Jaejung Song

X‐ray imaging is transforming battery research by delivering multiscale insights into structure, composition, and chemistry, spanning micrometer to nanometer scales. As indispensable components of energy storage, electric vehicles, and mobile devices, batteries face significant challenges due to their intricate electrochemical processes, hierarchical architectures, and inaccessible components such as buried interfaces and air‐sensitive materials. These complexities demand advanced techniques capable of uncovering localized effects and addressing the heterogeneity that often obscures critical phenomena. Advanced x‐ray imaging techniques are rising to meet these demands, bridging knowledge gaps by providing detailed visualization of battery processes in ways that conventional methods cannot. Operando x‐ray imaging, in particular, captures real‐time changes during battery cycling; enabling researchers to observe dynamic processes and material transformations that are otherwise inaccessible. This approach overcomes the limitations of traditional destructive post‐mortem analyses by offering a non‐invasive, real‐time window into battery operation. Recent advances in spatial resolution, computational power, and data analysis tools have made x‐ray imaging increasingly accessible and effective for studying critical phenomena, such as buried interfaces, phase transitions, and surface‐bulk differences. This work introduces four advanced x‐ray imaging techniques, outlining their principles, capabilities, and contributions to battery research. These methods illuminate key processes, advance our understanding of battery behavior, and guide targeted performance improvements. Finally, we explore the future of x‐ray imaging as a mainstream tool for addressing the pressing challenges in energy storage systems, emphasizing its pivotal role in guiding innovations for next‐generation batteries.

Hydrogen peroxide (H₂O₂), the simplest peroxide consisting of only hydrogen and oxygen, is globally used as a green oxidant. It is also a promising fuel source, and it can be produced on large scales in centralized containers. H₂O₂ is mainly produced by the anthraquinone process, but it involves energy-consuming reactions and generates organic waste. As the demand for H₂O₂ continues to grow, alternative technologies that overcome these drawbacks are sought for its generation. The generation of H₂O₂ through the redox reaction of water and oxygen can be a low-cost, sustainable, and efficient production method. However, this reaction requires active and stable catalysts. In general, H₂O₂ can be generated by the oxidation of H₂O at the anode of an electrochemical cell. Alternatively, H₂O₂ can also be formed by the reduction of O₂ at the cathode. Despite the progress in the development and advancement of materials that catalyze these reactions, further research is required to increase the electron transport rates and active sites of the catalyst. In this article, we review the available catalytic materials for the electrochemical production of H₂O₂ and provide a summary and outlook of this field.

PbS/CdS core/shell quantum dots (QDs) that emit at the second near‐infrared (NIR‐II, 1000–1700 nm) window are synthesized. The PbS seed size and CdS shell thicknesses are carefully controlled to produce bright and narrow fluorescence that are suitable for multiplexing. A polymer encapsulation yields polymer‐encapsulated NIR‐II QDs (PQDs), which provides the QDs with long‐term fluorescence stability over a week in biological media. Exploiting the simple bioconjugation capability of PQDs, folic acids are conjugated to PQDs that can efficiently label folate receptor overexpressing cell lines. The PQDs afford multiplexed and nearly real‐time longitudinal whole‐body in vivo imaging. Two NIR‐II QD probes are prepared: folic acid‐conjugated PQDs (FA‐PQDs) emitting at 1280 nm and unconjugated PQDs emitting at 1080 nm. The two PQDs are engineered to have compact and similar hydrodynamic sizes. A mixture of the folic acid‐conjugated PQD and unconjugated PQDs is injected intravenously into a tumor‐xenografted mouse, and the signals from them are monitored. This NIR‐II whole‐body imaging with the two PQDs provides precise evaluation of the active ligand‐assisted tumor‐targeting capability of the FA‐PQD probe because the hydrodynamic size control of the two PQDs effectively eliminates effects from the size‐dependent accumulations by permeations and retentions in tumors.

RNA interference (RNAi) is a mechanism in which small interfering RNA (siRNA) silences a target gene. Herein, we describe a DNA hydrogel capable of producing siRNA and interfering with protein expression. This RNAi-exhibiting gel (termed I-gel for interfering gel) consists of a plasmid carrying the gene transcribing siRNA against the target mRNA as part of the gel scaffold. The RNAi efficiency of the I-gel has been confirmed by green fluorescent protein (GFP) expression assay and RNA production quantification. The plasmid stability in the I-gel results in an 8-times higher transcription efficiency than that of the free plasmid. We further applied the I-gel to live cells and confirmed its effect in interfering with the GFP expression. The I-gel shows higher RNAi effect than plasmids in free form or complexed with Lipofectamine. This nanoscale hydrogel, which is able to produce RNA in a cell, provides a platform technology for efficient RNAi system.

Here we show that well-defined three dimensional DNA nanostructures can be synthesized from branched DNAs via hybridization and enzymatic ligation. The fabricated triangular pyramid DNA has been employed as a template for assembly of AuNPs. The electrostatic attraction between DNA structures and AuNPs has shown nonspecific assembly behavior and allowed the plasmonic absorption peaks of the assembled nanocomposites to be tuned from visible to near infrared by simple control of the mixing ratio.

Imaging the intrinsic optical absorption properties of nanomaterials with optical microscopy (OM) is hindered by the optical diffraction limit and intrinsically poor sensitivity. Thus, expensive and destructive electron microscopy (EM) has been commonly used to examine the morphologies of nanostructures. Further, while nanoscale fluorescence OM has become crucial for investigating the morphologies and functions of intracellular specimens, this modality is not suitable for imaging optical absorption and requires the use of possibly undesirable exogenous fluorescent molecules for biological samples. Here we demonstrate super-resolution visible photoactivated atomic force microscopy (pAFM), which can sense intrinsic optical absorption with ~8 nm resolution. Thus, the resolution can be improved down to ~8 nm. This system can detect not only the first harmonic response, but also the higher harmonic response using the nonlinear effect. The thermoelastic effects induced by pulsed laser irradiation allow us to obtain visible pAFM images of single gold nanospheres, various nanowires, and biological cells, all with nanoscale resolution. Unlike expensive EM, the visible pAFM system can be simply implemented by adding an optical excitation sub-system to a commercial atomic force microscope.

Recent technological advances have expanded fluorescence (FL) imaging into the second near-infrared region (NIR-II; wavelength = 1000–1700 nm), providing high spatial resolution through deep tissues. However, bright and compact fluorophores are rare in this region, and sophisticated control over NIR-II probes has not been fully achieved yet. Herein, we report an enzyme-activatable NIR-II probe that exhibits FL upon matrix metalloprotease activity in tumor microenvironment. Bright and stable PbS/CdS/ZnS core/shell/shell quantum dots (QDs) were synthesized as a model NIR-II fluorophore, and activatable modulators were attached to exploit photoexcited electron transfer (PET) quenching. The quasi type-II QD band alignment allowed rapid and effective FL modulations with the compact surface ligand modulator that contains methylene blue PET quencher. The modulator was optimized to afford full enzyme accessibility and high activation signal surge upon the enzyme activity. Using a colon cancer mouse model, the probe demonstrated selective FL activation at tumor sites with 3-fold signal enhancement in 10 min. Optical phantom experiments confirmed the advantages of the NIR-II probe over conventional dyes in the first near-infrared region.

‘Smart’ gold nanoparticles can respond to mild acidic environments, rapidly form aggregates, and shift the absorption to red and near-infrared. They were used as a photoacoustic imaging agent responsive to the cancer microenvironment, and have demonstrated the cancer-specific accumulation at the cellular level and an amplified signal which is twice higher than the control in vivo.

Herein, we show that DNA nanostructures have great potential as templates for the synthesis of shape-controlled metal nanostructures.