Standardized procedures important for improving single-component ceramic fuel cell technology

Standardized procedures important for improving single-component ceramic fuel cell technolog

BN Polymorphs in Hexagonal 2–7 Stacking Orders: First-Principles and High-Throughput Study

BN polymorphs are important basic materials in superhard materials, as well as in other industrial fields and in microelectronics. The ground-state phase of BN polymorphs has a 3C stacking order. In addition to 3C, eight BN polymorphs (2H, 4H, 5H, 6H-I, 6H-II, 7H-I, 7H-II, and 7H-III) are produced by a random sampling strategy combined with group theory and graph theory (RG2) in this work. It is found that the stack order of 2–7H BN polymorphs is basically similar to that of 3C BN, although with a slight difference. The calculated total energy of these 2–7H BN polymorphs is only 4–17 meV/atoms higher than that of 3C BN, and they are all dynamically and mechanically stable. In addition, their thermal stability at 1000 K is also studied by ab initio molecular dynamics (AIMD) techniques. A combination of tensile stress and hardness is sufficient to prove that BN is a superhard material in 2–7H BN polymorphs. The band gaps of 2–7H BN polymorphs are in the range of 6.19–6.98 eV, and they can be considered as promising ultrawide-bandgap semiconductors. Finally, the anisotropy in Young’s modulus and X-ray diffraction (XRD) patterns of 2–7H BN polymorphs are also investigated in this work

Proton Shuttles in CeO2/CeO2−δ Core–Shell Structure

A core-shell structure with a CeO2 core and a non-stoichiometry CeO2-d surface layer built up proton shuttles, leading to a super proton conductivity of 0.15 S cm-1 and advanced fuel cell performance, 661 mW cm-2 at 520 ºC. The surface induced conduction process was investigated through a heat-treatment procedure for CeO2 pellets at different temperatures. The surface layer was observed to experience ordering and disappearing after high temperature treatments. Proton conduction was verified via electrochemical impedance spectra, proton conducting isotopic effect and fuel cell measurement. The isotopic effect provided a direct evidence on proton conduction and proton conduction mechanism was further investigated based on the semiconductor nature with the intrinsic CeO2 (i-type) core and n-type CeO2-δ shell. The charged layers were formed at the interface of CeO2-δ/CeO2 core-shell heterostructure with a positively charged layer located at CeO2-δ side of the interface and negative charged layer located at the intrinsic CeO2. Due to the electrostatic repulsion between protons and the positively charged layer, protons’ transportation is limited at the surface region of the CeO2-δ shell. Thus, continuous “proton shuttles” are formed, resulting in super conductivity. This work presents a new methodology and scientific understanding for fast proton transport in general oxides and advanced proton ceramic fuel cells (PCFCs). </p

Semiconductor electrochemistry for clean energy conversion and storage

Semiconductors and the associated methodologies applied to electrochemistry have recently grown as an emerging field in energy materials and technologies. For example, semiconductor membranes and heterostructure fuel cells are new technological trend, which differ from the traditional fuel cell electrochemistry principle employing three basic functional components: anode, electrolyte, and cathode. The electrolyte is key to the device performance by providing an ionic charge flow pathway between the anode and cathode while preventing electron passage. In contrast, semiconductors and derived heterostructures with electron (hole) conducting materials have demonstrated to be much better ionic conductors than the conventional ionic electrolytes. The energy band structure and alignment, band bending and built-in electric field are all important elements in this context to realize the necessary fuel cell functionalities. This review further extends to semiconductor- based electrochemical energy conversion and storage, describing their fundamentals and working principles, with the intention of advancing the understanding of the roles of semiconductors and energy bands in electrochemical devices for energy conversion and storage, as well as applications to meet emerging demands widely involved in energy applications, such as photocatalysis/water splitting devices, batteries and solar cells. This review provides new ideas and new solutions to problems beyond the conventional electrochemistry and presents new interdisciplinary approaches to develop clean energy conversion and storage technologies