A Ce/Ru Codoped SrFeO3−δ Perovskite for a Coke-Resistant Anode of a Symmetrical Solid Oxide Fuel Cell

Boosting the Electrocatalytic Activity of Pr0.5Ba0.5FeO3-δ via Ni Doping in Symmetric Solid Oxide Electrolysis Cells

Symmetric solid oxide electrolysis cells (SSOECs) have garnered significant scientific interest due to their simplified cell architecture, robust operational reliability, and cost-effectiveness, for which a highly electrocatalytically active electrode is the decisive main factor. This work evaluates the electrochemical performance of Ni-doped Pr0.5Ba0.5FeO3-δ (PBF) perovskite materials, with a focus on Pr0.5Ba0.5Fe0.8Ni0.2O3-δ (PBFN). The experimental findings herein prove the exceptional electrocatalytic ability of PBFN in facilitating the oxygen evolution and carbon dioxide reduction reaction, surpassing the electrochemical performance of PBF. In addition, the PBFN symmetric cell has excellent performance for CO2 electrolysis, and the cell has a low polarization resistance value of 0.1 Ω·cm2. Moreover, it achieves an impressive current density value of 1.118 A·cm-2 under operating conditions of 2.0 V and 800 °C, which is superior to those of the PBF symmetric cell and the PBFN asymmetric cell. It also has a good structural and performance stability. These results imply a bright development prospect of PBFN as electrodes for SSOECs.

In Situ Generation of Pseudorutile Oxide as the Cathode for Direct Electrolysis of CO2

The conversion of CO2 into CO in high-temperature solid oxide electrolysis cells (SOECs) is an attractive route for the CO2 utilization using the intermittent renewables. The low-cost and highly catalytic cathode is important for the direct electrolysis of pure CO2. In this study, non-perovskite Fe0.5Mg0.25+0.5xTi0.25-0.5xNb1-xMoxO4 oxides (denoted as Mo-x when x is equal to 0, 0.1, and 0.2) are evaluated as the cathode of an SOEC for the direct electrolysis of CO2. Mo6+ doping converted the wolframite Mo-0 into an α-PbO2-type with cation disordering, while further doping to Mo-0.2 showed a wolframite with cation ordering again. The SOEC with Mo-0.2 as the cathode exhibits the best electrochemical performance for the direct electrolysis of CO2 as a large portion of the oxide converted into oxygen-deficient pseudorutile-type oxide with a nominal formula of M5O9 (M = cation). The pseudorutile, a crystallographic shear phase of rutile, can be obtained after 60 h of direct electrolysis in CO2 at a 1.3 V bias rather than a reduction under 5% H2. The SOEC with Mo-0.2 as the cathode imparted a stable current density of 0.45 A cm-2, which could be related to the production of pseudorutile decorated with nanoparticles of MoO2. These results show that molybdenum doping is an effective strategy for developing oxygen-deficient rutile (pseudorutile) for the electrolysis of CO2.

Exsolution Modeling and Control to Improve the Catalytic Activity of Nanostructured Electrodes

In situ exsolution for nanoscale electrode design has attracted considerable attention because of its promising activity and high stability. However, fundamental research on the mechanisms underlying particle growth remains insufficient. Herein, cation-diffusion-determined exsolution is presented using an analytical model based on classical nucleation and diffusion. In the designed perovskite system, the exsolution trend for particle growth is consistent with this diffusion model, which strongly depends on the initial cation concentration and reduction conditions. Based on the experimental and theoretical results, a highly Ni-doped anode and an electrochemical switching technique are employed to promote exsolution and overcome growth limitations. The optimal cell exhibits an outstanding maximum power density of 1.7 W cm^-2 at 900 °C and shows no evident degradation when operating at 800 °C for 240 h under wet H₂ . This study provides crucial insights into the developing and tuning of heterogeneous catalysts for energy-conversion applications.

Interfacial electron transfer in heterojunction nanofibers for highly efficient oxygen evolution reaction

Efficient catalysts for the oxygen evolution reaction (OER) are critical to the progress of electrochemical devices for clean energy conversion and storage. Although heterogeneous electrocatalysts have superior activity, it is a great challenge to elucidate electron transfer at surface catalytic sites and intrinsic mechanisms. Herein, we demonstrate a new type of heterostructure electrocatalyst in which Sr_0.9Ce_0.05Fe_0.95Ru_0.05O₃ fibers are hybridized with in situ grown RuO₂ nanoparticles (SCFR-RuO₂). We investigate its unique structure, electron transfer mechanisms related to the highly OER activity by combining experimental and theoretical calculations. Remarkably, SCFR-RuO₂ shows an optimized OER overpotential of 295 mV at 10 mA cm^-2. The promoted electron transfer and OER kinetics are ascribed to the coupling of electronic effects at the SCFR-RuO₂ heterostructure. A strong triangular relationship among overpotential-Tafel slope-work function is proposed to be a potential descriptor of OER activity in SCFR-RuO₂. These insights provide guidelines for tuning the OER performance via modified work functions in perovskite electrocatalysts.

Oxygen deficiency in Sr2FeO4-x: electrochemical control and impact on magnetic properties

The oxygen-deficient system Sr₂FeO_4-x was explored by heating the stoichiometric Fe⁴⁺ oxide Sr₂FeO₄ in well-defined oxygen partial pressures which were controlled electrochemically by solid-state electrolyte coulometry. Samples with x up to about 0.2 were obtained by this route. X-ray diffraction analysis reveals that the K₂NiF₄-type crystal structure (space group I4/mmm) of the parent compound is retained. The lattice parameter a slightly decreases while the c-parameter increases with increasing x, which is in contrast to the Ruddlesden-Popper system Sr₃Fe₂O_7-x and suggests removal of oxygen atoms from FeO₂ lattice planes. The magnetic properties were studied by magnetization, ⁵⁷Fe Mössbauer, and powder neutron diffraction experiments. The results suggest that extraction of oxygen atoms from the lattice progressively changes the elliptical spiral spin ordering of the parent compound to an inhomogeneous magnetic state with coexistence of long-range ordered regions adopting a circular spin spiral and smaller magnetic clusters.