Composite electrolytes have been widely applied in the ceria-related SOFCs free from the internal short circuit; however, a mathematical model has not been proposed to describe the charge transport mechanism in the composite electrolytes to date. In this work, the random distribution model and core–shell model are, respectively, developed to calculate mixed conductivities of the free electron, oxygen ion, and proton in the composite electrolytes with Sm0.2Ce0.8O2−δ (SDC) and BaCe0.8Sm0.2O3−δ (BCS) as an example. The connected probability of the electron transport path consisting of SDC particles is evaluated in the random distribution model, while the electron transport is intercepted by the BCS-based core–shell structure around the inner SDC particles. The simulation results by the core–shell model instead of the random distribution model are very consistent with the experimental data, indicating that the core–shell model can describe in a superior way the charge transport in the composite electrolytes. Meanwhile, the effects of the contact angle of adjacent SDC particles, BCS volume fraction, and temperature on the electrochemical performance are investigated considering the open circuit voltage, I–V curve, leakage current density, proton transport number, and cell efficiency. The results show that the open circuit voltage and proton current density increase while electron and oxygen ion current densities decrease with the increasing BCS volume fraction, leading to the increase of cell efficiency; the electron and oxygen ion conductivities increase while proton conductivity decreases with the increasing contact angle related to the sintering condition.
Contact-electrification is a universal effect for all existing materials, but it still lacks a quantitative materials database to systematically understand its scientific mechanisms. Using an established measurement method, this study quantifies the triboelectric charge densities of nearly 30 inorganic nonmetallic materials. From the matrix of their triboelectric charge densities and band structures, it is found that the triboelectric output is strongly related to the work functions of the materials. Our study verifies that contact-electrification is an electronic quantum transition effect under ambient conditions. The basic driving force for contact-electrification is that electrons seek to fill the lowest available states once two materials are forced to reach atomically close distance so that electron transitions are possible through strongly overlapping electron wave functions. We hope that the quantified series could serve as a textbook standard and a fundamental database for scientific research, practical manufacturing, and engineering.
Abstract Triboelectrification is a well-known phenomenon that commonly occurs in nature and in our lives at any time and any place. Although each and every material exhibits triboelectrification, its quantification has not been standardized. A triboelectric series has been qualitatively ranked with regards to triboelectric polarization. Here, we introduce a universal standard method to quantify the triboelectric series for a wide range of polymers, establishing quantitative triboelectrification as a fundamental materials property. By measuring the tested materials with a liquid metal in an environment under well-defined conditions, the proposed method standardizes the experimental set up for uniformly quantifying the surface triboelectrification of general materials. The normalized triboelectric charge density is derived to reveal the intrinsic character of polymers for gaining or losing electrons. This quantitative triboelectric series may serve as a textbook standard for implementing the application of triboelectrification for energy harvesting and self-powered sensing.
Although flexible supercapacitors (FSCs) have attracted tremendous attention, synthesis of supercapacitor electrodes that have outstanding electrochemical performance and excellent flexibility remains a continuous dilemma. Herein, conductive polymer composite hydrogels were synthesized via in situ polymerization of aniline (ANI) in a mixture of polyvinyl alcohol (PVA) and carbon nanotubes (CNTs), for which amino trimethylene phosphonic acid (ATMP) was employed as an organic doping acid. The as-prepared polyaniline (PANI)/PVA/ATMP/CNTs (PPAC) composite hydrogel electrodes exhibit a specific capacitance of up to 389.5 F g–1 at 0.5 A g–1, satisfactory long-term cycling stability (83.87% capacitance retained after 10,000 charge/discharge times), and outstanding flexibility (97% capacitance retained over 200 repeated bends), and the incorporation of ATMP enhanced electrochemical performances of PPAC composite hydrogel electrodes. Besides, the synergistic effects offered by high electrical conductivity of CNTs, pseudocapacitance of PANI, and the doping effect of ATMP may further contribute to the excellent electrochemical behavior of hydrogel electrodes. The result of the energy storage mechanism implied that the electrochemical process of the PPAC composite hydrogel electrode involved both diffusion-controlled and surface capacitive processes. The all-hydrogel-state FSC based on the PPAC hydrogel electrode shows a favorable energy density of 12.8 W h kg–1 at 125.0 W kg–1 as well as long-life stability of 77.31% capacitance retention after 10,000 charge/discharge cycles. This work is promising for the preparation of high-performance composite hydrogel electrodes for wearable and flexible energy storage devices.
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