Investigation of Water Impacts on Surface Properties and Performance of Air-Electrode in Reversible Protonic Ceramic Cells.

Water, being abundant and readily accessible, gains widespread usage as proton source in many catalysis and energy conversion technologies, including applications like reversible protonic ceramic cells (R-PCCs). Revealing the influence of water on the electrode surface and reaction kinetics is critical for further improving their electrochemical performance. Herein, a hydrophilic air-electrode PrBa0.875Cs0.125Co2O5+δ is developed for R-PCC, which demonstrates a remarkable peak power density of 1058 mW cm-2 in fuel cell mode and a current density of 1354 mA cm-2 under 1.3 V in electrolyzing steam at 650 °C. For the first time on R-PCC, surface protons' behavior in response to external voltages is captured using in situ FTIR characterizations. Further, it is shown that contrary to the bulk proton uptake process that is thought to follow hydrogenation reactions and lead to cation reductions. The air-electrode presents enriched surface protons occurring through oxidizing surface cations, as confirmed by depth-profiling XPS results. H/D isotope exchange experiments and subsequent electrochemical characterization analyses reveal that the presence of protons enhances surface reactions. This study fills the knowledge gap between water-containing atmospheres and electrochemical performance by providing insights into the surface properties of the material. These new findings provide guidance for future electrode design and optimization.

Chromium deposition and poisoning of La(0.8)Sr(0.2)MnO3 oxygen electrodes of solid oxide electrolysis cells.

The effect of the presence of an Fe-Cr alloy metallic interconnect on the performance and stability of La(0.8)Sr(0.2)MnO3 (LSM) oxygen electrodes is studied for the first time under solid oxide electrolysis cell (SOEC) operating conditions at 800 °C. The presence of the Fe-Cr interconnect accelerates the degradation and delamination processes of the LSM oxygen electrodes. The disintegration of LSM particles and the formation of nanoparticles at the electrode/electrolyte interface are much faster as compared to that in the absence of the interconnect. Cr deposition occurs in the bulk of the LSM oxygen electrode with a high intensity on the YSZ electrolyte surface and on the LSM electrode inner surface close to the electrode/electrolyte interface. SIMS, GI-XRD, EDS and XPS analyses clearly identify the deposition and formation of chromium oxides and strontium chromate on both the electrolyte surface and electrode inner surface. The anodic polarization promotes the surface segregation of SrO and depresses the generation of manganese species such as Mn(2+). This is evidently supported by the observation of the deposition of SrCrO4, rather than (Cr,Mn)3O4 spinels as in the case under the operating conditions of solid oxide fuel cells. The present results demonstrate that the Cr deposition is essentially a chemical process, initiated by the nucleation and grain growth reaction between the gaseous Cr species and segregated SrO on LSM oxygen electrodes under SOEC operating conditions.

Development of double-perovskite compounds as cathode materials for low-temperature solid oxide fuel cells.

A class of double-perovskite compounds display fast oxygen ion diffusion and high catalytic activity toward oxygen reduction while maintaining excellent compatibility with the electrolyte. The astoundingly extended stability of NdBa(1-x)Ca(x)Co2O(5+δ) (NBCaCO) under both air and CO2-containing atmosphere is reported along with excellent electrochemical performance by only Ca doping into the A site of NdBaCo2O(5+δ) (NBCO). The enhanced stability can be ascribed to both the increased electron affinity of mobile oxygen species with Ca, determined through density functional theory calculations and the increased redox stability from the coulometric titration.

Synthesis and photocatalytic activity of rhodium-doped calcium niobate nanosheets for hydrogen production from a water/methanol system without cocatalyst loading.

Rhodium-doped calcium niobate nanosheets were synthesized by exfoliating layered KCa(2)Nb(3-x)Rh(x)O(10-δ) and exhibited high photocatalytic activity for H(2) production from a water/methanol system without cocatalyst loading. The maximum H(2) production rate of the nanosheets was 165 times larger than that of the parent Rh-doped layered oxide. The quantum efficiency at 300 nm was 65%. In this system, the methanol was oxidized to formaldehyde (main product), formic acid, and carbon dioxide by holes, whereas electrons cause the reduction of water to H(2). The conductivity of the parent layered oxide was decreased by doping, which indicates the octahedral RhO(6) unit in the lattice of the nanosheet functions as an electron trap site. The RhO(6) units in the nanosheet probably also act as reaction sites for H(2) evolution.