Polyol Reduction Method Research Articles

Breaking the Pt Electron Symmetry and OH Spillover towards PtIr Active Center for Performance Modulation in Direct Ammonia Fuel Cell.

The growing interest in low-temperature direct ammonia fuel cells (DAFCs) arises from the utilization of a carbon-neutral ammonia source; however, DAFCs encounter significant electrode overpotentials due to the substantial energy barrier of the *NH2 to *NH dehydrogenation, compounded by the facile deactivation by *N on the Pt surface. In this work, a unique catalyst, Pt4Ir@AlOOH/NGr i.e., Pt4Ir/ANGr, is introduced composed of PtIr alloy nanoparticles controllably decorated on the pseudo-boehmite phase of AlOOH-supported nitrogen-doped reduced graphene (AlOOH/NGr) composite, synthesized via the polyol reduction method. The detailed studies on the structural and electronic properties of the catalyst by XAS and VB-XPS reveal the possible electronic modulations. The optimized Pt4Ir/ANGr composition exhibits a significantly improved onset potential and mass activity for AOR. The DFT study confirms the OHad species spillover by AlOOH and Pt4Ir (100) facilitates the conversion of the *NH2 to *NH with minimal energy barriers. Finally, testing of DAFC at the system level using a membrane electrode assembly (MEA) with Pt4Ir/ANGr as the anode catalyst, demonstrating the suitability of the catalyst for its practical applications. This study thus uncovers the potential of the Pt4Ir catalyst in synergy with ANGr, largely addressing the challenges in hydrogen transportation, storage, and safety within DAFCs.

Development of ruthenium-based catalysts for ammonia synthesis via polyol reduction method

In this work, ruthenium-based catalysts were synthesized via polyol reduction method with different metal oxides as support and caesium as promoter. The samples were characterized through XRD, ICP-OES, nitrogen physisorption and XPS. Then, the catalysts were tested for ammonia synthesis in the range of temperatures 548–673 K and pressures 1–5 MPa. The synthesized catalysts allowed an ammonia production rate approximately four times higher compared with the performances of similar catalytic formulations in literature (tested at same conditions). The best performance were achieved with the Cs–Ru/CeO2 (1%wt Cs, 5%wt Ru), reaching an ammonia production of nearly 73 mmol h−1∙gcat−1 at 673 K and 5 MPa. As showed by the XPS analysis, the increased Ce3+/Ce4+ ratio led to an enhancement of oxygen vacancies, which favoured the dissociative adsorption of nitrogen, that is the limiting step in the ammonia synthesis reaction. Such high catalytic activity can be ascribed to the beneficial effect of the polyol reduction method for the maximization of the exposure of active sites.

IrxCu0.5Ce0.5Ox/C nanocluster bifunctional electrocatalyst has high water splitting performance in acidic electrolyte

As an effective electrocatalyst for water decomposition, precious metals face limitations in widespread use due to their high cost. Incorporating other metals into precious metals to enhance electrocatalytic performance while reducing costs poses significant challenges. Within the realm of precious metals, Ir-based electrocatalysts have demonstrated remarkable catalytic activity for both oxygen evolution (OER) and hydrogen evolution (HER). This paper presents the synthesis of oxide-supported Ir-based catalysts containing Cu and Ce through a straightforward polyol reduction method. These catalysts exhibit notable OER and HER activity in acidic electrolytes. The addition of Ce increases oxygen vacancy, enhancing the catalytic performance of the optimized Ir3Cu0.5Ce0.5Ox/C clusters, surpassing IrO2 in OER with an overpotential of 274 mV at 10 mA cm−2. Moreover, these catalysts demonstrate outstanding performance when utilized as cathodes and anodes in H-type electrolytic cells. Overall, this study represents a significant advancement in the development of novel Ir-based electrocatalysts.

Ultra-Thin RuIr Alloy as Durable Electrocatalyst for Seawater Hydrogen Evolution Reaction.

The development of efficient, high-performance catalysts for hydrogen evolution reaction (HER) remains a significant challenge, especially in seawater media. Here, RuIr alloy catalysts are prepared by the polyol reduction method. Compared with single-metal catalysts, the RuIr alloy catalysts exhibited higher activity and stability in seawater electrolysis due to their greater number of reactive sites and solubility resistance. The RuIr alloy has an overpotential of 75 mV@10mA cm-2, which is similar to that of Pt/C (73mV), and can operate stably for 100 hours in alkaline seawater. Density functional theory (DFT) calculations indicate that hydrogen atoms adsorbed at the top sites of Ru and Ir atoms are more favorable for HER and are most likely to be the reactive sites. This work provides a reference for developing highly efficient and stable catalysts for seawater electrolysis.

Synthesis and morphology of Ag nanowires by fiber template method

The synthesis of traditional silver nanowires often uses a polyol method. There are many factors that affect the structure of silver nanowires, such as silver ion concentration, type and amount of reducing agent, oxygen concentration, stirring speed, temperature, and time. The synthesis conditions are harsh and difficult to replicate. In this paper, natural fibers and synthetic fibers were used as templates to assist the polyol reduction method to obtain silver nanowires with uniform structure. The effect of fiber types on the structure of silver nanowires were studied, including hemp fibers, wheat straw fibers, tobacco stem fibers, and polycarbonate fibers. Polycarbonate fibers induced the synthesis of silver nanowires with the highest aspect ratio, highest yield, and most uniform diameter distribution. The effect of polycarbonate fibers concentrations on the morphology and conductivity of silver nanowires were also studied. When the polycarbonate mass concentration was 8.5 × 10−4 g/mL, the aspect ratio of silver nanowires was the highest. The effect of polycarbonate fibers length (2 mm\\5 mm\\7 mm) on the morphology of silver nanowires were also studied. When the length of the template polycarbonate fibers was 7 mm, the length to diameter ratio and conductivity of the nanowires obtained are the best. Furthermore, the reaction kinetics of the reaction were studied via multiple sampling of silver nanowire reaction solutions and characterized by using UV–visible spectroscopy and scanning electron microscopy. The synthesis method of silver nanowires using fiber template is simple and fast, and can be used to synthesize silver nanowires with uniform diameter distribution on a large scale, thus solving the bottleneck problem of harsh synthesis conditions for silver nanowires. The resulting silver nanowires were blended with carboxymethyl cellulose to prepare conductive inks, which were coated on paper and cured at 180 °C for 30 min to achieve good conductivity.

Phosphorus-Modified Palladium and Tungsten Carbide/Mesoporous Carbon Composite for Hydrogen Oxidation Reaction of Proton Exchange Membrane Fuel Cells.

A composite material of tungsten carbide and mesoporous carbon was synthesized by the sol-gel polycondensation of resorcinol and formaldehyde, using cetyltrimethylammonium bromide as a surfactant and Ludox HS-40 as a porogen, and served as a support for Pd-based electrodes. Phosphorus-modified Pd particles were deposited onto the support using an NH3-mediated polyol reduction method facilitated by sodium hypophosphite. Remarkably small Pd nanoparticles with a diameter of ca. 4 nm were formed by the phosphorus modification. Owing to the high dispersion of Pd and its strong interaction with tungsten carbide, the Pd nanoparticles embedded in the tungsten carbide/mesoporous carbon composite exhibited a hydrogen oxidation activity approximately twice as high as that of the commercial Pt/C catalyst under the anode reaction conditions of proton exchange membrane fuel cells.

Pt-N catalytic centres concisely enhance interfacial charge transfer in amines functionalized Pt@MOFs for selective conversion of CO2 to CH4

Improving ligand-to-active metal charge transfer (LAMCT) by finely tuning the organic ligand is a decisive strategy to enhance charge transfer in metal organic frameworks (MOFs)-based catalysts. However, in most MOFs loaded with active metal catalysts, electron transmission encounters massive obstacle at the interface between the two constituents owing to poor LAMCT. Herein, amines (–NH2) functionalized MOFs (NH2-MIL-101(Cr)) encapsulated active metal Pt nanoclusters (NCs) catalysts are synthesized by the polyol reduction method and utilized for the photoreduction of CO2. Surprisingly, the introduction of –NH2 (electron donating) groups within the matrix of MIL-101(Cr) improved the electron migration through the LAMCT process, fostering a synergistic interaction with Pt. The combined experimental analysis exposed the high number of metallic Pt (Pt0) in Pt@NH2-MIL-101(Cr) catalyst through seamless electron shuttling from N of –NH2 group to excited Pt generating versatile hybrid Pt-N catalytic centres. Consequently, these versatile hybrid catalytic centres act as electro-nucleophilic centres, which enable the efficient and selective conversion of CO bond in CO2 to harvest CH4 (131.0 µmol.g−1) and maintain excellent stability and selectivity for consecutive five rounds, superior to Pt@MIL-101(Cr) and most reported catalysts. Our study verified that the precise tuning of organic ligands in MOFs immensely improves the surface-active centres, electron migration, and catalytic selectivity of the excited Pt NCs catalysts encaged inside MOFs through an improved LAMCT pathway.

Photocatalytic evaluation of disperse purple dye using Polyvinylpyrrolidone capped bare and Cu+2/Fe+3 codoped ZnO nano catalysts

Polyvinylpyrrolidone capped bare zinc oxide and codoped with cupric and ferric ions, have been fabricated by a facile polyol reduction method with ethylene glycol. The as-fabricated nanoparticles were calcinated to control their size and morphology. The fabricated nanoparticles were characterized using various techniques including X-ray diffraction, scanning electron microscopy, energy dispersion X-rays, UV–Vis spectroscopy, and Fourier transform infrared Spectroscopy. The results showed phase pure nanoparticles with wurtzite zinc oxide structure, and a blue shift in absorbance spectrum when zinc oxide was codoped with cupric and ferric ions.The study examined the degradation rate of disperse purple dye using bare and codoped zinc oxide nanoparticles in the solar region. Codoped nanocatalysts showed superior efficiency compared to bare zinc oxide. The kinetic analysis of the dye was conducted, revealing that the degradation of the dye followed a pseudo-first-order kinetics pattern. Furthermore, about 99 % degradation of the dye solution in 110 min by codoped zinc oxide as compared to bare zinc oxide (84 %) under solar light suggests Cu+2/Fe+3 codoped zinc oxide is an emerging tool for environmental remediation.

High-entropy PtCuSnWNb nanoalloys as efficient and stable catalysts for ethanol oxidation electrocatalysis.

Ternary nanoalloys used as electrochemical ethanol oxidation catalysts for direct ethanol fuel cells are confronted with poor stability issues under harsh acidic operating conditions. To address this issue, a carbon-supported quinary PtCuSnWNb high-entropy nanoalloy (denoted as PtCuSnWNb/C) was synthesized by using a polyol reduction method. Due to the unique high-entropy mixing states and strong catalyst-support interactions, PtCuSnWNb/C shows robust structural and compositional stability.

Nano-engineered catalysts for high-performance oxygen reduction reaction

The efficient energy conversion of fuel cells is greatly constrained by the slow oxygen reduction reaction (ORR) kinetics, which necessitates the use of highly active metal catalysts such as platinum (Pt). The critical challenge limiting large-scale usage of Pt is the capital cost that can be addressed through a prototypical approach by embedding metal nanoparticles (NPs), e.g., Pt NPs, in the conductive framework. However, previously reported embedding approaches are sophisticated and suffer from limited yields, leading to higher chemical process costs and remaining distant from commercial viability. Here, we report a facile, cost-effective and time-efficient structural tuning approach to synthesizing ultrafine Pt NPs impregnated within a conductive and highly porous carbon framework via a microwave-assisted polyol reduction method. Pt NPs with a uniform size of ∼2.27 nm can be successfully integrated within the pores of the carbon framework, enabling homogeneous dispersion. Benefiting from these highly dispersed and ultrafine Pt NPs, the electrochemical surface area (ECSA) is improved to 142.98 m²/gPt, 2.25 times higher than that of the commercial counterpart (63.52 m²/gPt). Furthermore, our structurally optimized catalyst composite features a remarkably catalytic activity with a high half-wave potential (E1/2) of 0.895 V and an improved mass activity (MA) of 0.2289 A/mgPt, 2.39-fold improvement compared to the commercial counterpart. In addition, orthogonal experiments were designed to identify the key process parameters for fabricating Pt/C catalysts, offering insights for scaled-up and industrial production.

One-Pot template free synthesis of bimetallic alloy Pt-M/C (M = Fe, Co & Cu) with improved activity for electrocatalytic oxidation of methanol

We prepared a simple, one-step synthesis of Pt-M (M = Co, Cu & Fe)/C supported on Vulcan-XC-72 carbon using the polyol reduction method. The morphology, structure and elemental composition of the prepared catalysts were confirmed by transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX). Electrochemical characterization including electrochemical impedance, cyclic voltammetry and chronoamperometry were studied to compare the electrochemical activity of the as-prepared catalyst with standard 20 wt % Pt/C. From transmission electron microscopy studies, the estimated average particle size for PtFe/C, PtCo/C and PtCu/C were 16, 12 and 10 nm respectively. In cyclic voltammetry studies, the PtFe/C catalyst exhibited the maximum current density for electrooxidation of methanol (14.88 mA cm−2), compared to PtCu/C (9.96 mA cm−2), PtCo/C (4.66 mA cm−2) and Pt/C (2.34 mA cm−2). Also, the negative sweep onset potential and greater If/Ib ratio verified the enhanced activity of the PtFe/C catalyst. The stability of the catalyst was studied using chronoamperometric methods, which reveals the slow decay of the prepared catalyst and higher current density for initial and final time intervals. Impedance studies confirm that the PtFe/C catalyst exhibits the smallest semicircle, suggesting a significantly higher electrooxidation rate in comparison to the other catalysts. The electrocatalytic activity of the prepared catalyst follows the order: PtFe/C > PtCu/C > PtCo/C > Pt/C.

The corrosion resistant Pt5Ce–CeO2 structure provides significant oxygen reduction catalysis

Platinum-based alloy catalysts have been extensively studied in the oxygen reduction reaction (ORR) because of their excellent performance. In this study, Pt5Ce–CeO2/C composite catalysts were synthesized by polyol reduction method and high-temperature calcination method. Owing to the dual effects of the alloying effect of forming Pt5Ce intermetallic compound and the electronic effect of CeO2 modulating the electronic structure of Pt, it exhibits further improved ORR performance than the commercial Pt/C catalysts. The material possesses a 1.0 V starting potential, a 0.83 V half-wave potential, high durability, and methanol resistance. It has strong ORR catalytic activity and works well in Zn-air batteries. The experimental findings demonstrate that metal oxide and alloy structure can be combined to enhance catalyst ORR performance.

Durability Study of Anode Catalysts from Iridium-Based Titanium Supports in Polymer Electrolyte Membrane Water Electrolyzers

Electrochemical water splitting has been recognized as one of the most promising methods for hydrogen production. Electrocatalysts are critical materials in water electrolysis. The sluggish reaction kinetics for the anode reaction, oxygen evolution reaction (OER), hinders the development of water electrolysis technology. Iridium-based material is an leading catalyst for OERs, but the high scarcity and high cost limit its application in polymer electrolyte membrane water electrolyzers (PEMWEs). Moreover, Ir dissolution during the OER operation is another limitation. Robust and effective support-based catalysts should be developed to reduce the catalyst loading and provide high durability in PEMWEs. Herein, we synthesized an OER catalyst of Ir deposited on Ti supports using a polyol reduction method. The Ir/Ti catalysts with different Ir loading were prepared and applied in the PEMWEs for performance evaluation. The cell performance (Figure 1A) with the optimized catalyst (Ir/Ti-50%Ir) exhibited better performance than the commercial IrO2 in the same low loading (0.1 mgIr cm-2) and very close current density (<10 mV difference) achieved at 4 A cm-2 as to the electrode with a high catalyst loading (0.4 mgIr cm-2). Accelerated stress tests (ASTs) performed between 2.0 V and 1.45 V were used to investigate the catalyst durability in the PEMWEs. Figure 1B shows a volcano shape for the correlation between degradation behavior and Ir percent in the catalyst. Our results, combined with the ex-situ characterization, provide a synthesis strategy for robust OER catalysts, and elucidate the catalyst degradation mechanism in the PEMWEs. Figure 1

Oxygen-vacancy-rich tungsten oxide boosted ultrasmall iridium nanoparticles for acidic oxygen evolution

Proton exchange membrane water electrolysis (PEMWE) exhibits the superior benefits including high gas purity, high power density and wide variable loading but is still limited by the prohibitive cost and dearth of iridium (Ir)-based anode catalysts. Herein, we report a low-loading Ir-based catalyst with ultrasmall iridium nanoparticles (1.46 ± 0.01 nm) supported on oxygen-vacancy-rich tungsten oxide nanofibers (WO3-x) through electrospinning combined with surfactant-free microwave-assisted polyol reduction method for active acidic oxygen evolution reaction (OER). According to structural analysis and theoretical calculation, the charge transfer from W to Ir is induced by the strong electronic interaction at the Ir and WO3-x interface, thereby raising the electron density surrounding the Ir sites and favoring to boost OER activity. The resultant Ir@WO3-x exhibits an excellent overpotential of ca. 276 mV@10 mA cm−2 and remarkable durability. This study offers a new path for promoting the activity and durability of electrocatalysts while minimizing the mass loading of Ir towards OER.

Visible Light-Promoted Enhanced Photocatalytic Hydrogen Generation by the CeF3:Ho3+-Incorporated TiO2 Nanosystem

Wide-spectrum solar energy harvesting is of great significance for high-band semiconductors. The present article describes the hydrogen generation from aqueous methanol over a TiO2 up-conversion (CeF3:Ho3+) nanosystem (CHT) under visible light irradiance. In situ CeF3:Ho3+ nanoparticle incorporation into TiO2 was carried out, and CeF3:Ho3+ nanoparticles (∼4 to 8 nm) were synthesized using a simple polyol reduction method using triethanolamine as a reducing agent. The XRD, UV–Vis, XPS, TEM, BET, and SEM studies reveal the successful formation of a CeF3:Ho3+-incorporated TiO2 nanosystem. The enhanced photocatalytic activity of the CeF3:Ho3+-incorporated TiO2 nanosystem (CHT) was asserted through the peak hydrogen evolution rate (79.85 μmol h–1) under visible light irradiance. Furthermore, the solar-to-hydrogen conversion efficiency (1.37%) and apparent quantum efficiency (4.00%) for the peak rate were calculated and indicated that this could be used as an effective photocatalyst system. The results obtained from wavelength-dependent photocatalytic tests demonstrate that the reaction proceeds through energy absorption from a wide-range wavelength of visible light. For the first time, the in situ incorporation of nano-sized up-conversion material CeF3:Ho3+ into TiO2 and its utility for efficient sustainable hydrogen generation under visible light irradiance were accomplished with ease.

Photocatalytic and Antibacterial Potential of Silver Nanocubes and Nanorods Synthesized via Polyol Reduction Method

Photocatalytic and Antibacterial Potential of Silver Nanocubes and Nanorods Synthesized via Polyol Reduction Method

Tamed synthesis of AgNPs for photodegradation and anti-bacterial activity: Effect of size and morphology

Organic dyes present in the effluents of paints, and textile industries are posing major environmental threats. Rapid decomposition of these dyes using non-toxic, renewable and cost-effective silver nanoparticles (AgNPs) is a pragmatic strategy. Therefore, in current research work, AgNPs with different size ranges have been prepared following the polyol reduction method by controlled exploitation of substrate/reducing agent molar ratio and pH of reaction media. AgNPs have been characterized by UV–Visible spectroscopy, Scanning Electron Microscope (SEM), Powder X-Ray Diffraction (XRD) and Energy Dispersive X-ray spectroscopy (EDS). Absorption peaks ranging from 420 to 465 nm confirmed the synthesis of AgNPs using surface plasmon resonance (SPR) bands. The increase in molar ratio and pH led to the blue shift in absorption bands which revealed the size reduction of AgNPs. XRD analysis confirmed the crystallite size (16–21 nm) and Face centered cubic (FCC) crystalline structure of AgNPs. EDS was utilized to check the purity of AgNPs. SEM confirmed the spherical morphology of AgNPs with a size range between 70 and 110 nm. The energy band gap was determined using the Tauc plot equation to correlate the catalytic properties of NPs with size. Different-sized AgNPs were utilized as photocatalysts for the degradation of Methylene blue (MB) dye under sunlight irradiation. AgNPs having an average size of 70 nm showed improved photocatalytic potential by 94% degradation of MB in 80 min. The AgNPs were also evaluated for their antibacterial activities against gram-positive and gram-negative strains of bacteria. Small-size AgNPs were found more active against gram-negative strains of bacteria.

An efficient Ag decorated CeO2 synergetic catalyst for improved catalytic reduction of lethal 4-nitrophenol

Catalytic reduction is considered an effective approach for the reduction of toxic organic pollutants from the environment, but finding an active catalyst is still a big challenge. Herein, Ag decorated CeO2 catalyst was synthesized through polyol reduction method and applied for catalytic reduction (conversion) of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). The Ag decorated CeO2 catalyst displayed an outstanding reduction activity with 99% conversion of 4-NP in 5 min with a 0.61 min−1 reaction rate (k). A number of structural characterization techniques were executed to investigate the influence of Ag on CeO2 and its effect on the catalytic conversion of 4-NP. The outstanding catalytic performances of the Ag-CeO2 catalyst can be assigned to strong synergistic interaction of Ag with CeO2 that prevents the aggregation of Ag species and also, helps in the exposure of more surface active metallic Ag0. In addition, the Ag-CeO2 catalyst shown remarkable durability up to several (five) repeated rounds, certifying its everyday applicability.

Combustion-Assisted Polyol Reduction Method to Prepare Highly Transparent and Efficient Pt Counter Electrodes for Bifacial Dye-Sensitized Solar Cells.

A combustion-assisted polyol reduction (CPR) method has been developed to deposit electrocatalytically efficient and transparent Pt counter electrodes (CEs) for bifacial dye-sensitized solar cells (DSSCs). Compared with conventional thermal decomposition of Pt precursors, CPR allows for a decrease in reduction temperature to 150 °C. The low-temperature processing is attributed to adding an organic fuel, acetylacetone (Hacac), which provides extra heat to lower reduction energy. In addition, the stable Pt complexes can simultaneously be formed in ethylene glycol (EG) and Hacac system, which leads to Pt nanoparticle size regulation. A ratio of Hacac to EG is optimized to achieve excellent electrocatalytic activity and high visible light transmittance for CEs. The bifacial DSSCs fabricated with CPR-Pt CEs (EG : Hacac=1 : 16) reach efficiencies of 6.71±0.16% and 6.41±0.15% in front and back irradiations, respectively.

Rare-earth modified platinum-based electrocatalysts incorporating anodic glycerol oxidation reactions while promoting cathodic hydrogen evolution reactions

Glycerol electrooxidation (GOR) is a safe and clean method for conversion of glycerol. In the course of this work, a series of PtxCe/C catalysts have been synthesized by successive polyol reduction methods as well as etching and calcination. Various physicochemical characterrisation and electrochemical measurements have demonstrated the excellent performance of Pt3Ce/C composites in glycerol oxidation (GOR) and hydrogen evolution reactions (HER). The Pt3Ce/C catalyst showed better performance in GOR and HER compared to commercially available Pt/C electrocatalysts. This paper demonstrates an energy efficient electrocatalyst for the simultaneous precipitation of hydrogen from glycerol oxidation.