Significant improvement of photocatalytic hydrogen generation rate over TiO2 with deposited CuO

TiO₂ photocatalyst with deposited CuO (CuO-TiO₂) was synthesized by the impregnation method using P25 (Degussa) as support, and exhibited high photocatalytic hydrogen generation activity from methanol/water solution. A substantial hydrogen evolution rate of 10.2 ml min⁻¹ (18,500 μmol h⁻¹ g⁻¹_catalyst) was observed over this efficient CuO-TiO₂ with optimal Cu content of 9.1 mol% from an aqueous solution containing 10 vol% methanol; this improved hydrogen generation rate is significantly higher than the reported Cu-containing TiO₂, including some Pt and Pd loaded TiO₂. Optimal Cu content of 9.1 mol% provided maximum active sites and allowed good light penetration in TiO₂. Over this efficient CuO-TiO₂, the hydrogen generation rate was accelerated by increasing the methanol concentration according to Freundlich adsorption isotherm. However, the photocatalytic hydrogen generation rate was suppressed under long time irradiation mainly due to accumulation of by-products, reduction of CuO and copper leaching, which requires further investigation.     

Tuning of electrocatalytic activity of mixed metal dichalcogenides supported NiMoP coatings for alkaline hydrogen evolution reaction

The mixed metal dichalcogenides combination of WS₂–MoS₂ was coated onto Cu substrate by electroless NiMoP plating technique and the electrocatalytic hydrogen evolution reaction (HER) performance was investigated. The enhanced structural, morphological parameters and boosted electrocatalytic performance of the various metal-metal molar ratio of WS₂–MoS₂ onto NiMoP plate were identified under variable operating conditions and it was successfully evaluated by various characterization techniques. The well-defined crystalline nature, phase, particle size, structure, elemental analysis and surface morphology of prepared coatings were analyzed by FESEM, XRD, AFM and EDS mapping. The electrochemical analysis was performed using open circuit potential (OCP) analysis, chronoamperometry (CA), electrochemical impedance spectroscopy (EIS), Tafel curves, linear sweep voltammetry (LSV), cyclic voltammetry (CV) and polarization studies to find the activity of prepared electrocatalyst towards electrochemical hydrogen evolution reactions. The performance of bare NiMoP and WS₂–MoS₂/NiMoP plates were compared and found that the HER activity of NiMoP can be reinforced by composite incorporation through the synergic effect arises with in the catalytic system, which improves surface roughness and enhances the magnitude of electrocatalyst toward HER. The achievement of enhanced catalytic performance of coatings was authenticate by the kinetic parameters such as decreases in Tafel slope (98 mV dec^?1), enhanced exchange current densities (9.32 × 10^?4 A cm^?2), and a lower overpotential. The consistent performance and durability of the catalyst were also investigated. The enhanced electrocatalytic activity of WS₂–MoS₂/NiMoP coatings increased with respect to the surface-active sites associated with combination of mixed dichalcogenides and the synergic effect arises in between different components present in the coating system. This work envisages the progressive strategies for the economical exploration of a novel WS₂–MoS₂/NiMoP water splitting catalyst used for large scale H₂ generation. The prepared WS₂–MoS₂/NiMoP embedded Cu substrate possess high catalytic activity due to its least overpotential of 101 mV at a benchmark current density of 10 mA cm^?2, which demonstrated the sustainable, efficient and promising electrocatalytic property of prepared catalyst towards HER under alkaline conditions.     

Improved energy conversion and storage performance enabled by hierarchical zigzag-like P-doped CuCo2O4 nanosheets based 3D electrode materials

Developing a bi-functional material which can meet both electrochemical water splitting and supercapacitors (SCs) is a hot spot in current research. In this study, hierarchical zigzag-like phosphorus doped CuCo₂O₄ nanosheets based 3D electrode materials were successfully synthesized via a hydrothermal method and followed by thermal treatment. Since the unique morphology of 2D nanosheets with zigzag-like edges could provide more reactive sites, which is not only conducive to the hydrogen evolution reaction (HER), but also conducive to the electrochemical energy storage. Meanwhile, the doping of phosphorus was adopted to improve the conductivity, which would further enhance the electrochemical properties of CuCo₂O₄. Thereafter, its performance for HER and SCs in 1 M KOH were systematically investigated. As an electrode for HER, it only required a low overpotential of 152 mV to reach 10 mA cm^?2 with a Tafel slope of 115.7 mV dec^?1. Furthermore, I-t test result showed an excellent stability. As an electrode for SCs, it exhibited a high specific capacity of 896.9C g^?1 at 1 A g^?1 in three-electrode system. All in all, the obtained hierarchical zigzag-like phosphorus doped CuCo₂O₄ nanosheets provided a feasible route for the design of bi-functional electrode materials both for energy conversion and storage.     

Enhanced hydrogen evolution reaction on highly stable titania‐supported PdO and Eu2O3 nanocomposites in a strong alkaline solution

In this work, PdO/TiO₂ and Eu₂O₃/TiO₂ nanocomposites (NCs) were synthesized using a new facile, template‐free, and one‐step solvothermal approach and characterized by several instrumentation techniques. X‐ray photoelectron spectroscopy studies revealed the presence of oxidized form of the Pd and Eu nanoparticles within the NC materials (PdO and Eu₂O₃). The two catalysts exhibited remarkable activity for the hydrogen evaluation reaction (HER) in a strong alkaline solution (4.0 M NaOH) with PdO/TiO₂ catalyst being the best, which recorded an exchange current density (j_o) of 0.26 mA cm^?2 and a Tafel slope (β_c) of 125 mV dec^?1. Such parameters are not far from those recorded for a commercial Pt/C catalyst (0.71 mA cm^?2 and 120 mV dec^?1) performed here under the same operating conditions. Eu₂O₃/TiO₂ catalyst recorded j_o and β_c values of 0.05 mA cm^?2 and 135 mV dec^?1. The Tafel slopes 125 and 135 mV dec^?1 calculated on the PdO/TiO₂ and Eu₂O₃/TiO₂ catalysts suggest a HER kinetics controlled by the Volmer step. PdO/TiO₂ catalyzed the HER with a high turnover frequency of 2.3 H₂/s at 0.2 V versus the reversible hydrogen electrode, while Eu₂O₃/TiO₂ catalyst only measured a turnover frequency value of 1.25 H₂/s at the same overpotential. The two catalysts exhibited excellent stability and durability after 10 000 cycles and 72 hours of controlled potential electrolysis at a high cathodic overpotential, reflecting their practical applicability. Scanning electron microscope and X‐ray photoelectron spectroscopy examinations revealed that the morphology and chemistry of both catalysts were not altered as a result of the performed long‐term stability and durability tests.     

Trace amounts of palladium-doped hollow TiO2 nanosphere as highly efficient electrocatalyst for hydrogen evolution reaction

Hollow titanium dioxide (TiO₂–H) sphere and Pd@TiO₂–H core-shell were successfully synthesized through hydrothermal method, and their electrocatalytic properties for hydrogen evolution reaction (HER) were evaluated The 0.05 wt%Pd@TiO₂–H achieved the lowest overpotential of 0.43V at 10 mA cm^?2 with a Tafer slope of 63 mV dec^?1, which were both apparently outperforming than that of the commercial TiO₂ (0.92 V, 636 mV dec^?1). Electrochemical stability was also confirmed by a negligible attenuation for polarization curves before and after 5000 cycles. The attractive performance can be attributed to the special hollow structural and Pd doping effect resulting in the increased amount of active sites. This study provides a special material to develop lower cost, more stable and efficient titanium oxide based electrocatalysts for HER.     

Enhanced photocatalytic activity in water splitting for hydrogen generation by using TiO2 coated carbon fiber with high reusability

In this study, TiO₂ coated carbon fiber (TiO₂@CF) was synthesized and used for the improvement of hydrogen (H₂) evolution. Obtained results from scanning electron microscopy (SEM), X-ray diffraction (XRD), gas adsorption analysis (BET), UV–vis diffuse (UV–vis), and X-ray photoelectron spectroscopy (XPS) confirmed that the surface area and light absorption of the material was significantly improved. The synthesized TiO₂@CF photocatalyst exhibited improved photocatalytic performance toward hydrogen generation. The enhancement of photocatalytic H₂ evolution capacity by TiO₂@CF was ascribed to its narrowed bandgap energy (2.76eV) and minimized recombination of photogenerated electron-hole pairs The hydrogen production rate by the TiO₂@CF reached 3.238 mmolg^?1h^?1, which was 4.8 times higher than unmodified TiO₂ (0.674 mmolg^?1h^?1). The synthesized TiO₂@CF was relatively stable with no distinct reduction in photocatalytic activity after five recycling runs. The photoluminescence and photocurrent were employed to support the photocatalytic H₂ production mechanism proposed mechanism.Based on these results, TiO₂@CF with unique properties, easy handle, and high reusability could be suggested as an efficient strategy to develop a high-performance photocatalyst for H₂ production.     

Electrocatalytic performances of oxygen-deficient titanium dioxide nanosheet coupled palladium nanoparticles for oxygen reduction and hydrogen evolution reactions

The development of multifunctional electrocatalysts is crucial for enhancing the efficiency of electrochemical conversion in energy devices. Here we have synthesized TiO_2-x nanosheets (NSs) supported metallic Pd nanoparticles (Pd/TiO_2-x NSs) as an electrocatalyst using a simple impregnation process. High electrochemical surface areas (ECSAs) and strong metal support interactions (SMSI) of the electrocatalyst showed improved ORR performance throughout a wide pH range under ambient conditions. The outstanding durability of the catalyst was proven by the square-wave potential cycling experiment at 60 °C. Additionally, it was shown that Pd/TiO_2-x NSs showed improved HER activity and stability in 0.5 M H₂SO₄. The catalyst had an overpotential of 19.5 mV for the 10 mA cm⁻² and a low Tafel slope of 41 mV dec⁻¹. The catalyst also showed higher stability for about 30 h in HER performance. This work will help in rationally building nanostructured electrocatalysts loaded on carbon-free support for efficient electrochemical energy storage devices.     

Heterostructured two dimensional materials of MXene and graphene by hydrothermal method for efficient hydrogen production and HER activities

Recent development on two-dimensional (2D) heterostructured graphene and MXene materials were explored for electrochemical water splitting hydrogen evolution reaction (HER) activity. The hybrid MXene/reduced graphene oxides as two-dimensional (2D) hybrid structures were prepared by facile hydrothermal techniques at 150 °C with MXene and RG hybrid layered composites. As-prepared electrocatalytic active materials have been confirmed through structural and surface morphological studies such as XRD, RAMAN, FT-IR and SEM analysis. The prepared 2D materials were carried out for HER activities due to attractive conductivity and mass transfer process. HER performance were tested from linear sweep voltammetry (LSV) cures. The prepared MX, RG and MX@RG hybrid electrocatalyst exhibited overpotential values as observed as 220 mV, 193 mV, 121 mV respectively at 10 mAcm^?2 cathodic on set. MX@RG hybrid heterostructure exhibited enhanced HER action with lowest overpotential (η = 121 mV) and good H₂ productions as an active future electrocatalyst for energy storage and conversion applications.     

Ni3Mo3N coupled with nitrogen-rich carbon microspheres as an efficient hydrogen evolution reaction catalyst and electrochemical sensor for H2O2 detection

Hydrogen evolution reaction (HER) and electrochemical analysis are two important fields of electrochemical research at present. We found that both HER and some electrochemical analytical reactions relied on the concentration of hydrogen ions (H⁺) in solution, so we intended to develop an electrode material that is sensitive to H⁺ and can be used for both HER and some electrochemical analyses. In this work, we synthesized Ni₃Mo₃N coupled with nitrogen-rich carbon microspheres (Ni₃Mo₃N@NC MSs) as highly efficient electrode material for HER and detection of Hydrogen peroxide (H₂O₂), which plays an important role in physiological processes. Here the aniline was used as the nitrogen and carbon sources to synthesize Ni₃Mo₃N@NC. The Ni₃Mo₃N@NC MSs showed high performance for HER in 1 M KOH solution with a small overpotential of 51 mV at 10 mA cm^?2 and superior stability. For H₂O₂ detection, a detection limit of 1 μM (S/N = 3), sensitivity of 120.3 μA·mM^?1 cm^?2 and linear range of 5 μM–40 mM can be achieved, respectively. This work will open up a low-cost and easy avenue to synthesize transition metal nitrides coupled with N-doped carbon as bifunctional electrode material for HER and electrochemical detection.     

Stable and high-performance N-micro/mesoporous carbon-supported Pt/Co nanoparticles-GDE for electrocatalytic oxygen reduction in PEMFC

The current research presented a novel type of stable and high-performance electrocatalyst for oxygen reduction reaction (ORR). For this purpose, N-micro/mesoporous carbon-supported Pt/Co nanoparticles (NPs) were synthesized through a two-step procedure. The Co–N-micro/mesoporous carbon support was first prepared by the direct carbonization of zeolitic imidazolate framework-67 (ZIF-67). Next, the N-micro/mesoporous carbon-supported Pt/Co NPs were synthesized by galvanic replacement of Pt (IV) ions with Co nanoparticles. The surface properties and chemical structure of the prepared electrocatalyst were measured by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), N₂ adsorption-desorption, energy dispersive spectrometry (EDS) techniques. The results confirmed the desirable properties of the prepared electrocatalyst which enhanced the ORR kinetic. The ORR performance of the prepared electrocatalyst was examined utilizing the catalyst coated membrane electrode (CCME) in the homemade half-cell. The ORR performance of N-micro/mesoporous carbon-supported Pt/Co NPs loaded on the gas diffusion electrode (Pt/Co-NC-GDE) was evaluated in an acidic solution. The electrochemical tests exhibited the superior current density and power density of the Pt/Co-NC-GDE (?58.7 mAcm^?2 at 0.3 V/RHE and 17.6 mW cm^?2) compared to those of Pt/C-GDE (?43.7 mAcm^?2, and 13.1 mW cm^?2). Furthermore, durability tests indicated the higher stability of Pt/Co-NC-GDE than Pt/C-GDE.     

MoS2-supported on free-standing TiO2-nanotubes for efficient hydrogen evolution reaction

The electrochemical production of hydrogen is a promising and flexible approach towards the conversion of intermittent renewable energy sources into clean chemical fuel. However, low-cost, efficient, and durable electrocatalysts are yet to be developed to attain economies of scale in hydrogen generation. In this study, we fabricated highly ordered free-standing TiO₂ nanotube arrays (TiO₂-NTs), by simply anodizing Ti foils. The tube length, diameter, wall thickness, and surface structure of the TiO₂-NTs can be controlled by adjusting the anodization conditions. Subsequently, we synthesized and supported MoS₂ layers on free-standing TiO₂-NTs as an active material for the hydrogen evolution reaction (HER), using a slow evaporation method. The layers of MoS₂ uniformly disperse on the entire surface of the TiO₂-NTs composite. The electrochemical test shows that the MoS₂-supported free-standing (MoS₂/TiO₂-NTs) system exhibits excellent HER performance in acidic media with a low overpotential at 10 mA cm⁻² (170 mV), as well as small Tafel slope (70 mV decade⁻¹). Also, the MoS₂/TiO₂-NTs displays superior durability for HER after 5000 continuous potential cycles between −0.4 and + 0.2 (V vs. RHE). Our results demonstrate the potential application of MoS₂/TiO₂-NTs composite for cost-effective electrochemical production of hydrogen.     

Chemically and thermally reduced graphene oxide supported Pt catalysts prepared by supercritical deposition

Reduced graphene oxide (RGO) is used in many energy applications, especially in Polymer Electrolyte Membrane (PEM) fuel cells, as carbon sourced catalyst support materials. In this study, thermally (T-RGO) and chemically (C-RGO) reduced GO support materials were synthesized for utilization in PEM fuel cells. Pt catalysts were synthesized using supercritical carbon dioxide (SCCO₂) deposition technique over synthesized support materials. Physical (BET, SEM-EDX, FTIR, RAMAN, XRD, TEM, ICP-MS and optical tensiometer) and electrochemical (CV, PEM fuel cell test) characterizations of synthesized support materials and corresponding Pt catalysts were performed. The differences between the structures of thermally and chemically reduced graphene oxide supports and their Pt catalysts were investigated. The ECSA values of the Pt/T-RGO and Pt/C-RGO catalysts are 19.86 m² g^?1 and 6.31 m² g^?1, respectively. The current and power density values of the Pt/T-RGO and Pt/C-RGO catalysts at 0.6 V are 84 mA cm^?2, 80 mA cm^?2 and 50 mW cm^?2, 45 mW cm^?2, respectively. Pt/T-RGO and Pt/C-RGO catalysts showed similar trend in PEMFC environment.     

Simple synthesis of honeysuckle-like CuCo2O4/CuO composites as a battery type electrode material for high-performance hybrid supercapacitors

In this paper, porous CuCo₂O₄/CuO composites with novel honeysuckle-like shape (CuCo₂O₄/CuO HCs) have been prepared for the first time by a simple hydrothermal method and followed with an additional annealing process in air. The unique CuCo₂O₄/CuO HCs consisted of dense and slender petals with length of 1.3–1.5 μm and width of about 50 nm, and possessed a specific surface area of 36.09 m² g^?1 with main pore size distribution at 10.63 nm. When used as the electrode materials for supercapacitors, the CuCo₂O₄/CuO HCs exhibited excellent electrochemical performances with a high specific capacity of 350.69 C g^?1 at 1 A g^?1, a rate capability of 78.6% at 10 A g^?1, and 96.2% capacity retention after 5000 cycles at a current density of 5 A g^?1. In addition, a hybrid supercapacitor (CuCo₂O₄/CuO HCs//AC HSC) was assembled using the CuCo₂O₄/CuO HCs as positive electrode and activated carbon (AC) as negative electrode. The HSC device delivered a specific capacity of 187.85 C g^?1 at 1 A g^?1 and a superior cycling stability with 104.7% capacity retention after 5000 cycles at 5 A g^?1, and possessed a high energy density of 41.76 W h kg^?1 at a power density of 800.27 W kg^?1. These outstanding electrochemical performances manifested the great potential of CuCo₂O₄/CuO HCs as a promising battery-type electrode material for the next-generation advanced supercapacitors with high-performance.     

Dysprosium doped copper oxide (Cu1-xDyxO) nanoparticles enabled bifunctional electrode for overall water splitting

The production of hydrogen, a favourable alternative to an unsustainable fossil fuel remains as a significant hurdle with the pertaining challenge in the design of proficient, highly productive and sustainable electrocatalyst for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Herein, the dysprosium (Dy) doped copper oxide (Cu_1-xDy_xO) nanoparticles were synthesized via solution combustion technique and utilized as a non-noble metal based bi-functional electrocatalyst for overall water splitting. Due to the improved surface to volume ratio and conductivity, the optimized Cu_1-xDy_xO (x = 0.01, 0.02) electrocatalysts exhibited impressive HER and OER performance respectively in 1 M KOH delivering a current density of 10 mAcm^?2 at a potential of ?0.18 V vs RHE for HER and 1.53 V vs RHE for OER. Moreover, the Dy doped CuO electrocatalyst used as a bi-functional catalyst for overall water splitting achieved a potential of 1.56 V at a current density 10 mAcm^?2 and relatively high current density of 66 mAcm^?2 at a peak potential of 2 V. A long term stability of 24 h was achieved for a cell voltage of 2.2 V at a constant current density of 30 mAcm^?2 with only 10% of the initial current loss. This showcases the accumulative opportunity of dysprosium as a dopant in CuO nanoparticles for fabricating a highly effective and low-cost bi-functional electrocatalyst for overall water splitting.     

The effect of annealing temperature,reaction time,and cobalt precursor on the structural properties and catalytic performance of CoS2 for hydrogen evolution reaction

In this study, cobalt disulfide (CoS₂) nanostructures are synthesized using a simple hydrothermal method. The effects of experimental parameters including cobalt precursor, reaction times, and reaction temperatures are investigated on the structure, morphology and electrocatalytic properties of CoS₂ for hydrogen evolution reaction (HER). The characterization of as-prepared catalysts is performed using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR), and X-ray photoelectron spectroscopy (XPS). The HER efficiency of the catalysts is examined using linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) methods in 0.5 M H₂SO₄ solution. Furthermore, chronoamperometry (CA) is used for stability evaluation. The catalyst obtained from cobalt acetate precursor, within 24 h at 200 °C exhibits superior electrocatalytic activity with a low onset potential (139.3 mV), low overpotential (197.3 mV) at 10 mA. cm^?2 and a small Tafel slope of 29.9 mV dec^?1. This study is a step toward understanding the effect of experimental parameters of the hydrothermal method on HER performance and developing optimal design approaches for the synthesis of CoS₂ as a common electrocatalyst.     

High electrochemical performance of PANI/CdO nanocomposite based on graphene oxide as a hybrid electrode materials for supercapacitor application

In the last decade, the production of clean and sustainable energy sources for energy storage purposes have grown dramatically due to the population growth and increasing demand for energy in the world. In this regard, supercapacitors have proved to be promising candidates in energy storage applications. Therefore, in this study, polyaniline/cadmium oxide/graphene oxide (PANI/CdO/GO) nanocomposite was prepared by co-precipitation method to evaluate the electrochemical performance. The structural and surface properties, morphology and particle size distribution were analyzed by XRD diffraction spectroscopy (XRD), field emission scanning electron microscope (FESEM), transmission electron microscope (TEM), N₂ adsorption-desorption, and Fourier transform infrared spectroscopy (FT-IR). Furthermore, the synthesized nanocomposite was applied as an active electrode material and its performance was investigated by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS) in terms of energy storage. The results of these tests confirmed that PANI/CdO/GO nanocomposite provides great electrochemical behavior, including specific capacity of 647 F g^?1, energy density of 116.6 W h kg^?1, power density of 388 W kg^?1 compared to the other electrode. According to the stability test, the initial capacity maintenance was about 82% after 500 charge-discharge cycles, which indicated relatively good electrochemical stability. Moreover, the impedance spectroscopy studies showed that the nanocomposite possessed much lower internal strength and charge transfer reaction resistance in comparison to the other synthesized materials. Based on these results, it was found that the prepared nanocomposite has a good performance in the field of energy storage.     

Ru/MoO2 decorated on CNT networks as an efficient electrocatalyst for boosting hydrogen evolution reaction

Generally, electrochemical hydrogen evolution reaction (HER) is hampered by slow kinetics and low round-trip efficiency. Electrocatalysts with a hierarchical structure and large surface area are expected to overcome these problems. Herein, we prepared a Ru/MoO₂/carbon nanotubes (RMC) hybrid with a hierarchical structure by a convenient solid-phase reaction (SPR) method, and studied the electrochemical activity for HER. After annealing as-prepared RuO₂/MoO₂/carbon nanotubes (ROMC) precursor in a tubular furnace under Ar atmosphere, RuO₂ and MoS₂ were in-situ transformed into Ru metal and MoO₂ phase by the redox SPR. Through various tests, we have confirmed that the new formed Ru metal and MoO₂ phase are combined and uniformly coated on the outer surface of CNTs. Interestingly, the RMC-500 exhibits the best HER performance with a low overpotential of 16 mV at l0 mA cm^?2, small Tafel slope of 45 mV dec^?1, higher electrochemical active surface area, and long-time durability in alkaline electrolyte.     

Crystalline ZnO and ZnO/TiO2 nanoparticles derived from tert-butyl N-(2 mercaptoethyl)carbamatozinc(II) chelate: Electrocatalytic studies for H2 generation in alkaline electrolytes

A newly synthesized zinc(II) complex, namely tert-butyl N-(2 mercaptoethyl)carbamatozinc(II) complex [Zn(Boc-S)₂] (Boc = tert-butyl N-[2-mercaptoethyl]carbamate), has been used as an organozinc precursor for the production of crystalline ZnO and ZnO/TiO₂ nanoparticles. The synthesized complex and the obtained nanomaterials were fully characterized using various spectroscopic and surface analysis techniques. Their surface morphology, chemical purity and stoichiometry have been investigated by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) as well as X-ray fluorescence. The synthesized Zn(II) molecular complex, ZnO and ZnO/TiO₂ nanomaterials have been tested in alkaline aqueous solution (1.0 MNaOH) for the hydrogen evolution reaction (HER) using various electrochemical techniques. The results revealed high HER catalytic performance of ZnO and ZnO/TiO₂ cathode materials, with the latter exhibiting higher catalytic activity recording an exchange current density (j_o) of 0.3 mA cm⁻². This current value, which approaches that of Pt wire (0.5 mA cm⁻²), cross-sectional area ~0.008 cm², is about 11 and 100 times greater than those measured for ZnO alone (0.028 mA cm⁻²) and TiO₂ alone (0.0032 mA cm⁻²), respectively. Moderate catalytic activity was recorded for the complex catalyst, namely GC-Zn(Boc-S)₂ with j_o value of (0.01 mA cm⁻²). Tafel slope values of 130 and 122 mV dec⁻¹ were calculated for ZnO and ZnO/TiO₂, respectively. Such Tafel slope values, which are close to that of the Pt wire (120 mV dec⁻¹), referred to a Volmer-controlled HER kinetics. Other important electrochemical parameters describing the kinetics of the HER, such as roughness factor (R_f) and turnover frequency (TOF) were also estimated and discussed. The high numerical values of the various HER kinetic parameters recorded for the ZnO/TiO₂ catalyst, in addition to its high stability and durability (stable for up to 10 000 continuous cathodic polarization cycles), besides maintaining its morphology and chemical composition after stability test (confirmed from SEM/EDX and XRD examinations), located it in a privileged position among the most efficient HER electrocatalysts reported in the literature.     

Synthesis and electrocatalytic activity of Ni0.85Se/MoS2 for hydrogen evolution reaction

Recently, the replacement of expensive platinum-based catalytic materials with non-precious metal materials to electrolyze water for hydrogen separation has attracted much attention. In this work, Ni_0.85Se, MoS₂ and their composite Ni_0.85Se/MoS₂ with different mole ratios are prepared successfully, as electrocatalysts to catalyze the hydrogen evolution reaction (HER) in water splitting. The result shows that MoS₂/Ni_0.85Se with a molar ratio of Mo/Ni = 30 (denoted as M30) has the best catalytic performance towards HER, with the lowest overpotential of 118 mV at 10 mA cm⁻², smallest Tafel slope of 49 mV·dec⁻¹ among all the synthesized materials. Long-term electrochemical testing shows that M30 has good stability for HER over at least 30 h. These results maybe due to the large electrochemical active surface area and high conductivity. This work shows that transition metal selenides and sulfides can form effective electrocatalyst for HER.     

Exfoliated colloidal MoS2 nanosheet with predominantly 1T phase for electrocatalytic hydrogen production

Exfoliated colloidal MoS₂ nano sheets with a size alternating from 5 to 10 nm have been successfully synthesized. The synthesis is accomplished through the formation of MoS₂/TiO₂ heterostructure containing single or weakly bounded 2–3 layer MoS₂ sheets coated on 10–15 nm TiO₂ nanoparticles, followed by selective removal of TiO₂ from the MoS₂/TiO₂ heterostructure. The synthesized sheets contain predominantly 1T phase (80%) with 2H phase. The electrochemical assessment demonstrates that colloidal MoS₂ nano sheets exhibits outstanding performance in electrocatalytic hydrogen evolution reaction (HER) with a very low Tafel slope of 56 mV/dec, low onset overpotential, and excellent cycling stability in acidic media. This process also offers a one-pot method for the large scale production of 1T-MoS₂ in its nano dimension.