One-Pot Synthesis of W2C/WS2 Hybrid Nanostructures for Improved Hydrogen Evolution Reactions and Supercapacitors

Constructing WS2/WO3-x heterostructured electrocatalyst enriched with oxygen vacancies for accelerated hydrogen evolution reaction

H2 produced through hydrogen evolution reaction (HER) is a shining star in the field of clean energy. Significant efforts have been dedicated to develop efficient and stable electrocatalysts to reduce the energy barrier and accelerate the kinetics of Hydrogen evolution reaction (HER) under various environments. Herein, we propose a strategy to accelerate the kinetics of HER under acid and alkaline environments by combining heterostructure engineering with defect engineering. We have successfully synthesized a series of WS2/WO3-x heterostructured catalysts, accompanied with substantial oxygen vacancies using a two-step synthesis method. With the partially sulfurization of WO3-x, the heterojunction interface of WS2 and WO3-x was formed along with the appearance of oxygen vacancies, which can facilitate the migration of electrons. The heterostructured catalyst enriched with oxygen vacancies (defined as WS2/WO3-x-2) demonstrates superior HER performance in acidic and alkaline electrolytes. At a current density of 10 mA cm-2, the WS2/WO3-x-2 heterostructured catalyst manifests an overpotential of 120 mV in the acidic electrolytes and a slightly higher overpotential of 150 mV in an alkaline environment. The overpotentials offer an improvement compared to reported W-based catalysts in terms of HER performance. This work provides guiding significance on the design of heterostructured catalysts with promising performance for HER in acidic and alkaline environments.

Vertical graphene nanowalls supported hybrid W2C/WOx composite material as an efficient non-noble metal electrocatalyst for hydrogen evolution

Research for the development of noble metal-free electrodes for hydrogen evolution has blossomed in recent years. Transition metal carbides compounds, such as W2C, have been considered as a promising alternative to replace Pt-family metals as electrocatalysts towards hydrogen evolution reaction (HER). Moreover, hybridization of TMCs with graphene nanostructures has emerged as a reliable strategy for the preparation of compounds with high surface to volume ratio and abundant active sites. The present study focuses in the preparation of tungsten carbide/oxide compounds deposited in a three-dimensional vertical graphene nanowalls (VGNW) substrate via chemical vapor deposition, magnetron sputtering and thermal annealing processes. Structural and chemical characterization reveals the partial carburization and oxidation of the W film sputtered on the VGNWs, due to C and O migration from VGNWs towards W during the high temperature annealing process. Electrochemical characterization shows the enhanced performance of the nanostructured hybrid W2C/WOx on VGNW compound towards HER, when compared with planar W2C/WOx films. The W2C/WOx nanoparticles on VGNWs require an overpotential of -252 mV for the generation of 10 mA cm-2. Chronoamperometry tests in high overpotentials reveal the compounds stability while sustaining high currents, in the order of hundreds of mA. Post-chronoamperometry test XPS characterization unveils the formation of a W hydroxide layer which favours hydrogen evolution in acidic electrolytes. We aspire that the presented insights can be valuable for those working on the preparation of hybrid electrodes for electrochemical processes.

Elucidating the performance of hexamethylene tetra-amine interlinked bimetallic NiCo-MOF for efficient electrochemical hydrogen and oxygen evolution

Bimetallic metal-organic frameworks (MOFs) play a significant role in the electrocatalysis of water due to their large surface area and availability of increased numbers of pores. For the inaugural time, we examine the effectiveness of a hexamethylene tetra-amine (HMT)-induced 3D NiCo-MOF-based nanostructure as a potent bifunctional electrocatalyst with superior performance for overall water splitting in alkaline environments. The structural, morphological, and electrochemical properties of the as-synthesized bifunctional catalyst were examined thoroughly before analyzing its behavior towards electrochemical water splitting. The HMT-based NiCo-MOF demonstrated small overpotential values of 274 mV and 330 mV in reaching a maximum current density of 30 mA cm-2 for hydrogen and oxygen evolution mechanisms, respectively. The Tafel parameter also showed favorable HER/OER reaction kinetics, with slopes of 78 mV dec-1 and 86 mV dec-1 determined during the electrochemical evaluation. Remarkably, the NiCo-HMT electrode exhibited a double-layer capacitance of 4 mF cm-2 for hydrogen evolution and 23 mF cm-2 for oxygen evolution, while maintaining remarkable stability even after continuous operation for 20 hours. This research offers a valuable blueprint for implementing a cost-effective and durable MOF-based bifunctional catalytic system that has proven to be effective for complete water splitting. Decomposition of water under higher current densities is crucial for effective long-term generation and commercial consumption of hydrogen.

Bifunctional CuS/Cl-terminated greener MXene electrocatalyst for efficient hydrogen production by water splitting

Metal sulfides and 2D materials are the propitious candidates for numerous electrochemical applications, due to their superior conductivity and ample active sites. Herein, CuS nanoparticles were fabricated on 2D greener HF-free Cl-terminated MXene (Ti₃C₂Cl₂) sheets by the hydrothermal process as a proficient electrocatalyst for the hydrogen evolution reaction (HER) and overall water splitting. CuS/Ti₃C₂Cl₂ showed an overpotential of 163 mV and a Tafel slope of 77 mV dec^-1 at 10 mA cm^-2 for the HER. In the case of the OER, CuS/Ti₃C₂Cl₂ exhibited an overpotential of 334 mV at 50 mA cm^-2 and a Tafel slope of 42 mV dec^-1. Moreover, the assembled CuS/Ti₃C₂Cl₂||CuS/Ti₃C₂Cl₂ electrolyzer delivered current density of 20 mA cm^-2 at 1.87 V for overall water splitting. The CuS/Ti₃C₂Cl₂ electrocatalyst showed excellent stability to retain 96% of its initial value for about 48 hours at 100 mA cm^-2 current density. The synthesis of CuS/Ti₃C₂Cl₂ enriches the applications of MXene/metal sulfides in efficient bifunctional electrocatalysis for alkaline water splitting.

Fabrication of Fe3O4-incorporated MnO2 nanoflowers as electrodes for enhanced asymmetric supercapacitor performance

Manganese dioxide (MnO2) is considered a promising aspirant for energy storage materials on account of its higher theoretical capacitance along with low capital cost.

Synergistically modified WS2@PANI binary nanocomposite-based all-solid-state symmetric supercapacitor with high energy density

WS2@PANI nanocomposite prepared by hydrothermal and physical blending method shows remarkably high specific capacitance and energy density while retaining excellent cyclic stability.

Highly Active Mo2C@WS2 Hybrid Electrode for Enhanced Hydrogen Evolution Reaction

Transition metal dichalcogenides (TMDs) are the auspicious inexpensive electrocatalysts for the hydrogen evolution reaction (HER) which has been broadly studied owing to their remarkable enactment, however the drought of factors understanding were highly influenced to hinder their electrocatalytic behavior. Recently, transition metal carbide (TMC) has also emerged as an attractive electrode material due to their excellent ionic and electronic transport behavior. In this work, Mo2C@WS2 hybrids have been fabricated through a simple chemical reaction method. Constructed heterostructure electrocatalyts presented the small Tafel slope of 59 and 95 mV per decade and low overpotential of 93 mV and 98 @10 mA·cm−2 for HER in acidic and alkaline solution, respectively. In addition, 24-h robust stability with the improved interfacial interaction demonstrated the suitability of hybrid electrocatalyst for HER than their pure form of Mo2C and WS2 structures. The derived outcomes describe the generated abundant active sites and conductivity enhancement in TMC/TMD heterostructure along with the weaken ion/electron diffusion resistance for efficient energy generation applications.

Novel WS2 /Fe0.95 S1.05 Hierarchical Nanosphere as a Highly Efficient Electrocatalyst for Hydrogen Evolution Reaction

Fe_0.95 S_1.05 with high reactivity and stability was incorporated into WS₂ nanosheets via a one-step solvothermal method for the first time. The resulted hybrid catalyst has much higher catalytic activity than WS₂ and Fe_0.95 S_1.05 alone, and the optimal WS₂ /Fe_0.95 S_1.05 hybrid catalyst was found by adjusting the feed ratio. The addition of Fe_0.95 S_1.05 was proven to be able to enhance the hydrogen evolution reaction (HER) activity of WS₂ , and vice versa. At the same time, it was found that the catalytic effect of the hybrid catalyst was the best when the feed ratio was W : Fe=2 : 1. In other words, we confirmed that there is a synergistic effect between W- and Fe-based sulfide hybrid catalysts, and validated that the reason for the improved HER performance is the strong interaction between the two in the middle sulfur. WS₂ /Fe_0.95 S_1.05 -2 hybrid catalyst leads to enhanced HER activity, which shows a low overpotential of ∼0.172 V at 10 mA cm^-2 , low Tafel slope of ∼53.47 mV/decade. This study supplies innovative synthesis of a highly active WS₂ /Fe_0.95 S_1.05 hybrid catalyst for HER.