A sustainable molybdenum oxysulphide-cobalt phosphate photocatalyst for effectual solar-driven water splitting

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Facile synthesis of Molybdenum oxysulphide-cobalt phosphate (MoO_xS_y-CoPi) novel material for solar water splitting.

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The MoO_xS_y-CoPI photocatalyst corresponded to the most stable oxidation states of Mo, Co, S, P, and O in the composite.

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Nanoflowers of MoO_xS_y-CoPI showed controlled thickness up to ∼10 nm, and variable interspaces of 200-400 nm were produced.

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Band-gap energy of 2.44 eV and significantly higher (7-8 folds) photocurrent density of MoO_xS_y-CoPI is recorded compared to MoO_xS_y and CoPI.

Introduction

Hydrogen is considered as a clean alternative green energy future fuel. Since the Honda-Fujishima effect for photoelectrochemical water splitting is known, there has been a substantial boost in this field. Numerous photocatalysts based on metals, semiconductors, and organic-inorganic hybrid-systems have been proposed. Several factors limit their efficiency, e.g., a stable PEC-WS setup, absorbing visible light, well-aligned band energy for charge transfer, electrons and holes, and their separation to avoid recombination and limited water redox reactions. Metallic doping and impregnation of stable and efficient co-catalysts such as Pt, Ag, and Au showed enhanced PEC-WS. We used Cobalt-based co-catalyst with molybdenum oxysulfide photocatalyst for effectual solar-driven water splitting.

Objectives

To develop photocatalysts for efficient PEC processes capable of absorbing sufficient visible light, good band energy for effective charge transfer, inexpensive, significant solar-to-chemical energy conversion efficiencies. Above all, it is developing such PEC-WS systems that will be commercially viable for renewable energy resources.

Methods

We prepared Molybdenum oxysulphide-cobalt phosphate photocatalyst for PEC-WS through a facile hydrothermal route using ammonium heptamolybdate, thiourea, and metallic Cobalt precursors.

Results

An effectual photocatalyst is produced for solar-driven water splitting. The conformal morphology of MoO_xS_y-CoPi nanoflowers is a significant feature, as observed under FE-SEM and HR-TEM. XRD confirmed the degree of purity and orthorhombic crystal structure of MoO_xS_y-CoPi. EDX and XPS identify the elemental compositions and corresponding oxidation states of each atom. A 2.44 eV band-gap energy is calculated for MoO_xS_y-CoPi from the diffused reflectance spectrum. Photo- Electrochemical Studies (PEC) under 1-SUN solar irradiation revealed 7-8 folds enhanced photocurrent (∼ 3.5 mA/cm2) generated from MoO_xS_y-CoPi/FTO in comparison to Co-PI/FTO (∼ 0.5 mA/cm2) and MoO_xS_y-/FTO respectively, within 0.5 M Na₂SO₄ electrolyte (@pH=7) and standard three electrodes electrochemical cell.

Conclusion

Our results showed MoO_xS_y-CoPi as promising photocatalyst material for improved solar-driven photoelectrochemical water splitting system.

Glass wool: a novel support for heterogeneous catalysis

Heterogeneous catalysis presents significant advantages over homogeneous catalysis such as ease of separation and reuse of the catalyst. Here we show that a very inexpensive, manageable and widely available material - glass wool - can act as a catalyst support for a number of different reactions. Different metal and metal oxide nanoparticles, based on Pd, Co, Cu, Au and Ru, were deposited on glass wool and used as heterogeneous catalysts for a variety of thermal and photochemical organic reactions including reductive de-halogenation of aryl halides, reduction of nitrobenzene, Csp3-Csp3 couplings, N-C heterocycloadditions (click chemistry) and Csp-Csp2 couplings (Sonogashira couplings). The use of glass wool as a catalyst support for important organic reactions, particularly C-C couplings, opens the opportunity to develop economical heterogeneous catalysts with excellent potential for flow photo-chemistry application.

An amorphous dual action electrocatalyst based on oxygen doped cobalt sulfide for the hydrogen and oxygen evolution reactions

Here we electrodeposit an amorphous bifunctional electrocatalyst that is active for both the HER and OER under alkaline conditions which is based on oxygen doped cobalt sulfide.

Ionic-Liquid-Modified Hybrid Materials Prepared by Physical Vapor Codeposition: Cobalt and Cobalt Oxide Nanoparticles in [C1C2Im][OTf] Monitored by In Situ IR Spectroscopy

The synthesis of ionic-liquid-modified nanomaterials has attracted much attention recently. In this study we explore the potential to prepare such systems in an ultraclean fashion by physical vapor codeposition (PVCD). We codeposit metallic cobalt and the room-temperature ionic liquid (IL) 1-ethyl-3-methylimidazolium trifluoromethanesulfonate [C1C2Im][OTf] simultaneously onto a Pd(111) surface at 100 K. This process is performed under ultrahigh-vacuum (UHV) conditions in the presence of CO, or in the presence of O2 and CO. We use time-resolved (TR) and temperature-programmed (TP) infrared reflection absorption spectroscopy (IRAS) to investigate the formation and stability of the IL-modified Co deposits in situ during the PVD-based synthesis. CO is used as a probe molecule to monitor the growth. After initial growth of flat Co films on Pd(111), multilayers of Co nanoparticles (NPs) are formed. Characteristic shifts and intensity changes are observed in the vibrational bands of both CO and the IL, which originate from the electric field at the IL/Co interface (Stark effect) and from specific adsorption of the [OTf](-) anion. These observations indicate that the Co aggregates are stabilized by mixed adsorbate shells consisting of CO and [OTf](-). The CO coverage on the Co particle decreases with increasing temperature, but some CO is preserved up to the desorption temperature of the IL (370 K). Further, the IL shell suppresses the oxidation of the Co NPs if oxygen is introduced in the PVCD process. Only chemisorbed oxygen is formed at oxygen partial pressures that swiftly lead to formation of Co3O4 in the absence of the IL (5 × 10(-6) mbar O2). This chemisorbed oxygen is found to destabilize the CO ligand shell. The oxidation of Co is not suppressed if IL and Co are deposited sequentially under otherwise identical conditions. In this case we observe the formation of fully oxidized cobalt oxide particles.

On the cobalt and cobalt oxide electrodeposition from a glyceline deep eutectic solvent

The electrodeposition of cobalt and cobalt oxides from a glyceline deep eutectic solvent is reported.

Electrodeposition in Ionic Liquids

Due to their attractive physico-chemical properties, ionic liquids (ILs) are increasingly used as deposition electrolytes. This review summarizes recent advances in electrodeposition in ILs and focuses on its similarities and differences with that in aqueous solutions. The electrodeposition in ILs is divided into direct and template-assisted deposition. We detail the direct deposition of metals, alloys and semiconductors in five types of ILs, including halometallate ILs, air- and water-stable ILs, deep eutectic solvents (DESs), ILs with metal-containing cations, and protic ILs. Template-assisted deposition of nanostructures and macroporous structures in ILs is also presented. The effects of modulating factors such as deposition conditions (current density, current density mode, deposition time, temperature) and electrolyte components (cation, anion, metal salts, additives, water content) on the morphology, compositions, microstructures and properties of the prepared materials are highlighted.

Controlled electrodeposition of nanostructured Pd thin films from protic ionic liquids for electrocatalytic oxygen reduction reactions

Nanostructured Pd thin films are prepared from protic ionic liquids via hydrogen-assisted electrodeposition for oxygen reduction reactions.

Heat treatment of electrodeposited NiO films for improved catalytic water oxidation

The heat treatment of electrodeposited nickel oxide (NiO) films showed remarkable improvements for catalytic water oxidation.