Hydrogen Evolution Reaction Applications Research Articles

Amorphous-crystalline transition-driven synthesis of Co single-atom catalysts on MoO3 for enhanced hydrogen evolution in acidic and alkaline media

Single atom catalysts (SACs) dispersed in metal oxide supports offer not only maximized catalyst utilization but also extended modulation capabilities through interactions between the SA and its support. However, achieving facile preparation and ensuring electrochemical durability of such SACs, particularly for hydrogen evolution reaction (HER) applications, remain formidable challenges. Our study addresses these issues by employing an amorphous-to-crystalline phase transition in MoO3 to synthesize a cobalt (Co) SA catalyst. This method facilitates the production of highly selective SA catalysts at low temperatures and ensures their enhanced stability in HER applications. The Co SA MoO3 catalyst exhibits superior performance in HER, operating effectively in both acidic and alkaline environments. Significantly, it maintains stable HER activity across these diverse electrolytic conditions. Our Density Functional Theory (DFT) calculations provide insights into the exceptional HER performance of Co SA MoO3. These calculations reveal that the strong affinity for hydrogen and water, facilitated by the modulation of the p-band orbitals at specific oxygen sites adjacent to the Co SA, establishes a thermoneutral pathway for HER. This study represents a pivotal advancement, showcasing a highly practical and robust single-atom catalyst, marking a significant stride towards sustainable energy solutions.

In Situ Growth of Interfacially Nanoengineered 2D-2D WS2/Ti3C2Tx MXene for the Enhanced Performance of Hydrogen Evolution Reactions.

In line with current research goals involving water splitting for hydrogen production, this work aims to develop a noble-metal-free electrocatalyst for a superior hydrogen evolution reaction (HER). A single-step interfacial activation of Ti3C2Tx MXene layers was employed by uniformly growing embedded WS2 two-dimensional (2D) nanopetal-like sheets through a facile solvothermal method. We exploited the interactions between WS2 nanopetals and Ti3C2Tx nanolayers to enhance HER performance. A much safer method was adopted to synthesize the base material, Ti3C2Tx MXene, by etching its MAX phase through mild in situ HF formation. Consequently, WS2 nanopetals were grown between the MXene layers and on edges in a one-step solvothermal method, resulting in a 2D-2D nanocomposite with enhanced interactions between WS2 and Ti3C2Tx MXene. The resulting 2D-2D nanocomposite was thoroughly characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman, Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS) analyses before being utilized as working electrodes for HER application. Among various loadings of WS2 into MXene, the 5% WS2-Ti3C2Tx MXene sample exhibited the best activity toward HER, with a low overpotential value of 66.0 mV at a current density of -10 mA cm-2 in a 1 M KOH electrolyte and a remarkable Tafel slope of 46.7 mV·dec-1. The intercalation of 2D WS2 nanopetals enhances active sites for hydrogen adsorption, promotes charge transfer, and helps attain an electrochemical stability of 50 h, boosting HER reduction potential. Furthermore, theoretical calculations confirmed that 2D-2D interactions between 1T/2H-WS2 and Ti3C2Tx MXene realign the active centers for HER, thereby reducing the overpotential barrier.

Enhanced electrochemical performances of SrMoO4/MWCNT-PVP nanocomposites as electrocatalyst for hydrogen evolution reaction

In this work, we have successfully synthesized the cost-effective, abundant in nature and environmentally friendly SrMoO4/MWCNT-PVP by using the co-precipitation technique for hydrogen evolution reaction (HER). Prepared nanocomposites were characterized by XRD, which confirms the formation of tetragonal structure of SrMoO4 and indexed with JCPDS (01-074-3912). Raman spectra confirm the combination of SrMoO4 with carbon composite (verified by D and G band 1.02 ID/IG ratio) and its functional group was further analyzed with the help of FTIR spectra. Synthesized product morphology was characterized by using SEM and TEM images, which confirms formation of well-defined dumb-bell shaped nanostructures with the combination of carbon nanotube and also it further confirms the formation of polycrystalline nature of the material. The elemental composition was analyzed by EDS images, which confirms the occurrence of Sr, Mo, O, and C in an appropriate form with a uniform distribution, respectively. MWCNT in SrMoO4 incorporation led to decrease overpotential of 204 mV and 110 mV/dec Tafel slope of the material, which was examined by the LSV curves and Tafel plot analysis. Electrochemical impedance spectroscopy was also investigated, and it delivered the small charge-transfer resistance of 248 Ω, which further supporting the HER analysis and denoting the promising HER kinetics. Therefore, our work unlocks a new path for the properly tuned nanostructured morphology of metal oxide with carbon composite for electrochemical hydrogen evolution reaction application.

Electrostatic co-assembly of FePS3 nanosheets and surface functionalized BCN heterostructures for hydrogen evolution reaction.

Advances in the hydrogen evolution reaction (HER) are intricately connected with addressing the current energy crisis and quest for sustainable energy sources. The necessity of catalysts that are efficient and inexpensive to perform the hydrogen evolution reaction is key to this. Following the ground-breaking discovery of graphene, metal thio/seleno phosphates (MPX3: M - transition metal, P - phosphorus and X - S/Se), two dimensional (2D) materials, exhibit excellent tunable physicochemical, electronic and optical properties, and are expected to be key to the energy industry for years to come. Taking this into account, a facile time-effective electrostatic restacking synthesis procedure has been followed to synthesize a 2D/2D heterostructure (FePS3@BCN) involving FePS3, one of the prominent MPX3 materials, with borocarbonitride (BCN), for hydrogen evolution reaction (HER). The piled up nanosheets of FePS3 and BCN are held together by an electrostatic force, and display extreme robustness under the harsh conditions of HER application. The amalgamated electrocatalyst achieved an overpotential of 187 mV at a current density of 10 mA cm-2 with a shallow Tafel slope of 41 mV dec-1, following the Volmer-Heyrovsky mechanism. The resilience of the electrocatalyst has been examined through chronoamperometric testing for long term stability, and it is stable for more than 14 hours, which shows the excellent electrocatalytic activity for hydrogen evolution reaction owing to the strategic approach to the catalyst design, the use of numerous electrochemically active sites, large surface area and a barrier-free channel for quick ion transfer.

Reduction mechanism of hydrothermally synthesized wide band gap ZnWO4 nanorods for HER application

This manuscript presents a detailed investigation of the synthesis of zinc tungstate (ZnWO4) nanoparticles and various characterizations of the as-synthesized sample to reveal its potential for hydrogen evolution reaction (HER). The study focuses on a simple and efficient hydrothermal method that facilitates the production of ZnWO4 nanoparticles, which involves the controlled reaction between zinc and tungstate ions in a specific solution. The resulting ZnWO4 nanoparticles were characterized by various characterization techniques which include XRD, UV-vis spectroscopy, TEM and electrochemical study to get insights into their size, structure, properties and electrochemical behaviour. The characterization includes the analysis of the nanoparticles' structural features and optical properties. The material’s electrochemical properties were also investigated by employing cyclic voltammetry (CV) and potentio electrochemical impedance spectroscopy (PEIS). The charge transfer process was studied for the material revealing its diffusion controlled behaviour and reduction peaks in the cathodic region. These properties suggest that the material is a potential candidate for HER catalysis.

Noble Metal Phosphides: Robust Electrocatalysts toward Hydrogen Evolution Reaction

AbstractFacing with serious carbon emission issues, the production of green H2 from electrocatalytic hydrogen evolution reaction (HER) has received extensive research interest. Almost all kinds of noble metal phosphides (NMPs) consisting of Pt‐group elements (i.e., Ru, Rh, Pd, Os, Ir and Pt) are all highly active and pH‐universal electrocatalysts toward HER. In this review, the recent progress of NMP‐based HER electrocatalysts is summarized. It is further take typical examples for discussing important impact factors on the HER performance of NMPs, including crystalline phase, morphology, noble metal element and doping. Moreover, the synthesis and HER application of hybrid catalysts consisting of NMPs and other materials such as transition metal phosphides, oxides, sulfides and phosphates, carbon materials and noble metals is also reviewed. Reducing the use of noble metal is the key idea for NMP‐based hybrid electrocatalysts, while the expanded functionality and structure‐performance relationship are also noticed in this part. At last, the potential opportunities and challenges for this kind of highly active catalyst is discussed.

Metal-organic framework derived transition metal sulfides grown on carbon nanofibers as self-supported catalysts for hydrogen evolution reaction

Metal-organic framework (MOF) derived transition metal-based electrocatalysts have received great attention as substitutes for noble metal-based hydrogen evolution catalysts. However, the low conductivity and easy detachments from electrodes of raw MOF have seriously hindered their applications in hydrogen evolution reaction. Herein, we report the facile preparation of Co-NSC@CBC84, a porous carbon-based and self-supported catalyst containing Co9S8 active species, by pyrolysis and sulfidation of in-situ grown ZIF-67 on polydopamine-modified biomass bacterial cellulose (PDA/BC). As a binder-free and self-supported electrocatalyst, Co-NSC@CBC84 exhibits superior electrocatalytic properties to other reported cobalt-based sulfide catalytic materials and has good stability in 0.5 M H2SO4 electrolyte. At the current density of 10 mA cm−2, only an overpotential of 138 mV was required, corresponding to a Tafel slope of 123 mV dec−1, owing to the strong synergy effect between Co-NSC nanoparticles and CBC substrate. This work therefore provides a feasible approach to prepare self-supported transition metal sulfides as HER catalysts, which is helpful for the development of noble metal-free catalysts and biomass carbon materials.

Active Electrochemical Catalysts for Ammonia and Hydrogen Evolution Reaction

An environmentally friendly alternative synthesis process is desired to produce NH3 with no CO2 emissions and low energy demand in a sustainable and ecological way in the future. The electrochemical method assisted by earth-abundant materials has been widely utilized for the chemical energy conversion. We have developed new earth-abundant layered structure metal sulfide based materials as active catalysts for electrochemically nitrogen reduction reaction. From electrochemical analysis, the Faraday efficiency of MoS2 and FeS2 for NRR can be achieve to~27% and 14% with good catalytic stability, respectively. The energy profile of the NRR reaction pathway on the catalysts will be performed by the density functional theoretical (DFT) calculation. Besides, there have been lots of studies on hydrogen evolution reaction (HER) catalytic activity using ultralow loading of Pt catalysts or even Pt single atom catalysts as well. However, Pt single atom deposited on the surface of the carbon or metal oxide material showed some drawbacks, such as high possibility of Pt desorption from the supported material in the electrolyte. Our work demonstrated that gold nanodendrites (Au NDs) with high facet surface was chosen as the supported materials for studying the relation between the low loading amount of Pt atoms and reaction mechanism of HER activity. Overall results provides a feasible approach to morphological control of metal sulfide and atomic deposition of Pt element on the specific substrate as active catalysts for NRR and HER applications, respectively.

Synthesis of Silver Nanoparticles from Silver Closo‐Dodecaborate Film for Enhanced Hydrogen Evolution

AbstractThe icosahedral closo dodecaborate cluster [B12H12]2− is gaining increasing interest due to its unique properties including the ease of functionalization, 3D aromaticity, and formation of metal salts with high ion conductivity. In this work, simple and effective preparation of silver closo dodecaborte (Ag2B12H12) films is reported by an electrochemical route. The size of the Ag2B12H12 particles in the films can be tuned from nanometers to micrometers by varying the electrochemical parameters. Ag nanoclusters with controllable sizes are successfully generated via electrochemical reduction reactions or thermal anneal of the Ag2B12H12 films. When tested for hydrogen evolution reaction (HER) in an acidic solution, the as‐prepared Ag nanoparticles deliver a current density of 10 mA cm−2 at 376 mV overpotential. This research sheds light on a new synthesis of [B12H12]2− based thin films, the generation of metal nano‐powders, and their application in HER or other applications.

Spontaneous hydrogen production on well-designed two-dimensional MoSi2N2P2 Janus structure: N-face versus P-face tuning

Based on the recently discovered two-dimensional non-Janus MoSi2N4 structure, we here study a well-designed two-dimensional Janus structure (MoSi2N2P2) for potential application in hydrogen evolution reaction (HER) via water splitting. We first confirm the stability of the MoSi2N2P2 structure using first-principles’ calculations in the framework of density functional theory by calculating cohesive energy, phonon dispersion, and ab-initio molecular dynamics evolution. We then investigate electronic and transport properties of the structure. The MoSi2N2P2 Janus structure exhibits an indirect (Γ→M) band gap of only 0.22 eV using PBE and 0.89 eV using the HSE06 hybrid functional. We also find that there is a large intrinsic electric field across the Janus structure, which tends to gather electrons at the P face. We also calculate the mobility of the Janus structure, showing that it has a high electron mobility (409 cm2/Vs) along the zigzag direction. We then show that compared with the P face, the N face gives a lower overpotential against HER, but not sufficient to activate HER process. Therefore, we investigate how the electronic properties and the HER overpotential of the Janus MoSi2N2P2 monolayer are affected by applying biaxial strain and external perpendicular electric field. Thus, the N face exhibits a higher degree of tunability than the P face toward HER overpotential. In particular by applying an electric field of 2.7 V/Å directing from the P face to the N face, the overpotential against the HER reaction on the N face can be adjusted to zero, showing that the well-designed Janus structure can exhibit a potential application for spontaneous HER water splitting.

Study on effect of vanadium doping in cesium tungsten bronze system and application in HER

Increasing demand for energy and the crisis of fossil fuels have led researchers to search for an alternative energy source. Hydrogen is the cleanest energy source producing water as fuel cells exhaust. However, producing hydrogen could be crucial as only some active catalysts produce pure hydrogen. The expense due to the scarcity of the state-of-the-art catalyst (platinum) for the Hydrogen Evolution Reaction (HER) is the main reason for the higher price of pure hydrogen as a fuel. In our present research, we chose the less expensive cesium tungsten bronzes (CTB) doped with various percentages of vanadium (5 mol% - 20 mol%) to study their HER performance. The materials were prepared hydrothermally at 180 °C at different reaction times. XRD revealed that, upon increasing the vanadium amount, the hexagonal phase of the CTB is transformed to the cubic phase at a higher reaction time. However, the hexagonal phase was retained after vanadium introduction with a lower reaction time. FT-IR, Raman, EDX, SIMS, XPS, and XRF spectroscopy confirmed the incorporation of vanadium into the bronze system. Vanadium-doped samples showed enhanced HER activity compared to the pure CTB. The 20% vanadium-doped hexagonal bronze showed the best HER performance in 0.5 M H2SO4 among all the vanadium-doped materials, which lowered the HER potential of the pure CTB (-0.665 V vs RHE) to -0.288 V vs RHE at -10 mA cm−2. This increase in activity was correlated with a higher surface area, higher electrochemical surface area, faster reaction kinetics with a lower Tafel slope, and a small charge-transfer resistance of the samples after V5+ incorporation compared to the pure CTB.

Ni-Ti3C2 MXene composite derived from Ni-metal organic framework for electrochemical hydrogen evolution reaction in acidic and alkaline medium

MOFs derived metal composites are found to be a potential electrocatalyst for energy storage and conversion process. In this work, Ni composite with MXene (Ni-Ti3C2) was synthesized by calcination of Ni-MOF at 650 °C and characterized by XRD, FE-SEM, FTIR and BET analysis. After calcination, the derived Ni composited Ti3C2 showed a high porosity and high surface area as compared to Ti3C2. The derived material was further used as electrode for Hydrogen Evolution Reaction (HER) and tested by various electrochemical analysis viz. Cyclic voltammetry (CV), Electrochemical impedance analysis (EIS) and Linear Sweep Voltammetry (LSV) in alkaline medium. The derived Ni-Ti3C2 in basic medium displays a small Tafel value of 56.15 mV/dec with acquired voltage of 181.15 mV due to the surface area and accessible catalytic active sites, which provides excellent mass transfer properties for derived Ni-Ti3C2 composite in basic medium. The kinetics of the HER reaction was found better in Ni-Ti3C2 MXene composite in basic medium than in acidic medium. The charge transfer resistances were obtained from the EIS plot and were found to be 3.98 Ω and 2.34 Ω for Ti3C2 and Ni-Ti3C2 respectively in acidic medium and 3.12 Ω and 1.98 Ω in basic medium. The low resistance observed for Ni-Ti3C2 in basic medium proves a higher electrocatalytic activity in Ni-Ti3C2 than Ti3C2. The cyclic stability of the Ni-Ti3C2 in basic medium was higher than Ti3C2. Thus the overall results show that the prepared composite is a potential catalyst for HER applications.

Defect-rich 1T-MoS2 nanosheets towards efficient electrochemical hydrogen evolution by simultaneous phase and defect engineering

Molybdenum sulfide (MoS2) has been considered as a promising candidate to replace Pt for the electrochemical hydrogen evolution reaction (HER). However, the disadvantages of inert basal planes and low conductivity limit its application in HER. Herein, we report a facile strategy to achieve simultaneous phase transition and defect engineering in MoS2 by adjusting the ratio of sulfur precursor to molybdenum precursor in the synthesis process. The excess thiourea are adsorbed on the surface of as-formed MoS2 nanocrystallites, which hinders the further crystallization process and creates a large amount of defects on the basal planes. Besides, ammonia ions could in situ insert into the interlayers of MoS2 and induce a phase transition from 2H–MoS2 to 1T-MoS2. The optimized defect-rich 1T-MoS2 catalyst shows a small overpotential of 232 mV at 10 mA cm−2 and Tafel slope of 61 mV dec−1 in acidic media. The superior HER activity is attributed to the defect-rich and 1T-phase structure, which contributes significantly enhanced electronic conductivity and greatly exposed active sites.

MoS2 catalysts with adjustable size and layer structure derived from polyoxometalates-ionic liquids complexes for hydrogen production and hydrogenation

In the period of energy conversion, the effective utilization of fossil fuels and the development of new energy sources are becoming extremely imperative. MoS2 have excellent catalytic activity for fuel hydrogenation and hydrogen production. However, the synthesis of highly dispersed MoS2 that can expose more active sites has been challenging. Herein, (DODA)6Mo7O24 with organic–inorganic core–shell structure was prepared by POMs-ILs (polyoxometalates-ionic liquids) self-assembly. MoS2 with adjustable size and layer structure derived from (DODA)6Mo7O24 by controllable confined-sulfidation effect for hydrogenation and hydrogen evolution reaction (HER). Among them, MoS2 (T280S1:4t30) has the lowest overpotential, and only 200 mV is needed to reach the current density of 10 mA·cm−2. At the same time, it has the optimal hydrogenation performance with the highest selectivity for octahydroanthracene and perhydroanthracene, along with a hydrogenation percentage of 48.04 % in the process of anthracene hydrogenation. Density functional theory demonstrated that the monolayer MoS2 was more favorable for water molecule dissociation and hydrogen molecule activation, which proves that the MoS2 has excellent catalytic activity for HER and hydrogenation simultaneously. This work is instructive for the synthesis of MoS2 and its application in HER and hydrogenation.

MoS2 Nanoflowers Grown on Plasma-Induced W-Anchored Graphene for Efficient and Stable H2 Production Through Seawater Electrolysis.

Herein, it is found that 3D transition metal dichalcogenide (TMD)-MoS2 nanoflowers-grown on 2D tungsten oxide-anchored graphene nanosheets (MoS2 @W-G) functions as a superior catalyst for the hydrogen evolution reaction (HER) under both acidic and alkaline conditions. The optimized weight ratio of MoS2 @W-G (MoS2 :W-G/1.5:1) in 0.5 M H2 SO4 achieves a low overpotential of 78mV at 10mA cm-2 , a small Tafel slope of 48mV dec-1 , and a high exchange current density (0.321mA cm⁻2 ). Furthermore, the same MoS2 @W-G composite exhibits stable HER performance when using real seawater, with Faradaic efficiencies of 96 and 94% in acidic and alkaline media, respectively. Density functional theory calculations based on the hybrid MoS2 @W-G structure model confirm that suitable hybridization of 3D MoS2 and 2D W-G nanosheets can lower the hydrogen adsorption: Gibbs free energy (∆GH* ) from 1.89eV for MoS2 to -0.13eV for the MoS2 @W-G composite. The excellent HER activity of the 3D/2D hybridized MoS2 @W-G composite arises from abundance of active heterostructure interfaces, optimizing the electrical configuration, thereby accelerating the adsorption and dissociation of H2 O. These findings suggest a new approach for the rational development of alternative 3D/2D TMD/graphene electrocatalysts for HER applications using seawater.

Highly porous interconnected MoP decorated graphene oxide as remarkably efficient electrocatalyst

Hydrogen (H2) production through water splitting has less viable applications due to the unfavourable kinetics of the reaction. Electrocatalysts with a robust structure, high levels of catalytic activity, and a high degree of stability are in high demand but challenging. This paper reports the synthesis of highly porous interconnected molybdenum phosphide (MoP) assembled with graphene oxide (GO) to form MoP/RGO hybrid electrocatalysts in a novel phosphorization process at a reasonably low temperature under an argon (Ar) atmosphere by a mixing and heat-treating method for the hydrogen evolution reaction (HER). Bifunctional MoP anchored on reduced graphene oxide (MoP/RGO) porous structures exhibited extra permeability for ion and electrolyte transport. An efficient MoP/RGO-based electrocatalyst exhibited brilliant electrocatalytic performance, having HER overpotential of 96 mV at a current density of 10 mA/cm2 with a low Tafel slope of 64 mV/dec in an alkaline solution. The effectiveness of an optimised electrocatalyst indicates significant HER activity for all intermediate chemical reactions. A highly efficient electrocatalyst also exhibited long-term stability with a minor potential decrease over 24 h. RGO shows great potential as a material possessing remarkable strength in the context of high temperature phosphorization. It effectively hinders particle agglomeration, enhances catalyst conductivity, and ultimately betters both the performance and durability of an electrocatalyst in HER applications.

Revolutionizing water treatment: Exploring the efficacy of MoS2/BN/rGO ternary nanocomposite in organic dye treated water for OER and HER applications

The novelty of the present work is synthesis of 2D layered molybdenum disulfide/boron nitrate/reduced graphene oxide (MoS2/BN/rGO) ternary nanocomposites for the first time through sonication assisted hydrothermal method and explore its suitability for HER/OER applications. Also the performance evaluation was carried out against normal Distilled water as well as MB dye treated water. Flower, disk and layered morphology of MoS2, BN and rGO, respectively was confirmed from field emission scanning electron microscopy (FESEM) images. Microstructural analysis was carried out using high resolution transmission electron microscopy (HRTEM) analysis. The ternary nanocomposite revealed better degradation efficiency about 98 % of degradation against methylene blue (MB) within 45 min and the recycle analysis revealed better stability for 7 cycles. For distilled water, during the oxygen evolution reaction (OER) analysis of ternary nanocomposite showed a less over potential at 0.61 V vs. RHE @ 10 mA/cm2 and Tafel slop was calculated to be 99 mV/dec. In the case of hydrogen evolution reaction (HER), over potential @ 10 mA/cm2 was about −0.044 V vs. RHE and the Tafel slop was observed to be 115 mV/dec. The photocatalytic treated waste water was examined for both HER and OER analysis where the potential at 10 mA was about −0.422 V and 1.96 V vs. RHE, for HER and OER, respectively. Further, the Tafel slop of both HER and OER was calculated to be 290 mV/dec and 121 mV/dec, respectively. The chronoamperometry analysis confirmed better stability of the ternary nanocomposite of MoS2/BN/rGO for a period of 12 h.

Investigating into the intricacies of charge storage kinetics in NbMn-oxide composite electrodes for asymmetric supercapacitor and HER applications

In this paper, we present an effortless hydrothermal method for depositing niobium and manganese composite oxides onto Ni-foam. The formation of the desired NbMn-oxide phase is confirmed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analytical tools. In the study, we systematically investigated the effect of varying Mn concentrations on the physicochemical properties and energy storage performance of the NbMn-oxide composite. The NbMn-oxide exhibited nanoplates assembled from sphere-shaped structures along with irregularly shaped rectangular blocks of nano/micro-structures, forming a porous framework. The electrode with an Mn concentration of 0.02 M displayed an areal capacitance of approximately 5987.8 mF/cm2 and an energy density of 0.13 mWh/cm2, even at a high current density of 10 mA/cm2. Additionally, the hydrogen evolution reaction (HER) performance of the NbMn-oxide composite electrode was evaluated and it exhibited an overpotential of 86 mV to achieve a current density of 10 mA/cm². The electrode also displayed stable performance for approximately 7 h, with only a slight increase in overpotential from − 0.218 to − 0.263 V against the reversible hydrogen electrode (RHE) during the stability test. The investigation of charge storage kinetics revealed the dominance of the diffusion process over the capacitive process, with the quasi-reversible redox reactions in the composite metal-oxides responsible for the high electrochemical performance. The assembled asymmetric supercapacitor device, utilizing NbMn-2 (positive) and activated carbon (negative) electrodes, demonstrated an impressive energy density of 0.20 mWh/cm2 at a power density of 3.75 mW/cm2, coupled with exceptional cyclability (97%). These findings highlight the potential of Nb-based composite electrodes for both supercapacitor and HER water-splitting applications and underscore their significant potential for electrochemical energy conversion and storage.

Heterostructure engineering of MoS2/Mo2CTx nanoarray via molten salt synthesis for enhanced hydrogen evolution reaction

Two-dimensional layered transition metal carbides (MXenes), have huge potential advantage for applications in hydrogen evolution reaction (HER). However, the hindered hydrogen evolution at large current densities and the instability of MXenes during HER remains major challenges. Herein, we report the MoS2/Mo2CTx nanoarray with aerophobic structure via molten salt synthesis. In situ vertical distribution of MoS2 nanoarray on the surface of Mo2CTx accelerates hydrogen gas release from the electrode, exhibiting significantly enhanced catalytic activity and stability to bare MoS2 and Mo2CTx. The MoS2/Mo2CTx nanoarray possesses excellent stability at −100 mA/cm2 for 100 h with only 3% overpotential increase. Our work provides guidance for developing high-stability MXene-based catalysts by virtue of in situ bonding between nanoarray and MXene.

Hierarchical BiFeO3/Cr2CTx MXene composite as a multifunctional catalyst for hydrogen evolution reaction and as an electrode material for energy storage devices

A multifunctional hierarchical Bismuth ferrite/chromium carbide (BiFeO3/Cr2CTx) MXene has been employed as both electrode material for supercapacitors as well as an electrocatalyst for electrocatalytic water splitting. Here, a facile method is suggested for synthesizing Cr2CTx MXene from the chromium aluminum carbide (Cr2AlC) MAX Phase. X-ray diffraction studies, Scanning electron microscopy, and high-resolution transmission electron microscopy indicate that the aluminum atomic layers are removed from Cr2AlC MAX structure. The electrochemical test reveals that the BiFeO3/Cr2CTx MXene composite, which is produced with less Al2O3, performs well in the hydrogen evolution reaction (HER) with a low overpotential of 128 mV in 1 M potassium hydroxide. 53.3 mV dec−1, and 0.16 Ω cm−2, respectively, are the values of the calculated Tafel slope and charge transfer resistance. In a dielectrode electrolysis system, BiFeO3/Cr2CTx MXene electrode needs only 1.81 V of cell potential to provide 10 mA cm−2 with long-term stability. The specific capacity of 671.2 C g−1 at a current density of 1 A g−1 is obtained for BiFeO3/Cr2CTx MXene electrode with 90% capacitance retention after 3000 cycles. The potential use of BiFeO3/Cr2CTx MXene towards HER and supercapacitor application is demonstrated by this study, which offers a gentle path for the fabrication of Cr2CTx MXene composites for energy storage and HER applications.