Degradation and Relaxation Effects of Ni Patterned Anodes in H[sub 2]–H[sub 2]O Atmosphere

Abstract

Patterned Ni anodes on normalY2normalO3 -stabilized ZrO2 (YSZ) represent a promising approach to determine the kinetics of electrochemical reactions in solid oxide fuel cells. Contrary to technical Ni/YSZ cermet anodes, the reaction zone for the hydrogen oxidation has the potential to be well defined. This study is focused on the reproducibility of electrochemical characterization results of patterned Ni anodes, with a parameter variation of the partial pressures of normalH2 and normalH2O , temperature, and polarization voltage. Considerable (electro)chemical relaxation and degradation processes with time constants in the order of some hours were found and are discussed: (i) an initial decrease in the line specific resistance (LSR) during the first 20–25 h of temperature exposure (T=800°C) attributed to a restructuring process in the Ni thin film, (ii) reversible changes in LSR upon variations of the partial pressure of normalH2 and normalH2O in correlation to the initial gas composition, and (iii) rapid reversible changes in LSR upon anodic and cathodic polarization voltages followed by a slow relaxation. The corresponding preconditions for reliable measurement series were deduced and yield the data set of the LSR values. Furthermore, a detailed comparison of the obtained LSR values with literature data is given.

Studying the CO–CO2 characteristics of SOFC anodes by means of patterned Ni anodes

“…Patterned Ni anodes with an area of 10.25 mm × 10.25 mm were fabricated on 8.5 mol% polycrystalline Y 2 O 3 -stabilized ZrO 2 (YSZ) substrates (Itochu Ceratec Corp., Japan) using a standard photolithography process [22], the procedure is described in our previous study [8]. The design of the pattern is composed of an area of 9.25 mm × 9.25 mm with parallel Ni stripes; in this study stripes with 25 m width, a spacing of 160 m and a thickness of 800 nm are chosen.…”

“…Several studies on electrooxidation, which are based on patterned Ni anodes, have been performed so far for the H 2 -H 2 O atmosphere [4][5][6][7][8]. In the most recent study, our group could attribute the observed discrepancies considering absolute values of the line specific resistance (LSR) and controversial parameter dependencies to different degradation and relaxation processes occurring during characterization of nominally stable patterned Ni anodes [8].…”

“…In the most recent study, our group could attribute the observed discrepancies considering absolute values of the line specific resistance (LSR) and controversial parameter dependencies to different degradation and relaxation processes occurring during characterization of nominally stable patterned Ni anodes [8]. The results of characterization in H 2 -H 2 O atmosphere indicate a hydrogen spillover mechanism [3,8,9].…”

Additive Manufacturing for Solid Oxide Cell Electrode Fabrication

“…The TPB lines in Figure 3a appear to have an irregular shape, compared to the shape of patterned Ni electrodes on YSZ obtained elsewhere (10)(11)(12)(13). Therefore it is difficult to make a direct comparison between the performance of patterned electrodes obtained in this work and in the literature.…”

Evaluation of electrochemical impedance spectra by the distribution of relaxation times

“…The parameterization of this model was supported by combining (i) microstructural parameters evaluated by means of FIB/SEM-tomography, 61) (ii) the line specific resistance of the triple phase boundary (TPB) determined by electrochemical impedance spectroscopy (EIS) on patterned model anodes, 62) (iii) the conductivity of the YSZ-matrix including the impact of NiO interdiffusion 63), 64) and (iv) the DRT as an additional quality criterion in the fitting procedure. 48) Please note, without considering the above mentioned parameters, a fitting of the spectra with even lower error levels would be possible.…”