Annie Le Gal La Salle

A Ni/Yttria‐stabilized zirconia (YSZ) cell with a (La_0.60Sr_0.40)_0.95Co_0.20Fe_0.80O_3–δ cathode is tested both in fuel cell and electrolysis modes. In fuel cell mode under dry air and wet H₂, the cell is operated between the open circuit voltage (OCV) and 0.4 V and reaches 330 mW cm⁻² at 850 °C for 157 mL min⁻¹ H₂ supply. The influence of temperature and air or hydrogen flow rate is studied, and impedance measurements show that below 0.8 V the electrolyte becomes the more resistive part of the cell. Nevertheless, fuel utilization yields are higher under oxygen or hydrogen depletion. If it is possible at 750 °C to work at low voltage during several hours in the entire voltage range, the voltage decrease must be limited at 850 °C. The cell can also be operated under wet air. The same cell can be operated in electrolysis mode, and a power density of 340 mW cm⁻² can be obtained at 0.3 V/OCV under 100 mL min⁻¹ wet (3% H₂O) 5% H₂–95% Ar mixture on the fuel side and dry or wet 100 mL min⁻¹ air flow on the air side. Nevertheless, bubbling air providing the air electrode in saltwater has an irreversible detrimental effect on the cell.

NiO has been incorporated into the Pr_0.5Ba_0.5MnO_3−δ perovskite to produce in situ exsolved Ni-catalyst on the PrBaMn₂O₅ anode material upon heating under a hydrogen atmosphere.

Due to their fuel flexibility and high efficiency solid oxide cells are a promising technology for sustainable energy production and storage. Nickel in combination with yttria-stabilized zirconia (YSZ) or gadolinium-doped ceria (GDC), forming Ni-YSZ or Ni-GDC cermets respectively, are the most widely adopted electrodes in solid oxide fuel cell fabrication. Currently, there is an increasing interest in cermet electrodes for hydrogen generation through high temperature steam electrolysis using solid oxide electrolysis cells (SOECs). However, durability remains a major issue for reliable operation of SOEC systems. A variety of processes accountable for permanent performance degradation of SOECs has been identified based on post-mortem cell analysis. Besides, transient/reversible degradation processes are typically examined by indirect methods, like impedance spectroscopy. The reason is that the application of material characterization techniques during SOEC operational conditions is challenging. In this work we provide a direct correlation between Ni-YSZ and Ni-GDC electrodes surface oxidation states and their performance during steam electrolysis using operando experimental evidence provided by near ambient pressure X-ray photoelectron and near edge X-ray absorption fine structure spectroscopy. We show that nickel surface oxidation may induce significant performance degradation in Ni-YSZ cathodes, while on the contrary has minor effects in Ni-GDC. Remarkably, we found that in case of Ni-GDC electrodes, small modification of GDC oxidation state can have an important impact on the electrolysis performance. The results highlight the crucial role of the cathode electrode surface oxidation state on the SOEC functionality and have potential implications for the design and operation strategies of more efficient and durable SOEC devices.

The cold sintering process (CSP) was applied for the first time to the high temperature proton conductor BaCe_0.8Zr_0.1Y_0.1O_3-δ. The CSP parameters were optimized in order to obtain the best relative density: the amount of water 0-20 wt.%, the pressing temperature 120-180°C and the pressure ranges between 125 to 500 MPa (for 30 minutes). We demonstrate the ability of CSP to achieve a relative density of 83% at only 180°C and 375 MPa using 5 wt.% water. It has been found that a post CSP annealing at 100°C improves the material relative density which reaches 93%. Ceramic materials were investigated for their microstructure-electrochemical properties relations. The ionic conductivity was measured between 150 and 800°C on dense and well defined microstructure materials. When the annealing temperature increases from 1000, 1100, 1200°C a large increase of the conductivity is observed reaching 2.3x10^-2 S·cm^-1 at 700°C for pellet sintered 10 h at 1200°C.