Hydrogen evolution on porous Ni cathodes modified by spontaneous deposition of Ru or Ir

Porous Ni deposits, prepared by cathodic deposition, were modified by immersing them in acid deaerated solutions containing Ru(III) or Ir(IV) chloride complexes with which they readily reacted, without any activation procedure, giving rise to spontaneous deposition of either Ru or Ir. The obtained electrodes were investigated by cyclic voltammetry, impedance spectroscopy and scanning electron microscopy. All data showed that the initial large area of the Ni deposits further increased upon immersion in solutions of noble metal complexes. EDX analyses proved that the deposition of Ru reached a limiting situation in some hours, while that of Ir was slower and continued for a longer time. The persistence of intense peaks due to the Ni(II)/Ni(III) redox system showed that Ru and Ir did not form a continuous layer able to prevent the contact between Ni and electrolyte. Hydrogen evolution was studied in 1 M NaOH solutions. Spontaneous deposition of both noble metals markedly improved the performance of porous Ni. The best results were achieved with Ir-modified electrodes, after immersion in Ir(IV) solution for 6 h. Tafel slopes and overpotentials of Ru-modified electrodes were not as low as those of Ir-modified electrodes.     

Ni and Mo coatings as hydrogen cathodes

The catalytic activity of hydrogen cathodes based on Ni/Mo coatings prepared in different ways has been investigated under conditions of advanced alkaline water electrolysis in 10m KOH at 100°C, in the current density range 0.05–1.0 A cm^–2. The activity of electrodeposited Ni/Mo and Ni/Mo/V coatings was quite low, apparently due to their low effective surface area. The activity of all thermally deposited Ni/Mo coatings, electrodeposited Ni/Mo/Cd coatings and of Raney nickel-Mo alloys has been found to be high. When accompanied by some current interruptions of various durations, however, it successively decreased during long-time electrolysis, especially when the residual potential of the electrode, after the current interruption, approached a certain threshold value. The rate of electrode deactivation depends on its mode of preparation as well as on electrolysis conditions, particularly on conditions during the current interruptions. The Mo content in the coating decreased quickly by a factor of 2–10 under operating values of both Tafel constants. The addition of Mo to the expressed as an increase in the absolute values of both Tafel constants. The addition of Mo to the Raney nickel improves its catalytic efficiency as long as Mo is not dissolved. The enhancing of catalytic activity by Mo in Raney nickel is partly caused by synergetic effects between Ni and Mo, as follows from their electronic structure, and partly by material stabilization as follows from comparison with the Raney nickel (Zn).     

析氢对电沉积镍枝晶生长的影响

采用点电极电沉积的方法,在环形电解池中用自行设计的试验装置研究了不同电压和NiSO4质量浓度时,析氢对电沉积金属镍枝晶二维生长行为的影响。研究发现,析氢对沉积产物的形貌影响显著,氢气的大量析出有利于枝晶产生分枝,使沉积物的形貌趋于致密。     

电沉积制备多孔Ni-Fe-Sn合金电极及其析氧性能

采用直流电沉积法在铜箔表面合成了多孔结构的Ni–Fe–Sn合金,用扫描电子显微镜、X射线能谱仪和X射线衍射仪对合金的微观组织形貌和相态进行了表征,用电化学工作站测试了合金电极在碱性环境中的析氧性能。结果表明,Ni–Fe–Sn合金电极主要由Ni3Sn2和FeNi3相组成,电极表面形成了多孔结构。在30wt% KOH溶液中,Ni–Fe–Sn合金的析氧过电位仅为261 mV(电流密度10 mA/cm2),Tafel斜率为69.9 mV/dec。电极在10 mA/cm2电流密度下能稳定工作12 h以上,具有良好的电化学稳定性。     

Crystalline/amorphous Ni/NixSy supported on hierarchical porous nickel foam for high-current-density hydrogen evolution

Manufacturing efficient and durable electrodes for alkaline water electrolysis under high-current-density conditions is a great challenge. Herein, Ni/Ni_xS_y heterostructure was grown on designed porous nickel foam (PNF) to construct Ni/Ni_xS_y-PNF electrode by a facile and scalable method for alkaline hydrogen evolution reaction (HER). The hierarchical porous structure and super-hydrophilic surface of Ni/Ni_xS_y-PNF accelerate the mass transfer and bubble detachment at high current densities. Theoretical calculations reveals that the enhanced HER activity of Ni/Ni_xS_y heterostructure is attributed to the stronger H₂O adsorption. The resulting Ni/Ni_xS_y-PNF electrode achieves current densities of 100 and 500 mA cm⁻² at low overpotentials of 61 and 121 mV, respectively. When applied for overall water splitting, the Ni/Ni_xS_y-PNF||Fe-Ni₃S₂-PNF electrolyser reaches a current density of 10 mA cm⁻² at an extremely low voltage of 1.32 V. This work provides an effective strategy for fabricating high-performance electrodes for practical water electrolysis.     

Fabrication and characteristics of porous Ni and NiO(Li) cathodes for MCFC

In-situ Ni andex-situ NiO(Li) cathodes were fabricated by cold pressing using Ni powder and Li₂CO₃ (in case ofexsitu cathode) with paraffin wax as a binder. The effects of compaction pressure, amount of binder, and sintering temperature on porosity, the average size of pore, Li^* cation fraction, and the fracture strength were investigated in this study. The optimum compaction pressure was 100 kg/cm² to prevent the brittleness and stress concentration caused by high compaction pressure. Also, 10 wt% of binder yielded best results and the strength decreased dramatically and revealed nonuniform pore and pore distribution beyond 10 wt%. To obtain reasonably high electric conductivity inexsitu cathode, the sintering temperature was chosen to be below 950°C to maintain the ration fraction of Li* is in the range of 0.02–0.06. In terms of the Ni-dissolution rate,exsitu cathode was more efficient thaninsitu cathode in the long-term operation except the initial 24hr period.     

Mechanistic study of the hydrogen evolution reaction on Ni-Zn and Ni-S cathodes

Electrodeposited Ni-Zn and Ni-S on a mild steel substrate have shown very good performance as cathode materials for the HER in alkaline media. The materials were studied previously with surface techniques and evaluated through current-potential curves and long term operation. This paper describes a detailed mechanistic study of the HER on Ni-Zn and Ni-S carried out with impedance techniques. In both cases the reaction proceeds through a Volmer-Heyrovsky mechanism. As predicted by kinetic theory, the temperature study shows that the energy of activation of the rate determining step is the same as the energy of activation of the overall reaction.This paper is dedicated to Professor Brian E. Conway on the occasion of his 65th birthday, and in recognition of his outstanding contribution to electrochemistry.     

氟化物电沉积铬中十八烷基三甲基氯化铵的阻氢作用

在硫酸铝、草酸钠、硫酸钠、氟化钠及硼酸的混合介质中,用极化曲线法研究了十八烷基三甲基氯化铵(简称1831)在铬电极表面的阻氢作用.采用正交试验,讨论了1831用量、温度、pH和搅拌速率对析氢电位负移量的影响,确定了最佳实验条件为:1831 20mg/L,温度35℃,pH 1.7,搅拌速率0.56mL/s.在该工艺条件下,金属铬沉积的电流效率提高了13.24%.实验证明,1831是氟化物体系中铬电沉积的有效阻氢剂.     

The effect of electrodeposition potential on catalytic properties of Ni nanoparticles for hydrogen evolution reaction (HER) in alkaline media

Journal of Applied Electrochemistry - The fabrication of non-precious electrocatalyst for water splitting has a great potential. So, Ni electrocatalysts are considered one of the most auspicious...     

电沉积镍-钼-钴泡沫合金析氢电极的工艺研究

以聚氨酯海绵为基体,通过导电化处理、电沉积Ni–Mo–Co合金以及热分解处理工艺,制备了Ni–Mo–Co泡沫合金。研究了七水合硫酸钴和二水合钼酸钠用量、电流密度、温度等电沉积工艺参数对合金析氢性能的影响。结果表明,在七水合硫酸钴用量为14g/L,二水合钼酸钠用量为10g/L,温度为35°C,电流密度为8A/dm2的条件下制备的泡沫合金有最高的析氢活性,具有很大的比表面积。扫描电镜观察显示,制备的Ni–Mo–Co合金为三维网状结构,合金骨架有大量的微裂纹,表面为均匀致密的球状颗粒。     

电沉积制备镍-铁-钨合金析氢电极的工艺研究

以紫铜片为基体电沉积制备了Ni–Fe–W合金电极。研究了镀液中不同组分的浓度和工艺条件对Ni–Fe–W合金析氢性能的影响,得到最佳镀液配方和工艺条件为:NiSO4·6H2O80g/L,FeSO4·7H2O20g/L,Na2WO4·2H2O0.020mol/L,Na3C6H5O7·2H2O 0.5 mol/L,H3BO3 0.65 mol/L,Na2SO4 0.1 mol/L,十二烷基硫酸钠0.1 g/L,pH 5~6,温度30°C,电流密度4 A/dm2,磁力搅拌800 r/min,时间30 min。在该条件下所得Ni–Fe–W合金电极表面Ni、Fe和W的原子分数为63.79%、34.35%和1.86%,具有较大的比表面积,在30%KOH溶液中的析氢催化活性较好。     

The degree of coverage of silver cathodes with adsorbed atomic hydrogen during hydrogen evolution in alkaline solutions

A method has been devised whereby fractions of a monolayer of adsorbed H, corresponding to the steady state concentration of H upon Ag electrodes during the evolution upon them of electrolytic H₂, may be measured to an accuracy of about 25%. It utilizes galvanostatic charging techniques to obtain the total quantities of electricity utilized in dissolving H anodically from the electrode under conditions when oxide is also formed upon it, and a further galvanostatic charging process by which a correction for the oxide formation can be made.Rigorous experimental conditions must be employed. Special techniques have been employed in preparing the surface of Ag electrodes in a reproducible state, in preparing the solution in a state relatively free from depolarizers, and in changing the mode of polarization of the electrode from constant cathodic current to constant anodic current in 2 μsec.The results are strongly dependent upon the current density of the anodic charging process, and reach a constant low value when this is sufficiently high. At an over-potential of −400 mV on Ag in o.r N NaOH, about 10% of the electrode surface is covered with H.The degree of coverage varies logarithmically with the current density of cathodic polarization. The presence of 10⁻⁴ moles/l As₂O₃ in the solution increases the steady state concentration of H by about 250%.The potential at which H dissolution commences, and the variation of the steady state coverage of the electrode, are consistent only with a rate-determining discharge of protons from water molecules, followed by a recombinative desorption. “Reduced rate constants” for the discharge and combinative desorption are calculated.     

脉冲和直流电沉积Ni-P合金电极析氢电催化性能的研究

在由250 g/L NiSO4·6H2O、45 g/L NiCl2·6H2O、36 g/LH3BO3、20 g/L NaH2PO2·H2O和0.05～0.10 g/L十二烷基硫酸钠组成的镀液(pH 4.0～5.5)中,分别用脉冲和直流电沉积法在镍片上获得了Ni-P合金镀层,并进行了对比研究,SEM测试结果表明,脉冲电沉积方法获得的Ni-P合金镀层表面更加细致,电化学测试结果表明,脉冲电沉积镀层的交换电流密度较大,具有良好的析氢电催化活性,优良的电化学稳定性和良好的结合力及耐蚀性.     

工艺参数对氢气泡模板法电沉积多孔镍薄膜比表面积的影响

以阴极析出的氢气泡为模板制备出多孔镍薄膜.用显微镜观察了孔壁结构、孔径大小和分布状况,用电化学工作站测试了多孔镍薄膜的阻抗性能并计算出其比表面积.通过正交试验确定的制备多孔镍的最佳工艺条件为:氯化铵1.5 mol/L,氯化镍0.1 mol/L,温度40℃,时间20 s.在最佳工艺条件下制备的薄膜孔分布均匀,结合力较好,...     

Influence of electrodeposition techniques on Ni nanostructures

Different Ni nanostructure arrays were fabricated by pulsed electrodeposition from a Watts bath inside the pores of anodic alumina membrane (AAM) templates. Under a trapezoidal waveform of potential, consisting of fast linear sweeps between 0 and −3 V (SCE) interleaved by delay times at 0 (10 s) and −3 V (0.1 s), Ni nanowires were grown. The rate of nanowires growth was constant up to 60 min of deposition. For longer times, the growth of nanowires was not uniform, and after about 180 min some nanowires reached the template surface exposed to the electrolyte. Under square potential pulses between the same potentials (pulse length 1 s), nanotubes of Ni are obtained. Morphological analysis of these nanostructures at different lengths revealed that the inner profile of nanotubes evolved from cylindrical to conical with increasing deposition time. The possibility to grow either nanowires or nanotubes in dependence of the potential waveform, as well as the growth rate of nanostructures were discussed taking into account the reaction of hydrogen evolution, occurring simultaneously with Ni electrodeposition.     

Characterisation of indentation microstructures for porous SOFC cathodes

In this study, high-resolution focused ion beam sectioning assisted with SEM imaging was used to study the indentation microstructures of porous bulks and films of a solid oxide fuel cell cathode material (La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ) sintered at different temperatures. The crack morphologies and pore-filling densification caused by crushing of particle networks were studied in details. Analysis showed distinct permanent deformation mechanisms of the indentation microstructures between porous bulks and films. Whilst remarkable porosity gradient was found for the porous films under both Berkovich and spherical indenters, the porous bulks were found to behave more like dense materials. Results also showed that radial cracks induced by Berkovich indentation on the bulks could not generate observable pop-in/pop-out events in the loading-unloading curves. However, when indenting with the spherical indenter on a thick film, the shear sliding of the particle networks immediately under the indenter could cause phenomenal disruption in the loading unloading curves shown.     

离子膜电解槽用纳米Ni-Mo合金阴极的制备及其催化析氢性能

采用正交实验法确定了电沉积N i-Mo合金的最佳工艺。通过测试N i-Mo合金在模拟氯碱工业离子膜电解槽工艺条件下的阴极极化曲线,考察了N i-Mo合金电极的催化析氢性能。结果表明,当电流密度为3.0kA/m2时,N i-Mo合金电极的析氢过电位较镀镍电极降低约400 mV,反应活化能仅为24.89 kJ/mol。扫描电镜观察到N i-Mo合金电极表面微观粗糙,X射线衍射测试结果表明,所制备的N i-Mo合金为纳米晶结构,平均晶粒尺寸为2.25 nm。     

Effect of electrodeposition parameters on the hydrogen permeation during Cu-Sn alloy electrodeposition

The Cu-Sn alloy coatings were synthesized on 27SiMn steel by direct current (DC), pulse current (PC) and pulse reverse current (PRC) electrodeposition techniques from pyrophosphate-based electrolyte. The hydrogen permeation behaviors during the electrodeposition by different techniques were investigated using Devanathan-Stachurski method. The results demonstrated that the hydrogen permeation amount of different electrodeposition techniques decreased in the order: DC > PC > PRC. Frequency and duty cycle have great effect on the sub-surface concentration C_o of atomic hydrogen and hydrogen permeation amount. The minimum of hydrogen permeation amount was observed at the frequency of 1000 Hz or 2500 Hz and the duty cycle of 40%. It indicates that the amount of permeated hydrogen in the steel during deposition can be reduced due to the decrease of C_o by PC and PRC methods.