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Four PrBa0.5Sr0.5Co1.5Fe0.5O5+δ (PBSCF)-La2NiO4+δ (LN) core-shell cathodes, designated as PL-0, PL-1, PL-3 and PL-5, are prepared by infiltrating LN solution into PBSCF scaffold, and they are investigated in terms of the effect of LN thickness on their electrochemical performance. PL-3 with a continuous LN coating of a moderate average thickness (∼9 nm) demonstrates the lowest initial polarization resistance (0.51 Ω cm2) and highest power density (0.71 W cm−2) among all the cathodes. Polarized at 400 mA cm−2 and 700 °C for up to 40 h, the polarization resistance of all the prepared cathodes increases to approach a stable level after early stage decrease due to current activation, and PL-3 exhibits a slower average rate of performance degradation (25%). The electrochemical performance improvement is mainly attributed to that LN has a relatively high oxygen surface exchange coefficient and continuous LN coating depresses Sr segregation at PBSCF/LN interface.

La 2 NiO 4+δ (LN)-coated PrBa 0.5 Sr 0.5 Co 1.5 Fe 0.5 O 5+δ (PBSCF) composite cathode, designated as PBSCF-LN, for the intermediate temperature solid oxide fuel cells (IT-SOFCs) is prepared by solution infiltration, and investigated comparatively with single phase PBSCF cathode in the half and full cells using Ag and/or Pt paste as the current collector. Compared with Pt, Ag current collector results in a decrease of cathode polarization resistance ( R P ) by an order of magnitude, which suggests that Ag is electrocatalytically active and not suitable for the use of studying the cathode performance of IT-SOFCs. The R P value of PBSCF-LN cathode is significantly lower than that of PBSCF cathode, no matter whether Pt or Ag current collector is used for the measurement. High power densities ranging from 0.24 to 0.94 W cm −2 at temperatures between 600 and 750 °C are achieved using a full cell with PBSCF-LN cathode. Upon exposure to a CO 2 -rich atmosphere, carbonate particles are formed on the surface of PBSCF cathode, causing irreversible degradation of electrochemical performance. In contrast, the surface of PBSCF-LN cathode remains clean, and its performance degradation due to CO 2 adsorption is recoverable.

The evolution of solid oxide fuel cell anode microstructure during operation has important affects on cell performances and degradation. The degradation expectation requires a quantitative evaluation of the microstructure. In this work, anode support unit cells from 4 stacks are sampled and their anode functional layers and supports’ microstructure are evaluated with Focused Ion Beam-Scanning Electron Microscope and optical microscope. The cells are also cut into button cells and perform electrochemical evaluations. These compared microstructures reveal a time-related Ni migration that occurs from the functional layer deep into the support layer and Ostwald ripening. The change of Ni also affects the pore structure in the support layer and influences concentration polarization. The impact of microstructure evolution on electrochemical performance is revealed by Electrochemical Impedence Spectrum tests and Distribution of Relaxation Time analysis.

Reduced La0.6Sr0.2Cr0.85Ni0.15O3 (LSCrN) contains exsolved Ni nanoparticles (LSCrN@Ni) and abundant oxygen vacancies. Thus, it is an excellent catalyst for CO2 dry reforming of CH4. To use CH4 directly in solid oxide fuel cells, Ni–Ce0.9Gd0.1O1.95 (GDC) anode-supported cells are fabricated with and without a layer of LSCrN@Ni-20 wt% GDC on top of the anode, which are defined as double anode supported cell (DASC) and conventional anode supported cell (CASC), respectively. They are investigated comparatively by X-ray diffraction, thermal expansion, thermogravimetry, scanning electron microscopy, and electrochemical performance measurement in H2 and 50%CO2–50%CH4 fuels. Both CASC and DASC demonstrate similarly high performance with H2 fuel, the maximum power density is 856 and 822 mW cm−2 at 750 °C, respectively. When 50%CO2–50%CH4 is used, DASC outperforms CASC significantly, showing a maximum power density of 758 mW cm−2 and an on-cell CH4 conversion of 85.5% at 750 °C. Also, DASC demonstrates a stable performance, and the cell voltage and CH4 conversion remain unchanged at 0.65 V and 84% without detectable carbon formation in the anode, while those of CASC decrease monotonously from the beginning with observable carbon formation during a test of 36 h under 400 mA cm−2 at 750 °C.

The solution impregnation technology was used to prepare a novel core-shell structure cathode for intermediate temperature solid oxide fuel cells (IT-SOFCs). The core was composed of porous Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) backbone with high oxygen conductivity, while the dense shell consisted of La0.8Sr0.2MnO3−δ (LSM) high catalytic activity and the excellent CO2-poisoning resistance. The presence of the dense LSM shell prevented the BSCF cathode from being poisoned by CO2, and improved its electrochemical performance. The best performance was achieved when the BSCF cathode was impregnated twice in the LSM precursor solution and coated by LSM shell.

Hematite based photoanode is promising for solar water splitting while suffers from poor charge transport and separation efficiency that limit its practical application. Herein, we demonstrate two types gradient Ti-doped Fe2O3 photoanodes (Fe2O3–Ti (TiO2 deposited on the top of Fe2O3) and Ti–Fe2O3 (Fe2O3 on the top of TiO2)) to enhance charge transport and separation efficiency. Interestingly, Fe2O3–Ti and Ti–Fe2O3 photoanodes exhibit almost identical PEC performance with photocurrent of 1.50 mA cm−2 at 1.23 V vs. the reversible hydrogen electrode (RHE). However, the onset potential of Ti–Fe2O3 photoanode displays a cathodic shift of 80 mV comparing with that of Fe2O3–Ti photoanode. Moreover, the charge separation efficiencies on the surface ( η s u r f a c e ) for Fe2O3–Ti and Ti–Fe2O3 can reach up to 96% at the higher potential range from 1.30 to 1.50 V vs. RHE, which are among the top values in the record of hematite-based photoanodes without co-cocatalyst. Further investigation demonstrates the forming of gradient Ti doping is not dependent on the location of the TiO2 layer, but mainly affected by the high annealing temperature. The enlarged contact area between hematite photoanode and the electrolyte, the improved charge separation efficiency, and increased charge carrier density are responsible for the enhanced PEC water splitting.

Pd 0.95 Mn 0.05 O-infiltrated (La 0.8 Sr 0.2 ) 0.95 MnO 3−δ –8 mol.% Y 2 O 3 stabilized ZrO 2 (LSM-YSZ) cathode is used to large size (11 × 11 × 0.1 cm) Ni-YSZ anode-supported planar cells for the first time and electrochemically evaluated in the intermediate temperature range from 650 to 800 °C with H 2 as the fuel and air as the oxidant. The initial open circuit voltage (OCV) of the cell is 1.15 V, and the achieved maximum power density increases from 328 to 734 mW cm −2 with the increase of testing temperatures from 600 to 800 °C, which is almost 2.6 times higher than that of the cell with conventional LSM-YSZ cathode. After each thermal cycle between 750 and 300 °C, the OCV remains almost unchanged and the cell voltage decreases less than 0.007 V, indicating that the cell is capable of thermal cycling. The cell voltage at 310 mA cm −2 and 750 °C declines linearly with testing time at a rate of 2.6 × 10 −4 V h −1 for the growth of the infiltrated Pd 0.95 Mn 0.05 O size, resulting in reduction of the total surface area of the particles. The mechanism of performance degradation of the cell with Pd 0.95 Mn 0.05 O-infiltrated LSM-YSZ composites cathode is discussed in detail.

Sm x Sr 1−x MnO 3 with x = 0.3, 0.5 and 0.8, denoted as SSM37, SSM55 and SSM82, respectively, have been prepared via a sol–gel route as materials for cathodes in solid oxide fuel cells. Their activities in the oxygen reduction reaction (ORR) have been evaluated in comparison with the state-of-the-art cathode material La 0.8 Sr 0.2 MnO 3 (LSM82) by electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) and thermogravimetry (TG). Among all the prepared cathodes, the SSM55 exhibits the lowest values, while the LSM82 exhibits the highest polarization resistance, at open circuit voltage (OCV) and temperatures from 650 to 800 °C. This result indicates that the prepared Sm x Sr 1−x MnO 3 is a promising replacement for LSM82 as cathode material for SOFCs, and the SSM55 represents the optimal concentration in Sm x Sr 1−x MnO 3 series. The remarkably high ORR activity of the SSM55 is ascribed to its high surface Mn 4+ /Mn 3+ and O ad /O lattice ratios and fast surface oxygen exchange kinetics.

Ni 0.9 Fe 0.1 -supported solid oxide fuel cells are fabricated by tape casting-screen printing-sintering process; and the activity for CH 4 reforming and electrochemical performance are examined with wet (3 vol.% H 2 O) CH 4 as the fuel at 650 °C, in comparison with Ni-supported cells. At a flow rate of 100 ml min −1 , the wet CH 4 is partially (35 vol.%) reformed to H 2 , CO and CO 2 in the Ni 0.9 Fe 0.1 anode-support, demonstrating a higher reforming activity than that of the Ni anode-support. The maximum power density is 1.01 Wcm −2 at a high limiting current density of 2.6 A cm −2 ; and cell voltage at 0.4 A cm −2 is slightly decreased from 0.65 to 0.60 V within 50 h durability test. This high performance is attributed to the Ni 0.9 Fe 0.1 anode-support that is more active for CH 4 reforming and resistant to carbon deposition than its Ni counterpart.

Porous Ni–Fe anode supports for intermediate solid oxide fuel cells are prepared by reducing the sintered NiO-(0–50 wt. %) Fe 2 O 3 composites in H 2 , their microstructure, redox and thermal expansion/cycling characteristics are systematically investigated. The sintered NiO–Fe 2 O 3 composites are consisted of NiO and NiFe 2 O 4 , and are fully reducible to porous metallic Ni–Fe alloys in H 2 at temperatures between 600 and 750 °C. The porous structure contains pores in bimodal distribution with larger pores between the sintered particles and smaller ones inside the particles. The oxidation resistance of the Ni–Fe alloy anode supports at 600 and 750 °C is increased by the addition of Fe, their oxidation kinetics obeys a multistage parabolic law in the form of ( Percentage weight gain / Specific surface area ) 2 = k p · t , where k p is the rate constant and t the oxidation time. The dimension of the Ni–Fe anode supports is slightly changed without disintegrating their structure, and Fe addition is beneficial to the redox stability. The TEC of the Ni–Fe alloy anode supports decreases with the increase of Fe content. The anode supports containing Fe is less stable in dimension during thermal cycles due to the continuous sintering, but the dimension change after thermal cycles is within 1%.

Highly visible-light response (Fe, Cr)-codoped La 2 Ti 2 O 7 photocatalysts are synthesized by sol–gel process. The crystal phase, morphology and optical absorption activity of the samples are characterized by X-ray diffraction, scanning electron microscope, X-ray photoelectron spectroscopy, and UV–vis diffuse reflectance spectra. The results reveal that the calcination temperature and dopant concentration have strong influence on the phase structures, crystallinity and morphology. The UV–vis diffuse reflectance spectra indicate that Fe and Cr ions codoping can extend optical absorption to the visible-light region and narrow the band gap obviously. The photocatalytic hydrogen and oxygen production activities are evaluated in CH 3 OH and AgNO 3 aqueous solution under solar light irradiation. NiO x (0.5 wt%) loaded (Fe, Cr)-0.005-LTO-1150 shows the best photocatalytic H 2 production activity with the productivity of 360.203 μmol g −1 h −1 and the apparent quantum efficiency of 2.44%, which suggests that the synergistic effect of Fe and Cr codoping is favorable to enhance the photocatalytic efficiency. The photocurrent of (Fe, Cr)-codoped La 2 Ti 2 O 7 is more than two times of that for Fe-doped La 2 Ti 2 O 7 photocatalyst. The efficient photocatalytic hydrogen production and the high photocurrent of (Fe, Cr)-0.005-LTO-1150 are originated from the optimized combination of the physical–chemical properties, the small band gap and the low recombination rate of photoelectron–holes.

Cubic perovskite Sm x Sr 1− x MnO 3 (SSM) surface and bulk models have been constructed to simulate the oxygen reduction reactions by employing first-principles calculations. The results demonstrate that oxygen vacancies can be formed easily in Sm 0.5 Sr 0.5 MnO 3 (SSM50). The oxygen migration barrier in bulk SSM50, which is predicted by the nudged elastic band (NEB) method, is the lowest, while the adsorption energy of O 2 molecular on SSM50 (100) surface is the lowest among the considered doping systems, indicating the potential application of SSM50 as a cathode for intermediate-temperature solid oxide fuel cell (IT-SOFC). The reaction mechanisms of oxygen reduction on SSM50 (100) surface have also been studied.

A versatile synthetic method, which is based on a low-temperature hydrothermal technique, is developed for the fabrication of a microporous ZnO/TiO2 composite catalyst with different structures (e.g., amorphous, amorphous/crystalline and crystalline). In particular, a novel microporous ZnO/TiO2 composite with amorphous/crystalline structure is obtained with a 3/1 M ratio of Ti/Zn. This novel ZnO/TiO2 composite heterostructure not only has a large specific surface area (311.9 m2 g−1) but also exhibits outstanding performance during solar water splitting reactions to generate hydrogen without a noble metal co-catalyst. Based on our in-depth mechanistic analysis, the synergistic effect between the amorphous ZnO and crystalline TiO2 is responsible for the enhanced performance of this material.