Fabrication and characterization of protonic-ceramic fuel cells and electrolysis cells utilizing infiltrated lanthanum nickelate electrodes

Abstract

High-temperature protonic ceramics (HTPCs) have gained interest as fuel cell and electrolysis cell electrolytes, as well as hydrogen separation membranes. The transport of hydrogen as opposed to oxygen results in several benefits and applications, including higher fuel efficiency, dehydrogenation of fuel streams, and hydrogen-based chemical synthesis. However, limited work has been done in the development of air/steam electrodes for these devices. This work presents the characterization of lanthanum nickelate, La[subscript 2]NiO[subscript 4+delta] (LN), as a potential air/steam electrode material for use with BaCe[subscript 0.2]Zr[subscript 0.7]Y[subscript0.1]O[subscript 3-delta] (BCZY27) HTPC electrolytes fabricated by the solid-state reactive sintering technique. Two types of devices were made; a symmetric cell used for electrode characterization, and a full fuel cell/electrolysis cell used for device performance characterization. The symmetric cell consists of a 1 mm thick BCZY27 substrate with identical air/steam electrodes on both sides. Air/steam electrodes were made by infiltrating [sim] 50 nm lanthanum nickelate nanoparticles into a BCZY27 porous backbone. The fuel cell/electrolysis cell consists of a 1mm thick Ni/BCZY27 anode support, a 25 [mu]m thick BCZY27 electrolyte, and a 50 [mu]m thick porous BCZY27 backbone infiltrated with lanthanum nickelate. Through symmetric cell testing, it was found that the electrode polarization resistance decreases with increasing oxygen content, indicating good oxygen reduction reaction characteristics. A minimum polarization resistance was found as 2.58 Ohm-cm[superscript 2] in 3% humidied oxygen at 700 [degrees]C. Full cell testing revealed a peak power density of 27 mW-cm[superscript -2] at 700 [degrees]C. Hydrogen flux measurements were also taken in the both galvanic/post-galvanic and electrolytic operation. Galvanic/post-galvanic fluxes exhibit a very high faradaic efficiency. However, electrolytic hydrogen fluxes were much lower than the calculated hydrogen faradaic flux, indicating a different charge carrier other than protons is dominating the conductivity of the BCZY27 electrolyte under electrolysis operation. In this work, it is proposed that high electrolytic overpotentials combined with oxygen incorporation into the electrolyte result in electron hole generation and migration through the electrolyte, creating an apparent electronic short. This result suggests the inadequacy of thin BCZY27 membranes in electrolytic devices.