High-performance and excellent thermal cycling stability of reversible protonic ceramic cells enabled by a promising Sr/Co-free PrNi0.5Fe0.5O3−δ air electrode

Abstract

Reversible protonic ceramic cells (R-PCCs) are increasingly recognized as highly effective energy conversion and storage devices at intermediate temperatures (400–600 °C) because of their remarkable ability to function reversibly in both fuel cell (FC) and electrolysis cell (EC) modes. To date, Sr and/or Co-based perovskite oxides have been intensively studied as promising air electrodes in R-PCCs. Nevertheless, these materials are impeded by the decline in power output under operating conditions caused by Sr segregation and the mismatch in the thermal expansion coefficient (TEC) between the air electrodes and conventional electrolytes. Here, we propose an electrocatalytically active and thermomechanically durable Sr/Co-free PrNi_0.5Fe_0.5O_3−δ (PNF) air electrode. The PNF air electrode is chemically compatible with the BaZr_0.4Ce_0.4Y_0.1Yb_0.1O_3−δ (BZCYYb4411) electrolyte and shows great chemical stability in H₂O and CO₂. The electrochemical properties of the PNF air electrode were evaluated by R-PCC single cells, which demonstrated a peak power density of 1.17 W cm⁻² in FC mode and a current density of −1.78 A cm⁻² at 1.3 V in EC mode at 600 °C. Furthermore, there was no observable decrease in stability after 200 h of electrolysis operation. By replacing Co with Fe in PrNi_0.5Co_0.5O_3−δ (PNC), in particular, the suppressed mismatch in the TEC between the PNF and BZCYYb4411 results in enhanced thermal cycling stability by changing the temperature between 600 and 400 °C in EC mode. Overall, the findings strongly suggest that the PNF has the ability to provide reliable and long-term operation for sufficient hydrogen production and electricity generation in R-PCCs.