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This study aims to produce diisopropyl ether (DIPE) via isopropanol dehydration using cobalt-phosphate-supported natural zeolite catalysts. The catalytic activities of the zeolite/CoO and zeolite/Co(H2PO4)2 were compared. The as-prepared catalysts were assessed using X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX), Fourier transform infrared (FTIR) spectroscopy, and N2 adsorption-desorption. Surface acidity was determined using the gravimetric method with pyridine as the probe. The results of this study showed that natural zeolite was favorably impregnated by CoO and Co(H2PO4)2 species. The impregnation process affected the textural and acidic features of the catalysts. The zeolite/Co(H2PO4)2 catalyst with a loading of 8 mEq.g-1 exhibited the highest surface acidity of 1.827 mmol.g-1. This catalyst also promoted the highest catalytic activity towards isopropanol dehydration, with an isopropanol conversion of 66.19%, DIPE selectivity, and yield of 46.72% and 34.99%, respectively. The cobalt phosphate species promoted higher catalytic activity for isopropanol dehydration than the CoO species. This study demonstrated the potential of cobalt phosphate-supported natural zeolite catalysts for DIPE production with adequate performance. Copyright © 2024 by Authors, Published by BCREC Publishing Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

In the quest for effective photocatalysts for hydrogen production via photocatalytic water splitting, ZnIn 2 S 4 has garnered considerable attention due to its high photocatalytic hydrogen evolution capability. In this study, boron-doped ZnIn 2 S 4 was successfully synthesized via a hydrothermal method, with a small amount of cobalt phosphate (Co-Pi) decorated on its surface. The hydrogen evolution rate of boron-doped ZnIn 2 S 4 was determined to be 5.2 mmol g−1 h−1, surpassing that of pure ZnIn 2 S 4 by 1.68 times. Moreover, with the addition of Co-Pi to boron-doped ZnIn 2 S 4 , the hydrogen production rate escalated to 29.7 mmol g−1 h−1, which is 9.58 times higher compared to pure ZnIn 2 S 4. UV–vis analysis revealed that boron doping introduced new energy levels into ZnIn 2 S 4 , effectively narrowing the bandgap and enhancing light absorption wavelength range. Furthermore, PL and XPS analyses indicate that Co-Pi effectively captures photogenerated holes (h+) in ZnIn 2 S 4 , retaining photogenerated electrons and overcoming the disadvantage of electron-hole pair recombination in ZnIn 2 S 4. The doping and loading of Co-Pi as a cocatalyst ultimately contribute to enhancing hydrogen production efficiency, thereby significantly improving the photocatalytic hydrogen evolution capability of ZnIn 2 S 4. This study provides a scalable idea for designing composite catalysts in which doping and co-catalysts work together. • ZnIn 2 S 4 (ZIS) was synthesized hydrothermally using ZnCl 2 , In(NO 3) 3 ·xH 2 O, and thioacetamide (TAA) as precursors. • Defective ZnIn 2 S 4 (B-ZIS) was hydrothermally synthesized from ZIS and NaBH 4. • B-ZIS-CP composites were prepared through the in situ photodeposition of cobalt phosphide (Co-Pi) onto B-ZIS. • The composite catalysts exhibited exceptional photocatalytic activity for hydrogen evolution. • B-ZIS-CP demonstrates remarkable separation efficiency of photogenerated electron-hole pairs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Stacked-layer structure of BCoPi enables facile adsorption of OER intermediates. • Electron deficient nature of borophene in BCoPi modulates oxidation states of Co. • Conductive borophene decreases charge transfer resistance increasing OER kinetics. • Borophene provides active sites in addition to Co. • BCoPi electrocatalyst exhibits excellent OER activity and outstanding stability. Developing efficient, low-cost, non-precious and stable electrocatalyst is necessary for sustainable electrocatalytic water splitting. Recently, borophene has emerged as a novel two-dimensional material with exciting properties. Although several researchers have theoretically predicted its applicability towards effective electrocatalytic water splitting, studies on its practical applications are still limited. In this regard, a mixed-valent cobalt phosphate/borophene nanohybrid (BCoPi) was synthesized using hydrothermal method, and its activity towards oxygen evolution reaction (OER) was systematically studied. The electron-deficient nature of borophene enables activation of catalytic sites and facilitates electron transport owing to its highly conductive nature. It can act as a proton acceptor along with phosphate groups, as well as provide multiple secondary active sites in addition to Co, breaking the scaling relation of OER. For BCoPi, achieving a current density of 50 mA cm−2, 100 mA cm−2 and 500 mA cm−2 requires an overpotential of 337 mV, 357 mV and 401 mV, respectively, in an alkaline medium, that are superior to pristine cobalt phosphate (CoPi). It also exhibits low Tafel slope of 61.81 mV dec−1, suggesting faster OER kinetics and excellent long-term stability. This study will extend the development and application of borophene-based heterostructures for highly active and stable electrocatalysts for various applications. [ABSTRACT FROM AUTHOR]

Molybdate intercalation significantly reduces the thickness of cobalt–nickel layered hydroxide, greatly increases its specific surface area, regulates its pore distribution, increases the crystal plane spacing, promotes the diffusion rate of hydroxide in it, and increases its specific capacity. Meanwhile, the bilayered MCN-LDH@CP electrode significantly improved the areal energy density and peak power density and cycle stability of the CoNi//Zn battery. The quasi-solid-state MCN-LDH@CP//Zn battery can still charge a mobile phone even when hammered and pierced, showing excellent safety and reliability. [Display omitted] Seeking cathode materials with high areal capacity and excellent cycling tolerance is a key step to develop aqueous rechargeable zinc-based alkaline batteries with high energy density, power density and excellent stability. Here, the bilayered cathode composite (MCN-LDH@CP) of molybdate intercalated cobalt–nickel layered hydroxide nanosheets (MCN-LDH) grown on cobalt phosphate octahydrate microsheet (CP) was prepared by a two-step hydrothermal process. Molybdate intercalation significantly reduces the thickness of cobalt–nickel layered hydroxide, greatly increases its specific surface area, regulates its pore distribution, increases the crystal plane spacing, promotes the diffusion rate of hydroxide in it, and increases its specific capacity. Meanwhile, the bilayered MCN-LDH@CP electrode significantly improved the areal energy density (2.89 mWh/cm2) and peak power density (111.22 mW/cm2) and cycle stability (97.8 % after 7000 cycles) of the CoNi//Zn battery. The excellent stability is mainly due to the fact that the MCN-LDH overlay inhibits the loss of P element of CP and improves the structural stability of the sample. The quasi-solid-state MCN-LDH@CP//Zn battery can still charge a mobile phone even when hammered and pierced, showing excellent safety and reliability. This work opens a new avenue to develop CoNi//Zn batteries with high energy density, power density and excellent tolerance. [ABSTRACT FROM AUTHOR]

The high electrons and holes recombination rate of ZnIn2S4 significantly limits its photocatalytic performance. Herein, a simple in situ photodeposition strategy is adopted to introduce the cocatalyst cobalt phosphate (Co-Pi) on ZnIn2S4, aiming at facilitating the separation of electron–hole by promoting the transfer of photogenerated holes of ZnIn2S4. The study reveals that the composite catalyst has superior photocatalytic performance than blank ZnIn2S4. In particular, ZnIn2S4 loaded with 5% Co-Pi (ZnIn2S4/5%Co-Pi) has the best photocatalytic activity, and the H2 production rate reaches 3593 μmol·g−1·h−1, approximately double that of ZnIn2S4 alone. Subsequent characterization data demonstrate that the introduction of the cocatalyst Co-Pi facilitates the transfer of ZnIn2S4 holes, thus improving the efficiency of photogenerated carrier separation. This investigation focuses on the rational utilization of high-content and rich cocatalysts on earth to design low-cost and efficient composite catalysts to achieve sustainable photocatalytic hydrogen evolution. [ABSTRACT FROM AUTHOR]

In the present work, carbon nitride quantum dots (CNQDs)‐modified cobalt phosphate (CoPi) composites CNQDs/CoPi‐x (x = 1, 2, 3) were prepared at room temperature and characterized by FTIR, XRD, UV–Vis DRS, EIS, SEM, TEM/HR‐TEM, XPS, and N2 gas adsorption. The morphologies and surface areas of CNQDs/CoPi‐x have no remarkable change after modification of CNQDs, compared with pure CoPi. The obtained CNQDs/CoPi‐x shows enhanced activity and stability of photocatalytic H2 evolution compared to pure CoPi using Eosin Y (EY) as a sensitizer and triethanolamine as an electron donor. The CNQDs/CoPi‐2 possesses the highest hydrogen evolution rate, 234.5 μmol h−1 g−1, upon visible light, which outshines that of CoPi by 2.4 times. It was believed that the enhanced photocatalytic performances of the CNQDs/CoPi‐2 could result from the boosted electron transfer from radical EY·− to CNQDs/CoPi‐2 by the employment of CNQDs; in addition, the visible‐light activity of CNQDs contributes to hydrogen evolution. The mechanism of photocatalytic hydrogen production was discussed. This study may contribute toward the development of production of "green hydrogen" using solar. [ABSTRACT FROM AUTHOR]

Hydrogen （H2 ), a renewable green energy source， has been widely focused on tackling environmental issues and fossil energy shortages. The development of low-cost， highly efficient and stable electrocatalysts towards hydrogen evolution reaction （HER） is one of the major challenges facing the large-scale utilization of hydrogen. Cobalt phosphide （CoP） has been widely studied in the field of electrocatalytic HER due to its metal-like properties and corrosion resistance in acid and alkali electrolytes. This review firstly elaborates the major advantages and challenges for CoP heterojunction as electrocatalyst for HER. Next， the different effects of the CoP heterojunction on HER are discussed. Finally， the prospects of CoP heterojunction for HER electrocatalysis are summarized and prospected. [ABSTRACT FROM AUTHOR]

The present work demonstrates electrochemical performance of cobalt phosphate (CP) thin films prepared by chemical bath deposition technique. The prepared (CP) films are of monoclinic phase with highly preferred orientation along (240) plane. Morphology studies on the CP films with different concentration reveal nanospheres along with the growth of intermediate nanosheets. The electrode with 3.5 M cobalt concentration (CP3) offers more active sites and enhanced electrochemical performance as compared to the other two electrodes, viz, CP1 and CP2 which contain lower concentration of cobalt. The CP3 electrode shows maximum specific capacitance of 678 Fg−1 at a scan rate of 10 mVs−1 and 90.46% capacitive retention after 10,000 cycles. The impact of capacitive and diffusive contributions to the total capacity of the electrodes is studied by employing Trasatti and Dunn's model. The results on the study of CP thin film electrodes establish their potential for the growing energy storage applications. [ABSTRACT FROM AUTHOR]

The different proportions of cobalt phosphate-containing nano-crystallite composite paints have been synthesized with CaCO3 and polyvinyl acetate adhesive. The abbreviations of these composite paints are CPM2, 2.50% Co3(PO4)2, CPM4, 4.49% Co3(PO4)2, and CPM6, 6.52% Co3(PO4)2. The specific heat capacity (Cp) of all these composite paints is found endothermic. The optimum value of Cp is observed for CPM2 composite paint among all paints. At 298 K, Cp of composite paints are 1.00 J g−1 K−1 for CPM2, 0.88 J g−1 K−1 for CPM4, and 0.81 J g−1 K−1 for CPM6. The Cp of Co3(PO4)2 is 0.94 J g−1 K−1 at 298 K. The ∼ 80% reflectance of polyvinyl acetate containing CaCO3 paint is reduced to ∼ 30% with the addition of 6.52% Co3(PO4)2. The composite paints are found semiconducting behavior due to band gap Eg 2.15 eV at λmax = 576 nm. The crystallite size of the CPM6 composite paint is 59.64 nm. [ABSTRACT FROM AUTHOR]

Copper and cobalt from industrial operations build up in the environment, posing a substantial health risk. This study examined how ethylenediaminetetraacetic acid (EDTA), citrate, and chloride ions affected the fluidized bed homogeneous granulation process' (FBHGP) ability to recover both individual and combination of copper and cobalt ions from simulated waste streams. A 99% copper removal and 95% granulation efficiency were attained in copper-based solutions. The soluble copper still present in the solution caused a 4% variation in the removal and granulation efficiencies. There were 99% removal and 99% granulation efficiencies in cobalt-based solutions. When EDTA was present in a copper-based solution, 95% removal and 86% granulation were reached, and for cobalt-based solutions, 95% and 91% were the removal and granulation efficiency, respectively. The presence of citrate in the copper-based solution obtained the removal of 83% and granulation efficiency of 54% at 0.1 MR of citrate to copper. No copper phosphate precipitate was formed when the MR was greater than 0.1. There were 96% removal and 92% granulation efficiency when citrate was present in cobalt-based solutions. The presence of chloride ions in copper solution achieved a 99% removal and 91% granulation efficiency, while in cobalt solutions, 99% removal and 98% granulation efficiency were attained. Solutions with combined copper and cobalt with chloride ions achieved 99% removal and 95% granulation efficiency for copper and 99% removal and 95% granulation efficiency for cobalt. The granule sizes decreased as the MR of the complexing agents to metal, and the concentration of chloride ions increased. The peaks on the XRD pattern exactly matched the peaks of cobalt phosphate hydrate (Co 3 (PO 4) 2 ·8 H 2 O). FBHGP has effectively recovered copper and cobalt from the waste streams of simulated metals. [ABSTRACT FROM AUTHOR]

Photoelectrochemical (PEC) solar water splitting is favourable for transforming solar energy into sustainable hydrogen fuel using semiconductor electrodes. Perovskite-type oxynitrides are attractive photocatalysts for this application due to their visible light absorption features and stability. Herein, strontium titanium oxynitride (STON) containing anion vacancies of SrTi(O,N)3−δ was prepared via solid phase synthesis and assembled as a photoelectrode by electrophoretic deposition, and their morphological and optical properties and PEC performance for alkaline water oxidation are investigated. Further, cobalt-phosphate (CoPi)-based co-catalyst was photo-deposited over the surface of the STON electrode to boost the PEC efficiency. A photocurrent density of ~138 μA/cm at 1.25 V versus RHE was achieved for CoPi/STON electrodes in presence of a sulfite hole scavenger which is approximately a four-fold enhancement compared to the pristine electrode. The observed PEC enrichment is mainly due to the improved kinetics of oxygen evolution because of the CoPi co-catalyst and the reduced surface recombination of the photogenerated carriers. Moreover, the CoPi modification over perovskite-type oxynitrides provides a new dimension for developing efficient and highly stable photoanodes in solar-assisted water-splitting reactions. [ABSTRACT FROM AUTHOR]

The high electrons and holes recombination rate of ZnIn2S4 significantly limits its photocatalytic performance. Herein, a simple in situ photodeposition strategy is adopted to introduce the cocatalyst cobalt phosphate (Co-Pi) on ZnIn2S4, aiming at facilitating the separation of electron–hole by promoting the transfer of photogenerated holes of ZnIn2S4. The study reveals that the composite catalyst has superior photocatalytic performance than blank ZnIn2S4. In particular, ZnIn2S4 loaded with 5% Co-Pi (ZnIn2S4/5%Co-Pi) has the best photocatalytic activity, and the H2 production rate reaches 3593 μmol·g−1·h−1, approximately double that of ZnIn2S4 alone. Subsequent characterization data demonstrate that the introduction of the cocatalyst Co-Pi facilitates the transfer of ZnIn2S4 holes, thus improving the efficiency of photogenerated carrier separation. This investigation focuses on the rational utilization of high-content and rich cocatalysts on earth to design low-cost and efficient composite catalysts to achieve sustainable photocatalytic hydrogen evolution.

Attractive technology for producing sustainable hydrogen with water electrolyzers was foreseen as one of the most promising ways to meet the increasing demands of renewable resources and electricity storage. Mainly used for the efficient generation of H2, water electrolysis involving hydrogen evolution reactions (HERs) depends on efficient and affordable electrocatalysts. Hydrogen is an effective fuel that can be produced by splitting water. Hence, the search for highly efficient HER catalysts is a major challenge as efficient hydrogen evolution catalysts are sought to replace catalysts such as platinum. Here, we describe a low-cost and highly effective electrocatalyst for the proper incorporation of the HER electrocatalyst with low overpotential, effective charge transfer kinetics, low Tafel slope, and good durability. By using a simple hydrothermal approach to produce Co3(PO4)2.8H2O/CNF, it is possible to attach Co3(PO4)2.8H2O to the surface of carbon nanofibers (CNFs), which also exhibit remarkable HER activity at an overpotential of 133 mV and produce a current density of 10 mA/cm2 and a 48 mV/decade for the Tafel slope. Large electrochemical surface areas and easy charge transfer from Co3(PO4)2.8H2O to the electrode through conductive Co3(PO4)2.8H2O/CNF composites are the reasons for the improved performance of Co3(PO4)2.8H2O/CNF.

The observation of a spontaneous electron enrichment at the apexes of bismuth vanadate (BiVO4) nanopyramidal arrays is achieved by performing synchrotron-based angular dependent X-ray absorption spectroscopy. In accordance with density function theory calculations, the formation of (112) facets enriched apexes is proposed. Such intrinsically electron-enriched (112) facets at the apexes produce a potential facilitating the diffusion of photoexcited holes, which not only mitigates the recombination with the photoexcited electrons, but also provide an active reaction site for the photoassisted selective growth of cobalt phosphate (CoPi), a well known and highly active co-catalyst for water oxidation at the apex of BiVO4 nanopyramids. Benefiting from the element-resolved properties of synchrotron-based X-ray spectroscopy, 3d electrons on the vanadium site are directly resolved by resonant inelastic X-ray scattering measurements. Due to this unique morphology, the charge at the apex is expected to induce a strong interaction with CoPi, as a result of the metal-to-ligand charge transfer spectroscopy feature observed from the cobalt site. Substantial evidences are collected by means of comprehensive soft X-ray spectroscopy techniques with high spectral resolution revealing the atomic-scale origin and the nature of the synergy as well as the strong correlation between its unique structural properties and the electronic structure of this novel highly-ordered hybrid photocatalyst and its significantly improved photoelectrochemical performance.

The observation of a spontaneous electron enrichment at the apexes of bismuth vanadate (BiVO4) nanopyramidal arrays is achieved by performing synchrotron-based angular dependent X-ray absorption spectroscopy. In accordance with density function theory calculations, the formation of (112) facets enriched apexes is proposed. Such intrinsically electron-enriched (112) facets at the apexes produce a potential facilitating the diffusion of photoexcited holes, which not only mitigates the recombination with the photoexcited electrons, but also provide an active reaction site for the photoassisted selective growth of cobalt phosphate (CoPi), a well known and highly active co-catalyst for water oxidation at the apex of BiVO4 nanopyramids. Benefiting from the element-resolved properties of synchrotron-based X-ray spectroscopy, 3d electrons on the vanadium site are directly resolved by resonant inelastic X-ray scattering measurements. Due to this unique morphology, the charge at the apex is expected to induce a strong interaction with CoPi, as a result of the metal-to-ligand charge transfer spectroscopy feature observed from the cobalt site. Substantial evidences are collected by means of comprehensive soft X-ray spectroscopy techniques with high spectral resolution revealing the atomic-scale origin and the nature of the synergy as well as the strong correlation between its unique structural properties and the electronic structure of this novel highly-ordered hybrid photocatalyst and its significantly improved photoelectrochemical performance.

Active site engineering for electrocatalysts is an essential strategy to improve their intrinsic electrocatalytic capability for practical applications and it is of great significance to develop a new excellent electrocatalyst for overall water splitting. Here, Co 3 O 4 /nickel foam (NF) and Co 2 (P 4 O 12)/NF electrocatalysts with flower-shaped and sea urchin-shaped structures are synthesized by a simple hydrothermal process and followed by a post-treatment method. Among them, Co 2 (P 4 O 12)/NF shows good catalytic activity for hydrogen evolution reaction (HER), and at the current density of 10 mA cm−2, the overpotential is only 113 mV Co 3 O 4 /NF exhibits good catalytic activity for oxygen evolution reaction (OER), and the overpotential is 327 mV at 20 mA cm−2. An alkaline electrolyzer with Co 3 O 4 /NF and Co 2 (P 4 O 12)/NF catalysts respectively as anode and cathode displays a current density of 10 mA cm−2 at a cell voltage of 1.59 V. This work provides a simple way to prepare high efficient, low cost and rich in content promising electrocatalysts for overall water splitting. [Display omitted] • Self-supporting materials avoid the use of adhesives. • Flower-shaped and sea urchin-shaped structures increase number of active sites. • Unique structure facilitates electrolyte immersion and separation of bubbles. • Oxygen vacancy-rich Co 3 O 4 can effectively catalyze OER. • Self-supporting Co 3 O 4 /NF and Co 2 (P 4 O 12)/NF display good electrochemical stability. [ABSTRACT FROM AUTHOR]

Understanding the structure-activity correlation is an important prerequisite for the rational design of high-efficiency electrocatalysts at the atomic level. However, the effect of coordination environment on electrocatalytic oxygen evolution reaction (OER) remains enigmatic. In this work, the regulation of proton transfer involved in water oxidation by coordination engineering based on Co 3 (PO 4 ) 2 and CoHPO 4 is reported. The HPO 4 2- anion has intermediate pK a value between Co(II)-H 2 O and Co(III)-H 2 O to be served as an appealing proton-coupled electron transfer (PCET) induction group. From theoretical calculations, the pH-dependent OER properties, deuterium kinetic isotope effects, operando electrochemical impedance spectroscopy (EIS) and Raman studies, the CoHPO 4 catalyst beneficially reduces the energy barrier of proton hopping and modulates the formation energy of high-valent Co species, thereby enhancing OER activity. This work demonstrates a promising strategy that involves tuning the local coordination environment to optimize PCET steps and electrocatalytic activities for electrochemical applications. In addition, the designed system offers a motif to understand the structure-efficiency relationship from those amino-acid residue with proton buffer ability in natural photosynthesis., (© 2024 Wiley‐VCH GmbH.)

Summary: Photoelectrochemical (PEC) catalysis offers promising strategies for sustainable development. This study demonstrated the synergistic catalytic behavior of ZrO2 and a cobalt phosphate on anodized TiO2 nanotubes (TNTs), which significantly enhanced the PEC performance for visible‐light‐driven water splitting reactions. The sequential addition of ZrO2/CoPi‐decorated TNTs was performed via electrodeposition and photoassisted electrodeposition. The substitution of Zr4+ by Ti4 can lead to the creation of oxygen vacancies, enabling electron trapping, reducing charge recombination, and thereby enhancing the charge transfer efficiency. Further, in the case of TNTs/ZrO2/CoPi photoanode, the CoPi WOC functioned as a hole‐transfer relay to promote the water‐splitting reaction. Specifically, incorporating ZrO2/CoPi rushes the surface reaction kinetics of TNTs and considerably improves charge transfer efficiency (ηCT = 90%), photocurrent density (0.86 mA/cm2 at 1.23 VRHE) and durability were obtained. Further, the mechanistic examination by impedance measurements showed the enhanced charge transfer, and surface conductivity for prepared materials. The proposed method can be widely used to develop electrodes made of other materials to produce solar fuels. [ABSTRACT FROM AUTHOR]

Photoelectrochemical (PEC) solar water splitting is favourable for transforming solar energy into sustainable hydrogen fuel using semiconductor electrodes. Perovskite-type oxynitrides are attractive photocatalysts for this application due to their visible light absorption features and stability. Herein, strontium titanium oxynitride (STON) containing anion vacancies of SrTi(O,N)3−δ was prepared via solid phase synthesis and assembled as a photoelectrode by electrophoretic deposition, and their morphological and optical properties and PEC performance for alkaline water oxidation are investigated. Further, cobalt-phosphate (CoPi)-based co-catalyst was photo-deposited over the surface of the STON electrode to boost the PEC efficiency. A photocurrent density of ~138 μA/cm at 1.25 V versus RHE was achieved for CoPi/STON electrodes in presence of a sulfite hole scavenger which is approximately a four-fold enhancement compared to the pristine electrode. The observed PEC enrichment is mainly due to the improved kinetics of oxygen evolution because of the CoPi co-catalyst and the reduced surface recombination of the photogenerated carriers. Moreover, the CoPi modification over perovskite-type oxynitrides provides a new dimension for developing efficient and highly stable photoanodes in solar-assisted water-splitting reactions.

Cobalt phosphate materials were prepared in the present work in one step at room temperature using different raw materials and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and N2 gas adsorption. Cobalt phosphates exhibit 3D flower-like structures, and the assembly of nanosheets (petals of the "flowers") of cobalt phosphate prepared with sodium phosphate and cobalt acetate as raw materials (denoted as Co-P(A)) is more incompact than that of cobalt phosphate prepared with diammonium hydrogen phosphate and cobalt nitrate as raw materials (denoted as Co-P(B)) due to the former's mildly basic environment. The cobalt phosphates show relatively high photocatalytic activity for H2 evolution reaction (HER) in the presence of Eosin Y as a sensitizer in an aqueous triethanolamine solution. The activity of Co-P(A) (0.40 mmol h−1 g−1) exceeds that of Co-P(B) (0.19 mmol h−1 g−1), which can be attributed to a more dispersive nanosheet and larger BET-specific surface area of Co-P(A). The mechanisms of photocatalytic HER and the formation of flower-like Co3(PO4)2 were discussed. The present system comprising of only abundant elements contributes toward the development of cost-efficient solar HER to achieve sustainable development. [ABSTRACT FROM AUTHOR]

In the quest for sustainable energy solutions, the optimization of the photoelectrochemical (PEC) performance of hematite photoanodes through cocatalysts represents a promising avenue. This study introduces a novel machine learning approach, leveraging subtraction descriptors, to isolate and quantify the specific effects of cobalt phosphate (Co-Pi) as a cocatalyst on hematite's PEC performance. By integrating data from various analytical techniques, including photoelectrochemical impedance spectroscopy and ultraviolet-visible spectroscopy, with advanced machine learning models, we successfully predicted the PEC performance enhancement attributed to Co-Pi. The Gaussian process regression (GPR) model emerged as the most effective, revealing the critical influence of the interfacial resistance, bulk resistance, and interfacial capacitance on the PEC performance. These findings underscore the potential of cocatalysts in improving charge separation and extending charge carrier lifetimes, thereby boosting the efficiency of photocatalytic reactions. This study not only advances our understanding of the cocatalyst effect in photocatalytic systems but also demonstrates the power of machine learning in modifying complex materials and guiding the development of optimized photocatalytic materials. The implications of this research extend beyond hematite photoanodes, offering a generalizable framework for enhancing the photoelectrochemical properties of a wide range of material modifications such as cocatalyst deposition, doping, and passivation.

[Display omitted] Hydrogen has attracted increasing attention as clean energy for fuel cells over the past decade. Photoelectrochemical (PEC) water splitting is considered the most feasible production method but its practical efficiency depends significantly on the photogeneration rate of electron (e−) and hole (h+) on a semiconductor photoanode and the rapid separation of these charge carriers. A proper match of small and large bandgap positions is also necessary. This paper presents a three-dimensional core–shell heterostructured tungsten trioxide/bismuth molybdate/cobalt phosphate (WO 3 /Bi 2 MoO 6 /Co‐Pi) photocatalyst synthesized using simultaneous hydrothermal and electrodeposition techniques. Uniform Bi 2 MoO 6 nanoflakes formed on WO 3 nanoplates as evidenced by various micro-spectroscopic techniques. The as-prepared WO 3 /Bi 2 MoO 6 /Co‐Pi hetero-photocatalyst exhibited significantly high photoelectrochemical activity, where its photocurrent efficiency was 4.6 times greater than that of the constituent WO 3. Such drastic improvement in the PEC properties can be corroborated by the appropriate bandgap alignment among WO 3 , Bi 2 MoO 6 , and Co‐Pi, resulting in a sufficient charge carrier density with efficient, fast charge-transport complementing their structural-morphological synergy. Furthermore, a heterojunction charge-transfer mechanism was proposed to verify the role of the co-catalyst, Co‐Pi, in enhancing the photocurrent at the WO 3 /Bi 2 MoO 6 photoanode under the same applied bias. [ABSTRACT FROM AUTHOR]

Main observation and conclusion: Tremendous efforts have been made to the development of highly active, stable hydrogen evolution reaction (HER) electrocatalysts based on earth‐abundant metal compounds. Recently, cobalt phosphorus (Co‐P) catalysts have received particular attention owing to their good performances for the HER. However, the reported Co‐P catalysts were not uniformly anchored on the substrates. Hence, developing Co‐P catalysts with a uniform surface structure for HER remains a major challenge. Herein, we utilized small molecule tris(4‐fluorophenyl)phosphane (PF) for preliminarily functionalizing carbon nanotubes (PF‐CNTs) via π–π stacking interactions. Using these as the substrate, amorphous cobalt phosphate (CoPi) catalysts could then be uniformly anchored on PF‐CNTs by electrodeposition method. These obtained CoPi/PF‐CNTs catalysts show an onset potential low to 29 mV, a low overpotential (105 mV in 0.5 mol/L H2SO4 at a current density of 10 mA·cm–2 with a Tafel plot of 32 mV·dec–1) and an excellent stability for HER in acidic electrolyte, which is a promising noble‐metal‐free HER catalyst. [ABSTRACT FROM AUTHOR]

Main observation and conclusion: Tremendous efforts have been made to the development of highly active, stable hydrogen evolution reaction (HER) electrocatalysts based on earth‐abundant metal compounds. Recently, cobalt phosphorus (Co‐P) catalysts have received particular attention owing to their good performances for the HER. However, the reported Co‐P catalysts were not uniformly anchored on the substrates. Hence, developing Co‐P catalysts with a uniform surface structure for HER remains a major challenge. Herein, we utilized small molecule tris(4‐fluorophenyl)phosphane (PF) for preliminarily functionalizing carbon nanotubes (PF‐CNTs) via π–π stacking interactions. Using these as the substrate, amorphous cobalt phosphate (CoPi) catalysts could then be uniformly anchored on PF‐CNTs by electrodeposition method. These obtained CoPi/PF‐CNTs catalysts show an onset potential low to 29 mV, a low overpotential (105 mV in 0.5 mol/L H2SO4 at a current density of 10 mA·cm–2 with a Tafel plot of 32 mV·dec–1) and an excellent stability for HER in acidic electrolyte, which is a promising noble‐metal‐free HER catalyst. [ABSTRACT FROM AUTHOR]

Electrolytic water splitting is the most effective approach for the production of oxygen and hydrogen as it uses water as a feedstock which is non-toxic, green, and inexpensive. Hydrogen generation by electrolysis of water is an important process for the production of renewable energy resources. The high cost, less abundance, poor stability, and carbon monoxide poisoning of currently used noble metals as electrocatalyst is the bottleneck of this technology. These limitations can be conquered by using transition metal phosphates. In particular, cobalt phosphate-based materials show favorable performance and stability for electrolytic water splitting. Furthermore, cobalt phosphates in combination with semiconductors act as a co-catalyst in solar water oxidation. The variable oxidation state of cobalt is beneficial for fast electron transfer. The phosphate group due to its unique lattice structure helps in the adsorption and dissociation of water on the surface of the electrode. This review will provide a brief outline of the structure and activity relation between cobalt phosphate-based materials. The electrocatalytic applications of these materials in water oxidation, hydrogen generation, and overall water splitting have also been discussed. The role of cobalt phosphate-based materials in water splitting using solar radiation is thoroughly explained. In the end, a diverse range of synthesis methods, challenges, and future prospects have been presented. [ABSTRACT FROM AUTHOR]

Variation of the MO absorbance under sunlight in the presence of (a) Ag 3 PO 4 / Co 3 (PO 4) 2 ,4H 2 O (10%). [Display omitted] • Ag 3 PO 4 /Co 3 (PO 4) 2 ,4H 2 O(10%) was prepared for the first time by hydrothermal/precipitation. • The hetero-junction was characterized by XRD, diffuse reflectance and FT-IR spectroscopy. • A total discoloration of the MO is observed after 60 min under solar irradiation. Ag 3 PO 4 /Co 3 (PO 4) 2 ,4H 2 O(10 %) hetero-junction was synthesized for the first time by hydrothermal/precipitation at room temperature. The samples were characterized by FT-IR spectroscopy, UV–Vis diffuse reflectance and SEM/EDX analysis. The photo electrochemical characterization of Co 3 (PO 4) 2 ,4H 2 O and Ag 3 PO 4 was reported separately. The FT-IR analysis corroborated the formation of the single phase with characteristic bands of Co-O and PO 4 3- units. The gaps of Co 3 (PO 4) 2 ,4H 2 O and Ag 3 PO 4 /Co 3 (PO 4) 2 ,4H 2 O(10 %) are 1.89 and 2.48 eV, respectively. Moreover, the title compound was tested for the degradation of Methyl Orange (MO). The results showed a total degradation within 60 min. under solar illumination, higher than that of Co 3 (PO 4) 2 ,4H 2 O alone. Photo activity is significantly improved thanks to efficient separation of (e-/h+) pairs. A photocatalytic mechanism of the MO oxidation on the hetero-junction was also proposed and discussed where the •OH radical is responsible for the mineralisation. This research paves the way for the synthesis of stable and efficient photocatalysts for the water treatment. A comparative study with the Rhodamine B (Rh B) was reported. [ABSTRACT FROM AUTHOR]

The supercapattery (hybrid energy storage device) has procured miraculous heed for their significant electrochemical performance, constitute combine features of supercapacitor (prodigious power density) and batteries (substantial energy density), still crave for electrode material with better electrochemical conduct. Here, cobalt phosphate ((Co 3 (PO 4) 2) nanostructures were synthesized using sonochemical and hydrothermal approach. The SEM, XRD, and EDX were employed to explore surface morphology, crystal structure, and elemental analysis respectively of as synthesized nanomaterials. The electrochemical performance was evaluated in two and three electrode assembly. The maximum specific capacity of 285 C g-1 at 3 mV/s and 221 C g-1 at 4.1 A g-1 has been obtained by sonochemically synthesized nanomaterial (S1). This electrode material with optimum electrochemical performance was further investigated for supercapattery application. Asymmetric device was fabricated, comprising activated carbon as negative and S1 as positive electrode material. The supercapattery device exhibits a specific capacity of 147.2 C g-1 bearing an outstanding energy density of 34.8 Whkg−1 with a power density of 425.0 W kg-1 at 0.5 A g-1. The device was found to have a remarkable power density of 6800.0 W kg-1 while retaining an energy density of 10.0 Whkg−1 with exceptional capacity preservation of 87.2% after 10,000 consecutive GCD cycles even at 8.0 A g-1. The device performance was further explored in terms of capacitive and diffusion controlled processes and found to have a maximum capacitive contribution of 63.8% at 100 mV s-1. The sonochemical method was found to be the optimal route to synthesize nanomaterials for energy storage applications. [Display omitted] • Cobalt phosphate is synthesized by sonochemical and hydrothermal approach. • High specific capacity of 221.4 C g-1 was obtained via sonochemically synthesized material (S1). • Supercapattery formed by coupling with S1 with activated carbon. • High power density of 6800 W kg-1 and high energy density of 34.75 Whkg−1. • Specific capacity retention of 87.2% after continues 10,000 GCD cycles. [ABSTRACT FROM AUTHOR]

Electrospinning (ES) is a most reliable method for synthesizing one dimensional (1D) fibrous material. Fibrous materials are having peculiar interest owing to their fascinating properties. For efficient hydrogen fuel generation, electrocatalytic water splitting is one of the finest way of producing hydrogen in a pure form. But it is encountered by the counter oxygen evolution reaction (OER) in more often. As of now, noble metal based catalysts are utilized in the commercial sector. Some of the disadvantages associated with the noble materials are restrict their usage commercially. To address this issue, herein, we have synthesized One dimensional (1D), hydrated porous cobalt phosphate fibrous network by an ES method and act as an electrocatalyst for OER in both alkaline and neutral media for the first time, which exhibits an overpotential of 245 and 457 mV respectively at a current density of 10 mAcm−2 with astonishing stability. Hydrated Cobalt phosphate fibrous network was synthesized by an electrospinning method (ES) and utilized as an electrocatalyst for water oxidation in alkaline and neutral media. In both the cases, Cobalt phosphate fibers have exhibits excellent electrocatalytic activity for OER reaction. Image 1 • Hollow porous Cobalt phosphate microfibers (MFs) have been synthesized via ES method. • Synthesized material has been subjected to OER study in different pH conditions. • It has shown the lower overpotential in both alkaline and neutral media. • It has shown excellent stability over 12 h in both pH conditions. [ABSTRACT FROM AUTHOR]

Near-field heterodyne transient grating (NF-HD-TG) responses of hematite (α-Fe 2 O 3 ) treated with cobalt phosphate (Co-Pi) were measured with the burn lasers inducing the depletion of the response by the removal of the trapped charge carriers in the target state, which is called charge carrier-selective heterodyne transient grating (CS-HD-TG) spectroscopic technique. We found that two distinct trap states co-existed in Co-Pi loaded on the surface of α-Fe 2 O 3 . One of them named r-SS2, of which potential was similar to that of r-SS1 in the surface of α-Fe 2 O 3 , acted as a recombination centre but could increase the lifetime of the trapped holes by the charge separation. We also revealed that the energetic position of the other (i-SS2), which has been regarded as the intermediate state for oxygen evolution reaction with low overpotential, was higher than that of i-SS1 in α-Fe 2 O 3 but lower than those of r-SS1 and r-SS2., (© 2024 Wiley-VCH GmbH.)

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Cocatalysts play important roles in photocatalytic and photoelectrochemical water splitting reactions. However, the formation of well-defined junctions between low dimensional semiconductors and cocatalysts is still challenging. In this study, CdS nanorod photoanodes loaded with cobalt phosphate (CoPi) cocatalyst were synthesized by a facile two-step route, in which CdS nanorods were prepared using a hydrothermal method followed by photo-assisted electrodeposition of CoPi. It was found that the formation of intimate junctions between CoPi and CdS nanorods in the form of Co–S bonding effectively facilitated the charge separation and lowered the activation energy of the water oxidation reaction. This resulted in highly efficient and stable photoelectrochemical water splitting on the CdS photoanode. The optimal CdS/CoPi photoanode showed a maximum photocurrent of 4.7 mA/cm2 at 0 V versus reversible hydrogen electrode under an AM 1.5 G solar simulator, which was 5.5-fold higher than that of bare CdS photoanode. This work expands the potential application of the cocatalyst CoPi in CdS photoanode systems and improves our understanding of the nature of cocatalysts with well-defined interface junctions in semiconductors. Well-defined interfacial junction with Co–S bonding over cobalt phosphate cocatalyzed CdS nanorod photoanode facilitates the charge separation and lowers the activation energy, thus achieving a considerable photocurrent of 4.7 mA/cm2 at 0 V vs. RHE. [ABSTRACT FROM AUTHOR]

The correlation between metal coordination and electrocatalytic water oxidation performance is elusive in many cobalt‐based materials. Herein, we designed an ideal Co phosphate‐based platform to explore the effect of coordination environment on oxygen evolution reaction (OER) activity. The cobalt geometry was modulated from octahedral to tetrahedral by simple removal of water ligands in Co3(PO4)2⋅8 H2O. Other features except the coordination structure in the two autologous materials remain similar. The two analogues display the same OER kinetics, but the anhydrous Co3(PO4)2 exhibits a greatly enhanced OER activity. On the basis of Raman and operando XAS results, the higher intrinsic activity of the Co tetrahedral sites is because they facilitate the formation of active high valent cobalt (hydr)oxide intermediates during OER. This work not only brings insights of OER on Co‐based electrocatalysts but also provides a reference system to study the effect of metal geometry on electrocatalysis. [ABSTRACT FROM AUTHOR]

A crystalline mesoporous cobalt phosphate (meso -CoPi) electrocatalyst is prepared using liquid crystal template of non-ionic surfactant of Brij®78. The physicochemical investigations of the electrocatalyst executed by surface area analyzer, XRD, transmission electron microscope submits creation of a mesoporous crystalline nanostructured of meso -CoPi with a surface area of 124 m2 g−1. This is an 10-fold greatness superior than that for bulk -CoPi particles produced without surfactant template. The meso -CoPi electrocatalyst comprises of metallic cobalt layered with a cobalt-oxo/hydroxo-phosphate layer which facilitates the electro-oxidation of methanol at modest overpotential of < 1.2 V vs RHE in alkaline solution. The methanol oxidation activity of the meso -CoPi catalyst shows more than 20-fold current increase at 1.4 V RHE in comparison to bulk -CoPi counterpart which due to the enhancement of the electroactive specific surface area. Liquid crystal template chemical approach provides a reproducible stage to synthesize mesoporous metal phosphates with improved electrocatalytic activities. [ABSTRACT FROM AUTHOR]

An extensive characterization of Co3(PO4)2 was performed by topological analysis according to Bader's Quantum Theory of Atoms in Molecules from the experimentally and theoretically determined electron density. This study sheds light on the reactivity of cobalt orthophosphate as a solid‐state heterogeneous oxidative‐dehydration and ‐dehydrogenation catalyst. Various faces of the bulk catalyst were identified as possible reactive sites given their topological properties. The charge accumulations and depletions around the two independent five‐ and sixfold‐coordinated cobalt atoms, found in the topological analysis, are correlated to the orientation and population of the d‐orbitals. It is shown that the (011) face has the best structural features for catalysis. Fivefold‐coordinated ions in close proximity to advantageously oriented vacant coordination sites and electron depletions suit the oxygen lone pairs of the reactant, mainly for chemisorption. This is confirmed both from the multipole refinement as well as from density functional theory calculations. Nearby basic phosphate ions are readily available for C−H activation. [ABSTRACT FROM AUTHOR]

Developing cost-efficient and high-performance non-noble metal electrocatalysts for oxygen reduction reaction is of great significance for large-scale commercialization of fuel cells. Here, a novel cobalt phosphate-embedded nitrogen and phosphorus co-doped graphene aerogel [labeled as Co3(PO4)2/N,P-GA] is prepared via combination of a facile hydrothermal apporoach with a pyrolysis procedure. The obtained Co3(PO4)2/N,P-GA catalysts display excellent catalytic performance in base media, with optimal Co3(PO4)2/N,P-GA-900 (the material prepared at pyrolysis temperature of 900°C) showing better catalytic activity for ORR than other as-obtained contrast materials in terms of the onset potential, half-wave potential and diffusion-limiting current density, even superior to the commercial Pt/C catalyst. Furthermore, the Co3(PO4)2/N,P-GA also possesses good methanol tolerance and excellent durability. The superior performance of Co3(PO4)2/N,P-GA is attributed to the hierachical porous structure, large BET surface area, N,P-codoping, cobalt phosphate-based nanoparticles loaded on graphene nanosheets, and synergistic effects between the doped active species. Therefore, it is expected to replace Pt/C as a promising fuel cell catalyst in alkaline direct methanol fuel cells.

In the present work, carbon nitride quantum dots (CNQDs)-modified cobalt phosphate (CoPi) composites CNQDs/CoPi-x (x = 1, 2, 3) were prepared at room temperature and characterized by FTIR, XRD, UV-Vis DRS, EIS, SEM, TEM/HR-TEM, XPS, and N 2 gas adsorption. The morphologies and surface areas of CNQDs/CoPi-x have no remarkable change after modification of CNQDs, compared with pure CoPi. The obtained CNQDs/CoPi-x shows enhanced activity and stability of photocatalytic H 2 evolution compared to pure CoPi using Eosin Y (EY) as a sensitizer and triethanolamine as an electron donor. The CNQDs/CoPi-2 possesses the highest hydrogen evolution rate, 234.5 μmol h -1  g -1 , upon visible light, which outshines that of CoPi by 2.4 times. It was believed that the enhanced photocatalytic performances of the CNQDs/CoPi-2 could result from the boosted electron transfer from radical EY ·- to CNQDs/CoPi-2 by the employment of CNQDs; in addition, the visible-light activity of CNQDs contributes to hydrogen evolution. The mechanism of photocatalytic hydrogen production was discussed. This study may contribute toward the development of production of "green hydrogen" using solar., (© 2023 American Society for Photobiology.)

We report the novel oxygen evolution reaction (OER) catalyst based on cobalt incorporated hydroxyapatite (CoHAP). Our catalyst is prepared on the surface of hydroxyapatite by ion exchange reaction in Co2+ aqueous solution. The cobalt content is approximately 1 wt. % based on ICP‐AES and XPS experiments. XRD, TEM, EDX experiments suggest that individual cobalt ions are adsorbed on the HAP surface in non‐aggregated manner. The cyclic voltammetry (CV) of CoHAP exhibits a weak oxidation peak at 1.10 V which is comparable to CV of in‐situ formed Co−Pi in previous literature. Tafel slope is approximately 80 mV/decade which is independent on the loading amount of CoHAP. The Faradaic efficiency is 94 % measured by quantitative analysis of O2 using gas chromatography. Bulk electrolysis verifies that CoHAP can be utilized OER catalyst at neutral pH with high stability. Our preparation method using hydroxyapatite as a solid phase phosphate source offers a new strategy to fabricate the OER catalysts. [ABSTRACT FROM AUTHOR]

Zinc lanthanum tantalum oxynitride [ZnLaTaON2] powders were synthesized by conventional solid state reaction. ZnLaTaON2 photoelectrodes were prepared by electrophoretic deposition of ZnLaTaON2 suspension in acetone onto ITO substrate. The photoelectrodes of ZnLaTaON2 were established to reveal photoelectrochemical properties for water oxidation reaction. Moreover, a cobalt phosphate (Co-Pi) was loaded on ZnLaTaON2 photoelectrodes via photodeposition method to enhance the photoelectrochemical water oxidation performances. Photocurrent voltage characteristics of the Co-Pi/ZnLaTaON2 photoelectrodes were enhanced with its effect which is more evidenced at lower water oxidation potentials. A relatively stable photocurrent density of 5 mA/cm2 at 1.5 V vs RHE was attained with the support of electron donor in alkaline phosphate solution. Comparatively, in Co-Pi/ZnLaTaON2 photoelectrodes, approximately threefold enhancement was noticed at 1.8 VRHE in assessment with parent photoelectrode. On the other hand, Co-Pi/ZnLaTaON2 photoelectrodes have been shown as an alternative pathway to improve the photoelectrochemical current gain through the PEC water oxidation reaction. [ABSTRACT FROM AUTHOR]

Abstract Electrodeposited cobalt phosphate has been reported as a valid alternative to noble metals as an electrocatalyst for the Oxygen Evolution Reaction (OER). In parallel, Atomic Layer Deposition (ALD) is increasingly being used in (photo)electrocatalytic applications. In this contribution we report on the electrocatalytic activity towards OER of ALD-prepared cobalt phosphate thin films. The selected ALD approach enables tuning of the Co-to-P atomic ratio, which is found to significantly affect the activity of the prepared electrocatalyst. Specifically, concurrently with a Co-to-P ratio increase from 1.6 to 1.9, the current density for OER increases from 1.77 mA/cm2 at 1.8 V vs. RHE (Reversible Hydrogen Electrode) to 2.89 mA/cm2 at 1.8 V vs. RHE. Moreover the sample with a Co-to-P ratio of 1.9 has superior performance when compared to electrodeposited cobalt phosphate thin films reported in the literature. Graphical abstract Unlabelled Image Highlights • Atomic layer deposited cobalt phosphate as oxygen evolution reaction catalyst. • Chemical composition of cobalt phosphate tuned using ALD supercycle approach • Current density for OER increases with cobalt-to‑phosphorus ratio in the film. • OER current density value of 2.89 mA/cm2 at 1.8 V vs. RHE for CoPi Co-rich sample • Superior performance of CoPi Co-rich compared to electrodeposited cobalt phosphate [ABSTRACT FROM AUTHOR]

Recently, nanomaterial lubricant additives have attracted the attention of tribologists. Herein, a novel cobalt phosphate octahydrates (CoP) nanoflower was synthesized, and as an oil-base additive, CoP exhibited extraordinary tribological performance for titanium alloy. Compared with the pure PAO8, the friction coefficient (COF) and wear rate (W R) has been reduced by 69.77% and 99.27% at a concentration of 10 wt% CoP. Besides, SEM, EDS, and XPS characterization confirmed that CoP could fill and repair the surface of titanium alloy to make the worn surface smoother, and be deposited on the surface to form a deposition layer to protect the titanium alloy from severe wear. The low shear force between CoP nanosheets in the deposition layer promotes lubrication, achieving low COF. [ABSTRACT FROM AUTHOR]