Current Density J0 Research Articles

Electrochemical recovery of dysprosium from LiCl-KCl melt aided by liquid Pb metal

To recover Dy from LiCl-KCl melt, the electroreduction mechanism of Dy(III) on liquid Pb electrode was first studied by CV and Tafel methods. Dy(III) was reducted on liquid Pb electrode at about −1.35 V which is more positive than that on W electrode due to the formation of Dy(Pb) solid solution: Dy(III) + Pb + 3e− = Dy(Pb). Tafel method was used to evaluate the exchange current density (j0) and charge transfer coefficient (α) of Dy(III)/Dy(Pb) couple on liquid Pb electrode, the influence of different scanning speeds and temperatures on j0 were studied. The linear dependence of j0 as a function of temperature was observed, from which the activation energy associated with Dy(III)/Dy(Pb) couple was also obtained. Then, the reduction process of Dy(III) on the Pb film coated on the W electrode was also performed to obtain more information of the Pb-Dy intermetallic compounds. Electrochemical signals associated with the formation of Pb3Dy, Pb2Dy, Pb4/5Dy and Pb3/5Dy, were observed. The deposition potentials and equilibrium potentials of different Pb-Dy intermetallic compounds were obtained, which are more positive than those of Dy(III) on W electrode. Thermodynamic properties of Pb-Dy intermetallic compounds at 713 K–803 K were calculated employing the determined equilibrium potentials. The metallic Dy was recovered through galvanostatic and potentiostatic electrolysis on liquid Pb cathode and the products were detected by SEM-EDS and XRD. The recovered Dy was found to be in the form of Pb3Dy intermetallic compound.

Bio-based Fe3O4/chitosan nanocomposite sensor for response surface methodology and sensitive determination of gallic acid

In this study, preparation of a novel bio-sensor based on Fe3O4/chitosan nanocomposites reported for electrochemical studies and determination of gallic acid (GA). Combination of chitosan with Fe3O4 nanoparticles causes to improve oxidation current of the GA. Characterization of the nanocomposite is carried out by different techniques such as X-ray diffraction, transmission electron microscopy, scanning electron microscopy, vibrating sample magnetometer, electrochemical impedance spectroscopy and cyclic voltammetry. Furthermore, multivariate optimization strategy is applied for simultaneous optimization of the chemical and instrumental parameters. Moreover, electrochemical behavior of GA at the surface of the nano-structured sensor is studied by various techniques such as chronoamperometry, chronocoulometry and linear sweep. Using these techniques, the diffusion coefficient (D = 5.05 × 10−4 cm2 s−1 and or 4.86 × 10−4 cm2 s−1), and the kinetic parameters containing the exchanging current density (j0 = 0.23 μA cm−2) and electron transfer coefficient (α = 0.1) are determined for GA, respectively. Then, the detection limit for GA is found to be 12.1 nM with a broad linear dynamic range 0.5–300.0 μM using differential pulse voltammetry DPV at the surface of the Fe3O4/chitosan sensor. Finally, the proposed method is successfully applied for the detection of the analyte in real samples.

Evolutionary PERC+ solar cell efficiency projection towards 24% evaluating shadow-mask-deposited poly-Si fingers below the Ag front contact as next improvement step

Monofacial PERC and bifacial PERC + solar cells have become the mainstream solar cell technology exhibiting conversion efficiencies around 22.5% in mass production. We determine a specific saturation current density J0,Ag = 1400 fA/cm2 of the screen-printed Ag front contact. When weighted with the contact area fraction of 3.0% the Ag metal contacts contribute 42 fA/cm2 to the total J0,total = 130 fA/cm2 thereby being a main limitation of the Voc. We investigate carrier selective poly-Si on oxide (POLO) fingers below the screen-printed Ag contacts of PERC + solar cells in order to minimize contact recombination. We name this solar cell PERC + POLO. Numerical simulations reveal that PERC + POLO cells exhibit an efficiency potential up to 24.1% which is 0.3%abs. higher compared to PERC + solar cells. In order to enable low-cost manufacturing of poly-Si fingers, we investigate for the first time the deposition of suitable a-Si fingers by plasma-enhanced chemical vapour deposition (PECVD) through a shadow mask in a vacuum chamber. We demonstrate a-Si fingers as narrow as 70 μm and as high as 250 nm. The parasitic deposition below the mask increases the a-Si finger width by less than 30 μm compared to the mask opening width. First test wafers demonstrate an implied Voc up to 716 mV of PECVD a-Si layers which are crystalized and doped in a subsequent POCl3 diffusion. Applying this process sequence, PERC + POLO cells could be manufactured with the established industrial PERC + process only adding the PECVD deposition of a-Si fingers through a shadow mask.

Pt0.25Ru0.75/N‐C as Highly Active and Durable Electrocatalysts toward Alkaline Hydrogen Oxidation Reaction

AbstractA series of uniform 3.0–3.8 nm Pt1−xRux particles supported on nitrogen‐doped carbon (N‐C) is synthesized by wet‐impregnation, high‐temperature reduction, and high‐temperature NH3 etching. As far as it is known, the resultant Pt0.25Ru0.75/N‐C exhibits the highest activity toward alkaline hydrogen oxidation reaction (HOR) in terms of mass specific exchange current density (j0,m, 1654 A gPtRu−1), that is 4.7 and 1.4 times of commercial Pt/C (352 A gPt−1) and PtRu/C (1213 A gPtRu−1), respectively. The remarkable activity originates from a high electrochemical active surface area (ECSA), weakened hydrogen binding energy (HBE), and appropriate oxophilic property. Additionally, the Pt0.25Ru0.75/N‐C displays much improved durability during potential cycling with respect to commercial Pt/C and commercial PtRu/C, likely arising from the stabilizing effect of nitrogen dopant of N‐C on Pt0.25Ru0.75. Furthermore, the single cell fabricated with 0.08 mgPt cm−2 of the Pt0.25Ru0.75/N‐C as the anode reaches a peak power density of 831 mW cm−2, which is 1.8 and 1.1 times of that fabricated with 0.2 mgPt cm−2 of commercial Pt/C and 0.13 mgPt cm−2 of commercial PtRu/C as the anode, respectively. This study exhibits that low‐platinum alkaline HOR electrocatalyst should be a highly promising approach for hydroxide exchange membrane fuel cells (HEMFCs).

Correlation of Exchange Current Density j₀ and the Standard Potential of the Metal Electrodes EM⁰ for the Hydrogen Evolution Reaction (HER)

The hydrogen evolution reaction (HER) is critical technologically in electrochemically energy systems. HER is also important fundamentally as 2H⁺ + 2e ⇌ H₂ provides the standard reference potential E0 H = 0.000 V in thermodynamics and HER serves as a primary and critical test case for kinetics theory.For HER electrocatalytic rates, the mechanism is historically broken down into three steps. The reaction sequence begins with adsorption and reduction of proton to form electrochemically adsorbed hydrogen. This is the Volmer step. H⁺ + e ⇄ Hads (Volmer)After the first Hads is formed, H2 can be formed by two pathways. In the Heyrovsky pathway, a second proton undergoes electrochemical hydrogen adsorption at the same metal atom to form hydrogen gas. Hads + H⁺ + e ⇄ H2 (Heyrovsky)In the Tafel pathway, electrochemically adsorbed hydrogens on adjacent metal atoms react to form H2. Hads + Hads ⇄ H2 (Tafel)HER electrode kinetics measured as exchange current densities j₀ are evaluated in accord with the Volmer-Heyrovsky-Tafel scheme.For HER at metal electrodes, log j₀ is known highly dependent on the metal of the electrodes with rates that vary > 10 orders of magnitude. HER data are evaluated according to these three steps, despite that properties of the metal are not explicit in the Volmer-Heyrovsky-Tafel scheme.Here, properties of the metal electrode are introduced through the standard potential E0 M. For metal M0, Mz+ + ze ⇌ M⁰ E0 M Data for log j₀ are taken from a paper by Trasatti (Electroanalytical Chemistry and Interfacial Electrochemistry (1972) 39, 163-184). Trasatti grouped the 31 metal electrodes into d and sp metals. For the d metals (transition metals), log j₀ is well and linearly correlated with E0 M, whereas for the sp metals, little to no correlation is found.Several points are considered. Higher HER rates are observed at transition metal electrodes with more positive values of E0 M.It is sketched that the initial step in the metal dependent HER process is release of electron(s) to form Mz+ immediately at the electrode surface.Where formation of Mz+immediately at the electrode solution interface is the initial step, log j₀ is anticipated linearly dependent on E0 M.The behavior is sketched within transition state or activated complex theory and is based on a transition state formed of electron(s) shared between the metal cation Mz+ and the proton H+.Formation of the transition state [(1/z)Mz+⋯e⋯H+]‡ precedes the Volmer step, and where applicable, is a rate determining step.Implications for overpotential η pinned by E0 M are considered. This may account for the counter intuitive observation that higher log j₀ are found on metals such as Pt where E0 M is more positive. A kinetic model is sketched where a component of the activation energy is set by F(E0 H-E0 M). Finally, the process of proposing an electrode dependent transition state and evaluating the thermodynamic and kinetic consequences may yield a general method for modeling interfacial electron transfer and electrocatalysis. Such a process may introduces electrode specific properties into the rate expressions a priori.

Electrode reaction of Pr(III) and coreduction of Pr(III) and Pb(II) on W electrode in eutectic LiCl-KCl

The electrode reaction of Pr(III) and coreduction of Pb(II) and Pr(III) were studied on an inert W electrode in eutectic LiCl-KCl to extract Pr from molten salt. The electrode process kinetic of Pr(III) on W electrode was firstly explored employing cyclic voltammetry (CV) and Tafel technique, such as the diffusion coefficient of Pr(III) in eutectic LiCl-KCl and the exchange current density (j0) for Pr(III)/Pr(0) couple and the electrode reaction activation energy. Then, various electrochemical techniques were used to investigate the coreduction of Pb(II) and Pr(III). Four cathode current peaks ascribed to the formation of PrxPby intermetallic compounds were detected, which indicated that the Pr could deposit on pre-deposited Pb film, react with Pb, and form PrxPby intermetallic compounds. Furthermore, the electrolytic products formed by galvanostatic electrolysis were characterized by scanning electron microscopy coupled with energy dispersive X-ray diffraction, which illustrated the formation of PrPb3 intermetallic compound in LiCl-KCl-PbCl2-PrCl3 melt.

Experimental investigation of charge transfer coefficient and exchange current density in standard fuel cell model for polymer electrolyte membrane fuel cells

Two representative parameters, exchange current density (j0) and charge transfer coefficient (α), in a standard fuel cell model of polymer electrolyte membrane fuel cells (PEMFCs) were experimentally investigated. The polarization characteristics and the corresponding electrochemical impedance spectra of the normal PEMFCs were measured and Tafel curves were calculated from them, where j0 and ? were finally calculated. As a result, the calculated j0 was 0.11- 0.70 A/cm2, while the α was 0.056-0.023, depending on the operating temperature. Here, the j0 is extremely overestimated while α is underestimated as compared with those in literature. Although the reason for such difference is not clear, it is expected that it could affect the predicted performance by the model significantly if the fuel cell performance is improved highly in the future so the activation overvoltage corresponding to identical current is lowered.

Influence of the exchange current density and overpotential for hydrogen evolution reaction on the shape of electrolytically produced disperse forms - Review

In this study, comprehensive survey of formation of disperse forms by the electrolysis from aqueous electrolytes and molten salt electrolysis has been presented. The shape of electrolitically formed disperse forms primarily depends on the nature of metals, determined by the exchange current density (j0) and overpotential for hydrogen evolution reaction as a parallel reaction to metal electrolysis. The decrease of the j0 value leads to a change of shape of dendrites from the needle-like and the 2D fern-like dendrites (metals characterized by high j0 values) to the 3D pine-like dendrites (metals characterized by medium j0 values). The appearing of a strong hydrogen evolution leads to formation of cauliflower-like and spongy-like forms (metals characterized by medium and low j0 values). The other disperse forms, such as regular and irregular crystals, granules, cobweb-like, filaments, mossy and boulders, usually feature metals characterized by the high j0 values. The globules and the carrot-like forms are a characteristic of metals with the medium j0 values. The very long needles were a product of molten salt electrolysis of magnesium nitrate hexahydrate. Depending on the shape of the disperse forms, i.e. whether they are formed without and with vigorous hydrogen evolution, formation of all disperse forms can be explained by either application of the general theory of disperse deposits formation or the concept of "effective overpotential". With the decrease of j0 value, the preferred orientation of the disperse forms changed from the strong (111) in the needle-like and the fern-like dendrites to randomly oriented crystallites in the 3D pine-like dendrites and the cauliflower-like and the spongy-like forms.

Synergistically Tuning Electronic Structure of Porous β‐Mo2C Spheres by Co Doping and Mo‐Vacancies Defect Engineering for Optimizing Hydrogen Evolution Reaction Activity

AbstractThe development of novel non‐noble electrocatalysts with controlled structure and surface composition is critical for efficient electrochemical hydrogen evolution reaction (HER). Herein, the rational design of porous molybdenum carbide (β‐Mo2C) spheres with different surface engineered structures (Co doping, Mo vacancies generation, and coexistence of Co doping and Mo vacancies) is performed to enhance the HER performance over the β‐Mo2C‐based catalyst surface. Density functional theory calculations and experimental results reveal that the synergistic effect of Co doping with Mo vacancies increases the electron density around the Fermi‐level and modulates the d band center of β‐Mo2C so that the strength of the MoH bond is reasonably optimized, thus leading to an enhanced HER kinetics. As expected, the optimized Co50‐Mo2C‐12 with porous structure displays a low overpotential (η10 = 125 mV), low‐onset overpotential (ηonset = 27 mV), and high exchange current density (j0 = 0.178 mA cm−2). Furthermore, this strategy is also successfully extended to develop other effective metal (e.g., Fe and Ni) doped β‐Mo2C electrocatalyst, indicating that it is a universal strategy for the rational design of highly efficient metal carbide‐based HER catalysts and beyond.

Thermodynamics and Kinetics Properties of Lanthanides (La, Ce, Pr, Nd) on Liquid Bismuth Electrode in LiCl-KCl Molten Salt

Electrochemical behaviors of lanthanide (i.e. La, Ce, Pr and Nd) chlorides in LiCl-KCl melt were demonstrated via cyclic voltammetry (CV) and open circuit potential (OCP) techniques at temperatures from 723 K to 873 K. An electrochemical galvanostatic intermittent titration technique (GITT) was performed to obtain the thermodynamic data of lanthanide (Ln) on liquid bismuth electrode. The relationship between activity coefficient and temperature were determined. Galvanostatic pulse (GP) and electrochemical impedance spectroscopy (EIS) as the transient measurements were performed to investigate the interfacial processes of Ln(III) on liquid Bi electrode. The exchange current densities j0 of Ln(III)/Ln were determined by fitting and equivalent circuits, that showed the linear relationship with temperature. In addition, the electrodepositions of La and Ce on liquid Bi electrodes were discussed on the formation of alloys. The products of phase composition and microstructure were conducted by XRD and SEM-EDS, respectively.

Electrochemical Mechanism of Trivalent Chromium Reduction in ChCl-EG Deep Eutectic Solvents Containing Trivalent Chromium

In this work, the cyclic voltammetry (CV) was used to investigate the redox process of Cr(III) on glassy carbon electrode (GC) in deep eutectic solvents (DESs), prepared using choline chloride (ChCl) and ethylene glycol (EG). The anode and cathode branches of the CV curve meant the process of deposition/dissolution equilibrium of trivalent chromium. The equilibrium potential (Eeq) of Cr(III)/Cr(0) was −0.964 V (vs Ag QRE). The analysis of the potentiostatic current density transient (chronoamperometry (CA)) results showed that the electrodeposition process of Cr(III) involved multiple processes, mainly jad, j3D and jWR. By calculating the amount of charge (Qad%, Q3D%, and QWR%) in each process, it can be found that the contribution rate could be controlled by the potential to increase Q3D%. The kinetic parameters of Cr nucleation/growth rate were determined from the standard model of 3D nucleation of diffusion-control, such as nucleation rate (A), active centre number density (N0), and diffusion coefficient (D). The ln(A) and η were used to calculate the nucleated Gibbs free energy (Δ∼G(nc)), the critical core size (nc), the current exchange density (j0), the transfer coefficient (α), and the surface tension (σ). The chromium coating was constituted by particles of Cr(0), Cr2O3 and Cr(OH)3.

Electrochemical Reaction of Sm(III) on Liquid Sn Electrode

The electrochemical study of Sm(III) ions was conducted on Sn film electrode in eutectic LiCl-KCl in the temperature range from 773 K to 923 K by a series of electrochemical techniques. The results of current reversal chronopotentiometry of Sm(III) on W electrode showed that the redox reaction related to Sm(III) is a kind of soluble/soluble system, which meant that Sm(III) was reduced to Sm(II) on W electrode. On Sn film electrode, the reduction of Sm(III) was found to be two-step process: Linear polarization (LP) and Tafel techniques were conducted to measure the exchange current density (j0) of Sm(II)/SmSn3 couple. The variation of j0 with temperature accords with the Arrhenius law, and the activation energy was evaluated to be 14.32 kJ mol−1 and 14.08 kJ mol−1, respectively. Moreover, the feasibility of extracting Sm on Sn film electrode was examined by constant potential electrolysis at −1.45 V in the LiCl-KCl-SmCl3-SnCl2 molten salt for 3 h. XRD result indicated the formation of SmSn3. Constant current and potential electrolysis were performed to extract metallic Sm on liquid Sn pool electrode. The alloy samples were characterized by SEM-EDS and XRD, which displayed the existence of SmSn3 and Sm4Sn3 phases in Sm-Sn alloys.

Synthesis of functional Ni2P/CC catalyst and the robust performances in hydrogen evolution reaction and nitrate reduction

The non-precious transition metal phosphides (TMPs) as robust and effective hydrogen evolution reaction (HER) catalysts have attracted enormous attention, due to the merits of earth-abundance, low price, desirable stability and high efficiency. However, the conventional preparation process of this kind of catalyst is inconvenient. Herein, we report a facile approach toward the fabrication of nickel phosphide (Ni2P) assembled on carbon cloth (CC) via the coupling method of electroless plating and low temperature phosphorization. Then, the crystallinity, morphology and chemical component of fabricated self-supporting Ni2P/CC catalyst employed for the HER process were characterized, and the HER property was successively evaluated in three types of electrolytes (i.e., acidic, neutral and alkaline solutions). The as-prepared Ni2P/CC catalyst displays a remarkable HER performance, which can be corroborated by the small Tafel slope (b = 50 mV dec−1), high exchange current density (j0 = 6.6 × 10−2 mA cm−2), acceptable overpotential (119 mV) to attain the current density of 10 mA cm−2, as well as the superb stability (<5% decay after 24 h potentiostatic test) in 0.5 M H2SO4. In addition, it should be noted that the HER process of Ni2P/CC catalyst can be competent for the reduction of nitrate from the solution, and an efficiency of 63.2% for this nutrient pollutant is achieved.

21.3%-efficient n-type silicon solar cell with a full area rear TiOx/LiF/Al electron-selective contact

In this work, we investigate an efficient electron-selective passivating contact with TiOx/LiF/Al contact structure, which offers both low surface recombination and specific contact resistance. Optimized TiOx layer thickness of 4 nm provides high quality surface passivation, achieving minority carrier lifetime of 3.03 ms on 5 Ω cm n-type wafers, with a saturated current density J0 of 23 fA/cm2. In addition, inserting a 1 nm LiF between the 4 nm TiOx and Al reduces the contact resistivity to 18 mΩ cm2. The low contact resistivity of TiOx/LiF/Al contact is attributed to barrier reduction from the low work function of LiF/Al stack. A champion solar cell efficiency of 21.3% has been achieved for an n-type crystalline silicon device with a full-area rear TiOx/LiF/Al contact, demonstrating the excellent potential of this passivating contact for fabricating high-efficiency silicon solar cells.

Flower-like platinum-cobalt-ruthenium alloy nanoassemblies as robust and highly efficient electrocatalyst for hydrogen evolution reaction

Exploring hydrogen evolution reaction (HER) catalyst with highly catalytic features in alkaline conditions is considered as significance for water splitting. In this study, a general and simple method was developed to prepare flower-like platinum-cobalt-ruthenium alloy nanoassemblies (PtCoRu NAs) by using murexide and cetyltrimethylammonium chloride (CTAC) as the co-structure-directing agents. Benefiting from the structural advantages and multimetallic compositions, the as-prepared PtCoRu NAs displayed remarkably enhanced electrocatalytic performance for the HER in 1.0 M KOH, with a low overpotential (η, 22 mV) to drive 10 mA cm−2, small Tafel slope (46 mV dec−1), and high exchange current density (j0, 3.30 mA cm−2) during the long-term electrolysis. The as-developed strategy sheds some valuable guidelines for preparing advanced multimetallic catalysts for production of hydrogen in fuel cells.

Anodic oxidations: Excellent process durability and surface passivation for high efficiency silicon solar cells

We investigate the versatility of anodically grown silicon dioxide (SiO2) films in the context of process durability and exceptional surface passivation for high efficiency (>23%) silicon solar cell architectures. We show that a room temperature anodic oxidation can achieve a thickness of ~70 nm within ~30 min, comparable to the growth rate of a thermal oxide at 1000 °C. We demonstrate that anodic SiO2 films can mask against wet chemical silicon etching and high temperature phosphorus diffusions, thereby permitting a low thermal budget method to form patterned structures. We investigate the saturation current density J0 of anodic SiO2/silicon nitride stacks on phosphorus diffused and undiffused silicon and show that a J0 of <10 fA cm−2 can be achieved in both cases. Finally, to showcase the anodic SiO2 films on a device level, we employed the anodic SiO2/silicon nitride stack to passivate the rear surface of an interdigitated back contact solar cell, achieving an efficiency of 23.8%.

Stable, predictable and training-free operation of superconducting Bi-2212 Rutherford cable racetrack coils at the wire current density of 1000\u2009A/mm2

High-temperature superconductors (HTS) could enable high-field magnets stronger than is possible with Nb-Ti and Nb3Sn, but two challenges have so far been the low engineering critical current density JE, especially in high-current cables, and the danger of quenches. Most HTS magnets made so far have been made out of REBCO coated conductor. Here we demonstrate stable, reliable and training-quench-free performance of Bi-2212 racetrack coils wound with a Rutherford cable fabricated from wires made with a new precursor powder. These round multifilamentary wires exhibited a record JE up to 950 A/mm2 at 30 T at 4.2 K. These coils carried up to 8.6 kA while generating 3.5 T at 4.2 K at a JE of 1020 A/mm2. Different from the unpredictable training performance of Nb-Ti and Nb3Sn magnets, these Bi-2212 magnets showed no training quenches and entered the flux flow state in a stable manner before thermal runaway and quench occurred. Also different from Nb-Ti, Nb3Sn, and REBCO magnets for which localized thermal runaways occur at unpredictable locations, the quenches of Bi-2212 magnets consistently occurred in the high field regions over a long conductor length. These characteristics make quench detection simple, enabling safe protection, and suggest a new paradigm of constructing quench-predictable superconducting magnets from Bi-2212.

Influence of Lattice Defect to Vortex Flow on Type II Superconductor

Adding defect on type II superconductor can influence to vortex dynamic. It declares vortex movement, so speed of vortex is more stable. In this research, we applied lattice defect. In case to study dynamics of the vortex in type II superconductor material, this study was based on numerical solution of the Time-Dependent Ginzburg Landau (TDGL) equations by means of finite difference method with Forward Time Centred Space (FTCS) scheme. Applied external current density Je and external magnetic field He to superconductor material generate a vortex flow from higher magnetic field to lower magnetic field. Furthermore, applied external current density Je without external magnetic field He generates vortex flow between lattice defects.

Numerical Study of the Influence of Defect on the Material Side in Vortex-Antivortex Formation Based on TDGL Equation

Dynamics of vortex-antivortex (VAV) annihilation due to a defect in the side of material has been successfully studied using TDGL Equation. This study was to find out how is the potential curve (V-t) when VAV annihilation occurs. Type II superconductor with κ = 1.3 and size of Lx × Ly = 50ξ0 × 50ξ0 was used here. This study was based on a numerical solution of the TDGL Equation by means of finite difference method with FTCS (Forward Time Centered Space) Scheme. The external current density Je = Jei was applied to the material without applying external magnetic field He. That is the way to bring up antivortex on the bottom of material and vortex on the upper of material. The defects were prepared with the size of 0.3ξ0 × 1ξ0. The defect on the material gives effect to the presence of vortex and antivortex. VAVs can only enter the material through the defect and not enter through another side. This is showing that the defect on the material provides the force which causes VAV more easily enter the material at the defect than another side. VAVs will enter continuously until they will meet each other and the annihilation of VAV occurs in the middle of the material. The sharp pulses (the high peak pulse) appeared during the vortex and antivortex annihilating each other. Besides, the small pulses raised the vortex and antivortex when they entered the material. When annihilation occurred, the potential curve produced the very high potential value for a moment and returned to its normal potential state. The presence of the defect on the material can increase superconductivity of material as well.

Highly Electroactive Ni Pyrophosphate/Pt Catalyst toward Hydrogen Evolution Reaction.

Robust electrocatalysts toward the resourceful and sustainable generation of hydrogen by splitting of water via electrocatalytic hydrogen evolution reaction (HER) are a prerequisite to realize high-efficiency energy research. Highly electroactive catalysts for hydrogen production with ultralow loading of platinum (Pt) have been under exhaustive exploration to make them cutting-edge and cost-effectively reasonable for water splitting. Herein, we report the synthesis of hierarchically structured nickel pyrophosphate (β-Ni2P2O7) by a precipitation method and nickel phosphate (Ni3(PO4)2) by two different synthetic routes, namely, simple cost-effective precipitation and solution combustion processes. Thereafter, Pt-decorated nickel pyrophosphate and nickel phosphate (β-Ni2P2O7/Pt and Ni3(PO4)2/Pt) were prepared by using potassium hexachloroplatinate and ascorbic acid. The fabricated novel nickel pyrophosphate and nickel phosphate/Pt materials were utilized as potential and affordable electrocatalysts for HER by water splitting. The detailed electrochemical studies revealed that the β-Ni2P2O7/Pt (1 μg·cm-2 Pt) electrocatalyst showed excellent electrocatalytic performances for HER in acidic solution with an overpotential of 28 mV at -10 mA·cm-2, a Tafel slope of 32 mV·dec, and an exchange current density ( j0) of -1.31 mA·cm-2, which were close to the values obtained using the Vulcan/Pt (8.0 μg·cm-2 Pt), commercial benchmarking electrocatalyst with eight times higher Pt amount. Furthermore, the β-Ni2P2O7/Pt electrocatalyst maintains an excellent stability for over -0.1 V versus RHE for 12 days, keeping j0 equal after the stability test (-1.28 mA cm-2). Very well-distributed Pt NPs inside the "cages" on the β-Ni2P2O7 structure with a crystalline pattern of 0.67 nm distance to the Ni2P2O7/Pt electrocatalyst, helping the Volmer-Tafel mechanism with the Tafel reaction as a major rate-limiting step, help to liberate very fast the Pt sites after HER. The high electrocatalytic performance and remarkable durability showed the β-Ni2P2O7/Pt material to be a promising cost-effective electrocatalyst for hydrogen production.