activity and cycling stability towards the splitting of water in acidic solution. Furthermore, a strategic balance of abundant active sites at the edge of the S–Mo–S layers with efficient electron transfer in the MoS₂/graphene hybrid catalyst plays a key role in controlling the electrochemical performance of the MoS₂ nanosheets. Most importantly, the hybrid MoS₂/graphene nanosheet paper shows excellent flexibility and high electrocatalytic performance under the various bending states. This work demonstrates an opportunity for the development of flexible electrocatalysts, which have potential applications in renewable energy conversion and energy storage systems.

An improved flexible hybrid MoS₂/graphene free-standing electrocatalyst paper was fabricated by a one-step in situ solvothermal process for hydrogen evolution reaction applications.

Noble-metal-free tungsten oxide/carbon (WOx/C) hybrid manowires for highly efficient hydrogen evolution

Developing active, stable, and low-cost electrocatalysts to generate hydrogen is a great challenge in the fields of chemistry and energy. Nonprecious metal catalysts comprised of inexpensive and earth-abundant transition metals are regarded as a promising substitute for noble metal catalysts used in hydrogen evolution reaction (HER), but are still practically unfeasible mainly due to unsatisfactory activity and durability. Here we report a facile two-step preparation method for WO_x nanowires with high concentration of oxygen vacancies (OVs) via calcination of W-polydopamine compound precursors. The resulting hybrid material possesses a uniform and ultralong 1D nanowires structure and a rough and raised surface, which can effectively improve the specific surface area. The products exhibit excellent performance for H₂ generation: the required overpotentials for 1 and 10 mA cm^-2 are 18 and 108 mV, the Tafel slope is 46 mV/decade, and the electrochemically active surface area is estimated to be ∼77.0 m² g^-1. After 1000 cycles, the catalyst works well without significant current density drop. Our experimental results verified metallic transition metal oxides as superior non-Pt electrocatalysts for practical hydrogen evolution reactions.

Stretchable Electronic Sensors of Nanocomposite Network Films for Ultrasensitive Chemical Vapor Sensing

A stretchable, transparent, and body-attachable chemical sensor is assembled from the stretchable nanocomposite network film for ultrasensitive chemical vapor sensing. The stretchable nanocomposite network film is fabricated by in situ preparation of polyaniline/MoS₂ (PANI/MoS₂ ) nanocomposite in MoS₂ suspension and simultaneously nanocomposite deposition onto prestrain elastomeric polydimethylsiloxane substrate. The assembled stretchable electronic sensor demonstrates ultrasensitive sensing performance as low as 50 ppb, robust sensing stability, and reliable stretchability for high-performance chemical vapor sensing. The ultrasensitive sensing performance of the stretchable electronic sensors could be ascribed to the synergistic sensing advantages of MoS₂ and PANI, higher specific surface area, the reliable sensing channels of interconnected network, and the effectively exposed sensing materials. It is expected to hold great promise for assembling various flexible stretchable chemical vapor sensors with ultrasensitive sensing performance, superior sensing stability, reliable stretchability, and robust portability to be potentially integrated into wearable electronics for real-time monitoring of environment safety and human healthcare.

Efficient Water-Splitting Electrodes Based on Laser-Induced Graphene

Electrically splitting water to H₂ and O₂ is a preferred method for energy storage as long as no CO₂ is emitted during the supplied electrical input. Here we report a laser-induced graphene (LIG) process to fabricate efficient catalytic electrodes on opposing faces of a plastic sheet, for the generation of both H₂ and O₂. The high porosity and electrical conductivity of LIG facilitates the efficient contact and charge transfer with the requisite electrolyte. The LIG-based electrodes exhibit high performance for hydrogen evolution reaction and oxygen evolution reaction with excellent long-term stability. The overpotential reaches 100 mA/cm² for HER, and OER is as low as 214 and 380 mV with relatively low Tafel slopes of 54 and 49 mV/dec, respectively. By serial connecting of the electrodes with a power source in an O-ring setup, H₂ and O₂ are simultaneously generated on either side of the plastic sheet at a current density of 10 mA/cm² at 1.66 V and can thereby be selectively captured. The demonstration provides a promising route to simple, efficient, and complete water splitting.

Surface Water Dependent Properties of Sulfur-Rich Molybdenum Sulfides: Electrolyteless Gas Phase Water Splitting

Sulfur-rich molybdenum sulfides are an emerging class of inorganic coordination polymers that are predominantly utilized for their superior catalytic properties. Here we investigate surface water dependent properties of sulfur-rich MoS_x (x = 3²/₃) and its interaction with water vapor. We report that MoS_x is a highly hygroscopic semiconductor, which can reversibly bind up to 0.9 H₂O molecule per Mo. The presence of surface water is found to have a profound influence on the semiconductor's properties, modulating the material's photoluminescence by over 1 order of magnitude, in transition from dry to moist ambient. Furthermore, the conductivity of a MoS_x-based moisture sensor is modulated in excess of 2 orders of magnitude for 30% increase in humidity. As the core application, we utilize the discovered properties of MoS_x to develop an electrolyteless water splitting photocatalyst that relies entirely on the hygroscopic nature of MoS_x as the water source. The catalyst is formulated as an ink that can be coated onto insulating substrates, such as glass, leading to efficient hydrogen and oxygen evolution from water vapor. The concept has the potential to be widely adopted for future solar fuel production.