Pt-based catalyst decorated by bimetallic FeNi2P with outstanding CO tolerance and catalytic activity for methanol electrooxidation

Subjected to CO poisoning and weak catalytic performance, there are still large barriers to the effective use of direct methanol fuel cells. Therefore, bimetallic FeNi₂P/C hybrid is synthesized by a facile hydrothermal method and low temperature phosphorization process. Subsequently, the as-synthesized FeNi₂P/C is employed as catalytic support to load Pt nanoparticles. Due to the existence of phosphorus and the difunctional effects of Fe and Ni, electrochemical results demonstrate that the prepared Pt–FeNi₂P/C compound exhibits an outstanding catalytic activity of 1125 mA·mg-1 Pt during methanol oxidation in acid solution, tower over that of Pt–FeP₄/C (721 mA·mg^-1_Pt), Pt–Ni₂P/C (588 mA·mg^-1_Pt) and Pt/C-JM (284 mA·mg^-1_Pt), separately. Significantly, bimetallic Pt–FeNi₂P/C hybrid shows the optimal anti poisoning tolerance, which onset potential is negatively shifted 0.2 eV in comparison of Pt/C-JM. Hence, Pt-based catalyst decorated by bimetallic phosphides with excellent anti poisoning tolerance would be a superb material to flourish the catalytic field.     

Titanium carbide nanoparticles supported Pt catalysts for methanol electrooxidation in acidic media

Titanium carbide (TiC) nanoparticles supported Pt catalyst for methanol electrooxidation is investigated for the first time. The resultant TiC/Pt catalysts are prepared by using a simple electrodeposition to load Pt nanoparticles on TiC nanocomposite. The electrodes are characterized by scanning electron microscopy and cyclic voltammetry. It is found that the TiC/Pt catalysts help alleviate the CO poisoning effect for methanol electrooxidation with a higher ratio of the forward anodic peak current (I_f) to the reverse anodic peak current (I_b). The improvement in the catalytic performance is attributed to the fact that TiC ameliorates the tolerance to CO adsorption on Pt nanoparticles. One possible mechanism to improve the CO tolerance of Pt taking TiC as supporting material in methanol electrooxidation is also proposed. The results suggest that TiC could be practical supporting materials to prepare electrocatalysts that are suitable for the methanol electrooxidation applications.     

Probing the enhanced methanol electrooxidation mechanism by promoted CO tolerance on the Pd catalyst modified with TaN: A combined experimental and theoretical study

The low-palladium Pd/TaN–C catalyst is synthesized by a surfactant-free solvothermal approach and exhibits high activity (2613.18 mA mg_Pd⁻¹), durability and CO tolerance for MOR (methanol oxidation reaction) in alkaline media, 12.4 folds that of the commercial Pd/C. XPS and electrochemical results indicate that the interfacial Pd–TaNO bond is generated. This also brings the enhancement of OH_ad adsorption responsible for anti-CO poisoning ability. Density Functional Theory (DFT) calculations indicate that the reaction pathway and the rate-determining step are changed for methanol decomposition to CO on the Pd₄/TaN(001) surface compared with Pd (111). The preferred pathway can be described as: CH₃OH→CH₃O→CH₂O→CHO→CO. Furthermore, the results indicate that the adsorption of OH is enhanced and the energy barrier of COOH formation from CO + OH is reduced with the high concentration of hydroxyl on the Pd₄/TaN(001) surface, further confirming the bi-functional effect of hydroxyl on the CO tolerance.     

A remarkable three-component RuO2-MnCo2O4/rGO nanocatalyst towards methanol electrooxidation

A three-part nano-catalyst including ruthenium oxide, manganese cobalt oxide, and reduced graphene oxide nanosheet in form of RuO₂-MnCo₂O₄/rGO is synthesized by one-step hydrothermal synthesis. The material is placed on a glassy carbon electrode (GCE) for electrochemical studies. The ability of these nano-catalysts in the oxidation process of methanol in an alkaline medium for usage in direct methanol fuel cells (DMFC) was examined with electrochemical tests of cyclic voltammetry (CV), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS). The effect of the addition of rGO to the nanocatalyst structure in the methanol oxidation reaction (MOR) process was investigated. We introduced the RuO₂-MnCo₂O₄/rGO as a nanocatalyst with excellent cyclic stability of 97% after 5000 cycles in the MOR process. Besides, the study of the Tafel plots and the effect of temperature and scan rate in the MOR process showed that RuO₂-MnCo₂O₄/rGO nanocatalyst has better electrochemical properties than MnCo₂O₄ and RuO₂-MnCo₂O₄. This high electrocatalytic activity could be related to the synergistic effect of placement of metal oxides of ruthenium, manganese, and cobalt near each other and putting them on rGO, which enhances conductivity and surface area and improve electron transfer. The decrease in the resistance against charge transfer and the increment in the anodic current density illustrated that the reaction rate is enhanced at higher temperature. Thus RuO₂-MnCo₂O₄/rGO shows robust stability and superior performance for MOR.     

Tungsten carbide as supports for Pt electrocatalysts with improved CO tolerance in methanol oxidation

One anti-CO-poisoning Pt-WC/C catalyst for methanol electro-oxidation is prepared in this work, through depositing platinum on tungsten carbide support using an intermittent microwave heating (IMH) method. The catalyst presents an improved methanol oxidation performance evidenced by a negative shift in onset potential, and increase of peak current density, compared with a commercial Pt/C one. CO stripping experiments indicate that the adsorbed CO is able to be oxidized and removed from the Pt-WC/C catalyst more easily, attesting the enhanced capability of anti-poisoning to CO-like species. Theoretical calculation further provides evidence that the surface electronic structure in Pt-WC/C and Pt/C catalysts is likely different. WC supports could lead to much stronger negative electronic property, which is beneficial for avoiding CO adsorption on the Pt-WC/C catalyst. In the mean time, the electron donating effect generated by WC supports also promotes the ability to oxidize the adsorbed CO-like species on catalysts. In good agreement with experimental results, the theoretical calculation proves the anti-CO-poisoning nature of the Pt-WC/C catalyst, and well explains the origin of the improvement in the electrochemical catalytic performance for effectively accelerating the oxidation of CO to CO₂ in methanol oxidation.     

Testing of carbon supported Pd-Pt electrocatalysts for methanol electrooxidation in direct methanol fuel cells

In the present work, a detailed characterization of the electrochemical behavior of carbon supported Pd-Pt electrocatalysts toward CO and methanol electrooxidation in direct methanol fuel cells is reported. Technical electrodes containing an ionomer in their catalyst layer were prepared for this purpose. CO and methanol electrooxidation reactions were used as test reactions to compare the electrocatalytic behavior of bimetallic supported nanoparticles in acidic liquid electrolyte and in solid polymer electrolyte (real fuel cell operating conditions). Experimental results in both environments are consistent and show that the electrochemical behavior of carbon supported Pd-Pt depends on their composition, giving the best performance in direct methanol single fuel cell with a Pd:Pt atomic ratio of 25:75 in the catalyst.     

Pt supported on boron,nitrogen co-doped carbon nanotubes (BNC NTs) for effective methanol electrooxidation

The research for electrocatalyst with high electroactivity and great CO-resistance ability for direct methanol fuel cells (DMFCs) is still a huge challenge. In this report, we develop Boron, Nitrogen co-doped carbon nanotubes (BNC NTs) as a support for Pt. Owing to the doping of boron, the catalyst not only provides extremely active sites for methanol oxidation reactions (MOR) but also protects Pt nanoparticles from agglutinating, performing superior electroactivity and excellent ability to anti CO poisoning. The X-ray photoelectron spectroscopy (XPS) results demonstrate the strong electron effect between Pt and B. Notably, the Pt/BNC NTs catalyst exhibits higher catalytic activity towards MOR and more superior durability in comparison with Pt/NC NTs and commercial JM Pt/C catalyst. The accelerated durability test (ADT) illustrates that Pt/BNC NTs catalyst can improve the issue of electrochemical surface area (ECSA) conservation, with only 30% diminish in comparison with the initial ECSA after 5000 cycles. The experiment result demonstrate that boron doping is the key step to improve the catalytic activities and CO-resistance ability due to the combination effects, involving firm B–C and N–C bonds, the stronger electron transfer in the nanotube structure among Pt, B and N, the stronger adsorption intensity of oxygen species from doped B.     

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.     

Boosting CO tolerance and stability of Pt electrocatalyst supported on sulfonated carbon nanotubes

CO tolerance and stability are of prominent importance for the anodic electrocatalyst utilized in direct methanol fuel cells (DMFCs). Due to the electrochemical instability of Ru atoms, the state-of-the-art DMFC anodic electrocatalyst (PtRu/C) is unable to survive for long time. Here, we report a newly designed Pt electrocatalyst with robust CO tolerance and stability after coating with poly(vinyl pyrrolidone) (PVP). Electrochemically active surface area (ESA) is negligibly affected by the PVP decoration; meanwhile, almost undetectable ESA loss is obtained for the PVP decorated Pt electrocatalyst. However, the ESA degradations for non-decorated and commercial CB/Pt electrocatalysts are found to be 30% and 40%, respectively. The improved stability is ascribed to the strong interaction between PVP and sulfonated carbon nanotubes. Also, the CO tolerance evaluated from the methanol oxidation reaction is ∼3 and 3.5 fold higher compared to non-decorated and commercial CB/Pt electrocatalysts, respectively, which is attributed to the hydrophilic PVP polymer accelerating the water absorption and formation of Pt(OH)_ads species to re-activate nearby CO poisoned Pt nanoparticles. Thus, decoration with PVP polymer can simultaneously promote the stability and CO anti-poisoning of Pt electrocatalyst.     

Impact of dehydrogenation on the methanol oxidation reaction occurring on carbon nanotubes supported Pt catalyst with low Pt loading

The electro-catalytic methanol oxidation reaction (MOR) has received considerable research attention due to its importance in the development of direct methanol fuel cells. In this study, the dehydrogenation step in MOR was investigated using low levels of platinum (Pt) which supported on carbon nanotubes as a catalyst. The concentration of H⁺ had a significant effect on the MOR activity of Pt catalysts supported by carbon nanotubes (Pt/CNTs), indicating that the dehydrogenation process was a critical step in MOR for Pt/CNTs with low Pt loading. Furthermore, the effects of Pt particle size and the distance between the Pt particles were investigated. We suggested a hypothesis: for the Pt catalyst with large particle size, only a few particles were needed for dehydrogenation to proceed; for the Pt catalyst with small particle size, many Pt particles were needed to form a network for the dehydrogenation reaction, but when the Pt particles were close enough, only a few Pt particles were needed. Our study provided insight into the electro-catalytic activity of Pt/CNTs from a mechanistic perspective.     

Novel hollow PtRu nanospheres supported on multi-walled carbon nanotube for methanol electrooxidation

A multi-walled carbon nanotube supported hollow PtRu nanosphere electrocatalysts was prepared at room temperature in a homogeneous solution employing cobalt metal nanoparticles as sacrificial templates. Transmission electron micrograph (TEM) measurements showed that carbon nanotube supported PtRu nanospheres were coreless and composed of discrete PtRu nanoparticles with the crystallite size of about 2.1 nm. X-ray diffraction (XRD) results showed that the hollow PtRu nanospheres had a face-centered cubic structure. Electrochemical measurements demonstrated that the carbon nanotube supported hollow PtRu nanosphere electrocatalysts exhibited enhanced electrocatalytic performance for methanol oxidation compared with carbon nanotube supported solid PtRu nanoparticles and commercial E-TEK PtRu/C (20 wt%) catalysts, which is crucial for anode electrocatalysis in direct methanol fuel cells (DMFCs).     

Pt and PtRu electrocatalysts supported on carbon xerogels for direct methanol fuel cells

Carbon xerogels (CXs) have been prepared by polycondensation of resorcinol and formaldehyde in water by the sol-gel method. Functionalization with diluted and concentrated nitric acid as oxidizing agents was carried out to create surface oxygen groups, acting as anchoring sites for metallic particles. Characterization techniques included nitrogen physisorption, scanning electron microscopy, temperature programmed desorption and temperature programmed oxidation. Functionalized xerogels were used as supports to synthesize Pt and PtRu electrocatalysts by a conventional impregnation method. Catalysts electrochemical activity towards the oxidation of methanol was studied by cyclic voltammetry and chronoamperometry to establish the effect of the surface chemistry on the catalysts synthesis. Carbon monoxide oxidation was also studied to determine the electrochemical active area and the CO tolerance of the as prepared catalysts. Results were compared to those obtained with commercial Pt/C and PtRu/C catalysts supported on Vulcan XC-72R (E-TEK). All electrocatalysts supported on carbon xerogel showed better performances than commercial ones, providing higher current density values for the oxidation of methanol.     

Research on a novel Ni-doped TiN modified N-doped CNTs supported Pt catalysts and their synergistic effect for methanol electrooxidation

A novel Ni-doped TiN modified N-doped CNTs hybrid nanotubes (N-CNTs@TiNiN) is constructed and serves as hybrid support for the platinum (Pt) catalyst. We prepare the N-CNTs@TiNiN support by a solvothermal process followed by a nitriding process. It is used as anodic catalyst support to test methanol electrooxidation. By contrast, the current density of Pt/N-CNTs (0.34 A mgpt^?1) is nearly 1.31 times more than Pt/CNTs (0.26 A mgpt^?1) while Pt/TiNiN (0.56 A mgpt^?1) is almost 1.33 times as much as Pt/TiN (0.42 A mgpt^?1). What's more, among all the catalysts investigated in this work, the novel Pt/N-CNTs@TiNiN (0.86 A mgpt^?1) shows the highest reactivity for methanol oxidation, which is also much more active and durable than the commercial JM Pt/C catalyst, showing only slight activity variation even after 12 000 potential cycles. The synthetic Pt/N-CNTs@TiNiN catalyst is researched on its electrocatalytic performance toward methanol electrooxidation and the high activity and durability might be mainly attributed to the electron transfer due to the synergistic effect of the robust TiNiN NPs and N-CNTs by inducing both co-catalytic and electronic effects.     

Worm-like Pt nanoparticles anchored on graphene with S,N co-doping and Fe3O4 functionalization for boosting the electrooxidation of methanol

Making use of synergy and introducing defects can effectively regulate the electronic structure of carbon nanomaterials, which is of great importance for achieving desired electrochemical performance. Herein, we report a facile protocol for preparing S, N-doped graphene with simultaneous ferroferric oxide functionalization (Fe₃O₄-SNG), which is then used as support to anchor Pt nanoparticles for catalyzing the anodic reaction of direct methanol fuel cells (DMFCs), the promising portable power sources that have small environmental footprint, compact system design, and higher volumetric energy density compared with existing technologies. The functionalization by Fe₃O₄ as well as S and N doping increases the defect level in graphene, and also affect the subsequent growth of Pt particles, leading to formation of Pt nanoparticles with worm-like morphology on the surface of Fe₃O₄-SNG support (Pt/Fe₃O₄-SNG). The electrochemical evaluations show that the worm-like Pt nanoparticles anchored on Fe₃O₄-SNG have larger electrochemically active surface areas and enhanced specific activities for methanol oxidation reaction (MOR) due to their strong electronic interaction with the supports, which also promotes the oxidative removal of the intermediate poisoning products formed during methanol electrooxidation, thereby improving the long-term stability of the Pt catalyst.     

Carbon supported Pt-shell modified PdCo-core with electrocatalyst for methanol oxidation

A catalyst for anode oxidation of methanol, carbon supported pseudo-core-shell PdCo@Pt particles with Pt shell is prepared via a two-step procedure, which consists of an organic colloid method and a surface replacement reaction step. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) are used for the catalysts characterization. The electrochemical surface areas (ECSA) are 6 and 4 times as large as those of Pt/C and PtRu/C catalysts, respectively. Furthermore, based on the Pt mass, the cyclic voltammetry (CV) and chronoamperometry results demonstrate that the electrocatalytic activity and stability of the PdCo@Pt/C catalyst for methanol oxidation are much higher than those of the Pt/C and PtRu/C catalysts. The PdCo@Pt/C catalyst is better utilization of Pt than pure Pt and Pt-based alloy catalysts.     

Reactivity of Pt/Ni supported on CeO2-nanorods on methanol steam reforming for H2 production: Steady state and DRIFTS studies

The reactivity of the PtNi supported on CeO₂-nanorods was performance on methanol steam reforming (MSR). CO_ads revealed that outer of the PtNi-catalyst could be mainly Pt-terminated and, CO_ads was slightly attenuated on the surface of the CeO₂-R. The catalytic performance of the bimetallic PtNi/CeO₂-NR catalyst exhibited better methanol conversion and H₂ selectivity than the monometallic samples. The surface species associated with the reaction mechanism from TPD-MSR-DRIFTS identified on the CeO₂-NR sample showed stronger bands associated at the methoxy species complemented with stretching C–H bands, while on the Pt/CeO₂-NR catalyst, the methoxy groups diminish indicating that it decomposes to CO and hydrogen and, new peaks of formate (HCOO^?) groups emerge. This finding suggests that the methoxy groups interacted with the surface oxygen of the support during the reaction to yield formate species and the Pt had important role to promote it as intermediary of the reaction.     

Effect of Co in the efficiency of the methanol electrooxidation reaction on carbon supported Pt

The effect of Co addition to carbon nanotubes supported Pt in the methanol oxidation reaction has been investigated by means of differential electrochemical mass spectrometry (DEMS). It has been observed that the CO₂ efficiency increases in carbon nanotubes supported PtCo compared to its homologous Pt catalysts, especially at potentials lower than 0.55 V. Despite of this, the Faradaic current reached by the bimetallic catalysts in the methanol electrooxidation was lower than those recorded on the monometallic samples. This is because Co addition difficult finding enough Pt vicinal sites for methanol dehydrogenation. On the other hand, it has been found that alloying Pt with Co, shifts down the d-band center of the larger element, so the strength of the interaction with adsorbates decreases. Consequently, it will be easier to oxidize CO_ad on the bimetallic surface. Furthermore, the necessary -OH_ad species for the CO_ad oxidation to CO₂ will be provided by the CNTs themselves.     

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 polyoxometalate-deposited Pt/CNT electrocatalyst via chemical synthesis for methanol electrooxidation

Polyoxometalate anion PMo₁₂O₄₀³⁻ (POM) is chemically impregnated into a Pt-supported carbon nanotubes (Pt/CNTs) catalyst that is prepared via a colloidal method. The POM-impregnated Pt/CNTs catalyst system (Pt/CNTs-POM) shows at least 50% higher catalytic mass activity with improved stability for the electrooxidation of methanol than Pt/CNTs or POM-impregnated Pt/C (Pt/C-POM) catalyst systems. The enhancement in electrochemical performance of the Pt/CNTs-POM catalyst system can be attributed to the combined beneficial effects of improved electrical conductivity due to the CNTs support, highly dispersed Pt nanoparticles on the CNTs, and increased oxidation power of the polyoxometalate that can assist oxidative removal of reaction intermediates adsorbed on the Pt catalyst surface.     

Carbon supported PdSn nanocatalysts with enhanced performance for ethanol electrooxidation in alkaline medium

In this work, simple chemical reduction method is used to prepare Pd–Sn nanocatalysts supported on carbon for ethanol electro-oxidation in alkaline environment using ethylene glycol as reductant. The composition, structure and morphologies of PdSn/f-C catalysts are investigated by X-ray diffraction, X-ray photoelectron spectroscopy, energy dispersive X-ray and transmission electron microscopy. The electro-chemical activity and durability of as-obtained PdSn/f-C nanocatalysts are investigated and determined by cyclic voltammetry and Chronoamperometric measurements. The obtained results demonstrate that as prepared PdSn/f-C nanocatalysts have uniform dispersion and small particle size. In addition to, the as prepared PdSn/f-C nanocatalysts have higher electro-chemical activity and better stability toward EOR in alkaline environment than those of Pd/f-C and commercial Pd/C (JM) nanocatalysts. Specifically, the electro-catalytic activity of Pd_1.5Sn/f-C nanocatalyst (3413.3${\text{mA}\text{mg}}_{\text{Pd}}^{-1}$) is almost 8.6 times higher than Pd/C (JM) nanocatalyst (355.2 ${\text{mA}\text{mg}}_{\text{Pd}}^{-1}$), which has competitive power among reported Pd–Sn catalysts. These results indicate that the uniform carbon supported PdSn nanostructure are promising electrocatalysts for direct ethanol fuel cells.