Electrophoretic deposition of carbon-supported octahedral Pt–Ni alloy nanoparticle catalysts for cathode in polymer electrolyte membrane fuel cells

The advanced electrochemical catalytic activity for oxygen reduction reaction (ORR) based on the octahedral Pt–Ni alloyed catalyst has been demonstrated. However, a means of fabricating catalyst electrodes for use in PEMFCs that is cost-effective, scalable, and maintains the high activity of Pt–Ni_alloy/C has remained out of reach. Electrophoretic deposition (EPD) is a colloidal production process that has a history of successful deployment at the industrial scale. Here, we report on the facile preparation of an effective and active cathode consisting of Pt–Ni alloy loaded on the carbon cloth substrate using the electrophoretic deposition (EPD) technique, in which the optimum applied voltages and suspension pH are systematically investigated to obtain the highly porous Pt–Ni_alloy/C catalyst electrode. In a half cell test, the EPD-made Pt–Ni_alloy/C catalyst electrodes fabricated at 45 V and in a solution with a pH of 9.0 yields the best performances. On the other, as an active cathode, the EPD-made Pt–Ni_alloy/C electrodes deliver a superior performance in single cell test, with the maximum power density reaches 7.16 W/mg_Pt, ～28.1% higher than that of the spray-made Pt/C conventional electrode. The outperformance is attributed to the significantly higher porosity and surface roughness of the EPD-made electrode.     

Flame aerosol synthesis of carbon-supported Pt–Ru catalysts for a fuel cell electrode

This study describes how a flame spray pyrolysis method was successfully used to synthesize PtRu catalysts supported by carbon agglomerates. Nearly spherical catalysts composed of metallic Pt and Ru with molar ratio of 1:1 were produced in the flame and their size was about 1.9 nm. X-ray diffraction measurements revealed that amorphous-like Ru was well mixed into the Pt crystalline lattices. Through cyclic voltammetry for methanol oxidation reaction and CO stripping, it was found that the electrochemical activities of the catalysts produced from this process are comparable to or slightly better than those of an equivalent commercial sample with the same composition.     

Binary Pt–Pd and ternary Pt–Pd–Ru nanoelectrocatalysts for direct methanol fuel cells

Nano-sized binary and ternary alloys are synthesized by polyol process on Vulcan XC72-R support. Nanostructured binary Pt–Pd/C catalysts are prepared either by co-deposition or by depositing on each other. Ternary Pt–Pd–Ru/C catalysts are prepared by co-deposition. The structural characteristics of the nanocatalysts are examined by TEM and XRD. Their electrocatalytic activity toward methanol oxidation and CO stripping curves were measured by electrochemical measurements and compared with that of commercial Pt/C catalyst. The results show that the binary nanocatalyst prepared by depositing the Pt precursor colloids on Pd-Vulcan XC-72R are more active toward methanol oxidation than that of the co-deposited binary alloy nanocatalyst. The co-deposited ternary Pt–Pd–Ru/C nanocatalyst based membrane electrodes assembly shows higher power density compared to the binary nanocatalysts as well as commercial Pt/C catalyst in direct methanol fuel cell. Significantly higher catalytic activity of the nanocatalysts toward methanol oxidation compared to that of the commercial Pt/C is believed to be due to lower level of catalyst poisoning.     

Investigation of a carbon-supported quaternary PtRuSnW catalyst for direct methanol fuel cells

An investigation was carried out in the electro-oxidation of methanol on a carbon-supported quaternary PtRuSnW catalyst prepared by a liquid-phase reduction method. As derived by X-ray diffraction and X-ray photoelectron spectroscopy, the catalyst was composed of metallic Pt, microcrystalline RuO₂ and SnO₂ phases and amorphous WO₃/WO₂ species. The electrochemical analysis was carried out in half-cell containing sulfuric acid electrolyte as well as in a liquid methanol-fed solid polymer electrolyte single-cell. The activity of catalyst in the half-cell varied as a function of the methanol concentration, it increased with CH₃OH molarity in the activation-controlled region and showed a maximum in 2 M CH₃OH at high currents. IR-free polarization curves showed that the activity of the quaternary catalyst was superior to Pt metal/C samples having the same Pt amount. The presence of semi-insulating metal oxides such as RuO₂, SnO₂ and WO₃ on the electrode surface exhibited a significant uncompensated resistance. The single-cell performance was lower than that predicted by the half-cell experiments mainly due to the methanol cross-over through the Nafion membrane.     

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.     

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.     

Preparation of carbon-supported Pt–Ru core-shell nanoparticles using carbonized polydopamine and ozone for a CO tolerant electrocatalyst

Carbon supported Ru@Pt/C catalysts with a Ru-rich core and Pt-rich shell structure are prepared by the solid-state diffusion of Pt and Ru via high-temperature heat treatment. In general, heat treatment at high temperatures causes a sintering effect that leads to the aggregation of nanoparticles into larger particles. Carbonized polydopamine is introduced as a protective coating to inhibit the movement of particles during the high-temperature heat treatment. This carbon layer, which inhibits the particle grain growth, should, however be removed after heat treatment because it blocks the active sites required for the hydrogen oxidation reaction. In this study, ozone treatment at room temperature for 15 min is used to effectively remove the carbon layer on the catalyst surface. Energy-dispersive X-ray spectroscopic line scan profile and X-ray photoelectron spectroscopic analysis confirm that the PtRu/C catalyst has a Ru-rich core and Pt-rich shell structure. From CO stripping voltammetry and polymer electrolyte membrane fuel cell tests using CO containing H₂ gas, the core-shell structured PtRu/C alloy formed by high-temperature annealing is demonstrated to have higher tolerance to CO poisoning than PtRu/C catalysts synthesized by co-deposition via the polyol method.     

Enhanced activity of Pt(HY) and Pt–Ru(HY) zeolite catalysts for electrooxidation of methanol in fuel cells

The investigation describes the synthesis of Pt and Pt–Ru catalysts by a new method using a HY zeolite support. The catalysts are used to study the anodic oxidation of methanol in an acidic medium to investigate their suitability for use in direct methanol fuel cells (DMFCs). The catalysts prepared in a HY zeolite support display significantly enhanced electrocatalytic activity in the order: HY<Pt/C<Pt(HY)<Pt–Ru/C<Pt–Ru(HY). The enhanced electrocatalytic activity is explained on the basis of the formation of specific CO clusters in zeolite cages.     

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.     

Electrochemical deposition of Au–Pt alloy particles with cauliflower-like microstructures for electrocatalytic methanol oxidation

Au–Pt alloy particles with cauliflower-like microstructures of varying Pt/Au ratios were electrodeposited on indium tin oxide (ITO) substrates by constant potential electrolysis at E = −0.25 V. The results of X-ray diffraction and X-ray photoelectron spectroscopy confirm that the bimetallic alloys can be obtained for different Pt/Au ratios including 4/1, 1/1 and 1/4. The formation of alloyed cauliflower-like microstructures may be the result of the fast formation of gold seeds as the core and subsequent simultaneous deposition of Au and Pt from cyclic voltammetric study. The effect of surface composition of Au–Pt alloy particles on electrocatalytic methanol oxidation were investigated in H₂SO₄ solution. The electrocatalytic abilities including electrochemical surface area, peak current density and the turnover number of methanol oxidation follow the order of Pt₄Au₁ > Pt > Pt₁Au₁. The results can be ascribed to that electronic effect may be prominent while bifunctional effect is insignificant for Au–Pt alloy systems because the electrocatalytic activity of Au is negligible in acidic media. Additionally, the Pt₄Au₁ electrode has superior kinetics of methanol electro-oxidation than monometallic Pt electrode by calculating the electron transfer coefficient (α).     

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.     

Direct methanol–air fuel cells with membranes plus circulating electrolyte

A new approach for direct methanol–air fuel cells (DMFC), with the advantage of reduced methanol crossover is discussed in this paper. Methanol traces in the circulated electrolyte are recovered and CO₂ bubbles in the cells are removed due to the forced methanol–electrolyte stream through the cell.Degradation of the catalyst is reduced since fuel cell electrodes degrade on activated stand without load to a higher extent than under load because high voltage on open circuit promotes carbon oxidation, catalyst changes, etc. Therefore, life expectancy increases with circulating electrolyte by removing the electrolyte from the cells between operating periods.     

Characterization and performance evaluation of Pt–Ru electrocatalysts supported on different carbon materials for direct methanol fuel cells

The paper addresses the effect of the carbon support on the microstructure and performance of Pt–Ru-based anodes for direct methanol fuel cells (DMFC), based on the study of four electrodes with a carbon black functionalized with HNO₃, a mesoporous carbon (CMK-3), a physical mixture of TiO₂ and carbon black and a reference carbon thermally treated in helium atmosphere (HeTT). It is shown that CMK-3 hinders the growth of the electrocatalyst nanoparticles (2.7 nm) and improves their distribution on the support surface, whereas the oxidized surfaces of HNO₃ carbon and TiO₂+carbon lead to larger (4–4.5 nm), agglomerated particles, and the lowest electrochemical active areas (54 and 26 m² g⁻¹, in contrast with 90 m² g⁻¹ for CMK-3), as determined from CO stripping experiments. However, HNO₃ and TiO₂ are characterized by the lowest CO oxidation potential (0.4 V vs. RHE), thus suggesting higher CO tolerance for the se electrodes. Tests in DMFC configuration show that the three modified electrodes have clearly better performance than the reference HeTT. The highest power density attained with electrodes supported on carbon treated with HNO₃ (65 mW cm⁻²/300 mA cm⁻² at 90 °C) and the equally interesting performance of the TiO₂-based electrodes (53 mW cm⁻²/300 mA cm⁻²), is a strong indication of the positive effect of the presence of oxygenated groups on the methanol oxidation reaction. The results are interpreted in order to identify separate microstructural (electrocatalyst particle size, porosity) and compositional (oxygenated surface groups, presence of oxide phase) effects on the electrode performance.     

Bipolar polymer electrolyte interfaces for hydrogen–oxygen and direct borohydride fuel cells

Direct borohydride fuel cells (DBFCs) using liquid hydrogen peroxide as the oxidant are safe and attractive low temperature power sources for unmanned underwater vehicles (UUVs) as they have excellent energy and power density and do not feature compressed gases or a flammable fuel stream. One challenge to this system is the disparate pH environment between the anolyte fuel and catholyte oxidant streams. Herein, a bipolar interface membrane electrode assembly (BIMEA) is demonstrated for maintaining pH control of the anolyte and catholyte compartments of the fuel cell. The prepared DBFC with the BIMEA yielded a promising peak power density of 110 mW cm⁻². This study also investigated the same BIMEA for a hydrogen–oxygen fuel cell (H₂–O₂ FC). The type of gas diffusion layer used and the gas feed relative humidity were found to impact fuel cell performance. Finally, a BIMEA featuring a silver electrocatalyst at the cathode in a H₂–O₂ FC was successfully demonstrated.     

Preparation and characterization of core–shell-like PbPt nanoparticles electro-catalyst supported on graphene for methanol oxidation

PbPt core–shell-like nanoparticles supported on graphene is successfully synthesized by a simply galvanic displacement reaction method. The composition, morphology, structure of the catalyst and activity towards methanol oxidation are characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV). Chronoamperometric and CV results reveal that PbPt core–shell-like nanoparticles catalyst has better activity towards methanol oxidation than the pure platinum prepared under the same conditions. These behaviors are attributed to an electronic effect of the inner Pb or the increase in the d-orbital vacancy of Pt in core–shell-like PbPt catalyst.     

Integrated carbon composite bipolar plate for polymer–electrolyte membrane fuel cells

The electrical resistance of bipolar plates for polymer–electrolyte membrane fuel cells (PEMFCs) should be very low to conduct the electricity generated with minimum electrical loss. The resistance of a bipolar plate consists of the bulk material resistance and the interfacial contact resistance when two such plates are contacted to provide channels for fuel and air (oxygen) supplies.     

Intermittent microwave synthesis of nanostructured Pt/TiN–graphene with high catalytic activity for methanol oxidation

A one-step and fast microwave technique was developed to synthesize graphene-supported TiN nanoparticles (TiN–G) directly from graphene and dihydroxybis (ammonium lactato) titanium (IV). During the synthesis graphene served as a reductant and template to reduce the Ti-precursor into TiN and then uniformly disperse TiN nanoparticles on it. Pt/TiN–G catalyst was also successfully prepared with the portion of Pt nanoparticles was anchored at the interface of TiN and graphene. Electrochemical measurements showed that the Pt/TiN–G catalyst exhibited improved catalytic activity for methanol oxidation and enhanced CO tolerance than those of Pt/G catalyst, attributed to the formation of –OH groups on the surface of TiN. And the –OH attached TiN assisted the conversion of CO into CO₂.     

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.     

Tangential and normal conductivities of Nafion® membranes used in polymer electrolyte fuel cells

Conductivity measurements of Nafion^® 112, 115 and 117 membranes in the normal direction are reported in this paper. The measurements were made by means of impedance spectroscopy as a function of temperature. The conductivity was measured directly on hot-pressed carbon paper/membrane/carbon paper samples fully immersed in deionized water. The data show that Nafion^® membranes are really isotropic and that tangential and normal direction conductivity measurements gave the same results when the same hydration level was utilized.     

Pt–Ru catalysts supported on carbon xerogels for PEM fuel cells

Pt–Ru electrocatalysts supported on carbon xerogels were synthesized by reduction of metal precursors with formate ions (SFM method). The carbon xerogel was chemically and heat treated in order to evaluate the different procedures to generate oxygenated groups on the surface. Temperature-programmed desorption (TPD) of xerogels showed that heat treatment of previously chemically modified support gradually removes the oxygenated groups from the carbon surface. Physical characterization of the catalyst was performed using X-ray dispersive energy (EDX) and X-ray diffraction (XRD) techniques. Results confirmed that Pt–Ru catalysts with similar metal content (20%) and atomic ratios (Pt:Ru 1:1) were obtained.