Ka-Young Park

Oxygen electrode reactions of doped BiFeO3 materials for low and elevated temperature fuel cell applications

Perovskite-based catalysts have been considered as candidate bifunctional electrocatalysts for oxygen evolution (OER) and reduction reactions (ORR) for unitized regenerative fuel cells (URFCs), because of their excellent catalytic activity and durability at low temperature. Furthermore, perovskite-structured materials can be utilized as an oxygen electrode material for solid oxide fuel cells (SOFCs) at even elevated temperatures due to their distinctive layered structure, providing great flexibility regarding the modification of their electronic configurations. Herein, we investigate whether alkaline earth metal-doped bismuth iron oxides (Bi0.6M0.4FeO3,xa0M = Ba, Sr, Ca, and Mg) can act as both bifunctional catalysts for URFCs and cathode materials for SOFCs. Among these, Bi0.6Ca0.4FeO3 (BCFO) exhibits remarkable OER and ORR catalytic performances, with better long-term stability than that of a pristine BiFeO3 (BFO) catalyst in alkaline media at room temperature. Moreover, the DC conductivity of BCFO is more than 2 to 3 orders of magnitude higher than that of the BFO material at 500–700 °C for SOFCs. In addition, BCFO has a αTEC value of 12.4 × 10−6 K−1 at 25–650 °C, which is near those of yttria-stabilized zirconia and rare-earth-doped ceria electrolytes. Hence, BCFO demonstrates potential as an oxygen electrode material for operation at room and elevated temperatures.

A Scientific Approach for Improving Sensitivity and Selectivity of Miniature, Solid-state, Potentiometric Carbon Monoxide Gas Sensors by Differential Electrode Equilibria Mechanism

Based on the differential electrode equilibria approach, potentiometric YSZ sensors with semiconducting oxide electrodes for CO detection are developed. To improve the selectivity, sensitivity and response-time of the sensor, our strategy includes (a) selection of an oxide with a semiconducting response to CO, (b) addition of other semiconducting materials, (c) addition of a catalyst (Pd), (d) utilization of combined p- and n-type electrodes in one sensor configuration, and (e) optimization of operating temperatures. Excellent sensing performance is obtained by a novel device structure incorporating La₂CuO₄ electrodes on one side and TiO₂- based electrodes on opposite substrate faces with Pt contacts. The resulting response produces additive effects for the individual La₂CuO₄ and TiO₂-based electrodes voltages, thereby realizing an even higher CO sensitivity. The device also is highly selective to CO versus NO with minor sensitivity for NO concentration, compared to a notably large CO sensitivity.