Synthesis and electrocatalytic performance of phosphotungstic acid-modified Ag@Pt/MWCNTs catalysts for oxygen reduction reaction

Boosting Oxygen Reduction Reaction Selectivity in Metal Nanoparticles with Polyoxometalates

The lack of selectivity toward the oxygen reduction reaction (ORR) in metal nanoparticles can be linked to the generation of intermediates. This constitutes a crucial constraint on the performance of specific electrochemical devices, such as fuel cells and metal-air batteries. To boost selectivity of metal nanoparticles, a novel methodology that harnesses the unique electrocatalytic properties of polyoxometalates (POM) to scavenge undesired intermediates of the ORR (such as HO2 -) promoting selectivity is proposed. It involves the covalent functionalization of metal nanoparticle's surface with an electrochemically active capping layer containing a new sulfur-functionalized vanadium-based POM (AuNP@POM). To demonstrate this approach, preformed thiolate Au(111) nanoparticles with a relatively poor ORR selectivity are chosen. The dispersion of AuNP@POM on the surface of carbon nanofibers (CNF) enhances oxygen diffusion, and therefore the ORR activity. The resulting electrocatalyst (AuNP@POM/CNF) exhibits superior stability against impurities like methanol and a higher pH tolerance range compared to the standard commercial Pt/C. The work demonstrates for the first time, the use of a POM-based electrochemically active capping layer to switch on the selectivity of poorly selective gold nanoparticles, offering a promising avenue for the preparation of electrocatalyst materials with improved selectivity, performance, and stability for ORR-based devices.

Preparation and characterization of a copper phosphotungstate/titanium dioxide (Cu-H3PW12O40/TiO2) composite and the photocatalytic oxidation of high-concentration ammonia nitrogen

Currently, the majority of wastewater with a high concentration of ammonia nitrogen (NH₄⁺/NH₃) is treated using biological methods, which have poor biodegradability and low removal efficiency. In this paper, a composite photocatalyst of copper phosphotungstate/titanium dioxide (Cu-H₃PW₁₂O₄₀/TiO₂) was prepared by sol-gel hydrothermal synthesis, and the composite catalyst was characterized by X-ray diffraction (XRD), UV-vis-diffuse reflectance spectroscopy (UV-VIS-DRS), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS)、scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The photocatalytic oxidation of a high-concentration NH₄⁺/NH₃ solution was carried out under ultraviolet (UV) light to explore the effects of different influencing factors on the photocatalytic effect and to optimize the reaction conditions. The prepared composite catalyst exhibited higher photocatalytic activity than that of TiO₂. When the initial concentration of the solution was 300 mg·L^-1, the initial pH was 11, the catalyst concentration was 1.5 g·L^-1, the loading level of Cu-H₃PW₁₂O₄₀ was 40%, and the aeration rate was 1.5 L·min^-1, the removal rate of NH₄⁺/NH₃ by the composite photocatalyst could reach >80%. Very little NO₂^- and NO₃^- were produced, and N₂ was the main product.

Ionic self-assembly of metalloporphyrin/heteropolyacid on multi-wall carbon nanotubes with enhanced electrocatalytic activity toward oxygen reduction reaction

We report the synthesis of a series of hybrid electrocatalysts toward oxygen reduction reaction (ORR) by ionic self-assembly of positively charged Fe(III) meso-tetra([Formula: see text]-methyl-4-pyridyl)porphyrin (FeP) with negatively charged H3PMo[Formula: see text]O[Formula: see text] (PMo[Formula: see text] in ethanol solution under ambient conditions in the presence of suspended multi-wall carbon nanotubes (MWCNTs). Self-assembled FeP/PMo[Formula: see text] was well-dispersed on MWCNTs with a tunable loading from 26.3% to 55.6%. Interestingly, the hybrid electrocatalysts demonstrated a much higher ORR activity than individual PMo[Formula: see text] and FeP in acidic media. We speculate that this activity enhancement might originate from a possible synergy between PMo[Formula: see text] and FeP. This study may be extended to the design and synthesis of other types of hybrid electrocatalysts for applications in electrochemical energy conversion, storage and sensing.

Highly Active PdNi/RGO/Polyoxometalate Nanocomposite Electrocatalyst for Alcohol Oxidation

A PdNi/RGO/polyoxometalate nanocomposite has been successfully synthesized by a simple wet-chemical method. Characterizations such as transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction analysis, and X-ray photoelectron spectroscopy are employed to verify the morphology, structure, and elemental composition of the as-prepared nanocomposite. Inspired by the fast-developing fuel cells, the electrochemical catalytic performance of the nanocomposite toward methanol and ethanol oxidation in alkaline media is further tested. Notably, the nanocomposite exhibits excellent catalytic activity and long-term stability toward alcohol electrooxidation compared with the PdNi/RGO and commercial Pd/C catalyst. Furthermore, the electrochemical results reveal that the prepared nanocomposite is attractive as a promising electrocatalyst for direct alcohol fuel cells, in which the phosphotungstic acid plays a crucial role in enhancing the electrocatalytic activities of the catalyst.