Interwoven WSe 2 /CNTs hybrid network: A highly efficient and stable electrocatalyst for hydrogen evolution

Feather-like few-layer WSe2 nanosheets grown on W substrates: an excellent electrocatalyst for the hydrogen evolution reaction

Thin films of few-layer WS₂ nanosheets and WSe₂ nanosheets were directly grown on W substrates via a scalable infrared-heating CVD method. The WSe₂ nanosheets are in a unique feather-like assembly, and mainly composed of the 2H phase, while the presence of a metallic 1T phase was confirmed through atomic resolution TEM observation. Feather-like WSe₂ nanosheets delivered excellent electrocatalytic performances for the HER in acid, including a low overpotential of 141 mV to yield a current at 10 mA cm^-2, and superb long-term stability at high currents. The highly efficient electrocatalysis is mainly attributed to the unique feather-like morphology of the WSe₂ nanosheets with numerous sharp barbules to help maximize the exposed edge sites, along with other beneficial factors including the presence of a 1T phase and slight O-doping.

Water electrolysis: from textbook knowledge to the latest scientific strategies and industrial developments

Replacing fossil fuels with energy sources and carriers that are sustainable, environmentally benign, and affordable is amongst the most pressing challenges for future socio-economic development. To that goal, hydrogen is presumed to be the most promising energy carrier. Electrocatalytic water splitting, if driven by green electricity, would provide hydrogen with minimal CO2 footprint. The viability of water electrolysis still hinges on the availability of durable earth-abundant electrocatalyst materials and the overall process efficiency. This review spans from the fundamentals of electrocatalytically initiated water splitting to the very latest scientific findings from university and institutional research, also covering specifications and special features of the current industrial processes and those processes currently being tested in large-scale applications. Recently developed strategies are described for the optimisation and discovery of active and durable materials for electrodes that ever-increasingly harness first-principles calculations and machine learning. In addition, a technoeconomic analysis of water electrolysis is included that allows an assessment of the extent to which a large-scale implementation of water splitting can help to combat climate change. This review article is intended to cross-pollinate and strengthen efforts from fundamental understanding to technical implementation and to improve the 'junctions' between the field's physical chemists, materials scientists and engineers, as well as stimulate much-needed exchange among these groups on challenges encountered in the different domains.

Implantation of WSe2 nanosheets into multi-walled carbon nanotubes for enhanced microwave absorption

Microwave absorption materials can protect humanity from harmful electromagnetic radiation, but it is still a challenge to absorb electromagnetic radiation with different bands simultaneously. Herein, an effective strategy for obtaining WSe₂@CNTs nanohybrids is reported. The conductive network and polarization of WSe₂@CNTs nanohybrids can be tailored by confinedly implanting WSe₂ nanosheets on multi-walled carbon nanotubes. The electromagnetic properties and microwave absorption performance of the nanohybrids are effectively adjusted via changing the hybrid ratio of WSe₂ and CNTs. Multi-band microwave absorption is achieved with up to three bands. The reflection loss (RL) of the sample can reach -60.1 dB, and the bandwidth can reach 4.24 GHz (RL ≤ -10 dB). The excellent microwave absorption performance is attributed to the conductance and multiple relaxations, as well as the synergistic effect of the two. This result confirms that WSe₂@CNTs nanohybrids are potential candidates for high-efficiency microwave absorbers and provide a valuable pathway for designing high-performance microwave absorption materials in the future.

A Polarization Boosted Strategy for the Modification of Transition Metal Dichalcogenides as Electrocatalysts for Water-Splitting

The design and fabrication of transition metal dichalcogenides (TMDs) are of paramount significance for water-splitting process. However, the limited active sites and restricted conductivity prevent their further application. Herein, a polarization boosted strategy is put forward for the modification of TMDs to promote the absorption of the intermediates, leading to the improved catalytic performance. By the forced assembly of TMDs (WS₂ as the example) and carbon nanotubes (CNTs) via spray-drying method, such frameworks can remarkably achieve low overpotentials and superior durability in alkaline media, which is superior to most of the TMDs-based catalysts. The two-electrode cell for water-splitting also exhibits perfect activity and stability. The enhanced catalytic performance of WS₂ /CNTs composite is mainly owing to the strong polarized coupling between CNTs and WS₂ nanosheets, which significantly promotes the charge redistribution on the interface of CNTs and WS₂ . Density functional theory (DFT) calculations show that the CNTs enrich the electron content of WS₂ , which favors electron transportation and accelerates the catalysis. Moreover, the size of WS₂ is restricted caused by the confinement of CNTs, leading to the increased numbers of active sites, further improving the catalysis. This work opens a feasible route to achieve the optimized assembling of TMDs and CNTs for efficient water-splitting process.

Hollow CoP/FeP4 Heterostructural Nanorods Interwoven by CNT as a Highly Efficient Electrocatalyst for Oxygen Evolution Reactions

Electrolysis of water to produce hydrogen is crucial for developing sustainable clean energy and protecting the environment. However, because of the multi-electron transfer in the oxygen evolution reaction (OER) process, the kinetics of the reaction is seriously hindered. To address this issue, we designed and synthesized hollow CoP/FeP₄ heterostructural nanorods interwoven by carbon nanotubes (CoP/FeP₄@CNT) via a hydrothermal reaction and a phosphorization process. The CoP/FeP₄@CNT hybrid catalyst delivers prominent OER electrochemical performances: it displays a substantially smaller Tafel slope of 48.0 mV dec⁻¹ and a lower overpotential of 301 mV at 10 mA cm⁻², compared with an RuO₂ commercial catalyst; it also shows good stability over 20 h. The outstanding OER property is mainly attributed to the synergistic coupling between its unique CNT-interwoven hollow nanorod structure and the CoP/FeP₄ heterojunction, which can not only guarantee high conductivity and rich active sites, but also greatly facilitate the electron transfer, ion diffusion, and O₂ gas release and significantly enhance its electrocatalytic activity. This work offers a facile method to develop transition metal-based phosphide heterostructure electrocatalysts with a unique hierarchical nanostructure for high performance water oxidation.

CVD growth of rhenium sulfide on carbon nanotubes as an anode for improving the performance of lithium ion batteries

Lithium ion batteries have widely been used for electronic devices and electric vehicles. However, commercial anodes, generally graphite, have not been improved a great deal. Thus, we successfully constructed ReS₂/carbon nanotube (CNT) composites by a chemical vapor deposition method, which exhibit excellent electrochemical performances when serving as anode materials for lithium ion batteries (LIBs). We confirmed that ReS₂ crystals are grown on the surface of the CNTs by using scanning electron microscopy and transmission electron microscopy. As a result, the LIBs show much better long-cycle and rate performances than bare ReS₂ and CNTs. The ReS₂/CNTs were assembled in coin cells CR2025, presenting a stability capacity of 488 mAh g^-1 at a rate of 5C. The anodes maintain a reversible capacity of 1050 mAh g^-1 after nearly 60 cycles at 0.2C, which indicates that it is a promising technique to improve the performance of LIBs.

Carbon nanotube spiderweb promoted growth of hierarchical transition metal dichalcogenide nanostructures for seamless devices

Hierarchical transition metal dichalcogenide (h-TMDC) nanostructures with abundant active edge sites and good electrical conductivity hold great promise for numerous applications. Here, we report a general method for the chemical synthesis of a series of large-area, free-standing h-TMDC films and their devices by using carbon nanotube (CNT) spiderwebs as both growth promoters and electrical/mechanical reinforcement networks. Our approach allows the seamless integration of h-TMDC nanostructures with abundant active edge sites and CNT networks with good electrical conductivity and mechanical flexibility. As a proof of concept, h-MoSe₂/CNT hybrid films with CNT contacts have been chemically synthesized and applied as flexible electrocatalytic devices for hydrogen evolution reaction (HER). Owing to the seamless connection between the CNT contacts and the electroactive h-TMDC/CNT nanostructures, the flexible electrocatalytic devices exhibited excellent mechanical stability and maintained stable electrocatalytic performance under cyclic bendings. Our method can be readily extended to the large-scale production of various h-TMDC/CNT hybrid films and their seamless devices.

Ultrahigh electrocatalytic activity with trace amounts of platinum loadings on free-standing mesoporous titanium nitride nanotube arrays for hydrogen evolution reactions

Minimizing Pt loadings on electrocatalysts for hydrogen evolution reactions (HERs) is essential for their commercial applications. Herein, free-standing mesoporous titanium nitride nanotube arrays (TiN NTAs) were fabricated to serve as a substrate for Pt loadings in trace amounts. TiN NTAs were prepared by thermal treatment of anodic TiO2 NTAs at 750 °C for 3 h in a NH3 atmosphere. The uniform TiN NTAs showed an inner diameter of ∼80 nm and a length of ∼7 μm, with many mesoporous holes ranging from 5 to 10 nm in diameter on the nanotube walls. Pt species dissolved from the Pt counter electrode in electrochemical cycling were redeposited on the mesoporous TiN NTAs to produce Pt-TiN NTAs with an ultra-low Pt loading of 8.3 μg cm-2. Pt-TiN NTAs exhibited 15-fold higher mass activity towards HER than the benchmark 20 wt% Pt/C in acidic media, with an overpotential of 71 mV vs. RHE at a current density of 10 mA cm-2, a Tafel slope value of 46.4 mV dec-1 and excellent stability. The performance of Pt-TiN NTAs is also much better than that of Pt species deposited on non-mesoporous nanotube arrays due to the shortcuts originating from the mesoporous holes on the nanotube walls for electron and mass transfer.

Layered transition metal dichalcogenide/carbon nanocomposites for electrochemical energy storage and conversion applications

Layered transition metal dichalcogenide (LTMD)/carbon nanocomposites obtained by incorporating conductive carbons such as graphene, carbon nanotubes (CNT), carbon nanofibers (CF), hybrid carbons, hollow carbons, and porous carbons exhibit superior electrochemical properties for energy storage and conversion. Due to the incorporation of carbon into composites, the LTMD/carbon nanocomposites have the following advantages: (1) highly efficient ion/electron transport properties that promote electrochemical performance; (2) suppressed agglomeration and restacking of active materials that improve the cycling performance and electrocatalytic stability; and (3) unique structures such as network, hollow, porous, and vertically aligned nanocomposites that facilitate the shortening of the ion and electrolyte diffusion pathway. In this context, this review introduces and summarizes the recent advances in LTMD/carbon nanocomposites for electrochemical energy-related applications. First, we briefly summarize the reported synthesis strategies for the preparation of LTMD/carbon nanocomposites with various carbon materials. Following this, previous studies using rationally synthesized nanocomposites are discussed based on a variety of applications related to electrochemical energy storage and conversion including Li/Na-ion batteries (LIBs/SIBs), Li-S batteries, supercapacitors, and the hydrogen evolution reaction (HER). In particular, the sections on LIBs and the HER as representative applications of LTMD/carbon nanocomposites are described in detail by classifying them with different carbon materials containing graphene, carbon nanotubes, carbon nanofibers, hybrid carbons, hollow carbons, and porous carbons. In addition, we suggest a new material design of LTMD/carbon nanocomposites based on theoretical calculations. At the end of this review, we provide an outlook on the challenges and future developments in LTMD/carbon nanocomposite research.

Scalable synthesis of self-assembled bimetallic phosphide/N-doped graphene nanoflakes as an efficient electrocatalyst for overall water splitting

In order to achieve clean hydrogen energy through overall water splitting, it is vitally important but still challenging to develop highly efficient and low-cost electrocatalysts to replace the noble metal-based electrocatalysts (e.g. Pt- and Ru-based catalysts). To address this issue, herein, we present a facile and scalable spray drying and subsequent phosphorization approach to synthesize iron-cobalt bimetallic nanoflakes encapsulated in N-doped graphene (FCP@NG). The optimized FCP@NG exhibits excellent performance in the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and overall water splitting. It demonstrates remarkable performance in the HER and superior activity in the OER, even outperforming the state-of-the-art RuO₂ catalyst. Being employed as both the cathode and anode on nickel foams, this FCP@NG hybrid demonstrates promising performance in overall water splitting with a very low potential of 1.63 V to deliver a current density of 10 mA cm^-2, which is superior among most of the recently reported transition-metal-based catalysts and comparable to the commercial Pt/RuO₂ cell. The outstanding electrocatalytic performance of FCP@NG is attributed to a synergistic effect of its bi-metallization, unique nanoflake structure and conductive N-doped graphene encapsulation. This work provides a scalable and low-cost strategy to synthesize nonprecious and bi-functional transition-metal-based catalysts with unique nanoarchitecture and outstanding catalytic performance for overall water splitting.

Self-assembled Co0.85Se/carbon nanowires as a highly effective and stable electrocatalyst for the hydrogen evolution reaction

Self-assembled Co_0.85Se/carbon nanowires, constructed by Co_0.85Se nanoparticles homogenously embedded into carbon nanowires (Co_0.85Se@CNWs), have been synthesized through a facile solvothermal reaction and selenylation process. Compared to the bare Co_0.85Se NWs, the Co_0.85Se@CNW hybrid demonstrates high efficiency and stability for HER. It has a small Tafel slope of 43.4 mV dec⁻¹, a low onset potential of 138 mV vs. RHE, and a high cycling stability with more than 95% current retention after 1500 voltammetry cycles. The outstanding HER performance of Co_0.85Se@CNWs is attributed to its unique particle-in-nanowire architecture, which not only prevents the Co_0.85Se nanoparticles from aggregation, but also provides a highly conductive CNW matrix to promote the charge transfer in the electrocatalytic reaction, further enhancing the catalytic activity. This work provides a new strategy to rationally design transition metal-based selenide hybrids as highly effective and stable electrocatalysts for HER.

Self-assembled Co_0.85Se/carbon nanowires constructed from Co_0.85Se nanoparticles homogenously embedded into carbon nanowires (Co_0.85Se@CNWs).

Ultrasensitive determination of thrombin by using an electrode modified with WSe2 and gold nanoparticles, aptamer-thrombin-aptamer sandwiching, redox cycling, and signal enhancement by alkaline phosphatase

A sensitive aptamer/protein binding-triggered sandwich assay for thrombin is described. It is based on electrochemical-chemical-chemical redox cycling using a glassy carbon electrode (GCE) that was modified with WSe₂ and gold nanoparticles (AuNPs). The AuNPs are linked to thrombin aptamer 1 via Au-S bonds. Thrombin is first captured by aptamer 1 and then sandwiched through the simultaneous interaction with AuNPs modified with thrombin-specific aptamer 2 and signalling probe. Subsequently, the DNA-linked AuNP hybrids result in the capture of streptavidin-conjugated alkaline phosphatase onto the modified GCE through the specific affinity reaction for further signal enhancement. As a result, a linear range of 0-1 ng mL^-1 and a detection limit as low as 190 fg mL^-1 are accomplished. The specificity for thrombin is excellent. Conceivably, this strategy can be easily expanded to other proteins by using the appropriate aptamer. Graphical abstract Schematic presentation of an electrochemical biosensor for thrombin based on WSe₂ and gold nanoparticles, aptamer-thrombin-aptamer sandwiching, redox cycling, and signal enhancement by alkaline phosphatase.

Nanocrystalline Co0.85Se Anchored on Graphene Nanosheets as a Highly Efficient and Stable Electrocatalyst for Hydrogen Evolution Reaction

For the first time, a porous and conductive Co_0.85Se/graphene network (CSGN), constructed by Co_0.85Se nanocrystals being tightly connected with each other and homogeneously anchored on few-layered graphene nanosheets, has been synthesized by a facile one-pot solvothermal method. Compared to unhybridized Co_0.85Se, CSGN exhibits much faster kinetics and better electrocatalytic behavior for hydrogen evolution reaction (HER). The HER mechanism of CSGN is improved to Volmer-Tafel combination, instead of Volmer-Heyrovsky combination, for Co_0.85Se. CSGN has a very low Tafel slope of 34.4 mV/dec, which is much lower than that of unhybridized Co_0.85Se (41.8 mV/dec) and is the lowest ever reported for Co_0.85Se-based electrocatalysts. CSGN delivers a current density of 55 mA/cm² at 250 mV overpotential, much larger than that of Co_0.85Se (33 mA/cm²). Furthermore, CSGN shows superior electrocatalytic stability even after 1500 cycles. The excellent HER performance of CSGN is attributed to the unique porous and conductive network, which can not only guarantee interconnected conductive paths in the whole electrode but also provide abundant catalytic active sites, thereby facilitating charge transportation between the electrocatalyst and electrolyte. This work provides insight into rational design and low-cost synthesis of nonprecious transition-metal chalcogenide-based electrocatalysts with high efficiency and excellent stability for HER.

Self-Assembled Coral-like Hierarchical Architecture Constructed by NiSe2 Nanocrystals with Comparable Hydrogen-Evolution Performance of Precious Platinum Catalyst

For the first time, self-assembled coral-like hierarchical architecture constructed by NiSe₂ nanocrystals has been synthesized via a facile one-pot DMF-solvothermal method. Compared with hydrothermally synthesized NiSe₂ (H-NiSe₂), the DMF-solvothermally synthesized nanocrystalline NiSe₂ (DNC-NiSe₂) exhibits superior performance of hydrogen evolution reaction (HER): it has a very low onset overpotential of ∼136 mV (vs RHE), a very high cathode current density of 40 mA/cm² at ∼200 mV (vs RHE), and an excellent long-term stability; most importantly, it delivers an ultrasmall Tafel slope of 29.4 mV dec^-1, which is the lowest ever reported for NiSe₂-based catalysts, and even lower than that of precious platinum (Pt) catalyst (30.8 mV dec^-1). The superior HER performance of DNC-NiSe₂ is attributed to the unique self-assembled coral-like network, which is a benefit to form abundant active sites and facilitates the charge transportation due to the inherent high conductivity of NiSe₂ nanocrystals. The DNC-NiSe₂ is promising to be a viable alternative to precious metal catalysts for hydrogen evolution.

An electrochemical microRNA sensing platform based on tungsten diselenide nanosheets and competitive RNA–RNA hybridization

In this work, we report an ultrasensitive electrochemical biosensor for microRNA-21 detection by using a competitive RNA–RNA hybridization configuration.