Electrochemical characterization of Ni–yttria stabilized zirconia electrode for hydrogen production in solid oxide electrolysis cells

• Published in: Journal of power sources 2013-10, Vol.240, p.721-728
• Main Authors: Dasari, Hari Prasad, Park, Sun-Young, Kim, Jeonghee, Lee, Jong-Ho, Kim, Byung-Kook, Je, Hae-June, Lee, Hae-Weon, Yoon, Kyung Joong
• Format: Article
• Language: English
• Subjects: Alternative fuels. Production and utilization; Applied sciences; Concentration (composition); Direct energy conversion and energy accumulation; Electrical engineering. Electrical power engineering; Electrical power engineering; Electrochemical conversion: primary and secondary batteries, fuel cells; Electrodes; Electrolysis; Energy; Energy. Thermal use of fuels; Equipments for energy generation and conversion: thermal, electrical, mechanical energy, etc; Exact sciences and technology; Fuel cells; Fuels; Hydrogen; Impedance; Impedance spectroscopy; Nickel; Oxidation; Oxides; Rate limiting process; Reduction (electrolytic); Solid oxide electrolysis cell; Solid oxide fuel cell; Spectra
• ISSN: 0378-7753; 1873-2755
• DOI: 10.1016/j.jpowsour.2013.05.033

Electrochemical performance of Ni–yttria stabilized zirconia (YSZ) electrode, which is widely used as the anode for solid oxide fuel cells (SOFCs), is evaluated for H2 production in solid oxide electrolysis cells (SOECs). The impedance spectra of Ni–YSZ electrode are composed of two major depressed arcs. The high-frequency impedance (>104 Hz) can be assigned to transfer of the charged species across the Ni/YSZ interface, and the mid-frequency arc (102∼103 Hz) is possibly associated with the gas–solid interaction such as adsorption, dissociation, desorption, etc. The impedance spectra are strongly influenced by the gas composition in both fuel cell (H2 oxidation) and electrolysis (H2O reduction) reactions; polarization resistance decreases with increasing concentration of the reactant species. In fuel cell mode, both high- and mid-frequency arcs increase with decreasing H2 concentration, while the impedance spectra are dominated by the mid-frequency arc and the high-frequency arc remains negligible even at low H2O concentration in electrolysis mode. Reaction mechanisms and elementary reaction pathways for H2 oxidation and H2O reduction are suggested based on impedance spectra. The minimum impedance is observed at 50% H2O in electrolysis mode, and further increase in H2O concentration causes degradation of the electrode performance, possibly due to local oxidation of Ni. •The electrochemical behavior of Ni–YSZ electrode is studied for steam electrolysis.•The high-frequency impedance is due to charge transfer across the Ni/YSZ interface.•The mid-frequency impedance is due to gas–solid interaction.•Polarization resistance decreases with increasing the reactant concentration.•The minimum impedance is observed at H2–50% H2O in electrolysis mode.