Hydrogen diffusivity, kinetics of H2O/H2 charge transfer and corrosion properties of LaNi5-powder, composite electrodes in 6 M KOH solution

J Solid State Electrochem

Bala

2013

The Randles-Sevčik relationship has been applied to evaluate atomic hydrogen diffusivity in massive LaNi 5 intermetallic compound. The electrode was cathodically hydrogenated in 6 M KOH solution (22°C), and then voltammetry measurements were carried out at various, very slow potential scan rates (υ =0.01-0.1 mV·s −1). At potentials more noble than the equilibrium potential of the H 2 O/H 2 system, the anodic peaks were registered as a consequence of oxidation of hydrogen absorbed in cathodic range. The peak potentials linearly increase with the logarithm of the scan rate with a slope of 0.059 V. The slope testifies to a symmetric charge transfer process with symmetry factor α =½. The peak currents linearly increase with the square root of the potential scan rate, and the straight line runs through the origin of the coordinate system. The slope of the I a (peak) =f(υ 1/2 ) straight line is a measure of the atomic hydrogen diffusion coefficient. Assuming the hydrogen concentration in the LaNi 5 material after cathodic exposure to be C 0,H =0.071 mol·cm −3 (63 % of theoretical value), the hydrogen diffusion coefficient equals D H =2.0· 10 −9 cm 2 s −1. Extrapolation of rectilinear segments of potentiodynamic polarization curves with Tafel slopes of 0.12 V and linear polarization dependencies from voltammetry tests allowed the exchange current densities of the H 2 O/H 2 system on the tested material to be determined. The exchange current densities on initially hydrogenated LaNi 5 alloy are close to 1 mA·cm −2

Section: Methodsmentioning

confidence: 99%

Hydrogen diffusivity in the massive LaNi5 electrode using voltammetry technique

J Solid State Electrochem

Bala

2013

“…W poprzednich pracach naszego zespołu [1][2][3][4][5][6] ocenialiśmy zdolność pochłaniania wodoru przez różnego typu materiały aktywne (materiały proszkowe na bazie stopów metali ziem rzadkich) w oparciu o pierwsze 10 cykli galwanostatycznego ładowania/rozładowania. Taką liczbę cykli uznawaliśmy jako wystarczającą, jako że maksymalne pojemności prądowe osiągane były po 6-9 cyklach.…”

Section: Wprowadzenieunclassified

“…W ciągu tych pierwszych kilku cykli utlenianiu ulegają pomijalnie małe ilości lantanu, zaś nikiel ulega tzw. korozji odwracalnej [2][3][4][5]. DOI: 10.17814/mechanik.2015.…”

Section: Wprowadzenieunclassified

“…Jak wynika z II prawa elektrolizy Faradaya, maksymalna teoretyczna pojemność prądowa stopów na bazie związku międzymetalicznego LaNi 5 [10]). Natomiast podczas rozładowania, prąd anodowy powoduje utlenianie zaabsorbowanego wcześniej wodoru.…”

Section: Wprowadzenieunclassified

“…Jak już wspomniano, oprócz utleniania wodoru, w procesie anodowym pewna niewielka część ładunku zużywana jest na utlenianie materiału elektrodowego [1,5,6]. Na podstawie wyznaczonego czasu rozładowania (przy zadanej szybkości rozładowania) możliwe jest określenie efektywnej pojemności prądowej elektrody wodorkowej.…”

Section: Wprowadzenieunclassified

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Inhibition of LaNi5 electrode decay in alkaline medium by electroless encapsulation of active powder particles

J Solid State Electrochem

Bala

2016

Surface of powdered LaNi 5 intermetallic compound has been modified by active particle coverage with electroless nickel (Ni-P). The electrode degradation process in 6 M KOH solution has been tested across 70 charge/ discharge cycles at −0.5 C/+0.5 C rates. It has been established that after approx. 25-35 initial cycles, the electrode degradation process fulfills first order chemical reaction kinetics law: logarithm of discharge capacity linearly decreases with cycle number. The rate constant for the Ni-P protected material is over 20 % lower than that of as received one. The surface modification also improves the alloy hydrogenation kinetics: exchange current densities of H 2 O/H 2 system are generally greater for modified material and, contrary to uncovered material, do not practically decrease with long-lasting cycling.