Search

Developing electrode materials with improved catalytic activity is inevitable (i) to achieve efficient electro-catalytic water splitting (EWS) and (ii) to construct high performance dye sensitized solar cells (DSSCs). To this aim, Nitrogen (N)-doped carbon-wrapped bimetallic CoCu alloys (i.e, CN@CoCu) are prepared by directly annealing the Cu-loaded Zeolitic Imidazolate Framework-67 (ZIF-67) metal-organic framework (MOF) and employed as (i) working electrode in EWS and (ii) counter electrode (CE) in DSSCs. The ZIF-67 MOF acts as a self-sacrificing template for the formation of CN@CoCu electrodes, whose electro-catalytic activity can be optimized by tuning the Co/Cu molar ratio (Cu = 0, 5%, 10%, 15% and 20%). The addition of 15% of Cu into the ZIF-67 (i.e., CN@CoCu-15), as the working electrode in water splitting has achieved lowest overpotential values of 91 and 256 mV towards hydrogen evolution reaction and oxygen evolution reaction, respectively. Also, for DSSCs applications, the same CN@CoCu-15 sample as CE displays an improved catalytic activity by 21% higher than that of conventional Pt CE towards tri-iodide redox reaction. Consequently, the CN@CoCu-15 based DSSCs device has achieved a PCE of 7.10% which is larger than that of conventional platinum CE (6.69%). The mechanism behind the improved catalytic activity is attributed to the significant reduction in the work function of CN@CoCu-15 (4.82 eV) compared to CN@Co (5.2 eV), as evidenced from Kelvin Probe Force Microscopic analysis. These findings proposed an efficient bifunctional electro-catalytic material with improved water-splitting performance and solar energy conversion. [Display omitted] • Carbon-wrapped CoCu electrode is prepared for water splitting and DSSC application. • The work function of the electrocatalyst is minimum (4.87) when Co/Cu ratio is 15. • It displays excellent catalytic activity towards KOH and triiodide electrolyte. • Water splitting has been achieved at 1.53 V with prepared CN@CoCu-15. • In DSSC, a PCE of 7.10 % is achieved with prepared CN@CoCu-15 as counter electrode. [ABSTRACT FROM AUTHOR]

Electrochemical water splitting is a promising approach towards a sustainable and renewable energy source. However, the demand for high anodic potential and sluggish kinetics of oxygen evolution reaction (OER) restrict the efficiency and feasibility of the water-splitting process. In this quest, transition metal oxides and alloys are considered potential candidates owing to their natural occurrence and high redox potential for OER. However, many associated challenges in their use are still there to be addressed. Here, we designed a new class of bismuth-doped iron oxide on exfoliated graphene oxide by optimizing the metal loading on the conductive support to facilitate the flow of charge during catalysis. The catalytic ability of the synthesized Bi-doped nanocomposites was evaluated in activating the OER under extreme alkaline conditions (1 MKOH). On screening different combinations, 20Bi–Fe2O3@GO was identified as the most efficient and sustainable electrocatalyst even under harsh operating conditions, with an onset potential of 1.48 V and a Tafel slope of 65 mV/dec. The current study offers a new class of Bi-doped electrocatalysts, where the precise doping of Bi and the optimized loading of metal was found the key to achieving low onset potential and high current density to initiate OER. [ABSTRACT FROM AUTHOR]

Two novel metal‐free organic dyes, namely the mono‐anchoring KMT1 and di‐anchoring KMT2 dyes, have been synthesized to function as photosensitizers for utilizing in photocatalytic hydrogen production systems. They adopt the donor‐donor‐π‐acceptor and donor‐donor‐(−π‐acceptor)2 configurations, respectively, featuring triphenylamine and fluorene moieties as electron donors, thiophene as the π‐bridges and cyanoacrylic acid as the acceptors/anchoring groups. It was found that the photocatalytic performance of the di‐anchoring dye significantly outperforms that of its mono‐anchoring counterpart. KMT2‐based photocatalytic system demonstrated remarkable performance, producing 3520 μmol (84.9 mL) of hydrogen over a span of 257 hours under blue light irradiation, with a turnover number (TON) of 56300, a turnover frequency (TOFi) of 1862.7 h−1, an initial hydrogen production activity (activityi) of 1164180 and an apparent quantum yield (AQYi %) of 19.9. This performance is among the top‐tier when compared to other dyes used in similar photocatalytic systems. The results clearly illustrate that the di‐anchoring dye possesses several advantages, including a broad absorption spectrum, higher absorptivity, and a relatively slower charge recombination rate. These attributes collectively contribute to its superior overall performance in photocatalysis. [ABSTRACT FROM AUTHOR]

The growing global population needs energy from clean and renewable resources to meet present and future demands. Ideally, green hydrogen is commonly considered the key to overcoming the energy problem and the future energy standard. One of the most promising technologies for the development of the hydrogen economy is electrolysis water splitting (WS) hydrogen (H 2) production; nevertheless, developing highly efficient environmentally sustainable electrocatalysts remains a serious issue for this technology. Transition metals (TMs) have achieved substantial progress in recent years, as a structural-based electrocatalyst developing especially noteworthy attention for the hydrogen evolution process (HER). These features have been proven to constitute the perfect electrocatalyst due to their advantages such as low cost, efficiency, stability, a large number of active sites, and great surface. This comprehensive review explains TMs-based chalcogenides and particular structural arrangements of multi-dimensional (1D, 2D, and 3D) electrocatalysts on different substrates for WS hydrogen production. The reaction process, the importance of the electrocatalyst, the advantages of the structural materials, and the efficiency that fluctuates with phase dimensions, have been investigated. Finally, the present issues and prospects of structural materials for WS were investigated in terms of HER and the perspective of this field was presented. [Display omitted] • Review of recent trends in electrochemical water splitting-H 2 Production using Transition Metals (TMs). • Role of different functional groups, morphology (1D, 2D & 3D) on electrochemical water splitting. • Design strategies for constructing TMs/nanostructures. • Comparing different catalyst architectures for optimal HER efficiency. [ABSTRACT FROM AUTHOR]

The design and application of semiconductor-based photocatalytic technology has a significant impact on addressing the world's energy crisis and environmental degradation by transforming solar energy into chemicals and fuels. Semiconductor-based photocatalyst, ceria (CeO2), which possesses unique 4f electrons, is superior to other metal oxide semiconductors owing to its defect-rich structure, multivalence state, surface oxygen vacancy, photostability, and eco-friendly properties. This critical review is taken up to report the basic mechanistic details of CeO2-based photocatalysis as well as several methods for boosting the activity and stability of this group of photocatalysts. Additionally, numerous photocatalytic applications of CeO2, such as H2 generation by water splitting and CO2 reduction to alcohols and hydrocarbon fuels, are introduced and summarized. In the end, a concise summary of the challenges and potential areas for future research in the synthesis of CeO2-based photocatalysts are also provided. This review is anticipated to provide directions for developing innovative CeO2-based photocatalysts with low-cost and high efficiency, which have the promising application possibilities to fulfill the pressing needs of alternative fuels. Graphical Abtract: [ABSTRACT FROM AUTHOR]

Climatic changes are reaching alarming levels globally, seriously impacting the environment. To address this environmental crisis and achieve carbon neutrality, transitioning to hydrogen energy is crucial. Hydrogen is a clean energy source that produces no carbon emissions, making it essential in the technological era for meeting energy needs while reducing environmental pollution. Abundant in nature as water and hydrocarbons, hydrogen must be converted into a usable form for practical applications. Various techniques are employed to generate hydrogen from water, with solar hydrogen production—using solar light to split water—standing out as a cost-effective and environmentally friendly approach. However, the widespread adoption of hydrogen energy is challenged by transportation and storage issues, as it requires compressed and liquefied gas storage tanks. Solid hydrogen storage offers a promising solution, providing an effective and low-cost method for storing and releasing hydrogen. Solar hydrogen generation by water splitting is more efficient than other methods, as it uses self-generated power. Similarly, solid storage of hydrogen is also attractive in many ways, including efficiency and cost-effectiveness. This can be achieved through chemical adsorption in materials such as hydrides and other forms. These methods seem to be costly initially, but once the materials and methods are established, they will become more attractive considering rising fuel prices, depletion of fossil fuel resources, and advancements in science and technology. Solid oxide fuel cells (SOFCs) are highly efficient for converting hydrogen into electrical energy, producing clean electricity with no emissions. If proper materials and methods are established for solar hydrogen generation and solid hydrogen storage under ambient conditions, solar light used for hydrogen generation and utilization via solid oxide fuel cells (SOFCs) will be an efficient, safe, and cost-effective technique. With the ongoing development in materials for solar hydrogen generation and solid storage techniques, this method is expected to soon become more feasible and cost-effective. This review comprehensively consolidates research on solar hydrogen generation and solid hydrogen storage, focusing on global standards such as 6.5 wt% gravimetric capacity at temperatures between −40 and 60 °C. It summarizes various materials used for efficient hydrogen generation through water splitting and solid storage, and discusses current challenges in hydrogen generation and storage. This includes material selection, and the structural and chemical modifications needed for optimal performance and potential applications. [ABSTRACT FROM AUTHOR]

Abstract Electrochemical water splitting is a promising approach towards a sustainable and renewable energy source. However, the demand for high anodic potential and sluggish kinetics of oxygen evolution reaction (OER) restrict the efficiency and feasibility of the water-splitting process. In this quest, transition metal oxides and alloys are considered potential candidates owing to their natural occurrence and high redox potential for OER. However, many associated challenges in their use are still there to be addressed. Here, we designed a new class of bismuth-doped iron oxide on exfoliated graphene oxide by optimizing the metal loading on the conductive support to facilitate the flow of charge during catalysis. The catalytic ability of the synthesized Bi-doped nanocomposites was evaluated in activating the OER under extreme alkaline conditions (1 MKOH). On screening different combinations, 20Bi–Fe2O3@GO was identified as the most efficient and sustainable electrocatalyst even under harsh operating conditions, with an onset potential of 1.48 V and a Tafel slope of 65 mV/dec. The current study offers a new class of Bi-doped electrocatalysts, where the precise doping of Bi and the optimized loading of metal was found the key to achieving low onset potential and high current density to initiate OER. Graphical abstract

The water oxidation reaction in photosystem II (PS II) produces most of the molecular oxygen in the atmosphere, which sustains life on Earth, and in this process releases four electrons and four protons that drive the downstream process of CO2 fixation in the photosynthetic apparatus. The catalytic center of PS II is an oxygen-bridged Mn4Ca complex (Mn4CaO5) which is progressively oxidized upon the absorption of light by the chlorophyll of the PS II reaction center, and the accumulation of four oxidative equivalents in the catalytic center results in the oxidation of two waters to dioxygen in the last step. The recent emergence of X-ray free-electron lasers (XFELs) with intense femtosecond X-ray pulses has opened up opportunities to visualize this reaction in PS II as it proceeds through the catalytic cycle. In this review, we summarize our recent studies of the catalytic reaction in PS II by following the structural changes along the reaction pathway via room-temperature X-ray crystallography using XFELs. The evolution of the electron density changes at the Mn complex reveals notable structural changes, including the insertion of OX from a new water molecule, which disappears on completion of the reaction, implicating it in the O-O bond formation reaction. We were also able to follow the structural dynamics of the protein coordinating with the catalytic complex and of channels within the protein that are important for substrate and product transport, revealing well orchestrated conformational changes in response to the electronic changes at the Mn4Ca cluster.

Accessible and superior electrocatalysts to overcome the sluggish oxygen evolution reaction (OER) are pivotal for sustainable and low-cost hydrogen production through electrocatalytic water splitting. The iron and nickel oxohydroxide complexes are regarded as the most promising OER electrocatalyst attributed to their inexpensive costs, easy preparation, and robust stability. In particular, the Fe-doped NiOOH is widely deemed to be superior constituents for OER in an alkaline environment. However, the facile construction of robust Fe-doped NiOOH electrocatalysts is still a great challenge. Herein, we report the facile construction of Fe-doped NiOOH on Ni(OH)2 hierarchical nanosheet arrays grown on nickel foam (FeNi@NiA) as efficient OER electrocatalysts through a facile in-situ electrochemical activation of FeNi-based Prussian blue analogues (PBA) derived from Ni(OH)2. The resultant FeNi@NiA heterostructure shows high intrinsic activity for OER due to the modulation of the overall electronic energy state and the electrical conductivity. Importantly, the electrochemical measurement revealed that FeNi@NiA exhibits a low overpotential of 240 mV at 10 mA/cm2 with a small Tafel slope of 62 mV dec−1 in 1.0 M KOH, outperforming the commercial RuO2 electrocatalysts for OER. [ABSTRACT FROM AUTHOR]

Photocatalytic water splitting is a cheap, clean and attractive hydrogen production method. In this study, using first-principles calculations, we design and demonstrate two-dimensional (2D) transition metal-doped MoSi 2 N 4 (TM-MoSi 2 N 4 , TM = Ge, Sn, W) materials as high-performance photocatalyst, which has high carrier mobility, optical absorption properties and solar-to-hydrogen (STH) efficiency. MoSi 2 N 4 was successfully synthesized experimentally [Hong et al., Science, 2020] and our results affirms the good stability of TM-MoSi 2 N 4 materials. Furthermore, we aim to demonstrate appropriate band alignment that facilitates the redox potential required for water splitting, enables efficient charge separation of photogenerated electron-hole pairs, promotes effective optical absorption, and supports high solar-to-hydrogen (STH) conversion efficiency. Last but not least, we reveal that the TM heteroatom doping can enhance the photocatalytic activity towards hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Especially, the Sn–MoSi 2 N 4 material provides an optimal hydrogen adsorption Gibbs free energy (ΔG H*) value of −0.02eV. Our work suggests that TM-MoSi 2 N 4 materials are superior photocatalysts for water splitting, which can be employed with low cost and high performance. [Display omitted] • First-principles calculations of the photocatalytic water decomposition. • It has high STH conversion efficiency and charge carrier mobility. • Metal doping can alter its photocatalytic activity. • Sn–MoSi 2 N 4 provides an optimal hydrogen adsorption Gibbs free energy (ΔG H*) value of −0.02eV. [ABSTRACT FROM AUTHOR]

A Z-scheme heterojunction photo(electro)catalyst was fabricated by coupling sulfonic acid-modified graphitic carbon nitride (SA-g-CN) with bismuth oxyiodide (BiOI). The SA-g-CN component was prepared via wet-impregnation, while BiOI was synthesized through a hydrothermal method. Comprehensive characterization elucidated the structural and morphological properties of the resulting composite. The SA-g-CN/BiOI exhibited exceptional performance in both photocatalytic degradation of tartrazine (TTZ) and photoelectrochemical oxygen evolution reaction (OER). Notably, 98.26% TTZ removal was achieved within 60 min of irradiation, while an OER onset potential of 0.94 V (vs. Ag/AgCl) and a high photocurrent density of 6.04 mA were recorded under AM 1.5G illumination. Band energy calculations based on Mott–Schottky measurements confirmed the formation of a Z-scheme heterojunction, which facilitated efficient charge separation and transfer, thereby enhancing catalytic activity. These findings establish the SA-g-CN/BiOI composite as a promising candidate for sustainable energy generation and environmental remediation applications. [ABSTRACT FROM AUTHOR]

The advancement of a sustainable and scalable catalyst for hydrogen production is crucial for the future of the hydrogen economy. Electrochemical water splitting stands out as a promising pathway for sustainable hydrogen production. However, the development of Pt‐free electrocatalysts that match the energy efficiency of Pt while remaining economical poses a significant challenge. This review addresses this challenge by highlighting latest breakthroughs in Pt‐free catalysts for the hydrogen evolution reaction (HER). Specifically, we delve into the catalytic performance of various transition metal phosphides, metal carbides, metal sulphides, and metal nitrides toward HER. Our discussion emphasizes strategies for enhancing catalytic performance and explores the relationship between structural composition and the performance of different electrocatalysts. Through this comprehensive review, we aim to provide insights into the ongoing efforts to overcome barriers to scalable hydrogen production and pave the way for a sustainable hydrogen economy. [ABSTRACT FROM AUTHOR]

This study investigates the effect of Ag-doping on the (001) surface of SrTiO 3 (STO) to enhance hydrogen production via water-splitting employing density functional theory (DFT) simulations. It was found that the heterolytic water dissociation on Ag-doped (001)-STO occurs via a first-order reaction with an energy barrier of 5.74 kJ/mol, representing a reduction of 94% compared to undoped (001)-STO. The Gibbs free energy of H 2 formation catalyzed by Ag-doped (001)-STO is approximately −302 kJ/mol, indicating the spontaneity of this process. Additionally, the surface band gap energy decreases by ∼2 eV after water-splitting, suggesting charge transfer from the Ag-doped STO to the water and leading to new electron-hole recombination states. This research underscores the potential of Ag-doping in enhancing the efficiency of hydrogen production through water-splitting, contributing to the development of greener and more efficient energy technologies. • Ag-(001)-STO catalyzes H 2 formation spontaneously, indicating potential for hydrogen production. • Ag-doped (001)-STO reduces water dissociation energy barrier by 94%, enhancing catalytic activity. • Water interaction induces resonance states in Ag-doped (001)-STO, lowering band gap by 0.95 eV. • Electronic analysis reveals midgap and low electron mobility bands in transition state, crucial for water-splitting. • The study contributes to photocatalysis by elucidating Ag-doping impact in perovskite semiconductors. [ABSTRACT FROM AUTHOR]

The proton exchange membrane water electrolysis system has long been considered a promising technique for the generation of hydrogen owing to its high electrolytic efficiency, reliability, and quick response to renewable energy sources. At present, noble metals and their oxides (e.g., Pt, IrO2, and RuO2) are widely used as high active electrocatalysts for accelerating the conversion efficiency of the water electrolysis process, especially in acidic media. Nevertheless, the scarcity and instability seriously impede their large‐scale application in practice. In the past years, metal‐organic frameworks (MOFs) have proven to be an ideal platform for designing efficient and cost‐effective electrodes due to their unique physicochemical properties. In this review, the fundamental catalytic mechanisms of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in acidic media are discussed first. Then, design strategies and advanced characterizations for MOF‐based water‐splitting catalysts are summarized. Finally, the recent research advances of MOF‐based electrocatalysts for HER and OER in acidic electrolytes, along with current challenges and future opportunities, are provided. [ABSTRACT FROM AUTHOR]

The development of base metal electrodes that can act as active and stable oxygen generating electrodes in water electrolysis systems, especially at low pH levels, remains a challenge. The use of suspensions as electrolytes for water splitting has until recently been limited to photoelectrocatalytic approaches. A high current density (j=30 mA/cm2) for water electrolysis has been achieved at a very low oxygen evolution reaction (OER) potential (E=1.36 V vs. RHE) using a SnO2/H2SO4 suspension–based electrolyte in combination with a steel anode. More importantly, the high charge–to–oxygen conversion rate (Faraday efficiency of 88 % for OER at j=10 mA/cm2 current density). Since cyclic voltammetry (CV) experiments show that oxygen evolution starts at a low, but not exceptionally low, potential, the reason for the low potential in chronoamperometry (CP) tests is an increase in the active electrode area, which has been confirmed by various experiments. For the first time, the addition of a relatively small amount of solids to a clear electrolyte has been shown to significantly reduce the overpotential of the OER in water electrolysis down to the 100 mV region, resulting in a remarkable reduction in anode wear while maintaining a high current density. [ABSTRACT FROM AUTHOR]

Light-drive hydrogen production using titanium-based perovskite is one sustainable way to reduce current reliance on fossil fuels, but its wide applications are still limited by high electron–hole recombination and sluggish surface reaction. Thus, the developments for low-cost and highly efficient co-catalysts remain urgent. Inspired by natural [NiFe]-hydrogenase active center structure, a hydrogenase-mimic, NiCo2S4 nanozyme was synthesized, and subsequently decorated onto the CaTiO3 to catalyze the hydrogen evolution reaction (HER). Among the following test, CaTiO3 with a 15% loading of NiCo2S4 nanozyme exhibited the highest HER rate of 307.76 µmol·g−1·h−1, which is 60 times higher than that of the CaTiO3 alone. The results reveal that NiCo2S4 not only significantly increased the charge separation efficiency of the photogenerated carriers, but also substantively lowered the HER activation energy. Mechanism studies show that NiCo2S4 readily splits H2O by forming the Ni(OH)-Co intermediate and only Ni in the bimetallic center alters the oxidation state during the HER process in a manner analogous to the [NiFe]-hydrogenase. In contrast to the often-expensive synthetic catalysts that rely on rare elements such as ruthenium and platinum, this study shows a promising way to develop the nature-inspired cocatalysts to enhance the photocatalysts' HER performance. [ABSTRACT FROM AUTHOR]

In heterogeneous catalysis, determining the optimal metal particle size is challenging due to the intricate relationship between particle size, electronic structure, and activity. Here, we investigate the size-dependent activity of Pt nanoparticle (PtNP)-based ZrO 2 catalyst for hydrogen evolution reaction (HER) and water-splitting reaction (WSR) using density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations. By analyzing different Pt nanoparticle sizes (Pt 4 , Pt 7 , Pt 11 , P 15 , Pt 19, and Pt 25) supported on ZrO 2 , we determined their optimized geometries, and electronic structures, and calculated the hydrogen adsorption energies (Δ G H) for HER and activation energies barrier (Δ ‡ G) for WSR. The calculated results demonstrate that Pt 11 is the optimal size for HER, exhibiting the lowest Δ G H (−0.066 eV), while Pt 15 shows the lowest Δ ‡ G (0.24 eV) for WSR. The density of states (DOS) shows that the occupied Pt states fill the gap of ZrO 2 (3.72 eV), significantly reducing the band gap (E g) of the PtNP/ZrO 2 composites. The most favorable configuration of the PtNP on ZrO 2 for HER and WSR is determined to be a three-Pt-layer structure with rooflike edges which corresponds to a nanoparticle size of ∼0.70–1.55 nm for experiments. These findings can be regarded as an effort toward the design and optimization of metal-based oxide catalysts for renewable energy applications. [Display omitted] • Investigations of effect of Pt nanoparticle size on the catalytic activity of ZrO 2 -based catalyst. • The occupied Pt states reduce the band gap of the PtNP/ZrO 2 composites, enabling visible light photocatalytic activity. • Identified Pt 11 and Pt 15 clusters to be optimal size for hydrogen evolution reaction (Pt 11) and water-splitting reactions. • The calculated optimal size corresponds to an approximate nanoparticle size range of 0.70–1.55 nm in experiments. • Three-Pt-layer structure with rooflike edges identified as the most favorable configuration for catalytic performance. [ABSTRACT FROM AUTHOR]

Photoanodes possessing multifunctionality for efficient clean fuel generation have garnered significant attention. In this study, we present successful fabrication of tungsten‐doped ZnO photoelectrodes, resulting in enhanced photoelectrochemical water‐splitting performance. A single‐step deposition process was employed to achieve thin films with excellent adhesion on FTO substrates, eliminating the need for post‐annealing treatments. The addition of tungsten into the ZnO matrix extended the optical absorbance range of the thin films to the visible spectrum, leading to improved photoelectrochemical performance under visible light irradiation. At an applied potential of 0.85 V vs. RHE, the as‐fabricated tungsten‐doped ZnO thin films exhibited a remarkable photocurrent density of 5218 μA/cm2, which was eight times higher than that of the undoped ZnO electrode. The incorporation of tungsten in the ZnO photoanode resulted in increased charge carrier density and enhanced visible light absorption, consequently elevating the photocurrent density. [ABSTRACT FROM AUTHOR]

Poly(3‐hexylthiophene) (P3HT) film was applied as a photoanode on an electron‐extracting layer‐coated upon a current‐collecting plastic substrate. The film soaked in an aqueous solution (pH 12) exhibited an enhanced anodic current with light illumination, and the photocurrent density (J) reached almost 100 μA/cm2 for its wound cylinder, which was accompanied by oxygen bubble evolution. The light ON/OFF response, light‐intensity proportion, and wavelength‐dependency of the J value supported the photo‐electrolytic function of the P3HT film. The hole‐injection efficiency of the film estimated for water oxidation using a solution involving a sacrificial reagent, was relatively high in the range of 46%–86%. Although an apparent activation energy of 39 kJ/mol for the electrolytic water oxidation in the dark suggested a chemical but catalytic pathway for the film anode, the temperature independence of the photocurrent indicated direct hole‐injection into water or hydroxide ions. The photoanode performance of the P3HT film for water oxidation was discussed in relation to the energy diagram including the highest occupied molecular orbital level. [ABSTRACT FROM AUTHOR]

Zinc oxide (ZnO) has been utilized for photocatalytic water splitting due to its excellent performance, low cost, non-toxicity, thermal stability, and chemical stability. However, despite these remarkable properties, ZnO has significant drawbacks, such as photocorrosion and an inability to utilize visible light due to its wide band gap of 3.3-3.4 eV. Structurally, ZnO exists in three different forms: rocksalt, cubic blende, and hexagonal wurtzite. It has been reported that the wurtzite structure produces more H2 compared to its counterparts. Herein, we discuss several techniques for synthesizing zinc oxide and how incorporating zinc oxide nanoparticles with metal oxides, sulfides, and other materials can enhance its performance in the visible light region. Recently, integrating ZnO with TiO2 –Ag using an S-scheme heterostructure boosted the H2 activity rate to approximately 60.0 mmol/g/h, which is about 166 times superior to pristine ZnO. This improvement is attributed to the enhanced light absorption and charge transfer facilitated by Ag doping. This review examines ZnO-based photocatalytic H2 generation via water splitting with different modification strategies and explores future outlooks for improving performance of ZnO.

In this work, samarium doped Ni-Zn catalysts with a composition of Ni0.9Zn0.1SmyFe2-yO4 (y = 0–0.03) are made by inorganic sol–gel auto-combustion (SC) route. These Ni-Zn materials depict the forming of typical cubic crystal structure (Fd3m) and it is affirmed by the X-ray diffraction plots. The existence of cubic, spherical, and aggregated shaped grains with an average grain size that falls in between the range of 188 to 316 nm are confirmed from the FESEM images of prepared materials. According to the photo catalytic water splitting research findings, the total hydrogen yield for the Ni-Zn1, Ni-Zn2, Ni-Zn3, and Ni-Zn4 catalysts after four hours are 16.17, 15.02, 23.47 and 24.99 mmol gcat-1. Among all the compositions, the Ni-Zn4 photocatalyst exhibits the maximum photocatalytic performance of 24.99 mmol gcat-1. However, the Ni-Zn4 sample also shows the high electro catalytic hydrogen evolution reaction (HER) performance. With their outstanding photo/electro performance, the synthesized Sm-doped Ni-Zn nanoferrites shows great promise as potential candidates for the green hydrogen generation.

Utilization of zinc oxide as a photoanode in photoelectrochemical (PEC) water splitting is cost-effective and environmentally friendly choices compared to noble metals, although some enhancements are required to address the limited light absorption and significant charge recombination. Iron as metal doping and nanorod structure, on the other hand, offers solutions to overcome these limitations. An in-depth study employing iron-doped zinc oxide nanorods using various concentrations of iron fabricated through a chemical bath deposition (CBD) method due to its high-quality results and scale-up feasibility, shows enhanced structures, electrical characteristics, optical properties, charge transfer speed, and overall effectiveness in converting solar energy to hydrogen. This dopant was effectively integrated into the photoanode, resulting in a reduction of the bandgap to 3.19 eV and the creation of nanorods that are both thinner and longer. The photocurrent density for the oxygen evolution reaction (OER) is 6 mA/cm2, and for the hydrogen evolution reaction (HER), it is 1.3 mA/cm2. Electrochemical Impedance Spectroscopy shows lower resistance and an improved diffusion coefficient, resulting in reduced energy requirements for hydrogen production. The solar-to-hydrogen efficiency is also reported at 4.7%. This method shows potential for future progress and possible performance improvements. [Display omitted] • Iron doping in ZnO nanorods for photoelectrochemical (PEC) fabricated using chemical bath deposition (CBD) method. • PEC performance is evaluated using morphology, absorbance, charge carrier, photocurrent density, and surface reaction. • This dopant lowers the bandgap to 3.19 eV, resulting in thinner and longer nanorods. • The Oxygen Evolution Reaction has a photocurrent density 6 mA/cm2, while the Hydrogen Evolution Reaction has 1.3 mA/cm2. • STH efficiency is 4.7%, which is higher than ZnO nanorods without doping, which is under 1%. [ABSTRACT FROM AUTHOR]

Hydrogen generation by photocatalytic water-splitting holds great promise for addressing the serious global energy and environmental crises, and has recently received significant attention from researchers. In this work, a method of assembling GeC/MXY (M = Zr, Hf; X, Y = S, Se) heterojunctions (HJs) by combining GeC and MXY monolayers (MLs) to construct direct Z-scheme photocatalytic systems is proposed. Based on first-principles calculations, we found that all the GeC/MXY HJs are stable van der Waals (vdW) HJs with indirect bandgaps. These HJs possess small bandgaps and exhibit strong light-absorption ability across a wide range. Furthermore, the built-in electric field (BIEF) around the heterointerface can accelerate photoinduced carrier separation. More interestingly, the suitable band edges of GeC/MXY HJs ensure sufficient kinetic potential to spontaneously accomplish water redox reactions under light irradiation. Overall, the strong light-harvesting ability, wide light-absorption range, small bandgaps, large heterointerfacial BIEFs, suitable band alignments, and carrier migration paths render GeC/MXY HJs highly efficient photocatalysts for overall water decomposition. [ABSTRACT FROM AUTHOR]

70% of the earth's surface is covered by the ocean, and it represents a promising and renewable clean energy reservoir that waits for further exploration. Although hydrogen (H2) boasts a high energy density of 143 MJ kg−1 and environmentally friendly attributes, the widespread commercialization of green H2 production remains a formidable challenge. With huge amounts of water, the ocean presents an opportunity for generating H2 fuel through the process of seawater electrolysis. This review introduces ocean‐driven, self‐powered blue energy conversion devices, including triboelectric nanogenerators (TENGs), magnetoelastic generators (MEGs), and solar cells. They are able to convert renewable energy from the ocean, including water waves, wind, and solar energy, into electricity for on‐site seawater‐splitting and H2 generation. This review systematically reports this compelling approach by introducing the fundamental principles of the devices and showcasing the practical applications. Additionally, aiming to promote future research in the field of sustainable energy, this review also delves into the development of novel ocean energy harvesting systems with high energy conversion efficiency for large‐scale and effective H2 production. [ABSTRACT FROM AUTHOR]

Hydrogen, one of the most promising forms of new energy sources, due to its high energy density, low emissions, and potential to decarbonize various sectors, has attracted significant research attention. It is known that electrocatalytic hydrogen production is one of the most widely investigated research directions due to its high efficiency in the conversion of electricity to H2 gas. However, given the limited reserves and high cost of precious metals, the search for non-precious metal-based catalysts has been widely explored, for example, transition metal phosphides, oxides, and sulfides. Despite this interest, a detailed survey unveils that the surface and internal structures of the alternative catalysts, including their surface reconstruction, composition, and electronic structure, are poorly studied. As a result, a disconnection in the structure–property relationship severely hinders the rational design of efficient and reliable non-precious metal-based catalysts. In this review, by focusing on Ni5P4, a bifunctional catalyst for water splitting, we systematically summarize the material motifs pertaining to the different synthetic methods, surface characteristics, and hydrolysis properties. It is believed that a cascaded correlation may provide insights toward understanding the fundamental catalytic mechanism and design of robust alternative catalysts for hydrogen production. [ABSTRACT FROM AUTHOR]

Although great progress has been made in improving hydrogen production, highly efficient catalysts, which are able to produce hydrogen in a fast and steady way at ambient temperature and pressure, are still in large demand. Here, we report a [NiCo]-based hydrogenase mimic, NiCo2O4 nanozyme, that can catalyze robust hydrogen evolution spontaneously in water without external energy input at room temperature. This hydrogenase nanozyme facilitates water splitting reaction by forming a three-center Ni–OH–Co bond analogous to the [NiFe]-hydrogenase reaction by using aluminum as electron donor, and realizes hydrogen evolution with a high production rate of 915 L·h−1 per gram of nanozymes, which is hundreds of times higher than most of the natural hydrogenase or hydrogenase mimics. Furthermore, the NiCo2O4 nanozyme can robustly disrupt the adhesive oxidized layer of aluminum and enable the full consumption of electrons from aluminum. In contrast to the often-expensive synthetic catalysts that rely on rare elements and consume high energy, we envision that this NiCo2O4 nanozyme can potentially provide an upgrade for current hydrogen evolution, accelerate the development of scale-up hydrogen production, and generate a clean energy future. [ABSTRACT FROM AUTHOR]

Recently, bi-functional electrocatalytic materials have the potential for both the hydrogen evaluation reaction (HER) and oxygen evaluation reaction (OER) in the alkaline medium. In the present investigation, the cobalt sulfide/cobalt oxide hanged on the nitrogen-doped activated carbon nanosheets (CoS/CoO@NAC) as nanocomposites were synthesized through the hydrothermal and then the carbonization processes. The X-ray diffraction peaks observed in the CoS/CoO@NAC nanocomposites revealed the presence of CoS, CoO, and N-doped activated carbon nanosheets which confirmed the formation of binary nanocomposites. The BET analysis of CoS/CoO@NAC nanocomposites resulted an enhancement of the surface area of about 1038.57 m2/g along with the pore size and pore volume of 3.23 nm and 0.442 cc/g, respectively. The CoS/CoO@NAC, nanocomposites were used for bi-functional catalysis which divulged the low over potential for both HER and OER analyses at about −0.266 V and 0.199 V vs. RHE, respectively at 10 mA/cm2 current density in the alkaline medium. [Display omitted] • CoS/CoO@NAC nanocomposites synthesized by hydrothermal and carbonization processes. • CoS/CoO@NAC nanocomposites showed an enhancement of surface area of 1038.57 m2/g. • HER analysis of CoS/CoO@NAC shows an overpotential of −0.266 V. • OER analysis of CoS/CoO@NAC shows an overpotential of 0.2654 V. • CoS/CoO/NAC suitable for the bi-functional electrocatalyst in an alkaline medium. [ABSTRACT FROM AUTHOR]

Hydrogen is considered a promising substitute for traditional fossil fuels because of its widespread sources, high calorific value of combustion, and zero carbon emissions. Electrocatalytic water-splitting to produce hydrogen is also deemed to be an ideal approach; however, it is a challenge to make highly efficient and low-cost electrocatalysts. Single-atom catalysts (SACs) are considered the most promising candidate to replace traditional noble metal catalysts. Compared with SACs, dual-atom catalysts (DACs) are capable of greater attraction, including higher metal loading, more versatile active sites, and excellent catalytic activity. In this review, several general synthetic strategies and structural characterization methods of DACs are introduced, and recent experimental advances in water-splitting reactions are discussed. The authors hope that this review provides insights and inspiration to researchers regarding DACs in electrocatalytic water-splitting. [ABSTRACT FROM AUTHOR]

Polymeric carbon nitrides (CN) have gained significant interest as photoanodes in photoelectrochemical cells (PEC). A widely researched approach for synthesizing CN films with controlled optical and photoelectrochemical properties relies on using supramolecular assemblies as the precursors for thermal polymerization over a transparent conductive substrate. However, the formation of supramolecular assemblies is highly dependent on the temperature and solubility in a given solvent, limiting the full potential of this method. Moreover, the intercalation of metal ions is challenging due to the use of polar solvents. Here, this study shows a new way of synthesizing supramolecular assemblies with metal ions using a solvothermal approach. The solvent, monomer composition, salt quantity, reaction temperature, and film thickness are varied in this study. As a result, well‐attached, uniform CN films with good optoelectronic properties are achieved. The synthesized photoactive CN films exhibit very low onset potentials and reach ≈0.13, ≈0.15, and 0.30 ± 0.01 mA cm−2 photocurrents in 0.1 m phosphate buffer (neutral) solution, 0.1 m KOH(aq) (basic) solution, and 0.1 m KOH solution containing 10 vol.% triethanolamine as the hole scavenger, respectively. [ABSTRACT FROM AUTHOR]

Low-cost and highly efficient cathode and anode materials are required for proton exchange membrane and alkaline water electrolyzers. The present work demonstrates the development of a bifunctional cathode and anode material for hydrogen and oxygen evolution reactions (HER/OER) in an alkaline environment. The bimetallic Ni–Mo selenide is fabricated over the MXene (Ti 3 C 2 T x) grown over the activated carbon fibers by an inexpensive, simple one-step and eco-friendly approach. The electrocatalyst NiMoSe/Ti 3 C 2 T x @CC is developed via a hydrothermal method wherein NiMoSe is observed to grow highly dense nanoporous structure as confirmed by various characterization techniques. Highest activity for HER is observed using NiMoSe/Ti 3 C 2 T x @CC with only overpotential of 203 mV at 10 mA cm−2 with low Tafel slope (45 mV dec−1). The catalyst is also proven to support OER activity with requirement of 320 mV as overpotential at 10 mA cm−2, thus better than commercial IrO 2 (η 10 = 380 mV). The Tafel slope obtained by NiMoSe/Ti 3 C 2 T x @CC for OER is found to be minimum (189 mV dec−1) along with a very low charge transfer resistance (3.04 Ω) and high electrochemical surface area (0.0378 mF cm−2). The NiMoSe/Ti 3 C 2 T x @CC is found to be highly stable for HER/OER with 1000 LSV cycles. The work highlights the development of a cost-effective and efficient Ti 3 C 2 T x (MXene) based bifunctional electrocatalyst for oxygen evolution and hydrogen evolution reactions (OER/HER) in an alkaline medium (1 M KOH). The bimetallic Ni–Mo selenide is fabricated over the MXene on the activated carbon fibers by an inexpensive, simple, one-step hydrothermal method. The highly dense nanoporous structure shows an overpotential of 203 mV at 10 mA cm−2 for HER in alkaline medium. The corresponding overpotential for OER is 320 mV which has been found better than commercial IrO 2 catalyst (η 10 = 380 mV). In addition, NiMoSe/Ti 3 C 2 T x @CC bears a high electrochemically active surface area (0.0378 mF cm−2), low charge transfer resistance (3.04 Ω), and high stability (1000 LSV cycles) for both OER and HER. [Display omitted] • Bifunctional NiMoSe/Ti 3 C 2 T x @CC was synthesized via one step hydrothermal route. • Overpotential (η 10) for HER was found to be 203 mV. • For OER, overpotential (η 10) was found 320 mV, better than commercial IrO 2. • 1000 LSV cycle and 30 h stability was conducted for HER and OER. [ABSTRACT FROM AUTHOR]

This comprehensive review explores recent advancements in immobilization strategies for graphitic carbon nitride (g-C3N4), a metal-free photocatalyst that has gained significant attention for its optical and physicochemical properties comparable to traditional photocatalysts like TiO2. However, a critical challenge regarding their application has emerged from the difficulty of its recovery due to its powdery nature. Therefore, several alternatives are being explored to immobilize this material, facilitating its recovery and reuse. This review systematically categorizes various physical and chemical immobilization techniques, providing an in-depth analysis of their advantages, drawbacks, and applications. Techniques such as encapsulation, electrospinning, casting, and coating, along with their adaptations for g-C3N4, are thoroughly examined. Additionally, the impact of these strategies on enhancing the photocatalytic efficiency and operational stability of g-C3N4, particularly in environmental applications, is also assessed. Thus, this review aims to provide valuable insights and guide future research in the realms of photocatalysis and environmental remediation. The review contributes to the understanding of how immobilization strategies can optimize the performance of g-C3N4, furthering its potential applications in sustainable and efficient environmental solutions. [ABSTRACT FROM AUTHOR]

The development of efficient and earth-abundant electrocatalysts for water splitting is necessary and crucial. In this study, NiMn 2 O 4 nanosheets and nanosphericals were grown on Ni foam by microwave synthesis at 150 °C and 175 °C and the corresponding synthesized materials were referred to as NIM-150 and NIM-175, respectively. These materials were subsequently used as bifunctional electrocatalysts for the oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and overall water splitting. The NIM-175 electrocatalyst showed a lower overpotential of 250 mV for the OER and 248 mV for the HER at 10 mA cm−2, and a smaller Tafel slope of 218 mV dec−1 for the OER and 198 mV dec−1 for the HER, compared to NIM-150. The NIM-150 and NIM-175 electrocatalysts exhibited excellent stability for overall water splitting. • The temperature-dependent morphology was obtained through the microwave method. • NiMn 2 O 4 electrocatalysts were grown on Ni foam using microwave synthesis at 150 °C and 175 °C. • NIM-175 shows the nanosheets along with spherical-shaped morphologies. • The NIM-150 and NIM-175 electrocatalysts showed excellent stability for overall water splitting. [ABSTRACT FROM AUTHOR]

Solar thermochemical CeO 2 -based H 2 O splitting cycle was thermodynamically analyzed to ascertain the optimal thermal reduction (T H) and re-oxidation (T L) temperatures and evaluate the solar-to-fuel conversion efficiency (η solar − to − fuel ) of the cycle. The equilibrium composition of CeO 2 , CeO 1.72 , CeO 1.83 and O 2 exhibited that the thermal reduction initiated at 1400 K thereby attaining 100 % TR at 2734 K. The observed variations in Gibbs free energy (Δ G) correspond to the feasibility of the re-oxidation step of CeO 1.83 and CeO 1.72 at 1050 K and 1200 K respectively. It was reported that the absorption efficiency of solar reactor (η abs − solar − reactor − WS ) decreases from 95.6 % to 37 %, as the T H increases from 1400 K to 2734 K. The results show that η solar − to − fuel reached the maximum value of 7.45 % for CeO 1.72 and 7.69 % for CeO 1.83 at 61.72 % TR of CeO 2 without heat recuperation. Further, the η solar − to − fuel attained the maximum value of 14.92 % and 13.54 % for CeO 1.83 and CeO 1.72 , respectively at the %TR of CeO 2 of 80 % with 50 % heat recuperation. The solar-to-fuel conversion efficiency (η solar − to − fuel ) further can be increased with the optimization of oxygen partial pressure (P O 2 ) and molar flow rate of reduction regents (Ar or N 2). • Thermal reduction of CeO 2 started at 1400 and attained 100 % TR at 2734 K. • Re-oxidation of CeO 1.83 and CeO 1.72 was feasible at 1050 K and 1200 K, respectively. • η s o l a r − t o − f u e l attained 7.45 % and 7.69 % for CeO 1.72 and CeO 1.83 , respectively without HR. • η s o l a r − t o − f u e l reached 14.92 % and 13.54 % for CeO 1.83 and CeO 1.72 , respectively with 50 % HR. [ABSTRACT FROM AUTHOR]

Commercialization of photoelectrochemical (PEC) water‐splitting devices requires the development of large‐area, low‐cost photoanodes with high efficiency and photostability. Herein, we address these challenges by using scalable fabrication techniques and porous transport layer (PTLs) electrode supports. We demonstrate the deposition of W‐doped BiVO4 on Ti PTLs using successive‐ionic‐layer‐adsorption‐and‐reaction methods followed by boron treatment and chemical bath deposition of NiFeOOH co‐catalyst. The use of PTLs that facilitate efficient mass and charge transfer allowed the scaling of the photoanodes (100 cm2) while maintaining ~90 % of the performance obtained with 1 cm2 photoanodes for oxygen evolution reaction, that is, 2.10 mA cm−2 at 1.23 V vs. RHE. This is the highest reported performance to date. Integration with a polycrystalline Si PV cell leads to bias‐free water splitting with a stable photocurrent of 208 mA for 6 h and 2.2 % solar‐to‐hydrogen efficiency. Our findings highlight the importance of photoelectrode design towards scalable PEC device development. [ABSTRACT FROM AUTHOR]

Transition metal sulfide and oxide nanomaterials are gaining popularity as catalysts for electrochemical water splitting because of their cost effectiveness, durability, and stability without using noble metals. Our study focuses on a hybrid electrocatalyst, NiS‐enriched FeNi2S4/ZnCr2O4, which is synthesized in two steps by sol‐gel followed through thermal decomposition in an aqueous solution by a hydrothermal process. We investigated its potential application in the electrochemical oxygen evolution reaction (OER). Powder X‐ray diffraction and X‐ray photoelectron spectroscopy analyses were used to determine the chemical composition and structure. The results showed that the FeNi2S4 structure has an enriched NiS phase. Additionally, the morphology of the synthesized FeNi2S4/ZnCr2O4 was revealed by field emission scanning electron microscopy (FE‐SEM). Under alkaline (1 M KOH) conditions, the FeNi2S4/ZnCr2O4 hybrid nanostructure showed a low overpotential value of 295 mV (Tafel slope, 59 mV dec−1) for OER activities due to the synergistic effects of FeNi2S4 and ZnCr2O4. Furthermore, the hybrid nanostructure demonstrated its long‐term stability and efficiency as an electrocatalyst for OER activities, surpassing previously reported superior electrocatalysts and state‐of‐the‐art materials. [ABSTRACT FROM AUTHOR]

Efficient delafossite CuCoO 2 photo(electro)catalysts necessitate effective separation and transport of photogenerated carriers to enable the production of solar fuel. Addressing this requirement, the current study employed facet engineering to induce the surface polarization effect. Hydrothermal conditions were utilized to prepare CuCoO 2 photo(electro)catalysts with diverse morphologies and sizes. Specifically, CuCoO 2 hexagonal nanosheets, predominantly exposing the (001) facet and possessing a thickness of 120 nm, exhibited optimal performance, as evidenced by a photocurrent density of 40 μA/cm2 under zero-bias conditions and 90 % degradation of tetracycline hydrochloride within 150 min. To overcome the limitations associated with hydrothermal preparation, Ca substitutional doping was employed. This doping strategy caused disruption of the O–Cu–O dumbbell-like structural motif, transforming CuCoO 2 into an open-layered structure while simultaneously reducing the thickness of CuCoO 2 hexagonal nanosheets to 30 nm. Consequently, an enhancement in the photo(electro)catalytic performance was achieved. By striking a balance between the surface polarization effect and the doping effect, CuCoO 2 hexagonal nanosheets with 0.5 % Ca doping content and a thickness of 80 nm exhibited the most significant photo(electro)catalytic performance. This study presents a feasible strategy and concept for optimizing the morphology and hydrothermal preparation conditions of CuCoO 2 nanomaterials, leading to improved photo(electro)catalytic performance. [Display omitted] • Surface polarization enhances carrier separation and transport in CuCoO 2 photoelectrodes. • CuCoO 2 hexagonal nanosheets exhibit superior photo(electro)catalytic activity. • Ca doping overcomes limitations in hydrothermal synthesis for preparation thinner CuCoO 2 nanosheets. [ABSTRACT FROM AUTHOR]

For the energy conversion technology, it is crucial to design catalysts for water splitting applications namely Oxygen evolution reaction and Hydrogen evolution reaction (OER and HER) with improved stability and activity using practically used methods. The development of a cost-effective, efficient, and durable electrocatalysts is necessary for the performance of water splitting. Herein, CoFe 2 O 4 /Fe 2 O 3 , and C-CoFe 2 O 4 /Fe 2 O 3 (Carbon doped) electrocatalysts were synthesized by using the facile calcination approach, speeding up catalytic kinetics for water splitting applications. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Scanning electron microscopy (SEM) were used to structurally characterize the synthesized electrocatalysts. Cyclic voltammetry, linear sweep voltammetry, Mott-Schottky, and electrochemical impedance spectroscopy were performed to evaluate the electrochemical performance of the electrocatalysts. In OER, CoFe 2 O 4 /Fe 2 O 3 @CNT showed efficient catalytic activity with an overpotential of 260 mV current density and a Tafel slope of 183 mV dec−1. Whereas for the HER, carbon-doped CoFe 2 O 4 /Fe 2 O 3 shows outstanding catalytic activity with an overpotential of 236 mV current density and a Tafel slope of 146 mV dec−1. This simple and successful method proposes a new method for the fabrication of ferrites and oxides, potentially improving the electrochemical performance of systems related to energy. • CoFe 2 O 4 /Fe 2 O 3 , and C-CoFe 2 O 4 /Fe 2 O 3 electrocatalysts were synthesized via facile method. • In OER, CoFe 2 O 4 /Fe 2 O 3 @CNT showed efficient catalytic activity. • The material exhibited 260 mV overpotential and 183 mV dec−1 tafel slope. • The carbon-doped CoFe 2 O 4 /Fe 2 O 3 showed outstanding catalytic activity. [ABSTRACT FROM AUTHOR]

In this paper, a facile one step synthesis method for the preparation of C-, B-, P- and S-doped g-C 3 N 4 by incorporation of small concentration of doping element precursor into urea during thermal polycondensation is reported leading to much lower doping levels than the ones usually reported. The as-obtained doped g-C 3 N 4 photocatalytic materials are deeply characterized in terms of structural, morphological, surface and optical properties. Doping yields beneficial surface morphology modulation along with improved optical, electronic and photocatalytic properties. In particular, C-doped and S-doped g-C 3 N 4 show, after deposition of gold nanoparticles (<1 wt%), enhanced photocatalytic performance (at least twice as high as the undoped photocatalyst, to achieve ca. 610 μmol/h/g) for the production of H 2 by water splitting under solar light in the presence of low content (1 vol%) of triethanolamine (TEOA) as sacrificial agent. The most remarkable activity results from the incorporation of traces of S dopant, mainly inserted into interplanar hollow cavities. The enhanced activity is attributed to a combination of high surface area, location of the S dopant and small size of the co-catalyst NPs, which induces enhanced visible light harvesting, enhanced charge carrier separation and enhanced proton recombination. This work highlights the benefits of the optimized low-level doping strategy to overcome the main limitations of g–C 3 N 4 –based photocatalysts. [Display omitted] • H 2 production by water splitting with non-metal doped g-C 3 N 4 using low amount (1 vol%)TEOA. • Enhanced H2 production rate induced by trace level (<0.1 wt%) of S-dopant. • Benefits of low-level doping strategy to overcome the main limitations of g-C 3 N 4. • One-pot easy synthesis of non-metal doping of g-C 3 N 4 during thermal polycondensation. • Those photocatalyst exhibit enhanced visible light harvesting properties. [ABSTRACT FROM AUTHOR]

A very simple electrochemical top-down procedure was employed to obtain pure graphene quantum dots (GQDs) in water and using only graphite as carbonaceous precursor. The graphitic structure of the GQDs has been clearly observed by high-resolution transmission electronic microscopy (HRTEM). Then, the synthesis of N-doped GQDs was allowed by the addition of ammonia in the solution. The nitrogen doping was plainly evidenced by X-ray photoelectron (XPS) and Raman spectroscopies. The role of the electrolytic solution employed during the synthesis has been also discussed. Finally, these N-doped and non-doped GQDs were further used to prepare hybrids by grafting them onto ZnO semi-conductors, and their photocatalytic properties towards water-splitting were investigated. Interestingly, a very important enhancement of the amount of dihydrogen produced was observed with N-doped GQDs, compared to ZnO alone or to hybrids prepared with non-doped GQDs.

Abstract Tuning the electronic properties of transition metals using pyrophosphate (P2O7) ligand moieties can be a promising approach to improving the electrochemical performance of water electrolyzers and supercapacitors, although such a material’s configuration is rarely exposed. Herein, we grow NiP2O7, CoP2O7, and FeP2O7 nanoparticles on conductive Ni-foam using a hydrothermal procedure. The results indicated that, among all the prepared samples, FeP2O7 exhibited outstanding oxygen evolution reaction and hydrogen evolution reaction with the least overpotential of 220 and 241 mV to draw a current density of 10 mA/cm2. Theoretical studies indicate that the optimal electronic coupling of the Fe site with pyrophosphate enhances the overall electronic properties of FeP2O7, thereby enhancing its electrochemical performance in water splitting. Further investigation of these materials found that NiP2O7 had the highest specific capacitance and remarkable cycle stability due to its high crystallinity as compared to FeP2O7, having a higher percentage composition of Ni on the Ni-foam, which allows more Ni to convert into its oxidation states and come back to its original oxidation state during supercapacitor testing. This work shows how to use pyrophosphate moieties to fabricate non-noble metal-based electrode materials to achieve good performance in electrocatalytic splitting water and supercapacitors.

The water oxidation reaction in photosystem II (PS II) produces most of the molecular oxygen in the atmosphere, which sustains life on Earth, and in this process releases four electrons and four protons that drive the downstream process of CO2 fixation in the photosynthetic apparatus. The catalytic center of PS II is an oxygen-bridged Mn4Ca complex (Mn4CaO5) which is progressively oxidized upon the absorption of light by the chlorophyll of the PS II reaction center, and the accumulation of four oxidative equivalents in the catalytic center results in the oxidation of two waters to dioxygen in the last step. The recent emergence of X-ray free-electron lasers (XFELs) with intense femtosecond X-ray pulses has opened up opportunities to visualize this reaction in PS II as it proceeds through the catalytic cycle. In this review, we summarize our recent studies of the catalytic reaction in PS II by following the structural changes along the reaction pathway via room-temperature X-ray crystallography using XFELs. The evolution of the electron density changes at the Mn complex reveals notable structural changes, including the insertion of OX from a new water molecule, which disappears on completion of the reaction, implicating it in the O—O bond formation reaction. We were also able to follow the structural dynamics of the protein coordinating with the catalytic complex and of channels within the protein that are important for substrate and product transport, revealing well orchestrated conformational changes in response to the electronic changes at the Mn4Ca cluster.

Climatic changes are reaching alarming levels globally, seriously impacting the environment. To address this environmental crisis and achieve carbon neutrality, transitioning to hydrogen energy is crucial. Hydrogen is a clean energy source that produces no carbon emissions, making it essential in the technological era for meeting energy needs while reducing environmental pollution. Abundant in nature as water and hydrocarbons, hydrogen must be converted into a usable form for practical applications. Various techniques are employed to generate hydrogen from water, with solar hydrogen production—using solar light to split water—standing out as a cost-effective and environmentally friendly approach. However, the widespread adoption of hydrogen energy is challenged by transportation and storage issues, as it requires compressed and liquefied gas storage tanks. Solid hydrogen storage offers a promising solution, providing an effective and low-cost method for storing and releasing hydrogen. Solar hydrogen generation by water splitting is more efficient than other methods, as it uses self-generated power. Similarly, solid storage of hydrogen is also attractive in many ways, including efficiency and cost-effectiveness. This can be achieved through chemical adsorption in materials such as hydrides and other forms. These methods seem to be costly initially, but once the materials and methods are established, they will become more attractive considering rising fuel prices, depletion of fossil fuel resources, and advancements in science and technology. Solid oxide fuel cells (SOFCs) are highly efficient for converting hydrogen into electrical energy, producing clean electricity with no emissions. If proper materials and methods are established for solar hydrogen generation and solid hydrogen storage under ambient conditions, solar light used for hydrogen generation and utilization via solid oxide fuel cells (SOFCs) will be an efficient, safe, and cost-effective technique. With the ongoing development in materials for solar hydrogen generation and solid storage techniques, this method is expected to soon become more feasible and cost-effective. This review comprehensively consolidates research on solar hydrogen generation and solid hydrogen storage, focusing on global standards such as 6.5 wt% gravimetric capacity at temperatures between −40 and 60 °C. It summarizes various materials used for efficient hydrogen generation through water splitting and solid storage, and discusses current challenges in hydrogen generation and storage. This includes material selection, and the structural and chemical modifications needed for optimal performance and potential applications.