Identification and electrochemical characterization of in situ produced and added reduced oxygen species in molten Li2CO3 + K2CO3

Gadolinia-doped ceria mixed with alkali carbonates for SOFC applications: II – An electrochemical insight

“…By the one hand, the presence of CO 2 increases the proportion of CO 3 2À , but contrarily to the composite with the lower ratio of carbonates, it increases significantly the conductivity. By the other hand, the presence of oxygen might favour the following interfacial reactions, producing peroxide or superoxide species known to exist in molten carbonates [45]:…”

Oxidative Dissolution of Tungsten Metal in Na2CO3 under Ar–O2–CO2 Atmosphere

“…The existence of O2 2− /O2 − ions at high partial pressure of CO2 has been intensively reported in MCFC researches. [29][30][31][32][33][34][35][36][37][38][39][40][41][42] Their high stability at low partial pressure was also experimentally confirmed. 43,44 According to the report by Andersen, 43 when the O2-O2 − -O2 2− -O 2− equilibria were attained for various carbonate molten salts of Li, Na, and/or K by holding in O2 (1 atm) after adding 3 mol% O 2− ions, a large amount of the added O 2− ions reacted with O2 gas to form O2 2− /O2 − ions at the low partial pressure of CO2 (the estimated order of 10 −4 or 10 −3 atm) by the formed gas in CO3 2− dissociation.…”

“…In the potential sweep to the negative direction, a small reduction current is observed from the rest potential, then a large reduction current starts at approximately −0.85 V. The reduction current sharply increases at −1.7 V. After the reversal of the sweep direction, the oxidation current starts to flow at 0 V and has a peak at 0.7 V. The potential of the quasi-reference electrode can be calibrated to the value indicated in the potential-diagram (Fig. 7)under the conditions that the O2/O 2− reaction is electrochemically reversible and the potential of the reference electrode corresponds to the O2/O 2− equilibrium at the given partial pressure.O2 (g) + 4e − = 2O 2− (l) equilibrium potential of the Au quasi-reference electrode is 0.455 V (vs. O2 (1 atm)/O 2− (a = 1)) at = 6 × 10 −4 atm and = 0.2 atm, the calibration enables analysis of the cyclic voltammogram.Here, the calibration assumption should be noticed that the reversibility for electrochemical reaction[41] is unknown for low partial pressure of CO2 although it is well-known for high partial pressure and the utilization of an Au electrode in 67%CO2-33%O2 gas as a reference electrode has been established. The oxidation at potentials more positive than 0 V indicates the evolution of O2 gas.…”

Ionic transport mechanism of La0.9Sr0.1Ga0.8Mg0.2O2.85-(Li/Na)2CO3 composite electrolyte for low temperature SOFCs

“…Comparing the effect of the nitrogen atmosphere on LSGM-30 wt% (Li/ Na) 2 CO 3 composite electrolyte it was observed that the conductivity in the nitrogen atmosphere was the lowest in the high temperature range (500e650 C), because there were no additional ions source in nitrogen atmosphere. Under oxygen atmosphere, a conductivity value was slightly higher than under nitrogen atmosphere above the bulk melting point, the presence of oxygen provided some new ions for composite electrolyte conduction, such as peroxide or superoxide species, which could also explain the enhancement in composite electrolyte ion conductivity despite the little amount of peroxide [18]. Under hydrogen atmosphere, there is no obvious transition temperature was within the scope of the test temperature, but combined with others the conductivity got obvious improvement at low temperature (400 C).…”