Yihan Ling

Synthesis of Ni-substituted Bi7Fe3Ti3O21 ceramics and their superior room temperature multiferroic properties

Layer-structured bismuth complex oxides Bi7Fe3−xNixTi3O21 (0 ≤ x ≤ 2) (BFNT) were synthesized using a low-temperature combustion synthesis method. X-ray diffraction patterns and high-resolution transmission electron microscopy analysis indicated that the samples presented a six-layer Aurivillius structure. Substituting Fe sites by Ni ions inside the lattice was found to be effective in enhancing the multiferroic properties at or above the room-temperature. The sample with a composition of x = 1 exhibited a large remnant magnetization (2Mr = 1.32 emu g−1) that is about five hundred times higher than that in un-substituted Bi7Fe3Ti3O21 ceramics. The work is an important step in the effort to find a single phase and a fully functioning multiferroic material.

A robust carbon tolerant anode for solid oxide fuel cells

Solid oxide fuel cells (SOFCs) have been attracting remarkable attention as one of the most promising green energy conversion devices in the recent years. However, a high susceptibility of commonly used Ni-based anodes to carbon coking is a major challenge to the successful commercialization of SOFCs. In this study, a robust anode with Ni/TiO2−δ nano-network interfaces is reported, for low-cost SOFCs working at intermediate temperatures. This anode demonstrates an acceptable power density, and good stability with humidified (3% H2O) methane. X-ray diffraction (XRD) Rietveld refinement, X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), and high resolution transmission electron microscopy (HRTEM) images reveal that the Ni/TiO2−δ network-composite anode forms from the in-situ reductive decomposition of NiTiO3. Numerous Ni/TiO2−δ interfaces that facilitate the water adsorption and the water-mediated carbon-removing reactions form during this decomposition process. Density functional theory calculations predict that at the Ni/TiO2−δ interfaces, the dissociated OH from H2O (adsorbed on TiO2−δ) reacts with C (locating on Ni) to produce CO and H species, which are then electrochemically oxidized (combined with O2−) to CO2 and H2O at the triple-phase boundaries of the anode.摘要固体氧化物燃料电池是一种有应用前景的绿色能源转化装置, 目前得到了广泛关注, 然而传统的Ni基金属陶瓷阳极容易因积碳而失活是固体氧化物燃料电池商业化的一个发展瓶颈. 本研究基于低成本的中温固体氧化物燃料电池, 发展了一种稳健的具有纳米网状结构的Ni-TiO2−δ阳极材料, 以潮湿的甲烷为燃料展现了良好的电化学性能和长期稳定性. 结合X射线衍射, X射线光电子能谱, 电子顺谱共振及高分辨透射电镜等测试结果, 揭示了NiTiO3阳极支撑体原位还原形成了具有纳米网状结构的Ni-TiO2−δ新型阳极, 可以吸附大量的水, 从而可以通过水重整过程有效地实现积碳转移. 密度泛函理论计算解释了积碳转移过程, 在阳极的三相界面处, 被TiO2−δ吸附的水解离的OH与Ni吸附积碳发生电化学反应生成CO和H, 进而氧化成CO2和H2O.

Synthesis and characterization of a Sr0.95Y0.05TiO3−δ-based hydrogen electrode for reversible solid oxide cells

Reversible solid oxide cells (RSOCs) can generate electricity as solid oxide fuel cells (SOFC) facing a shortage of electricity and can also store the electricity as solid oxide electrolysis cells (SOEC) at the time of excessive electricity. The composite Sr0.95Y0.05TiO3−δ–Sm0.2Ce0.8O1.9 (SYT–SDC) as the hydrogen electrode provides a promising alternative for a conventional Ni/YSZ. The possible charge compensation mechanism of SYT is described as Sr0.95Y0.05Ti0.95−2δ4+Ti2δ+0.053+O3−δ. The Ti3+ is approximately 11.73% in the reduced SYT by XRD Rietveld refinement, electron paramagnetic resonance (EPR) and thermogravimetry (TG) analysis. Voltage–current curves and impedance spectra are measured as a function of applied voltages to characterize the cells. The bulk resistance (Ro) and the electrode polarization resistance (Rp) at open circuit voltages (OCV) at 750 °C are 9.06 Ω cm2 and 10.57 Ω cm2, respectively. The Ro values have a small amount of changes with small slopes both in the SOFC (−0.29 Ω cm2 V−1) and SOEC mode (0.5 Ω cm2 V−1), whereas the Rp values decrease all the time with the increasing voltages at both the SOFC (−2.59 Ω cm2 V−1) and SOEC mode (−9.65 Ω cm2 V−1), indicating that the electrical conductivity and electro-catalytic property of the SYT-based hydrogen electrode can be improved under the SOEC mode.