Metal-Doped Catalysts for Hydrogen Evolution Reaction

The highly efficient electrochemical hydrogen evolution reaction (HER) provides a promising way to solve energy and environment problems. In this work, various transition metals (Fe, Co, Ni, Cu, Ag, and Pt) were selected to support on molybdenum carbides by a simple organic-inorganic precursor carburization process. X-ray diffraction (XRD) analysis results indicated that the ß-MO₂C phase was formed in all metal-doped samples. X-ray photo­electron spectroscopy analysis indicated that the binding energy of MO₂+ species (MO₂C) shifted to a lower value after metal was doped on the molybdenum carbide surface. Comparing with pure ß-MO₂C, the elec­trocatalytic activity for HER was improved by transition metal doping on the surface. Remarkably, the catalytic activity improvement was more obvious when Pt was doped on molybdenum carbide (2% Pt-MO₂C). The 2% Pt-MO₂C required a ?_10 of 79 mV, and outperformed that of pure ß-MO₂C (?10 = 410 mV) and other transition metal doped molybdenum carbides, with a small Tafel slope (55 mV/dec) and a low onset overpo­tential (32 mV) in 0.5 M H₂SO₄. Also, the 2% Pt-MO₂C catalyst demonstrated a high stability for the HER in 0.5 M H₂SO₄. This work highlights a feasible strategy to explore efficient electrocatalysts with low cost via engineering on the composition and nanostructure

Nanosheets of CuCo₂O₄ as a High-Performance Electrocatalyst in Urea Oxidation

The urea oxidation reaction (UOR) is a possible solution to solve the world’s energy crisis. Fuel cells have been used in the UOR to generate hydrogen with a lower potential compared to water splitting, decreasing the costs of energy production. Urea is abundantly present in agricultural waste and in industrial and human wastewater. Besides generating hydrogen, this reaction provides a pathway to eliminate urea, which is a hazard in the environment and to people’s health. In this study, nanosheets of CuCo₂O₄ grown on nickel foam were synthesized as an electrocatalyst for urea oxidation to generate hydrogen as a green fuel. The synthesized electrocatalyst was characterized using X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. The electroactivity of CuCo₂O₄ towards the oxidation of urea in alkaline solution was evaluated using electrochemical measurements. Nanosheets of CuCo₂O₄ grown on nickel foam required the potential of 1.36 V in 1 M KOH with 0.33 M urea to deliver a current density of 10 mA/cm2. The CuCo₂O₄ electrode was electrochemically stable for over 15 h of continuous measurements. The high catalytic activities for the hydrogen evolution reaction make the CuCo₂O₄ electrode a bifunctional catalyst and a promising electroactive material for hydrogen production. The two-electrode electrolyzer demanded a potential of 1.45 V, which was 260 mV less than that for the urea-free counterpart. The study suggests that the CuCo₂O₄ electrode can be a promising material as an efficient UOR catalyst for fuel cells to generate hydrogen at a low cost

Molybdenum Oxides for Energy Generation and Storage Using Efficient Clean Method

To solve the growing energy issues, significant efforts have been focused on the search of earth-abundant ele­ments that can provide multifunctional behavior for both energy generation and storage. Due to the low-cost and rich chemical nature, transition metal oxide nanostructures have been used in the fabrication of energy devices, such as fuel cells and lithium batteries. In this work, nickel, cobalt and iron molybdates were synthesized via a simple hydrothermal method in order to fabricate electrodes for oxygen evolution reaction (OER) and a superca­pacitor. FeMoO₄ required an overpotential of 294 mV to achieve a current density of 10 mA/cm2 for oxygen evolution reaction, which is lower than the overpotential required for NiMoO₄ and CoMoO₄ to do the same process. For the energy storage properties, the highest specific capacitance was achieved by FeMoO₄ electrode (11.5 F/cm2 at a current density of 1 mA/cm2). Galvanostatic charge-discharge measurements were performed and showed a better discharge time for iron molybdate. The capacitance retention and coulombic efficiency ex­hibited excellent performance over 5,000 cycles. In conclusion, molybdates, mainly FeMoO₄, could be a promis­ing material for the advancement of energy generation and storage devices

Electrocatalytic Properties of Lanthanum-based Perovskites for Water Splitting and Energy Storage Applications

Recent changes in global weather patterns have punctuated the need for mollification through a cleaner energy option. As part of the plan, hydrogen production for fuel cells offers substantial power without carbon emissions. Overall water splitting, with the aid of a low cost electrocatalyst could prove to be an abundant green fuel source. Utilizing readily available transition metals, three perovskite nanostructures were studied as a multifunctional material for hydrogen production as well as energy storage. LaCoO₃ (LCO), LaFeO₃ (LFO), and LaMnO₃ (LMO) were synthesized and characterized by X-ray diffraction and then dip coated onto nickel foam as electrodes in a standard three electrode system. The electrochemical properties were analyzed with electrochemical impedance spectroscopy (EIS), line scan voltammetry (LSV), and cyclic voltammetry (CV) for its electro-catalytic activity towards both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) as well as its effectiveness as a supercapacitor. It was shown that electrocatalytic activity toward OER was highly dependent on the material composition. Accordingly, LFO had the lowest overpotential voltage of 316 mV at 10 mA/cm2 compared with 376 mV (LCO) and 419 mV (LMO). Toward HER, LMO showed overpotential voltage of 176 mV at 10 mA/cm2, while LCO and LFO showed 221 mV and 230 mV, respectively. Measured at a common current density of 0.5 A/g, the specific capacitance of LMO was 105 F/g over LCO (45 F/g) and LFO (35 F/g). Further investigation for fabrication of devices for energy storage and water splitting electrolyzer application has been considered

Almond Based Electrocatalyst for Fuel Cell Applications

Hydrogen is considered one of the cleanest energy sources. Water spitting is one of the efficient ways to produce hydrogen as a fuel at the industrial level. Water splitting via electrolysis requires an efficient electrocatalyst to reduce the voltage required for water splitting. Currently, precious metals such as platinum are considered as one of the most efficient electrocatalysts for hydrogen production via electrolysis of water. The current challenge is to find a cost-effective alternative for this process. Molybdenum and carbon are low cost and abundant mate­rials which could be used for the synthesis of cost-effective electrocatalysts for hydrogen production. In this work, we used almond as a source for carbon for the synthesis of molybdenum carbide for sustainable and affordable hydrogen production. X-ray diffraction confirmed the phase purity of the synthesized molybdenum carbide. Electrocatalytic activities of molybdenum carbide were investigated in detail. It was observed that molybdenum carbide needs a small voltage to generate hydrogen via electrolysis process. Molybdenum carbide showed an overpotential of 117 mV and 180 mV in alkaline and acidic media, respectively to achieve a current density of 10 mA/cm2, which are among the best-reported results. Our study suggests that earth-abundant materials could be used for the synthesis of highly efficient electrocatalysts for electrochemical water splitting to generate hydrogen as a clean fuel

Construction of High-Performance 3D Nanostructured Flower-Like Iron-Nickel Sulfide for Supercapacitor

The global energy crisis and environmental pollution have stimulated increasing attention to developing clean and renewable alternative energy sources. One of the most efficient and greenest energy storage devices is supercapacitor which could store energy via electrical double layer and redox reactions. Supercapacitors are widely employed for many portable electronics and hybrid electric vehicles due to their high-power density, fast charge-discharge rate, and good cycle stability. In this work, 3D nanostructured flower-like iron-nickel sulfide was synthesized on the nickel foam using a facile hydrothermal method. The iron-nickel sulfide electrode showed out­standing performance for supercapacitor with a high areal capacitance of 13.2 F/cm2 at the scan rate of 1 mV/s and 4.9 F/cm2 at the current density of 5 mA/cm2, respectively. The specific capacitance of iron-nickel sulfide was 11 and 54 times higher than that of iron-nickel oxide and nickel foam at 5 mA/cm2, respectively. Further­more, the iron-nickel sulfide electrode displayed good rate capability in the charge-discharge study. Our research suggests that designing a highly porous and 3D nano-flower like iron-nickel sulfide material could be a way to improve the charge storage capacity of energy storage devices

Expendable Graphite as an Efficient Flame-Retardant for Novel Partial Bio-Based Rigid Polyurethane Foams

Study presents a novel bio-polyol synthesized using carvone, an extract from caraway, spearmint, or dill seeds via facile thiol-ene reaction

Magnetic Susceptibility of Polyaniline and Polyaniline-Polymethylmethacrylate Blends

While heat-capacity measurements on polyaniline yield density of states at the Fermi level N(EF) of the order of 3 states/(eV-2 rings), a value of 16 states/(eV-2 rings) was reportedly found from magnetic susceptibility measurements. We report here our magnetic susceptibility measurements, which, in agreement with the heat-capacity results, yield N(EF) of the order of 2 states/(eV-2 rings). These results firmly establish the metallic nature of charge carriers in the polyaniline family

Pauli-like magnetic susceptibility in emeraldine base polyaniline

Magnetic susceptibility measurements on emeraldine base (EB) polyaniline are found to exhibit a Pauli-like behavior up to a temperature of 475 K. A simple albeit physically realistic model involving spin-pairs is shown to lead to such a dependence on temperature. The analysis of the data indicates that polarons in EB are created in pairs and that the intra-pair interactions encompass a broad distribution of antiferromagnetic exchange couplings. The results on EB are further shown to have essential implications for a correct interpretation of the magnetic susceptibility data in doped conducting polymers

Derivation and evaluation of the fourth moment of NMR lineshape in zero-field

An expression for the fourth moment in zero-field NMR has been analytically derived and numerically evaluated for a rigid cubic lattice. Model simulations have been performed to calculate the second moment, the fourth moment, the ratio of the fourth moment to the square of the second moment, and the width of the resonance line for a crystal and a polycrystalline material in high-field as well as in zero-field NMR. The simulation results allow us to draw two conclusions: (1) zero-field NMR gives sharper and better defined spectra than the high-field NMR and (2) the ratio of the high- to zero-field resonance line-widths is 4 for a crystal, whereas it is 11 for a polycrystalline material