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

Alkaline water splitting is an attractive method for sustainable hydrogen production. Owing to the sluggish kinetics of alkaline water reduction and oxidation, it is crucial to understand the mechanism of the hydrogen evolution reaction/oxygen evolution reaction (HER/OER) and construct efficient electrocatalysts based on the structure–activity relationship. This review describes the fundamentals of the alkaline HER and OER, the design of noble and nonnoble HER electrocatalysts with low energy barriers, OER electrocatalysts based on binding energy, electronic structure, lattice oxygen, and surface reconstruction as well as the recent developments of bifunctional HER/OER electrocatalysts. Future perspectives towards alkaline water splitting electrocatalysts are also proposed.

Recent progress made in the mechanism comprehension and design of electrocatalysts for alkaline water splitting

Recent Advances on Water-Splitting Electrocatalysis Mediated by Noble-Metal-Based Nanostructured Materials

Isolated atoms featuring unique reactivity are at the heart of enzymatic and homogeneous catalysts. In contrast, although the concept has long existed, single-atom heterogeneous catalysts (SACs) have only recently gained prominence. Host materials have similar functions to ligands in homogeneous catalysts, determining the stability, local environment, and electronic properties of isolated atoms and thus providing a platform for tailoring heterogeneous catalysts for targeted applications. Within just a decade, we have witnessed many examples of SACs both disrupting diverse fields of heterogeneous catalysis with their distinctive reactivity and substantially enriching our understanding of molecular processes on surfaces. To date, the term SAC mostly refers to late transition metal-based systems, but numerous examples exist in which isolated atoms of other elements play key catalytic roles. This review provides a compositional encyclopedia of SACs, celebrating the 10th anniversary of the introduction of this term. By defining single-atom catalysis in the broadest sense, we explore the full elemental diversity, joining different areas across the whole periodic table, and discussing historical milestones and recent developments. In particular, we examine the coordination structures and associated properties accessed through distinct single-atom-host combinations and relate them to their main applications in thermo-, electro-, and photocatalysis, revealing trends in element-specific evolution, host design, and uses. Finally, we highlight frontiers in the field, including multimetallic SACs, atom proximity control, and possible applications for multistep and cascade reactions, identifying challenges, and propose directions for future development in this flourishing field.

Single-Atom Catalysts across the Periodic Table.

Single Atoms and Clusters Based Nanomaterials for Hydrogen Evolution, Oxygen Evolution Reactions, and Full Water Splitting

High-Performance Hydrogen Evolution by Ru Single Atoms and Nitrided-Ru Nanoparticles Implanted on N-Doped Graphitic Sheet

Practical hydrogen production using high-efficiency, low-cost, and stable oxygen electrodes is crucial for a sustainable clean energy future. Herein we report a graphene-nanoplatelets-supported (Ni,Fe) metal–organic framework (MOF) as a superior and ultra-durable (>1000 h) anode for alkaline water electrolysis. The MOF on carbon-fiber paper electrodes requires an overpotential η = 220 mV to achieve a current density j = 10 mA cm−2 (η = 180 mV on nickel foam for j = 20 mA cm−2) with a Tafel slope of 51 mV per decade, high turnover frequency (1.22 s−1), high faradaic efficiency (99.1%), and long-term durability of >1000 h in continuous electrolysis. In an alkaline anion exchange membrane water electrolyzer (AAEMWE), it exhibits a record current density of 540 mA cm−2 at 1.85 V at 70 °C, outperforming the state-of-the-art Pt/C//IrO2. A breakthrough strategy introduced in membrane electrode assembly fabrication by extending the electrical contact with an aqueous electrolyte offers an additional OH− transport pathway to regenerate the original conductivity of the AAEMWE in continuous electrolysis, without any significant change in the pH of the electrolyte. These findings open up durable, high-performance AAEMWE and direct solar-to-fuel conversion, especially to replace high-cost proton exchange membrane water electrolysis that already works with ultra-pure water.

Graphene-nanoplatelets-supported NiFe-MOF: high-efficiency and ultra-stable oxygen electrodes for sustained alkaline anion exchange membrane water electrolysis

Recent Advancement of p- and d-Block Elements, Single Atoms, and Graphene-Based Photoelectrochemical Electrodes for Water Splitting

DOI: 10.1002/aenm.202000768 conveniences have raised serious concerns over global warming.[1] In this regard, harnessing solar energy for the electricity would be an immediate and effective remedy to the menacing global warming issues. Solar energy is an endless green energy source that offers 1000 times of power that the entire planet requires, while photovoltaic technology provides an ideal and clean route to be pursued.[2] An electronic device that converts solar energy into electricity is known as a photovoltaic cell.[3] With power conversion efficiencies (PCEs) reaching steadily beyond 25.2%, just marginally smaller than those of Si solar cells, perovskite solar cells (PSCs) have grabbed intensive attractions in the field of photovoltaic research.[4] However, the commercial scaling of PSCs will greatly rely on paths to reduced fabrication cost, enhanced PCE, and improved stability.[5] In addition to the great success of PSCs, halide perovskites are also promising materials for various high-performance optoelectronic devices such as lightemitting diodes (LEDs),[6] scintillators,[7] and photo detectors[8] due to their excellent photoluminescence quantum yield (PLQY), tunable bandgap, solution processability, and charge transport properties.[9] The halide perovskites have a general formula ABX3, where “A” corresponds to monovalent organic or inorganic cations such as methylammonium (CH3NH3, MA+), formamidinium (NH2 = CHNH2, FA+) or Cs+, “B” can be divalent metal cations such as Pb2+ and Sn2+, and “X” can be anions of the VII A group (halides) of the periodic table, namely I, Br, or Cl.[10] These halide perovskites are salts that can easily take up moisture if packed improperly. Light exposure can easily break the fragile bonds in perovskites, create halogen vacancies or interstitial pairs allowing them to migrate, and convert any oxygen present inside the crystals into highly active superoxide.[11] Even under moderate temperature and light/heat exposure, the perovskites can react with most of the metals, with heat causing organic species to volatilize, whereas light promotes mobility of ions inside the crystal.[12] Furthermore, the fracture energy of the perovskites is extremely low in the order[13] <1 J m−2. On the contrary, the perovskites possess an extremely high thermal expansion coefficient of the order of nearly ten times in magnitude to that of glass. Eventually, thermal stresses Moisture, heat, and light instabilities of halide perovskites (HPs) represent a serious Achilles’ heel that must be overcome, to enable future advancements in perovskite-based optoelectronic devices such as solar cells and light-emitting diodes. The instabilities are attributed to the unavoidable fragile ionic bonding between cationic and anionic parts of HPs during their formation. Surface passivation of HPs by various surface-passivating materials has proven to be an attractive approach to stabilize perovskites against moisture, heat, and light, keeping intact their structural integrity and ionic bonding. Herein, the experimental and theoretical background for degradation mechanisms of HPs is reviewed along with various surface passivating materials to stabilize HPs. Finally, the existing challenges associated with thin-film and device fabrication and an outlook for improving the stability of perovskites in optoelectronics are presented

Aditya Narayan Singh

Papers

Single Atoms and Clusters Based Nanomaterials for Hydrogen Evolution, Oxygen Evolution Reactions, and Full Water Splitting

High-Performance Hydrogen Evolution by Ru Single Atoms and Nitrided-Ru Nanoparticles Implanted on N-Doped Graphitic Sheet

Graphene-nanoplatelets-supported NiFe-MOF: high-efficiency and ultra-stable oxygen electrodes for sustained alkaline anion exchange membrane water electrolysis

Recent Advancement of p- and d-Block Elements, Single Atoms, and Graphene-Based Photoelectrochemical Electrodes for Water Splitting

Interface Engineering Driven Stabilization of Halide Perovskites against Moisture, Heat, and Light for Optoelectronic Applications