Comparison study of electrocatalytic activity of reduced graphene oxide supported Pt–Cu bimetallic or Pt nanoparticles for the electrooxidation of methanol and ethanol

Pt–Cu bimetallic nanoparticles supported on reduced graphene oxide (Pt–Cu/RGO) were synthesized through the simple one-step reduction of H₂PtCl₆ and CuSO₄ in the presence of graphene oxide (GO) at room-temperature. The Pt–Cu/RGO was characterized with UV–vis spectrophotometer, X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy and its catalytic behavior for the direct oxidation of methanol was investigated. Compared to Pt/RGO and Pt/C catalysts, Pt–Cu/RGO hybrids exhibited markedly superior catalytic activity for the electrocatalytic oxidation of methanol and ethanol. This improved catalytic activity can be attributed to the dendritic structure of the Pt–Cu bimetallic nanoparticles.     

Evaluation of the stability and durability of Pt and Pt–Co/C catalysts for polymer electrolyte membrane fuel cells

Carbon supported Pt and Pt–Co nanoparticles were prepared by reduction of the metal precursors with NaBH₄. The activity for the oxygen reduction reaction (ORR) of the as-prepared Co-containing catalyst was higher than that of pure Pt. 30 h of constant potential operation at 0.8 V, repetitive potential cycling in the range 0.5–1.0 V and thermal treatments were carried out to evaluate their electrochemical stability. Loss of non-alloyed and, to a less extent, alloyed cobalt was observed after the durability tests with the Pt–Co/C catalyst. The loss in ORR activity following durability tests was higher in Pt–Co/C than in Pt/C, i.e. pure Pt showed higher electrochemical stability than the binary catalyst. The lower stability of the Pt–Co catalyst during repetitive potential cycling was not ascribed to Co loss, but to the dissolution–re-deposition of Pt, forming a surface layer of non-alloyed pure Pt. The lower activity of the Pt–Co catalyst than Pt following the thermal treatment, instead, was due to the presence of non-alloyed Co and its oxides on the catalyst surface, hindering the molecular oxygen to reach the Pt sites.     

Performance studies of Pd–Pt and Pt–Pd–Au catalyst for electro-oxidation of glucose in direct glucose fuel cell

Platinum is employed as anode catalyst for low temperature electro-oxidation of glucose in direct glucose fuel cell (DGFC), but it suffers from poisoning by intermediate oxidation products. In the present investigation, palladium and gold precursors are added with platinum precursor to form low metal loading (∼15–20% by wt.) carbon supported catalyst by NaBH₄ reduction technique. The prepared PtPdAu/C (metal ratio 1:1:1) and PdPt/C (metal ratio 4:1) catalysts are tested in DGFC. The Physical characterization of electro-catalysts by scanning electron microscope, transmission electron microscope, energy dispersive X-ray, X-ray diffraction and thermo-gravimetric analysis confirms the formation of nano-sized metal particles on carbon substrate with two prominent homogeneous bi- or tri-metallic crystal phases for PtPdAu/C. The cyclic voltammetry studies carried out for glucose (0.05 M) oxidation in (0.5 M KOH) alkaline medium shows the metal catalysts can efficiently electro-oxidize glucose. The catalysts tested as anode in a batch type DGFC using commercial activated charcoal as cathode produced peak power density of 0.52 mW cm⁻² for both PdPt/C and PtPdAu/C in 0.3 M glucose in 1 M KOH solution.     

Effect of surface composition of Pt–Fe nanoparticles for oxygen reduction reactions

The aim of this work is primarily to rationalize the effect of surface composition on electrocatalytic activity. To investigate this point, we compared two types of nanoparticles with a different surface composition, namely Fe-rich and Pt–Fe mixed surfaces. We synthesized highly dispersed carbon-supported Pt₁Fe_x (x = 1, 2, and 3) nanoparticles with the Fe-rich surface (∼2 nm), through a preferential interaction of a capping agent and the metal, i.e., Fe-OOC. The electronic structure and electrocatalytic properties of Pt₁Fe_x nanoparticles with the Fe-rich surface were found to be virtually independent from the Pt/Fe ratio. In contrast, nanoparticles with the Pt–Fe mixed surface, prepared by utilizing the difference of segregation energy, showed a clear dependence of the electronic and electrochemical characteristics on the amount of Pt and Fe, possibly because of the interaction between these two metals on the surface of the electrocatalysts. Compared to Pt, the Pt₁Fe₂ nanoparticles with the Pt–Fe mixed surface showed the highest enhancement in the activity of the oxygen reduction reaction. This resulted from the development of a more electrochemically stable structure of the Pt–Fe mixed surface. This study demonstrated that the electrocatalytic properties of the Pt–Fe nanoparticles can be tuned using the surface composition rather than the bulk composition.     

Enhancing the durability of multi-walled carbon nanotube supported by Pt and Pt–Pd nanoparticles in gas diffusion electrodes

This work tries to improve the durability of electrocatalysts of gas diffusion electrodes (GDEs) by using multi-walled carbon nanotube supported Pt–Pd bimetallic (Pt–Pd/MWCNT). The durability investigation of multi-walled carbon nanotube supported metals was evaluated by a repetitive potential cycling (RPC) corrosion test and by extended constant potential (ECP) experiments. Potential cycling tests were performed from −0.3 to 1.2 V at 50 mV s⁻¹ in 1 mol L⁻¹ H₂SO₄. Extended constant potential (ECP) durability test were also carried out on the GDEs by 30 h of constant potential operation at 0.8 V vs. Ag/AgCl. The smaller performance loss was observed on the GDE using Pt–Pd/MWCNT as electrocatalyst compared with GDE using Pt/MWCNT during both durability tests. ICP analysis also suggests that the dissolution of Pt nanoparticles from the carbon nanotube surface is hindered when Pd is present.     

Double oxalates of Rh(III) with Ni(II) and Co(II) – Effective precursors of nanoalloys for hydrocarbons steam reforming

Heteronuclear coordination compounds of d-metals are suitable single-source precursors for bimetallic nanoalloys, which often show extraordinary catalytic properties due to synergetic effect. In particular, Ni- and Rh-based catalysts are highly effective in low temperature steam reforming processes. Double oxalates of Rh with Ni and Co of the formula {[Rh(H₂O)₂(C₂O₄)μ-(C₂O₄)]₂M(H₂O)₂}·6H₂O (M = Ni, Co) were synthesized and structurally characterized. According to thermogravimetric analysis, the complexes decompose completely in He and H₂ atmospheres to form corresponding nanoalloys at ∼300 °C. The calcination in O₂ atmosphere leads to formation of spinel type mixed oxide. The supported Co–Rh/Al₂O₃ and Ni–Rh/Al₂O₃ catalysts were prepared by impregnation of double oxalate complexes in porous support with subsequent calcination and tested in propane low temperature steam reforming in CH₄ excess. The Co-containing catalyst showed comparable activity regarding to pure Rh/Al₂O₃ sample, while bimetallic Ni–Rh/Al₂O₃ catalyst revealed to be appreciably more active, than monometallic catalysts with higher active component loadings. Rh–Ni catalyst allowed for complete propane conversion at T ≈ 350 °C, whereas for Rh catalyst the temperature was T ≈ 410 °C, and Rh–Co did not reach complete C₃H₈ conversion at all.     

Catalytic behaviour of Mn2.94M0.06O4-δ (M=Pt,Ru and Pd) catalysts for low temperature water gas shift (WGS) and CO oxidation

Noble metal (Pt, Ru and Pd) substituted Mn₃O₄ catalysts have been synthesized in this work by a sonochemical route. The catalysts were characterised by XRD, XPS, TEM, H₂-TPR and BET surface area analyser and the activity of these catalysts was tested towards low temperature water gas shift reaction (WGS) and CO oxidation reaction. It was observed that these catalysts have the tetragonal crystalline structure of Mn₃O₄ and the average particle size was found in the range of 12 nm–22 nm. H₂-TPR results show that the strong metal support interaction between substituted metal and Mn₃O₄ leads to high reducibility and makes these catalysts active for WGS and CO oxidation. Pt substituted Mn₃O₄ showed higher activity towards WGS compared to other synthesized catalysts and 99.9% conversion was observed at 260 °C without methane formation. The activation energy of Mn_2.94Pt_0.06O_4-δ was found to be 59 ± 0.6 kJ/mol. DRIFTS analysis was carried out to propose the reaction mechanism for water gas shift and CO oxidation. Redox mechanism was hypothesized for WGS and used to correlate the experimental data over Pt substituted Mn₃O₄. Similarly, kinetic parameters were estimated based on Langmuir-Hinshelwood mechanism for CO oxidation over Pd substituted Mn₃O₄ which showed better activity compare to other synthesized catalysts and 99.9% conversion was observed at 175 °C. The activation energy was calculated from Arrhenius plot which was found to be 30 ± 0.4 kJ/mol.     

Kinetics of hydrogen evolution reaction on stabilized Ni,Pt and Ni–Pt nanoparticles obtained by an organometallic approach

Both (Ni, Pt) and bimetallic (Ni_xPt; x = 1, 2, 3) nanoparticles have been synthesized by hydrogenation of Ni(cod)₂ ad Pt₂(dba)₃ in the presence of a weak coordinating ligand, hexadecylamine (CH₃(CH₂)₁₅NH_2, HDA). These nanostructures were characterized by different techniques (Fourier Transform-Infrared Spectroscopy (FT-IR), High-Resolution Transmission Electron Microscopy (HRTEM)), and were evaluated as Hydrogen Evolution Reaction electrocatalysts in 0.5 M sulfuric acid. The effects of varying the platinum amount during the synthesis were systematically studied by Cyclic Voltammetry (CV), polarization measurements and electrochemical impedance spectroscopy (EIS) techniques. HRTEM shows that the bimetallic nanostructures display a different morphology compared to that observed for pure Ni and Pt ones. The process of hydrogen adsorption–desorption in the as-prepared electrodes seems to occur in (110) and (100) facets. It was found that the increase in the activity for the HER is due to an increased electrochemical active surface area (ECSA) and/or stabilization in the case of elemental electrode materials; and to the effect of Pt amount in the case of the Ni–Pt nanostructures (synergistic effect leads to lower overpotential). It has been established that the main pathway for the HER is Volmer–Heyrovsky.     

Electrodeposition of Pt–Ru and Pt–Ru–Ni nanoclusters on multi-walled carbon nanotubes for direct methanol fuel cell

A full-electrochemical method is developed to deposit three dimension structure (3D) flowerlike platinum-ruthenium (PtRu) and platinum-ruthenium-nickel (PtRuNi) alloy nanoparticle clusters on multi-walled carbon nanotubes (MWCNTs) through a three-step process. The structure and elemental composition of the PtRu/MWCNTs and PtRuNi/MWCNTs catalysts are characterized by transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray polycrystalline diffraction (XRD), IRIS advantage inductively coupled plasma atomic emission spectroscopy (ICP-AES), and X-ray photoelectron spectroscopy (XPS). The presence of Pt(0), Ru(0), Ni(0), Ni(OH)₂, NiOOH, RuO₂ and NiO is deduced from XPS data. Electrocatalytic properties of the resulting PtRu/MWCNTs and PtRuNi/MWCNTs nanocomposites for oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) are investigated. Compared with the Pt/MWCNTs, PtNi/MWCNTs and PtRu/MWCNTs electrodes, an enhanced electrocatalytic activity and an appreciably improved resistance to CO poisoning are observed for the PtRuNi/MWCNTs electrode, which are attributed to the synergetic effect of bifunctional catalysis, three dimension structure, and oxygen functional groups which generated after electrochemical activation treatment on MWCNTs surface. The effect of electrodeposition conditions for the metal complexes on the composition and performance of the alloy nanoparticle clusters is also investigated. The optimized ratios for PtRu and PtRuNi alloy nanoparticle clusters are 8:2 and 8:1:1, respectively, in this experiment condition. The PtRuNi catalyst thus prepared exhibits excellent performance in the direct methanol fuel cells (DMFCs). The enhanced activity of the catalyst is surely throwing some light on the research and development of effective DMFCs catalysts.     

Decomposition of hydrogen iodide over Pt–Ir/C bimetallic catalyst

Decomposition of hydrogen iodide (HI) is one of the key reactions in the sulfur–iodine (S–I) thermochemical water splitting promising for the massive hydrogen production. Much effort has been made to explore the preparation of high performance catalyst for this hydrogen-producing reaction. Although platinum has long been found to be an efficient metallic catalyst, it was prone to agglomerate at elevated temperature resulting in a decrease in the hydrogen yield. A series of bimetallic Pt–Ir/C catalysts were prepared by electroless plating to investigate the effect of Ir/Pt molar ratio on the HI conversion compared with Pt/C and Ir/C catalysts. The physical properties and morphology of the catalysts were characterized by BET, XRD, TEM and ICP-AES. The synergistic effect of platinum and iridium with respect to HI decomposition was confirmed by the fact that the bimetallic Pt–Ir/C-0.77 catalyst with 1 wt% Pt loading and 0.77 wt% Ir loading showed much higher catalytic activity and thermostability compared with Pt/C and Ir/C catalyst. Based on the experimental results obtained, it may be concluded that the bimetallic Pt–Ir/C catalyst was supposed to be a cost-effective and high performance catalyst promising to be employed for the hydrogen production via the S–I thermochemical water splitting cycle.     

Durability study of Pt–Pd/C as PEMFC cathode catalyst

In this paper, Pt–Pd/C and Pt/C catalysts were evaluated and compared. The catalysts were evaluated as oxygen reduction reaction (ORR) catalysts in half cell test under potential cycling, and cathode catalysts in single cell test under dynamic loading simulating the vehicle operation. Physical and electrochemical techniques were applied to investigate the structure, performance and durability of those catalysts. The electrochemical active surface area (ECA) loss, particle size distribution, polarization behavior and electrochemistry impedance spectroscopy (EIS) suggested that the Pt–Pd/C showed a better durability than Pt/C.     

Evaluation of Pt–Ru–Ni and Pt–Sn–Ni catalysts as anodes in direct ethanol fuel cells

In this study, the electrooxidation of ethanol on carbon supported Pt–Ru–Ni and Pt–Sn–Ni catalysts is electrochemically studied through cyclic voltammetry at 50 °C in direct ethanol fuel cells. All electrocatalysts are prepared using the ethylene glycol-reduction process and are chemically characterized by energy-dispersive X-ray analysis (EDX). For fuel cell evaluation, electrodes are prepared by the transfer-decal method. Nickel addition to the anode improves DEFC performance. When Pt₇₅Ru₁₅Ni₁₀/C is used as an anode catalyst, the current density obtained in the fuel cell is greater than that of all other investigated catalysts. Tri-metallic catalytic mixtures have a higher performance relative to bi-metallic catalysts. These results are in agreement with CV results that display greater activity for PtRuNi at higher potentials.     

Synthesis and characterization of Cu core Pt–Ru shell nanoparticles for the electro-oxidation of alcohols

Cu@Pt–Ru core–shell supported electrocatalysts have been synthesized by a two-step process via a galvanic displacement reaction. XRD diffraction and EDX analysis, and cyclic voltammetry measurements revealed the presence of nanoparticles composed by a Cu-rich Pt–Cu core surrounded by a Pt-rich Pt–Ru shell. Cyclic voltammetry and chronoamperometric measurements showed that as-synthesized core–shell materials exhibit superior catalytic activity towards methanol and ethanol electro-oxidation compared to a commercial Pt–Ru/C catalyst with higher Pt loading. This behavior can be associated with the lattice mismatch between the Pt-rich shell and the Cu rich core, which in turn produces lattice-strain, surface ligand effects and a large amount of surface defect sites. In addition, the core–shell electrodes displayed a better catalytic activity and lower onset potentials for ethanol oxidation than for methanol oxidation.     

Heat-voltaic effect of pSi-n(ZnSe)1 ? x ? y (Si2) x (GaP) y structures

pSi-n(ZnSe)_{1 ? x ? y} (Si₂) _x (GaP) _y (0 ≤ x ≤ 0.03, 0 ≤ y ≤ 0.09) structures with a thin buffer layer of a solid solution of (Si₂)_{1 ? x ? y} (ZnSe) _x (GaP) _y (0 ≤ x ≤ 0.01, 0 ≤ y ≤ 0.01) located in the transient band of the p-n junction have been synthesized from a limited volume of tin solution melt by liquid-phase epitaxy. The heat-voltaic effect revealed in such a structure is explained by heat generation of electron-hole pairs with the participation of isovalent impurities of ZnSe and GaP, which introduce energy levels into the forbidden gap of silicon.     

Electroactivity of high performance unsupported Pt–Ru nanoparticles in the presence of hydrogen and carbon monoxide

The electrochemical activity of high performance unsupported (1:1) Pt–Ru electrocatalyst in the presence of hydrogen and carbon monoxide has been studied using the thin-film rotating disk electrode (RDE) technique. The kinetic parameters of these reactions were determined in H₂- and CO-saturated 0.5 M H₂SO₄ solutions by means of cyclic voltammetry, including CO stripping, and RDE voltammetry. Pt–Ru/Nafion inks were prepared in one step with different Nafion mass fractions, allowing determining the ionomer influence in electrocatalytic response and obtaining the kinetic current density in absence of mass-transfer effects, being 41 and 12 mA cm² (geometrical area), for H₂ and CO oxidation, respectively. These values correspond to mass activities of 1.37 and 0.40 A mg_Pt¹ and to specific activities of 1.52 and 0.44 mA cm_Pt². The Tafel analysis confirmed that hydrogen oxidation was a two-electron reversible reaction, while CO oxidation exhibited an irreversible behavior with a charge-transfer coefficient of 0.42. The kinetic results for CO oxidation are in agreement with the bifunctional theory, in which the reaction between Pt–CO and Ru–OH is the rate-determining step. The exchange current density for hydrogen reaction was 0.28 mA cm² (active surface area), thus showing similar kinetics to those found for carbon-supported Pt and Pt–Ru electrocatalyst nanoparticles.     

The adsorption and dissociation of H2O on TiO2(110) and M/TiO2(110) (M = Pt,Au) surfaces–A computational investigation

The adsorption and dissociation of H₂O on clean TiO₂(110) and metal-deposited M/TiO₂(110) (M = Pt and Au) surfaces were studied by performing calculations of periodic density-functional theory. M/TiO₂(110) surfaces catalytically decompose H₂O with barriers (decreased by ca. 15–19 kcal/mol) much smaller than for their clean TiO₂(110) counterparts. The Au-deposited TiO₂ surface has the least energy barrier (ca. 3.5 kcal/mol less than the Pt analogue), explicable with a Bader charge analysis.     

CO tolerance of nano-architectured Pt–Mo anode electrocatalysts for PEM fuel cells

PEM fuel cell membrane electrode assemblies with Nafion electrolytes and commercial Pt-based cathodes were tested with Pt_0.8Mo_0.2 alloy and MoO_x@Pt core–shell anode electrocatalysts for CO tolerance and short-term stability to corroborate earlier thin-film RDE results. Polarization curves at 70 °C for the Pt_0.8Mo_0.2 alloy in H₂ with 25–1000 ppm CO showed a significant increase in CO tolerance based on peak power densities in comparison to PtRu electrocatalysts. MoO_x@Pt core–shell electrocatalysts, which showed extremely high activity for H₂ in 1000 ppm CO during RDE studies, performed relatively poorly in comparison to the Pt_0.8Mo_0.2 and PtRu alloys for the same total catalyst loading on a per area basis in MEA testing. The discrepancy is attributed to residual stabilizer from the core–shell synthesis impacting catalyst-ionomer interfaces. Nonetheless, the MoO_x@Pt electrochemical performance is superior on a per-gram-of-precious-metal basis to the Pt_0.8Mo_0.2 electrocatalyst for CO concentrations below 100 ppm. Due to cross-membrane Mo migration, the stability of the Mo-containing anode electrocatalysts remains a challenge for developing stable enhanced CO tolerance for low-temperature PEM fuel cells.     

Facile synthesis of supported Pt–Cu nanoparticles with surface enriched Pt as highly active cathode catalyst for proton exchange membrane fuel cells

Carbon supported Pt–Cu catalyst (PtCu/C) with surface enriched Pt was synthesized by annealing the Pt-deposited Cu particles. X-ray diffraction (XRD) results indicate the formation of disordered Pt–Cu alloy phase with a high level of Cu/Pt atomic ratio. X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma (ICP) analysis confirm the surface enrichment of Pt. Electrochemical measurements show that PtCu/C has 3.7 times higher Pt mass activity toward the oxygen reduction reaction (ORR) than commercial Pt/C. The enhanced ORR activity of PtCu/C is attributed to the modified electronic properties of surface Pt atoms, which reduces the surface blocking of the ORR oxygenated species.