Preparation and activity of carbon-supported porous platinum as electrocatalyst for methanol oxidation

In this paper, we reported a novel electrocatalyst, Vulcan XC-72-supported porous platinum nano-particles (Pt_p/C) for methanol oxidation. In the preparation of Pt_p/C, platinum precursor was first adsorbed on carbon and then reduced by l-ascorbic acid in ethylene glycol solution. The structure and morphology of Pt_p/C and its activity toward methanol oxidation were characterized by transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) measurement, X-ray diffraction (XRD), energy-dispersion spectrometer (EDS), cyclic voltammetry (CV), and chronoamperometry (CA), with a comparison of the electrocatalyst prepared with sodium borohydride as reducer (Pt_s/C). It is found that both electrocatalysts have similar particle size but have different surface morphology of platinum and thus exhibit different electrocatalytic activity toward methanol oxidation. The platinum particle size of both electrocatalysts is 3–5 nm, but the corresponding BET surface areas are different significantly, 131.6 m² g⁻¹ and 87.7 m² g⁻¹ for Pt_p/C and Pt_s/C, respectively, indicative of the porous structure of platinum particles in Pt_p/C. The peak current for methanol oxidation on CV is 167 mA mg⁻¹ and 44 mA mg⁻¹ for Pt_p/C and Pt_s/C, respectively, indicative of the high electrocataytic activity of Pt_p/C toward methanol oxidation. The result from CA shows that Pt_p/C has good stability as the electrocatalyst for methanol oxidation.     

Studies of electrochemical performance of carbon supported Pt-Cu nanoparticles as anode catalysts for direct borohydride-hydrogen peroxide fuel cell

Carbon supported Pt-Cu bimetallic nanoparticles are prepared by a modified NaBH₄ reduction method in aqueous solution and used as the anode electrocatalyst of direct borohydride-hydrogen peroxide fuel cell (DBHFC). The physical and electrochemical properties of the as-prepared electrocatalysts are investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), cyclic voltammetry (CV), chronoamperometry (CA), chronopotentiometry (CP) and fuel cell test. The results show that the carbon supported Pt-Cu bimetallic catalysts have much higher catalytic activity for the direct oxidation of BH₄⁻ than the carbon supported pure nanosized Pt catalyst, especially the Pt₅₀Cu₅₀/C catalyst presents the highest catalytic activity among all as-prepared catalysts, and the DBHFC using Pt₅₀Cu₅₀/C as anode electrocatalyst and Pt/C as cathode electrocatalyst shows as high as 71.6 mW cm⁻² power density at a discharge current density of 54.7 mA cm⁻² at 25 °C.     

Carbon supported Pt-Y electrocatalysts for the oxygen reduction reaction

Carbon supported Pt₃Y (Pt₃Y/C) and PtY (PtY/C) were investigated as oxygen reduction reaction (ORR) catalysts. After synthesis via reduction by NaBH₄, the alloy catalysts exhibited 10-20% higher mass activity (mA mg_Pt⁻¹) than comparably synthesized Pt/C catalyst. The specific activity (μA cm_Pt⁻²) was 23 and 65% higher for the Pt₃Y/C and PtY/C catalysts, respectively, compared to Pt/C. After annealing at 900 °C under a reducing atmosphere, Pt₃Y/C-900 and PtY/C-900 catalysts showed improved ORR activity; the Pt/C and Pt/C-900 (Pt/C catalyst annealed at 900 °C) catalysts exhibited specific activities of 334 and 393 μA cm_Pt⁻², respectively, while those of the Pt₃Y/C-900 and PtY/C-900 catalysts were 492 and 1050 μA cm_Pt⁻², respectively. X-ray diffraction results revealed that both the Pt₃Y/C and PtY/C catalysts have a fcc Pt structure with slight Y doping. After annealing, XRD showed that more Y was incorporated into the Pt structure in the Pt₃Y/C-900 catalyst, while the PtY/C-900 catalyst remained unchanged. Although these results suggested that the high ORR activity of the PtY/C-900 catalyst did not originate from Pt-Y alloy formation, it is clear that the Pt-Y system is a promising ORR catalyst which merits further investigation.     

MoO2 nanocrystals down to 5 nm as Pt electrocatalyst promoter for stable oxygen reduction reaction

The single molybdenum oxide (MoO₂) crystals down to 5 nm in diameter on carbon (denoted as C-MoO₂) are synthesized based on ion-exchange principle for the first time. The structures, morphologies, chemical and electrocatalytic performances of as-synthesized nanomaterials are characterized by physical, chemical and electrochemical methods. The results indicate that electrocatalysts made with Pt nanoparticles supporting on C-MoO₂ (denoted as Pt/C-MoO₂) are highly active and stable for oxygen reduction reaction (ORR) in fuel cells. A mass activity of 187.4 mA mg⁻¹_Pt at 0.9 V is obtained for ORR, which is much higher than that on commercial Pt/C (TKK) electrocatalyst (98.4 mA mg⁻¹_Pt). Furthermore, the electrochemical stability of Pt/C-MoO₂ is more excellent than that of Pt/C (TKK). The origin of the improvement in catalytic activity can be attributed to the synergistic or promotion effect of MoO₂ on Pt. The improvement in electrochemical stability is due to the strong interaction force between Pt and MoO₂.     

Study of ethanol electro-oxidation in acid environment on Pt3Sn/C anode catalysts prepared by a modified polymeric precursor method under controlled synthesis conditions

A carbon-supported binary Pt₃Sn catalyst has been prepared using a modified polymeric precursor method under controlled synthesis conditions. This material was characterized using X-ray diffraction (XRD), and the results indicate that 23% (of a possible 25%) of Sn is alloyed with Pt, forming a dominant Pt₃Sn phase. Transmission electron microscopy (TEM) shows good dispersion of the electrocatalyst and small particle sizes (3.6 nm ± 1 nm). The polarization curves for a direct ethanol fuel cell using Pt₃Sn/C as the anode demonstrated improved performance compared to that of a PtSn/C E-TEK, especially in the intrinsic resistance-controlled and mass transfer regions. This behavior is probably associated with the Pt₃Sn phase. The maximum power density for the Pt₃Sn/C electrocatalyst (58 mW cm⁻²) is nearly twice that of a PtSn/C E-TEK electrocatalyst (33 mW cm⁻²). This behavior is attributed to the presence of a mixed Pt₉Sn and Pt₃Sn alloy phase in the commercial catalysts.     

Electrospray deposition of catalyst layers with ultra-low Pt loadings for PEM fuel cells cathodes

Suspensions of Pt/C catalyst nanoparticles in Nafion^®-alcohol solutions have been electrosprayed over carbon paper to prepare cathodes for proton exchange membrane fuel cells (PEMFC). Catalyst layers with platinum loading ranging from 0.1 mg_Pt cm⁻² down to 0.0125 mg_Pt cm⁻² and different Nafion^® contents were obtained by this method. Morphological studies of the catalyst layers by SEM inspection showed fractal structures with a high dispersion of catalyst. Fuel cell performance of membrane-electrode assemblies (MEAs) made from these cathodes revealed a strong dependence on the Nafion^® concentration in the electrosprayed suspension. In the platinum loading range 0.1-0.025 mg_Pt cm⁻² and optimal Nafion^® content, a linear relation between fuel cell power density and platinum loading has been found, such that a reduction of platinum content by a factor 4 only reduces the performance by roughly a factor 2. However for the lowest platinum loading investigated, 0.0125 mg_Pt cm⁻², a sharp drop in performance was noticed.     

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.     

Structure of carbon-supported Pt-Ru nanoparticles and their electrocatalytic behavior for hydrogen oxidation reaction

The electrochemical activity towards hydrogen oxidation reaction (HOR) of a high performance carbon-supported Pt-Ru electrocatalyst (HP 20 wt.% 1:1 Pt-Ru alloy on Vulcan XC-72 carbon black) has been studied using the thin-film rotating disk electrode (RDE) technique. The physical properties of the Pt-Ru nanoparticles in the electrocatalyst were previously determined by transmission electron microscopy (TEM), high resolution TEM, fast Fourier transform (FFT), electron diffraction and X-ray diffraction (XRD). The corresponding compositional and size-shape analyses indicated that nanoparticles generally presented a 3D cubo-octahedral morphology with about 26 at.% Ru in the lattice positions of the face-centred cubic structure of Pt. The kinetics for HOR was studied in a hydrogen-saturated 0.5 M H₂SO₄ solution using thin-film electrodes prepared by depositing an ink of the electrocatalyst with different Nafion contents in a one-step process on a glassy carbon electrode. A maximum electrochemically active surface area (ECSA) of 119 m² g Pt⁻¹ was found for an optimum Nafion composition of the film of about 35 wt.%. The kinetic current density in the absence of mass transfer effects was 21 mA cm⁻². A Tafel slope of 26 mV dec⁻¹, independent of the rotation rate and Nafion content, was always obtained, evidencing that HOR behaves reversibly. The exchange current density referred to the ECSA of the Pt-Ru nanoparticles was 0.17 mA cm⁻², a similar value to that previously found for analogous inks containing pure Pt nanoparticles.     

Synthesis and characterization of quaternary PtRuIrSn/C electrocatalysts for direct ethanol fuel cells

To find a more durable anode with high performance for direct ethanol fuel cells (DEFCs), the present study investigates a series of quaternary electrocatalysts, Pt₃₀Ru₃₀Ir_40−xSn_x/C (wt.%), for the ethanol electro-oxidation reaction (EOR). The carbon-supported Pt₃₀Ru₃₀Ir_40−xSn_x/C electrocatalysts were prepared by a known impregnation-reduction (borohydride) method. The microstructure and chemical composition were determined by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM). The activity of the electrocatalysts for EOR was compared to commercial Pt₆₇Ru₃₃/C (HISPEC5000) using linear sweep voltammetry (LSV) based on similar Pt loading. The results of this study show that electrocatalyst composition with 10 and 20% Ir (wt.%) exhibit higher electrocatalytic activity than the commercial PtRu electrocatalyst. The single fuel cell testing at 90 °C comparing Pt₃₀Ru₃₀Ir_40−xSn_x/C to commercial Pt₆₇Ru₃₃/C and Pt₈₃Sn₁₇/C anodes showed an enhancement of Pt activity (normalized to Pt loading) in the following order: Pt₃₀Ru₃₀Ir₁₀Sn₃₀ > Pt₃₀Ru₃₀Sn₄₀ ≥ Pt₃₀Ru₃₀Ir₄₀ ≥ Pt₈₃Sn₁₇ > Pt₆₇Ru₃₃. After a long-term performance test, the activity changed to the following order: Pt₃₀Ru₃₀Ir₁₀Sn₃₀ > Pt₃₀Ru₃₀Ir₄₀ > Pt₃₀Ru₃₀Sn₄₀ > Pt₈₃Sn₁₇ > Pt₆₇Ru₃₃. Pt₃₀Ru₃₀Ir₁₀Sn₃₀/C exhibited both a higher performance with a specific power density of 29 mW mg_Pt⁻¹ without O₂ backpressure at the cathode and an excellent long-term stability in a DEFC operating at 90 °C.     

Platinum nanoparticles supported on electrospinning-derived carbon fibrous mats by using formaldehyde vapor as reducer for methanol electrooxidation

The Pt nanoparticles have been well dispersed on electrospinning-derived carbon fibrous mats (CFMs) by using formaldehyde vapor as reducer to react with H₂PtCl₆·6H₂O adsorbed on the CFMs at 160 °C. The prepared electrodes of Pt-CFMs have been characterized by using scanning electron microscopy, transmission electron microscopy and X-ray diffraction spectroscopy, and the performance of the electrodes for methanol oxidation has been investigated by using cyclic voltammetry, chronoamperometry, quasi-steady state polarization and electrochemical impedance spectroscopy techniques. The results demonstrate that Pt-CFMs electrodes exhibit peak current density of 445 mA mg⁻¹ Pt, exchange current of 235.7 μA cm⁻², charge transfer resistance of 16.1 Ω cm² and better stability during the process of methanol oxidation, which are superior to the peak current density of 194 mA mg⁻¹ Pt, exchange current of 174.7 μA cm⁻² and charge transfer resistance of 39.4 Ω cm² obtained for commercial Pt/C supported on CFMs. It indicates that the novel process in which formaldehyde vapor is used as reducer to prepare Pt catalyst with high performance can be developed.     

ZIF derived mesoporous carbon frameworks with numerous edges and heteroatom-doped sites to anchor nano-Pt electrocatalyst

We report the use of nitrogen-doped three-dimensional carbon frameworks (N-MCF) to promote the catalytic performance of nano-sized Pt electrocatalyst for the catalysis of oxygen reduction reaction (ORR). The N-MCF, obtained by pyrolysis of zeolitic imidazolate framework, provides abundant edges, defects, and heteroatom-doped sites to anchor Pt nanoparticles, leading to strong Pt-support interaction and excellent particle dispersion within its three-dimensional mass transport channels. Electrochemical results show only 8 mV degradation in the half-wave potential after accelerated durability test for the N-MCF supported Pt catalysts. Meanwhile, the mass activity and specific activity of Pt/N-MFC could reach 246 mA mg⁻¹_Pt and 0.276 mA cm⁻² at 0.90 V_RHE, which is better than that of commercial Pt/C. Moreover, the high Pt utilization of Pt/N-MFC (186 mg _Pt kW⁻¹) could reach 1.9 times than that of fuel cell fabricated with commercial Pt/C cathode.     

Platinum supported on hydroxyl-grafted poly (3,4-ethylenedioxythiophene)-modified RuCo,N-tridoped bamboo-like carbon nanotubes for direct methanol fuel cell

The development of highly active and efficient heterogeneous catalytic oxidation system has become an attractive research field. In this paper, a catalyst (RuCo/N-CNT@PEDOT-OH/Pt) from platinum nanoparticles (Pt NPs) supported on hydroxyl-grafted poly(3,4-ethylenedioxythiophene) (PEDOT–OH)-modified RuCo, N-tridoped bamboo-like carbon nanotubes (RuCo/N-CNT) are used for direct methanol fuel cell (DMFC). The electrocatalytic activity of RuCo/N-CNT@PEDOT-OH/Pt is systematically compared with RuCo/N-CNT/Pt (Pt NPs supported on RuCo/N-CNT without PEDOT-OH) in the methanol oxidation reaction (MOR). The growth mechanism of carbon nanotubes and the role of heteroatom doping in the electrocatalytic process is explored. The catalysts show excellent electrocatalytic performance with high stability for MOR. It is found that the mass activity (MA) of the RuCo/N-CNT@PEDOT-OH/Pt (1961.3 mA mg^?1_Pt) for MOR was higher than that of RuCo/N-CNT/Pt (1470.1 mA mg^?1_Pt) and the commercial Pt/C catalysts (281.0 mA mg^?1_Pt), indicating the positive effect of the PEDOT-OH in the electrocatalytic MOR. In addition, density functional theory (DFT) calculations verify the possible mechanism pathways of the obtained RuCo/N-CNT@PEDOT-OH/Pt catalyst. This presented catalyst offers new inspiration for designing efficient electrocatalysts for methanol oxidation.     

Investigation of Pt/WC/C catalyst for methanol electro-oxidation and oxygen electro-reduction

A Pt/WC/C catalyst is developed to increase the methanol electro-oxidation (MOR) and oxygen electro-reduction (ORR) activities of the Pt/C catalyst. Cyclic voltammetry and CO stripping results show that spill-over of H⁺ occurs in Pt/WC/C, and this is confirmed by comparing the desorption area values for H⁺ and CO. A significant reduction in the potential of the CO electro-oxidation peak from 0.81 V for Pt/C to 0.68 V for Pt/WC/C is observed in CO stripping test results. This indicates that an increase in the activity for CO electro-oxidation is achieved by replacing the carbon support with WC. Preferential deposition of Pt on WC rather than on the carbon support is investigated by complementary analysis of CO stripping, transmission electron microscopy and concentration mapping by energy dispersive spectroscopy. The Pt/WC/C catalyst exhibits a specific activity of 170 mA m⁻² for MOR. This is 42% higher than that for the Pt/C catalyst, viz., 120 mA m⁻². The Pt/WC/C catalyst also exhibits a much higher current density for ORR, i.e., 0.87 mA cm⁻² compared with 0.36 mA cm⁻² for Pt/C at 0.7 V. In the presence of methanol, the Pt/WC/C catalyst still maintains a higher current density than the Pt/C catalyst.     

Surfactant-assisted synthesis of platinum nanoparticle catalysts for proton exchange membrane fuel cells

High-performance platinum nanoparticle catalysts (Pt–NPCs) remain the most widespread applied electrocatalysts for oxygen reduction reaction (ORR). Here, cetyltrimethylammonium bromide (CTAB), a surface-controlling agent, is introduced to modulate the microstructure and size of Pt nanoparticles (NPs) via a microwave-assisted heating process. The Pt-NPC assisted by 5 wt% CTAB exhibits the highest mass activity (MA) of 0.072 A mg_Pt^?1 and specific activity (SA) of 0.077 mA cm^?2, higher than those of commercial Pt/C (0.023 A mg_Pt^?1 and 0.035 mA cm^?2). Transmission electron microscopy (TEM) results indicate that Pt NPs are uniformly dispersed onto carbon supports with an average size of 2.39 nm. When applied in membrane electrode assembly (MEA), it exhibits the highest power density of 1.142 W cm^?2, which is about 1.24 times larger than that of commercial Pt/C.     

Preparation and properties of thin Pt-Ir films deposited by dc magnetron co-sputtering

A series of Pt-Ir thin films envisaged for application as fuel cell cathodic catalysts are deposited by dc co-sputtering from pure metal targets. To achieve different metal ratios, the sputtering power applied on the iridium target (P_Ir) is varied in the range 0-100 W at constant power of the Pt target (P_Pt). The influence of the sputtering power on the film composition, morphology, and surface structure is analysed by energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The catalytic activity towards oxygen reduction reaction (ORR) is evaluated in sulphuric acid solutions applying the methods of cyclic voltammetry and potentiodynamic polarization curves. The performed morphological and electrochemical investigations reveal that catalytic efficiency of the co-sputtered Pt-Ir films is superior compared to pure Pt. The ORR is most intensive on the sample deposited at power ratio P_Pt:P_Ir = 100:30 W containing 11 at.% Ir that has also the most developed active surface. The ORR current density for this film achieved at 0.825 V in acid solution (4.1 mA cm⁻²) is about 6 times higher than for pure Pt (0.67 mA cm⁻²). The improved activity of the thin co-sputtered Pt-Ir over Pt allows for essential reduction of the catalyst loading at preserved performance.     

Effect of thermal annealing on the properties of Corich core–Ptrich shell/C oxygen reduction electrocatalyst

The properties and the oxygen reduction reaction (ORR) characteristics of Pt/C and Co_{rich core}–Pt_{rich shell}/C, which were prepared by the thermal decomposition and the chemical reduction methods, annealed in the various conditions were investigated. The alloying degree and grain size of Co_{rich core}–Pt_{rich shell}/C analyzed by XRD was increased from 13.10% and 2.45 nm to 42.83% and 2.62 nm by increasing the time for annealing at 400 °C in N₂ (annealing condition 1) from 0 to 15 h. When the Co_{rich core}–Pt_{rich shell}/C was annealed in air at 250 °C and then reduced in 6% H₂ at 400 °C (annealing condition 2), the alloying degree and grain size were obtained to be 47.26% and 3.79 nm, respectively. The decrease in the atomic ratio of Co/Pt from 4.77 to 1.34 by annealing Co_{rich core}–Pt_{rich shell}/C in condition 1 from 0 to 15 h was deduced to be the increase in the Pt loading by the reduction of residual Pt precursor to Pt. The mass and specific activities (MA, SA) of the ORR at 0.9 V (versus RHE) on Pt/C annealed in condition 2 were obtained to be 4.11 A g⁻¹ and 6.12 μA cm⁻², respectively. The MA and SA of Co_{rich core}–Pt_{rich shell}/C annealed by condition 2 were 10.07 A g⁻¹ and 11.27 μA cm⁻².     

Ni–Pt/C as anode electrocatalyst for a direct borohydride fuel cell

In this study, a series of Ni–Pt/C and Ni/C catalysts, which were employed as anode catalysts for a direct borohydride fuel cell (DBFC), were prepared and investigated by XRD, TEM, cyclic voltammetry, chronopotentiometry and fuel cell test. The particle size of Ni₃₇–Pt₃/C (mass ratio, Ni:Pt = 37:3) catalyst was sharply reduced by the addition of ultra low amount of Pt. And the electrochemical measurements showed that the electro-catalytic activity and stability of the Ni₃₇–Pt₃/C catalysts were improved compared with Ni/C catalyst. The DBFC employing Ni₃₇–Pt₃/C catalyst on the anode (metal loading, 1 mg cm⁻²) showed a maximum power density of 221.0 mW cm⁻² at 60 °C, while under identical condition the maximum power density was 150.6 mW cm⁻² for Ni/C. Furthermore, the polarization curves and hydrogen evolution behaviors on all the catalysts were investigated on the working conditions of the DBFC.     

PtCo incorporated porous carbon nanofiber as a promising oxygen reduction electrocatalyst

Designing oxygen reduction reaction (ORR) catalysts with high activity and long durability is significant for the development of proton exchange membrane fuel cells. Herein, the optimized platinum nanowires are used as templates for inducing growth of cobalt-containing metal-organic framework, deriving uniform nanofibers. After the calcination, the metal ions are transferred into the nitrogen-rich porous carbon, and wrapped by the carbon skeleton to form the PtCo bimetal incorporated nanofibers as high-performance ORR electrocatalyst. The Pt₄Co@NC-900 catalyst yields high specific activity (1.37 mA cm⁻²) in comparison to Pt/C (0.38 mA cm⁻²). The mass activity (MA) of Pt₄Co@NC-900 catalyst is approximately 3.8-fold higher than that of the commercial Pt/C under acidic conditions. After the accelerated durability tests, the Pt₄Co@NC-900 catalyst presents only 16% loss in MA, while Pt/C catalyst retains 73.0% of the initial MA. The improved ORR performance can be ascribed to the synergistic interaction between Co and Pt.     

Performance of supported Au–Co alloy as the anode catalyst of direct borohydride-hydrogen peroxide fuel cell

Au–Co alloys supported on Vulcan XC-72R carbon were prepared by the reverse microemulsion method and used as the anode electrocatalyst for direct borohydride-hydrogen peroxide fuel cell (DBHFC). The physical and electrochemical properties were investigated by energy dispersive X-ray (EDX), X-ray diffraction (XRD), cyclic voltammetry, chronamperometry and chronopotentiometry. The results show that supported Au–Co alloys catalysts have higher catalytic activity for the direct oxidation of BH₄⁻ than pure nanosized Au catalyst, especially the Au₄₅Co₅₅/C catalyst presents the highest catalytic activity among all as-prepared Au–Co alloys, and the DBHFC using the Au₄₅Co₅₅/C as anode electrocatalyst shows as high as 66.5 mW cm⁻² power density at a discharge current density of 85 mA cm⁻² at 25 °C.