Boosting Photothermocatalytic Oxidation of Toluene Over Pt/N-TiO2: The Gear Effect of Light and Heat

Photothermal catalysis is extremely promising for the removal of various indoor pollutants owing to its photothermal synergistic effect, while the low light utilization efficiency and unclear catalytic synergistic mechanism hinder its practical applications. Here, nitrogen atoms are introduced, and Pt nanoparticles are loaded on TiO2 to construct Pt/N-TiO2-H2, which exhibits 3.5-fold higher toluene conversion rate than the pure TiO2. Compared to both photocatalytic and thermocatalytic processes, Pt/N-TiO2-H2 exhibited remarkable performance and stability in the photothermocatalytic oxidation of toluene, achieving 98.4% conversion and 98.3% CO2 yield under a light intensity of 260 mW cm-2. Furthermore, Pt/N-TiO2-H2 demonstrated potential practical applicability in the photothermocatalytic elimination of various indoor volatile organic compounds. The synergistic effect occurs as thermocatalysis accelerates the accumulation of carboxylate species and the degradation of aldehyde species, while photocatalysis promotes the generation of aldehyde species and the consumption of carboxylate species. This ultimately enhances the photothermocatalytic process. The photothermal synergistic effect involves the specific conversion of intermediates through the interplay of light and heat, providing novel insights for the design of photothermocatalytic materials and the understanding of photothermal mechanisms.

Glycerol Electro-Oxidation in Alkaline Medium with Pt-Fe/C Electrocatalysts Synthesized by the Polyol Method: Increased Selectivity and Activity Provided by Less Expensive Catalysts

We have investigated platinum catalysts containing iron as a modifier to obtain catalysts with superior electrocatalytic activity toward glycerol electro-oxidation in an alkaline medium. The electrocatalysts, supported on carbon Vulcan, were synthesized by the polyol method. The physicochemical characterization data showed that the metals were well distributed on the carbon support and had small particle size (2 nm). The Pt:Fe metal ratio differed from the nominal composition, indicating that reducing iron with platinum was difficult, even though some parameters of the synthesis process were changed. Electrochemical analyses revealed that PtFe/C was more active and stable than commercial Pt/C was, and analysis of the electrolysis by-products showed that iron addition to Pt/C boosted the glycerol conversion and selectivity for glyceric acid formation.

Enhanced Activity of Oxygen Reduction Reaction on Pr6O11-Assisted PtPr Alloy Electrocatalysts

Pt-based alloy catalysts for oxygen reduction reaction (ORR) with outstanding performance have been well-studied in recent years. Among these, Pt-lanthanide alloy catalysts have been developed with quite a competitive ORR activity. However, to promote practical applications of a proton-exchange membrane fuel cell (PEMFC), catalysts with superior activity are still being explored. Herein, we present the Pr₆O₁₁-assisted Pt-Pr catalyst exhibiting further improved ORR activity than the state-of-the-art Pt/C. A simple annealing treatment is applied after the synthesis of the Pt-Pr alloy, obtaining Pr₆O₁₁ nanoparticles attached to the surface of the Pt-Pr alloy to form a Pt-Pr/Pr₆O₁₁ composite catalyst. Experimental and theoretical studies reveal that the electronic state of Pt in the Pt-Pr/Pr₆O₁₁ system is modified. It was found that the strong oxophilicity of Pr adjusts the active site of Pt and promotes the adsorption and dissociation of O₂. The preeminent intrinsic ORR activity on the Pt-Pr/Pr₆O₁₁ catalyst reaches the promoted specific activity (2.01 mA cm^-2) and mass activity (1.3 A mg_Pt^-1), which were 5.91- and 5.90-fold higher than those obtained by the state-of-the-art Pt/C catalyst (0.34 mA cm^-2 and 0.22 A mg_Pt^-1). This study provides us with an idea that the ORR performance of Pt-based alloy could be enhanced with the assistance of the metal oxide phase.

Liquid Metal Interfacial Growth and Exfoliation to Form Mesoporous Metallic Nanosheets for Alkaline Methanol Electroreforming

Two-dimensional (2D) materials have spurred great interest in the field of catalysis due to their fascinating electronic and thermal transport properties. However, adding uniform mesopores to 2D metallic materials has remained a great challenge owing to the inherent high surface energy. Here, we introduce a generic liquid metal interfacial growth and exfoliation strategy to synthesize a library of penetrating mesoporous metallic nanosheets. The formation of liquid-metal/water interface promotes the adsorption of metal ion-encapsulated copolymer micelles, induces the self-limiting galvanic replacement reaction, and enables the exfoliation of products under mechanical agitation. These 2D mesoporous metallic nanosheets with large lateral size, narrow thickness distribution, and uniform perforated structure provide facilitated channels and abundant active sites for catalysis. Typically, the generated mesoporous PtRh nanosheets (mPtRh NSs) exhibit superior electroactivity and durability in hydrogen evolution reaction as well as methanol electrooxidation in alkaline media. Moreover, the constructed symmetric mPtRh NSs cell requires only a relative low electrolysis voltage to achieve methanol-assisted hydrogen production compared with traditional overall water electrolysis. The work reveals a specific growth pattern of noble metals at the liquid-metal/water interface and thus introduces a versatile strategy to form 2D penetrating mesoporous metallic nanomaterials with extensive high-performance applications.

Highly Ordered Pt-Based Nanoparticles Directed by the Self-Assembly of Block Copolymers for the Oxygen Reduction Reaction

Designing Pt-based nanoparticle (NP) catalysts is of great interest for the lowering of Pt usage and the enhancement of catalytic activity on the proton-exchange membrane fuel cells (PEMFCs). However, it is still challenging to develop well-arrayed catalyst NPs on supports over multiple-length scales. Herein, we presented a facile strategy of producing well-ordered Pt-based NPs toward oxygen reduction reaction (ORR) catalysts assisted by the self-assembly of block copolymers. In contrast to the conventional Pt/C ORR catalysts with a random dispersion on carbon, the as-prepared Pt, PtCo, and PtCo@Pt NPs in our work were hexagonally arranged with a uniform quasi-spherical shape and ordered distribution. The systematic study related to their ORR activities revealed that the PtCo@Pt core-shell NP arrays were more active and more durable than PtCo, Pt, and the commercial Pt/C catalyst. In the rotating-disk electrode test, a half-wave potential (E_1/2) of 0.86 V versus RHE and a 4-e ORR mechanism were found for PtCo@Pt. Single-cell performance showed that the current density and the peak power density of PtCo@Pt achieved 0.86 A/cm²@0.7 V and 1.05 W/cm², respectively, with a Pt loading of ∼0.15 mg/cm² on the cathode. Also, they held 81.4 and 82.9% retention, respectively, after the durability test in the single-cell test. Density functional theory calculation results revealed that PtCo@Pt NPs had a lower d-band center and a weaker oxygen binding energy compared to Pt and PtCo, which contributed to the enhancement of the ORR activity.

Engineering oxygen vacancies via amorphization in conjunction with W-doping as an approach to boosting catalytic properties of Pt/Fe-W-O for formaldehyde oxidation

Engineering functional defects in support materials has gained ever-increasing attention as a novel approach to boosting the catalytic performance of oxide-supported catalysts. Herein, we demonstrate the feasibility of engineering oxygen vacancy in iron oxide through amorphization in conjunction with foreign cation doping and elucidate the important role of support functionality in the catalytic oxidation of formaldehyde (HCHO). A supported Pt catalyst on Fe-W-O amorphous nanosheets (denoted as Pt/a-Fe-W-O) was synthesized using a one-step solvothermal method. This simple method allowed us to simultaneously create abundant oxygen vacancies in the substrate and to ensure uniform dispersion of tiny Pt nanoparticles with an average diameter of 1.4 nm on the high-surface-area substrate. This renders an increased possibility of Pt/O-vacancy coexistence in close proximity, which synergistically boosts the formation of active oxygen and surface hydroxyl species. Consequently, the Pt/a-Fe-W-O catalyst with an optimal W/Fe molar ratio of 0.08:1 and a 1.51 wt% Pt loading exhibited a high specific reaction rate of 68.3 μmol g_Pt^-1 s^-1 and excellent stability during 24 h continuous test, outperforming most existing HCHO oxidation catalysts. Our study highlights the importance of functional oxygen defects in construction of synergistic active sites for promoting the reactions requiring multiple active species.

Facet- and defect-engineered Pt/Fe2O3 nanocomposite catalyst for catalytic oxidation of airborne formaldehyde under ambient conditions

Formaldehyde (HCHO) is one of the most infamous indoor pollutants that imposes a great threat to human health. Herein, we report the development of a high-performance Pt/Fe₂O₃ catalyst for HCHO oxidation employing a facet- and defect-engineering strategy, with special focus on the surface structure effect of α-Fe₂O₃ on the catalytic properties. A supported Pt nanocatalyst on hollow octadecahedral α-Fe₂O₃ with exclusively exposed {113} and {104} facets was prepared using a hydrothermal method followed by impregnation-reduction treatment. The high-index facets of α-Fe₂O₃ render the formation of abundant oxygen vacancies and an improved dispersion of Pt nanoparticles. This led to an increased Pt/O-vacancy coexistence in close proximity, which collaboratively promote the generation of active oxygen and surface OH species. As a consequence, the Pt/Fe₂O₃-HO catalyst exhibited impressively high and stable activity towards HCHO oxidation at room temperature, which was five-fold higher than that of the supported Pt catalyst on commercial α-Fe₂O₃.

Kinetic Isotope Effect as a Tool To Investigate the Oxygen Reduction Reaction on Pt-based Electrocatalysts - Part II: Effect of Platinum Dispersion

We investigated the oxygen reduction reaction (ORR) mechanism on Pt nanoparticles (NPs) dispersed on several carbon blacks with various physicochemical properties (i. e. specific surface ranging from 80 to 900 m²  g^-1 , different graphitization degree, etc.). Using the kinetic isotope effect (KIE) along with various electrochemical characterizations, we determined that the rate determining step (RDS) of the ORR is a proton-independent step when the density of Pt NPs on the surface of the carbon support is high. Upon decrease of the density of Pt NPs on the surface, the RDS of the ORR starts involving a proton, as denoted by an increase of the KIE >1. This underlined the critical role played by the carbon support in the oxygen reduction reaction electrocatalysis by Pt supported on high surface area carbon.

Interfacial Engineering in PtNiCo/NiCoS Nanowires for Enhanced Electrocatalysis and Electroanalysis

Searching for new anti-poisoning Pt-based catalysts with enhanced activity for alcohol oxidation is the key in direct alcohol fuel cells (DAFCs). However, in the traditional strategy for designing bimetallic or multimetallic alloy is still difficult to achieve a satisfactory heterogeneous electrocatalyst because the activity often depends on only the surface atoms. Herein, we fabricate the multicomponent active sites by creating a sulfide structure on 1D PtNiCo trimetallic nanowires (NWs), to give a PtNiCo/NiCoS interface NWs (IFNWs). Owing to the presence of sulfide interfaces, the PtNiCo/NiCoS IFNWs enable an impressive methanol/ethanol oxidation reaction (MOR/EOR) performance and excellent anti-CO poisoning tolerance. They have the MOR and EOR mass activities of 2.25 Amg^-1 _Pt and 1.62 Amg^-1 _Pt , around 1.26, 3.21 and 1.46, 2.96 times higher than those of PtNiCo NWs and commercial Pt/C, respectively. CO-stripping and XPS measurements further demonstrate that the new interfacial structure and optimal bonding of Pt-CO can result in accelerating the removal of surface adsorbed carbonaceous intermediates. Moreover, such a unique structure has also demonstrated a much-improved ability for the electrochemical detection of some important molecules (H₂ O₂ and NH₂ NH₂ ).

A Spatially Confined gC3N4-Pt Electrocatalyst with Robust Stability

Metal catalysts (e.g., Pt) have a variety of applications in energy conversion devices including polymer electrolyte fuel cells (PEFCs); however, they commonly confront a crucial issue of poor stability. Herein, a structural model of spatially confining supported Pt nanoparticles is determined to improve the stability of metal catalysts, wherein graphitic carbon nitride (gC₃N₄) supported Pt nanoparticles (gC₃N₄-Pt) are spatially confined by carbon nanospheres (CNSs). The resulting CNSs-Pt/gC₃N₄ catalyst demonstrates a surprising retention rate of electrochemical surface area as high as 85.0%, much higher than that of the commercial Pt/C catalyst (45.2%), and the half-wave potential is reduced by only 11 mV compared with 54 mV for Pt/C after 6000 scanning cycles. In addition, CNSs also serve as a conductive agent to increase electron transfer pathways on Pt surfaces, and the unique spatial confinement structure with an open framework ensures the mass transfer. Moreover, the methanol oxidation reaction (MOR) activity of CNSs-Pt/gC₃N₄ gets elevated by 2.1 times that of Pt/C in terms of the anodic peak current. The stabilized catalyst model and its derivative structures can be applied to various metal catalyst systems.

Engineering Pt/Pd Interfacial Electronic Structures for Highly Efficient Hydrogen Evolution and Alcohol Oxidation

Tailoring the interfacial structure of Pt-based catalysts has emerged as an effective strategy to improve catalytic activity. However, little attention has been focused on investigating the relationship between the interfacial facets and their catalytic activity. Here, we design and implement Pd-Pt interfaces with controlled heterostructure features by epitaxially growing Pt nanoparticles on Pd nanosheets. On the basis of both density functional theory calculation and experimental results, we demonstrate that charge transfer from Pd to Pt is highly dependent on the interfacial facets of Pd substrates. Therefore, the Pd-Pt heterostructure with Pd(100)-Pt interface exhibits excellent activity and long-term stability for hydrogen evolution and methanol/ethanol oxidation reactions in alkaline medium, much better than that with Pd (111)-Pt interface or commercial Pt/C. Interfacial crystal facet-dependent electronic structural modulation sheds a light on the design and investigation of new heterostructures for high-activity catalysts.

TiO2 Nanotube-Carbon (TNT-C) as Support for Pt-based Catalyst for High Methanol Oxidation Reaction in Direct Methanol Fuel Cell

In this study, TiO₂ nanotubes (TNTs) were synthesized via a hydrothermal method using highly concentrated NaOH solutions varying from 6 to 12 M at 180 °C for 48 h. The effects of the NaOH concentration and the TNT crystal structure on the performance for methanol oxidation were investigated to determine the best catalyst support for Pt-based catalysts. The results showed that TNTs produced with 10 M NaOH exhibited a length and a diameter of 550 and 70 nm, respectively; these TNTs showed the best nanotube structure and were further used as catalyst supports for a Pt-based catalyst in a direct methanol fuel cell. The synthesized TNT and Pt-based catalysts were analysed by FESEM, TEM, BET, EDX, XRD and FTIR. The electrochemical performance of the catalysts was investigated using cyclic voltammetry (CV) and chronoamperometric (CA) analysis to further understand the methanol oxidation in the direct methanol fuel cell (DMFC). Finally, the result proves that Pt-Ru/TNT-C catalyst shows high performance in methanol oxidation as the highest current density achieved at 3.3 mA/cm² (normalised by electrochemically active surface area) and high catalyst tolerance towards poisoning species was established.