Antoni Budniok

Ni+Ti composite layers as cathode materials for electrolytic hydrogen evolution

Abstract Ni+Ti composite layers were obtained by electrolytic codeposition of nickel and titanium powder from an electrolyte containing Ti powder suspension. Their chemical composition depends on the amount of titanium powder dispersed in galvanic bath as well as on the size of titanium grains. From the analysis of the Auger spectra line profile of Ti (LMV) the presence of nonstoichiometric Ti oxides and NiTi intermetallic compounds on the layers’ surface was observed. The obtained layers were used as electrode materials for hydrogen evolution in an alkaline environment. Based on recorded j–E curve, the Tafel equation parameters for this process were determined. Electrochemical impedance spectroscopy was used to study the interfacial properties at electrode overpotential η=−0.2 V . It was found, that investigated Ni+Ti composite layers are characterized by increased electrochemical activity for hydrogen evolution compared to nickel coatings. Their greater activity in this process may be attributed to the developed electrode surface arising from the incorporation of Ti powder into the nickel matrix as well as to the presence of nonstoichiometric titanium oxides and intermetallic Ni−Ti compounds. The values of surface roughness factors Rf were also determined.

Production and properties of composite layers based on an Ni–P amorphous matrix

Composite layers Ni–P + Co, Ni–P + W and Ni–P + Ti were obtained in galvanostatic conditions, at jdep = 0.200 A cm−2. The x-ray diffraction method was used to determine the phase composition of the layers and atomic absorption spectrometry was applied to specify their chemical composition. A metallographic microscope, stereoscopic microscope and Form Talysurf-type profilograph were used for cross-section and surface morphology characterization of the layers. The behaviour of the obtained layers was investigated in the process of hydrogen evolution reaction from 5 M KOH using classical methods (voltammetry, steady-state polarization) and electrochemical impedance spectroscopy (EIS). Based on recorded steady-state polarization curves, the Tafel equation parameters for this process were determined. EIS was used to study the interfacial properties at electrode overpotential ΔE = −0.200 V. It was found that the investigated Ni–P + Co layer is characterized by increased electrochemical activity for hydrogen evolution compared to Ni–P + W and Ni–P + Ti layers. Greater activity of the Ni–P + Co layer in this process may be attributed to the developed electrode surface. The values of surface roughness factor Rf were also determined.

CoPSc2O3 layers for electrolytic oxygen evolution

Composite CoPSc2O3 electrolytic layers were obtained in galvanostatic conditions on a copper substrate at temperature 298 K in the current density range from 0.0039 to 0.062 A cm−2, from a cobalt electrolyte containing a suspension of Sc2O3. For comparison, CoP layers were also obtained in the same current conditions. Using the potentiodynamic method, the polarization curve was plotted for the process of oxygen electroevolution from the KOH solutions. On this basis it was possible to determine the values of the Tafel equation parameters for the oxygen evolution process. These values were then taken as the criteria for evaluating oxygen evolution capacity on the composite layers and on the CoP layers not containing Sc2O3.

Electrolytical obtaining of Ni-Mo coatings with polypyrrole

Electrolytic coatings Ni-Mo with PPy were obtained by electrodeposition and electropolymerization from a galvanic bath containing Ni2+, MoO4 2–, ClO4 – ions and pyrrole (Py). The cyclic chronovoltamperommetric curve was used to determine the potential and current density of electrodeposition process. As the electropolymerization is anodic process while the electrodeposition is cathodic one, the electrode was working alternately as anode and cathode. The process was conducted under alternating potentiostatic or galvanostatic conditions. Comparative tests were carried out for Ni-Mo alloy. The results of structural investigation of the obtained coatings by the X-ray diffraction method show, the Ni-Mo layers are nanocrystalline solid solution of molybdenum in nickel (α phase), whereas the Ni-Mo+PPy coatings are characterized by decreased peaks coming from Ni-Mo base. Surface morphology of obtained Ni-Mo+PPy and Ni-Mo coatings was investigated by scanning microscope. It was stated, that the coatings obtained by alternating potentiostatic method exhibit multilayer character, whereas the coatings obtained under alternating galvanostatic conditions are characterized by the presence of Ni-Mo nanoagglomerates plated on polymer surface.

NiPNiO electrolytic layers as anode materials

Composite electrolytic layers were obtained on an amorphous nickel base with the addition of nickel oxide, in galvanostatic conditions at a temperature of 293 K, from a nickel-plating electrolyte in the coating containing a suspension of nickel oxide. The content of nickel oxide in the coatings depends on the conditions in which they were obtained. Using the potentiodynamic method, for these composite layers the polarisation curves of the oxygen electroevolution process from the 1 M KOH solution were determined. For comparison, curves were also plotted for copper and an amorphous Ni-P electrode. The electrodes were subjected to anode-cathode cycling in the range from the potential of oxygen evolution to the potential of hydrogen evolution. For the modified electrode materials, the characteristics of the oxygen electroevolution process were again determined. From these results the influence of the electrode material, and also the influence and advantage of preliminary modification of the surfaces of the electrodes on the process of oxygen evolution in an alkaline environment, were estimated. It was indicated that a correlation exists between the values of the exchange current of the oxygen electroevolution reaction and the electro-oxidation ability of ethanoloamine on the electrode materials studied.

Electrolytic oxygen evolution on NiPSc2O3 composite layers

Abstract Composite NiPSc 2 O 3 electrolytic layers were obtained in galvanostatic conditions on a copper substrate at temperature 298 K at the current density 20 mA cm −2 , from a nickel electrolyte containing a suspension of 25–125 g crystalline Sc 2 O 3 . For comparison, NiP layers were also obtained in the same current conditions. The phase composition of the layers were investigated by the X-ray diffraction method using a Philips diffractometer and Cu Kα radiation. The chemical composition of the layers was determined by the atomic absorption method using a Perkin-Elmer spectrophotometer. The cyclic chronovoltamperometric method was used to determine the behavior of the NiPSc 2 O 3 and NiP layers as a function of their chemical and phase composition and also of KOH concentration in the solution. Using the potentiodynamic method, the polarization curve was plotted for the process of oxygen electroevolution from the 5M KOH solutions. On this basis it was possible to determine the values of the Tafel equation parameters for the oxygen evolution process. These values were then taken as the criteria for oxygen evolution on the composite NiPSc 2 O 3 layers and on the NiP layers.

Electrolytic composite CoPTiO2 layers as electrode materials for oxygen electroevolution

Abstract Electrolytic composite layers Co P TiO 2 were obtained by electrolytic codeposition of cobalt and TiO 2 on a copper substrate from an electrolyte containing a suspension of TiO 2 (100 g dm −3 ). The process of electrodeposition was carried out under galvanostatic conditions, in the current density range of 17–40 mA cm −2 with a constant value of electric charge Q = 0.12 A h. For comparison, Co-P alloys were also obtained under the same conditions and comparative tests were conducted on them. The phase and chemical composition of layers were determined depending on deposition current density. Electrochemical tests were preceded by electromodification of layers aimed at obtaining an active surface layer. Investigated layers were subjected to a cyclic cathode-anode polarization in the potential range from the value of the hydrogen evolution potential to the value of the oxygen evolution potential for 3 h in 5 M KOH solution. On the surface prepared in such a way the final i-E relation was recorded for each type of layer. After such electrochemical pretreatment, all layers were tested for the process of oxygen evolution in alkaline environment. It was ascertained that incorporation of small amounts of crystalline TiO 2 in the amorphous Co-P matrix improved the rate of oxygen electroevolution on these layers.

The electrodeposition and properties of Zn-Ni + Ni composite coatings

The Zn-Ni+Ni coatings were deposited under galvanostatic conditions at the current density range from 20 to 60 mA cm−2. The influence of deposition current density on surface morphology, chemical and phase composition and corrosion resistance of obtained coatings, was investigated. Structural investigations were conducted by X-ray diffraction method. Surface morphology and surface chemical composition of the obtained coatings were determined by a scanning electron microscope. Studies of electrochemical corrosion resistance were carried out in the 5% NaCl solution, using potentiodynamic and Scanning Kelvin Probe (SKP) methods. A possibility of incorporation of nickel powder from a suspension bath to the Zn-Ni matrix, during galvanostatic deposition was demonstrated. The results of chemical composition analysis show that the Zn-Ni + Ni coatings contain approximately 15–18% at Ni. It was found that surface morphology, surface chemical and phase composition of Zn-Ni + Ni coatings depend in small degree on deposition current density. However, the current density influences distribution of nickel powder on the surface of these coatings. The optimal values of current density on account of corrosion resistance, are found to be j = 40–50 mA cm−2.

Structure and electrochemical corrosion resistance of the passivated Fe-40at.%Al binary alloy in sulfuric acid solution

The electrochemical corrosion resistance of the passivated Fe-40at.%Al binary alloy has been investigated in sulfuric acid at 25°C. Structural investigations were conducted by XRD method and confirmed a single phase material of the ordered B2 structure. Electrochemical corrosion behavior was determined using potentiodynamic polarization and EIS methods. Anodic polarization measurements revealed a passive behavior of the tested electrode. Detailed characteristics of the Fe-40at.%Al electrode | passive film | solution interface as a function of the electrode potential in the fully passive range of 0.5  E  1.5 V, was investigated. The impedance behavior was determined by a highly doped n-i-n structure (n-type semiconductor – insulator – n-type semiconductor).

The Influence of Sodium Molybdate on the Properties of Zn-Ni Layers Obtained by Electrolytic Deposition

This study was undertaken in the aim to try the limit of extraction of Zn from Zn-Ni system. The aim was realized by the addition of MoO42- ions into the galvanic bath containing Ni2+ and Zn2+ ions. Zn-Ni-Mo layers were deposited under galvanostatic conditions on (OH18N9) austenitic steel substrate. The influence of Na2MoO4 concentration in a bath on the surface morphology, chemical and phase composition and the corrosion resistance of obtained layers, was investigated. The properties of Zn-Ni-Mo layers were compared to the properties of electrolytic Zn-Ni layer. Structural investigations were performed by the X-ray diffraction (XRD) method. The surface morphology and chemical composition and surface chemical elements distribution of deposited layers were studied using a scanning electron microscope. Electrochemical corrosion resistance investigations were done by classical Stern method and electrochemical impedance spectroscopy. The potentiodynamic curves in the range of  0.05V to the potential of open circuit, were obtained. On the base of these curves the parameters like corrosion potential- Ecor, corrosion current density- icor and the polarization resistance- Rp were determined. These values served as a measure of the corrosion resistance of obtained layers. Results of impedance investigations were presented on the Nyquist Z”= f (Z’) and the Bode log Z = f (log) and  = f (log), diagrams. On the basis on this research, it was exhibited that surface morphology, chemical composition of Zn-Ni-Mo layers are dependent on Mo contents. The optimal content of Na2MoO4 in the bath for the sake of corrosion resistance in 5% NaCl, is found to be 1.2 gdm-3.