Ni Cathode Research Articles

Analysis of the microstructure and physical properties of La0.85Sr0.15Ga0.8Mg0.2O2.825 and Ce0.85Sm0.15O1.925 composite electrolytes used in solid oxide fuel cells

(100–xwt%) La0.85Sr0.15Ga0.8Mg0.2O2.825 (LSGM1520)+(xwt%) Ce0.85Sm0.15O1.925 (SDC15)(x=0, 2, 5, 7, 10, and 100) composite electrolytes were synthesized by a solid-state reaction. The microstructures and electrical properties of the electrolytes were analyzed by X-ray diffractometry, Raman spectroscopy, scanning electron microscopy, thermomechanical analysis, and impedance spectroscopy. The electrolytes, LSGM1520 and 95wt% LSGM1520–5wt% SDC15, based on a La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF6428) cathode and Ce0.8Sm0.2O1.9–Ni (SDC20-Ni) cathode were used to form two SOFCs. The thermal expansion coefficients of the composites ranged from 10.5×10−6/°C to 12×10−6/°C at 200–600°C and 12×10−6/°C to 15×10−6/°C at 600–800°C. The performances and current density of LSCF6428/LSGM1520/SDC20-Ni and LSCF6428/95L05S/SDC20-Ni are 264mW/cm2 and 1.00A/cm2 at 774°C, and 182mW/cm2 and 0.97A/cm2 at 789°C, respectively, and their open circuit voltages (OCV) are ∼1.0–1.1V.

Effects of Current Collector Materials on Performances of Micro-Tubular Solid Oxide Electrolysers for Splitting CO2

As renewable energy sources are inherently intermittent, their increasing contributions to electricity grids will necessitate large-scale energy storage to balance supply and demand. Storing electrical energy in chemical bonds by electrolysis of CO2 and / or H2O is one option to achieve this. We chose solid oxide reactors for this application, inter alia, because in principle they can be operated cyclically in electrolyser (SOE) and fuel cell (SOFC) modes. Results will be presented of measurements of ohmic and electrode polarization resistances and global performances for CO2 splitting to CO and O2 in micro-tubular solid oxide electrolysers (SOEs), with different types of current collectors; electrolysis of steam and (CO2 + steam) exhibited similar behaviour. Silver or nickel wire current collectors, with and without silver or nickel paste, were used to contact the 220 μm thick inner lumen Ni-YSZ electrode (SOE cathode) of micro-tubular solid oxide electrolysers [1] (SOEs: Ni-YSZ|YSZ|YSZ-LSM|LSM) incorporating 34 μm thick yttria-stabilized zirconia (YSZ) electrolyte, and 40 μm thick lanthanum strontium manganite (LSM, SOE anode), as described previously for CO2 reduction [2]. Silver wire and paste was used as the current collector for the LSM electrode. As shown in Fig. 1, the best performance (ca. 1 A cm-2 at 1.5 V (thermo-neutral potential difference) at 800 °C) was achieved for reactors with nickel wire current collectors alone, implying metallic pastes had no net beneficial effects on area-specific ohmic resistances. Furthermore, applying silver paste had a detrimental effect on the Ni cathode polarization resistance, for reasons that will be presented. Fig. 2 shows polarization and ohmic resistance data at open circuit; similar behaviour was exhibited with potential differences applied to reactors. Ohmic resistances were expected to decrease by using silver wire, due to its higher electronic conductivity compared to nickel, but no stable cell performance was achieved.

Structural Evolution of High Capacity Li-Rich 0.5Li2MnO3*0.5LiMO2 (M=Mn, Ni and Co) Cathode Materials during Electrochemical Cycling

Li-rich cathode materials with a general chemical formula (x)Li2MnO3*(1-x)LiMO2 (M= Mn, Ni and Co) are in spotlights since last few years. They offer reversible capacities in excess of ~250 mAh/g when charged above 4.5 V, which is significantly higher than that delivered by the commercially available LiCoO2 (~140 mAh/g) cathode material, and exhibit high rate capabilities[1]. However despite their attractive properties, no clear consensus exists on how the two components, namely Li2MnO3 and LiMO2 of Li-rich materials coexist and how the structure evolves upon cycling. Herein, we report bulk and surface structural modifications in Li-rich cathode materials during electrochemical cycling using X-ray absorption spectroscopy (XAS). In-operando XAS measurements in the transmission mode at the Mn, Ni and Co K-edges of the material provided information about bulk structural changes, while the O K-edge Near-Edge X-ray absorption fine structure (NEXAFS) measurements in the total-electron yield (TEY) mode provided information about the near-surface structural modifications. It is observed that the type and amount of transition metal (TM) ions determine the structural integration between the two components of Li-rich materials. For instance, higher Co contents tend to reduce the formation of Li2MnO3-type domains and promote a layered Li(1+x)MO2-type structure, while higher Mn and Ni contents give rise to the formation of a large amount of well-ordered Li2MnO3 domains[2][3]. During activation, lithium extraction from Li2MnO3 domains occurs with a concurrent removal of oxygen, giving rise to the formation of a layered MnO2-type structure[4]. The observed preferential reduction in the amplitude of the first peak (Mn-O) in Fig.1, representing the first coordination shell of oxygen atoms around the central Mn atom, also confirms the oxygen removal from the material during activation. Lithium reinsertion into a layered MnO2-type structure formed during activation, gives rise to the formation of a structure which is similar to the original Li2MnO3, but Li and O deficient[4]. Consistent structural modifications were observed for the O K-edge NEXAFS spectra of the material during activation (Fig.2). It is observed that oxygen removal occurs only during the first cycle, and presumably, it is the necessary step in activating the Li2MnO3 component of Li-rich materials. During subsequent cycles, lithium extraction and reinsertion in Li2MnO3 domains may involve the unusual participation of oxygen anions into redox processes. The average valence state of Mn in Li2MnO3 domains remains 4+ at all times. Quite contrarily, electrochemical processes in LiMO2 domains involve conventional redox processes of TM ions. Lithium deintercalation from LiMO2domains results into the formation of O1-type stacking faults within the O3 structure, while lithium intercalation reverts these O1-type stacking faults back to the original O3-type. In order to clarify structural modifications occurring during cycling, we investigated charged and discharged samples in the 2nd, 10th and 25th cycles. It is observed that after the initial oxygen release during activation, no major changes occur in Li2MnO3 domains during subsequent cycling. On the other hand, structural changes in LiMO2 domains are also quite similar to those observed during the 1st cycle. Interestingly, there was no indication of a spinel-like phase being formed upon cycling, as speculated in the literature. As reported previously, both Li2MnO3 and LiMO2 experience structural degradation when used independently as cathode materials in cells and cycled above 4.5 V[4][5]. In case of Li-rich materials, however, none of these components show degradation after 25th cycle. These results highlight the role of both the components in Li-rich materials. Apparently, the randomly distributed Li2MnO3 domains in Li-rich materials act as a source of excess lithium for the redox-active LiMO2 domains and impart greater overall structural stability above 4.5 V. On the other hand, conventional redox processes of TM ions in the LiMO2 component help to overcome parasitic side reactions in the Li2MnO3 component above 4.5 V involving the electrolyte[4].

The development of catalytic performance by coating Pt–Ni on CMI7000 membrane as a cathode of a microbial fuel cell

Performance of cathode materials in microbial fuel cell (MFC) from dairy wastewater has been investigated in laboratory tests. Both cyclic voltammogram experiments and MFC tests showed that Pt–Ni cathode much better than pure Pt cathode. MFC with platinum cathode had the maximum power density of 0.180Wm−2 while MFC with Pt:Ni (1:1) cathode produced the maximum power density of 0.637Wm−2, even if the mass mixing ratio of Pt is lower in the alloy were used. The highest chemical oxygen demand (COD) removal efficiency was around 82–86% in both systems. The cyclic voltammogram (CV) analyses show that Pt:Ni (1:1) offers higher specific surface area than Pt alone does. X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) results showed that entire Pt:Ni (1:1) alloys can reduce the oxygen easily than pure platinum, even though less precious metal amount. The main outcome of this study is that Pt–Ni, may serve as a alternative catalyst in MFC applications.

Investigation of multilayered TiSiC/NiC protective coatings

TiSiC/NiC multilayer coatings with different bilayer periods (Λ) in the range of 2.5–19.8 nm were deposited on Si wafers and steel (316 L and C 45) substrates using cathodic arc evaporation technique with TiSi and Ni cathodes in methane atmosphere. TiSiC and NiC single layers were also prepared as reference coatings. The coatings were analyzed for elemental and phase composition, microstructure, morphology, modulation periodicity, mechanical properties, and for the tribological characteristics in 0.9% NaCl corrosive solution.Cross-sectional SEM images presented well-defined multilayered structures. It has been shown that the properties of the multilayers depended strongly on the bilayer period, the best characteristics being obtained for the TiSiC/NiC coating with Λ = 4.8 nm. This coating was found to outperform the TiSiC monolithic film, revealing lower residual stress (σ = −0.88 GPa), improved adhesion (critical load Lc = 57 N), lower friction coefficient (μ = 0.16) and higher wear resistance (wear rate K = 0.7 × 10−6 mm3 N−1m−1) when compared to TiSiC coating: σ = −3.12 GPa, Lc = 36 N, μ = 0.38, K = 2.9 × 10−6 mm3 N−1m−1.

Batteries: An Advanced Na–FeCl2 ZEBRA Battery for Stationary Energy Storage Application (Adv. Energy Mater. 12/2015)

Sodium-metal chloride batteries, ZEBRA, are considered as one of the most important electrochemical devices for stationary energy storage applications because of its advantages of good cycle life, safety, and reliability. However, sodium-nickel chloride (Na-NiCl2) batteries, the most promising redox chemistry in ZEBRA batteries, still face great challenges for the practical application due to its inevitable feature of using Ni cathode (high materials cost). In this work, a novel intermediate-temperature sodium-iron chloride (Na-FeCl2) battery using a molten sodium anode and Fe cathode is proposed and demonstrated. The first use of unique sulfur-based additives in Fe cathode enables Na-FeCl2 batteries can be assembled in the discharged state and operated at intermediate-temperature (<200°C). The results in this work demonstrate that intermediate-temperature Na-FeCl2 battery technology could be a propitious solution for ZEBRA battery technologies by replacing the traditional Na-NiCl2 chemistry.

Kinetics of hydrogen evolution reaction in alkaline electrolysis on a Ni cathode in the presence of Ni–Co–Mo based ionic activators

This paper presents investigations on the influence of in-situ ionic activation using combination of three d-metals: Ni, Co and Mo on the hydrogen evolution reaction (HER) mechanism and kinetics. Polarization measurements were performed to obtain kinetic parameters for the HER and the results are presented to show Tafel slopes, exchange current densities and apparent energy of activation. The values of the kinetic parameters confirm the existence of two Tafel slopes, in the case of NiCoMo based ionic activators (i.a.) in the investigated temperature range, with very high values of the exchange current density. Electrochemical impedance spectroscopy measurements were employed to further investigate the origin of the obtained electrocatalytic effect on the HER. The measurements were performed at several overpotentials and temperatures. It was found that co-deposition of Ni, Co and Mo species on the Ni cathode results in a large number of active sites for hydrogen adsorption, and a synergetic effect giving electronic structure suitable for the HER, are the main factors contributing to the enhanced HER kinetics. It was shown that EIS measurements had a crucial role in determining the HER mechanism, especially with the complex in-situ activation of the alkaline electrolysis.

(Invited) High Temperature CO2 Electrolysis on La(Sr)Fe(Mn)O3 Oxide Cathode by Using LaGaO3 Based Electrolyte

Solid oxide electrolysis cells (SOECs) for converting CO2 to more useful chemical species are attracting considerable attention because of their high electrolytic efficiency, offering the possibility of direct conversion of CO2 to CO (CO2 → CO + 1/2O2). Heat energy supplied to SOECs can maximize electrolysis efficiency, offering both thermodynamic and kinetic advantages. The generated CO can be used as a fuel gas, converted into syngas via reaction with H2, or to reduce iron oxide to pure iron in the iron-making process. The application of SOECs and related technologies can contribute to a more sustainable economy. For the electrolyte in SOECs, ZrO2 doped with 8 mol% of Y2O3 (YSZ) has always been used because of its chemical stability and mechanical strength. However, an electrolyte for CO2 electrolysis with lower internal resistance and increased efficiency is highly desirable. LaGaO3-based electrolytes have higher oxide-ion conductivities and transport numbers, which can lead to higher energy conversion efficiency; hence, a doped-LaGaO3 electrolyte (La0.9Sr0.1Ga0.8Mg0.2O3, LSGM) has been tested in this study. For CO2 electrolysis, another drawbacks is formation of C since electrolysis potential is close to that of CO formation. Although metals, particularly Ni, are widely used as cathodes in CO2 electrolysis cells, we found that a LaFeO3−δ-based perovskite cathode (La0.6Sr0.4Fe0.8Mn0.2O3−δ, LSFM6482) showed the highest activity for CO2 electrolysis among the examined oxides with a current density for CO2 electrolysis of 0.52 A/cm2 at 1.6 V and 1173 K. Among the cells using a La0.6Sr0.4Fe0.9M0.1O3−δ-based oxide cathode (M = Mn, Co, Ni, or Cu) for CO2 electrolysis at 1073K. Mn was the most effective Fe replacement on the B site, and the La0.6Sr0.4Fe0.9Mn0.1O3−δ cathode showed the highest activity and current density for CO2 electrolysis of this set of cathodes. Among the tested dopants, Mn and Co have ionic sizes most similar to Fe and a smaller size mismatch between the host and dopant cations in the perovskite structure, which should suppress dopant segregation and minimize detrimental effects of cation segregation. Overall, among the examined cations, Mn was the best dopant for the B site of the LaFeO3 cathode. A cell consisting of BLC64/LSGM/LSFM6482 exhibited the highest CO2 electrolysis activity (a current density of 0.52 A/cm2 at 1.6 V and 1173 K) of all cathodes investigated in this study and reduced CO2 at a rate of 153 μmol/cm2•min at 1173 K and 1.6 V with negligible carbon formation. The observed electrolysis current density was close to that of a Ni cathode but smaller than that of a Ni–Fe cathode, which is one of the most active cathodes for CO2 electrolysis. An LSFM6482 oxide cathode seems to be effective for improving not only initial cathodic performance but also long-term stability. LSFM6482 could be a potential candidate for high-temperature CO2 electrolysis. Further details of electrode reaction will be discussed based on impedance analysis and CO2 partial pressure.

An Advanced Na–FeCl2 ZEBRA Battery for Stationary Energy Storage Application

Sodium‐metal chloride batteries, ZEBRA, are considered one of the most important electrochemical devices for stationary energy storage applications because of its advantages of good cycle life, safety, and reliability. However, sodium–nickel chloride (Na–NiCl2) batteries, the most promising redox chemistry in ZEBRA batteries, still face great challenges for the practical application due to its inevitable feature of using Ni cathode (high materials cost). Here, a novel intermediate‐temperature sodium–iron chloride (Na–FeCl2) battery using a molten sodium anode and Fe cathode is proposed and demonstrated. The first use of unique sulfur‐based additives in Fe cathode enables Na–FeCl2 batteries can be assembled in the discharged state and operated at intermediate temperature (&lt;200 °C). The results presented demonstrate that intermediate‐temperature Na–FeCl2 battery technology could be a propitious solution for ZEBRA battery technologies by replacing the traditional Na–NiCl2 chemistry.

Electrodeposition of nanocrystalline Zn–Ni coatings with single gamma phase from an alkaline bath

Nanocrystalline Zn–Ni (grain size about 26nm) alloy coatings were electrodeposited on carbon steel substrates in alkaline bath with 5,5′-dimethylhydantoin (DMH) as the complexing agent. The coatings with 13wt.%–16wt.% Ni content and the electrolyte with high current efficiency (>85%) were achieved at the optimized parameters, i.e., Ni2+/(Zn2++Ni2+) ratio 0.32, current density 2A·dm−2, temperature 50°C and agitation speed 1000rpm. The electrochemical behavior of the bath has been studied by cyclic voltammetry (CV), chronopotentiometry (CE) and cathodic polarization. Results show that the deposition of Zn–Ni alloys occurs at moderate overpotential and the rotation speed and bath temperature have a strong effect on cathodic polarization curves. The effects of Ni2+/(Zn2++Ni2+) ratio, current density, temperature and agitation speed on Ni content and cathode current efficiency were investigated. Studies indicate that the phase structure, grain size, microhardness and corrosion resistance of deposits are directly dependent on Ni content in deposits. The phase structure of deposits changes from a mixture of η-phase and γ-phase to single γ-phase with (411) plane orientation. Furthermore, the grain size decreases with the increase of Zn content in deposits and the increase in current density can also lead to the decrease in grain size. The increase in microhardness of deposits is strongly affected by the increase of Ni content in deposits rather than the Hall–Petch relationship. Zn–Ni alloy coatings with about 13wt.% Ni content present best corrosion resistance and the bath has a good stability.

Ultrahigh purification in concentrated NaOH by electrowinning for solar cell application

High purity sodium hydroxide (NaOH) solution is extremely important in the large-scale manufacturing of impurity-free silicon (Si) wafers for solar cells. In this paper, we demonstrate the purification of highly concentrated NaOH via electrowinning. By optimizing temperature, current density, and the type of electrode for both anodes and cathodes, we maximized the selectivity toward cathodic deposition of Fe and Ni. Our results suggest that removal of metal impurities in the concentrated 50wt.% NaOH is highly dependent on the reactor temperature (>90°C) due to enhanced reaction kinetics and decreased solution viscosity. Meanwhile, current density has limited effect on the metal removal efficiency. We further demonstrate that the cathodic deposition of Fe and Ni strongly relies on the type of electrode pair used, with platinum (Pt) and nickel (Ni) as the anode and cathode, respectively, exhibiting the best removal performance. The good electrochemical performance arises from the high catalytic activity of Pt anode and good stability of Ni cathode from the highly corrosive concentrated alkaline conditions. Following these results, we recommend future scientific and technical studies on the use of electrowinning as a possible alternative to the costly membrane-based purification techniques.

Delithiation Mechanisms in Acid of Spinel LiMn2-xMxO4 (M = Cr, Fe, Co, and Ni) Cathodes

The products formed by the chemical extraction of lithium from LiMn2-xMxO4 (M = Cr, Fe, Co, and Ni) with aqueous sulfuric acid have been structurally and chemically characterized. The amount of lithium extracted is found to be proportional to the initial Mn3+ content, confirming the reaction mechanism, LiMn3+Mn4+O4 → 0.75 Mn2O4 + 0.5 Li2O + 0.5 MnO. Thus, no lithium is extracted from LiMn1.54+Ni0.52+O4 as there is no Mn3+, while complete delithiation occurs in LiMn3+Mn4+O4 to give Mn2O4. The amount of lithium extracted from the other samples is in good agreement with that calculated from the Mn3+ content. The XRD data confirm the maintenance of the spinel structure for the delithiated samples, while the redox titration confirmed the maintenance of oxygen content at 4.0, indicating that no protons were inserted into the lattice during delithiation. The findings could provide more insight on the problem of metal dissolution from cathode materials in lithium-ion batteries.

Selective hydrodechlorination of 3,5,6-trichloropicolinic acid at an activated silver cathode: Synthesis of 3,5-dichloropicolinic acid

Electrochemical reduction of 3,5,6-trichloropicolinic acid (3,5,6-T) at glassy carbon, Ni, Cu, and Ag cathodes in aqueous solutions at different pH values was investigated. Experiments suggest that the selectivity of the reduction strongly depends on the cathode materials used and the pH of the aqueous solutions. A high selectivity for the hydrodechlorination of 3,5,6-T to 3,5-dichloropicolinic acid (3,5-D) has been achieved exclusively at an activated Ag cathode and at pH 3: a selectivity of 95% at 42% conversion under potentiostatic mode and a selectivity of 89% at 88% conversion under intentiostatic mode. An explanation is proposed for this high selectivity.

Benzylamine-directed growth of olivine-type LiMPO4nanoplates by a supercritical ethanol process for lithium-ion batteries

Olivine-type LiMPO4 (M = Fe, Mn, Co and Ni) cathode materials hold promise for next-generation of lithium-ion batteries and future applications as hybrid electric vehicles or electric vehicles. In lithium intercalation olivine compounds, the lithium diffusion along a channel is highly anisotropic which is mainly confined to the channel along the [010] direction. Thus, nanosheets or nanoplates with shortened Li ion diffusion distance along the [010] direction are enabled to accelerate the lithium intercalation rate and improve power density of the batteries. Herein, we report the production of high-quality thin LiMPO4 nanoplates with exposed {010} facets by a rapid supercritical fluid processing. The unique structure of the olivine nanocrystals with a shortened Li ion diffusion pathway allows fast extraction/insertion of Li ions in the structures. Thus, the LiMPO4 nanoplates provide high capacity and high rate capacity and excellent cyclability.

Electrochemical Synthesis of NiSi2 from a NaCl-NaF-K2SiF6 Melt on a Ni Cathode

The aim of this work was to examine the possibility of producing nickel silicides by the electrolysis of molten salts, containing silicon ions, on a nickel cathode. Possibility of electrodeposition of nickel disilicide from molten salts was investigated by thermodynamic calculation, voltametric investigation and electrolysis experiments. The electrochemical behavior of the NaCl–NaF–K2SiF6 molten salts system was studied by cyclic voltammetry. The electrolysis was carried out in a NaCl–NaF–K2SiF6 melt in a glassy carbon crucible at 7200C in argon atmosphere; a nickel plate was used as the cathode. Cathode products were analyzed by X-ray and JEM-2100F SEM. Coatings of nickel disilicide were deposited from NaCl-NaF-K2SiF6 melts on a Ni cathode at 7200C in argon atmosphere.

Electrochemical Synthesis of NiSi2 from a NaCl-NaF-K2SiF6 Melt on a Ni Cathode

Nickel silicides are used as Schottky barrier and as ohmic contacts owing to the combination of properties typical of metal (high electrical conductivity) and nonmetal (low heat conductivity) [1]. Nickel silicides are usually produced by the thermal vacuum spraying of nickel on single-crystalline silicon plates [2]. The objective of this work was to examine the possibility of obtaining nickel silicides by electrolysis of molten salts, containing silicon ions, on a Ni cathode. It can be concluded from thermodynamic calculation that silicon discharge depolarization through NiSi2 formation is 0.110 V at 993K: I. Ni + 2Si = NiSi2 The electrochemical behaviour of the system NaCl-NaF-K2SiF6 was studied by cyclic voltammetry. A glassy carbon crucible served as a vessel for the melt and as an auxiliary electrode; a Ni wire was used as the working electrode; the measurements were made with respect to glassy carbon reference electrode 7200С in argon atmosphere. Current-potential curves exhibited, at potentials more positive (~100 mV) than silicon discharge potential, a new irreversible electrochemical process followed by a chemical reaction. Up to 25 mm thick dense NiSi2 layers have been obtained by the electrolysis of a NaCl-NaF-K2SiF6 melt on a Ni plate at 7200С in argon atmosphere at current density of 50 mA/cm2 (Fig. 1.), which was confirmed by X-ray phase analysis. The chemical composition map of metallographic section shows the silicon distributions.On the base of thermodynamic calculation, voltammetric investigation and electrolysis experiments, it has been show that nickel disilicides can by electrochemical synthesized in a NaCl-NaF-K2SiF6 melt at 7200С on a nickel cathode in argon atmosphere. References M. Lawrence, A. Dass, David B. Fraser, Chih-shihWei, Appl. Phys. Lett. 58, 1308 (1991).Y. He, J.Y. Feng, W.Z. Li, Journal of Crystal Growth, 254, 70-74 (2003).Fig. 1. SEM micrograph: cross-section of a Ni cathode after the electrolysis of a NaCl-NaF-K2SiF6 melts at 7200С in Ar atmosphere.

Electrogenerated-bases promoted electrochemical synthesis of N-bromoamino acids from imines and carbon dioxide

In this paper, the one-step synthesis of N-bromoamino acids has been developed by electrolyzing imines and carbon dioxide (4 MPa). The electrosynthesis was performed in an undivided cell with Ni cathode and Al sacrificial anode containing n-Bu4NBr–DMF as supporting electrolyte with a constant current at room temperature. The N-bromoamino acids were afforded in moderate to good yields rather than traditional α-amino acids. To explore the truth, some influenced factors (cathode materials, supporting electrolyte, and electricity etc.) were investigated. The experimental results indicated that the NH group of the α-amino acid could be deprotonated by alkyl anion R− (carbanion, a strong base), followed by the oxidation of hypobromous acid resulted from the two-step oxidation of the bromide ion at the anode, and produced the N-bromoamino acid. Finally, the reaction mechanism was briefly discussed.

Hydrogen evolution and corrosion products on iron cathodes in hot alkaline solution

To better understand the reactivation of nickel cathodes by iron, the study was performed on iron membranes in 25% KOH at 80 °C. Membranes were cathodically treated and anodically polarised, and simultaneously hydrogen permeation was measured with the electrochemical technique. During cathodic potential sweeps, three peaks of current and of hydrogen permeation occurred. The peaks at about −0.80 V and −1.30 V vs. SHE were ascribed to reduction of Fe3O4 to HFeO2− and H+, and of HFeO2− to Fe, respectively. Electric charge of anodic oxidation of cathodically pretreated membranes was by over two orders of magnitude higher than the charge of desorbing hydrogen, and it increased with the pretreatment time. This was ascribed mainly to the oxidation of iron and its corrosion products. It was proposed that the reactivating effect of iron on Ni cathodes can be associated with the enhanced reactivity of iron freshly deposited by reduction of HFeO2−.

Hydrogen Evolution Reaction Kinetics on Electrodeposited Pt-M (M = Ir, Ru, Rh, and Ni) Cathodes for Ammonia Electrolysis

Metallic and bimetallic electrocatalysts of the type PtxM1-x (where M = Ru, Rh, Ir, Ni) electrodeposited on carbon fiber paper were evaluated as electrocatalysts for the hydrogen evolution reaction (HER) in an ammonia electrolytic cell. The addition of 1 M ammonia resulted in an increase in the HER overpotential for all electrocatalysts except Rh. The bimetallic electrocatalysts offer higher HER activity compared to metallic ones with the trend Pt-Ir > Pt-Rh > Pt-Ru > Pt-Ni. The enhanced activity of the bimetals is attributed to the synergistic activity. Ammonia adsorption is specific to the more electropositive alloying material, leaving the Pt sites active for hydrogen underpotential deposition and HER. Increasing the loading by a factor of two resulted in a decrease in the pore size thereby leading to a poor three-phase electrocatalyst, which in-turn causes a decrease in the HER electrocatalytic activity in the presence and absence of 1 M ammonia. Maximum electrocatalytic activity was achieved with a Pt-Ir electrocatalyst with a loading (Me / [Me + Pt]) of 13%, a Pt content of 68% and an intercrystallite distance of 7.2 nm.

Electrode Performance of Newly Developed Ni-W-S Deposited Alloy for Alkaline Water Electrolysis

Ni-W-S coatings were fabricated by electroplating. The bath denoted as “Ni-W-S No.1” was derived from a neutral pH bath for Ni-W alloy plating. Furthermore, sulfosalicylic acid was added as a stress reducer in order to prevent surface cracks. In the solution denoted as “Ni-W-S No.2” contains sodium tungstate, as a source of tungsten, sodium citrate. Plating solution denoted as “Ni-S” is same bath with Ni-W-S No.2 without sodium tungstate. Ni-W-S electrodes showed significantly excellent characteristics as a cathode for alkaline water electrolysis. Specifically, the Ni-W-S electrode in which sulfosalicylic acid was added as a stress reducer exhibited an excellent performance comparing to conventional Ni-S and Ni cathode. In order to obtain the performances of thus obtained electrode for alkaline water electrolysis, an electrode surface morphology was observed by SEM and the film composition was evaluated by EDX. In order to specify the crystal structure, XRD was employed. Furthermore, in order to evaluate the durability performance as a cathode for water electrolysis, sequential changes in electrode performance was investigated periodically using LSV while performing long-term electrolysis test for 48 hours. Furthermore the prevention of sulfur dissolution during cathodic polarization was monitored.