La_0.8Sr_0.2Co_1-xNi_xO_3-δ as the Efficient Triple Conductor Air Electrode for Protonic Ceramic Cells

Abstract

Highly efficient mixed H + /e − /O 2− triple conducting air electrodes are indispensable for improving the electrochemical performance of protonic ceramic fuel cells and electrolysis cells (PCFC/ECs) operating at intermediate temperatures. This study demonstrates that single perovskite-type La 0.8 Sr 0.2 Co 1-x Ni x O 3-δ families (LSCN, x = 0−0.3) are efficient H + /e − /O 2− triple conductors due to a pronounced hydration ability at elevated temperatures with a related enthalpy of −107 kJ mol −1 . Thermogravimetry confirmed that the oxides were capable of a 0.01 mole fraction proton uptake at 600 °C and p H2O of 0.023 atm. Reversible protonic ceramic cells were fabricated using these oxides as an air electrode and exhibited promising performance with a peak power density of 0.88 W cm −2 in fuel cell mode and an electrolysis current of 1.09 A cm −2 at a thermal neutral voltage in electrolysis cell mode at 600 °C. Impedance analysis confirmed that the polarization resistance of the La 0.8 Sr 0.2 Co 0.7 Ni 0.3 O 3-δ cell was 0.09 Ω cm 2 under an open circuit potential at 600 °C, which is much smaller than the polarization resistances reported for cells with a single or double perovskite-type triple conductor. The current results indicate that mixed H + /e − / O 2− triple phase conducting LSCN oxides are promising air electrodes for protonic ceramic cells operating in the intermediate temperature region at approximately 600 °C.

Advanced Cathode Materials for Protonic Ceramic Fuel Cells: Recent Progress and Future Perspectives

“…[18] and c) triple conducting single-phase cathode; d) Summary of PPDs for PCFCs with the three types of cathodes. [12,16,19,32,[63][64][65]68,70,74,75,91,92,94,101,103,105,108,120] To summarize, although few PCFCs with composite cathodes display excellent electrochemical performances, most of the PCFCs with triple composite cathodes prepared by the methods mentioned above exhibit unsatisfactory electrochemical performances. For example, their PPDs were lower than 0.5 W cm -2 and R p values were larger than 0.4 Ω cm -2 (Figure 17d, Table 2) at 600 °C.…”

“…The C H value roughly estimated from the gap of the two TGA curves was equal to 0.01 mol unit −1 at 600 °C. [92] Other methods have also been developed for the preliminary determination of proton uptake by oxides, which could be efficient for initial material screening. That is, the mass loss at the intermediate temperature was measured and combined with theoretical calculations.…”

Metal/Oxide Heterojunction Boosts Fuel Cell Cathode Reaction at Low Temperatures

“…Arrhenius plots of the R p (solid plot in grey‐shade region) in this work and comparison with the reported R p of La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3−δ (LSCF; ○) for PCFC [ 43 ] and SOFC, [ 44 ] and recently reported triple‐conducting (H + /O 2− /e − ) cathode materials (black hollow plot): BaCo 0.7 (Ce 0.8 Y 0.2 ) 0.3 O 3−δ (□; BCCY [ 17 ] ), La 0.8 Sr 0.2 Co 0.7 Ni 0.3 O 3−δ (×; LSCN [ 19 ] ), PrBa 0.5 Sr 0.5 Co 1.5 Fe 0.5 O 5+δ (⧾; PBSCF [ 14 ] ), Ba 0.9 Co 0.4 Fe 0.4 Zr 0.1 Y 0.1 O 3−δ (D; B0.9CFZY [ 46 ] ), and PrBa 0.8 Ca 0.2 Co 2 O 5+δ ‐BaCoO 3−δ composite (∇; PBCC‐BCO [ 47 ] ). The plots in the red‐shaded region represent the R p of Sc50‐cell at −0.4 V versus OCV.…”

“…Surprisingly, the R p of HMFCs is lower than that of the PCFCs when using triple‐conducting (H + /O 2− /e − ) cathode materials [ 14,17,19,46,47 ] (Figure 7a). As widely recognized, PCFCs with triple‐conducting cathodes have lower cathodic R p than cells with MIEC cathodes because the effective reaction areas of the former extend to the overall electrode surface owing to the proton conductivity, whereas those of the latter are limited only to the TPB.…”

“…A major cause of the low performance has been attributed to the high cathode polarization resistance. Paradoxically, the choice of proton‐conducting ceramics not only complicates intricate cathode reactions but also shrinks the effective reaction area to the 2D gas–electrolyte–cathode triple‐phase boundary (TPB) [ 16–19 ] because of the mismatch between the primary ion carriers of the electrolyte and cathode. Therefore, it is of great significance to explore strategies for enhancing cathode reactions in limited TPB zones on PCFCs.…”