Water Splitting Reaction Research Articles

Operando Surface X‐Ray Diffraction Studies of Epitaxial Co3O4 and CoOOH Thin Films During Oxygen Evolution: pH Dependence

AbstractTransition metal oxides, especially cobalt oxides and hydroxides, are of great interest as precious metal free electrode materials for the oxygen evolution reaction (OER) in electrochemical and photoelectrochemical water splitting. Here, we present detailed studies of the potential‐ and pH‐dependent structure and structural stability of Co3O4 and CoOOH in neutral to alkaline electrolytes (pH 7 to 13), using operando surface X‐ray diffraction, atomic force microscopy, and electrochemical measurements. The experiments cover the pre‐OER and OER range and were performed on epitaxial Co3O4(111) and CoOOH(001) films electrodeposited on Au(111) single crystal electrodes. The CoOOH films were structurally perfectly stable under all experimental conditions, whereas Co3O4 films exhibit at all pH values reversible potential‐dependent structural transformations of a sub‐nanometer thick skin layer region at the oxide surface, as reported previously for pH 13 (F. Reikowski et al., ACS Catal. 2019, 9, 3811). The intrinsic OER activity at 1.65 V versus the reversible hydrogen electrode decreases strongly with decreasing pH, indicating a reaction order of 0.2 with respect to [OH−]. While the Co3O4 spinel is stable at pH 13, intermittent exposure to electrolytes with pH≤10 results in dissolution as well as gradual degradation of its OER activity in subsequent measurements at pH 13.

Quasi-1D Oxides as Electrocatalysts for Water-Splitting: Case Study of Sr9M2Mn5O21 (M = Co, Ni, Cu, Zn).

We have demonstrated that multimetal oxides with a quasi-1D structure can be effective electrocatalysts for water electrolysis. Four materials have been systematically investigated, namely, Sr9Co2Mn5O21, Sr9Ni2Mn5O21, Sr9Cu2Mn5O21, and Sr9Zn2Mn5O21, comprising 1D chains of face-sharing MnO6 octahedra and MO6 trigonal prisms (M = Co, Ni, Cu or Zn), which are held together by strontium ions located between the chains. These materials show a consistent trend in electrocatalytic properties for both half-reactions of water-splitting, i.e., oxygen evolution and hydrogen evolution reactions (OER and HER). In particular, Sr9Ni2Mn5O21 has an outstanding performance for OER, with an overpotential of 0.37 V, which is lower than those of many 3D and 2D oxides, and rivals the activity of noble metal catalysts, such as RuO2. This is important given that the OER is considered the bottleneck of the water-slitting process. Chronopotentiometry studies, combined with X-ray photoelectron spectroscopy (XPS) and X-ray diffraction experiments pre- and post-reaction, indicate that Sr9Ni2Mn5O21 is highly stable and retains its structural integrity upon electrocatalytic reactions. This study highlights the potential of quasi-1D oxides as active electrocatalysts for water-splitting.

Creating an intermediate energy band to boost the photoelectrochemical efficiency of TiO2 for solar-driven hydrogen production

The utilization of photoelectrochemical processes for hydrogen generation from water and solar energy offers a promising avenue to replace non-renewable energy sources. Nevertheless, achieving high-performance photoanode electrodes poses a significant challenge. In this study, we present the synthesis cerium and chromium-doped TiO2 (CeCrTiO2) is produced through a simple, scalable, and cost-effective hydrothermal method on a fluorine-doped tin oxide (FTO) substrate. the introduction of Ce and Cr impurities is highlighted for its role in creating an impurity band within CeCrTiO2. This impurity band is instrumental in enhancing the separation and movement of electrons and holes, contributing to the improved performance of CeCrTiO2 as a photoanode in photoelectrochemical applications. Hence, the photocurrent density value of CeCrTiO2 is 4.5 times higher than that of bare TiO2. This suggests that CeCrTiO2 exhibits improved efficiency in generating a photocurrent when exposed to light, indicating enhanced photoelectrochemical performance. The amount of hydrogen produced by CeCrTiO2 is noted to be 4.88 times greater than that of bare TiO2. This highlights the material's effectiveness in harnessing solar energy to drive the water-splitting reaction, leading to a higher yield of hydrogen gas. The synthesis of CeCrTiO2 through a hydrothermal method results in a photoanode with significantly enhanced performance, positioning it as a promising candidate for advancing photoelectrochemical processes aimed at replacing non-renewable energy sources.

A density functional study of type I to type II crossover in g-C3N4/CoN4 heterostructure in presence of external perturbation

Herein, we report the impact of external perturbation on the photocatalytic performance of g-C3N4/CoN4 heterojunction and concomitant transition from type-I to type-II. The state-of-the-art theoretical modeling presented here is the first study on dynamic role of strain and electric field on g-C3N4/CoN4 heterojunction and its potential application as a solar-driven water splitting reaction. Utilizing the density functional theory (DFT) calculation, V. N. et al. recently reported the photocatalytic activity of g-C3N4/MN4 (M = Mn, Fe and Co) heterojunction [J. Comput. Chem. 2024, 45, 2518-2529, https://doi.org/10.1002/jcc.2746412] and subsequently established g-C3N4/CoN4 as a type I heterojunction for photocatalytic water splitting reaction [Phys. Chem. Chem. Phys. 2024, 26, 21117–21133]. In the present study, we applied external perturbation in the form of mechanical strain, electric field and evaluated the electronic structure properties of the system along with the detailed examination of concomitant optical and magnetic properties of g-C3N4/CoN4 heterojunction. The switching of photocatalytic feature from type I to type II originates due to the crossover between valence band maxima (VBM) of g-C3N4 and CoN4 in presence of external perturbation. Notably, the resulting system acts as a type II photocatalyst for water splitting reaction while applying compressive (negative) strain of −2 to −6% and an electric field of −0.5 and +0.5 V/Å, respectively. Accumulation of photogenerated electrons and holes separately in g-C3N4 and CoN4 units confirms the perceptible separation of charge carriers and thereby reduces the recombination compared to un-perturbed system. A red-shifted absorption maximum (689 nm), superior charge transfer (0.9e), and clear separation of photogenerated electrons and holes are the origin of enhanced photocatalytic efficiency of g-C3N4/CoN4 heterojunction in the presence of external perturbation. We believe that our work will provide enough evidence to the experimentalists to achieve such a system in practice leading to human-friendly applications.

Photocatalytic seawater splitting by Earth-abundant catalysts: metal-semiconductor metamaterials made of plasmonic magnesium diboride and transitional metal dichalcogenides.

Metal-semiconductor metamaterials hold great promise for photocatalytic water splitting due to their excellent light harvesting in a broad spectral range as well as efficient charge carrier generation and transfer. In majority of such metamaterials, semiconductors are used to initiate the water splitting reaction, while their metal counterparts are employed to improve light harvesting through plasmonic effects. Here, we describe for the first time an exceptional reversed case of metal-semiconductor photocatalysts in which metals are used to initiate the water splitting reaction and semiconductors are employed to improve light harvesting through blackbody effect and serve as co-catalysts. The studied photoanodes are made of non-noble plasmonic MgB2 combined with transition metal dichalcogenides (TMDCs). The plasmonic resonances of the MgB2 component contribute to field confinement, plasmon-exciton coupling, and hot-electron transfer providing an enhancement of photoactivity in the entire solar spectrum capable of water splitting. The TMDC component provides impedance matching and enhances light absorption by the metal catalyst. We demonstrate seawater splitting with MgB2-TMDCs photoanodes attaining current densities of ~ 3 mA⋅cm-2 at solar radiation. The overall efficiency of hydrogen production in seawater splitting by sunlight with the help of the studied photoanodes is 3% at bias voltage of Vbias = 0.3 V.

Tailoring the Heterointerfaces of Earth-Abundant Transition-Metal Nanoclusters on Nickel Oxide Nanosheets for Enhanced Overall Water Splitting through Electronic Structure Optimization.

Evolving highly competent and economical electrocatalysts for alkaline water electrolysis is crucial in renewable hydrogen energy technologies. The slow hydrogen evolution reaction (HER)/oxygen evolution reaction (OER) kinetics under alkaline electrolytes, still, has troubled developments in high-performance green hydrogen production systems. Herein, we demonstrate the tailoring of the interface of earth-abundant transition-metal nanoclusters (MNCs), including iron (Fe), cobalt (Co), nickel (Ni), and copper (Cu) nanoclusters on nickel oxide nanosheets (M NCs|NiO NS) through metal-support interaction for enriched overall water splitting under an alkaline electrolyte. The strong metal-metal oxide interaction allows alteration of the binding capabilities of hydrogen ions (*H) and hydroxyl ions (*OH) on Ni electrodes. Specifically, the robust interaction between Fe and NiO reveals optimized binding of H* and OH* energies, facilitating the water-splitting reaction under an alkaline electrolyte. In addition, the improved HER/OER catalytic activity is attained with the Fe NCs|NiO NS with small overpotentials of ∼62.0 and ∼380.0 mV for the HER and OER, respectively, a high mass activity of ∼90.0 A g-1, a turnover frequency of ∼5.94 s-1, and long-lasting stability via offering abundant electrochemical active sites, three-dimensional (3D) morphologies, and high dispersion of nanoclusters that provide effective charge and mass transport processes. This study provides a promising strategy for the effective design of efficient bifunctional electrocatalysts based on earth-abundant materials for alkaline water electrolyzers.

Chemically driven BaTiO3–CoFe2O4 nanocomposite with strong dielectric and low leakagecharacteristics for electrocatalytic water splitting reaction

The switchable electronic properties at the surface of ferroelectric nanomaterials offer possibilities for electrocatalytic hydrogen and oxygen evolution reactions, HER and OER respectively. Here, 0.5(BaTiO3)-0.5(CoFe2O4) (abbreviated as BTCF0.5) are prepared chemically. The material shows a high dielectric constant in the order of 107. Nyquist plot is consistent with non-Debye-type and negative temperature coefficient of resistance (NTCR) characteristics with low leakage current. BTCF0.5 shows superior electrocatalytic HER and OER with a low overpotential of ∼156 and ∼284 mV at current density10 mA/cm2 along with Tafel slopes of 43.37 mV/dec and 41.52 mV/dec respectively. The stability of the electrocatalyst is checked through a chronoamperometry test and up to 1000 cycles of CV both for HER and OER operations. The non-traditional behavior of the nanocomposite may make it highly desirable for usage in numerous renewable and sustainable energy-related applications in the present-day scenario.

Cooperativity in Fe2N5P dual-atomic site: Designing dual atom catalysts for water-splitting reactions

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An investigation on g-C3N4/ZnS/SnO2 ternary nanocomposites for electrochemical alkaline water splitting and photocatalytic methylene blue decomposition reactions

An investigation on g-C3N4/ZnS/SnO2 ternary nanocomposites for electrochemical alkaline water splitting and photocatalytic methylene blue decomposition reactions

Pt Single Atom-Doped Triphasic VP-Ni3P-MoP Heterostructure: Unveiling a Breakthrough Electrocatalyst for Efficient Water Splitting.

Enhancement of an alkaline water splitting reaction in Pt-based single-atom catalysts (SACs) relies on effective metal-support interactions. A Pt single atom (PtSA)-immobilized three-phased PtSA@VP-Ni3P-MoP heterostructure on nickel foam is presented, demonstrating high catalytic performance. The existence of PtSA on triphasic metal phosphides gives an outstanding performance toward overall water splitting. The PtSA@VP-Ni3P-MoP performs a low overpotential of 28 and 261 mV for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) at a current density of 10 and 25 mA cm-2, respectively. The PtSA@VP-Ni3P-MoP (+,-) alkaline electrolyzer achieves a minimum cell voltage of 1.48 V at a current density of 10 mA cm-2 for overall water splitting. Additionally, the electrocatalyst exhibits a substantial Faradaic yield of ≈98.12% for H2 and 98.47% for O2 at a current density of 50 mA cm-2. Consequently, this study establishes a connection for understanding the active role of single metal atoms in substrate configuration for catalytic performance. It also facilitates the successful synthesis of SACs, with a substantial loading on transition metal phosphides and maximal atomic utilization, providing more active sites and, thereby enhancing electrocatalytic activity.

Photocatalytic Hydrogen Production Using TiO2‐based Catalysts: A Review

AbstractPhotocatalytic water splitting is an environmentally friendly hydrogen production method that uses abundant renewable resources such as water and sunlight. While Titanium dioxide (TiO2) photocatalyst exhibits excellent properties, its high band gap limits absorption to ultraviolet (UV) irradiation, resulting in low photo conversion efficiency. This review explores various modification techniques aimed at enhancing the efficiency of TiO2 under visible light irradiation. Factors influencing the photocatalytic water splitting reaction, such as catalyst structure, morphology, band gap, sacrificial reagents, light intensity, temperature, and potential of Hydrogen (pH) are examined. This review also summarizes different catalyst synthesis methods, and types of photocatalytic reactors, and provides insights into quantum yield. Finally, the review addresses the challenges and future outlook of photocatalytic water splitting.

Highly efficient oxygen carrier NiFeP (oxy) hydroxides nanoparticle embedded in N-doped porous carbon derived from bio-waste for bifunctional electrocatalysts

Developing cost-effective, readily available materials for efficient hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in water splitting is a crucial step toward enhancing the profitability and sustainability of energy conversion systems. This research introduces a novel synthesis method for NiFeP/NPC OHs from banana peel bio-waste, a method that could revolutionize the field of materials science and electrochemistry. The use of metallic phosphides, known for their excellent electrical conductivity and catalytic activity, as bifunctional catalysts, combined with the efficient synthesis of nanoporous carbons (NPC) from banana peel bio-waste (BPW), could pave the way for a new era of sustainable and cost-effective energy conversion. By chemically activating different porogens, such as nickel, iron, and phosphorus (NiFeP), to form (oxy) hydroxides (OHs), functional carbonaceous structures with a high density of pores and large specific surface areas can be achieved. The resulting materials, designated as NiFeP/NPC OHs, are characterized by their remarkable porosity, high conductivity, large surface area, and chemical stability. These properties make NiFeP/NPC OHs particularly suitable for electrocatalysis, where they exhibit outstanding activity in both HER and OER. The optimized NiFeP/NPC OHs material shows a very low overpotential of 93 mV for HER and 243 mV for OER at 10 mA cm⁻2 and high durability over 100 h. Moreover, the bifunctional NiFeP/NPC OHs electrode demonstrates exceptional catalytic activity and stability in alkaline solutions. This study not only highlights the innovative synthesis of NPC from BPW and the cost-effective fabrication of NiFeP/NPC OHs but also sparks curiosity about the potential of this novel synthesis method.

Cover: Journal of the Chinese Chemical Society 10/2024

Focus of the figure: Spray pyrolysis being as a low‐cost synthesis technique to prepare CuMnO2 thin films that deliver the enhanced performance of the photoelectrocatalytic water splitting reaction. More details about this figure will be discussed by Dr. Ming‐Hsi Chiang and his co‐workers on pages 1203‐1210 in this issue. image

Unveiling the facet-dependent electrocatalytic activity of a 3D-CoSn(OH)6 perovskite material for overall water splitting: Interfacial engineering with Mn3+ and CH3COO- ions

In this study, we report morphologically dependent electrocatalytic oxygen and hydrogen evolution reactions in an alkaline medium. The bifunctional electrocatalyst such as cobalt tin hydroxide (CoSn(OH)6) was prepared by hydrothermal method. Importantly, tuning the morphological variation of CoSn(OH)6 into cubes, octa- and dodecahedra and their corresponding growth mechanisms are analyzed and explored the electrochemical studies. Among the different morphologies, the CoSn(OH)6 dodecahedron (CTH-DH) displays a substantially enhanced overall electrocatalytic water splitting reaction. It is firmly due to the [Mn3+] and [CH3COO-] ions do enable the morphological progression of the CTH cubic crystals with more facets. The highly active catalytic sites on the facets of CTH-DH permit the adsorption of abundant OH groups during the hydrogen and oxygen evolution reactions. Moreover, in a two-electrode system, the CTH-DH ǁ CTH-DH electrolyzer exhibits a cell potential of 1.60 V at 10 mA cm–2 with a remarkable reliable long-term stability. In addition, the structural transformations of the as-prepared CoSn(OH)6 crystals are monitored before and after electrocatalysis using TEM study. As a result, the study highlights the potential of Mn-containing CTH-DH facets as viable electrocatalysts in efficient H2 production.

Deciphering promotion of MoP over MoC in Pt catalysts for methanol-assisted water splitting reaction

Molybdenum-based compounds show promising promotion effects on Pt catalysts for energy-relevant catalysis reactions. Herein, a more effective promotion effect of MoP than MoC was found in assisting Pt nanoparticles for methanol-assisted hydrogen generation in light of the strong metal-support interaction and synergistic effect between Pt and MoP/C nanospheres. Electrochemical analyses and theoretical calculations demonstrated that Pt-MoP/C facilitated the oxidation and removal of CO intermediates more effectively than Pt-MoC/C. This enhanced performance was attributed to the distinct 6-coordination environment of hexagonal MoP and the elevated electron density of Mo induced by phosphorus. These structural and electronic features significantly enhanced electron transfer to Pt, thereby creating strong metal-support interaction and synergistic effect to improve the overall catalytic efficiency. Especially, the unique activities of Moδ+ and Moδ- in the MoP modified the surface structure of Pt, lowered the Pt d-band center, and optimized the local chemical state of Pt atoms, which resulted in more optimized adsorption energy and charge transfer capabilities of intermediates. The Pt-MoP/C electrolyzer thus showed both lower cell voltage than that of Pt-MoC/C and Pt/C electrolyzers in water splitting and methanol-assisted water splitting for hydrogen generation. This study offers insightful information about the promotion effect of molybdenum-based compounds in Pt catalyst systems in energy-relevant catalysis reactions.

ZnSnS Nanoparticles Synthesized by Simple SMI Technique for Photocatalytic Application

Photocatalysis, driven by semiconductor nanoparticles under visible or ultraviolet light, has emerged as a powerful and sustainable approach for environmental remediation and clean energy production. In this study, we investigate the photocatalytic potential of tin (0, 2, 4, 6, 8, 10) mole % alloyed with zinc sulfide (ZnSnS) nanoparticles as efficient catalysts for various environment and energy-related applications. ZnSnS nanoparticles were produced via a simple microwave irradiation technique. Comprehensive structural characterization through X-ray diffraction (XRD), FESEM, EDAX and HRTEM confirmed the successful incorporation of tin atoms into the ZnS crystal lattice. Optical study indicated significant blue shifts in the absorption edge, extending the light absorption into the visible region, a key advantage for photocatalytic applications. Photocatalytic experiments were conducted to evaluate the performance of Zn-alloyed SnS nanoparticles in degrading organic pollutants and hydrogen evolution from water splitting reactions. Our results revealed remarkable enhancements in photocatalytic activity. The enhanced efficiency can be credited to the creation of fresh energy levels within the bandgap, aiding in the separation and movement of charges, and also to the heightened light absorption caused by the reduced bandgap. Furthermore, stability tests indicated the durability of (ZnSnS) nanoparticles, making them suitable candidates for long-term applications in real-world environments. The observed photocatalytic activity enhancements hold promise for addressing environmental issues, including wastewater treatment, air purification, and hydrogen production for clean energy.

Plasma‐electrified synthesis of atom‐efficient electrocatalysts for sustainable water catalysis and beyond

The downsizing of metal structures to the nano and atomic level, thereby creating nanoparticle catalysts (NPCs), sub‐nanometer cluster catalysts (SNCCs) or single atom catalysts (SACs), has gained significant interest. In particular, synthesizing these types of catalysts using low temperature plasma electrified methods is an emerging field which is highly applicable to electrochemical water splitting for the sustainable production of green hydrogen. Surface modification via plasma treatment provides a route for nanoparticle immobilization or single atom trapping which ensures high atom utilization during electrolysis reactions. Plasma can also be used to create NPCs, SNCCs and SACs from various precursors as well as modify their surface properties once formed which impacts significantly on the oxygen evolution reaction and hydrogen evolution reaction. Therefore, in this review we emphasize the role that low temperature plasma electrified synthetic strategies play in electrocatalyst development for water splitting reactions and explore the crucial relationship between the electronic and coordination environment of atom efficient catalysts and their resulting catalytic activity. We also discuss methods to characterize these types of catalysts and the possibility for scaling up this technology which will be required for commercial applications.

Construction of NiFe/MnNiCo-LDH heterostructure for enhanced oxygen evolution reaction for efficient water splitting

Developing highly efficient and cost-effective oxygen evolution reaction (OER) catalysts is pivotal for advancing sustainable energy storage and conversion technologies. Herein, NiFe/MnNiCo-LDH was successfully prepared by in-situ growth method. The OER performance of this composite material had been significantly enhanced through bimetallic atom modification and cation doping strategies. These modifications not only enhanced the electronic conductivity but also regulated the electron distribution within the catalyst structure. As a result, NiFe/MnNiCo-LDH can reach a current density of 10 mA cm−2 at an overpotential of only 227 mV in the OER reaction. Moreover, the catalyst exhibited remarkable durability and maintained its high performance over an extended period of 48 h during the water splitting reaction. In this work, the potential of dual modification methods for optimizing catalytic properties of OER materials was investigated.

Ionic covalent organic framework-MXene heterojunction constructed by electrostatic interaction for stable electrocatalytic hydrogen generation

Constructing stable electrocatalysts by pyrolysis-free technique is an important topic in hydrogen-evolution reaction (HER) for water splitting reactions. Covalent organic frameworks (COFs), an emerging class of porous materials, offer ideal candidates owing to their abundant active sites and unique structures. Herein, a novel pyrolysis-free heterostructure was constructed using electrostatic interactions between an ionic COF (JUC-628) and Ti3C2Tx (MXene) nanosheets, which exhibits an impressively low overpotential of 137 mV at 10 mA cm−2 and excellent catalytic activity and stability for five days operation under alkaline conditions. Theoretical calculations depict that the formation of a stable heterostructure between MXene nanosheets and JUC-628 is the critical factor underlying the outstanding catalytic performance. Moreover, the optimized catalyst showed superior hydrogen-evolution capability in alkaline seawater electrolysis, highlighting the first successful application of a COF-based catalyst for hydrogen production from seawater electrolysis. As a leading covalent organic porous material–based catalyst for HER, as a proof of concept, this study represents a novel strategy to construct efficient electrocatalysts by COFs directly without the pyrolysis technique.

In Situ Photoelectrodeposited Polyaniline on Ti‐Doping Hematite For Highly Selective Photoelectrochemical Oxygen Demand Determination

AbstractChemical Oxygen Demand (COD), as a detection indicator of water pollution, is of particular importance in assessing organic pollution in water. Furthermore, accurate and simple measuring COD methods are essential for water quality assessment and pollution control. However, the photoelectrochemical oxygen demand (PECOD) measurement, as one of the measuring COD methods, is affected by the reaction of water splitting, which is one of the hindrances to the commercialization of the analytical method of the PeCOD measurement. Hence, to overcome this challenge, a new PANI/Ti:Fe2O3 photoanode is constructed by hydrothermal and photoelectrochemical (PEC) deposition methods and investigated their optical properties and photoactivity. Under optimization conditions, it is discovered that the oxidation of organic compounds produces a net steady‐state current (inet) is directly proportional to COD concentration, with a detection limit of 1 mM glucose solution and a wide linear detection range of 1–78.125 mM, which is suitable for high concentration of glucose detection. As has been noted, PANI/Ti:Fe2O3 photoanode overcomes the obstacles to the practical application and eventual commercialization of the PECOD technology.