Catalytic activity,stability and impedance behavior of PtRu/C,PtPd/C and PtSn/C bimetallic catalysts toward methanol and formic acid oxidation

PtRu, PtPd and PtSn with weight ratios of (2:1) on carbon black (Vulcan XC-72) supported bimetallic catalysts were prepared by using microwave method via chemically reduction of H₂PtCl₆·6H₂O, RuCl₃, PdCl₂ and SnCl₂·2H₂O precursors with ethylene glycol (EG). These prepared catalysts were systematically investigated and obtained results were compared with commercial Pt black, PtRu black catalysts and with each other. The catalysts were characterized with XRD, ICP-MS, EDS and TEM. The electrocatalytic activities, stability and impedance of the catalysts were investigated in sulfuric acid/methanol and sulfuric acid/formic acid mixtures using electrochemical measurements. The results showed that PtSn/C catalyst showed comparable activity and durability with commercial Pt/C catalyst toward methanol oxidation. The synthesized PtRu/C catalyst was found to completely oxidize methanol and it showed more catalytic activity than commercial PtRu catalyst. Bimetallic PtPd/C catalyst gave better activity than both commercial Pt black and synthesized Pt/C catalyst for oxidation of formic acid. Higher electrochemical active surface areas were obtained with supported bimetallic catalysts.     

Shape-tunable Pt–Ag nanocatalysts with excellent performance for oxygen reduction reaction

Shape-tunable PtAg nanocatalysts including PtAg nanoflowers (NFs) and PtAg nanowires (NWs) are prepared by a facile hydrothermal reduction method, via adjusting the precursor ratio of Pt/Ag and subsequent UV-irradiation. Physicochemical characterizations reveal that the as-prepared catalysts have a porous structure, which forms from the conversion of AgCl to Ag nanoparticles. These features favor both oxygen mass transfer and accessibility of active sites. The as-prepared Pt₁Ag₄ NWs exhibit superior catalytic performances for ORR. The mass activity of Pt₁Ag₄ NWs is 11.4 times higher than that of 20% Pt/C. More important, the electrochemically active surface area (ECSA) of Pt₁Ag₄ NWs is 2.5 times larger than that of commercial Pt/C.     

Facile construction of pompon-like PtAg alloy catalysts for enhanced ethylene glycol electrooxidation

In the drive toward energy crisis, direct ethylene glycol cells have received a great deal of attention, but its commercial development has been greatly restricted due to the lack of cost-effective anodic catalysts. Therefore, it is essential to design a suitable catalyst with excellent performance. To this end, we herein report a facile one-pot tactic for successfully synthesizing the pompon-like PtAg nanocrystals (NCs) with marvelous electrocatalytic activity and amazing long-term stability. More specifically, the results have proved that the pompon-like PtAg possessed the superior mass activity of 5042.9 mA mg^?1 towards ethylene glycol oxidation reaction (EGOR) under the alkaline condition, 5.4-fold enhancements than that of commercial Pt/C. Upon the basis of our investigation, we attributed the better catalytic activity to abundant available surface active sites and synergistic effect, as well as the brushy hairs on the surface of PtAg NCs. There is no doubt that the as-obtained nanocatalysts show a great prospect for serving as excellent anode catalyst in fuel cells and beyond.     

High performance Pd-based catalysts for oxidation of formic acid

Two novel catalysts for anode oxidation of formic acid, Pd₂Co/C and Pd₄Co₂Ir/C, were prepared by an organic colloid method with sodium citrate as a complexing agent. These two catalysts showed better performance towards the anodic oxidation of formic acid than Pd/C catalyst and commercial Pt/C catalyst. Compared with Pd/C catalyst, potentials of the anodic peak of formic acid at the Pd₂Co/C and Pd₄Co₂Ir/C catalyst electrodes shifted towards negative value by 140 and 50 mV, respectively, meanwhile showed higher current densities. At potential of 0.05 V (vs. SCE), the current density for Pd₄Co₂Ir/C catalyst is as high as up to 13.7 mA cm⁻², which is twice of that for Pd/C catalyst, and six times of that for commercial Pt/C catalyst. The alloy catalysts were nanostructured with a diameter of ca. 3–5 nm and well dispersed on carbon according to X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements. The composition of alloy catalysts was analyzed by energy dispersive X-ray analysis (EDX). Pd₄Co₂Ir/C catalyst showed the highest activity and best stability making it the best potential candidate for application in a direct formic acid fuel cell (DFAFC).     

Highly dispersed platinum nanoparticles on graphitic carbon nitride: A highly active and durable electrocatalyst for oxidation of methanol,formic acid and formaldehyde

Finding efficient electrocatalyst for oxidation of small organic molecules such as methanol (CH₃OH), formic acid (HCOOH), formaldehyde (HCHO) etc. is essential for the development of their respective direct fuel cells. We report here highly dispersed platinum nanoparticles (PtNPs) on carbon nitride (CN_x) were successfully synthesized by the ultrasound mediated sodium borohydride reduction of H₂PtCl₆ in presence of CN_x nanosheets. This platinum–carbon nitride (Pt/CN_x) composite exhibited superior electrocatalytic activity towards oxidation of CH₃OH, HCOOH and HCHO in acid media. The mass activity, onset potential, tolerance to carbon monoxide (CO) poisoning and long term durability for the catalytic oxidation of CH₃OH, HCOOH, HCHO on Pt/CN_x catalyst in acid media is much higher than that of commercial Pt/C catalyst. The mass activity of Pt/CN_x catalyst at ～0.64 V (forward scan) is 310 mA/mg_Pt which is 2.7 time higher than that of commercial Pt/C for methanol oxidation. The electrooxidation of HCOOH on Pt/CN_x occurs via dual mechanism with greatly enhanced oxidation through dehydrogenation pathway in comparison with commercial Pt/C. The mass activity on Pt/CN_x at 0.3 V (vs. NHE) is 25 times higher than that of Pt/C for oxidation of HCOOH. The superior catalytic activity and durability of this Pt/CN_x catalyst can be attributed to high dispersion of PtNPs and strong catalyst support interaction.     

Study of core-shell platinum-based catalyst for methanol and ethylene glycol oxidation

A Ru_core-Pt_shell, XC72-supported catalyst was synthesized in a two-step process: first, by deposition of Ru on XC72 by the polyol process and then by deposition of Pt on the XC72-supported Ru, with NaBH₄ as reducing agent. The structure and composition of this core-shell catalyst were determined by EDS, XPS, TEM and XRD. Electrochemical characterization was determined with the use of cyclic voltammetry and chronoamperometry. The methanol and ethylene glycol oxidation activities of the core-shell catalyst were studied at 80 °C and compared to those of a commercial catalyst. It was found to be significantly better (in terms of A g⁻¹ of Pt) in the case of methanol oxidation and worse in the case of ethylene glycol oxidation. Possible reasons for the lower ethylene glycol oxidation activity of the core-shell catalyst are discussed.     

Carbon supported platinum–gold alloy catalyst for direct formic acid fuel cells

The Pt–Au nanoparticles with 1:1 atomic ratio supported on carbon powder were prepared by the co-reduction method using N,N-dimethylformamide coordinated Pt–Au complex as a precursor. Cyclic voltammetry results demonstrated that the PtAu/C catalyst exhibited a higher activity for the formic acid oxidation reaction than did the commercial Pt/C catalyst, reflected by its lower onset potential and higher peak current. The fuel cell performance test at 60 °C showed that the direct formic acid fuel cell with the PtAu/C catalyst yielded about 35% higher power density than did the cell with the Pt/C catalyst.     

Preparation of Pt nanoparticles on carbon support using modified polyol reduction for low-temperature fuel cells

Highly dispersed Pt nanoparticles supported on Vulcan XC-72R were prepared by a modified polyol reduction for low-temperature fuel cells. The modified polyol reduction was controlled with various concentrations of reducing agent and reduction times at 90 °C. The 20 wt% Pt/C catalyst prepared under an optimum reduction condition (reduction temperature = 90 °C, ethylene glycol/H₂O volume ratio = 1, and reduction time = 10 h) exhibited the highest electrochemical active surface area (EAS) and methanol oxidation activity due to the small Pt nanoparticles (1.2 nm) with quite a narrow size distribution between 0.5 and 2 nm. The 40 wt% Pt/C catalyst was prepared using the optimum condition to confirm the applicability of the preparation method. The synthesized 40 wt% Pt/C catalyst had smaller-sized Pt nanoparticles (1.3 nm) and a higher EAS than that of a commercial 40 wt% Pt/C catalyst. With pure H₂ (anode) and air (cathode), a PEMFC using the synthesized 40 wt% Pt/C catalyst as a cathode had higher single-cell performance than that of the commercial catalyst.     

Facile synthesis of PtAu alloy nanoparticles with high activity for formic acid oxidation

We report the facile synthesis of carbon supported PtAu alloy nanoparticles with high electrocatalytic activity as anode catalysts for direct formic acid fuel cells (DFAFCs). PtAu alloy nanoparticles are prepared by co-reducing HAuCl₄ and H₂PtCl₆ with NaBH₄ in the presence of sodium citrate and then deposited on Vulcan XC-72R carbon support (PtAu/C). The obtained catalysts are characterized with X-ray diffraction (XRD) and transmission electron microscope (TEM), which reveal the formation of PtAu alloy nanoparticles with an average diameter of 4.6 nm. Electrochemical measurements show that PtAu/C has seven times higher catalytic activity towards formic acid oxidation than Pt/C. This significantly enhanced activity of PtAu/C catalyst can be attributed to noncontinuous Pt sites formed in the presence of the neighbored Au sites, which promotes direct oxidation of formic acid.     

Remarkable catalytic activity of electrochemically dealloyed platinum–tellurium nanoparticles towards formic acid electro-oxidation

Aiming to improve the activity of Pt-based catalysts for formic acid electro-oxidation, dealloyed Pt_xTe_y/C catalysts were prepared via electrochemical leaching process. The dealloyed-Pt₃Te/C catalyst presented superior activity and stability for formic acid electro-oxidation. The mass activities of dealloyed-Pt₃Te/C at 0.25 V and 0.4 V vs. SCE were about 10.6 and 16.5 times as high as that of commercial Pt/C, respectively. It is found that the FAEO on D-Pt₃Te/C is mainly through dehydrogenation pathway. The weak CO adsorption, increased electrochemical specific area and ensemble effect are suggested as reasons for the remarkable enhancement.     

Comparison of methanol and ethylene glycol oxidation by alloy and Core-Shell platinum based catalysts

Two Core-Shell, Ru_Core-Pt_Shell and IrNi_Core-PtRu_Shell, XC72-supported catalyst were synthesized in a two-step deposition process with NaBH₄ as reducing agent. The structure and composition of the Core-Shell catalysts were determined by EDS, XPS and XRD. Electrochemical characterization was performed with the use of cyclic voltammetry. Methanol and ethylene glycol oxidation activities of the Core-Shell catalysts (in terms of surface and mass activities) were studied at 80 °C and compared to those of a commercial Pt-Ru alloy catalyst. The surface activity of the alloy based catalyst, in the case of methanol oxidation, was found to be superior as a result of optimized surface Pt:Ru composition. However, the mass activity of the PtRu/IrNi/XC72 was higher than that of the alloy based catalyst by ∼50%. Regarding ethylene glycol oxidation, while the surface activity of the alloy based catalyst was slightly higher than that of the Pt/Ru/XC72 catalyst, the latter showed ∼66% higher activities in terms of A g⁻¹ of Pt. These results show the potential of Core-Shell catalysts for reducing the cost of catalysts for DMFC and DEGFC.     

A novel Central Composite Design based response surface methodology optimization study for the synthesis of Pd/CNT direct formic acid fuel cell anode catalyst

At present, carbon nanotube supported Pd catalysts are synthesized via NaBH₄ reduction method to investigate their electro catalytic activity thorough formic acid electro oxidation. In order to optimize the synthesis conditions such as %Pd amount (X₁), NaBH₄ amount (times, X₂), water amount (ml, X₃), and time (min., X₄), Central Composite Design (CCD) experiments are designed and determined by the Design-Expert program to determine the maximum observed current (mA/mgPd). Formic acid electro oxidation current density of the catalyst is computed by the model as 974.80 mA/mg Pd for the catalyst prepared at optimum operating conditions (41.14 for %Pd amount, 280.23 NaBH₄ amount, 26.80 ml water amount, and 167.14 min time) obtained with numerical optimization method in CCD. This computed value is very close to the experimentally measured value as 920 mA/mg Pd. Finally, formic acid fuel cell measurements were performed on the Pd/CNT catalyst prepared at optimum operating conditions and compared with the commercial Pd black and Pt black catalysts. As a result, Pd/CNT exhibits better performance compared to Pd black, revealing that Pd/CNT is a promising catalyst for the direct formic acid fuel cell measurements.     

Surfactant-free room temperature synthesis of PdxPty/C assisted by ultra-sonication as highly active and stable catalysts for formic acid oxidation

Formic acid oxidation is usually catalyzed on PdPt bimetallic catalysts, which are synthesized by co-reduction of noble metal precursors in the presence of high molecular capping agents. In this work, surfactant-free Pd_xPt_y/C catalysts are synthesized by H₂ reduction in ethylene glycol assisted with ultrasonication vibration at room temperature. Nanoparticle agglomeration in the course of preparation has been sufficiently curbed by strong mechanical ultrasonication instead of traditionally-employed surfactants. As a result, “clean” surfactant-free Pd_xPt_y/C catalysts necessitate only simple washing before collection. The catalysts are characterized by transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The compositionally optimized Pd₁₀₀Pt₁/C catalyst registers a mass activity of 3171 A g⁻¹ (Pt + Pd) for formic acid oxidation in 0.5 M H₂SO₄+0.5 M HCOOH, which lists one of the best results reported so far and surpasses that of a commercial Pd/C by 5.6 times. Stability of the catalysts is investigated by cyclic voltammetric as well as chronoamperometric evaluations. This work offers a convenient and environmentally benign room-temperature route to synthesize highly active and stable catalysts for formic acid oxidation.     

Influence of the synthesis method on the properties of Pt catalysts supported on carbon nanocoils for ethanol oxidation

Pt electrocatalysts supported on carbon nanocoils (CNCs) were prepared by the sodium borohydride (BM), formic acid (FAM) and ethylene glycol (EGM) reduction methods in order to determine the influence of the synthesis method on the physicochemical and electrochemical properties of Pt/CNC catalysts. For this purpose, physicochemical properties of these materials were studied by means of energy dispersive X-ray analyses, X-ray diffraction and N₂-physisorption, whereas their electrochemical activity towards ethanol and carbon monoxide oxidation was studied using cyclic voltammetry and chronoamperometry. Furthermore, in order to complete this study, the results obtained for Pt/CNC catalysts were compared with those obtained for Pt catalysts supported on Vulcan XC-72R (commercial support) prepared by the same methods and for the commercial Pt/C catalysts from E-TEK. Results showed that, for all studied methods, CO oxidation occurred at more negative potentials on Pt/CNC catalysts than on Pt/Vulcan and Pt/C E-TEK ones. On the other hand, higher current densities for the ethanol electrooxidation were obtained when CNCs were used as support for BM and EGM. It is concluded that optimizing the synthesis method on CNC, materials with enhanced electrooxidation properties could be developed.     

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.     

Microwave assisted,facile synthesis of Pt/CNT catalyst for proton exchange membrane fuel cell application

The present study aims at developing a high performing Pt/CNT catalyst for ORR in PEM fuel cell adopting modified chemical reduction route using a mixture of NaBH₄ and ethylene glycol (EG) as reducing agent. In order to select the most suitable reduction conditions to realize high performing catalyst, heating of the reaction mixture is done following two methods, conventional heating (CH) or microwave (MW) irradiation. The synthesized Pt/CNT catalysts were extensively characterized and evaluated in-situ as ORR catalyst in PEM fuel cell. A comparison of their performance with the standard, commercial Pt/C catalyst was also made. The results showed deposition of smaller Pt nanoparticles with uniform distribution and higher SSA for Pt/CNT-MWH compared to Pt/CNT-CH. In-situ electrochemical characterization studies revealed higher ESA, lower charge transfer resistance, lower activation over-potential loss and higher peak power density compared to the cathode with Pt/CNT-CH and Pt/C. This study suggests the viability of MW assisted, metal particle deposition as a simple, yet effective method to prepare high performing Pt/CNT catalyst for ORR in PEM fuel cell.     

Cytosine assisted aqueous synthesis of AgPt hollow alloyed nanostructures as highly active electrocatalyst for ethylene glycol oxidation and hydrogen evolution

Herein, a simple one-pot aqueous method was developed for synthesis of AgPt hollow alloyed nanostructures (AgPt HANS) with polyvinylpyrrolidone (PVP) and cytosine as the dispersing agent and eco-friendly growth-director, respectively. The synthesized architectures displayed the improved catalytic performance toward ethylene glycol oxidation reaction (EGOR) relative to commercial Pt black in alkaline media. Meanwhile, the catalyst exhibited the enhanced catalytic activity for hydrogen evolution reaction (HER) with the positive onset potential (E_onset, ?39 mV) and a small Tafel slope (40 mV dec^?1) relative to commercial Pt/C (20 wt%, ?31 mV, 33 mV dec^?1) in 0.5 M H₂SO₄, along with the more positive E_onset (?34 mV) and a smaller Tafel slope (59 mV dec^?1) in 0.5 M KOH compared with Pt/C (?35 mV, 85 mV dec^?1).     

PtRu/C catalysts synthesized by a two-stage polyol reduction process for methanol oxidation reaction

Highly dispersed Ru/C catalysts are prepared using high viscosity glycerol as a reducing agent and are treated in H₂ atmosphere to ensure stability. A Pt^∧Ru/C catalyst is prepared by an ethylene glycol process based on the pre-formed Ru/C. The catalyst is tested for methanol oxidation reaction at room temperature and is compared with the activity of the as-prepared PtRu/C alloyed catalyst (prepared by co-reduction of Pt and Ru precursors) and commercial PtRu/C from E-TEK. The catalysts are extensively characterized by Transmission electron microscope (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Electrochemical measurements by cyclic voltammetry (CV) showed consistently high catalytic activities and improved CO resistance for the Pt^∧Ru/C catalyst.     

High-performance high-entropy quinary-alloys as anode catalysts for direct ethylene glycol fuel cells

Noble metals are the most commonly used electrocatalysts, but due to the high-cost and scarcity, improving their utilization has become a hot topic. As the Pt-based high-entropy alloy (HEA) can greatly increase the activity of catalyst and increase the utilization of noble metal, herein, a HEA with promising performance in ethylene glycol oxidation reaction (EGOR) is developed. The EGOR results show that, the onset potential of PtPdAuNiCo/C is 0.55 V, which is 20 mV lower than Pt/C (0.57 V) reference. Besides, the PtPdAuNiCo/C exhibits a high activity of 0.482 A mg^?1_PtPdAu, which is 2.18 times of Pt/C (0.221 A mg^?1_Pt) reference. And the current retention rate of PtPdAuNiCo/C (81.3%) is also higher than Pt/C (73.0%) reference in 500-cycle stability test. When as-obtained PtPdAuNiCo/C assembled into a direct ethylene glycol fuel cell, it exhibits a high-power density of 8.38 mW cm^?2. It is 1.40 times than that of Pt/C (6.00 mW cm^?2) reference. This work would be a good reference to HEA materials application on electrocatalysis in future.     

Carbon-supported PtAu alloy nanoparticle catalysts for enhanced electrocatalytic oxidation of formic acid

The understanding of the electrocatalytic activity of bimetallic nanoparticle catalysts requires the ability to precisely control the composition and phase properties. In this report, we describe a new strategy in the preparation of a series of carbon supported platinum-gold bimetallic nanoparticles with various bimetallic compositions which were loaded onto a carbon black support and subjected subsequently by thermal treatment (Pt_100−mAu_m/C). The Pt_100−mAu_m/C catalysts are characterized by X-ray diffraction (XRD), transmission electron spectroscopy (TEM), and induced coupled plasma-atomic emission spectroscopy (ICP-AES). The XRD pattern for the bimetallic nanoparticles shows single-phase alloy character. This ability enabled us to establish the correlation between the bimetallic composition and the electrocatalytic activity for formic acid (FA) electrooxidation. The electrocatalytic activities of the catalysts toward FA oxidation reaction are shown to strongly depend on the bimetallic PtAu composition. Within a wide range of bimetallic composition, the Pt₅₀Au₅₀/C catalyst shows the highest electrocatalytic activity for the FA oxidation, with a mass activity eight times higher than that of Pt/C. The high performance of the PtAu/C catalyst can be ascribed to the increased selectivity toward the FA dehydrogenation at the decreased availability of adjacent Pt atoms.