Interpenetrated Structures for Enhancing Ion Diffusion Kinetics in Electrochemical Energy Storage Devices.

The architectural design of electrodes offers new opportunities for next-generation electrochemical energy storage devices (EESDs) by increasing surface area, thickness, and active materials mass loading while maintaining good ion diffusion through optimized electrode tortuosity. However, conventional thick electrodes increase ion diffusion length and cause larger ion concentration gradients, limiting reaction kinetics. We demonstrate a strategy for building interpenetrated structures that shortens ion diffusion length and reduces ion concentration inhomogeneity. This free-standing device structure also avoids short-circuiting without needing a separator. The feature size and number of interpenetrated units can be adjusted during printing to balance surface area and ion diffusion. Starting with a 3D-printed interpenetrated polymer substrate, we metallize it to make it conductive. This substrate has two individually addressable electrodes, allowing selective electrodeposition of energy storage materials. Using a Zn//MnO2 battery as a model system, the interpenetrated device outperforms conventional separate electrode configurations, improving volumetric energy density by 221% and exhibiting a higher capacity retention rate of 49% compared to 35% at temperatures from 20 to 0 °C. Our study introduces a new EESD architecture applicable to Li-ion, Na-ion batteries, supercapacitors, etc.

The impacts of dopants on the small polaron mobility and conductivity in hematite - the role of disorder.

Hematite (α-Fe2O3) is a promising transition metal oxide for various energy conversion and storage applications due to its advantages of low cost, high abundance, and good chemical stability. However, its low carrier mobility and electrical conductivity have hindered the wide application of hematite-based devices. Fundamentally, this is mainly caused by the formation of small polarons, which show conduction through thermally activated hopping. Atomic doping is one of the most promising approaches for improving the electrical conductivity in hematite. However, its impact on the carrier mobility and electrical conductivity of hematite at the atomic level remains to be illusive. In this work, through a kinetic Monte-Carlo sampling approach for diffusion coefficients combined with carrier concentrations computed under charge neutrality conditions, we obtained the electrical conductivity of the doped hematite. We considered the contributions from individual Fe-O layers, given that the in-plane carrier transport dominates. We then studied how different dopants impact the carrier mobility in hematite using Sn, Ti, and Nb as prototypical examples. We found that the carrier mobility change is closely correlated with the local distortion of Fe-Fe pairs, i.e. the more stretched the Fe-Fe pairs are compared to the pristine systems, the lower the carrier mobility will be. Therefore, elements which limit the distortion of Fe-Fe pair distances from pristine are more desired for higher carrier mobility in hematite. The calculated local structure and pair distribution functions of the doped systems have remarkable agreement with the experimental EXAFS measurements on hematite nanowires, which further validates our first-principles predictions. Our work revealed how dopants impact the carrier mobility and electrical conductivity of hematite and provided practical guidelines to experimentalists on the choice of dopants for the optimal electrical conductivity of hematite and the performance of hematite-based devices.

3D-on-2D: A Physiologically Relevant and Gel-Free In Vitro Coculture Method to Assay Antimetastatic Agents.

Metastasis of cancer cells leads to 90% of lethality among cancer patients. A crucial step in the hematogenous spread of metastatic cancer is the detachment of cells from the primary tumor followed by invasion through nearby blood vessels (Wong and Hynes. Cell Cycle 5(8):812-817, 2006). This is common to several solid tumors, including medulloblastoma (Van Ommeren et al. Brain Pathol 30:691-702, 2020). Because invasion is a crucial step in metastasis, the development of assays studying invasion are important for identifying antimetastatic drugs. There is always a need to develop better 3D in vitro models that not only mimic the complexity of in vivo architecture of solid tumors and their microenvironment, but are also simple to execute in medium to high throughput. We developed an in vitro coculture invasion assay that relies on the binary interaction between cancer cells and endothelial cells for research on tumor invasion and antimetastatic drug discovery. The goal of the current protocol is to use the simplicity of a two-dimensional endothelial cell culture to create a gel-free physiological substratum that can facilitate cancer cell invasion from a 3D cancer spheroid. This provides a simple and reproducible biomimetic 3D cell-based system for the analysis of invasion capacity in large populations of tumor spheroids. Using this assay, we can compare the effect of invasion inhibitors/activators on cancer spheroids. The results are analyzed by manual scoring of images for the presence or absence of sprouting from cancer spheroids. This enables simple and fast analysis of metastasis, which facilitates multiparameter examination.