2D Nanomaterials for Photocatalytic Hydrogen Production (original) (raw)
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Two-Dimensional Materials and Composites as Potential Water Splitting Photocatalysts: A Review
Catalysts
Hydrogen production via water dissociation under exposure to sunlight has emanated as an environmentally friendly, highly productive and expedient process to overcome the energy production and consumption gap, while evading the challenges of fossil fuel depletion and ecological contamination. Various classes of materials are being explored as viable photocatalysts to achieve this purpose, among which, the two-dimensional materials have emerged as prominent candidates, having the intrinsic advantages of visible light sensitivity; structural and chemical tuneability; extensively exposed surface area; and flexibility to form composites and heterostructures. In an abridged manner, the common types of 2D photocatalysts, their position as potential contenders in photocatalytic processes, their derivatives and their modifications are described herein, as it all applies to achieving the coveted chemical and physical properties by fine-tuning the synthesis techniques, precursor ingredients a...
Nano Energy
Heterojunction catalyst can facilitate efficient photoelectrochemical (PEC) hydrogen evolution by reducing a potential barrier for charge transfer at the semiconductor/electrolyte interface. Such a heterojunction effect at the atomic thickness limit has not yet been explored although it can be strengthened because of strong built-in field and ultrafast charge transfer across the junction. Here, we first investigate a novel strategy to boost the hydrogen evolution performance of the p-type WSe 2 photocathode via reducing the overpotential with an atomically thin heterojunction catalyst comprising MoS 2 and WS 2 monolayers. To unveil an effective role of the heterojunction by isolating its kinetic contribution from other collective catalytic effects, we develop and utilize an in situ scanning PEC microscopy, which enables the spatially-resolved visualization of the enhanced photocatalytic hydrogen evolution performance of the heterojunction. Notably, significant reduction in overpotential, from +0.28 ± 0.03 to −0.04 ± 0.05 V versus (vs.) the reversible hydrogen electrode (RHE), is achieved when the MoS 2 /WS 2 heterojunction is introduced as a catalyst even without intentional generation of catalytic sites. As a result, the photocurrent of~4.0 mA cm −2 occurs even at 0 V vs. RHE. Furthermore, the beneficial effect of the atomically scaled vertical heterojunction is explained by the built-in potential resulted from efficient charge transfer in type-II heterojunctions with the support of first-principles calculations. Our demonstration not only offers an unprecedented approach to investigating the fundamental PEC characteristics in relation to the tailored properties of a catalyst but also proposes a new catalytic architecture, thereby enabling the design of highly efficient PEC systems.
International Journal of Hydrogen Energy, 2018
Hydrogen production through photoelectrochemical (PEC) water-splitting process has drawn significant research attention because it is a promising clean source of energy for improving earth climate in the future. Two-dimensional (2D) graphene and transition metal dichalcogenides (TMDCs), as the core of the system, have become versatile materials for the development of photocatalyst due to their distinct optical, electrical, thermal and mechanical properties. TMDCs have received significant consideration because of low-cost and earth-abundant catalysts that can replace noble metals, such as Pt. Therefore, comprehensive discussions on the structure and properties of 2D graphene and layered TMDCs materials are presented. We also gather and review various fabrication methods for TMDCsbased and graphene-TMDCs-based photocatalysts that can affect the PEC performance and hydrogen evolution. The inherent limitations and several future trends on 2D graphene and layered TMDCs-based photocatalyst for PEC water-splitting application are also discussed.
2D/2D heterostructured photocatalyst: Rational design for energy and environmental applications
Science China Materials
Two-dimensional/two-dimensional (2D/2D) hybrid nanomaterials have triggered extensive research in the photocatalytic field. The construction of emerging 2D/2D heterostructures can generate many intriguing advantages in exploring high-performance photocatalysts, mainly including preferable dimensionality design allowing large contact interface area, integrated merits of each 2D component and rapid charge separation by the heterojunction effect. Herein, we provide a comprehensive review of the recent progress on the fundamental aspects, general synthesis strategies (in situ growth and ex situ assembly) of 2D/2D heterostructured photocatalysts and highlight their applications in the fields of hydrogen evolution, CO 2 reduction and removal of pollutants. Furthermore, the perspectives on the remaining challenges and future opportunities regarding the development of 2D/2D heterostructure photocatalysts are also presented.
Hydrogen Evolution Reaction Activity of Graphene−MoS 2 van der Waals Heterostructures
Determining a suitable noble-metal-free catalyst for hydrogen evolution reaction (HER) by photo-electrocatalytic (PEC) water splitting is an enduring challenge. Here, the molecular origin of number of layers and stacking sequence-dependent PEC HER performance of MoS 2 /graphene (MoS 2 /GR) van der Waals (vdW) vertical heterostructures is studied. Density functional theory (DFT) based calculations show that the presence of MoS 2 induces p-type doping in GR, which facilitates hydrogen adsorption in the GR side compared to the MoS 2 side with ΔG H closer to 0 eV in the MoS 2 /GR bilayer vertical stacks. The activity maximizes in graphene with monolayer MoS 2 and reduces further for bilayer and multilayers of MoS 2. The PEC HER performance is studied in various electrodes, namely, single-layer graphene, single-and few-layered MoS 2 , and their two different types of vertical heterojunctions having different stacking sequences. The graphene on top of MoS 2 sequence showed the highest photoresponse with large reaction current density and lowest charge-transfer resistance toward HER, in aggrement with the DFT calculations. These findings establish the role of stacking sequence in the electrochemistry of atomic layers, leading to the design of new electrocatalysts by combinatorial stacking of a minimal number of layers. R ecent advances in van der Waals (vdW) solids of atomic layers invoke the possibility of new types of vertical quantum heterojunctions having atomically sharp interfaces between dissimilar materials. 1 Strong covalent bonds provide sufficient in-plane stability to two-dimensional (2D) crystals, whereas relatively weak vdW interactions are sufficient to keep the stack together. 1 These vertical structures are found to have novel interface-induced physical and chemical properties. 2,3 Recently, these heterostructures have also been studied for their efficacy toward electrocatalytic activities. 4 It is established that in most of the 2D layers, basal planes (defect-free) are inactive toward any catalytic reactions. 4 However, it is found that formation of heterostructures, where the atomic layers are placed one over the other with dissimilar atomic layers, can drastically change the inherent electrocatalytic activities of individual layers toward certain reactions, even leading to the activity of a basal plane that otherwise is inactive. It has been reported that this is due to the effect of a built-in electric field formed among the dissimilar layers or their metallic substrates. 5−7 The authors have recently reported that in vdW solids-based photoelectrochemistry not only the selection of layers but also their stacking order (layer sequencing or which layer is exposed to the electrolyte or analyte) also matters in deciding the net catalytic performance. 7 The photoelectrocatalytic (PEC) response of a few-layered MoS 2 and single-layer graphene was studied, and it is found that the graphene on top of MoS 2 (MSGR) has a PEC efficacy toward hydrogen evolution reaction (HER), 4e − + 4H + → 2H 2 , in acidic medium that is higher than that of MoS 2 on top of graphene (GRMS), though MoS 2 is the photoactive material and visible light has little effect on the PEC performance of graphene. 7 Similar stacking sequence effect has been observed in WS 2 /MoS 2 vdW vertical stacks by another research group. 7 The mechanism leading to this new parameter called " stacking sequence " is not completely understood yet, and here a molecular mechanism for these observed effects is proposed based on density functional theory (DFT) calculations and subsequent layer-dependent HER studies.
An Overview of the Photocatalytic H2 Evolution by Semiconductor-Based Materials for Nonspecialists
Journal of the Brazilian Chemical Society, 2020
The solar-to-chemical energy conversion is promising to tackle sustainability challenges toward a global future. The production of H 2 from sunlight represents an attractive alternative to the use of carboniferous fossil fuels to meet our energy demands. In this context, the water splitting reaction photocatalyzed by semiconductors that can be excited under visible or near-infrared light excitation represents an attractive route to the clean generation of H 2. In this review, we present an overview of the most important concepts behind the H 2 generation, from water splitting, promoted by semiconductor-based systems for readers that were recently introduced to the water splitting topic. Then, we present the main classes of photocatalysts based on semiconductors. For each class of semiconductors, we focused on the examples that lead to the highest activities towards the H 2 production and discuss the operation principles, advantages, performances, limitations, and challenges. We cover metal oxides, sulfides, and nitrides. We also discuss strategies in which these materials are combined, including hybridization with metal nanoparticles, other semiconductors, and carbon dots, to achieve improved performances and circumvent the limitations of the individual counterparts.
International Journal of Environmental Analytical Chemistry, 2020
Due to urbanisation and industrialisation, the growing rate of population is in high demand of green and sustainable energy. Fossil fuels seem to be less concern due to its rapid depletion and emission of toxic gases including CO 2 So, the production of cost effective and clean energy has attracted much attention of scientists. Solar fuels such as hydrogen is a cost effective and clean energy source, and it is abundantly present in our environment. It is also an energy charge carrier, and it has the ability to fulfil the increasing demand of energy. Hydrogen-based energy system can build the bridges for future. There are many methods for energy production but photocatalysis is better among all of them. In photocatalysis process, photocatalysts are used. The non-stoichiometric graphene and ceramic-based nanocomposites photocatalysts are found to be efficient and potential for numerous applications in materials science, bioimages, nanomedicine, drug delivery, energy harvesting, pharmaceuticals and biosensors. The unique physio-chemical properties like optical, electrical, mechanical strength and thermal facilitate graphene to render graphene-based nanomaterials suitable for electroanalytical-chemistry, electrochemical-sensors and photocatalysis. This review explains the graphenebased photocatalysts for solar fuel production, their fabrication and recent development in graphene-based photocatalyst. The challenges and potential future perspectives of these multifaceted materials are discussed here as well. This review article boosts up the forthcoming scientists to improve the device performance with interdepending free-standing graphene and additional host material.
Frontiers in Chemistry
Photocatalytic hydrogen generation from direct water splitting is recognized as a progressive and renewable energy producer. The secret to understanding this phenomenon is discovering an efficient photocatalyst that preferably uses sunlight energy. Two-dimensional (2D) graphitic carbon nitride (g-C3N4)-based materials are promising for photocatalytic water splitting due to special characteristics such as appropriate band gap, visible light active, ultra-high specific surface area, and abundantly exposed active sites. However, the inadequate photocatalytic activity of pure 2D layered g-C3N4-based materials is a massive challenge due to the quick recombination between photogenerated holes and electrons. Creating 2D heterogeneous photocatalysts is a cost-effective strategy for clean and renewable hydrogen production on a larger scale. The 2D g-C3N4-based heterostructure with the combined merits of each 2D component, which facilitate the rapid charge separation through the heterojunctio...
Journal of Physics and Chemistry of Solids, 2023
Of late, two-dimensional van der Waals heterostructures (vdWHs) have gained tremendous attention for water-splitting to produce hydrogen (H2) fuel. This work demonstrates various configurations of vdWHs made up of monolayer boron arsenide (BAs) and germanium carbide (GeC) that exhibit outstanding photocatalytic properties in the water-splitting process to generate H2 fuel. The absorption coefficient of the proposed BAs/GeC vdWHs is more than 105 cm−1, which exceeds the extensive conversion efficiency of optoelectronic materials. The absorption coefficient can be further tuned and reaches a maximum value of 2.6x10^6 cm−1 when applying an external strain. Dynamically tunable bandgaps in the range of 0.78–2.02 eV are found in these vdWHs by applying a biaxial strain. A strong photocatalytic water splitting action throughout the ultraviolet to optical spectrum region is found when a biaxial strain of −6% to +6% is applied. The favorable characteristics of the proposed BAs/GeC vdWHs could help enhance H2 fuel generation via water splitting.