There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Sustainable hydrogen production is an essential prerequisite of a future hydrogen economy. Water electrolysis driven by renewable resource-derived electricity and direct solar-to-hydrogen conversion based on photochemical and photoelectrochemical water splitting are promising pathways for sustainable hydrogen production. All these techniques require, among many things, highly active noble metal-free hydrogen evolution catalysts to make the water splitting process more energy-efficient and economical. In this review, we highlight the recent research efforts toward the synthesis of noble metal-free electrocatalysts, especially at the nanoscale, and their catalytic properties for the hydrogen evolution reaction (HER). We review several important kinds of heterogeneous non-precious metal electrocatalysts, including metal sulfides, metal selenides, metal carbides, metal nitrides, metal phosphides, and heteroatom-doped nanocarbons. In the discussion, emphasis is given to the synthetic methods of these HER electrocatalysts, the strategies of performance improvement, and the structure/composition-catalytic activity relationship. We also summarize some important examples showing that non-Pt HER electrocatalysts could serve as efficient cocatalysts for promoting direct solar-to-hydrogen conversion in both photochemical and photoelectrochemical water splitting systems, when combined with suitable semiconductor photocatalysts.

Noble metal-free hydrogen evolution catalysts for water splitting

A fundamental change has been achieved in understanding surface electrochemistry due to the profound knowledge of the nature of electrocatalytic processes accumulated over the past several decades and to the recent technological advances in spectroscopy and high resolution imaging. Nowadays one can preferably design electrocatalysts based on the deep theoretical knowledge of electronic structures, via computer-guided engineering of the surface and (electro)chemical properties of materials, followed by the synthesis of practical materials with high performance for specific reactions. This review provides insights into both theoretical and experimental electrochemistry toward a better understanding of a series of key clean energy conversion reactions including oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). The emphasis of this review is on the origin of the electrocatalytic activity of nanostructured catalysts toward the aforementioned reactions by correlating the apparent electrode performance with their intrinsic electrochemical properties. Also, a rational design of electrocatalysts is proposed starting from the most fundamental aspects of the electronic structure engineering to a more practical level of nanotechnological fabrication.

Design of electrocatalysts for oxygen- and hydrogen-involving energy conversion reactions

The urgent need of clean and renewable energy drives the exploration of effective strategies to produce molecular hydrogen. With the assistance of highly active non-noble metal electrocatalysts, electrolysis of water is becoming a promising candidate to generate pure hydrogen with low cost and high efficiency. Very recently, transition metal phosphides (TMPs) have been proven to be high performance catalysts with high activity, high stability, and nearly ∼100% Faradic efficiency in not only strong acidic solutions, but also in strong alkaline and neutral media for electrochemical hydrogen evolution. In this tutorial review, an overview of recent development of TMP nanomaterials as catalysts for hydrogen generation with high activity and stability is presented. The effects of phosphorus (P) on HER activity, and their synthetic methods of TMPs are briefly discussed. Then we will demonstrate the specific strategies to further improve the catalytic efficiency and stability of TMPs by structural engineering. Making use of TMPs as cocatalysts and catalysts in photochemical and photoelectrochemical water splitting is also discussed. Finally, some key challenges and issues which should not be ignored during the rapid development of TMPs are pointed out. These strategies and challenges of TMPs are instructive for designing other high-performance non-noble metal catalysts.

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Recent advances in transition metal phosphide nanomaterials: synthesis and applications in hydrogen evolution reaction

Shape selective synthesis of nanostructured Rh hexagons has been demonstrated with the help of a modified chemical vapor deposition using rhodium acetate. An ultralow threshold field of 0.72V∕μm is observed to generate a field emission current density of 4×10−3μA∕cm2. The high enhancement factor (9325) indicates that the origin of electron emission is from nanostructured features. The smaller size of emitting area, excellent current density, and stability over a period of more than 3h are promising characteristics for the development of electron sources.

Enhanced field emission from hexagonal rhodium nanostructures

Field emission investigation of single Fe-doped SnO2 wire

Electrochemical determination of semicarbazide on cobalt oxide nanoparticles: Implication towards environmental monitoring

Urea Electro-Oxidation Catalyzed by an Efficient and Highly Stable Ni–Bi Bimetallic Nanoparticles

Musculoskeletal conditions are the most commonly occurring medical conditions, and they have a considerable influence on the quality of health and living standard of the millions of people across the world. Annually, around the globe, approximately 2.3 million bone-tissue graft transplants are performed. The bone fracture, osteoporosis, osteoarthritis, and various neoplastic disorders are the common clinical problems related with bone and skeletal system. The common approaches to these bone problems are autografts or allografts. These protocols have certain limitations such as resorption, donor site morbidity, compromised supply, rejection rate up to 50% at some sites, and the risk of inducing transmissible diseases. Consequently, considerable attention has been directed toward the use of bioactive materials as synthetic grafts for bone regeneration. These include hydroxyapatite (HAP), tricalcium phosphate, bioactive glass, and glass ceramics. More significantly, calcium phosphates are the major constituent of bone mineral. The most extensively used synthetic calcium phosphate ceramic for bone replacement is HAP with a chemical formula of Ca 10 (PO 4 ) 6 (OH) 2 . It has Ca:P molar ratio of 1.667 and is regarded as the most stable composition compared to other calcium phosphate ceramic within a pH range of 4.2–8.0. Calcium phosphate cement is one of the most important types of bioceramic material. In combination with various calcium phosphates, an injectable paste can be formed, which is cured over a period of time, in which resultant product is a carbonate apatite. The cements cure in situ and are gradually resorbed and replaced by a newly formed bone. The concept of a bioactive glass was pioneered by Hench and colleagues. The composition of Bioglass is a series of special designed glasses, consisting of a Na 2 O–CaO–SiO 2 glass with the addition of P 2 O 5 , B 2 O 3 , and CaF 2 . A biologically active hydroxycarbonate apatite layer is formed on the surface of bioactive glasses in vitro and in vivo. The chemical properties could be controlled in bioactive glasses and eventually its bonding to tissue. Certain specialized compositions of Bioglass (e.g., 45S5) can bond to soft tissue as well as bone, in either bulk or particulate form. Moreover, apatite-wollastonite glass-ceramic, with an assembly of small apatite particles effectively reinforced by β-wollastonite exhibit not only bioactivity, but also a fairly high mechanical strength. Mechanical properties like the bending strength, toughness against fracture, and Young’s modulus of A-W glass-ceramic are the highest among bioactive glasses and glass-ceramics enabling it to be used in some compression load-bearing applications. Overall, the advantages of bioactive glasses are the magnitude of their surface reactivity and the ability to change the chemical composition, thus facilitating bonding with variety of tissues. Mechanical properties are the drawback as these materials have relatively low bending strength in comparison to other ceramic materials. The bioactive calcium phosphate ceramics, bioglasses, and glass-ceramics form a mechanically strong interfacial bond with bone. The strength of the bond is normally equivalent to or greater than the strength of the host bone, depending on test conditions. Therefore, all of these materials have excellent bioactivity. Nevertheless, bioactive ceramics have a flexural strength, strain-to-failure, and fracture toughness, which is less than the bone and the elastic modulus is greater than the bone. In other words, most bioactive materials have a less-than-optimal biomechanical compatibility when used in load-bearing applications. An approach to mitigate this problem involves designing and structural tailoring of bioactive composites. The concept of matching the mechanical behavior of an implant, with the tissue to be replaced in order to solve the problem of stress shielding of conventional biomaterials, was proposed by Bonfield et al. Thus, the composite approach can significantly meet the challenge of a long life, as a demand for the new-generation implant materials. Calcium phosphate ceramics, bioglasses, and glass ceramics are generally considered to be bone bioactive ceramics. These materials generally get bonded to the surrounding osseous tissue and enhance further bone-tissue formation. The direct bone bonding to bioactive glasses was first observed and reported by Hench et al., since then considerable progress has been made in understanding the basic mechanism of the formation of bone and biomaterial bond and its effect on bone formation.

Bhaskar R. Sathe

Papers

Enhanced field emission from hexagonal rhodium nanostructures

Field emission investigation of single Fe-doped SnO2 wire

Electrochemical determination of semicarbazide on cobalt oxide nanoparticles: Implication towards environmental monitoring

Urea Electro-Oxidation Catalyzed by an Efficient and Highly Stable Ni–Bi Bimetallic Nanoparticles

Bioactive ceramic composite material stability, characterization, and bonding to bone