Editorial

This Special Issue of the Journal of Electrochemical Science and Engineering presents papers form the Fifth Regional Symposium on Electrochemistry – South East Europe (RSE - SEE5) held in Pravetz, Bulgaria, June 7 - 11, 2015

Investigation of Ni- and Co-Based Bifunctional Electrocatalysts for Carbon-Free Air Electrodes Designed for Zinc-Air Batteries

Ni- and Co-oxide materials have promising electrocatalytic properties towards the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR), and attract with low cost, availability, and environmental friendliness. The stability of these materials in alkaline media has made them the most studied candidates for practical applications such as a gas diffusion electrode (GDE) for rechargeable metal-air batteries. In this work, we propose a novel concept for a carbon-free gas GDE design. A mixture of catalyst (Co3O4, NiCo2O4) and polytetrafluoroethylene was hot pressed onto a stainless-steel mesh as the current collector. To enhance the electrical conductivity and, thus, increase ORR performances, up to 70 wt.% Ni powder was included. The GDEs produced in this way were examined in a half-cell configuration with a 6 M KOH electrolyte, stainless steel counter electrode, and hydrogen reference electrode at room temperature. Electrochemical tests were performed and coupled with microstructural observations to evaluate the properties of the present oxygen electrodes in terms of their bifunctionality and stability enhancement. The electrochemical behavior of the new types of gas-diffusion electrodes, Ni/Co3O4 and Ni/NiCo2O4, shows acceptable overpotentials for OER and ORR. Better mechanical and chemical stability of electrodes consisting of Ni/NiCo2O4 (70:30 wt.%) was registered. Doi: 10.28991/ESJ-2023-07-03-023 Full Text: PD

Impedance Behavior of LSCF/YDC/LSCF Symmetrical Half Cell Prepared by Plasma Spray

Impedance studies of electrolyte supported symmetrical half cells La0,6Sr0,4Co0,2Fe0,8O3- /Ce0,85Y0,15O2-/La0,6Sr0,4Co0,2Fe0,8O3- with electrodes deposited by atmospheric plasma spraying (APS) show that the applied technique influences reversibly the substrate properties, introducing additional contribution to the interface substrate/electrode. After thermal treatment in temperature range 100-800oC during the impedance measurements, an annealing effect is observed. It eliminates the additional increase of the electrolyte resistivity and increases slightly the polarization resistance. The observed effect could be related to thermally and/or mechanically induced local microstructure defects, caused by the APS procedure. The obtained results show that for stabilization of the cell’s performance, annealing should be performed after the APS deposition. It can be supposed that an appropriate annealing atmosphere may prevent the electrodes deactivation

New Insights on the Nickel State Deposited by Hydrazine Wet-Chemical Synthesis Route in the Ni/BCY15 Proton-Conducting SOFC Anode

Yttrium-doped barium cerate (BCY15) was used as an anode ceramic matrix for synthesis of the Ni-based cermet anode with application in proton-conducting solid oxide fuel cells (pSOFC). The hydrazine wet-chemical synthesis was developed as an alternative low-cost energy-efficient route that promotes ‘in situ’ introduction of metallic Ni particles in the BCY15 matrix. The focus of this study is a detailed comparative characterization of the nickel state in the Ni/BCY15 cermets obtained in two types of medium, aqueous and anhydrous ethylene glycol environment, performed by a combination of XRD, N2 physisorption, SEM, EPR, XPS, and electrochemical impedance spectroscopy. Obtained results on the effect of the working medium show that ethylene glycol ensures active Ni cermet preparation with well-dispersed nanoscale metal Ni particles and provides a strong interaction between hydrazine-originating metallic Ni and cerium from the BCY15 matrix. The metallic Ni phase in the pSOFC anode is more stable during reoxidation compared to the Ni cermet prepared by the commercial mechanical mixing procedure. These factors contribute toward improvement of the anode’s electrochemical performance in pSOFC, enhanced stability, and a lower degradation rate during operation

Differential analysis of SOFC current-voltage characteristics

Solid Oxide Fuel Cells (SOFCs) are regarded as a promising technology for economic power generation due to their high efficiency and large fuel flexibility. Durability is a severe hurdle towards their deployment. The near future Targets in respect to Degradation Rate (DR) are about 0.1%kh-1, which needs improved monitoring and diagnostics.This work aims at introducing a new approach based on Differential Analysis of the i-V curves, named DiVA. It operates with the Differential Resistance Rd and its evolution during long term testing. Two new performance indicators are introduced. Since derivatives are more sensitive to small deviations, the Differential Resistance Analysis (DRA) ensures increased sensitivity and information capability in respect to degradation monitoring and diagnostics, which is demonstrated on a small stack during thermal cycling conditions - before and after first thermal cycle, on button cells tested up to 9000 h, as well as on button cells operating in fuel cell and in electrolysis mode. The results show that DRA is several times more sensitive in comparison with the classical DR evaluation based on registration of the voltage decrease at constant current

Impedance spectroscopy studies of dual membrane fuel cell

This paper reports impedance studies of a dual membrane fuel cell - an innovative design based on the idea for a junction between an oxygen ion conducting cathode/electrolyte part and proton conducting anode/electrolyte part through a mixed oxygen ion and proton conducting porous membrane. Thus oxy- gen, hydrogen and water are located in three independent chambers. This concept allows avoiding all the severe pitfalls connected to the presence of water at electrodes in both SOFC and PCFC. The performed measurements of the 3 compartments and the data analysis are improved by introducing some special- ized approaches and techniques, which are discussed. The impedance contribution in the proof of the new concept is also presented

Application of yttrium doped barium cerate for improvement of the dual membrane SOFC design

International audienceRecently a new design of solid oxide fuel cell (SOFC) named dual membrane fuel cell (dmFC) has been introduced and proved. It is based on the introduction of three independent compartments for hydrogen, oxygen and water, which eliminate the dilution of the fuel or the oxidizer respectively in the SOFC construction or in its proton conducting (pSOFC) modification. Due to the registered sufficient mixed ionic conductivity of BaCe0.85Y0.15O2.925 (BCY15), a simplified modification in respect to shaping technology and construction is introduced. It's performance is better than the one of pSOFC cell produced with the same material and shaping procedure: 76 mW/cm2 (dmFC thickness 1.1 mm) against 71 mW/cm2 (pSOFC thickness 0.66 mm) at 700 °C. Impedance measurements carried out down to 1 mHz ensure information about the water formation and behaviour in the separate central membrane compartment of the dmFC design, which brings to performance improvements, registered also in electrolyser mode of operation