Stability Of Pt Nanoparticles Research Articles

CeO2 Nanoislands Enhance the Activity and Stability of Pt Nanoparticles Supported on Fibrous Mesoporous SiO2 for Catalytic Combustion of Propane

CeO₂ Nanoislands Enhance the Activity and Stability of Pt Nanoparticles Supported on Fibrous Mesoporous SiO₂ for Catalytic Combustion of Propane

Spatial Confinement of Pt Nanoparticles in Carbon Nanotubes for Efficient and Selective H2 Evolution from Methanol.

H2 generation from methanol-water mixtures often requires high pressure and high temperature (200-300°C). However, CO can be easily generated and poison the catalytic system under such high temperature. Therefore, it is highly desirable to develop the efficient catalytic systems for H2 production from methanol at room temperature, even at sub-zero temperatures. Herein, carbon nanotube-supported Pt nanocomposites are designed and synthesized as high-performance nano-catalysts, via stabilization of Pt nanoparticles onto carbon nanotube (CNT), for H2 production upon methanol dehydrogenation at sub-zero temperatures. Therein, the optimal Pt/CNT nanocomposite presents the superior catalytic performance in H2 production upon methanol dehydrogenation at the expense of B2(OH)4, with the TOF of 299.51min-130 oC. Compared with other common carriers, Pt/CNT exhibited the highest catalytic performance in H2 production, emphasizing the critical role of CNT in methanol dehydrogenation. The confinement of Pt nanoparticles by CNTs is conducive to inhibiting the aggregation of Pt nanoparticles, thereby significantly increasing its catalytic performance and stability. The kinetic study, detailed mechanistic insights, and density functional theory (DFT) calculation confirm that the breaking of O─H bond of CH3OH is the rate-controlling step for methanol dehydrogenation, and both H atoms of H2 are supplied by methanol. Interestingly, H2 is also successfully produced from methanol dehydrogenation at -10°C, which absolutely solves the freezing problem in the H2 evolution upon water-splitting reaction.

(Invited) Enhancement of Activity of Low-Pt-Content-Catalysts Toward Oxygen Reduction through Admixing with Metal Oxide Cocatalysts

The proton-exchange membrane fuel cell (PEMFC) technology is one of the most promising approaches for energy conversion in automotive applications. Despite the use of expensive noble metal electrocatalysts, the sluggish kinetics of the oxygen reduction reaction (ORR) in acid media, and formation of the undesirable hydrogen peroxide intermediate are still the main drawbacks, on top of the stability problems, when it comes to the widespread commercialization of PEMFC devices. The progress in this subject is greatly hindered by the high cost and scarcity of the state-of-the-art platinum-based materials which are regarded as the most effective cathode catalysts. Therefore, most of the current research studies have been devoted to the optimization of active centers and maximization of their utilization, which should allow the lowering of the cathode Pt loadings without loss of performance and durability. Unfortunately, the problem of electrochemical stability and the danger of generation of higher quantities of the undesirable hydrogen peroxide intermediate may become even more serious in the case of systems utilizing lower amounts of the Pt catalystAmong important strategies is hybridization, activation, and stabilization of carbon-supported Pt catalysts by functionalization through admixing with certain nanostructured and typically substoichiometric metal oxides. Special attention is paid to application of the bi- or multi-metallic Pt-based alloys in their various forms and structures. Additionally, doping of carbon carriers with heteroatoms would produce surface functional groups and active centers capable of not only improving the catalysts’ performance, but also affecting their stability. Among other important issues are such features as porosity, hydrophilicity, and degree of graphitization of carbon components, in addition to the existence of metal–support interactions, high electrochemical active surface area, electronic structure of interfacial Pt, and the feasibility of adsorptive or activating interactions with oxygen molecules.Platinum is a main catalyst for the electroreduction of oxygen, the reaction of primary importance to the technology of low-temperature fuel cells. Because of high cost of platinum. there is a need to significantly lower its loadings at interfaces. But then O2-reduction proceeds often at less positive potentials and produces higher amounts of undesirable H2O2-intermediate. Hybrid supports, which utilize metal oxides (e.g., CeO2, WO3, Ta2O5, Nb2O5, ZrO2), stabilize Pt and carbon nanostructures, diminish their corrosion while exhibiting high activity toward the four-electron (most efficient) reduction of oxygen. Porosity of carbon supports facilitates dispersion and stability of Pt nanoparticles. The catalytic efficiency depends on geometric (decrease of Pt–Pt bond distances) and electronic (increase of d-electron vacancy in Pt) factors, in addition to possible metal-support interactions and interfacial structural changes affecting adsorption and activation of O2-molecule.

Strong Metal-Support Interaction – a Tool for Enhancing the Hydrogen Evolution Reaction Performance

Renewable and green energy transition and meeting ever-increasing energy demands are among modern society's most pressing challenges. Currently, the world's energy systems rely on fossil fuels, leading to significant environmental pollution, including anthropogenic CO2 emissions and subsequent climate changes. The concept of hydrogen economy was first proposed half a century ago as a way to overcome these challenges by using hydrogen as the primary energy carrier instead of fossils.1 However, hydrogen production remains one of the significant obstacles to realizing the hydrogen economy, as steam reforming of methane derived from natural gas is still the dominant method of industrial-scale production, contributing significantly to the undesired emissions. Water electrolysis powered by renewables such as wind and sun energy is a sustainable way to produce high-purity hydrogen. In electrolyzers, hydrogen is obtained at the cathode side through the electrochemical hydrogen evolution reaction (HER), while the oxygen evolution reaction (OER) occurs at the anode. The HER is one of the most intensely studied electrochemical processes as it is of paramount importance for both fundamental and applicable aspects of electrocatalysis and physical chemistry in general. Traditionally, Pt has been known as the best monometallic HER catalyst due to its close-to-optimal interaction with adsorbed hydrogen atoms, which are reaction intermediates.2 However, due to its scarcity and high price, significant research efforts are being invested in designing alternative Pt-free electrocatalysts for (not only) HER. While promising results have been reported with different abundant materials such as sulfides, nitrides, carbides, and phosphides, their applicability is still challenged by rather inferior activity with respect to Pt and rapid deactivation, especially in corrosive acidic media. Currently, state-of-the-art HER catalysts are based on Pt nanoparticles dispersed over high-surface-area carbon supports (Pt/C). The main downside of such composites is the weak interaction between carbon and Pt particles, which means that support cannot affect the intrinsic activity of Pt sites. Moreover, this weak interaction results in the degradation of Pt/C due to particle detachment, agglomeration, or coalescence during HER. Upgrading the overall performance of Pt/C may be achieved by employing alternative supports able to trigger strong metal-support interaction (SMSI). SMSI can alter the electronic structure of the metallic active sites and increase their activity, while also it can lead to the stronger anchoring of nanoparticles with the support, improving stability. Different materials, such as pre-functionalized carbons, carbides, and metal oxides, have been reported to be able to provide SMSI.In this work, we investigated HER on a carbon-ceramic catalyst composed of Pt nanoparticles supported on titanium oxynitride (TiONx) embedded on reduced graphene oxide nanoribbons (Pt/TiONx).3 TiONx was obtained by incorporating nitrogen into TiO2 and provides the main merits of carbon supports, such as electrical conductivity and high surface area, combined with the ability to trigger SMSI. The screening of the electrocatalytic performance of the Pt/TiONx composite for HER revealed enhancement with respect to the Pt/C benchmark, which we ascribe to the effect of the TiONx substrate via SMSI. To confirm this, XPS was performed to compare the electronic states of Pt in Pt/TiONx and Pt/C catalysts, which revealed the ability of TiONx to trigger SMSI. DFT calculation provided additional confirmation of SMSI between the TiONx support and Pt nanoparticles and its impact on both HER activity and stability enhancement. The results presented in this work open up a perspective of using TiONx as an alternative support able to improve the catalytic performance of various active sites for different electrochemical reactions. References (1) Bockris, J. O. M. The Hydrogen Economy: Its History. Int J Hydrogen Energy 2013, 38 (6), 2579–2588. https://doi.org/10.1016/j.ijhydene.2012.12.026.(2) Hansen, J. N.; Prats, H.; Toudahl, K. K.; Mørch Secher, N.; Chan, K.; Kibsgaard, J.; Chorkendorff, I. Is There Anything Better than Pt for HER? ACS Energy Lett 2021, 1175–1180. https://doi.org/10.1021/acsenergylett.1c00246.(3) Smiljanić, M.; Panić, S.; Bele, M.; Ruiz-Zepeda, F.; Pavko, L.; Gašparič, L.; Kokalj, A.; Gaberšček, M.; Hodnik, N. Improving the HER Activity and Stability of Pt Nanoparticles by Titanium Oxynitride Support. ACS Catal 2022, 12 (20), 13021–13033. https://doi.org/10.1021/acscatal.2c03214. Figure 1

Controllable design of N-doped carbon nanotubes with assembled Pt nanoparticles for methanol oxidation reaction

Deep eutectic solvents (DESs), consisting of Brønsted/Lewis acids and bases, hold great promise in the efficient development of nanomaterials due to their unique properties, including high viscosity and enhanced surface tension. Herein, we present a facile strategy for the controllable fabrication of N-doped carbon nanotubes (NCNTs) using DES as a solvent and co-reagent. The prepared NCNTs are favorable to stabilize Pt nanoparticles, resulting in superior catalytic activity, high stability and excellent CO-tolerance for methanol oxidation reaction (MOR). Density functional theory (DFT) calculations reveal that, the d-band center of Pt in Pt/NCNTs is in close proximity to its Fermi energy level. Moreover, the Pt/NCNTs exhibit greater stability of the key COOH intermediate compared to Pt/CNT, resulting in a decreased energy barrier for CO to COOH step. These findings contribute to the enhanced catalytic activity observed in Pt/NCNTs. Furthermore, the relationship of the catalytic performance and doping content of NCNTs was also revealed in this work. This study introduces a new strategy for the efficient dispersion and high stabilization of Pt nanoparticles, offering promising prospects in other catalytic reactions beyond MOR.

Pt nanoparticles stabilized within MOF derivative on inverse opal ZnO for acetone prediction

We report a surface anchoring strategy for encapsulating Pt nanoparticles into MOF derivative cavities on inverse opal (IO) ZnO to enhance the sensing properties of metal oxide semiconducting gas sensors. This approach offers significant advantages over existing methods which are limited in synthetic modes and stability. Through in-situ growing ZIF-8 derivative (ZD) onto IO-ZnO, we achieve effective confinement and stabilization of Pt nanoparticles in small size and remarkable catalytic activity as confirmed by CO-TPR. Meanwhile, in-situ growth of ZD supply abundant adsorption sites for gas sensing as verified by acetone-TPR. The sensing material, IO-Pt@ZD/ZnO, comprising Pt nanoparticles encapsulated in IO-ZnO and confined in ZD is prepared for acetone sensor, which exhibits highly sensitivity (S = 36.4 vs. 100 ppm) and robust repeatability (130 cycles at 275 °C for 50 days). Meanwhile, Deep Neural Networks are applied to predict acetone concentration in moisture ambience from an individual sensor (Mean Square Error = 0.05 %). This work establishes a promising prospect for rational construction of metal oxide semiconducting combined with noble metal nanoparticles for highly catalytic activity, robust stability, and outstanding sensitivity in gas sensor application.

Improving the HER Activity and Stability of Pt Nanoparticles by Titanium Oxynitride Support.

Water electrolysis powered by renewables is regarded as the feasible route for the production of hydrogen, obtained at the cathode side through electrochemical hydrogen evolution reaction (HER). Herein, we present a rational strategy to improve the overall HER catalytic performance of Pt, which is known as the best monometallic catalyst for this reaction, by supporting it on a conductive titanium oxynitride (TiONx) dispersed over reduced graphene oxide nanoribbons. Characterization of the Pt/TiONx composite revealed the presence of small Pt particles with diameters between 2 and 3 nm, which are well dispersed over the TiONx support. The Pt/TiONx nanocomposite exhibited improved HER activity and stability with respect to the Pt/C benchmark in an acid electrolyte, which was ascribed to the strong metal–support interaction (SMSI) triggered between the TiONx support and grafted Pt nanoparticles. SMSI between TiONx and Pt was evidenced by X-ray photoelectron spectroscopy (XPS) through a shift of the binding energies of the characteristic Pt 4f photoelectron lines with respect to Pt/C. Density functional theory (DFT) calculations confirmed the strong interaction between Pt nanoparticles and the TiONx support. This strong interaction improves the stability of Pt nanoparticles and weakens the binding of chemisorbed H atoms thereon. Both of these effects may result in enhanced HER activity.

Stabilization of Pt nanoparticles within MOFs for selective hydrogenation of hazardous 4-nitrophenol to valuable 4-aminophenol: Confinement and synergistic effect

Precious metal nanoparticles (NPs) are a kind of promising hydrogenation catalyst. However, the particle size, stabilization and uniform dispersion of precious metal NPs is always a great challenge. Herein, Pt NPs were synthesized with controlled particle size and uniformly confined within the pores of Fe-BDC MOFs via an eco-friendly polyol reduction method and evaluated for selective hydrogenation of 4-Nitrophenols (4-NiPh) to 4-Aminophenols (4-AmPh). Metal-Organic Frameworks (MOF), a promising host material, provide a large surface area and pore volumes for evenly accommodating the Pt NPs with controlled particle size. The as-prepared Pt/Fe-BDC catalyst exhibited higher catalytic hydrogenation activity under mild conditions. Interestingly, the Pt/Fe-BDC catalyst exhibited superior catalytic activity with low Pt loading (0.47%) than that of the Pt/Fe3O4 catalyst. A series of bulk and surface structural characterizations including XRD, FTIR, TEM, XPS and CO-FTIR, etc., were conducted to examine the outstanding performance of the Pt/Fe-BDC catalyst. The outstanding catalytic hydrogenation performance of Pt/Fe-BDC catalyst was attributed to the large surface area, pore volume and additional functional groups of MOFs. The large surface area and pore volume of Fe-BDC MOFs control the Pt particle size (1.9 ​nm), and high uniform dispersion (59%) due to confinement effect, while the presence of additional functional groups in Fe-BDC MOFs synergistically interacts with Pt species to generate more exposed surface active metallic Pt0.

Dispersion and stability mechanism of Pt nanoparticles on transition-metal oxides

The heterogeneous catalysts of Pt/transition-metal oxides are typically synthesized through calcination at 500 °C, and Pt nanoparticles are uniformly and highly dispersed when hydrogen peroxide (H2O2) is applied before calcination. The influence of H2O2 on the dispersion and the stability of Pt nanoparticles on titania-incorporated fumed silica (Pt/Ti–FS) supports was examined using X-ray absorption fine structure (XAFS) measurements at the Pt L3 and Ti K edges as well as density functional theory (DFT) calculations. The local structural and chemical properties around Pt and Ti atoms of Pt/Ti–FS with and without H2O2 treatment were monitored using in-situ XAFS during heating from room temperature to 500 °C. XAFS revealed that the Pt nanoparticles of H2O2-Pt/Ti–FS are highly stable and that the Ti atoms of H2O2-Pt/Ti–FS support form into a distorted-anatase TiO2. DFT calculations showed that Pt atoms bond more stably to oxidized–TiO2 surfaces than they do to bare- and reduced–TiO2 surfaces. XAFS measurements and DFT calculations clarified that the presence of extra oxygen atoms due to the H2O2 treatment plays a critical role in the strong bonding of Pt atoms to TiO2 surfaces.

(Digital Presentation) A Study on the Poly(Amidoamine) Dendrimer Encapsulated Platinum Nanoparticles for Hydrogen Evolution Reaction in Proton Exchange Membrane Water Electrolyzer

Hydrogen is a non-polluting energy carrier being considered for use in many sectors, including transportation, chemical industry, as well as the energy storage. The main motivation is to reduce utilizing fossil fuels and thus to stop global warming. Hence, speeding up research and development efforts in hydrogen production is critical to ensuring a sufficient share of hydrogen to be used in the envisaged economy sectors in the coming decades. Proton exchange membrane water electrolyzis (PEM WE) is the perspective technology to supply, in combination with the renewable energy sources, so called green hydrogen connected with a zero carbon dioxide emissions. This technology is characterized by high process intensity, good faradaic efficiency, quick response time and the possibility of high-pressure operation [1]. Important aspect, however, represents improvement of its economic competitiveness to the alternative hydrogen production routes. Important aspect represents an effective electrocatalysis of the desired electrode reactions.Number of catalysts are being studied for the hydrogen evolution reaction (HER). However, to the date, Pt-based nanoparticular catalysts are still considered to be a state of the art, robust option for use as a cathode catalyst in PEM WE. But the high cost and limitted stability are still obstacle to use Pt based catalysts in PEM WE effectivelly [1]. Hence, the effort has to be made to improve the stability of Pt nanoparticles and thus to retain its catalytic activity even under reduced loads. Poly(amidoamine) dendrimer (PAMAM) encapsulation of the nanoparticles represents a promising approach to solve this issue. PAMAM works as a template, protecting encapsulated Pt nanoparticles without passivating their surface and preventing them from agglomeration. This approach has been validated by using dendrimer encapsulated Pt nanparticles (Dend-Pt) as an oxygen reduction reaction catalyst in the fuel cells [2]. The PAMAM are monodispersed macromolecules, having a three-dimensional structure. Typically, there are three types of PAMAM, namely cationic (-NH2), anionic (-COONa) and neutral (-OH). Thus, the charge of the surface groups determines the dendrimer type. Based on the size and molecular weight, each type of PAMAM dendrimers has been classified into different generation for example, G1 and G10 are denoted as 1st and 10th generations, respectively [2].The goal of this work is to reduce Pt load required for efficient and stable HER in a PEM WE. PAMAM encapsulated Dend-Pt incorporated into multilayer graphene oxide (MLG) are used for this purpose.At first, the most suitable dendrimer template for Pt encapsulation needs to be identified and an optimum loading improving its HER efficiency in PEM WE determined. Our previous communication has proved the excellent HER activity of the carbon supported Dend-Pt, revealing an important role of the various carbon supports in enhancing conductivity, stability and catalytic activity of the Dend-Pt for HER [3]. Thus, Dend-Pt were synthesized encapsulated within the different types of dendrimer templates with varying surface end groups (-NH2, -COONa and –OH). Different generations of each type of dendrimer were used. The synthesis method consists in a simple chemical reduction in an aqueous solvent at the room temperature. The encapsulated amount of Pt was fixed for the each dendrimer under study. Commercially available MLG was used as a carbon support. The Dend-Pt was incorporated into MLG through chemical covalent linkage using (1-ethyl-3-(3-dimethylaminopropyl) carbodiimide) (EDC) and N-hydroxyl sulfoxuccinimide (NHS) as the cross-linking agents. The amount of the cross-linking agents (EDC and NHS) used was optimised as a the mass ratio of Dend-Pt and MLG with respect to the HER activity of the resulting catalyst. The formation of the zero-valent Dend-Pt was confirmed using UV-Vis absorption and XPS spectroscopy. The structure of Dend-Pt and MLG/Dend-Pt composites were determined using TEM. The loading of the Dend-Pt on MLG surface was determined using the ICP-OES spectrometry. The electrochemical HER catalysis by different catalysts was studied by means of voltammetric methods and electrochemical impedance spectroscopy in an environment of the 0.5 M H2SO4 electrolyte solution. As a proof of concept, the PEM water electrolysis in single-cell setup was perfomed using either a commercial catalyst (40% Pt/C) or Dend-Pt as a cathode catalyst. Iridium dioxide was used as an anode catalyst.AcknowledgementThe authors gratefully acknowledge financial support from “The Grant Agency of the Czech Republic” (GAČR) under project no. 20-21105Y.Reference:[1] M. Prokop, M. Drakselova, K. Bouzek, Curr Opin Electrochem, 20 (2020) 20-27.[2] B. Devadas, A.P. Periasamy, K. Bouzek, Coord. Chem. Rev, 444 (2021) 214062.[3] B. Devadas, T. Imae, Electrochem. Communications, 72 (2016) 135-139. Figure 1

Atomic rearrangement on YMn2O5 modified Pt-based diesel oxidation catalyst for promoted performance

To improve the stability of Pt nanoparticles, the redox cycles with oxidation at 800 °C and reduction at 250 °C for three times were adopted on the Mn-mullite doped Pt-based catalysts (Pt-YMO/SA-Red) to rearrange the Pt atoms. The light-off temperature toward CO/C3H6/NO oxidation on Pt-YMO/SA-Red decreases by 20–60 °C, and the NO maximum conversion is improved by 27 % than the catalyst with only oxidation treatment at 800 °C (Pt-YMO/SA-Oxi). Characterization results verify that the interaction of Pt with YMn2O5 on Pt-YMO/SA-Red is reinforced via redox cyclic treatment to inhibit the aggregation of platinum particles and promote the formation of active oxygen species, in comparison to Pt-YMO/SA-Oxi. The easier active oxygen regeneration and more active platinum sites contribute to the excellent catalytic performances and stability. In addition, the mechanism for the high CO/C3H6/NO oxidation performance are analyzed via the detected reaction intermediate species.

Magnéli TiO2 as a High Durability Support for the Proton Exchange Membrane (PEM) Fuel Cell Catalysts

Proton exchange membrane fuel cells (PEMFCs) cathode catalysts’ robustness is one of the primary factors determining its long-term performance and durability. This work presented a new class of corrosion-resistant catalyst, Magnél TiO2 supported Pt (Pt/Ti9O17) composite, synthesized. The durability of a Pt/Ti9O17 cathode under the PEMFC operating protocol was evaluated and compared with the state-of-the-art Pt/C catalyst. Like Pt/C, Pt/Ti9O17 exhibited exclusively 4e− oxygen reduction reaction (ORR) in the acidic solution. The accelerated stress tests (AST) were performed using Pt/Ti9O17 and Pt/C catalysts in an O2-saturated 0.5 M H2SO4 solution using the potential-steps cycling experiments from 0.95 V to 0.6 V for 12,000 cycles. The results indicated that the electrochemical surface area (ECSA) of the Pt/Ti9O17 is significantly more stable than that of the state-of-the-art Pt/C, and the ECSA loss after 12,000 potential cycles is only 10 ± 2% for Pt/Ti9O17 composite versus 50 ± 5% for Pt/C. Furthermore, the current density and onset potential at the ORR polarization curve at Pt/C were significantly affected by the AST test. In contrast, the same remained almost constant at the modified electrode, Pt/Ti9O17. This demonstrated the excellent stability of Pt nanoparticles supported on Ti9O17.

Studies on Synthesis of Sub‐Nanometre Size Pt Particles Stabilized on ZrO2 Matrix for Formic Acid Mediated Synthesis of γ‐Valerolactone

AbstractA single‐step synthesis and stabilization of Pt nanoparticles on a nano‐zirconia (12‐13 nm) support matrix by a facile template‐assisted solvothermal method has been described. The formation of Pt nano‐material has been confirmed with XRD, HRTEM, and XPS analysis. The TEM results confirmed the formation of spherical‐shaped platinum with an average size of 0.8 nm. This single‐step and facile synthesis is an advanced approach to controlling the size of the support material and governs the dispersion of NPs in the support matrix. The catalytic activity of Pt nanoparticles supported on ZrO2 was studied for the conversion of levulinic acid to γ‐Valerolactone by a formic acid‐mediated hydrogenation reaction. The catalyst was found to be highly stable as it did not lose its catalytic activity even after four consecutive cycles. Moreover, the density functional theory (DFT) method was employed to investigate how the energy of activation is influenced by increasing the Pt cluster size.

Support Morphology Effect on Selective Hydrogenation of 3-Nitrostyrene to 3-Vinylaniline over Pt/α-Fe2 O3 Catalysts.

Selective hydrogenation of substituted nitroaromatic compounds is an extremely important and challenging reaction. Supported metal catalysts attract much attention in this reaction because the properties of metal nanoparticles (NPs) can be modified by the nature of the support. Herein, the support morphology on the catalytic performance of selective hydrogenation of 3-nitrostyrene to 3-vinylaniline was investigated. Pt NPs supported on octadecahedral α-Fe2 O3 supports with a truncated hexagonal bipyramid shape (Pt/α-Fe2 O3 -O) and rod-shaped α-Fe2 O3 supports (Pt/α-Fe2 O3 -R) were prepared by glycol reduction method. Detailed characterizations reveal that the electronic structure and dispersion of Pt NPs can be modified by the supports. The Pt/α-Fe2 O3 -O catalyst exhibited superior catalytic performance for hydrogenation of 3-nitrostyrene because of its low coordinated Pt sites and the small Pt NPs size, which is benefit from the high-index exposed surfaces of truncated hexagonal bipyramid-shaped α-Fe2 O3 support. The structural evolution during the catalytic reaction was investigated in detail by identical location transmission electron microscopy (IL-TEM) method, which found that the high cycling activity of Pt/α-Fe2 O3 -O catalyst during the cycle experiment results from the stability of Pt NPs.

Anchoring Highly Dispersed Pt Electrocatalysts on TiOx with Strong Metal-Support Interactions via an Oxygen Vacancy-Assisted Strategy as Durable Catalysts for the Oxygen Reduction Reaction.

Pt electrocatalysts with high activity and durability have still crucial issues for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). In this study, a novel catalyst consisting of Pt nanoparticles (NPs) on TiOx/C composites (TiOx-Vo-H/C) with abundant oxygen vacancies (Vo) is proposed, which is abbreviated as PTO-Vo-H/C. The introduction of Vo helps anchor highly dispersed Pt NPs with low loading and strengthen the strong metal-support interaction (SMSI), which benefits to the enhanced ORR catalytic activity. Moreover, the accelerated durability test (ADT) demonstrates the higher retention of ORR activity for PTO-Vo-H/C. Experimental and theoretical analyses reveal that electronic interactions between Pt NPs and TiOx/C composite support give rise to an electron-rich Pt NPs and strong SMSI effect, which is favorable for the electron transfer and stabilization of Pt NPs. More importantly, the assembled PEMFC with PTO-Vo-H/C shows only 6.9% of decay on maximum power density after 3000 ADT cycles while the performance of Pt/C sharply decreased. This work provides a new insight into the unique vacancy regulation of dispersive Pt on metal oxides for superior ORR performance.

Charge-transfer regulated visible light driven photocatalytic H2 production and CO2 reduction in tetrathiafulvalene based coordination polymer gel

The much-needed renewable alternatives to fossil fuel can be achieved efficiently and sustainably by converting solar energy to fuels via hydrogen generation from water or CO2 reduction. Herein, a soft processable metal-organic hybrid material is developed and studied for photocatalytic activity towards H2 production and CO2 reduction to CO and CH4 under visible light as well as direct sunlight irradiation. A tetrapodal low molecular weight gelator (LMWG) is synthesized by integrating tetrathiafulvalene (TTF) and terpyridine (TPY) derivatives through amide linkages and results in TPY-TTF LMWG. The TPY-TTF LMWG acts as a linker, and self-assembly of this gelator molecules with ZnII ions results in a coordination polymer gel (CPG); Zn-TPY-TTF. The Zn-TPY-TTF CPG shows high photocatalytic activity towards H2 production (530 μmol g−1h−1) and CO2 reduction to CO (438 μmol g−1h−1, selectivity > 99%) regulated by charge-transfer interactions. Furthermore, in situ stabilization of Pt nanoparticles on CPG (Pt@Zn-TPY-TTF) enhances H2 evolution (14727 μmol g−1h−1). Importantly, Pt@Zn-TPY-TTF CPG produces CH4 (292 μmol g−1h−1, selectivity > 97%) as CO2 reduction product instead of CO. The real-time CO2 reduction reaction is monitored by in situ DRIFT study, and the plausible mechanism is derived computationally.

Enhancement of Activity and Development of Low Pt Content Electrocatalysts for Oxygen Reduction Reaction in Acid Media.

Platinum is a main catalyst for the electroreduction of oxygen, a reaction of primary importance to the technology of low-temperature fuel cells. Due to the high cost of platinum, there is a need to significantly lower its loadings at interfaces. However, then O2-reduction often proceeds at a less positive potential, and produces higher amounts of undesirable H2O2-intermediate. Hybrid supports, which utilize metal oxides (e.g., CeO2, WO3, Ta2O5, Nb2O5, and ZrO2), stabilize Pt and carbon nanostructures and diminish their corrosion while exhibiting high activity toward the four-electron (most efficient) reduction in oxygen. Porosity of carbon supports facilitates dispersion and stability of Pt nanoparticles. Alternatively, the Pt-based bi- and multi-metallic catalysts, including PtM alloys or M-core/Pt-shell nanostructures, where M stands for certain transition metals (e.g., Au, Co, Cu, Ni, and Fe), can be considered. The catalytic efficiency depends on geometric (decrease in Pt–Pt bond distances) and electronic (increase in d-electron vacancy in Pt) factors, in addition to possible metal–support interactions and interfacial structural changes affecting adsorption and activation of O2-molecules. Despite the stabilization of carbons, doping with heteroatoms, such as sulfur, nitrogen, phosphorus, and boron results in the formation of catalytically active centers. Thus, the useful catalysts are likely to be multi-component and multi-functional.

Optimizing Aerosol Jet Printing Process of Platinum Ink for High-Resolution Conductive Microstructures on Ceramic and Polymer Substrates.

Printing nano-ink with platinum nanoparticles to generate conductive microstructures for electronics on different types of substrates has gained increasing interest in recent years. To solve the problem of the low conductivity of platinum (Pt) nano-ink, we synthesized chemically pure Pt nanoparticles with sizes of 18.2 ± 9.0 nm by spark discharge method. A low toxic solvent, ethylene glycol with water, was used to ensure the aggregation stability of Pt nanoparticles. Polyvinylpyrrolidone was used as an adhesive additive and binder in the nano-ink. Narrow and conductive Pt lines were generated by aerosol jet printing technology. The resistivity of the Pt lines sintered at 750 °C on alumina substrate was found to exceed the bulk Pt by about 13%. Moreover, the Pt film fabricated on polymer substrates has demonstrated excellent mechanical flexibility in terms of twisting tests.

Pt Nanoparticles Confined by Zirconium Metal-Organic Frameworks with Enhanced Enzyme-like Activity for Glucose Detection.

Metal nanozymes hold promise for chemical and biological applications, and their implementation relies on high catalytic efficiency and stability. Using the metal–organic framework as an ideal carrier for well-dispersed ultra-small metal nanoparticles (NPs) is beneficial for improving the catalytic efficiency of nanozymes. In this study, a zirconium-based metal organic framework (UiO-66) with good chemical stability and high porosity was synthesized and used to construct Pt/UiO-66 nanocomposites. The percentage of Pt in UiO-66 can be tuned easily by adjusting the feeding amount of PtCl42–. Because of the confinement effect of mesopores, the Pt particles with an average diameter of 3.8 nm are formed and dispersed throughout the pores of the UiO-66 particle. The Pt/UiO-66 composites show efficient oxidase- and peroxidase-like activity. Both the oxidase- and peroxidase-like activities are dependent on the Pt percentage. Pt/UiO-66-6% exhibits enhanced peroxidase-like activity, ∼3.9 times higher than that of commercial Pt/C with 10 wt % Pt. We propose that the construction of Pt/UiO-66 increased the utilization efficiency and stability of Pt NPs and provided more active sites for catalytic reactions. Using the peroxidase-like activity of Pt/UiO-66, a colorimetric method that can be used for actual blood glucose detection was developed for the specific detection of glucose with a limit of detection of 0.033 mM.

Atom-by-atom analysis of sintering dynamics and stability of Pt nanoparticle catalysts in chemical reactions.

Supported Pt nanoparticles are used extensively in chemical processes, including for fuel cells, fuels, pollution control and hydrogenation reactions. Atomic-level deactivation mechanisms play a critical role in the loss of performance. In this original research paper, we introduce real-time in-situ visualization and quantitative analysis of dynamic atom-by-atom sintering and stability of model Pt nanoparticles on a carbon support, under controlled chemical reaction conditions of temperature and continuously flowing gas. We use a novel environmental scanning transmission electron microscope with single-atom resolution, to understand the mechanisms. Our results track the areal density of dynamic single atoms on the support between nanoparticles and attached to them; both as migrating species in performance degradation and as potential new independent active species. We demonstrate that the decay of smaller nanoparticles is initiated by a local lack of single atoms; while a post decay increase in single-atom density suggests anchoring sites on the substrate before aggregation to larger particles. The analyses reveal a relationship between the density and mobility of single atoms, particle sizes and their nature in the immediate neighbourhood. The results are combined with practical catalysts important in technological processes. The findings illustrate the complex nature of sintering and deactivation. They are used to generate new fundamental insights into nanoparticle sintering dynamics at the single-atom level, important in the development of efficient supported nanoparticle systems for improved chemical processes and novel single-atom catalysis.This article is part of a discussion meeting issue ‘Dynamic in situ microscopy relating structure and function’.