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.
An overview and perspective of catalysts made of cheap, abundant elements including Co, Ni and Fe for electric-driven or solar-driven water splitting will be presented and discussed.
Hydrogen is essential to many industrial processes and could play an important role as an ideal clean energy carrier for future energy supply. Herein, we report for the first time the growth of ...crystalline Cu3P phosphide nanosheets on conductive nickel foam (Cu3P@NF) for electrocatalytic and visible light-driven overall water splitting. Our results show that the Cu3P@NF electrode can be used as an efficient Janus catalyst for both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). For OER catalysis, a current density of 10 mA/cm2 requires an overpotential of only ∼320 mV and the slope of the Tafel plot is as low as 54 mV/dec in 1.0 M KOH. For HER catalysis, the overpotential is only ∼105 mV to achieve a catalytic current density of 10 mA cm–2. Moreover, overall water splitting can be achieved in a water electrolyzer based on the Cu3P@NF electrode, which showed a catalytic current density of 10 mA/cm2 under an applied voltage of ∼1.67 V. The same current density can also be obtained using a silicon solar cell under ∼1.70 V for both the HER and the OER. This new Janus Cu3P@NF electrode is made of inexpensive and nonprecious metal-based materials, which opens new possibilities based on copper to exploit overall water splitting for hydrogen production. To the best of our knowledge, such high performance of a copper-based water oxidation and overall water splitting catalyst has not been reported to date.
Abstract
In the literature, organic materials with both aggregation-induced emission (AIE) and aggregation-caused quenching (ACQ) effects that can emit with multiple bands both in the solution and ...aggregated state are rarely reported. Herein we report a novel chiral dual-emissive bismacrocycle with tunable aggregation-induced emission colors. A facile four-step synthesis strategy is developed to construct this rigid bismacrocycle, (1,4)8cycloparaphenylenophane (
SCPP8
), which possesses a 1,2,4,5-tetraphenylbenzene core locked by two intersecting polyphenylene-based macrocycles. The luminescent behavior of
SCPP8
shows the unique characteristics of both ACQ effect and AIE effect, inducing remarkable redshift emission with near white-light emission.
SCPP8
is configurationally stable and possesses a novel shape-persistent bismacrocycle scaffold with a high strain energy. In addition,
SCPP8
displays enhanced circularly polarized luminescence properties due to AIE effect.
Large π-conjugated conductive two-dimensional (2D) metal–organic frameworks (MOFs)
via
the bottom-up approach have recently emerged as novel and interesting 2D materials. For the first time, herein ...we demonstrate the design and successful bottom-up fabrication of a novel noble-metal-free nickel phthalocyanine-based 2D MOF (NiPc–MOF) for highly efficient water oxidation catalysis. This NiPc–MOF can be easily grown on various substrates. The thin film deposited on FTO showed high catalytic oxygen evolution reaction (OER) activity with a very low onset potential (<1.48 V, overpotential < 0.25 V), high mass activity (883.3 A g
−1
), and excellent catalytic durability. To the best of our knowledge, this present 2D MOF film catalyst represents the best OER catalytic activity among molecular catalyst-based materials reported so far. This work represents the first synthesis of a nickel phthalocyanine-based 2D MOF material and application of the π-conjugated 2D MOF for water oxidation.
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‐C3N4).
Black phosphorus (BP) is discovered as the missing metal‐free elemental photocatalyst. Few‐layer BP nanosheets are prepared via a facile solid‐state mechanochemical method, exhibiting a visible light H2 evolution rate of 512 µmol h−1 g−1 without using any noble metal cocatalyst, which is increased by ≈18 times relative to that of bulk BP. Thus the missing photocatalytic property of BP is discovered.
Highly efficient, visible-light-induced hydrogen (H
2
) production
via
water splitting can be achieved without the help of a cocatalyst by using a noble-metal-free core–shell photocatalyst, in which ...zinc sulfide (ZnS) nanoparticles as the protective shell are anchored on the surface of cadmium sulfide nanorods (CdS NRs). Due to the close interfacial contact of component semiconductors, the electronic structure of CdS is strongly coupled with that of ZnS nanoparticles, leading to efficient transfer of charge carriers between them and the improvement of the CdS photostability. The CdS/ZnS NR photocatalyst showed much higher catalytic activity for H
2
production than CdS NRs and ZnS under visible light irradiation (
λ
> 420 nm), which is probably due to fast transfer of the photogenerated charge carriers and/or electron tunneling in the one-dimensional core–shell nanorod structure. Under optimal conditions, the highest hydrogen evolution rate reached 239 μmol h
−1
mg
−1
, which is much greater than ZnS and CdS NRs and also among the best cocatalyst-free photocatalysts for H
2
production. The average apparent quantum yield can be achieved as ∼16.8% after 8 h of irradiation (monochromatic light at 420 nm ± 5 nm). A possible mechanism for the photocatalytic reaction based on CdS/ZnS NRs is also discussed.
For the first time, noble-metal-free nickel phosphide (Ni2P) was used as an excellent catalyst precursor for water oxidation catalysis. The lowest onset potential was observed at ∼1.54 V (vs. RHE) ...and a Tafel slope of 60 mV dec(-1) was obtained in alkaline solution (pH = 13.6).
Nature utilizes solar energy to extract electrons and release protons from water, a process called photosynthetic water oxidation or oxygen evolution. This sunlight-driven reaction is vital to the ...planet because it directly produces dioxygen and couples with photosystem I to generate the reducing equivalents for the reduction of carbon dioxide to carbohydrates (also known as CO
2
fixation). Inspired by this natural process, people are intensely interested in water splitting using sunlight to convert and store solar energy into chemical energy, which is believed to be able to ultimately solve the energy problem that we are facing. Water splitting can be separated into two half reactions, namely water oxidation and water reduction, and they can be studied individually. Catalysts are very helpful in both reactions. Recent progress in finding new highly efficient water oxidation catalysts (WOCs) has shed light on this complicated four-electron/four-proton reaction and made it possible to catalyze water oxidation using mononuclear metal complexes. This article focuses on molecular catalysts that are able to perform catalytic water oxidation at single metal sites. Different series of catalysts (or precatalysts) made of ruthenium, iridium and earth abundant elements (iron, cobalt, and manganese) that can be applied in chemical, electrochemical and photochemical (light-driven) water oxidation are summarized, and their catalytic mechanisms are discussed in detail. Finally, the future outlook and perspective to design and develop catalysts that are efficient, cheap and stable are presented.
An overview of transition metal-based catalysts with a single metal site for chemical, electrochemical and photocatalytic water oxidation will be presented and discussed.
Copper oxide nanomaterials as noble-metal-free electrocatalysts for catalytic water oxidation reaction with good performance (onset potential at ∼0.90V vs. Ag/AgCl, and low slope of the Tafel plot ...54.5mV/dec).
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•Noble-metal-free copper oxide (CuO) electrocatalysts for water oxidation.•CuO nanowires material shows good catalytic performance.•The onset overpotential for water oxidation is low.•Good stability, high Faradaic efficiency, and low slope of the Tafel plot.
Copper oxide (CuO) is a quite cheap and abundant material but there are very few reports of using it as water oxidation catalyst (WOC). In this present study, we report for the first time that CuO nanomaterials synthesized from simple copper salts can be used as WOCs with good activity. CuO materials with different morphologies (microspheres, nanosheets, nanowires) were facilely synthesized without using any template or surfactants. The influence of different morphologies and sizes on the catalytic activity toward oxygen evolution was investigated. Among the four kinds of samples tested, CuO nanowire material exhibited the lowest overpotential for water oxidation and CuO microsphere material had the best catalytic current densities from 1.10–1.40V. Based on the CV scans, in optimal conditions for these nanomaterials, water oxidation can be achieved under an onset potential of ∼0.90V at pH 9.2. The slope of the Tafel plot is 54.5mV/dec. The Tafel plot also shows appreciable catalytic current at η=340mV (onset) and that a current density of ∼0.1mA/cm2 required an overpotential at η=430mV. The Faradaic efficiency was measured to be >95%. The CuO samples were further characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS).
It has been anticipated that learning from nature photosynthesis is a rational and effective way to develop artificial photosynthesis system, but it is still a great challenge. Here, we assembled a ...photoelectrocatalytic system by mimicking the functions of photosystem II (PSII) with BiVO4 semiconductor as a light harvester protected by a layered double hydroxide (NiFeLDH) as a hole storage layer, a partially oxidized graphene (pGO) as biomimetic tyrosine for charge transfer, and molecular Co cubane as oxygen evolution complex. The integrated system exhibited an unprecedentedly low onset potential (0.17 V) and a high photocurrent (4.45 mA cm–2), with a 2.0% solar to hydrogen efficiency. Spectroscopic studies revealed that this photoelectrocatalytic system exhibited superiority in charge separation and transfer by benefiting from mimicking the key functions of PSII. The success of the biomimetic strategy opened up new ways for the rational design and assembly of artificial photosynthesis systems for efficient solar-to-fuel conversion.
