Computational studies of electrochemical CO2 reduction on chalcogen doped Cu4 cluster

By use of the theoretical method of density functional theory (DFT), we systemically investigate the chalcogen doped Cu₄ metal clusters (Cu₄O, Cu₄S, and Cu₄Se) as catalysts for the electrochemical CO₂ reduction with toluene as solvent. These doped clusters have efficient catalytic properties which can reduce CO₂ to CH₄ and a small amount of CH₃OH. In the case of CO₂ hydrogenation to CH₄, the reaction barrier of the Cu₄O cluster and Cu₄S cluster are reduced by 0.37 eV and 0.15 eV, respectively, compared with the pristine Cu₄ cluster. The calculation results also show the overpotentials for the CO₂ hydrogenation to CH₄ in the order of Cu₄S < Cu₄O < Cu₄Se. In?addition, the geometry structures, the electronic properties, and the reaction free energies on the chalcogen doped Cu₄ clusters are also discussed to further reveal the reaction mechanism in the CO₂ electroreduction process. We hope that our present work will enlighten extensive studies on the modified electrode to decrease the limiting potential and provide a reference for the subsequent studies.     

Mo2C embedded on nitrogen-doped carbon toward electrocatalytic nitrogen reduction to ammonia under ambient conditions

Electrochemical nitrogen reduction reaction (e-NRR) is an attractive prospect for ammonia production under mild conditions using renewable energy. However, developing efficient and stable electrocatalysts for driving e-NRR remains a great challenge. Herein, inspired by the biological nitrogen fixation via active Mo-nitrogenase, molybdenum carbide on N-doped porous carbon (Mo₂C/NC) derived from Mo/Zn-ZIFs was developed for the first time, as an efficient e-NRR electrocatalyst under ambient conditions. In 0.1 M Na₂SO₄ electrolyte, the Mo₂C/NC catalyst achieved a maximum NH₃ yield rate of 70.6 μmol h^?1 g_cat.^?1 and a faradaic efficiency of 12.3% at ?0.2 V vs. RHE. Additionally, Mo₂C/NC displayed favorable electrochemical selectivity and durability during the longtime electrolysis, attributed to the structural and electrochemical stability of Mo₂C and ZIFs-derived carbon framework. This work provides new perspectives upon metal carbides and their compounds as catalysts for efficient e-NRR.     

Single transition metal atom anchored on g-C3N4 as an electrocatalyst for nitrogen fixation: A computational study

Electrocatalytic nitrogen reduction reaction (NRR) provides a green and sustainable way to produce ammonia at ambient conditions. The key to realize highly efficient NRR is the catalysts. To design highly active electrocatalysts for NRR, the multistep mechanism involved in NRR must be clearly unraveled. Herein, single V atoms anchored on g-C₃N₄ is identified to be an efficient electrocatalyst for NRR by screening single 3d transition metal (TM = Sc to Zn) atoms anchored by g-C₃N₄ (TM@g-C₃N₄) through density functional theory calculations. NRR takes place on V@g-C₃N₄ preferentially through distal path with a relatively low limiting potential of ?0.55 V. The outstanding NRR performance of V@g-C₃N₄ is found from the peculiar electronic structure of V after anchored in the six-fold cavity of g-C₃N₄ and the good transmitter role of V for electron transfer between N_xH_y species and g-C₃N₄. Moreover, the formation energy and dissolution potential indicate that V@g-C₃N₄ is thermodynamically and electrochemically stable and the aggregation of V atoms is unfavorable thermodynamically, signifying that the synthesis of V@g-C₃N₄ is feasible in experiments. Our work screens out a superior noble metal-free NRR electrocatalyst and will be helpful for the development of ambient artificial nitrogen fixation.     

Heterostructured Co3O4/VO2 nanosheet array catalysts on carbon cloth for hydrogen evolution reaction

Developing highly efficient, low-cost, and robust water splitting hydrogen production catalysts is critical for hydrogen energy applications. This study presents the synthesis of Co₃O₄/VO₂ heterogeneous nanosheet structures on carbon cloth (Co₃O₄/VO₂/CC). The obtained Co₃O₄/VO₂/CC hybrid catalyst has a low overpotential of 108 mV at a current density of 10 mA cm^?2, a Tafel slope of 98 mV dec^?1, and high stability in 1.0 M KOH for 10 h. The experimental results and density functional theory (DFT) calculations results also show that Co₃O₄ coupled with VO₂ in Co₃O₄/VO₂/CC can optimize hydrogen adsorption energy and facilitate electron transport, thereby accelerating the catalytic kinetics for hydrogen evolution reaction (HER). This work also provided an alternative method to design and construct non-noble metal oxide-based catalysts for alkaline hydrogen production.     

Facile fabrication of mesoporous carbon nanofibers with unique hierarchical nanoarchitecture for electrochemical hydrogen storage

A colloidal silica incorporated porous anodic aluminum oxide (AAO) was utilized as a dual-template to prepare mesoporous carbon nanofibers (MCNFs). Such a strategy is simple because it takes advantage of commercially available materials (i.e., colloidal silica and AAO) and the templates can be removed in one step. The as-prepared MCNF shows a hierarchical nanostructure consisting of open macroporous channel connected with large mesopores and micropores. As a result of the large surface area and unique hierarchical nanoarchitecture which facilitates fast mass and electron transport, the MCNF reveals a discharge capacity of 679 mA h g⁻¹ at 25 mA g⁻¹. This value is significantly greater than that (i.e., 394 mA h g⁻¹) observed for an ordered mesoporous carbon (OMC) with a similar specific surface area. Furthermore, at 3000 mA g⁻¹, the MCNF demonstrates a discharge capacity of 585 mA h g⁻¹, which is about twice that (i.e., 256 mA h g⁻¹) of the OMC.     

Fe(III) grafted MoO3 nanorods for effective electrocatalytic fixation of atmospheric N2 to NH3

Electrocatalytic nitrogen reduction reaction (ENRR) offers a carbon-neutral process to fix nitrogen into ammonia, but its feasibility depends on the development of highly efficient electrocatalysts. Herein, we report that Fe ion grafted on MoO₃ nanorods synthesized by an impregnation technique can efficiently enhance the electron harvesting ability and the selectivity of H⁺ during the NRR process in neutral electrolyte. In 0.1 M Na₂SO₄ solution, the electrocatalyst exhibited a remarkable NRR activity with an NH₃ yield of 9.66 μg h^?1 mg^?1_cat and a Faradaic efficiency (FE) of 13.1%, far outperforming the ungrafted MnO₃. Density functional theory calculations revealed that the Fe sites are major activation centers along the alternating pathway.     

Sonochemical synthesis of CeVO4 nanoparticles for electrochemical hydrogen storage

In this study, the synthesis of cerium vanadate (CeVO₄) nanoparticles using ammonium metavanadate, cerium (III) nitrate hexahydrate as the primary reactant and hydrazine as the source of OH^? was presented in the absence and presence of ultrasonic waves. Reaction control was performed using OH^? and ethylenediamine sources. Other parameters such as solvent, surfactant, power, and time were also examined. Nanostructures were analyzed by XRD, FESEM, FTIR, DLS, BET, and EDS. FESEM results showed that using ultrasonic irradiation, relatively fine spherical nanoparticles were formed in one step while uniform spherical nanostructures were formed in a two-step path. The obtained product was used for electrochemical storage of hydrogen. The discharge capacity of spherical nanoparticles of CeVO₄ with high uniformity was recorded at about 4299 mAh/g.     

Green synthesis,characterization and investigation of the electrochemical hydrogen storage properties of Dy2Ce2O7 nanostructures with fig extract

Nanostructured Dy₂Ce₂O₇ with good electrochemical hydrogen storage properties has been produced utilizing a novel and green method in the presence of fig extract, for the first time. Fig extract has been employed as novel kind of fuel in the production of pure Dy₂Ce₂O₇. By varying the notable factor, temperature for production, Dy₂Ce₂O₇ structures can be created that are different in morphological features and Coulombic efficiency as well as electrochemical hydrogen storage properties. Diverse techniques have been adopted to examine and characterize the formed Dy₂Ce₂O₇ with the aid of fig extract. Electrochemical hydrogen storage features of the diverse Dy₂Ce₂O₇ samples (formed with the aid of fig extract) have been compared with chronopotentiometry technique at potash solution. Our findings reveal that the nanostructured Dy₂Ce₂O₇ fabricated with the aid of fig extract at 400 ^°C can possess the best efficiency for store hydrogen. Usage of fig extract, the new and eco-friendly fuel, for synthesis of the nanostructured Dy₂Ce₂O₇ that is efficiently capable to store hydrogen (renewable type of energy carrier), can be helpful to decline and stop the environmental pollution.     

Green synthesis and characterization of SnO2, CuO,Fe2O3/activated carbon nanocomposites and their application in electrochemical hydrogen storage

The goal of this study is to produce environmentally friendly nanomaterials that have a high hydrogen storage capacity. The researchers in this study used inexpensive natural bitumen to produce activated carbon (substratum) and a green solution synthesis combustion method to produce CuO, Fe₂O₃, and SnO₂ nanoparticles using a Mint extract as the source material. Metal oxides such as CuO, Fe₂O₃ and SnO₂ are used to increase hydrogen storage capacity and Columbic efficiency. AC and AC/SnO₂, AC/CuO, and AC/Fe₂O₃ nanocomposites have been confirmed via XRD (X-ray diffraction), TEM (transmission electron microscopy), EDX (energy-dispersive X-rays), FT-IR (fourier transform infrared), scanning electron microscope (SEM), and adsorption and desorption analysis of N₂ (BET). In terms of discharge capacity, AC/CuO, AC/Fe₂O₃, and AC/SnO₂ display respective capacities of 2250, 2500, and 3600 mAh/g after 20 cycles, respectively. Of all the sample materials, the AC/SnO₂ nanocomposite with the highest hydrogen storage capacity has the lowest Columbic efficiency. This implies that a sample with 54% Columbic efficiency, such as AC/CuO nanocomposite, is a more suitable specimen.     

Facile in-situ electrochemical fabrication of highly efficient nickel hydroxide-iron hydroxide/graphene hybrid for oxygen evolution reaction

Oxygen evolution reaction (OER) is an essential process in energy conversion and storage, especially in water electrolysis, while developing active and low-cost catalysts is the key to maximizing O₂ production. Here a facile three-electrode electrolysis system is firstly applied to synthesize nickel hydroxide-iron hydroxide/graphene hybrid. To fully utilize the electrical energy and simplify the catalyst synthesis, we made graphite exfoliated into graphene at the cathode and nickel-iron hydroxide synthesized at the anode simultaneously. The best electrocatalytic performance of Ni–Fe/G for OER shows an overpotential of 280 mV (without iR compensation) at 10 mA cm^?2, superior to commercial RuO₂ (341 mV). Results show that the introduction of Fe in Ni–Fe/G not only converts part of α-Ni(OH)₂ into more active β-Ni(OH)₂, but promotes the electric conductivity and electrochemically active surface area (ECSA) of the obtained Ni–Fe/G, therefore Ni–Fe/G shows the superior OER performance. The OER activity of Ni–Fe/G can be further adjusted by experiment conditions including electrolysis time and electrolyte concentration. This work provides a novel and facile method for highly efficient OER via engineering the non-noble metal hydroxide/graphene hybrid.     

Facile electrodeposition fabrication of molybdenum-tungsten sulfide on carbon cloth for electrocatalytic hydrogen evolution

In this work, we have described a facile fabrication of molybdenum-tungsten sulfide on carbon cloth (Mo-W-S/CC) by one-step electrodeposition process. The morphology, composition and catalytic property of as-prepared samples have been characterized through scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray photo-electron spectroscopy (XPS) and electrochemical methods. The electrodeposition conditions have been optimized systematically. Mo-W-S/CC has achieved excellent performance and durability as an electrocatalyst for hydrogen evolution reaction (HER) in acidic electrolytes.     

Theoretical screening of highly efficient single-atom catalysts for nitrogen reduction based on a defective C3N monolayer

Conversion of N₂ to NH₃ through electrochemical technology is one of the most attractive and promising alternatives to the traditional Haber-Bosch method. However, exploring the promising electrocatalysts with high stability, activity and selectivity for nitrogen reduction reaction (NRR) is still an important and long-standing challenge to accelerate the green production of NH₃. Herein, through the first-principles high-throughput screening, we systematically investigated the potentiality of single transition metal (TM) anchored on defective C₃N monolayer as TM-V_CC candidates for N₂ fixation. We carried out a comprehensive screening and systematical evaluation for stability, catalytic activity and selectivity toward NRR on TM-V_CC candidates. Our results reveal that, among 26 candidates, Mn-V_CC can significantly suppress HER and exhibit the outstanding NRR activity, with the most favorable limiting potential of ?0.75 V through the distal pathway, which is better than the currently stepped catalyst Ru (0001). More impressively, such a satisfactory NH₃ conversion is primarily ascribed to the strong back-donation interactions between d-electrons of Mn atom and the anti-orbitals of N₂ molecule, as well as efficient charge transfer of electrochemical process. Our findings not only broaden the development prospect of SACs for N₂ reduction but also pave a way for rational design and rapid screening of highly active C₃N-based catalysts for NRR.     

Amorphous MoS2 nanosheets on MoO2 films/Mo foil as free-standing electrode for synergetic electrocatalytic hydrogen evolution reaction

A facile oxidation-sulfidation strategy is proposed to fabricate the vertically aligned amorphous MoS₂ nanosheets on MoO₂ films/Mo foil (MF) as free-standing electrode, which features as the integration of three merits (high conductivity, abundant exposures of active sites, and enhanced mass transfer) into one electrode for hydrogen evolution reaction (HER). Density functional theory (DFT) calculations reveal the strong interaction between MoS₂ and MoO₂, which can enhance the intrinsic conductivity with narrow bandgap, and decreases hydrogen adsorption free energy (ΔG_H1 = ~0.06 eV) to facilitate the HER process. Benefiting from the unique hierarchical structure with amorphous MoS₂ nanosheets on conductive MoO₂ films/MF to facilitate the electron/mass transfer by eliminate contact resistance, controllable number of stacking layers and size of MoS₂ slabs to expose more edge sites, the optimal MoS₂/MoO₂/MF exhibits outstanding activity with overpotential of 154 mV at the current density of 10 mA cm⁻², Tafel slope of 52.1 mV dec⁻¹, and robust stability. Furthermore, the intrinsic HER activity (vs. ECSA) on MoS₂/MoO₂/MF is significantly enhanced, which shows 4.5 and 18.6 times higher than those of MoS₂/MF and MoO₂/MF at overpotential of 200 mV, respectively.     

Exploration of carbon additives to the synthesis of Cu2Mo6S8 structures and their electrocatalytic activity in oxygen reduction reaction

Catalytic processes are contemplated as break point in generating alternative and sustainable energy platforms. The cathodic oxygen reduction reaction (ORR) is an important catalytic system, mainly finding practice in fuel cell and metal-air battery technologies. This work presents the synthesis, structural characterization and electrocatalytic properties of three different Cu₂Mo₆S₈ structures as alternative ORR electrocatalysts. The effect of different carbon additives during synthesis was studied and no positive influence of the carbon addition was indicated. Our findings show that only the bare Cu₂Mo₆S₈ enhances the ORR electro-performance to class with the state-of-the-art ORR catalysts. Excellent stability of 10,000 consecutive ORR cycles, a superior onset potential of 0.894 V and half-wave (E_1/2) potential of 0.641 V vs. reversible hydrogen electrode (RHE) increase the noteworthiness of the Cu₂Mo₆S₈ electrodes. Aside from experimental investigations, density functional theory calculations deliver profound knowledge on the structural and electronic properties (electronic band structure, partial density of states and electron density) of Cu₂Mo₆S₈.     

Hydrothermal synthesis and electrochemical hydrogen storage performance of porous hollow NiSe nanospheres

We have successfully fabricated the uniform porous hollow NiSe nanospheres composed of nanoparticles via a mild hydrothermal method. The growth mechanism of these hollow nanospheres was proposed based on a series of contrast experimental observations depending on different reaction conditions (including time, temperature, reactant ratio and the amount of ammonia water) as well as our understandings. We also investigated the Raman stretching modes of NiSe hollow nanospheres. Meanwhile, we have also studied the properties of magnetism and electrochemical hydrogen storage of the NiSe nanospheres. The method in our report might provide alternative synthetic approach for other metal selenides with hollow structures in the future.     

Facile hydrothermal synthesis of combined MoSe2PS nanostructures on nickel foam with superior electrocatalytic properties for hydrogen evolution reaction

Producing an efficient and inexpensive electrocatalyst for use in the water electrolysis process is the most efficient and logical way to industrialize this method to produce hydrogen as a clean and alternative fuel for fossil fuels. In this study, combined and unique MoSe₂PS nanostructures are synthesized on nickel foam by three steps hydrothermal process. Microstructural observations reveal the unique morphology of the petals covered by the elongated nano-blades. A high electrocatalytic performance is attained with this nanostructure in hydrogen evolution reaction, so that the 90 mV overpotential is achieved at a current density of ?10 mA/cm². The near-platinum activity is due to the unique and combined nanostructure due to the synergistic properties of S and P on MoSe₂ as well as the high electrochemical active sites in the specimen. Additionally, excellent stability of the synthesized electrocatalyst is observed in the alkaline medium for 30 h, which confirms its potential application in relevant industries such as fuel cells and transportation.     

Facile synthesis and hydrogen storage application of nitrogen-doped carbon nanotubes with bamboo-like structure

This paper reports a facile method for the preparation of nitrogen-doped carbon nanotubes (N-doped CNTs) that shows enhanced hydrogen storage capacity. The synthesis method involves simple pyrolysis of melamine using FeCl₃ as catalyst in tube furnace. The materials were characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, elemental analysis, Raman spectroscopy, and nitrogen adsorption–desorption analysis. The results indicated that the prepared N-doped CNTs have a bamboo-like structure with thin compartment layers. The nitrogen doping concentration, specific surface area, and total pore volume of the N-doped CNTs were determined to be 1.5 at%, 135 m²/g, and 0.38 cm³/g, respectively. The hydrogen adsorption measurements at 77 K showed that the N-doped CNTs exhibits gravimetric hydrogen uptake of 0.21 wt% at 1 bar and 1.21 wt% at 7 bar. At room temperature, hydrogen uptake as high as 0.17 wt% at 298 K and 19 bar is achieved, which is among the highest data reported for the N-doped carbon materials under the same condition.     

Properties of BaYO3 perovskite and hydrogen storage properties of BaYO3Hx

In this study, Density Functional Theory (DFT) calculations have been performed for BaYO₃ perovskite with the generalized gradient approximation (GGA) as implemented in Vienna Ab-initio Simulation Package (VASP). The structural optimization of BaYO₃ perovskite have been studied for the five possible phases: cubic, tetragonal, hexagonal, orthorhombic and rhombohedral to determine the most stable phase of BaYO₃ perovskite. It has been found that the cubic phase is the most stable one and electronic and mechanical properties of this phase have been investigated. Moreover, the elastic anisotropy has been visualized in detail by plotting the directional dependence of compressibility, Poisson ratio, Young's and Shear moduli for cubic phase. Then, hydrogen bonding to BaYO₃ perovskite has been conducted and hydrogen storage properties of BaYO₃H_x (x = 3 and 9) such as: formation energy, cohesive energy and gravimetric hydrogen storage capacity have been analyzed. Having no study about BaYO₃ perovskite and hydrogen bonding in the literature makes this study the first considerations of BaYO₃ perovskite. Hence, this work could enlighten the possible future studies.     

An investigation of Li-decorated N-doped penta-graphene for hydrogen storage

By making use of first principles calculations, lithium-decorated (Li-decorated) and nitrogen-doped (N-doped) penta-graphene (PG) was investigated as a potential material for hydrogen storage. The geometric and electronic structures of two types of N-doped PG were studied, and the band gaps were 1.86 eV and 2.06 eV, respectively, depending on the positions of the substitution. The probable adsorption sites for Li atoms on topside and downside were calculated. Hydrogen molecules were added one by one to Li-decorated N-doped PG to research the maximum hydrogen gravimetric density. It is found that up to 5 hydrogen molecules on topside and 8 hydrogen molecules on downside can be adsorbed around a Li atom, and the average adsorption energies are in the range of physical adsorption processes (0.1–0.4 eV). The gravimetric densities can reach 7.88 wt% for N-doped PG with Li decoration. Our results suggest that Li-decorated N-doped PG is a significantly promising material for hydrogen storage.