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

J. Appl. Cryst.の発刊に際して

2.3. Evaluation of Photocatalytic Water Splitting 6507 2.3.1. Photocatalytic Activity 6507 2.3.2. Photocatalytic Stability 6507 3. UV-Active Photocatalysts for Water Splitting 6507 3.1. d0 Metal Oxide Photocatalyts 6507 3.1.1. Ti-, Zr-Based Oxides 6507 3.1.2. Nb-, Ta-Based Oxides 6514 3.1.3. W-, Mo-Based Oxides 6517 3.1.4. Other d0 Metal Oxides 6518 3.2. d10 Metal Oxide Photocatalyts 6518 3.3. f0 Metal Oxide Photocatalysts 6518 3.4. Nonoxide Photocatalysts 6518 4. Approaches to Modifying the Electronic Band Structure for Visible-Light Harvesting 6519

Semiconductor-based Photocatalytic Hydrogen Generation

As a fascinating conjugated polymer, graphitic carbon nitride (g-C3N4) has become a new research hotspot and drawn broad interdisciplinary attention as a metal-free and visible-light-responsive photocatalyst in the arena of solar energy conversion and environmental remediation. This is due to its appealing electronic band structure, high physicochemical stability, and “earth-abundant” nature. This critical review summarizes a panorama of the latest progress related to the design and construction of pristine g-C3N4 and g-C3N4-based nanocomposites, including (1) nanoarchitecture design of bare g-C3N4, such as hard and soft templating approaches, supramolecular preorganization assembly, exfoliation, and template-free synthesis routes, (2) functionalization of g-C3N4 at an atomic level (elemental doping) and molecular level (copolymerization), and (3) modification of g-C3N4 with well-matched energy levels of another semiconductor or a metal as a cocatalyst to form heterojunction nanostructures. The constructi...

Graphitic Carbon Nitride (g-C3N4)-Based Photocatalysts for Artificial Photosynthesis and Environmental Remediation: Are We a Step Closer To Achieving Sustainability?

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

This article reviews recent significant advances in the field of water splitting. Catalysts play very important roles in two half reactions of water splitting - water reduction and water oxidation. Considering potential future applications, catalysts made of cheap and earth abundant element(s) are especially important for economically viable energy conversion. This article focuses only on catalysts made of cobalt (Co), nickel (Ni) and iron (Fe) elements for water reduction and water oxidation. Different series of catalysts that can be applied in electrocatalytic and photocatalytic water spitting are discussed in detail and their catalytic mechanisms are introduced. Finally, the future outlook and perspective of catalysts made of earth abundant elements will be discussed.

Catalysts made of earth-abundant elements (Co, Ni, Fe) for water splitting: Recent progress and future challenges

A photocatalytic noble metal-free system for the generation of hydrogen has been constructed using Eosin Y (1) as a photosensitizer, the complex [Co(dmgH)2pyCl]2+ (5, dmgH = dimethylglyoximate, py = pyridine) as a molecular catalyst, and triethanolamine (TEOA) as a sacrificial reducing agent. The system produces H2 with an initial rate of ∼100 turnovers per hour upon irradiation with visible light (λ > 450 nm). Addition of free dmgH2 greatly increases the durability of the system addition of 12 equiv of dmgH2 (vs cobalt) to the system produces ∼900 turnovers of H2 after 14 h of irradiation. The rate of H2 evolution is maximum at pH = 7 and decreases sharply at more acidic or basic pH. Spectroscopic study of photolysis solutions suggests that hydrogen production occurs through protonation of a CoI species to give a CoIII hydride, which then reacts further by reduction and protolysis to give CoII and molecular hydrogen.

Making Hydrogen from Water Using a Homogeneous System Without Noble Metals

Photocatalytic hydrogen evolution via water splitting is an attractive scientific and technological goal to address the increasing global demand for clean energy and to reduce the climate change impact of CO2 emission. Although tremendous efforts have been made, hydrogen production by a robust and highly efficient system driven by visible light still remains a significant challenge. Herein we report that nickel phosphide, as a cocatalyst to form a well-designed integrated photocatalyst with one-dimensional semiconductor nanorods, highly improves the efficiency and durability for photogeneration of hydrogen in water. The highest rate for hydrogen production reached ∼1200 μmol h−1 mg−1 based on the photocatalyst. The turnover number (TON) reached ∼3 270 000 in 90 hours with a turnover frequency (TOF) of 36 400 for Ni2P, and the apparent quantum yield was ∼41% at 450 nm. The photoinduced charge transfer process was further confirmed by steady-state photoluminescence spectra and time-resolved photoluminescence spectra. Such extraordinary performance of a noble-metal-free artificial photosynthetic hydrogen production system has, to our knowledge, not been reported to date.

Extraordinarily efficient photocatalytic hydrogen evolution in water using semiconductor nanorods integrated with crystalline Ni2P cocatalysts

The complex [Co(dmgH)2pyCl]2+ (1, dmgH = dimethylglyoximate, py = pridine) has been used as a molecular catalyst for visible light driven hydrogen production in the presence of [Pt(tolylterpyridine)(phenylacetylide)]+ (3) as a photosensitizer and triethanolamine (TEOA) as a sacrificial reducing agent. Complex 3 is quenched oxidatively by [Co(dmgH)pyCl]2+ (1) with a rate constant kq of 1.27 x 10(9) M(-1) s(-1). Photogeneration of H2 is only seen when 1 + 3 + TEOA are all present. H2 production is maximized for this system at pH 8.5 and declines to very low levels at pH 12. Irradiation of the reaction solution initially containing 1.61 x 10(-2) M TEOA, 1.11 x 10(-5) M of 3, and 1.99 x 10(-4) M of Co catalyst 1 in MeCN/water (3:2 v/v) at pH = 8.5 for 10 h with lambda > 410 nm yields 400 turnovers of H2. When TEOA is 0.27 M, approximately 1000 turnovers are obtained after 10 h of irradiation. Spectroscopic study of the photolyses solutions suggests that H2 formation proceeds via Co(I) and protonation to form Co(III) hydride species.

A Homogeneous System for the Photogeneration of Hydrogen from Water Based on a Platinum(II) Terpyridyl Acetylide Chromophore and a Molecular Cobalt Catalyst

Metal-free elemental photocatalysts for hydrogen (H2 ) evolution are more advantageous than the traditional metal-based inorganic photocatalysts since the nonmetal elements are generally cheaper, more earth-abundant, and environmentally friendly. Black phosphorus (BP) has been attracting increasing attention in recent years based on its anisotropic 2D layered structure with tunable bandgap in the range of 0.3-2.0 eV; however, the application of BP for photocatalytic H2 evolution has been scarcely reported experimentally although being theoretically predicted. Herein, for the first time, the visible light photocatalytic H2 evolution of BP nanosheets prepared via a facile solid-state mechanochemical method by ball-milling bulk BP is reported. Without using any noble metal cocatalyst, the visible light photocatalytic hydrogen evolution rate of BP nanosheets reaches 512 µmol h-1 g-1 , which is ≈18 times higher than that of the bulk BP, and is comparable or even higher than that of graphitic carbon nitrides (g-C3 N4 ).

Pingwu Du

Papers

Catalysts made of earth-abundant elements (Co, Ni, Fe) for water splitting: Recent progress and future challenges

Making Hydrogen from Water Using a Homogeneous System Without Noble Metals

Extraordinarily efficient photocatalytic hydrogen evolution in water using semiconductor nanorods integrated with crystalline Ni2P cocatalysts

A Homogeneous System for the Photogeneration of Hydrogen from Water Based on a Platinum(II) Terpyridyl Acetylide Chromophore and a Molecular Cobalt Catalyst

Black Phosphorus Revisited: A Missing Metal-Free Elemental Photocatalyst for Visible Light Hydrogen Evolution.