Effective PtAu nanowire network catalysts with ultralow Pt content for formic acid oxidation and methanol oxidation

Pt is the ideal anode catalyst in fuel cells. In this paper, in order to increase the utilization of Pt, the PtAu nanowire networks (NWNs) with ultralow content of Pt are fabricated by a simple silicon monoxide (SiO) reduction method without any capping agent. PtAu NWNs supported on carbon black with Pt content of 1 wt% (Pt₀.₀₅Au NWNs) are employed as catalysts for formic acid oxidation (FAO) and methanol oxidation reaction (MOR), whose mass activities are as high as 4998.9 and 2282.3 mA∙mg_Pt⁻¹, respectively. The network structure facilitates the electron transfer and increases the stability of the catalysts. The PtAu composite experiences compressive lattice strain as confirmed by X-ray powder diffraction (XRD). The Pt₀.₀₅Au NWNs catalyst with low Pt content results in the largest strain variation compared with PtAu composited of other ratios, which may downshift the d-band center of Pt and lead to the higher electrocatalytic activity in oxidation reaction.     

Crystalline nickel boride nanoparticle agglomerates for enhanced electrocatalytic methanol oxidation

In this paper, crystalline Ni₃B nanoparticle agglomerates have been successfully prepared via dry-powder annealing of the solution-produced amorphous nickel boride. The electron microscopy (EM) images indicate that the Ni₃B nanomaterial is composed of numerous nano-sized particles with a diameter ranging from 100 to 200 nm. The electrocatalytic characteristics of nickel boride in an alkaline medium were observed by cyclic voltammetry (CV) and chronoamperomerty (CA). Compared to the amorphous nickel boride/Ni foam (ANB/NF), the crystalline Ni₃B/Ni foam (CNB/NF) electrode exhibits a higher catalytic performance with low initial oxidation potential of 0.35 V and a high anodic oxidation current density of 62 A g⁻¹ at 0.55 V in a 6 M KOH solution with 0.5 M methanol. And the CNB/NF electrode shows good long-term cycling stability and the catalytic current of methanol retains 87% of the initial value after 1000 time cycles. The CNB/NF electrode should be a promising candidate for alkaline direct methanol fuel cells (DMFCs).     

Pt nanoparticles modified Au dendritic nanostructures: Facile synthesis and enhanced electrocatalytic performance for methanol oxidation

A facile and simple method is presented for the synthesis of bimetallic composites, Pt nanoparticles modified dendritic Au nanostructures (PtNPs/DGNs), in which dendritic Au was deposited on a glassy carbon electrode via a potentiostatic method and sphere-like Pt nanoparticles were decorated on Au substrates through a chemical reduction reaction. The compositions, morphologies, and structures of the PtNPs/DGNs were characterized by X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and energy dispersive X-ray spectroscopy. Results indicated that bimetallic composites were successfully synthesized and spherical Pt nanoparticles were dispersed evenly on dendritic Au substrates. The number of Pt nanoparticles on Au surface was regulated by controlling the chemical reduction deposition time, allowing the electrocatalytic properties of the composite towards methanol oxidation to be tuned. Electrochemical measurements, including cyclic voltammetry and chronoamperometry, were performed to investigate the electrochemical properties and electrocatalytic behaviors of the PtNPs/DGNs towards methanol oxidation. Pt nanoparticles partially covered dendritic Au exhibited dramatically enhanced electrocatalytic activity (3.947 mA cm^?2), which was 2.65 times that of commercial carbon-supported Pt nanoparticles (1.487 mA cm^?2), along with much improved poisoning tolerance (current decline: 70.85% vs 99.36%). These enhanced performances were likely caused by the large active electrochemical area of the bimetallic nanocomposites and the change in the electronic structure of Pt when the Au surface was modified with fewer Pt nanoparticles.     

Preparation of Pt/NiO-C electrocatalyst and heat-treatment effect on its electrocatalytic performance for methanol oxidation

Pt catalyst supported on Vulcan XC-72R containing 5 wt% NiO (Pt/NiO–C) showed larger electrochemical active surface area and higher electrochemical activity for methanol oxidation than Pt catalyst supported on Vulcan XC-72R using polyol method without NiO addition. Prepared Pt/NiO–C electrocatalyst was heat-treated at four temperatures (200, 400, 600, and 800 °C) in flowing N₂. X-ray diffraction and temperature-programmed desorption results indicated that NiO was reduced to Ni in inert N₂ during heat-treatments at temperatures above or equal to 400 °C, while oxygen from NiO reacted with carbon support due to the catalytic effect of Pt. The reduced Ni formed an alloy with Pt, which, according to the X-ray photoelectron spectroscopy data, resulted in a shift to a lower binding energy of Pt 4f electrons. The Pt/NiO–C electrocatalyst heat-treated at 400 °C showed the best activity in methanol oxidation due to the change in Pt electronic structure by Ni and the minimal aggregation of Pt particles.     

Highly dispersed ultrafine Pt nanoparticles on nickel-cobalt layered double hydroxide nanoarray for enhanced electrocatalytic methanol oxidation

Highly dispersed ultrafine Pt nanoparticles (NPs) were loaded on a nickel-cobalt layered double hydroxide (NiCo-LDH) nanoarray that was grown on Ni foam (NF) via an in situ redox reaction without any external agent between Co²⁺ (Co(OH)₂) in NiCo-LDH and PtCl₆^2-. The obtained Pt/NiCoLDH/NF composite was used as a catalyst for methanol oxidation in alkaline media, showing much higher electrocatalytic activity and better anti-poisoning ability and stability for methanol oxidation than commercial Pt/C, mainly because of the uniform dispersion of ultrafine Pt NPs, the synergistic effect and stable support of NiCoLDH. The NiCoLDH nanoarray effectively increased the specific surface area and location sites for supporting Pt NPs and enhanced the catalytic performance and tolerance to intermediate species. This enhancement was probably due to the synergistic effect between Pt and the NiCo-LDH nanosheets, in which the LDH can provide adequate OH^?_ads species for accelerating the methanol oxidation reaction (MOR).     

PtIr alloy nanowire assembly on carbon cloth as advanced anode catalysts for methanol oxidation

The interconnecred PtIr alloy nanowires were uniformly deposited on carbon cloth via One-step wet chemistry method, which diameter is averaged to be 5 nm with a length of 50–200 nm. The carbon cloth supported PtIr nanowire assembly (PtIr NA/CC) shows a larger electrochemical active surface area (ECSA) due to its 3D nanostructure and a high CO-resistance as a result from the synergistic effect of PtIr alloy. The PtIr NA/CC exhibits an extremely high mass activity and a reliable long-term stability toward methanol oxidation reaction (MOR). The superior catalytic performance on MOR can match and even surpass those best Pt-based nanowires reported recently in the literature.     

High efficient electrocatalytic oxidation of methanol on Pt/polyindoles composite catalysts

Novel composite catalysts have been fabricated by the electrodeposition of Pt onto the glassy carbon electrode (GC) modified respectively with polyindole (PIn) and poly(5-methoxyindole) (PMI) and used for the electrooxidation of methanol in acid solution of 0.5 M H₂SO₄ containing 1.0 M methanol. As-formed composite catalysts are characterized by SEM, XRD and the electrochemical methods. The results of the catalytic activity for methanol oxidation show that the two composite catalysts exhibit higher catalytic activity and stronger poisoning-tolerance than Pt/polypyrrole/GC (Pt/PPy/GC) and Pt/GC. Electrochemical impedance spectroscopy indicates that the methanol electrooxidation on the composite catalysts at various potentials shows different impedance behaviors. At the same time, the charge-transfer resistance for electrooxidation of methanol on Pt/PIn/GC and Pt/PMI/GC is smaller than those on Pt/PPy/GC and Pt/GC. The present study shows a promising choice of Pt/PIn and Pt/PMI as composite catalysts for methanol electrooxidation.     

Enhanced electrocatalytic methanol oxidation properties by photo-assisted Fe2O3 nanoplates

In this paper, visible-light-driven two-dimensional (2D) Fe₂O₃ nanoplates with exposed (001) facets were first adopted to act as Pt support for photo-assisted electrocatalytic methanol oxidation. Under simulated solar light and visible light illumination Pt-2D Fe₂O₃ nanoplates displayed 2.32 and 1.30 times higher electrocatalytic activities for methanol oxidation than in dark condition, respectively. Besides, 2D Fe₂O₃ nanoplates owns much better electrocatalytic activities for methanol oxidation than Fe₂O₃ particles whether in dark, visible light or simulated solar light illumination. The nice photo-assisted electrocatalytic methanol oxidation activities of Pt-2D Fe₂O₃ nanoplates can be attributed to 2D structure enhanced the oxidation activities of photogenerated holes to oxidize OH⁻ to hydroxyl radical (·OH) as well as its large specific surface area. Our experimental results suggest that photo-assisted and two-dimensional strategy of semiconductors are promising ways to further improve the electrocatalytic activities for methanol oxidation in DMFCs.     

Analysis of performance losses of direct methanol fuel cell with methanol tolerant PtCoRu/C cathode electrode

The long-term stability of PtCoRu/C to methanol crossover has been evaluated in a direct methanol fuel cell (DMFC) configuration. The DMFC has been subjected to continuous operation under potential step cycles. The degradation of the DMFC with PtCoRu/C has been followed by comparison of the power density curves recorded after 0, 60 and 312 h of continuous operation, and compared to that recorded for a DMFC with Pt/C. Electrochemical Impedance Spectra (EIS) were recorded directly from the DMFCs and used to identify the main degradation phenomena responsible for the loss of performance of the used fuel cell. AC impedance spectra show that the resistance of the anode reaction increases while resistance associated to the cathode reaction decreases after the long-term stability tests; however, the analysis of the power density curves unequivocally show that the performance of the DMFCs goes down during the stability tests. This apparent contradiction can be explained by taking into account the changes between the fresh and used PtCoRu/C observed by X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses. During the potential step cycles Ru dissolves form PtCoRu/C leading to Pt-enriched catalysts which are more active for the oxygen reduction reaction (lower resistance) but less tolerant to methanol (lower power density).     

Facile synthesis of Pd-Ru-P ternary nanoparticle networks with enhanced electrocatalytic performance for methanol oxidation

Liquid fuel cells have attracted broad research interests for past several decades, especially for direct methanol fuel cells (DMFCs) because of their compact volume, environmentally benign and easy storage. Exploring cost-effective electrocatalysts toward methanol electrooxidation is meaningful for the development of (DMFCs). Herein, a series of PdRu/P network catalysts have been fabricated and modified via a facile and reproducible method taking benzyl alcohol, hydrazine hydrate as solvent and reducing agents, respectively. Profiting from the 3D network structure, the synergistic effect together with the increased electron mobility induced by the addition of nonmetal phosphorous (P). The PdRu/P catalysts display markedly improved efficient electrocatalytic activity with excellent current peak, more negative onset potential, as well as superior long-term stability compared to commercial Pd/C, PdRu and Pd/P prepared under the same condition. In this work, we highlight the effect of the incorporation of nonmetals P on the electrocatalytic performance of PdRu binary catalysts, which will contribute to broadening the application of nonmetal P or even for other nonmetals for electrooxidation. Our efforts will dedicate to accelerating the commercialization of efficient and stable anode catalysts in fuel cells by means of doping transition metals or nonmetals into Pd.     

Titanium dioxide as support material for Pt1Pd3 toward methanol oxidation

The electrocatalytic oxidation of methanol on the Pt₁Pd₃ nanoparticles supported on rutile TiO₂ in alkaline solution is investigated. The Pt₁Pd₃ nanoparticles are prepared by the chemical co-reduction of the precursors of Pt and Pd and then loaded on TiO₂. The Pt₁Pd₃ nanoparticles with sizes of about 2–4 nm and a certain degree of aggregation are dispersed on TiO₂. The position and shape of the methanol oxidation peak on Pt₁Pd₃/TiO₂ are more similar to those on Pt/TiO₂ than those on Pd/TiO₂, while Pt₁Pd₃/TiO₂ exhibits higher catalytic activity, e.g., a significantly higher peak intensity, than Pt₁Pd₃/C, Pt/TiO₂ and Pd/TiO₂. This indicates the advantage of TiO₂ as a support material and the strong synergy between the Pt₁Pd₃ and TiO₂ and between the Pt and Pd. Moreover, Pt₁Pd₃/TiO₂ has a high tolerance for the poisoning caused by CO. Rutile TiO₂ is shown to be suitable as a support material for the Pt₁Pd₃ to achieve enhanced catalytic activity and stability.     

Construction of three-dimensional hierarchical Pt/TiO2@C nanowires with enhanced methanol oxidation properties

Three-dimensional (3D) hierarchical Pt/TiO₂@C core-shell nanowire networks with high surface area have been constructed via wet chemical approaches. The 3D TiO₂ nanowire framework was in situ synthesized within a porous titanium foam by hydrothermal method followed by carbon coating and self-assembled growth of ultrathin Pt nanowires. Structural characterization indicates that single crystalline ultrathin Pt nanowires of 3–5 nm in diameter were vertically distributed on the anatase TiO₂ nanowires covered with a 2–4 nm thin carbon layer. The 3D hierarchical Pt/TiO₂@C nanostructure demonstrates evidently higher catalytic activities towards methanol oxidation than the commercial Pt/C catalyst. The catalytic current density of the hierarchical catalyst is 1.6 times as high as that of the commercial Pt/C, and the oxidation onset potential (0.35 V vs. Ag/AgCl) is more negative than the commercial one (0.46 V vs. Ag/AgCl). Synergistic effect between the ultrathin Pt nanowires and the TiO₂@C core-shell nanostructure accounts for the enhanced catalytic properties, which can be determined by X-ray photoelectron spectroscopy (XPS) investigation. The obtained hierarchical Pt/TiO₂@C nanowire networks promise great potential in producing anode catalysts for direct methanol fuel cells applications.     

Solution plasma method assisted with MOF for the synthesis of Pt@CoOx@N-C composite catalysts with enhanced methanol oxidation performance

The key to direct methanol fuel cells (DMFCs) is the anode catalyst for methanol oxidation reaction (MOR) which has good catalytic activity and stability. Pt@CoO_x@N-C catalysts were synthesized by compounding Pt nanoparticles and CoO_x with nitrogen-doped porous carbon (N-C). Pt nanoparticles were prepared by solution plasma technique. CoO_x@N-C are derived from zeolitic-imidazolate-framework-67 (ZIF-67) by heat treatment at 700 °C. For MOR, Pt@CoO_x@N-C exhibits an outstanding electrocatalytic performance (mass activity of 2400 mA mg_Pt⁻¹) and stability (70% remained after 300 cycles) under acidic condition, which owing to the synergistic effects among the Pt nanoparticles, CoO_x and nitrogen-doped porous carbon. Pt@CoO_x@N-C shows such mass activity superior to that of Pt/C (460 mA mg_Pt⁻¹) due to the fact that CoO can adsorb –OH in the solution and then assist Pt to oxidize the CO-like intermediates to CO₂ which improves the resistance to CO poisoning of Pt nanoparticles. Therefore, solution plasma method assisted with metal-organic frameworks have good development prospects on synthesis of highly efficient electrocatalysts.     

Pt modified TiO2 nanotubes electrode: Preparation and electrocatalytic application for methanol oxidation

Pt nanoparticles decorated TiO₂ nanotubes (Pt/TiO₂NTs) modified electrode has been successfully synthesized by depositing Pt in TiO₂NTs, which were prepared by anodization of the Ti foil. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and electrochemical methods were adopted to characterize their structures and properties. The Pt/TiO₂NTs electrode shows excellent electrocatalytic activity toward methanol oxidation reaction (MOR) in alkaline electrolyte without UV irradiation.     

Preparation of PtNi hollow nanospheres for the electrocatalytic oxidation of methanol

We report the synthesis and characterization of hollow PtNi nanospheres by chemical successive-reduction method. The results of X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) account for the alloy formation between Pt and Ni and electronic structure change of Pt in the alloy. The prepared nanospheres show a high activity and stability for electrocatalytic oxidation of methanol as compared to the commercial Pt/C catalyst and the co-reduced PtNi nanoparticles. The reasons of the high electrocatalytic activity of the hollow PtNi nanospheres were discussed.     

Fe-doped CoP nanotube heterostructure enhanced the catalytic activity of Pt nanoparticles towards methanol oxidation reaction

Developing the efficient and stable anode catalysts of direct methanol fuel cell has been a pivotal requirement for its extensive commercial application. Herein, we design the Fe-doped CoP nanotube heterostructure as the co-catalyst of Pt-based catalyst via combining a facile hydrothermal with phosphorization process, subsequently, the traditional NaBH₄ reduction method is utilized to deposit Pt nanoparticles. As anticipated, Fe species have been successfully doped into CoP to generate the Fe-doped CoP nanotube heterostructure, and the involved characterizations identify that Pt–C/Fe₂–CoP catalyst exhibits admirable mass activity (1237 mA·mg⁻¹_Pt) towards methanol oxidation reaction, which is approximately 2.04 and 3.66 times as high as the Pt–C/CoP (607 mA·mg⁻¹_Pt) and Pt–C–H (338 mA·mg⁻¹_Pt). After stability test, the decline ratio of mass activity for Pt–C/Fe₂–CoP (83.43%) is markedly preferable to Pt–C/CoP (94.92%) and Pt–C–H (98.67%) catalysts. The enhanced catalytic activity and durability can be imputed to the formation of uniform Pt nanoparticles and co-catalysis effect of Fe-doped CoP nanotube heterostructure since the introduction of hetero-metal cations is able to effectively accelerate the charge transfer rate and adjust the electronic structure of material. Therefore, the fabrication of nanotube heterostructure and introduction of hetero-metal may provide a new direction to the development of other high-efficiency electrocatalysts.     

Platinum-nickel bimetallic catalyst doped with rare earth for enhancing methanol electrocatalytic oxidation reaction

Platinum (Pt) is often used as anodic catalyst for direct methanol fuel cell (DMFC). However, platinum is difficult to achieve large-scale application because of its low stability and high cost. In this work, the electrocatalytic activity and stability of the Pt-based catalyst for methanol oxidation (MOR) are significantly improved by adding Ce and Ni to the catalyst. Additionally, the rare earth element-Pr (Dy) is also chosen to be added into the catalysts for comparison. A series of PtMNi (M = Ce, Pr, Dy) catalysts are prepared by impregnation and galvanic replacement reaction methods using carbon black as support. The electrocatalytic mass activity of PtCeNi/C, PtDyNi/C, PtPrNi/C and Pt/C is 3.92, 1.86, 1.69 and 0.8 A mg_Pt⁻¹, respectively. The mass activity of these the above four catalysts after stability measurement is 3.14, 1.49, 1.27 and 0.72 A mg_Pt⁻¹. Among them, PtCeNi/C has the highest catalytic activity. These as-prepared catalysts are also characterized by various analyzing techniques, such as TEM, HRTEM, XRD, XPS, ICP-OES, STEM, STEM-EDS elemental mapping and line-scanning etc. It shows that PtCeNi/C exhibits best catalytic activity (3.92 A mg_Pt⁻¹) among the as-obtained catalysts, 4.9 times higher than that of commercial Pt/C (0.8 A mg_Pt⁻¹). PtCeNi/C is also with excellent anti-CO poisoning ability. The outstanding catalytic performance of PtCeNi/C for the MOR is mainly attributable to uniform-sized PtCeNi nanoparticles, uniform Ni, Ce and Pt element distribution, and electron interaction among Pt-, Ni- and Ce-related species (electron transferring from Pt to CeO₂).     

High electrocatalytic activity and stability of PtAg supported on rutile TiO2 for methanol oxidation

Rutile TiO₂ is used as a support for the PtAg nanoparticles, and the catalytic activity and stability of PtAg/TiO₂ for the electrooxidation of methanol are investigated. The PtAg nanoparticles with a Pt:Ag atomic ratio of 1:1 are prepared by the chemical co-reduction of the precursors of Pt and Ag, and physical characterizations reveal that the PtAg nanoparticles are evenly dispersed on TiO₂. PtAg/TiO₂ shows significantly higher catalytic activity and stability than PtAg/C, Pt/TiO₂ and Pt/C for methanol oxidation in both alkaline and acidic solutions, indicating that rutile TiO₂ is superior to carbon black as supports and PtAg is superior to Pt in achieving high catalytic activity. Rutile TiO₂ is also shown to be superior to anatase TiO₂ as supports for the PtAg nanoparticles. The results of this study suggest high potential of rutile TiO₂ as a support material for electrocatalysts.     

A novel TiN coated CNTs nanocomposite CNTs@TiN supported Pt electrocatalyst with enhanced catalytic activity and durability for methanol oxidation reaction

The application of direct methanol fuel cells (DMFCs) is hampered by not only low activity but also poor stability and poor CO tolerance by the Pt catalyst. Herein, a novel titanium nitride coated multi-walled carbon nanotubes (CNTs@TiN) hybrid support was successfully synthesized by a facile solvothermal process followed by a nitriding process, and this hybrid support was used as Pt support for the oxidation of methanol. The structure, morphology and composition of the synthesized CNTs@TiN exhibits a uniform particle perfect coating with high purity and interpenetrating network structure. Notably, Pt/CNTs@TiN also showed excellent stability, experiencing only a slight performance loss after 5000 potential cycles. The onset potential (0.34 V) of CO oxidation on Pt/CNTs@TiN is obviously more negative than that on the Pt/TiN (0.38 V) and Pt/CNTs (0.48 V) in the first forward scan. In the Pt 4f XPS spectra, plentiful Pt atoms existed as Pt(II) in the Pt/CNTs and Pt/TiN catalysts, while a relatively smaller amount of Pt(II) was observed in the Pt/CNTs@TiN catalyst. The synthetic Pt/CNTs@TiN catalyst was studied with respect to its electrocatalytic activity and durability and CO tolerance toward methanol oxidation might be mainly attributed to the strongly coupled Pt–TiN and the fast electron-transport network structure. This work may provide more insight into developing novel catalyst supports of various transition metal nitrides coated CNTs for DMFCs with high activity and good durability and excellent CO tolerance.     

The electrochemical oxidation of methanol on a Pt/TNTs/Ti electrode enhanced by illumination

A Pt/TNTs/Ti electrode is prepared by electrochemically depositing Pt using the modulated pulse current method onto high density, well ordered and uniformly distributed TiO₂ nanotubes (TNTs) on a Ti substrate. The results show that the performance and anti-poison ability of the Pt/TNTs/Ti electrode for methanol electro-oxidation under illumination is remarkably enhanced and is even better than the best bi-metallic Pt-Ru catalysts. CO poisoning is no longer a problem during methanol electro-oxidation with the Pt/TNTs/Ti electrode under illumination.