Role Of Cocatalyst Research Articles

Metal Cocatalyst Engineering in Metal-Semiconductor Hybrid Photocatalysts Achieves a Fivefold Enhancement of Hydrogen Evolution.

This study explores the optimal morphology of photochemical hydrogen evolution catalysts in a one-dimensional system. Systematic engineering of metal tips on precisely defined CdSe@CdS dot-in-rods is conducted to exert control over morphology, composition, and both factors. The outcome yields an optimized configuration, a Au-Pt core-shell structure with a rough Pt surface (Au@r-Pt), which exhibits a remarkable fivefold increase in quantum efficiency, reaching 86 % at 455 nm and superior hydrogen evolution rates under visible and AM1.5 G irradiation conditions with prolonged stability. Kinetic investigations using photoelectrochemical and time-resolved measurements demonstrate a greater extent and extended lifetime of the charge-separated state on the tips as well as rapid water reduction kinetics on high-energy surfaces. This approach sheds light on the critical role of cocatalysts in hybrid photocatalytic systems for achieving high performance.

Optimization of carrier transfer kinetics of BiOIO3 using TFA·/TFA- reversible redox pairs of TFA molecules as co-catalysts for efficient photoelectrochemical water splitting system

Co-catalyst loading on photoelectrodes is considered to be an effective way to accelerate charge transfer. However, the bonding between most of the co-catalysts and photoelectrodes tends to be weak, which severely limits the role of co-catalysts in the catalytic system. Based on the above problems, we introduced trifluoroacetic acid (TFA) as a homogeneous molecular co-catalyst in the layered BiOIO3 catalytic system for the first time. The BiOIO3-TFA photoelectrode exhibited excellent photoelectrochemical performance under light and applied bias voltage. The photocurrent density reached up to 0.228 μA cm−2, which was 2.11 times higher than that before modification, while the overpotential was negatively shifted by 183 mV. The results showed that the photogenerated electron-hole pairs in BiOIO3 are excited and transferred to the TFA causing the CO double bond to break to form a TFA radical (TFA·), which is then reduced to TFA-. This cyclic redox reaction accompanied by fast hole transfer can greatly reduce the recombination behavior during carrier transport. This work demonstrates a new form of co-catalyst for photoelectrochemical water splitting. Highly water-soluble molecules and TFA·/TFA- reversible reactions have considerable potential for the development of new co-catalysts. It also provides ideas for the establishment of new, efficient catalytic systems for inhibiting carrier recombination.

Roles of Cocatalysts in Biomass Photo(electro)refining

AbstractPhotosynthesis converts solar energy, carbon dioxide, and water into biomass, offering a renewable energy and chemical source. Biomass photo(electro)refining (BPeR) emerges as a sustainable alternative to petrochemicals for fuel and chemical production. However, BPeR faces challenges due to photocatalyst limitations, necessitating the integration of cocatalysts. Cocatalysts significantly impact the efficiency, selectivity, and durability of BPeR reactions, yet their roles require systematic elucidation and understanding. This review explores how cocatalysts impact the carbon bond functionalization, cleavage, and formation in biomass and its derivatives. It discusses their crucial roles in charge carrier generation, separation, and transportation, particularly in catalyzing surface reactions such as hydrogen‐involved reactions, generation, and manipulation of oxygen or carbon radicals, and the C─C/O/H bond transformations. Additionally, it outlines challenges and prospects for developing cocatalysts to enhance BPeR efficiency and durability, boosting the viability of biomass as a sustainable source of energy and materials.

Thiamine (Vitamin B1) Promoted Organic Transformations: A Recent Updates.

Due to the growing significance of sustainable and environmentally friendly organic transformations, there has been increasing interest in utilizing vitamins as catalysts owing to their green nature, biocompatibility, and ease of preparation. Among these, Vitamin B1, also known as thiamine stands out for its nonflammable, water-soluble, inexpensive, and non-toxic characteristics. This review summarized recent developments on the catalytic application of Vitamin B1 in organic transformations, particularly in facilitating C-C and C-X (N, O, S) bond formations, thus demonstrating its efficacy in synthesizing complex molecules. Vitamin B1 exhibits versatility in these reactions, functioning as both an organocatalyst as well as a co-catalyst or ligand with other metal catalysts. The review also delves into the application of thiamine diphosphate-dependent enzymes as catalysts in organic reactions, drawing inspiration from natural enzymatic processes. Additionally, the mechanistic intricacies of thiamine-catalyzed reactions and the roles of co-catalysts or additives are thoroughly examined, providing insights into reaction pathways and facilitating informed catalyst design strategies.

MoC nanoparticles embedded in superior thin g-C3N4 nanosheets for efficient photocatalytic activity

Photogenerated charge carrier transfer efficiency in graphitic carbon nitride (g-C3N4) based heterostructures depended strongly on the interface nature. In this paper, MoC nanoparticles less than 5 nm were implanted in superior thin g-C3N4 nanosheets to create high charge carrier separation and transfer efficiency. Cubic MoC in N-doped graphitic carbon was first fabricated using dicyandiamide and ammonium molybdate tetrahydrate at 800 °C. The MoC nanoparticles were homogeneously implanted in g-C3N4 nanosheets by further thermal polymerization of bulk g-C3N4 prepared using melamine and MoC/C composites to create a Schottky junction which was confirmed by band gap analysis and free radical capture test. Melamine and dicyandiamide also play important role to create highly efficient catalysts. The MoC nanoparticles revealed fine crystallinity. A well-developed interface between MoC and g-C3N4 was observed. Because of high conductivity of MoC, well-developed interface, and co-catalyst role of MoC, the MoC/g-C3N4 junction exhibited ideal photocatalytic activity for dye degradation and water splitting. The kinetic constant rate of Rhodamine B degradation using a MoC/g-C3N4 sample created by optimized conditions was 0.061 min−1 which was 8.7 times of that of pristine g-C3N4 nanosheets. In the case of without co-catalyst addition, the photocatalytic hydrogen generation rate using this composite sample was 233.0 μmol g−1 h−1 which was 15.2 times of that of initial g-C3N4 nanosheets. These results supply an efficient approach for the first time to homogeneously distribute small cubic MoC nanoparticles in superior thin g-C3N4 nanosheets to construct heterostructures and greatly reduce photogenerated charge carrier recombination.

Natural redox mediator anthraquinone aloe-emodin facilitated the in-situ mineralized γ-FeO(OH) membrane for the removal of tannic acid through photocatalytic-PMS activation

The growing utilization of Traditional Chinese Medicine (TCM) has resulted in an increase in wastewater. Herein, a new kind of organic-inorganic redox mediator membrane by immobilizing γ-FeO(OH) and aloe-emodin(AE) with the characteristic large π-conjugation anthraquinone structure on PVDF membrane was innovatively achieved. AE exhibiting both electron deficiency and redox activity possesses a co-catalyst role in degradation of tannic acid (TA), aiding in the separation of charge carriers through the sequential hydrogenation and dehydrogenation of AE. The removal rates of TA were 92.8 % in the tannic acid solution and 60.3 % in the simulated rhubarb wastewater by the AE-γ-FeO(OH) membrane under PMS+Vis conditions in 45 min. Also, they show a higher recovery of pure water flux and owning good fouling performance. Overall, this current work presents a novel approach for the design and preparation of organic-inorganic photocatalytic composite membrane using readily available natural products for the purification TCM wastewater.

CuO/Sb2S3 Nanoarchitectures for Enhanced Charge Generation/Separation for Photoelectrochemical Hydrogen Evolution

Developing an efficient photocathode system using abundant earth materials is crucial for the effective process of Photoelectrochemical (PEC) water splitting. Achieving successful charge transfer between heterojunctions is a key consideration in creating an innovative photocathode that considers cost-effectiveness, material abundance, and PEC performance. In our study, we synthesized a p-type narrow band gap photocathode using copper oxide (CuO) with an energy gap (Eg) of 1.5 eV through a hydrothermal method. We then enhanced its performance by decorating it with antimony sulfide (Sb2S3) nanospheres (NSs) using a simple chemical bath deposition (CBD) technique, resulting in the formation of a CuO/Sb2S3 NSs heterojunction.The fabricated heterojunction demonstrated superior PEC performance compared to the bare CuO. Specifically, we observed a significant increase in photocurrent density for the CuO/Sb2S3 NSs photocathode (J = -1 mA.cm-2) compared to CuO alone (J = -0.3 mA.cm-2) at a standard potential of 0 V vs RHE in a 0.5 M Na2SO4 solution with a pH of 6.85. This improvement can be attributed to the enhanced generation and separation of charge carriers. Furthermore, the CuO/Sb2S3 heterojunction exhibited remarkable photostability over a period of 2.5 h, with no degradation in photocurrent density. The Sb2S3 acted as a sensitizer, reducing the recombination rate of electron-hole pairs (e-/h+) within the CuO/Sb2S3 NSs, thereby enhancing the overall performance. The CuO/Sb2S3 NSs photocathode exhibited an ABPE% of 0.1%, while the ABPE% for CuO alone was 0.03%. This indicates a significant improvement in the performance of the CuO/Sb2S3 NSs photocathode. Onset potential (Eonset) was also observed to shift in a positive direction in CuO/Sb2S3 NSs as compared to CuO only. Eonset for the films followed a trend having CuO/Sb2S3 NSs (0.85 VRHE) > CuO (0.78 VRHE). Notably, this improvement is attributed to increased light absorption and a reduced recombination rate compared to the pristine CuO photocathode. Moreover, electrochemical impedance spectroscopy (EIS) studies provided evidence of enhanced electron transfer rates occurring at the interface between the heterojunction and the electrode/electrolyte interface. UV-Visible and photoluminescence (PL) emission spectra results indicated that the CuO/Sb2S3 NSs heterojunction exhibited an extended absorption spectrum and a reduced rate of recombination, further supporting the enhanced performance. Additionally, electrochemical impedance spectroscopy studies revealed lower charge transfer resistance in the CuO/Sb2S3 NSs heterojunction compared to CuO alone.These findings open up new avenues for the development of novel photocathodic materials and heterojunctions utilizing copper-based binary oxides/chalcogenides for efficient solar harvesting applications.References(1) Kumar, M.; Singh, A.; Meena, B.; Sahu, P. K.; Subrahmanyam, C. Decoration of Spherical Sb2S3 over CuO Nanoflakes for Efficient Photoelectrochemical Hydrogen Generation. Results Eng. 2023, 101513. https://doi.org/10.1016/j.rineng.2023.101513.(2) Kumar, M.; Meena, B.; Subramanyam, P.; Suryakala, D.; Subrahmanyam, C. Emerging Copper-Based Semiconducting Materials for Photocathodic Applications in Solar Driven Water Splitting. Catalysts 2022, 12 (10), 1198. https://doi.org/10.3390/catal12101198.(3) Kumar, M.; Meena, B.; Subramanyam, P.; Suryakala, D.; Subrahmanyam, C. Recent Trends in Photoelectrochemical Water Splitting: The Role of Cocatalysts. NPG Asia Mater. 2022, 14 (1), 88. https://doi.org/10.1038/s41427-022-00436-x. Figure 1

Ammonium Tetrakis(pentafluorophenyl)borate: Preparation and Application in Olefin Coordination Polymerization as the Cocatalyst Compound.

Metallocene catalysts have attracted much attention from academia and industry for their excellent catalytic activity in the field of olefin polymerization. Cocatalysts play a key role in metallocene catalytic systems, which can not only affect the overall catalytic activity, but also have an obvious influence on the structure and properties of the polymer. Although methylaluminoxane (MAO) is currently the most widely used cocatalyst, its price increases the production cost of polyolefin materials. Ammonium tetrakis(pentafluorophenyl)borate has shown excellent performance in polymerization, being one of the best substitutes for the traditional cocatalyst MAO. Compared with the main catalyst, whose composition and structure are relatively complex, the research on cocatalyst is very limited. This review mainly introduces the research history, preparation methods, and application progress in polymerization of ammonium tetrakis(pentafluorophenyl)borate, deepening our understanding of the role of cocatalyst in polymerization, with the hope of inspiring brand-new thinking on improving and enhancing the overall performance of catalyst systems.

Cocatalyst activity mapping for photocatalytic materials revealed by the pattern-illumination time-resolved phase microscopy.

Photocatalytic water-splitting represents a promising avenue for clean hydrogen production, necessitating an in-depth understanding of the photocatalytic reaction mechanism. The majority of the photocatalytic materials need cocatalysts to enhance the photo-oxidation or reduction reactions. However, the working mechanism, such as collecting charge carriers or reducing the reaction barrier, is not clear because they disperse inhomogeneously on a surface, and it is difficult to follow the local charge carrier behavior. This study employs the pattern-illumination time-resolved phase microscopy (PI-PM) method to unravel the spatial charge carrier behavior in photocatalytic systems, utilizing time-resolved microscopic image (refractive index change) sequences and their clustering analyses. This approach is robust for studying the change in local charge carrier behavior. We studied two major cocatalyst effects on photocatalysts: TiO2 with/without Pt and hematite with/without CoPi. The PI-PM method, supported by charge type clustering and the effects of scavengers, allowed for the analysis of local activity influenced by cocatalysts. This approach revealed that the introduction of cocatalysts alters the local distribution of charge carrier behavior and significantly impacts their decay rates. In TiO2 systems, the presence of Pt cocatalysts led to a local electron site on the micron scale, extending the lifetime to a few tens of microseconds from a few microseconds. Similarly, in hematite films with CoPi, we observed a notable accumulation of holes at cocatalyst sites, emphasizing the role of cocatalysts in enhancing photocatalytic efficiency. The study's findings highlight the complexity of charge carrier dynamics in photocatalytic processes and the significant influence of cocatalysts.

Recent advances in cocatalyst engineering for solar‐driven overall water splitting

AbstractSolar‐driven overall water splitting using particulate photocatalysts represents a viable and attractive paradigm to produce H2. To achieve sustainable artificial photosynthesis, considerable effort has been devoted in enhancing the overall efficiency and stability of photocatalysts. More specifically, modifying the photocatalyst surface with suitable cocatalysts can significantly enhance its water‐splitting performance. In this minireview, we describe recent advances with respect to the hybridization strategies in constructing high‐performance cocatalyst/photocatalyst systems. We first discuss the fundamental concepts and principles governing the photocatalytic water splitting and the important role of cocatalysts. Subsequently, we examine the strengths and drawbacks of conventional and emerging cocatalyst loading strategies. Special consideration is given to the structure–activity relationship of cocatalysts to achieve efficient photocatalytic H2 production from pure H2O. Finally, the remaining key challenges and possible future directions in the discovery and further exploration of cocatalyst materials are also discussed. We anticipate this review will provide insights and inspire more research interest in designing high‐performance cocatalysts for photocatalytic overall water splitting.

BiVO4 Photoanodes Enhanced with Metal Phosphide Co-Catalysts: Relevant Properties to Boost Photoanode Performance.

Achieving highly performant photoanodes for oxygen evolution is key to developing photoelectrochemical devices for solar water splitting. In this work, BiVO4 photoanodes are enhanced with a series of core-shell structured bimetallic nickel-cobalt phosphides (MPs), and key insights into the role of co-catalysts are provided. The best BiVO4 /Ni1.5 Co0.5 P and BiVO4 /Ni0.5 Co1.5 P photoanodes achieve a 3.5-fold increase in photocurrent compared with bare BiVO4 . It is discovered that this enhanced performance arises from a synergy between work function, catalytic activity, and capacitive ability of the MPs. Distribution of relaxation times analysis reveals that the contact between the MPs, BiVO4 , and the electrolyte gives rise to three routes for hole injection into the electrolyte, all of which are significantly improved by the presence of a second metal cation in the co-catalyst. Kinetic studies demonstrate that the significantly improved interfacial charge injection is due to a lower charge-transfer resistance, enhanced oxygen-evolution reaction kinetics, and larger surface hole concentrations, providing deeper insights into the carrier dynamics in these photoanode/co-catalyst systems for their rational design.

Hydrogen Catalysis By Macrocyclic Pyrrole Catalysts

We have designed hangman porphyrins for the study of hydrogen evolution catalysis. The hangman constructs utilize a pendant acid/base functionality within the secondary coordination sphere that is “hung” above the redox platform onto which the substrate binds. In this way, the delivery of a proton can precisely be controlled to substrate bonded to the metal of the macrocycle, thus ensuring efficient coupling between the proton and electron. Beyond the benefits of proton-coupled electron transfer (PCET), we have uncovered the impactful role of co-catalysts on electrocatalytic hydrogen production at the macrocyclic platform. Hydrogen evolution from a weak acid, acetic acid, occurs at extremely high rates in the presence of tertiary amine as a co-catalyst. These findings reveal controlled proton delivery and co-substrates as important design principles for creating efficient hydrogen evolution catalysts.

Fe2TiO5-based photoanodes application in expanded photoelectrochemistry derived from the construction of heterojunction with the co-catalyst role

The Fe2TiO5 photoelectrode is limited in photoelectrochemical field (PEC) due to the slow charge transfer kinetics, short carrier diffusion distances and low separation efficiency. Hence, the Fe2TiO5/NiCo-LDH photoelectrodes with dual roles of co-catalyst and heterojunction are constructed, in which the photogenerated carriers are effectively separated and the conductivity is enhanced. At the same time, the surface state of the Fe2TiO5-based photoanode is modulated by the co-catalyst, which drives charge transfer into the electrolyte. With the synergistic effect of inhibiting photogenerated carrier complexation and accelerating charge transfer, the OER photocurrent density of Fe2TiO5/NiCo-LDH photoelectrode is enhanced to 2.42 mA/cm2, which is 3.4 folds higher than that of pristine Fe2TiO5. Specifically, Fe2TiO5/NiCo-LDH photoanode exhibits good stability and photoelectrochemical performance in hydrogen sulfide oxidation reaction (SOR). Similar to the OER, the sulphur oxidation photocurrent density of Fe2TiO5/NiCo-LDH photoelectrodes is enhanced to 0.21 mA/cm2, which is 2 folds higher than that of pristine Fe2TiO5. This work provides a new idea for the modification of Fe2TiO5 photoanodes and also explores a pioneering demonstration for the photoelectrochemical decomposition of hydrogen sulfide.

A novel loading strategy of Mo-O/Mo-S cocatalysts based on the photocorrosion property of CdS

The promoting role of cocatalysts is not only dependent on their physical and chemical properties, but also closely related to their loading methods and nanostructures. In this study, by converting the disadvantages of CdS photocorrosion into the advantages of cocatalysts loading, a novel cocatalyst loading strategy is adopted to promote the photocatalytic H2 evolution performance of CdS. Using 1D CdS nanorods as primary photocatalyst, a limited amount of Mo-O cocatalyst (e.g. CdMoO4-MoOx) was in-situ deposited on the photocorrosive surface of CdS under intensive irradiation, and further transformed into few-layer Mo-S (e.g. MoS2-CdMoS4) nanofins by a facile ion-exchange method. The as-synthesized CdS@MoS2-CdMoS4 heterojunctions show a surprising “boiling” effect in visible-light-driven H2 evolution process (∼40.3 mmol·h−1·g−1).

Catalytic Methods for Producing Higher 2-Ketones: Prospects for the Wacker System in the Oxidation of α-Olefins

Abstract—Methods developed over the past 60 years for the preparation of unbranched С6–С14 2-ketones by catalytic oxidation of linear α-olefins have been analyzed and summarized. Particular attention has been paid to the consideration of the catalytic Wacker system, which is important for industrial organic synthesis, and the proposed ways for its modification. Methods for controlling the reaction selectivity have been discussed, and the role of co-catalysts, oxidizing agents, and ligands has been considered.

Bifunctional carbon dots as cocatalyst and reactor decorating an organic photocatalyst for H2 production from water-splitting in an emulsion

CDs were used to modify an organic semiconductor of p(DB) and the optimal sample exhibits efficient H2 evolution under visible light in an o-xylene-in-water emulsion by photo-splitting of water. The CDs play both the roles of cocatalyst and reactor.

Enhanced Photoredox Activity of BiVO4/Prussian Blue Nanocomposites for Efficient Pollutant Removal from Aqueous Media under Low-Cost LEDs Illumination

Bismuth vanadate (BiVO4, BV) is a widely explored photocatalyst for photo(electro)chemical applications, but its full photocatalytic potential is hindered by the fast recombination and low mobility of photogenerated charge carriers. Herein, we propose the photodeposition of different amounts of Prussian blue (PB) cocatalysts on the surface of monoclinic BV to obtain BV-PB composite photocatalysts with increased photoactivity. The as-prepared BV and BV-PB composites were characterized by an array of analytic techniques such scanning eletron microscopy (SEM), transmission eletron microscopy (TEM), X-day diffraction (XRD), and spectroscopic techniques including Fourier-transform infrared spectroscopy (FTIR), diffuse reflectance spectroscopy (DRS), electrochemical impedance spectroscopy (EIS), photoluminescence (PL), and Raman spectroscopy. The addition of PB not only increases the absorption of visible light, as indicated by DRS, but also improves the charge carriers’ transfer across the photocatalysts/solution interface and hence reduces electron-hole (e−-h+) recombination, as confirmed by EIS and PL measurements. Resultantly, the BV-PB composite photocatalysts with optimum PB loading exhibited enhanced Cr(VI) photoreduction efficiency as compared to pristine BV under visible light illumination from low-power blue light-emitting diodes (LEDs), thanks to the cocatalyst role of PB which mediates the transfer of photoexcited conduction band (CB) electrons from BV to Cr(VI) species in solution. Moreover, as compared to pristine BV and BV + H2O2, a drastic increase in the methylene blue (MB) photo-oxidation efficiency was observed for BV-PB in the presence of a minute quantity of H2O2 due to a synergic effect between the photocatalytic and Fenton-like processes. While pure BV photodegraded around 70% of MB dye within 120 min, the BV-PB/H2O2 and BV/H2O2 system could degrade almost 100% of the dye within 20 min (kobs. = 0.375 min−1) and 40 min (kobs. = 0.055 min−1), respectively. The practical approach employed in this work may pioneer new prospects for synthesizing new BV-based photocatalytic systems with low production costs and high photoredox efficiencies.

Accelerating Photocatalytic Activity by Tailoring Cocatalysts on Polycrystalline Tungsten(VI) Oxide Microplates

AbstractIn this study, the structure–activity relationship of the WO3 photocatalyst and the role of cocatalysts deposited on the WO3 surface were analyzed. Investigation of the phase transformation of WO3 microplates revealed that amorphous WO3 was progressively crystallized into monoclinic WO3 during consecutive thermal treatments. The obtained WO3 microplates were used for the photocatalytic decomposition of organic dyes under simulated solar light irradiation to understand the effect of the crystal structure on the photocatalytic activity. The crystal phase of the WO3 microplates with a monoclinic structure was optimal for the photocatalytic reaction. However, the effects of the crystal phase and the surface area of the WO3 sample were very small, and a deposited metal cocatalyst was essential for achieving photocatalytic activity. The detailed mechanisms and influence of cocatalysts on the WO3 surface were discussed.

A Minireview on the Role of Cocatalysts in Semiconductor-Based Photocatalytic CH4 Conversion

A Minireview on the Role of Cocatalysts in Semiconductor-Based Photocatalytic CH₄ Conversion

Correction to “Decoration of Graphene Quantum Dots on TiO2 Nanostructures: Photosensitizer and Cocatalyst Role for Enhanced Hydrogen Generation”

Correction to “Decoration of Graphene Quantum Dots on TiO₂ Nanostructures: Photosensitizer and Cocatalyst Role for Enhanced Hydrogen Generation”