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.     

Electrochemical characterization of a NiCo/Zn cathode for hydrogen generation

Hydrogen is considered to be the most promising candidate as a future energy carrier. One of the most used technologies for the electrolytic hydrogen production is alkaline water electrolysis. However, due to the high energy requirements, the cost of hydrogen produced in such a way is high.In continuous search to improve this process using advanced electrocatalytic materials for the hydrogen evolution reaction (HER), high area NiCo/Zn electrodes were prepared on AISI 304 stainless steel substrates by electrodeposition. After preparing, the alloys were leached of to remove part of the zinc and generate a porous layer (type Raney electrodes). The presence of a thin Ni layer between the substrate and the Raney coating favour the adherence of the latter. The porous NiCo/Zn electrode was characterized by SEM, EDX, confocal laser microscopy, and electrochemical impedance spectroscopy. HER on this electrode was evaluated in 30 wt.% KOH solution by means of polarization curves, hydrogen discharge curves, and galvanostatic tests. Results show that the developed electrode presents a most efficient behaviour for HER when comparing with the smooth Ni cathode. The high electrode activity was mainly attributed to the high surface area of the developed electrode.     

Experimental investigation of solar-hydrogen energy system performance

Recently, the Solar-hydrogen energy system (SHES) becomes a reality thanks as well as a very common topic to energy research in Egypt as it is now being the key solution of different energy problems including global warming, poor air quality and dwindling reserves of liquid hydrocarbon fuels. Hydrogen is a flexible storage medium for energy and can be generated by the electrolysis of water. It is more particularly advantageous and efficient when the electrolyzer is simply coupled to a source of renewable electrical energy. This paper examines the operation of alkaline water electrolysis coupled with solar photovoltaic (PV) source for hydrogen generation with emphasis on the electrolyzer efficiency. PV generator is simulated using Matlab/Simulink to obtain its characteristics under different operating conditions with solar irradiance and temperature variations. The experimental alkaline water electrolysis system is built in the fluid mechanics laboratory of Menoufiya University and tested at certain input voltages and currents which are fed from the PV generator. The effects of voltage, solution concentration of electrolyte and the space between the pair of electrodes on the amount of hydrogen produced by water electrolysis as well as the electrolyzer efficiency are experimentally investigated. The water electrolysis of different potassium hydroxide aqueous solutions is conducted under atmospheric pressure using stainless steel electrodes. The experimental results showed that the performance of water electrolysis unit is highly affected by the voltage input and the gap between the electrodes. Higher rates of produced hydrogen can be obtained at smaller space between the electrodes and also at higher voltage input. The maximum electrolyzer efficiency is obtained at the smallest gap between electrodes, however, for a specified input voltage value within the range considered.     

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.     

Prospects for hydrogen production by water electrolysis to be competitive with conventional methods

With the impending unavailability of oil and natural gas, hydrogen will be produced on a large scale in the United States (1) from coal, or (2) by water electrolysis using electricity derived from nuclear or solar energy. In many parts of the world which lack fossil fuels, the latter will be the only possible method. The cost of purification of hydrogen produced from fossil fuels will increase its cost to about the same level as that of electrolytic hydrogen. When hydrogen is required in relatively small quantities too, the electrolytic method is advantageous. To minimize the cost of hydrogen produced by water electrolysis, it is necessary to reduce capital costs and approach 100% energy efficiencies. Areas of research, which will be necessary to achieve these goals are: (1) maximization of surface areas of electrodes; (2) use of thin electrolyte layers; (3) increase of operating temperature in alkaline water electrolysis cells to about 120–150°C; (4) selection and evaluation of separator materials; (5) electrocatalysis of the hydrogen and oxygen electrode reaction; (6) mixed oxides as oxygen electrodes; and (7) photoelectrochemical effects. The progress made to date and proposed studies on these topics are briefly dealt with in this paper. The General Electric Solid Polymer Water Electrolyzer and Teledyne Alkaline Water Electrolysis Cells, operating at about 120–150°C, look most promising in achieving the goals of low capital cost and high energy efficiency.     

Electrocatalytic activation of Ni electrode for hydrogen production by electrodeposition of Co and V species

Hydrogen is considered to be the most promising candidate as a future energy carrier. One of the most used technologies for the electrolytic hydrogen production is alkaline water electrolysis. Electrode materials used in alkaline water electrolysis are mainly made from Ni or Ni-based alloys due to their desirable mechanical and chemical stability in hot and alkaline solution. Considerable research effort has been conducted on enhancement of electrocatalytic activity of Ni electrodes.     

Intermetallics as advanced cathode materials in hydrogen production via electrolysis

Intermetallics phases along Mo–Pt phase diagram have been investigated as cathode materials for the production of hydrogen by electrolysis from water KOH solutions, in an attempt to increase the electrolytic process efficiency. These materials were compared with conventional cathodes (Fe and Ni), often used in the alkaline electrolysis, and also with the intermetallic Ti–Pt. An significant upgrade of the electrolytic efficiency using intermetallics in pure KOH electrolyte was achieved in comparison with conventional cathode materials.     

A highly efficient hydrogen generation electrolysis system using alkaline zinc hydroxide solution

Alkaline water electrolysis is a well-established conventional technique for hydrogen production. However, due to its relatively high energy consumption, the cost of hydrogen produced by this technique is still high. Here in this work, we report for the first time the application of alkaline zinc hydroxide solution (composed of sodium zincate and potassium zincate in NaOH and KOH solutions, respectively) as an efficient, simple and recursive electrolyte for producing clean hydrogen through a continuous dual-step electrolysis process. The ionic conductivity, electrodes current density, and hydrogen evolution rate were measured in a wide range of the electrolyte concentrations (0.1–0.59 M). Also, the cell efficiency was studied at different ranges of current density (0.09–0.25 A/cm2) and applied potential (1.8–2.2 V). Results indicated that the application of alkaline zinc hydroxide solution at the optimum electrolyte concentration can enhance the hydrogen evolution rate minimally by a factor of 2.74 (using sodium zincate) and 1.47 (using potassium zincate) compared to the conventional alkaline water electrolysers. The results of this study could be helpful to better understand the electrochemical behaviour of the alkaline water electrolysers when sodium zincate and potassium zincate are used as ionic activators for enhancing hydrogen evolution.     

Design of ternary Al-Sn-Fe alloy for fast on-board hydrogen production, and its application to PEM fuel cell

An Al-Sn-Fe alloy is designed to increase the hydrogen generation rate even in weak alkaline water through the effective removal of Al oxide. Al-1wt.%Sn-1wt.%Fe alloy exhibits the hydrogen generation rate about 6 times higher than pure Al and 1.6 times higher than Al-1wt.%Fe alloy. Increases in exchange current density of Al alloys are in good accordance with increases in hydrogen generation rate. The addition of Sn in Al-Fe alloy can increase the hydrolysis rate by accelerating the breakdown of passive film (Al(OH)₃ and Al₂O₃) in an alkaline solution. Hence, the Al-1wt.%Sn-1wt%Fe alloy shows a much higher hydrogen generation rate than pure Al and Al-1wt.%Fe alloy in relatively weak alkaline water. In the hydrolysis of Al-1wt.%Sn-1wt%Fe, Fe accelerates the hydrogen production by inducing simultaneously both inter-granular and galvanic corrosion, whereas Sn increases the hydrogen generation rate by breaking the Al oxide down effectively. Based on the increase in the hydrogen generation rate of Al-1wt.%Fe and Al-1wt.%Sn-1wt%Fe alloys over pure Al, the contribution to the increase of Fe and Sn are calculated to be 63% and 27%, respectively. Because the same amount of power is obtained by PEMFC using 6 times less Al-Sn-Fe alloy than pure Al, the weight and volume of on-board hydrogen production reactor can be reduced significantly by alloying Al with a small amount of Fe and Sn.     

纯铜、纯然电极和铜钴合金电极在碱性介质中的光电化学研究

用动电位伏安法对纯铜电极,纯钴电极以及含钴量5.1%,9.7%,15%,25%和40％的铜钴合金电极在硼砂－硼酸缓冲溶液（pH8.5)中的光电化学行为进行了研究,纯铜电极,纯钴电极和铜钴合金电极均显示P－型光响应,纯铜电极的光响应来自Cu2O,纯钴电极的光响应主要来自Co3O4,铜钴合金电极的光响应来自Cu2O和Co3O4的共同作用,纯铜电极在阳极氧化过程中存在着Cu的阳极溶解和电极表面生成Cu2O膜的反应,温度升高有利于Cu2O膜的生成,除氧与否影响纯铜电极的成膜反应,纯钴电极电位正向扫描时不湿示光响应,负向扫描时显示阴极光电流,铜钴合金是极的光响应随含钴量而变化。     

纯铜、纯钴电极和铜钴合金电极在碱性介质中的光电化学研究

用动电位伏安法对纯铜电极、纯钴电极以及含钴量5.1%、9.7%、15%、25%和40%的铜钴合金电极在硼砂—硼酸缓冲溶液(pH8.5)中的光电化学行为进行了研究。纯铜电极、纯钴电极和铜钴合金电极均显示P-型光响应,纯铜电极的光响应来自Cu2O,纯钴电极的光响应主要来自Co3O4,铜钴合金电极的光响应来自Cu2O和Co3O4的共同作用。纯铜电极在阳极氧化过程中存在着Cu的阳极溶解和电极表面生成Cu2O膜的反应,温度升高有利于Cu2O膜的生成,除氧与否影响纯铜电极的成膜反应。纯钴电极电位正向扫描时不显示光响应,负向扫描时显示阴极光电流。铜钴合金电极的光响应随含钴量而变化。     

Nanostructured Ni–Co alloy electrodes for both hydrogen and oxygen evolution reaction in alkaline electrolyzer

Ni–Co alloy nanostructured electrodes with high surface area were investigated both as a cathode and anode for an alkaline electrolyzer. Electrodes were obtained by template electrosynthesis at room temperature. The electrolyte composition was tuned in order to obtain different NiCo alloys. The chemical and morphological features of nanostructured electrodes were evaluated by EDS, XRD and SEM analyses. Results show that electrodes with different composition of Ni and Co, made of nanowires well anchored to the substrate, were obtained. For both hydrogen and oxygen evolution reactions, electrochemical and electrocatalytic tests, performed in 30% w/w KOH aqueous solution, were carried out to establishing the best alloy composition. Mid-term tests conducted at a constant current density were also reported. Nanostructured electrodes with a Co atomic composition of 94.73% have the best performances for both hydrogen and oxygen evolution reactions. In particular, with this alloy, a potential of ?0.43 V (RHE) and of 1.615 V (RHE) was measured for hydrogen and oxygen evolution reaction at ?50 mA cm^?2 and at 50 mA cm^?2, respectively, after 6 h of electrolysis. The calculated Tafel's slopes for HER and OER were ?0.105 and 0.088 V/dec, respectively. Furthermore, HER and OER η₁₀ potential values were measured founding ?0.231 V (RHE) and 1.494 V (RHE) respectively.     

Performance of SPE electrodes in electrolytic regeneration process of desulfurization of iron complex

In the alkaline system, the iron complex was used to absorb hydrogen sulfide to obtain sulfur, and the iron complex absorbent was oxidized and regenerated at the anode by electrolysis method for recycling, and hydrogen was obtained at the cathode. This process can recover both hydrogen and sulfur from hydrogen sulfide and avoid the harsh conditions of strong acidity. In this paper, SPE electrode is used in the oxidation and regeneration process of iron complex. The results show that the oxidation current density of iron complex at SPE electrodes are one order of magnitude higher than that of traditional electrodes, and the current efficiency is slightly lower than that of traditional electrode. The current efficiency of carbon cloth SPE electrode reaches 90% from 0.25 to 0.5V, the performance of complexed iron oxidation is better than that of the stainless-steel mesh SPE electrode, and the side reaction is mainly EDTA oxidation reaction.     

Three-dimensional nickel nanodomes: Efficient electrocatalysts for water splitting

Highly efficient and stable three-dimensional (3D) Ni nanodome (Ni-NDs) arrays were fabricated as candidate cathode materials for alkaline water splitting. The NDs were prepared by a combined methods of soft lithography-nanosphere lithography, physical vapor deposition (PVD) and electrochemical deposition using polydimethylsiloxane (PDMS) as template. The water splitting activity of the 3D nanostructures were examined in 6 M KOH solution using polarization and electrochemical impedance spectroscopy techniques. The data obtained showed that well-structured and uniformly distributed Ni-NDs could be fabricated using this combined method. The ND arrays perform excellent hydrogen evolution activity with respect to Ni plate as a reference point since their nano-sized roughness results in larger real surface area. By comparing with Ni plate, lower hydrogen onset potential (85 mV) and charge transfer resistance (90.1%) as well as higher current density (90.4%) corresponding to the amount of evolved hydrogen were observed at the NDs. The Ni-NDs have high time-stability in the electrolysis conditions. It is believed that the Ni-ND arrays contribute to the design of novel electrocatalytic electrodes as candidate supporting materials.     

Conceptual design of large scale water electrolysis plant using solid polymer electrolyte technology

In an energy conscious environment, the key to the applicability of water electrolysis as a means for generation of hydrogen in bulk quantities is the achievement of high efficiencies (i.e. over 90%) at high enough current densities to keep the capital costs within economic bounds. The solid polymer electrolyte (SPE) water electrolysis technology developed by the General Electric Company is now demonstrating these efficiencies at current densities up to 500 A ft⁻², and the results of recent laboratory testing show a potential for increasing this to 2000 A ft⁻² within the next 10 years. This capability now makes water electrolysis one of the most promising methods for generating hydrogen from nuclear, solar or other non-fossil fuel energy sources.

The performance and life test results are shown including laboratory cells on which future performance projections are based. The design and development status of a scaled-up electrolysis cell suitable for large-sized hydrogen generation plants is described. Estimated capital costs and operating costs are projected from which the resultant hydrogen costs are calculated.     

Development and testing of a novel catalyst-coated membrane with platinum-free catalysts for alkaline water electrolysis

A stable, platinum-free catalyst-coated anion-exchange membrane with a promising performance for alkaline water electrolysis as an energy conversion technology was prepared and tested. A hot plate spraying technique used to deposit electrodes 35 or 120 μm thick on the surface of an anion-selective polymer electrolyte membrane. These thicknesses of 35 and 120 μm corresponding to the catalyst load of 2.5 and 10 mg cm⁻². The platinum free catalysts based on NiCo₂O₄ for anode and NiFe₂O₄ for cathode were used together with anion selective polymer binder in the catalyst/binder ratio equal to 9:1. The performance of the prepared membrane-electrode assembly was verified under conditions of alkaline water electrolysis using different concentrations of liquid electrolyte ranging from 1 to 15 wt% KOH. The electrolyser performance was compared to a cell utilizing a catalyst-coated Ni foam as the electrodes. The prepared membrane-electrode assembly stability at a current load of 0.25 A cm⁻² was verified by a 72-hour electrolysis test. The results of the experiments indicated the possibility of a significant reduction of the catalyst loading compared to a catalyst-coated substrate approach.     

Corrosion-resistant non-noble metal electrodes for PEM-type water electrolyzer

Developing cheap and highly durable non-noble metal catalysts for water electrolysis to sustainably produce hydrogen as alternatives to platinum-based catalysts is essential. Herein, we report graphene-encapsulated NiMo alloys as acid-stable non-noble metal catalyst electrodes. The graphene-encapsulated NiMo cathode showed a highly stable performance in the potential cycling test (10,000 cycles) from 0 to 5.0 A cm⁻² and 100 h of durability at a 2.2 V constant cell voltage. A balance between catalytic activity and corrosion in acidic environments was achieved by tuning the number of N-doped graphene layers. Through their application in a full-cell PEM-type water electrolyzer, we verify that noble metal catalysts can be replaced by non-noble metal catalysts. Such cheap acid-stable non-noble metal electrodes have promising practical applications in PEM-type water electrolysis.     

Ni alloy nanowires as high efficiency electrode materials for alkaline electrolysers

The fabrication and characterization of nickel-alloy electrodes for alkaline electrolysers is reported. Three different alloys (Ni–Co, Ni–Zn and Ni–W) at different composition were studied in order to determine the optimum condition. Nanostructured electrodes were obtained by template electrodeposition into a nanoporous membrane, starting from aqueous solution containing the two elements of the alloy at different concentrations. Composition of alloys can be tuned by electrolyte composition and also depends on the difference of the redox potential of elements and on the presence of complexing agents in deposition bath. Electrochemical and electrocatalytic tests, aimed at establishing the best alloy composition, were carried out for hydrogen evolution reaction. Then, test conducted at a constant current density in potassium hydroxide (30% w/w) aqueous solution were also performed. For all investigated alloys, very encouraging results were obtained and in particular Ni–Co alloys richer in Co showed the best performance.     

Low overvoltage electrocatalysts for hydrogen evolving electrodes

An electrocatalyst for hydrogen evolving cathodes has been developed for use in alkaline media. The materials employed in manufacturing the coating are relatively cheap transition metals. The results of a variety of performance tests are reported. The electrodes exhibit a low overvoltage for hydrogen evolution (70–90 mV at 70°C and 1A cm^?2 in 5 N KOH), stability to abuse (e.g. current interruption or reversal) and a long cathode life under operating conditions.     

Enhanced hydrogen production through alkaline electrolysis using laser-nanostructured nickel electrodes

This study describes the fabrication of ultrafast laser-induced periodic nanostructures on Nickel sheets and their use as cathodes in alkaline electrolysis. For the first time, to the best of our knowledge, laser-nanostructured Ni sheets were used as cathode electrodes in a custom-made electrolysis cell at actual, Hydrogen producing conditions, and their efficiency has been compared to the untreated Nickel sheets. The electrochemical evaluation showed higher J_peaks, lower overpotential, and enhanced double-layer capacitance for the nanostructured electrode. A decrease in the Tafel slope was also found for the nanostructured electrode. The hydrogen production efficiency was found to be 3.7 times larger for the laser-nanostructured Nickel electrode, which was also confirmed by current-time measurements during electrolysis. Also, a novel approach is proposed to improve the stability of the current density during electrolysis and, therefore, the hydrogen production process by about 10%.