LaPrNiO_4+δ Nano-Columnar Thin Films as Oxygen Electrodes for Reversible Solid Oxide Cells

This work explores the potential of La_1-xPr_xNiO_4+δ thin films fabricated by Pulsed Injection Metal–Organic Chemical Vapor Deposition as oxygen electrodes for low-temperature solid oxide cells. La_1-xPr_xNiO_4+δ materials offer promising mixed ionic and electronic conductivity and high oxygen reduction reaction kinetics. In this study, we focus on the microstructural and electrochemical properties of LaPrNiO_4+δ thin films deposited at various temperatures (600–650 ℃), revealing that a two-temperature deposition process yields nano-architectured films with a dense bottom film and a porous nano-columnar top layer of the same material. Electrochemical impedance spectroscopy and electrical conductivity relaxation experiments demonstrate enhanced surface exchange coefficients compared to bulk LaPrNiO_4+δ and La₂NiO_4+δ and high performance, with polarization resistances as low as 0.10 Ω cm² at 600 ℃ and 1.00 at 500 ℃. To better understand the electrochemical behavior of these electrodes, we investigated the limiting mechanisms of oxygen reduction by analyzing the kinetic response to varying oxygen partial pressures and performing detailed impedance analyses. These nano-columnar LaPrNiO_4+δ oxygen electrodes were also deposited on commercial half-cells, enabling the resulting full cells to operate successfully in both reversible solid oxide fuel cell and electrolysis cell modes, reaching a performance of 0.34 W cm⁻² at 600 ℃ in reversible solid oxide fuel cell mode. This work underscores the promise of LaPrNiO_4+δ thin films for efficient low-temperature-solid oxide cells while addressing challenges in durability and stability.