Polyacrylonitrile-based carbon nanofibers (PAN-based CNFs) have great potential to be used for carbon dioxide (CO₂) capture due to their excellent CO₂ adsorption properties. The porous structure of PAN-based CNFs originates from their turbostratic structure, which is composed of numerous disordered stacks of graphitic layers. During the carbonization process, the internal structure is arranged toward the ordered graphitic structure, which significantly influences the gas adsorption properties of PAN-based CNFs. However, the relation between structural transformation and CO₂ capture is still not clear enough to tune the PAN-based CNFs. In this paper, we show that, with increasing carbonization temperature, the arrangement of the PAN-based CNF’s structure along the stack and lateral directions takes place independently: gradually aligning and merging along the stack direction and enlarging along the lateral direction. Further, we correlate the structural arrangement and the CO₂ adsorption properties of the PAN-based CNFs to propose a comprehensive structural mechanism. This mechanism provides the knowledge to understand and tailor the gas adsorption properties of PAN-based CNFs.

In situ transmission electron microscopy (TEM) research has enabled better understanding of various battery chemistries (Li-ion, Li–S, metal–O₂, Li, and Na metal based, etc.), which fueled substantial developments in battery technologies. In this review, we highlight some of the recent developments shedding new light on battery materials and electrochemistry via TEM. Studying battery electrode processes depending on the type of electrolytes used and the nature of electrode–electrolyte interfaces established upon battery cycling conditions is key to further adoption of battery technologies. To this end, in situ/operando TEM methodologies would require accommodating alongside correlation microscopy tools to predict battery interface evolution, reactivity, and stability, for which the use of x-ray computed tomography and image process via machine learning providing complementary information is highlighted. Such combined approaches have potential to translate TEM-based battery results into more direct macroscopic relevance for the optimization of real-world batteries.

The influence of ethylenediaminetetraacetic acid (EDTA) electrolyte additive on the performance of Zn−air batteries with near‐neutral chloride‐based electrolytes was examined for primary and secondary batteries. The electrochemical measurements indicated that Zn is not completely active in neat 2 M NaCl, but still could be discharged up to 1 mA cm⁻² around −1.0 V_Ag/AgCl. The characterization of the Zn surfaces revealed the existence of a passive film consisting of Simonkolleite, Zn(OH)₂, and/or ZnO. The EDTA additive enhanced the discharge voltages by 200 mV to −1.2 V_Ag/AgCl indicating an active Zn surface. The effect of EDTA is explained by its chelation abilities with Zn²⁺ before formation of hydroxide or oxide species. The Zn−air cells with EDTA were operated up to 930 h with specific energies up to 840 Wh kg_Zn⁻¹. The cells could also be cycled up to 70 cycles while providing enhanced discharge voltages at 1.15 V over 50 cycles. The positive effect of EDTA is dependent on the amount of free EDTA molecules. Nevertheless, the Zn−air cells showed better performance in terms of higher discharge voltage, discharge energies, and lower overpotentials in presence of EDTA.

High energy density electrochemical systems such as metal batteries suffer from uncontrollable dendrite growth on cycling, which can severely compromise battery safety and longevity. This originates from the thermodynamic preference of metal nucleation on electrode surfaces, where obtaining the crucial information on metal deposits in terms of crystal orientation, plated volume, and growth rate is very challenging. In situ liquid phase transmission electron microscopy (LPTEM) is a promising technique to visualize and understand electrodeposition processes, however a detailed quantification of which presents significant difficulties. Here by performing Zn electroplating and analyzing the data via basic image processing, this work not only sheds new light on the dendrite growth mechanism but also demonstrates a workflow showcasing how dendritic deposition can be visualized with volumetric and growth rate information. These results along with additionally corroborated 4D STEM analysis take steps to access information on the crystallographic orientation of the grown Zn nucleates and toward live quantification of in situ electrodeposition processes.

Liquid phase transmission electron microscopy (TEM) provides a useful means to study a wide range of dynamics in solution with near-atomic spatial resolution and sub-microsecond temporal resolution. However, it is still a challenge to control the chemical environment (such as the flow of liquid, flow rate, and the liquid composition) in a liquid cell, and evaluate its effect on the various dynamic phenomena. In this work, we have systematically demonstrated the flow performance of an in situ liquid TEM system, which is based on ‘on-chip flow’ driven by external pressure pumps. We studied the effects of different chemical environments in the liquid cell as well as the electrochemical potential on the deposition and dissolution behavior of Cu crystals. The results show that uniform Cu deposition can be obtained at a higher liquid flow rate (1.38 μ l min ⁻¹ ), while at a lower liquid flow rate (0.1 μ l min ⁻¹ ), the growth of Cu dendrites was observed. Dendrite formation could be further promoted by in situ addition of foreign ions, such as phosphates. The generality of this technique was confirmed by studying Zn electrodeposition. Our direct observations not only provide new insights into understanding the nucleation and growth but also give guidelines for the design and synthesis of desired nanostructures for specific applications. Finally, the capability of controlling the chemical environment adds another dimension to the existing liquid phase TEM technique, extending the possibilities to study a wide range of dynamic phenomena in liquid media.