Two-dimensional materials as catalysts, interfaces, and electrodes for an efficient hydrogen evolution reaction.

Two-dimensional (2D) materials have been significantly investigated as electrocatalysts for the hydrogen evolution reaction (HER) over the past few decades due to their excellent electrocatalytic properties and their structural uniqueness including the atomically thin structure and abundant active sites. Recently, 2D materials with various electronic properties have not only been used as active catalytic materials, but also employed in other components of the HER electrodes including a conductive electrode layer and an interfacial layer to maximize the HER efficiency or utilized as templates for catalytic nanostructure growth. This review provides the recent progress and future perspectives of 2D materials as key components in electrocatalytic systems with an emphasis on the HER applications. We categorized the use of 2D materials into three types: a catalytic layer, an electrode for catalyst support, and an interlayer for enhancing charge transfer between the catalytic layer and the electrode. We first introduce various scalable synthesis methods of electrocatalytic-grade 2D materials, and we discuss the role of 2D materials as HER catalysts, an interface for efficient charge transfer, and an electrode and/or a growth template of nanostructured noble metals.

Revisiting Solution-Based Processing of van der Waals Layered Materials for Electronics.

Following the significant discovery of van der Waals (vdW) layered materials with diverse electronic properties over more than a decade ago, the scalable production of high-quality vdW layered materials has become a critical goal to enable the transformation of fundamental studies into practical applications in electronics. To this end, solution-based processing has been proposed as a promising technique to yield vdW layered materials in large quantities. Moreover, the resulting dispersions are compatible with cost-effective device fabrication processes such as inkjet printing and roll-to-roll manufacturing. Despite these advantages, earlier works on solution-based processing methods (i.e., direct liquid-phase exfoliation or alkali-metal intercalation) have several challenges in achieving high-performance electronic devices, such as structural polydispersity in thickness and lateral size or undesired phase transformation. These challenges hinder the utilization of the solution-processed materials in the limited fields of electronics such as electrodes and conductors. In the meantime, the groundbreaking discovery of another solution-based approach, molecular intercalation-based electrochemical exfoliation, has shown significant potential for the use of vdW layered materials in scalable electronics owing to the nearly ideal structure of the exfoliated samples. The resulting materials are highly monodispersed, atomically thin, and reasonably large, enabling the preparation of electronically active thin-film networks via successful vdW interface formation. The formation of vdW interfaces is highly important for efficient plane-to-plane charge transport and mechanical stability under various deformations, which are essential to high-performance, flexible electronics. In this Perspective, we survey the latest developments in solution-based processing of vdW layered materials and their electronic applications while also describing the field's future outlook in the context of its current challenges.

Solution-Processed MoS2 Film with Functional Interfaces via Precursor-Assisted Chemical Welding.

Molybdenum disulfide (MoS2) presents fascinating properties for next-generation applications in diverse fields. However, fully exploiting the best properties of MoS2 in largescale practical applications still remains a challenge due to lack of proper processing methods. Solution-based processing can be a promising route for scalable production of MoS2 nanosheets, but the resulting assembled film possesses an enormous number of interfaces that significantly compromise the intrinsic electrical properties. Herein, we demonstrate the solution processing of MoS2 and subsequent precursor-assisted chemical welding to form defective MoS2-x at the nanosheet interfaces. The formation of defective MoS2-x significantly reduces the electrical contact resistances, and thus the chemically welded MoS2 film exhibits more than 2 orders of magnitude improved electrical conductivity. Furthermore, the chemical welding provides MoS2-x interface induced additional defect originated functionalities for diverse applications such as broadband photodetection over the near-infrared range and improved electrocatalytic activity for hydrogen evolution reactions. Overall, this precursor-assisted chemical welding strategy can be a facile route to produce high-quality MoS2 films with low-quality defective MoS2-x at the interfaces having multifunctionalities in electronics, optoelectronics, and electrocatalysis.

Pheochromocytoma with Brain Metastasis: A Extremely Rare Case in Worldwide.

Pheochromocytoma (PCC) is a neuroendocrine tumor that mainly arises from the medulla of the adrenal gland. Some PCCs become malignant and metastasize to other organs. For example, it typically involves skeletal system, liver, lung, and regional lymph nodes. However, only a few cases of PCC with brain metastasis have been reported worldwide. We report a case of metastatic brain tumor from PCC in South Korea in 2016. A 52-year-old man presented with headache, dizziness and motor aphasia. He had a medical history of PCC with multi-organ metastasis, previously underwent several operations, and was treated with chemotherapy and radiotherapy. Brain MRIs showed a brain tumor on the left parietal lobe. Postoperative pathology confirmed that the metastatic brain tumor derived from malignant PCC. This is the first report PCC with brain metastasis in South Korea.