Effects of magnetic field and pulse potential on hydrogen production via water electrolysis

This experiment uses nickel electrodes and adds pulse potential and magnetic force when producing hydrogen via water electrolysis and explores how related parameters are affected by magnetohydrodynamics and pulse potential. Experiments showed that the Lorentz force of the magnetic field changes the direction of convective flow of the electrolyte, which affects the flow of bubbles during electrolysis. Adding a magnetic field increases the rate of current density by roughly 15% under a normal temperature, a distance of 2 mm between electrodes and a potential of 4 V. Pulse potential instantaneously increases current and accelerates both the movement of bubbles from the electrode surface and the mass transfer rate in the electrolyte, which lowers electrochemical polarization in the diffussion layer and further increases hydrogen production efficiency. When the duty cycle is 10% and the pulse on‐time is 10 ms, almost 88% of overall power is converted, and current density increases by 680 mA/cm², which is an increase of roughly 38%. Generally, pulse potential and magnetic field effects enhance each other when added under suitable pulse potential and basic potential. Copyright © 2013 John Wiley & Sons, Ltd.     

Technical feasibility of a proton battery with an activated carbon electrode

The technical feasibility of a small-scale ‘proton battery’ with a carbon-based electrode is demonstrated for the first time. The proton battery is one among many potential contributors towards meeting the gargantuan demand for electrical energy storage that will arise with the global shift to zero greenhouse emission, but inherently variable, renewable energy sources. Essentially a proton battery is a reversible PEM fuel cell with an integrated solid-state electrode for storing hydrogen in atomic form, rather than as molecular gaseous hydrogen in an external cylinder. It is thus a hybrid between a hydrogen-fuel-cell and battery-based system, combining advantages of both system types. In principle a proton battery can have a roundtrip energy efficiency comparable to a lithium ion battery. The experimental results reported here show that a small proton battery (active area 5.5 cm²) with a porous activated carbon electrode made from phenolic resin and 10 wt% PTFE binder was able to store in electrolysis (charge) mode very nearly 1 wt% hydrogen, and release on discharge 0.8 wt% in fuel cell (electricity supply) mode. A significant design innovation is the use of a small volume of liquid acid within the porous electrode to conduct protons (as hydronium) to and from the nafion membrane of the reversible cell. Hydrogen gas evolution during charging of the activated carbon electrode was found to be very low until a voltage of around 1.8 V was reached. Future work is being directed towards increasing current densities during charging and discharging, multiple cycle testing, and gaining an improved understanding of the reactions between hydronium and carbon surfaces.     

NiO hollow microspheres as efficient bifunctional electrocatalysts for Overall Water-Splitting

Development of efficient, earth-abundant and low-cost electrocatalyst for effective water electrolysis is highly demanding for production of sustainable hydrogen energy. In this paper, we report the cost-effective synthetic protocol for porous NiO hollow spheres in large scale through a simple spray drying strategy, using aqueous nickel ammonium carbonate complex solution, followed by calcination. The synthesized NiO hollow spheres calcined at 300 °C (NiO-300) are porous, made of nanoparticles in size range of 10–16 nm with a size range of 2.5–4 μm and total surface area of 120 m²/g. The NiO-300 exhibited excellent bifunctional electrocatalytic water splitting characteristic, both OER, and HER, in basic solution. NiO-300 modified glassy carbon electrode showed superior water electrolysis kinetics and to achieve 10 mA cm^?2 current density, it required 370 mV overpotential for OER and 424 mV overpotential for HER in 1 M KOH. It is also worked well with cost-effective plastic chip electrode. An assembled two-electrode system by pairing NiO modified plastic chip electrode as both anode and cathode in a 1.0 M KOH electrolyte for overall water splitting exhibit clear bubble formation at 1.6 V potential.     

Electrocatalytic properties of Ti2Ni/Ni-Mo composite electrodes for hydrogen evolution reaction

A composite electrode as hydrogen cathodes composed of Ti₂Ni hydrogen absorbing alloys and a Ni-Mo electrocatalyst was prepared for alkaline water electrolysis. The electrocatalytic properties of hydrogen evolution reaction (HER) are carried out in a 30 wt% KOH solution at 70 °C. The surface morphology and chemical composition of the cathode were also examined. The experimental results show that the composite cathode has a low hydrogen overpotential (ca. 60 mV at 70 °C in 30 wt% KOH) and excellent stability under conditions of continuous electrolysis and intermittent electrolysis with power interruption shutdown. The stability mechanism of the cathode against intermittent electrolysis is discussed.     

Porous electrode improving energy efficiency under electrode-normal magnetic field in water electrolysis

The porous electrodes (Ni, Cu) with 110 pores per inch (PPI) are adopted in water electrolysis for hydrogen production under normal-to-electrode magnetic field. The result shows that the voltage drop between electrodes can be reduced up to 2.5% under 0.9 T field, and the electric energy efficiency is improved correspondingly. Based on the numerical simulation method, the micro-magnetohydrodynamic (micro-MHD) convection induced by Lorentz force within the porous structure is found. The results showed that although the apparent current direction is parallel to magnetic field outside the porous electrode, the electric field may be distorted within the porous structure, and the Lorentz force is involved near the rib of the micro structure where the current is not parallel to the magnetic field any more. Micro-MHD plays the role of strengthening the mass transfer and facilitating bubble to eject from the porous structure, which results in the cell voltage decreasing. The combined application of porous electrode and magnetic field should be potential to further improve energy efficiency of water electrolysis for hydrogen production.     

Enhanced hydrogen generation by water electrolysis employing carbon nano-structure composites

The present study describes the hydrogen generation through electrolysis by using graphene-carbon nanotube (GC) nano-composite electrode. Synthesis of GC nano-composites of various compositions utilizing solution admixing approach has been done. Structural, morphological, microstructural and analysis of quality of various carbon nano-composites have been investigated by using XRD, SEM, TEM, Raman and FTIR techniques. To determine the electrochemical catalytic performance of GC composites, these have been used as working electrode (anode) for electrolysis of water in an alkaline medium (1 M NaOH). The results reveal that the GC73 (70 wt% graphene and 30 wt% CNT) nano-composite is an optimum anode material for hydrogen production. The highest hydrogen production rate of 487 l/h-m² has been observed for the composite GC 73. Based on Tafel plot and FTIR characterizations, a feasible mechanism for this high hydrogen yield has been put forward.     

Hydrogen bubble evolution from magnetized nickel wire electrode

How to reduce the bubble coverage of the electrode is one of the key issues in water electrolysis which is related to the reduction of energy consumption. In this work, the magnetized nickel electrode with 100 μm diameter is used as working electrode in hydrogen evolution reaction (HER) during alkaline water electrolysis (1 mol/L, KOH). According to the experimental observation, both of the bubble's diameter and number have decreased at the magnetized surface compared with the unmagnetized one. The B–H loop measurement shows that the residual magnetic field intensity (Br) of the magnetized nickel electrode is up to 0.03 T. It can be found from the numerical simulation result that the residual magnetic field exactly right brings the Lorentz force and magnetohydrodynamic (MHD) convection near the electrode surface, which play the role of helping hydrogen bubble release from the electrode, even if the external magnetic field is absent in experiment. The new finding may develop a new way of utilizing magnetic field in water electrolysis for gas product elimination and energy conservation.     

Pulsed current water splitting electrochemical cycle for hydrogen production

A pulsed current 3 D MnO₂ electrode water splitting electrochemical cycle is being proposed for hydrogen production. In 3D MnO₂ electrochemical cycle, the reactions take place at the solid/liquid and solid/gas two phase boundaries. Also, this electrochemical cycle should be able to generate hydrogen and oxygen gas separately at different periods of time. Here, we applied an interrupted pulsed current to reduce the overpotential caused by diffusion layers in conventional direct current electrolysis. The pulsed current, which disturbs the formation of the ion diffusion layer in the vicinity of the electrodes, is observed to be effective above 50 Hz. The best electrolysis performance was recorded at a current density of 0.2 A cm^?2, and the observed cell voltage was 1.69 V at 25 °C for a pulse frequency of 500 Hz, which is less than the corresponding conventional alkaline electrolysis.     

Energy and exergy analyses of hybrid photocatalytic hydrogen production reactor for CuCl cycle

The present paper concerns electrochemical, energy, exergy and exergoeconomic analyses of a hybrid photocatalytic-based hydrogen production reactor which is capable of replacing the electrolysis sub-system of the CuCl thermochemical cycle. Several operating parameters, such as current density, reactor temperature, ambient temperature and electrode distance, are varied to study their effects on the hydrogen production rate, the cost of hydrogen production and energy and exergy efficiencies. The present results show that the voltage drops across the anolyte solution (sol 1), catholyte solution (sol 2), an anode, cathode, and cation exchange membrane vary from 0.005 to 0.016 V, 0.004–0.013 V, 1.67–2.168 V, 0.18–0.22 V and 0.06–0.19 V, respectively with an increase in current density from 0.5 to 1.5 A/cm². The energy and exergy efficiencies of the hybrid photocatalytic hydrogen production reactor decrease from 5.74 to 4.54% and 5.11 to 4.04%, respectively with an increase in current density.     

Influence of bimetallic nanoparticles composition and synthesis temperature on the electrocatalytic activity of NiMn-incorporated carbon nanofibers toward urea oxidation

High efficiency, cost effectivity and the availability of hydrogen are the advantages of electrolysis as a strategy for urea-containing wastewater treatment. Composition, morphology, and synthesis-temperature distinctly affect the performance of the functional electro-catalysts. NiMn-incorporated carbon nanofibers are introduced as effective electrocatalysts for urea oxidation process. Studying the influence of the metallic nanoparticles composition indicated that the nanofibers obtained from an electro-spun solution containing 10 wt% manganese acetate reveal the best performance in terms of both of onset potential and current density. Typically, the nanofibers obtained from electros-pun solutions having 0, 5, 10 and 15 wt% manganese acetate showed 540, 495, 430 and 510 mV (vs. RHE) and 56, 32, 79 and 29 mA/cm² onset potentials and current densities, respectively at calcination temperature of 850 °C and 2 M urea solution. On the other hand, due to the impact on the crystallinity and final morphology, change in calcination temperature reflects the observable influence on the catalyst performance. At 2 M urea solution, the detected onset potentials and current densities were 590, 470, 430 and 440 mV, and 5, 22, 79 and 69 mA/cm² for the nanofibers calcined at 550, 700, 850 and 1000 °C, respectively. Accordingly, these results indicated that the synthesis temperature must be maintained at 850 °C. Overall, the study emphasizes the importance of optimizing the bimetallic electrocatalysts composition and synthesis temperature. Moreover, it was detected that the carbon nanofibers prepared from poly(vinyl alcohol) reveal high electric conductivity compared to the commercial nanofibers obtained from the expensive polyacrylonitrile polymer.     

Studies on the hydrogen evolution reaction on different stainless steels

The hydrogen generation by water electrolysis process is a promising technology. The materials commonly utilized for water electrolysis are those based on Raney Nickel and their alloys, but these materials are expensive. We choose a material with nickel presence, more cheap and versatile like stainless steel. In this work, we report the study of hydrogen evolution reaction (her) on different stainless steel electrodes in alkaline solutions (NaOH and KOH). The electrochemical behavior of stainless steel in alkaline medium was studied by cyclic voltammetry. In addition, we designed and developed an alkaline electrohydrolyzer prototype which consists of the anode and cathode electrodes which were made of different types of stainless steel and the electrolyte was KOH. We determined the appropriate electrolyte, stainless steel electrode and voltage for the efficient hydrogen production.     

Hydrogen evolution reaction of low carbon steel electrode in hydrochloric acid as a source for hydrogen production

The hydrogen evolution reaction (HER) (cathodic reaction) of low carbon steel electrode immersed in hydrochloric acid was investigated as a source for hydrogen production. Corrosion rate, hydrogen evolution rate, and current density increase with the increase of HCl concentration. Theoretically and practically, every 1 g of iron produces about 0.036 g of hydrogen. Therefore, the hydrogen production efficiency over the immersion period is about 100%. High correlation coefficient (close to +1) statistically indicates that there is a strong relation between loss in weight and the amount of evolved hydrogen (as dependent variable) and both time of immersion and acid concentrations (as independent variables). Application of the hydrogen produced by low carbon steel electrode has been performed on storage material. The tested material absorbs about 6 wt.% of hydrogen under atmospheric pressure and room temperature.     

预磁极化条件下PEM水电解制氢特性与效率研究

为提高质子交换膜（proton exchange membrane,PEM）水电解制氢速率、降低电解所需能耗,针对磁场预极化条件下蒸馏水的分子极性和应力特性进行研究,通过构建磁场环境下氢质子的能级跃迁微观物理模型与磁化矢量——极化氢质子浓度对应的宏观数学模型,对不同磁场强度下电解液的离子电导率、电流密度和制氢速率进行定性和定量分析,并利用自主搭建的可调节预磁极化PEM水电解制氢试验平台对所提出方法的有效性进行重复试验。试验结果表明,经过预磁极化处理的蒸馏水电导率提高了2~3倍,且随着磁场强度的增加,PEM电解电流密度不断增大,极间电圧不断减小,制氢速率明显提升。     

Preparation,characterization and hydrogen production performance of MoPd deposited carbon felt/Mo electrodes

Mo-coated carbon felt (C) supporting material modified by electrochemical deposition of trace amounts of MoPd binary composites having various metal ratios and characterized using various techniques. To our best knowledge, these materials is being reported firstly. The hydrogen evolution activity of the electrodes tested in 1 M KOH solution using electrochemical techniques. It shown that MoPd modified electrodes have large surface area, which is very beneficial for the rate of hydrogen evolution reaction (HER). Pd and Mo metals almost homogeneously distributes over the surface and no local aggregations are appeared. The loading of MoPd binary deposits over the Mo-coated C supporting material enhances the rate of the HER more and more when compared to the base substrate. The hydrogen evolution performance of the composites is depending on the metal ratios. The enhanced current density at the C/Mo-Mo₅₀Pd₅₀ electrode at ?1.60 V(Ag/AgCl) is 79.1% with respect to the C felt and 48.1% with respect to the C/Mo modified supporting material. The reduction in resistance related to hydrogen gas releasing at 100 mV overpotential was 97.2% and 58.6% with respect to bare C felt and C/Mo supporting material. The high hydrogen releasing performance of the PdMo-modified electrocatalysts related to intrinsic catalytic activities of Pd and Mo, a possible synergism between these metals and enhanced real surface area of the electrode. The C/Mo-Mo₅₀Pd₅₀ electrode has excellent electrochemical and physical stability during the long time electrolysis. Therefore, it is expected that the procedure applied here contribute to literature since the modifying C support by an active metal provides activation of electrocatalysts. Due to superior properties, we can suggest C/Mo-Mo₅₀Pd₅₀ electrode as promising cathode material for industrial water electrolysis which can reduces the energy input.     

Improvements of water electrolysis in alkaline media at intermediate temperatures

Studies were carried out on the electrochemical splitting of hydrogen from water in an aqueous KOH solution at 110–140°C and in molten hydroxides at 300–400°C with the aim of increasing the energy efficiency of hydrogen production. The investigations on the electrolysis in an aqueous KOH solution were concentrated on developing metal oxide diaphragms and improved activated Ni electrodes. At 140°C and a pressure of 8 bar, a cell voltage of 1.55 V was obtained at a current density of 500 mA cm^?2. In molten NaOH at 350°C, a cell voltage of 1.3 V was achieved at a current density of 500 mA cm^?2. However, current yields were only ca 90%, due to side reactions producing peroxides. The formation of peroxides is significantly reduced in a LiOH/NaOH melt. Current yields of 100% have now been obtained at a cell voltage of 1.45 V and current density 500 mA cm^?2. The hydrogen and oxygen formed are separated by a Ni-diaphragm which is cathodically protected to eliminate corrosion.     

Gas-phase electrolysis of hydrobromic acid using PTFE-bonded carbon electrode

The gas phase electrolysis of hydrobromic acid (48 wt%) was investigated for the development of the bromine-based thermochemical hydrogen production process, by using PTFE-bonded carbon electrode. Investigation of the anodic behaviour by using a half cell showed that the electrode performance was largely affected by the type of carbon used, the fabrication pressure, the content of PTFE, and the hydrophobicity of the electrode. The anodic potential was stable for 10 h at the current density of 144 mA cm⁻². The loading of Pt catalyst was very effective on the cathodic behavior. When adopted to a fuel-cell type electrolyser, the PTFE-bonded electrode showed better performance than the graphite-felt electrode; the current density of 120 mA cm⁻² and HBr conversion of 45% were achieved at cell voltage of 0.80 V at 423 K.     

Hydrogen production by electrolysis of a phosphate solution on a stainless steel cathode

The catalytic properties of phosphate species, already shown on the reduction reaction in anaerobic corrosion of steels, are exploited here for hydrogen production. Phosphate species work as a homogeneous catalyst that enhances the cathodic current at mild pH values. A voltammetric study of the hydrogen evolution reaction is performed using phosphate solutions at different concentrations on 316L stainless steel and platinum rotating disk electrodes. Then, hydrogen is produced in an electrolytic cell using a phosphate solution as the catholyte. Results show that 316L stainless steel electrodes have a stable behaviour as cathodes in the electrolysis of phosphate solutions. Phosphate (1 M, pH 4.0/5.0) as the catholyte can equal the performance of a KOH 25%w solution with the advantage of working at mild pH values. The use of phosphate and other weak acids as catalysts of the hydrogen evolution reaction could be a promising technology in the development of electrolysis units that work at mild pH values with low-cost electrodes and construction materials.     

Porous nickel electrodes in water electrolysis 1. Electrode preparation and polarization studies in strong alkali

Replacement of “plate” electrodes in water electrolysis cells by porous nickel electrodes leads to many advantages resulting in reduced specific energy consumption for hydrogen production. Yet, the behaviour of porous electrodes in alkaline or acidic electrolysis has not been extensively studied; available data at temperatures above 70°C is negligible. This paper describes the techniques developed to prepare the porous electrodes, their physical characteristics and their performance in strong alkali as hydrogen and oxygen gas electrodes. Steady state cell polarization studies over a range of 100 to 10,000 ASM at different temperatures were carried out in 6N KOH solution for different electrode samples prepared by alloy electrodeposition and powder metallurgy methods. Electrodes prepared by these two methods were compared with respect to their electrochemical performance. The current carrying capacity at a given overvoltage was evaluated for different electrode thicknesses. These electrodes have been used successfully in test modules of bipolar filter press type construction for hydrogen production.     

An aluminum/cobalt/iron/nickel alloy as a precatalyst for water oxidation

Among different strategies, water splitting toward hydrogen production is a promising process to store energy from intermittent sources. However, the anodic water oxidation is a bottleneck for water splitting. In this paper, we report an aluminum/cobalt/iron/nickel alloy as a precatalyst for the electrochemical water oxidation. The alloy electrode contains different metal ions including cobalt, iron, and nickel which all are efficient for water oxidation is tested. We characterized this electrode using scanning electron microscopy, transmission electron microscopy, diffuse reflectance infrared Fourier transform spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and electrochemical methods. After stabilization, the electrode shows an onset overpotential of 200.0 mV and affords a current density of 3.5 mA cm^?2 at an overpotential of 600.0 mV in KOH solution at pH 13.