Photokatalysatoren auf Graphenbasis für die Produktion von Solarbrennstoffen

Recent Progress in Multifunctional Graphene-Based Nanocomposites for Photocatalysis and Electrocatalysis Application

The global energy shortage and environmental degradation are two major issues of concern in today's society. The production of renewable energy and the treatment of pollutants are currently the mainstream research directions in the field of photocatalysis. In addition, over the last decade or so, graphene (GR) has been widely used in photocatalysis due to its unique physical and chemical properties, such as its large light-absorption range, high adsorption capacity, large specific surface area, and excellent electronic conductivity. Here, we first introduce the unique properties of graphene, such as its high specific surface area, chemical stability, etc. Then, the basic principles of photocatalytic hydrolysis, pollutant degradation, and the photocatalytic reduction of CO₂ are summarized. We then give an overview of the optimization strategies for graphene-based photocatalysis and the latest advances in its application. Finally, we present challenges and perspectives for graphene-based applications in this field in light of recent developments.

2D Transition Metal Dichalcogenides for Photocatalysis

Two-dimensional (2D) transition metal dichalcogenides (TMDs), a rising star in the post-graphene era, are fundamentally and technologically intriguing for photocatalysis. Their extraordinary electronic, optical, and chemical properties endow them as promising materials for effectively harvesting light and catalyzing the redox reaction in photocatalysis. Here, we present a tutorial-style review of the field of 2D TMDs for photocatalysis to educate researchers (especially the new-comers), which begins with a brief introduction of the fundamentals of 2D TMDs and photocatalysis along with the synthesis of this type of material, then look deeply into the merits of 2D TMDs as co-catalysts and active photocatalysts, followed by an overview of the challenges and corresponding strategies of 2D TMDs for photocatalysis, and finally look ahead this topic.

Towards Sustainable Oxalic Acid from CO2 and Biomass

To quickly and drastically reduce CO2 emissions and meet our ambitions of a circular future, we need to develop carbon capture and storage (CCS) and carbon capture and utilization (CCU) to deal with the CO2 that we produce. While we have many alternatives to replace fossil feedstocks for energy generation, for materials such as plastics we need carbon. The ultimate circular carbon feedstock would be CO2 . A promising route is the electrochemical reduction of CO2 to formic acid derivatives that can subsequently be converted into oxalic acid. Oxalic acid is a potential new platform chemical for material production as useful monomers such as glycolic acid can be derived from it. This work is part of the European Horizon 2020 project "Ocean" in which all these steps are developed. This Review aims to highlight new developments in oxalic acid production processes with a focus on CO2 -based routes. All available processes are critically assessed and compared on criteria including overall process efficiency and triple bottom line sustainability.

Coupling of Solar Energy and Thermal Energy for Carbon Dioxide Reduction: Status and Prospects

Enormous efforts have been devoted to the reduction of carbon dioxide (CO₂ ) by utilizing various driving forces, such as heat, electricity, and radiation. However, the efficient reduction of CO₂ is still challenging because of sluggish kinetics. Recent pioneering studies from several groups, including us, have demonstrated that the coupling of solar energy and thermal energy offers a novel and promising strategy to promote the activity and/or manipulate selectivity in CO₂ reduction. Herein, we clarify the definition and principles of coupling solar energy and thermal energy, and comprehensively review the status and prospects of CO₂ reduction by coupling solar energy and thermal energy. Catalyst design, reactor configuration, photo-mediated activity/selectivity, and mechanism studies in photo-thermo CO₂ reduction will be emphasized. The aim of this Review is to promote understanding towards CO₂ activation and provide guidelines for the design of new catalysts for the efficient reduction of CO₂ .

Bipyridine-Assisted Assembly of Au Nanoparticles on Cu Nanowires To Enhance the Electrochemical Reduction of CO2

We report a new strategy to prepare a composite catalyst for highly efficient electrochemical CO₂ reduction reaction (CO₂ RR). The composite catalyst is made by anchoring Au nanoparticles on Cu nanowires via 4,4'-bipyridine (bipy). The Au-bipy-Cu composite catalyzes the CO₂ RR in 0.1 m KHCO₃ with a total Faradaic efficiency (FE) reaching 90.6 % at -0.9 V to provide C-products, among which CH₃ CHO (25 % FE) dominates the liquid product (HCOO^- , CH₃ CHO, and CH₃ COO^- ) distribution (75 %). The enhanced CO₂ RR catalysis demonstrated by Au-bipy-Cu originates from its synergistic Au (CO₂ to CO) and Cu (CO to C-products) catalysis which is further promoted by bipy. The Au-bipy-Cu composite represents a new catalyst system for effective CO₂ RR conversion to C-products.

WXy /g-C3 N4 (WXy =W2 C, WS2 , or W2 N) Composites for Highly Efficient Photocatalytic Water Splitting

The development of earth-abundant, economical, and efficient photocatalysts to boost water splitting is a key challenge for the practical large-scale application of hydrogen energy. In this study, g-C₃ N₄ loaded with different tungsten compounds (W₂ C, WS₂ , and W₂ N) is found to exhibit enhanced photocatalytic activities. W₂ C/g-C₃ N₄ displays the highest activity for the photocatalytic reaction with a H₂ evolution rate of up to 98 μmol h^-1 , as well as remarkable recycling stability. The excellent photocatalytic activity of W₂ C/g-C₄ N₃ is attributed to the suitable band alignment in W₂ C/g-C₄ N₃ and high HER activity of the W₂ C cocatalyst, which promotes the separation and transfer of carriers and hydrogen evolution at the surface. These findings demonstrate that the tungsten carbide cocatalyst is more active for the photocatalytic reaction than the sulfide or nitride, paving a way for the design of novel and efficient carbides as cocatalysts for photocatalysis.

In Situ-Fabricated 2D/2D Heterojunctions of Ultrathin SiC/Reduced Graphene Oxide Nanosheets for Efficient CO2 Photoreduction with High CH4 Selectivity

Photoreduction of CO₂ into fuel molecules such as CH₄ represents a promising route to simultaneously explore renewable energy and alleviate global warming. However, the implementation of such a process is hampered by low product yields and poor selectivity. A 2D/2D heterojunction of ultrathin SiC and reduced graphene oxide (RGO) nanosheets was fabricated in situ for efficient and selective photoreduction of CO₂ . Ultrathin SiC suppresses significant charge recombination in the bulk phase, thus providing more energetic electrons. The robust 2D/2D heterojunction allows fast transfer of energetic electrons from SiC to RGO. Combining the vital role of RGO in facilitating CO₂ activation, the optimized SiC/RGO exhibits an electron-transfer rate of 58.17 μmol h^-1  g^-1 towards CO₂ reduction, 2.7 times that of pure SiC (20.25 μmol h^-1  g^-1 ). About 92 % of the transferred electrons from SiC are devoted to generating CH₄ (6.72 μmol h^-1  g^-1 ). Such high efficiency and selectivity are mainly a result of the densely accumulated energetic electrons within RGO, which facilitate the eight-electron process to produce CH₄ . This work will inspire the design of catalyst/cocatalyst systems for efficient and selective photoreduction of CO₂ .

Heterostructured WS2 -MoS2 Ultrathin Nanosheets Integrated on CdS Nanorods to Promote Charge Separation and Migration and Improve Solar-Driven Photocatalytic Hydrogen Evolution

Solar-driven photocatalytic hydrogen evolution is important to bring solar-energy-to-fuel energy-conversion processes to reality. However, there is a lack of highly efficient, stable, and non-precious photocatalysts, and catalysts not designed completely with expensive noble metals have remained elusive, which hampers their large-scale industrial application. Herein, for the first time, a highly efficient and stable noble-metal-free CdS/WS₂ -MoS₂ nanocomposite was designed through a facile hydrothermal approach. When assessed as a photocatalyst for water splitting, the CdS/WS₂ -MoS₂ nanostructures exhibited remarkable photocatalytic hydrogen-evolution performance and impressive durability. An excellent hydrogen evolution rate of 209.79 mmol g^-1  h^-1 was achieved under simulated sunlight irradiation, which is higher than the values for CdS/MoS₂ (123.31 mmol g^-1  h^-1 ) and CdS/WS₂ nanostructures (169.82 mmol g^-1  h^-1 ) and the expensive CdS/Pt benchmark catalyst (34.98 mmol g^-1  h^-1 ). The apparent quantum yield reached 51.4 % at λ=425 nm in 5 h. Furthermore, the obtained hydrogen evolution rate was better than those of several noble-metal-free catalysts reported previously. The observed high rate of hydrogen evolution and remarkable stability may be a result of the ultrafast separation of photogenerated charge carriers and transport between the CdS nanorods and the WS₂ -MoS₂ nanosheets, which thus increases the number of electrons involved in hydrogen production. The proposed designed strategy is believed to potentially open a door to the design of advanced noble-metal-free photocatalytic materials for efficient solar-driven hydrogen production.

Hierarchical Layered WS2 /Graphene-Modified CdS Nanorods for Efficient Photocatalytic Hydrogen Evolution

Graphene-based ternary composite photocatalysts with genuine heterostructure constituents have attracted extensive attention in photocatalytic hydrogen evolution. Here we report a new graphene-based ternary composite consisting of CdS nanorods grown on hierarchical layered WS2 /graphene hybrid (WG) as a high-performance photocatalyst for hydrogen evolution under visible light irradiation. The optimal content of layered WG as a co-catalyst in the ternary CdS/WS2 /graphene composites was found to be 4.2 wt %, giving a visible light photocatalytic H2 -production rate of 1842 μmol h(-1)  g(-1) with an apparent quantum efficiency of 21.2 % at 420 nm. This high photocatalytic H2 -production activity is due to the deposition of CdS nanorods on layered WS2 /graphene sheets, which can efficiently suppress charge recombination, improve interfacial charge transfer, and provide reduction active sites. The proposed mechanism for the enhanced photocatalytic activity of CdS nanorods modified with hierarchical layered WG was further confirmed by transient photocurrent response. This work shows that a noble-metal-free hierarchical layered WS2 /graphene nanosheets hybrid can be used as an effective co-catalyst for photocatalytic water splitting.