A metal-free polymeric photocatalyst for hydrogen production from water under visible light
TL;DR: It is shown that an abundant material, polymeric carbon nitride, can produce hydrogen from water under visible-light irradiation in the presence of a sacrificial donor.
Abstract: The production of hydrogen from water using a catalyst and solar energy is an ideal future energy source, independent of fossil reserves. For an economical use of water and solar energy, catalysts that are sufficiently efficient, stable, inexpensive and capable of harvesting light are required. Here, we show that an abundant material, polymeric carbon nitride, can produce hydrogen from water under visible-light irradiation in the presence of a sacrificial donor. Contrary to other conducting polymer semiconductors, carbon nitride is chemically and thermally stable and does not rely on complicated device manufacturing. The results represent an important first step towards photosynthesis in general where artificial conjugated polymer semiconductors can be used as energy transducers.
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TL;DR: This work couple graphitic-carbon nitride with nitrogen-doped graphene to produce a metal-free hybrid catalyst, which shows an unexpected hydrogen evolution reaction activity with comparable overpotential and Tafel slope to some of well-developed metallic catalysts.
Abstract: Electrocatalytic reduction of water to molecular hydrogen via the hydrogen evolution reaction may provide a sustainable energy supply for the future, but its commercial application is hampered by the use of precious platinum catalysts. All alternatives to platinum thus far are based on nonprecious metals, and, to our knowledge, there is no report about a catalyst for electrocatalytic hydrogen evolution beyond metals. Here we couple graphitic-carbon nitride with nitrogen-doped graphene to produce a metal-free hybrid catalyst, which shows an unexpected hydrogen evolution reaction activity with comparable overpotential and Tafel slope to some of well-developed metallic catalysts. Experimental observations in combination with density functional theory calculations reveal that its unusual electrocatalytic properties originate from an intrinsic chemical and electronic coupling that synergistically promotes the proton adsorption and reduction kinetics.
1,774 citations
TL;DR: The homogeneous substitution of sulfur for lattice nitrogen and a concomitant quantum confinement effect are identified as the cause of this unique electronic structure and the excellent photoreactivity of C(3)N(4-x)S(x), which may shed light on general doping strategies for designing potentially efficient photocatalysts.
Abstract: Electronic structure intrinsically controls the light absorbance, redox potential, charge-carrier mobility, and consequently, photoreactivity of semiconductor photocatalysts. The conventional approach of modifying the electronic structure of a semiconductor photocatalyst for a wider absorption range by anion doping operates at the cost of reduced redox potentials and/or charge-carrier mobility, so that its photoreactivity is usually limited and some important reactions may not occur at all. Here, we report sulfur-doped graphitic C(3)N(4) (C(3)N(4-x)S(x)) with a unique electronic structure that displays an increased valence bandwidth in combination with an elevated conduction band minimum and a slightly reduced absorbance. The C(3)N(4-x)S(x) shows a photoreactivity of H(2) evolution 7.2 and 8.0 times higher than C(3)N(4) under lambda > 300 and 420 nm, respectively. More strikingly, the complete oxidation process of phenol under lambda > 400 nm can occur for sulfur-doped C(3)N(4), which is impossible for C(3)N(4) even under lambda > 300 nm. The homogeneous substitution of sulfur for lattice nitrogen and a concomitant quantum confinement effect are identified as the cause of this unique electronic structure and, consequently, the excellent photoreactivity of C(3)N(4-x)S(x). The results acquired may shed light on general doping strategies for designing potentially efficient photocatalysts.
1,762 citations
TL;DR: In this article, a review summarizes the recent significant progress on the design of g-C3N4-based heterostructured photocatalysts and their special separation/transfer mechanisms of photogenerated charge carriers.
Abstract: Photocatalysis is considered as one of the promising routes to solve the energy and environmental crises by utilizing solar energy. Graphitic carbon nitride (g-C3N4) has attracted worldwide attention due to its visible-light activity, facile synthesis from low-cost materials, chemical stability, and unique layered structure. However, the pure g-C3N4 photocatalyst still suffers from its low separation efficiency of photogenerated charge carriers, which results in unsatisfactory photocatalytic activity. Recently, g-C3N4-based heterostructures have become research hotspots for their greatly enhanced charge carrier separation efficiency and photocatalytic performance. According to the different transfer mechanisms of photogenerated charge carriers between g-C3N4 and the coupled components, the g-C3N4-based heterostructured photocatalysts can be divided into the following categories: g-C3N4-based conventional type II heterojunction, g-C3N4-based Z-scheme heterojunction, g-C3N4-based p–n heterojunction, g-C3N4/metal heterostructure, and g-C3N4/carbon heterostructure. This review summarizes the recent significant progress on the design of g-C3N4-based heterostructured photocatalysts and their special separation/transfer mechanisms of photogenerated charge carriers. Moreover, their applications in environmental and energy fields, e.g., water splitting, carbon dioxide reduction, and degradation of pollutants, are also reviewed. Finally, some concluding remarks and perspectives on the challenges and opportunities for exploring advanced g-C3N4-based heterostructured photocatalysts are presented.
1,759 citations
TL;DR: Recent advances in the use of graphene and other 2D materials in catalytic applications are reviewed, focusing in particular on the catalytic activity of heterogeneous systems such as van der Waals heterostructures (stacks of several 2D crystals).
Abstract: Graphene and other 2D atomic crystals are of considerable interest in catalysis because of their unique structural and electronic properties. Over the past decade, the materials have been used in a variety of reactions, including the oxygen reduction reaction, water splitting and CO2 activation, and have been shown to exhibit a range of catalytic mechanisms. Here, we review recent advances in the use of graphene and other 2D materials in catalytic applications, focusing in particular on the catalytic activity of heterogeneous systems such as van der Waals heterostructures (stacks of several 2D crystals). We discuss the advantages of these materials for catalysis and the different routes available to tune their electronic states and active sites. We also explore the future opportunities of these catalytic materials and the challenges they face in terms of both fundamental understanding and the development of industrial applications.
1,683 citations
TL;DR: Graphene and graphitic carbon nitride composite photocatalysts were prepared by a combined impregnation−chemical reduction strategy involving polymerization of melamine in the presence of graphene oxide (precursors) and hydrazine hydrate (reducing agent), followed by thermal treatment at 550 °C under flowing nitrogen as mentioned in this paper.
Abstract: Graphene and graphitic carbon nitride (g-C3N4) composite photocatalysts were prepared by a combined impregnation−chemical reduction strategy involving polymerization of melamine in the presence of graphene oxide (precursors) and hydrazine hydrate (reducing agent), followed by thermal treatment at 550 °C under flowing nitrogen. The resulting graphene/g-C3N4 composite photocatalysts were characterized by X-ray diffraction, transmission electron microscopy, UV−visible spectrophotometry, nitrogen adsorption, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, and photoluminescence spectroscopy. The transient photocurrent response was measured for several on−off cycles of intermittent irradiation. The effect of graphene content on the rate of visible-light photocatalytic hydrogen production was studied for a series of graphene−graphitic carbon nitride composite samples containing Pt as a cocatalyst in methanol aqueous solutions. This study shows that graphene sheets a...
1,660 citations
References
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TL;DR: The CASTEP program as mentioned in this paper is a computer program for first principles electro-Nic structure calculations, and some of its features and capabilities are described and near-future development plans outlined.
Abstract: CASTEP Computer program / Density functional theory / Pseudopotentials / ab initio study / Plane-wave method / Computational crystallography Abstract. The CASTEP code for first principles electro- nic structure calculations will be described. A brief, non- technical overview will be given and some of the features and capabilities highlighted. Some features which are un- ique to CASTEP will be described and near-future devel- opment plans outlined.
9,884 citations
TL;DR: An advance in the catalysis of the overall splitting of water under visible light is described: the new catalyst is a solid solution of gallium and zinc nitrogen oxide, modified with nanoparticles of a mixed oxide of rhodium and chromium, which functions as a promising and efficient photocatalyst in promoting the evolution of hydrogen gas.
Abstract: Enhancing catalytic performance holds promise for hydrogen production by water splitting in sunlight.
2,537 citations
TL;DR: Direct water electrolysis was achieved with a novel, integrated, monolithic photoelectrochemical-photovoltaic design that splits water directly upon illumination; light is the only energy input.
Abstract: Direct water electrolysis was achieved with a novel, integrated, monolithic photoelectrochemical-photovoltaic design. This photoelectrochemical cell, which is voltage biased with an integrated photovoltaic device, splits water directly upon illumination; light is the only energy input. The hydrogen production efficiency of this system, based on the short-circuit current and the lower heating value of hydrogen, is 12.4 percent.
2,052 citations
TL;DR: In this article, the Gibbs free energy was calculated to determine the lowest energy structure of a transition metal oxide surface in thermodynamic equilibrium with an oxygen-rich environment, and it was shown that the commonly assumed stoichiometric termination is only favorable at low oxygen chemical potentials, i.e., low pressures and/or high temperatures.
Abstract: Using density-functional theory we calculate the Gibbs free energy to determine the lowest-energy structure of a ${\mathrm{RuO}}_{2}(110)$ surface in thermodynamic equilibrium with an oxygen-rich environment. The traditionally assumed stoichiometric termination is only found to be favorable at low oxygen chemical potentials, i.e., low pressures and/or high temperatures. At a realistic O pressure, the surface is predicted to contain additional terminal O atoms. Although this O excess defines a so-called polar surface, we show that the prevalent ionic model, that dismisses such terminations on electrostatic grounds, is of little validity for ${\mathrm{RuO}}_{2}(110).$ Together with analogous results obtained previously at the (0001) surface of corundum-structured oxides, these findings on (110) rutile indicate that the stability of nonstoichiometric terminations is a more general phenomenon of transition metal oxide surfaces.
1,612 citations
TL;DR: In this article, the development of visible-light-driven photocatalysts focusing on the refinement of non-oxide-type photocatalyst such as (oxy)nitrides and oxysulfides is discussed.
Abstract: Overall water splitting to form hydrogen and oxygen over a heterogeneous photocatalyst using solar energy is a promising process for clean and recyclable hydrogen production in large-scale. In recent years, numerous attempts have been made for the development of photocatalysts that work under visible-light irradiation to efficiently utilize solar energy. This article presents recent research progress in the development of visible-light-driven photocatalysts, focusing on the refinement of non-oxide-type photocatalysts such as (oxy)nitrides and oxysulfides.
1,341 citations
"A metal-free polymeric photocatalys..." refers background in this paper
...There are some cases where N 2 evolution and sulphur deposition are observed as a result of oxidative decomposition of the photocatalys...
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