Mechanism Of Water Splitting Research Articles

Noble-metal-free Bi-OZIS nanohybrids for sacrificial-agent-free photocatalytic water splitting: With long-lived photogenerated electrons

The production of hydrogen via the hydrogen evolution reaction, reliant on the use of valuable sacrificial agents, is not conducive to large-scale photocatalytic hydrogen generation. A more pragmatic approach involves the creation of catalyst materials free from noble metals, which possess enduring photogenerated electrons suitable for catalyzing hydrogen evolution from undiluted water. In our research, x%Bi-OZIS nanohybrids were effectively synthesized. Remarkably, the hydrogen evolution rate for the 10 %Bi-OZIS sample reached 170.22 μmol g-1h−1, marking an enhancement of 11.8 times over pure ZIS and 3.7 times over OZIS, achieved without resorting to sacrificial agents. Notably, post-light exposure, H2O2 presence was identified in the water solution. The strategy of substituting some of the sulfur with oxygen doping extends the lifespan of the photogenerated carriers. Further, the introduction of Bi spheres onto the OZIS nanosheet surfaces substantially reduces electron-hole interband recombination. These adaptations collectively augment the photogenerated electron lifespan in x%Bi-OZIS nanohybrids, leading to heightened photocatalytic redox proficiency. This research outlines a method for devising an economical solar-driven water splitting mechanism devoid of sacrificial agents.

Investigating the multiferroic properties within triphasic systems to comprehend the mechanisms of water splitting

In the present study, a triphasic-based system was prepared using constituents such as Lanthanum Calcium Manganite (LCM), Cobalt Ferrite (CF), and Barium Titanate (BT) in different proportions. The composition (1-x)LCM: x(0.7CF-0.3BT), where x = 0, 0.1, 0.2, 0.3, and 1, was employed to produce the triphasic system-based materials using a solid-state reaction technique. X-ray diffraction results confirmed the development of the triphasic phase in the composites through the JCPDS card number of the major peaks. The average crystallite size calculated from XRD data was found to vary with increasing 0.7CF-0.3BT concentration in LCM. FTIR spectroscopy indicates alterations in the main peaks with an increase in content of 0.7CF-0.3BT, suggesting the formation of triphasic composites. The upward trend in dielectric permittivity suggests the successful occurrence of Maxwell-Wagner polarization, indicating relaxor behavior at lower frequency values. Impedance spectroscopy reveals dielectric relaxation and the contribution of charge carriers in triphasic composites, along with the impact of grain and grain boundaries. Magnetization analysis at room temperature approves an increase in saturation magnetization in composites i.e., 0.7LCM-0.3(0.7CF-0.3BT) triphasic material exhibiting a maximum saturation magnetization of 13.04 emu/g. Magnetoelectric behaviour is observed in triphasic materials at different AC magnetic fields. The 0.9LCM-0.1(0.7CF-0.3BT) triphasic hydroelectric cell achieved a peak current of 1.29 mA and showed enhanced stability over time. Its I-V characteristics revealed a short-circuit current of 3.5 mA, an open-circuit voltage of 0.85 V, and an off-load power output of 2.97 mW. The triphasic system demonstrates improved structural, electrical, and hydroelectric cell (HEC) performance offering promising prospects for use in magnetoelectric and hydroelectric devices.

Strain-Induced Photocatalytic H2 Production over BiVO4 in Pure Water without Any Cocatalyst.

In this study, BiVO4 nanosheets (BiVO4-NS) were prepared by a facile hydrothermal method. It is found that sonication-induced strain can effectively promote the H2 production over BiVO4-NS in the presence of pure water without any cocatalysts. With the assistance of the sonication, the H2 production over BiVO4-NS is 1.344 mmol·g-1 after 3 h simulated sunlight irradiation, which is 24.8 times higher than that of BiVO4-NS without sonication (0.054 mmol·g-1). In addition, the products of water oxidation are determined to be hydroxyl radicals and hydrogen peroxide. Moreover, BiVO4-NS also shows obviously enhanced photoactivity than that of the commercially available BiVO4 nanoparticles (BiVO4-C). The improved photoactivity of BiVO4-NS is attributed to the effective charge separation and low charge transfer resistance. The underlying mechanism of sonication-promoted water splitting is investigated by a variety of controlled experiments. The results show that ultrasonic waves can produce obvious strain inside the sample, which results in lattice distortion of BiVO4. Therefore, the conduction band of BiVO4 is obviously negative shifted, which is beneficial for H2 production. In addition, the strain in BiVO4 also produces local polarization of the sample, which effectively promotes the charge transfer and separation process. It is hoped that our study could provide a new strategy for achieving efficient photocatalytic water splitting.

Facile synthesis of g-C3N4@porphyrin nanofiber composite via self-assembly as photoelectrode for efficient photoelectrochemical water splitting

The creation of self-assembled porphyrin nanostructures and their organised arrays has garnered significant attention, with the objective of mimicking natural light-harvesting mechanisms and energy storage, as well as pioneering novel nanostructured materials for use in photocatalytic processes. This study explored the formation of porphyrin nanofibers onto the surface of g-C3N4 via self-assembly, creating a photoelectrode with remarkable potential for efficient photoelectrochemical (PEC) water splitting. By integrating these two distinct materials, the resultant hybrid structure leverages the unique properties of both components, enhancing the overall performance of the photoelectrochemical system. The fabrication process involves acid-base neutralization-induced self-assembly, leading to the formation of a well-distributed composite. The resulting photoelectrode exhibits improved charge separation and enhanced light absorption properties. Experimental analyses, encompassing techniques such as scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and photocurrent measurements, validate the successful integration of the hybrid material and its notable photocatalytic efficiency. The porphyrin nanofiber was evenly distributed over the surface of the generated g-C3N4@porphyrin hybrid material. The photoelectrochemical measurements showed a remarkable enhancement in the photocurrent when using g-C3N4@porphyrin photoelectrode in the light-irradiating condition compared to the dark condition. The possible PEC water-splitting mechanism by g-C3N4@porphyrin photoelectrode was also proposed and discussed. This work showcases a promising avenue for advancing the field of photoelectrochemical water splitting through innovative material design and assembly strategies.

Pivotal role of water vapor–mediated defect engineering on SrTiO3 nanofiber toward efficient photocatalytic water splitting

The oxygen vacancies (OVs) have played key roles as either charge carrier traps for inhibiting recombination or directly as active sites for photocatalytic redox reactions. In this study, the population and types of oxygen vacancies within the electrospun SrTiO3 nanofibers were modulated through water vapor and air atmosphere annealing respectively. Combining the distinctive 1D nanofibrous structure with optimized OVs, the water vapor–mediated OVs-rich SrTiO3 nanofibers achieved a significant enhancement in specific surface area and porosity, effectively suppressing the recombination of photogenerated carriers. The OVs can effectively promote the conversion of photon excitons into charge carriers, accelerate the carrier separation, and facilitate surface redox reaction. The optimized water vapor–mediated STO-W-700 exhibited abundant active sites and rapid surface charge separation/migration across the nanofibers, leading to an exceptional hydrogen production performance of 296.82 μmolg/h. During the photocatalytic process, the OVs act synergistically with nearby metal sites to optimize the adsorption energy of reactants. This work not only provides an effective pathway for manipulating oxygen vacancies through water vapor–mediated defect engineering strategy, but also reveals a new water splitting mechanism, laying the foundation for further research and development of efficient solar energy conversion technologies.

Deactivation mechanism for water splitting: Recent advances

AbstractHydrogen (H2) has been regarded as a promising alternative to fossil‐fuel energy. Green H2 produced via water electrolysis (WE) powered by renewable energy could achieve a zero‐carbon footprint. Considerable attention has been focused on developing highly active catalysts to facilitate the reaction kinetics and improve the energy efficiency of WE. However, the stability of the electrocatalysts hampers the commercial viability of WE. Few studies have elucidated the origin of catalyst degradation. In this review, we first discuss the WE mechanism, including anodic oxygen evolution reaction (OER) and cathodic hydrogen evolution reaction (HER). Then, we provide strategies used to enhance the stability of electrocatalysts. After that, the deactivation mechanisms of the typical commercialized HER and OER catalysts, including Pt, Ni, RuO2, and IrO2, are summarized. Finally, the influence of fluctuating energy on catalyst degradation is highlighted and in situ characterization methodologies for understanding the dynamic deactivation processes are described.

Superior photoelectrodes of nanostructured Mo-doped CuO thin film for green hydrogen generation from photoelectrochemical water-splitting

Green hydrogen has an audible echo in the clean energy field. In this piece of work, pure and Mo-doped CuO thin films were deposited at different substrate temperatures on the Indium Tin Oxide (ITO) by the DC/RF sputtering technique. The prepared samples were utilized to generate hydrogen gas within the photoelectrochemical water-splitting mechanism. Crystallographic planes (−111), and (200) were the preferred orientations for pure and Mo-doped CuO thin films. Moreover, the average crystallite size was doubled by Mo doping reaching 25.8 nm. FE-SEM microscopic image exhibits that the pure and Mo–CuO thin films have a regular distribution with a small size. The optical band gap has rosed by doping from 1.8 eV to 2.05 eV. Then, it increased to 2.3 eV and 2.4 eV at temperatures of 100 °C and 200 °C respectively. Pure and Mo–CuO thin films were applied as photocathodes for hydrogen generation with water water-splitting technique. The photoelectrochemical application revealed a photocurrent density of ∼2.25 mA/cm2 for Mo-doped CuO photoelectrode at room temperature. This optimum photoelectrode was studied for stability and electrochemical impedance. In addition, the incident photon to current efficiency (IPCE%) was 4.47 % at 500 nm. The applied bias photon to current conversion efficiency (ABPE%) was 4.25 % at −0.38V. As a result of the above, pure and Mo-doped CuO photoelectrodes are low-cost thin films and have a high-efficiency performance for green hydrogen generation industrially.

Subtle 2D/2D MXene-Based Heterostructures for High-Performance Electrocatalytic Water Splitting.

Developing efficient electrocatalysts is significant for the commercial application of electrocatalytic water splitting. 2D materials have presented great prospects in electrocatalysis for their high surface-to-volume ratio and tunable electronic properties. Particularly, MXene emerges as one of the most promising candidates for electrocatalysts, exhibiting unique advantages of hydrophilicity, outstanding conductivity, and exceptional stability. However, it suffers from lacking catalytic active sites, poor oxidation resistance, and easy stacking, leading to a significant suppression of the catalytic performance. Combining MXene with other 2D materials is an effective way to tackle the aforementioned drawbacks. In this review, the focus is on the accurate synthesis of 2D/2D MXene-based catalysts toward electrocatalytic water splitting. First, the mechanisms of electrocatalytic water splitting and the relative properties and preparation methods of MXenes are introduced to offer the basis for accurate synthesis of 2D/2D MXene-based catalysts. Then, the accurate synthesis methods for various categories of 2D/2D MXene-based catalysts, such as wet-chemical, phase-transformation, electrodeposition, etc., are systematically elaborated. Furthermore, in-depth investigations are conducted into the internal interactions and structure-performance relationship of 2D/2D MXene-based catalysts. Finally, the current challenges and future opportunities are proposed for the development of 2D/2D MXene-based catalysts, aiming to enlighten these promising nanomaterials for electrocatalytic water splitting.

Recent advances in the role of MXene based hybrid architectures as electrocatalysts for water splitting.

The development of non-noble metal based and cost-effective electrocatalysts for water splitting has attracted significant attention due to their potential in production of clean and green hydrogen fuel. Discovered in 2011, a family of two-dimensional transition metal carbides, nitrides, and carbonitrides, have demonstrated promising performance as electro catalysts in the water splitting process due to their high electrical conductivity, very large surface area and abundant catalytic active sites. However, their-long term stability and recyclability are limited due to restacking and agglomeration of MXene flakes. This problem can be solved by combining MXene with other materials to create their hybrid architectures which have demonstrated higher electrocatalytic performance than pristine MXenes. Electrolysis of water encompasses two half-cell reactions, hydrogen evolution reaction (HER) at the cathode and oxygen evolution reaction (OER) at the anode. Firstly, this concise review explains the mechanism of water splitting. Then it provides an overview of the recent advances about applications of MXenes and their hybrid architectures as HER, OER and bifunctional electrocatalysts for overall water splitting. Finally, the recent challenges and potential outlook in the field have been presented. This concise review may provide further understanding about the role of MXene-based hybrid architectures to develop efficient electrocatalysts for water splitting.

Photocatalytic nanomaterials and their implications towards biomass conversion for renewable chemical and fuel production.

Photocatalytic processes have recently gained popularity as a sustainable and energy-efficient method for converting biomass. This article gives a comprehensive overview of recent improvements in the photocatalytic conversion of biomass into useful chemicals and fuels utilizing various photocatalytic materials. The work delves into the assessment of diverse biomass sources and their preparation techniques, in addition to the synthesis of plasmonic nanoparticles as photocatalysts from biomass, offering a thorough examination. This review article provides detailed techniques for fabricating and synthesizing plasmonic nanoparticles. Furthermore, the study discusses advancements in coupling photo-oxidation alongside the hydrogen evolution mechanism for water splitting. Furthermore, prospective research topics are suggested, such as conducting a systematic analysis of photocatalysis's redox potential, developing more effective catalysts, broadening the variety of reaction types, and establishing industrial-scale photocatalytic production. Plasmonic photocatalysts have been utilized to convert biomass into H2 for energy, and to explore hypothesized molecular routes for the photocatalytic oxidation of 5-hydroxymethylfurfural (HMF), which may then be converted into 2,5-furandicarboxylic acid (FDCA). This review also discusses the surface functionalization of nanophotocatalysts with -COOH, NH2, and OH groups to increase their reactivity. Reactive oxygen species (ROS) formed on the surface of nanophotocatalysts under UV or solar light play a crucial role in photocatalytic reactions. Our review has shown many challenges and difficulties related to CO2 hydrogenation reactions in the presence of sustainable H2, powered by renewable energy sources. This is very critical for achieving a transition to net-zero emissions. These technologies will drive forward the development of biomass conversion processes into CO2-based fuels. This paper explores recent advancements in the conversion of biomass-derived CO2 into valuable chemicals using plasmonic nanophotocatalysts. In addition to this, density functional theory (DFT) calculations also reveal how functional groups help stabilize these nanoparticles and enhance electron density through photo-adsorption. This study provides a remarkable and significant review that examines current trends, future directions, and ongoing debates in this field, focusing on reaction conditions, catalyst design, and proposed mechanisms for producing valuable chemicals. These chemicals include single-carbon compounds like formaldehyde, formic acid, and methanol, as well as C2 + compounds such as acetic acid, ethanol, methyl formate, and oxyethylene ethers. Additionally, it addresses the current state of liquid-phase CO2 hydrogenation in the presence of photocatalysts, highlighting existing challenges and potential research paths. The paper also provides an overview of the advances and challenges in the electro- and photocatalytic oxidation of HMF (hydroxymethylfurfural), detailing strategies for creating high-value chemicals through these oxidation processes. These methods, which may involve reactions like the hydrogen evolution reaction, organic substrate reduction, CO2 reduction reaction, or N2 reduction reaction, are summarized and analyzed. Furthermore, the catalytic efficiency and mechanisms of various catalyst types in these conversion systems are introduced and discussed. Electron paramagnetic resonance and scavenger studies reveal the major active species (˙OH and ˙O2 -) in the photocatalytic conversion of biomass to different value-added products.

Synthesis of highly efficient (Cr, Gd) co-doped CdS quantum dots for photocatalytic H2 evolution beneath artificial solar light irradiation

To meet the future energy demand, the design, and development of novel, economical with efficient hydrogen (H2) fuel production rate and more stable photocatalytic material are most crucial and necessary. Numerous sunlight-active semiconductor nanostructures have been materialized for photocatalytic reactions towards hydrogen evolution. Nevertheless, their reliable application has been restricted through less photocatalytic efficiency and less stability provoked by the recombination of charge carriers. In the direction of to minimize the recombination rate among the charge carriers and enhance photocatalytic water splitting mechanism towards hydrogen evolution Co-doping of transition and rare earth elements to the host lattice is a promising strategy in functional material engineering to minimize the recombination rate among the charge carriers and enhance the photocatalytic water splitting mechanism towards hydrogen evaluation. In this view, herein, the chemical synthesis, structural, optical, and photocatalytic characteristics of pristine CdS, CdS:Cr (1 at%), CdS: (Cr, Gd (1 at%)) and CdS: (Cr, Gd (2 at%)) quantum dots for competent photocatalytic H2 fuel evolution. Furthermore, the rate of H2 of CdS: (Cr, Gd (2 at%)) quantum dots is almost 23 times greater than that of pristine CdS quantum dots with more stability. Hence, we strongly believe that, CdS: (Cr, Gd (2 at%)) quantum dots are reliable and potential semiconductor compounds for efficient photocatalytic hydrogen evolution for environmental purification.

Controllable synthesis of crystal-amorphous heterostructures in transition metal phosphide and enhancement mechanism for overall water splitting

The crystal-amorphous (c-a) heterostructure is a promising structure for electrocatalysts in water electrolysis. In this study, stable, efficient, and abundant c-a interfaces were formed by synchronously synthesizing crystalline FeP and amorphous MoP on foam ferrum by controlling the crystalline phase transition temperature. In 1 M KOH, the a-MoP/FeP@FF catalyst showed overpotentials of 75 mV and 253 mV for HER and OER processes, respectively, at a current density of j10. The Tafel slopes were small at 60 mV∙dec−1 and 77 mV∙dec−1 for HER and OER, respectively. Theoretical calculations indicate that the c-a interface optimizes the overall electronic structure, enabling Mo and Fe to have excellent HER and OER activity, respectively. The two types of active sites collaborate fully to promote overall water splitting. This study confirms that the c-a heterostructure can significantly enhance the catalytic performance of transition metal phosphides and explains the mechanism of enhanced catalytic activity. This synthesis method and reaction mechanism not only apply to other transition metal phosphides but also provide reference for other types of catalysts.

Mo-doped one-dimensional needle-like Ni3S2 as bifunctional electrocatalyst for efficient alkaline hydrogen evolution and overall-water-splitting

Hydrogen energy plays an important role in clean energy system and is considered the core energy source for future technological development owing to its lightweight nature, high calorific value, and clean combustion products. The electrocatalytic conversion of water into hydrogen is considered a highly promising method. An electrocatalyst is indispensable in the electrocatalytic process, and finding an efficient electrocatalyst is essential. However, the current commercial electrocatalysts (such as Pt/C and Ru) are expensive; therefore, there is a need to find an inexpensive and efficient electrocatalyst with high stability, corrosion resistance, and high electrocatalytic efficiency. In this study, we developed a cost-effective bifunctional electrocatalyst by incorporating molybdenum into nickel sulfide (Ni3S2) and subsequently tailoring its structure to achieve a one-dimensional (1D) needle-like configuration. The hydrogen production efficiency of nickel sulfide was improved by changing the ratio of Mo doping. By analyzing the electrochemical performance of different Mo-doped catalysts, we found that the Ni3S2-Mo-0.1 electrocatalyst exhibited the best electrocatalytic effect in 1 M KOH; at a current density of 10 mA cm−2, it exhibited overpotentials of 120 and 279 mV for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively; at a higher current density of 100 mA cm−2, the HER and OER overpotentials were 396 and 495 mV, respectively. Furthermore, this electrocatalyst can be used in a two-electrode water-splitting system. Finally, we thoroughly investigated the mechanism of the overall water splitting of this electrocatalyst, providing valuable insights for future hydrogen production via overall-water-splitting.

Mechanism of water splitting based on NiCoP bonded by carbon quantum dots

Mechanism of water splitting based on NiCoP bonded by carbon quantum dots

Synthesis and testing of NixZn1-xFe2O4/CNTs photoresponsive magnetic composite catalysts for hydrogen generation from water splitting

The world is facing environmental pollution and energy shortage challenges due to the enormous wastage of organic pollutants by industries and the rapid growth of the human population. Photocatalysis has been reported as an efficient technology to mitigate these two emerging issues. This study investigated heterojunction photocatalysts based on NixZn1-xFe2O4/CNTs for enhanced H2 production from water splitting. The role of CNTs in accepting electrons during redox reactions, improving the photocatalytic activity and stability of NiZnFe2O4, and reducing the recombination of charge carriers is also elaborated in this study. The synthesized NixZn1-xFe2O4/CNTs composites were characterized using several methods, including SEM, EDX, FTIR, XRD, and UV–Vis-DRS to examine their magnetic electrical, opto-physical, and photocatalytic activity. The maximum hydrogen evolution rate of 4550 μmolh−1g−1 was observed using N0.4Z0.6FC0.3, which is 5 and 2.3 times greater than that of NZF and Ni0.1Zn0.9FC0.3 catalysts, respectively. The successive cycles of hydrogen production using N0.4Z0.6FC0.3 showed strong stability and reusability of this catalyst. The photocatalytic mechanism of water splitting using NixZn1-xFe2O4/CNTs photocatalysts is also deduced in this study.

Unveiling the Oxygen Evolution Mechanism with FeNi (Hydr)oxide under Neutral Conditions.

Large-scale solar-driven water splitting is a way to store energy, but it requires the development of practical and durable oxygen evolution reaction (OER) catalysts. The present paper aims to investigate the mechanism of the OER, local pH, high-valent metal ions, limitations, conversions, and details during the OER in the presence of FeNi foam using in situ surface-enhanced Raman spectroscopy. This research also explores the use of in situ surface-enhanced Raman spectroscopy for detecting species on foam surfaces during the OER. The acidic media around the electrode not only limit the process but also affect the phosphate ion protonation and overall catalysis effectiveness. The study proposes that FeNi hydroxides serve as true catalysts for OER under neutral conditions, rather than FeNi phosphates. However, phosphate species remain crucial for proton transfer and water molecule adsorption. Changes observed in pH at the open-circuit potential suggest new insights concerning the coordination of Ni(II) to phosphate ions under certain conditions. By extrapolating the Tafel plot, the overpotential for the onset of OER was determined to be 470 mV. Furthermore, the overpotentials for current densities of 1 and 5 mA/cm2 were 590 and 790 mV, respectively. These findings offer valuable insights into the advancement of the OER catalysts and our understanding of the underlying mechanism for efficient water splitting; both are crucial elements for the purpose of energy storage.

Revealing the electrocatalytic mechanism of layered crystalline CoMoO4 for water splitting: A theoretical study from facet selecting to active site engineering

Deciphering the atomic-level properties and mechanism of electrocatalysts for water splitting is vital for the development of highly active non-noble-metal catalysts. Herein, we conduct a detailed study of layered crystalline CoMoO4 using density functional theory (DFT) calculations. The layered arrangement of CoMoO4 along the [110] lattice direction is observed, and the two thermodynamically stable and most exposed (110)A and (001)A crystal facets are selected among all low-index facets by surface energy calculations and Wulff construction to study the electrocatalytic activity for alkaline water splitting and corresponding mechanism. CoMoO4 with an exposed (110)A facet (i.e., CMO (110)A) exhibited a high hydrogen evolution reaction (HER) activity, with a ΔGH* of 0.22 eV, which is similar to that of Pt because the adsorbed H is allowed to interact with two oxygen atoms (O3 and Oadj). The (110)A facet also possesses better H2O adsorption and dissociation abilities than the (001)A facet, benefiting the HER performance in alkaline solutions. Moreover, the overpotential of the (110)A facet for the electrocatalytic oxygen evolution reaction (OER) is only 0.74 V according to the Gibbs free-energy calculation, this overpotential is lower than that of the (001)A facet (0.84 V) owing to the stronger binding and more stable adsorption states between Co and O for the intermediate *O. By allowing us to identify highly active facets and sites, this approach guided the selective synthesis of CoMoO4 and its isostructural substances, such as Mn(Ni, Fe)MoO4 nanocatalysts, for alkaline water splitting.

Bismuth-based nanomaterials-assisted photocatalytic water splitting for sustainable hydrogen production

The rapidly increase in the world's population has resulted in a corresponding increase in the energy demand. This demand is largely being met by fossil fuels for power generation, industrial fuel and transportation. However, due to the limited availability of fossil fuels and their negative effects on the environment. The use of fossil fuels results in by-products such as carbon, nitrogen and sulfur oxides which have negative impacts on the environment. Therefore. There is an urgent need to develop alternative greener energy sources that are sustainable and have minimal environmental impacts. Hydrogen is one such alternative energy source of attention. Harvesting sunlight through the use of solar panels is already being employed at domestic and commercial levels. Photocatalytic water splitting, which aims to produce hydrogen by utilizing unlimited sources including water and sunlight, is another potential process for alternative energy production. The conversion of water into hydrogen and oxygen through sunlight is an innovative process that directly converts sunlight into chemical energy in the form of hydrogen and oxygen via photocatalytic water splitting. Numerous photocatalytic materials are available for photocatalytic hydrogen production, but bismuth-based materials are the most suitable as they are non-toxic, economical, opto-electronically active, have suitable band positions for photocatalysis, and exhibit excellent photo-stability.To provide summary of latest research in the field of photocatalytic water splitting, a comprehensive review is favorable to suggest future research directions aimed at discovering solutions to current challenges. This review emphasizes the need for alternative energy sources and the competitiveness of photocatalytic water splitting for hydrogen production. The mechanism and thermodynamics of the photocatalytic water splitting have been discussed, along with the properties of an ideal photocatalyst for photocatalytic hydrogen production with a special focus on the bismuth-based photocatalysts. The optimization of synthetic and photocatalytic processes is crucial for commercial use with much improved hydrogen production in terms of cost and quantity without harming environment at any stage. Furthermore, current challenges and future perspectives have been presented for upcoming research in this domain.

Research Progress of ZnIn2S4-Based Catalysts for Photocatalytic Overall Water Splitting

Photocatalytic overall water splitting in solar–chemical energy conversion can effectively mitigate environmental pollution and resource depletion. Stable ternary metal indium zinc sulfide (ZnIn2S4) is considered one of the ideal materials for photocatalytic overall water splitting due to its unique electronic and optical properties, as well as suitable conduction and valence band positions for suitable photocatalytic overall water splitting, and it has attracted widespread researcher interest. Herein, we first briefly describe the mechanism of photocatalytic overall water splitting, and then introduce the properties of ZnIn2S4 including crystal structure, energy band structure, as well as the main synthetic methods and morphology. Subsequently, we systematically summarize the research progress of ZnIn2S4-based photocatalysts to achieve overall water splitting through modification methods such as defect engineering, heterostructure construction, and co-catalyst loading. Finally, we provide insights into the prospects and challenges for the overall water splitting of ZnIn2S4-based photocatalysts.

Impact of carbon nanotubes concentrations on the performance of carbon nanotubes/zinc oxide nanocomposite for photoelectrochemical water splitting

Under the influence of visible light, the photoelectrochemical (PEC) method of water splitting offers a green method for producing sustainable hydrogen. In this work, several volume ratios of carbon nanotubes (CNTs) were incorporated in the zinc oxide (ZnO) matrix to prepare ZnO/CNTs nanocomposites on a glass substrate as photoelectrodes for hydrogen production. These electrodes were synthesized via the spray pyrolysis technique and chemical vapor deposition. Various approaches were used to analyze the chemical composition, crystal structure, morphology, and optical properties of pure ZnO and ZnO/CNTs nanocomposites. The structural properties showed that crystallite size is decreased from 44.2 nm to 36.8 nm, and the optical shows that the energy bandgap (Eg) enhanced from 3.07 to 2.87 eV for pure ZnO and the optimum sample of ZnO/7 mL CNTs nanocomposite, respectively. The maximum photocurrent density (Jph) was found for the 7 mL CNTs among the produced ZnO/X CNTs nanostructures. The value of Jph for ZnO/7 mL CNTs (200.7 µA/cm2) is around 33 times greater compared with pure ZnO (6.96 µA/cm2). At 490 nm, the incident photon-to-current efficiency (IPCE) of ZnO/7 mL CNTs is roughly 9.85 %. The ZnO/CNTs photoelectrode showed a hydrogen evolution rate of 4.34 mmole/h.cm2. The improved photoelectrode additionally exhibits strong chemical stability and a lengthy lifetime under visible light without photo-corrosion. Finally, the electrochemical impedance spectroscopy and the PEC water-splitting mechanism for ZnO/CNTs were discussed. This study presents a simple method that enables the fabrication of inexpensive and efficient ZnO/CNTs photoelectrode for renewable energy applications.