Superior catalytic performances of platinum nanoparticles loaded nitrogen-doped graphene toward methanol oxidation and hydrogen evolution reaction

Nitrogen and Sulfur Co-Doped Graphene Composite Aerogel Microspheres Supporting Pt Electrode-Catalyzed Methanol Electro-Oxidation Reaction

Nitrogen and sulfur co-doped graphene composite aerogel microspheres containing pyrolyzed carbon (NS-GAMs@C) are prepared by pressure-spraying the graphene oxide (GO) dispersion with water-soluble phenolic resin and thiourea, followed by freeze shaping, freeze-drying, and high-temperature carbonization. The resulting NS-GAMs@C possesses interconnected porous structures with large surface areas and high doping levels of N/S elements. Furthermore, the platinum nanoparticles (Pt NPs) are grown onto the NS-GAMs@C via a solvothermal reduction reaction to obtain the Pt/NS-GAMs@C microspheres with an average particle size of ∼32.25 μm. The residual carbon species in situ formed by the high-temperature carbonization of phenolic resin can act as intercalation compounds to reduce the self-stacking of graphene sheets, which contributes to an enhanced specific surface area and doping level. The N/S co-doping in NS-GAMs@C improves the interaction between the Pt and carriers, reduces the size of Pt NPs, ensures their even distribution, and increases the proportion of highly active Pt (111) crystal planes. Consequently, the methanol oxidation activity of Pt/NS-GAMs@C is significantly improved compared to undoped materials. Specifically, the optimized Pt/NS-GAMs@C composites demonstrate a remarkable mass activity of 840.11 mA·mg-1 Pt for methanol electrooxidation, which is approximately 2.39, 3.94, 3.41, and 1.75 times higher than that of commercial Pt/C, Pt/rGO (reduced GO), Pt/GAMs without doping, and Pt/NS-GAB@C (bulk aerogel), respectively. Additionally, the Pt/NS-GAMs@C exhibits long-term electrocatalytic stability. This research provides a novel catalyst system based on aerogel microspheres for methanol electrooxidation fuel cells.

Green and sustainable use of macadamia nuts as support material in Pt-based direct methanol fuel cells

The successful commercialization of direct methanol fuel cells (DMFCs) is hindered by inadequate methanol oxidation activity and anode catalyst longevity. Efficient and cost-effective electrode materials are imperative in the widespread use of DMFCs. While Platinum (Pt) remains the primary component of anodic methanol oxidation reaction (MOR) electrocatalysts, its utilization alone in DMFC systems is limited due to carbon monoxide (CO) poisoning, instability, methanol crossover, and high cost. These limitations impede the economic feasibility of Pt as an electrocatalyst. Herein, we present the use of powdered activated carbon (PAC) and granular activated carbon (GAC), both sourced from macadamia nut shells (MNS), a type of biomass. These bio-based carbon materials are integrated into hybrid supports with reduced graphene oxide (rGO), aiming to enhance the performance and reduce the production cost of the Pt electrocatalyst. Electrochemical and physicochemical characterizations of the synthesized catalysts, including Pt-rGO/PAC-1:1, Pt-rGO/PAC-1:2, Pt-rGO/GAC-1:1, and Pt-rGO/GAC-1:2, were conducted. X-ray diffraction analysis revealed crystallite sizes ranging from 1.18 nm to 1.68 nm. High-resolution transmission electron microscopy (HRTEM) images with average particle sizes ranging from 1.91 nm to 2.72 nm demonstrated spherical dispersion of Pt nanoparticles with some agglomeration across all catalysts. The electrochemical active surface area (ECSA) was determined, with Pt-rGO/GAC-1:1 exhibiting the highest ECSA of 73.53 m2 g-1. Despite its high ECSA, Pt-rGO/GAC-1:1 displayed the lowest methanol oxidation reaction (MOR) current density, indicating active sites with poor catalytic efficiency. Pt-rGO/PAC-1:1 and Pt-rGO/PAC-1:2 exhibited the highest MOR current densities of 0.77 mA*cm-2 and 0.74 mA*cm-2, respectively. Moreover, Pt-rGO/PAC-1:2 and Pt-rGO/PAC-1:1 demonstrated superior electrocatalytic mass (specific) activities of 7.55 mA/mg (0.025 mA*cm-2) and 7.25 mA/mg (0.021 mA*cm-2), respectively. Chronoamperometry tests revealed Pt-rGO/PAC-1:2 and Pt-rGO/PAC-1:1 as the most stable catalysts. Additionally, they exhibited the lowest charge transfer resistances and highest MOR current densities after durability tests, highlighting their potential for DMFC applications. The synthesized Pt supported on PACs hybrids demonstrated remarkable catalytic performance, stability, and CO tolerance, highlighting their potential for enhancing DMFC efficiency.

Principles of Photocatalysts and Their Different Applications: A Review

Human existence and societal growth are both dependent on the availability of clean and fresh water. Photocatalysis is a type of artificial photosynthesis that uses environmentally friendly, long-lasting materials to address energy and environmental issues. There is currently a considerable demand for low-cost, high-performance wastewater treatment equipment. By changing the structure, size, and characteristics of nanomaterials, the use of nanotechnology in the field of water filtration has evolved dramatically. Semiconductor-assisted photocatalysis has recently advanced to become among the most promising techniques in the fields of sustainable energy generation and ecological cleanup. It is environmentally beneficial, cost-effective, and strictly linked to the zero waste discharge principle used in industrial effluent treatment. Owing to the reduction or removal of created unwanted byproducts, the green synthesis of photoactive nanomaterial is more beneficial than chemical synthesis approaches. Furthermore, unlike chemical synthesis methods, the green synthesis method does not require the use of expensive, dangerous, or poisonous ingredients, making it a less costly, easy, and environmental method for photocatalyst synthesis. This work focuses on distinct greener synthesis techniques utilized for the production of new photocatalysts, including metals, metal doped-metal oxides, metal oxides, and plasmonic nanostructures, including the application of artificial intelligence and machine learning to the design and selection of an innovative photocatalyst in the context of energy and environmental challenges. A brief overview of the industrial and environmental applications of photocatalysts is also presented. Finally, an overview and recommendations for future research are given to create photocatalytic systems with greatly improved stability and efficiency.

Green Synthesis of Metal Oxides Semiconductors for Gas Sensing Applications

During recent decades, metal oxide semiconductors (MOS) have sparked more attention in various applications and industries due to their excellent sensing characteristics, thermal stability, abundance, and ease of synthesis. They are reliable and accurate for measuring and monitoring environmentally important toxic gases, such as NO₂, NO, N₂O, H₂S, CO, NH₃, CH₄, SO₂, and CO₂. Compared to other sensing technologies, MOS sensors are lightweight, relatively inexpensive, robust, and have high material sensitivity with fast response times. Green nanotechnology is a developing branch of nanotechnology and aims to decrease the negative effects of the production and application of nanomaterials. For this purpose, organic solvents and chemical reagents are not used to prepare metal nanoparticles. On the contrary, the synthesis of metal or metal oxide nanoparticles is done by microorganisms, either from plant extracts or fungi, yeast, algae, and bacteria. Thus, this review aims at illustrating the possible green synthesis of different metal oxides such as ZnO, TiO₂, CeO₂, SnO₂, In₂O₃, CuO, NiO, WO_3, and Fe₃O₄, as well as metallic nanoparticles doping.

In-situ oxidation of Palladium-Iridium nanoalloy anchored on Nitrogen-doped graphene as an efficient catalyst for methanol electrooxidation

Palladium (Pd)-based materials have been widely used as catalysts for the methanol oxidation reaction (MOR). Unfortunately, the catalytic activity was limited by structure, carbon monoxide intermediates (CO_ads) tolerance and stability. It was currently difficult to be used in large-scale commercial production. Herein, to further improve their electrocatalytic activity, a facile oxidation method to achieve in-situ oxidation of palladium-iridium (PdIr) alloy on nitrogen-doped graphene (NGS) is used, which is named as Pd-Ir-O/NGS. The new catalyst exhibits remarkable MOR activity (1374.8 mA mg^-1), CO_ads tolerance (the onset oxidation potential reach 0.725 V) and stability (the current density retention rate after 500 cycles of cyclic voltammetry is 44.9%). As a catalyst for MOR, the Pd-Ir-O/NGS has more outstanding electrocatalytic performance compared with commercial Pd/C and other counterparts. The mechanism study shows that the excellent catalytic performance is attributed to (1) the synergistic electronic effect of Pd-Ir-O due to the introduction of Ir and O, (2) the insertion of O into PdIr alloy that kinetically accelerated the oxidation of poisoning methoxy intermediates and (3) the vital roles of unique three-dimensional (3D) structure of NGS with abundant nitrogen atoms. Our findings herald a new paradigm for the modification of palladium-based materials for MOR and provide an alternative design principle for novel 3D carbon-based material for various application.

Boron carbonitride with tunable B/N Lewis acid/base sites for enhanced electrocatalytic overall water splitting

In-depth research on energy storage and conversion is urgently needed; thus, water splitting has become a possible method to achieve sustainable energy utilization. However, traditional carbon material with high graphitization degree exhibits a relatively low electrocatalytic oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) activity as it is electrochemically inert. In this work, according to the Lewis theory of acids and bases and the density functional theory (DFT) results, which show that the enriched heteroatom of B/N in the boron carbonitride (BCN) system may introduce stronger adsorption strength of OH*/H₂O, respectively, we have designed and synthesized self-supporting BCN materials with different enrichment degrees of B/N (B-BCN/N-BCN) using carbon paper as substrate. Furthermore, by adjusting the contents of B and N, the optimum electrocatalytic performance of overall water splitting was obtained in which the onset voltage of water splitting on B-BCN//N-BCN was lower than 1.60 V. Our strategy of synthesizing materials with different heteroatom enrichment to improve the electronic environment of materials has opened up new opportunities for developing efficient metal-free electrocatalysts.

Magnetic field strength controlled liquid phase syntheses of ferromagnetic metal nanowire

The effect of the external magnetic field strength on the morphology of metal nickel (Ni) nanowires synthesized via electroless deposition is investigated. Under strong magnetic fields, Ni nanoparticles, precursors of Ni nanowires, easily align along the magnetic field to form straight nanowires with smooth surfaces. In contrast, under weak magnetic fields, branched Ni nanowires with rough surfaces are formed. By leveraging this magnetic effect on the morphology of Ni nanowires, simply changing the external magnetic field can synthesize various types of Ni nanowire nonwovens. Furthermore, different forms of Ni nanowires were grown on the sheet by the similar electroless deposition reaction on a non-magnetic copper metal sheet. The macroscopic morphology of this composite is closely correlated with the microstructures of Ni nanowires.

Basal-Plane Catalytic Activity of Layered Metallic Transition Metal Ditellurides for the Hydrogen Evolution Reaction

We report the electrochemical hydrogen evolution reaction (HER) of two-dimensional metallic transition metal dichalcogenides (TMDs). TMTe2 (TM: Mo, W, and V) single crystals were synthesized and characterized by optical microscopy, X-ray diffraction, and electrochemical measurements. We found that TMTe2 acts as a HER-active catalyst due to the inherent catalytic activity of its basal planes. Among the three metallic TMTe2, VTe2 shows the best HER performance with an overpotential of 441 mV and a Tafel slope of 70 mV/dec. It is 668 mV and 137 mV/dec for MoTe2 and 692 mV and 169 mV/dec for WTe2. Even though VTe2 has the lowest values in the exchange current density, the active site density, and turn-over-frequency (TOF) among the three TMTe2, the lowest charge transfer resistance (RCT) of VTe2 seems to be critical to achieving the best HER performance. First-principles calculations revealed that the basal-plane-active HER performance of metallic TMDs can be further enhanced with some Te vacancies. Our study paves the way to further study of the inherent catalytic activity of metallic 2D materials for active hydrogen production.

Strongly confined localized surface plasmon resonance (LSPR) bands of Pt, AgPt, AgAuPt nanoparticles

Multi-metallic alloy nanoparticles (NPs) can enable the advanced applications in the energy, biology, electronics, optics and catalysis due to their multi-functionality, wide tunable range and electronic heterogeneity. In this work, various mono-, bi- and tri-metallic nanostructures composed of Ag, Au and Pt are demonstrated on transparent c-plane sapphire (0001) substrates and the corresponding morphological and optical characteristics are thoroughly investigated. The resulting Pt and AuPt NPs in this study demonstrate much enhanced LSPR responses as compared to the pure Pt NPs from the previous studies, which was contributed by the synergistic effect of Au and Pt and improved surface morphology. These results are sharply distinct in terms of surface morphology and elemental variability from those obtained by the dewetting of monometallic Ag, Au and Pt films under the similar growth conditions, which is due to the distinct dewetting kinetics of the bi-layer and tri-layer films. These NPs exhibit strongly enhanced localized surface plasmon resonance (LSPR) bands in the UV-VIS wavelengths such as dipolar, quadrupolar, multipolar and higher order resonance modes depending upon the size and elemental composition of NPs. The LSPR bands are much stronger with the high Ag content and gradually attenuated with the Ag sublimation. Furthermore, the VIS region LSPR bands are readily blue shifted along with the reduction of NP size. The Ag/Pt bi-layers and Ag/Au/Pt tri-layers are systematically dewetted and transformed into various AgPt and AgAuPt nanostructures such as networked, elongated and semispherical configurations by means of enhanced surface diffusion, intermixing and energy minimization along with the temperature control. The sublimation of Ag atoms plays a significant role in the structural and elemental composition of NPs such that more isolated and semispherical Pt and AuPt NPs are evolved from the AgPt and AgAuPt NPs respectively.

Graphene Nanoarchitectonics: Recent Advances in Graphene-Based Electrocatalysts for Hydrogen Evolution Reaction

Under the double pressures of both the energy crisis and environmental pollution, the exploitation and utilization of hydrogen, a clean and renewable power resource, has become an important trend in the development of sustainable energy-production and energy-consumption systems. In this regard, the electrocatalytic hydrogen evolution reaction (HER) provides an efficient and clean pathway for the mass production of hydrogen fuel and has motivated the design and construction of highly active HER electrocatalysts of an acceptable cost. In particular, graphene-based electrocatalysts commonly exhibit an enhanced HER performance owing to their distinctive structural merits, including a large surface area, high electrical conductivity, and good chemical stability. Considering the rapidly growing research enthusiasm for this topic over the last several years, herein, a panoramic review of recent advances in graphene-based electrocatalysts is presented, covering various advanced synthetic strategies, microstructural characterizations, and the applications of such materials in HER electrocatalysis. Lastly, future perspectives on the challenges and opportunities awaiting this emerging field are proposed and discussed.

Controlled PtIr nanoalloy as an electro-oxidation platform for methanol reaction and ammonia detection

Herein, a surfactant-free, ethylene glycol-mediated synthesis of PtIr nanoalloys was optimized. In particular, a post-synthesis treatment was identified as the key step in order to determine the nanoparticles size and their organization in the nanostructure, depending on the presence of a reducing agent and on pressure conditions. After synthesis, the as-obtained nanomaterials were broadly characterized: SEM and TEM images, EDX maps and XRD spectra showed the formation of nanorods with a few nanometers size and similar quantitative compositions of platinum and iridium. Afterward, the electrocatalytic activity towards the methanol oxidation reaction of the synthesized nanomaterials was tested and the best sample, treated under a hydrogen/nitrogen flow at 10 bar, exhibits a negligible onset potential (0.058 V) and a very high If/Ib ratio (2.5). Moreover, the aforementioned sample was tested as an electrochemical sensor for the detection of small traces of ammonia in an aqueous solution with a limit of detection of 4.88 μM. The sensor was tested also in simulated wastewater coming from the fertilizer industry, showing proper operation and excellent selectivity.

Methanol Oxidation on Graphenic-Supported Platinum Catalysts

Graphene oxide (GO), reduced graphene oxide by thermal treatment (rGO-TT), nitrogen-modified rGO (N-rGO), and carbon Vulcan were synthesized and employed in the current work as catalyst support for Pt nanoparticles, to study their properties and impact toward the methanol oxidation reaction (MOR) in sulfuric acid medium. Several physicochemical techniques, such as X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), Transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), Raman, and elemental analysis were employed to characterize the novel materials, while potentiodynamic and potentiostatic methods were used to study catalytic performance toward the methanol oxidation reaction in acidic medium. The main results indicate a high influence of the support on the surface electronic state of the catalyst, and consequently the catalytic performance toward the MOR is modified. Accordingly, Pt/N-rGO and Pt/rGO-TT show the lowest and the highest catalytic performance toward the MOR, respectively.

Preparation method of Ni@Pt/C nanocatalyst affects the performance of direct borohydride-hydrogen peroxide fuel cell: Improved power density and increased catalytic oxidation of borohydride

The Ni@Pt/C electrocatalysts were synthesized using two different methods: with sodium dodecyl sulfate (SDS) and without SDS. The metal loading in synthesized nanocatalysts was 20wt% and the molar ratio of Ni: Pt was 1:1. The structural characterizations of Ni@Pt/C electrocatalysts were investigated by field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HR-TEM). The electrocatalytic activity of Ni@Pt/C electrocatalysts toward BH₄^- oxidation in alkaline medium was studied by means of cyclic voltammetry (CV), chronopotentiometry (CP), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS). The results showed that Ni@Pt/C electrocatalyst synthesized without SDS has superior catalytic activity toward borohydride oxidation (22016.92Ag_Pt^-1) in comparison with a catalyst prepared in the presence of SDS (17766.15Ag_Pt^-1) in NaBH₄ 0.1M at 25°C. The Membrane Electrode Assembly (MEA) used in fuel cell set-up was fabricated with catalyst-coated membrane (CCM) technique. The effect of Ni@Pt/C catalysts prepared with two methods as anode catalyst on the performance of direct borohydride-hydrogen peroxide fuel cell was studied. The maximum power density was obtained using Ni@Pt/C catalyst synthesized without SDS at 60°C, 1M NaBH₄ and 2M H₂O₂ (133.38mWcm^-2).

Platinum–copper doped poly(sulfonyldiphenol/cyclophosphazene/benzidine)–graphene oxide composite as an electrode material for single stack direct alcohol alkaline fuel cells

Schematic representation of the preparation of a metal nanoparticle (Pt and Pt–Cu)-decorated poly(SDP/CP/BZ)–GO composite.