Shell Catalysts Research Articles

High Activation Protocol and Cu-O2 Treatment for Highly Active Pd Core-Pt Shell Catalyst for PEFCs

Introduction Carbon supported Pd core-Pt shell catalyst (Pt/Pd/C) is a promising alternative to the conventional Pt/C catalyst because of high Pt utilization and enhancement of ORR activity [1]. Recently, we found that ORR specific activity of the Pt/Pd/C catalyst was drastically enhanced with an accelerated durability test (ADT) conducted at 80°C [2]. During the ADT, the Pt shell rearranged associated with the Pd core dissolution and a compressive strain was induced in the Pt shell, which is considered to enhance the ORR specific activity [2]. However, ECSA of the catalyst decreased after the ADT. Thus, we developed a high activation protocol (HAP) using GC electrode to mitigate the ECSA decay and enhance ORR mass activity [3]. In this study, we explored influence of potential range in the HAP on ECSA decay and ORR activity enhancement of the Pt/Pd/C catalyst. Furthermore, we developed a Cu-O2 treatment to scale-up the HAP on the GC electrode for mass-production of highly activated Pt/Pd/C catalyst. Experimental Pt/Pd/C catalyst was synthesized with a modified Cu-UPD/Pt replacement process [2]. A carbon supported Pd core (Pd/C, Pd size: 4.6 nm, Pd loading: 30 wt.%, Ishifuku Metal Industry) was stirred in 50 mM H2SO4 containing 10 mM CuSO4 with co-existence of a metallic Cu sheet at 5°C under Ar atmosphere. After stirring for 5 h, the Cu sheet was removed and K2PtCl4 was added to replace under potentially deposited Cu shell on the Pd core surface with the Pt shell. ADT was carried out using rectangular wave potential cycling of 0.6 (3 s)-1.0 V (3 s) vs. RHE in Ar saturated 0.1 M HClO4 at 80℃ for 10,000 cycles. The Pt/Pd/C catalyst was characterized by TG, XRF, XRD, TEM and CV. ORR activity of the catalyst was evaluated with RDE technique in O2 saturated 0.1 M HClO4 at 25°C. Results and Discussion We explored influence of potential range in the HAP on electrochemical properties of the Pt/Pd/C catalyst using rectangular potential cycling of 0.05~0.8 V (300 s for low potential) to 1.0 V (300 s for high potential) vs. RHE performed in Ar saturated 0.1 M HClO4 at 80℃ for 30 cycles. Changes in ECSA and ORR activity of the catalyst are demonstrated in Fig. 1. In comparison to ADT, ECSA decay of the Pt/Pd/C catalyst was mitigated with the HAP. Interestingly, ORR specific activity of the catalyst was largely enhanced when the low potential range was 0.2~0.6 V, which largely enhanced ORR mass activity of the catalyst. At the low potential range (0.2~0.6 V), it is considered that Pt shell rearrangement associated with Pd core dissolution was advanced due to sufficient oxidation/reduction of Pt and Pd. At low potential of 0.05 V, since hydrogen adsorbs on the Pt, it is considered that hydrogen adsorption hindered rearrangement of the Pt shell [4] and the ORR activity was not largely enhanced. We further developed a Cu-O2 treatment to scale-up the HAP performed on GC electrode. In the Cu-O2 treatment, the Pt/Pd/C catalyst powder (200 mg) is stirred at 80℃ for 300 s in 2 M H2SO4 containing 0.1 M CuSO4 with co-existence of a metallic Cu sheet under N2 atmosphere, where equilibrium potential of Cu2+/Cu (ca. 0.3 V) is applied to the catalyst powder when it contacts with the Cu sheet. Next, the Cu sheet is removed and O2 gas is introduced for 300 s, where equilibrium potential of ORR (ca. 1.0 V) is applied to the catalyst (Fig. 2). Figure 3 summarizes changes in ECSA and ORR mass activity of the Pt/Pd/C catalyst with the HAP and the Cu-O2 treatment (30 cycles). Compared with the HAP, the Cu-O2 treatment equivalently mitigated ECSA decay and enhanced ORR mass activity of the catalyst by ca. 3 times of reference carbon supported Pt catalyst (Pt/C, Pt size: 2.8 nm, Pt loading: 46 wt.%, TEC10E50E, TKK), indicating that the Cu-O2 treatment mimics the HAP on the GC electrode and is suitable for mass-production of highly activated Pt/Pd/C catalyst. Acknowledgement This work was supported by NEDO, Japan.

ORR Properties for Model Pt-Shell Layers Prepared on Nitrogen-Beam Irradiated Pt25Ni75(111) Substrate

Introduction Pt–M (M = Fe, Co, Ni, Cu, Pd, etc.) alloy and Pt/M core–shell nanoparticles have been intensively studied as oxygen reduction reaction (ORR) catalysts for polymer electrolyte fuel cells (PEFCs). As for the core–shell catalysts, the core elements easily dissolve in the electrolyte under the PEFCs operating conditions, leading to degradation of the catalytic activity. To control dissolution behavior of the core elements, Kuttiyiel et al. proposed the structure of Pt–shell/nitride–core nanostructures and demonstrated that nitride core is effective not only for enhancing ORR activity but also for improving durability [1]. For developing the practical Pt–M catalysts, it is significant to clarify a role of the nitrogen atoms located at the core–shell interface. In this study, we fabricate model catalyst structures that composed of Pt(111) epitaxial layers on low–energy N2–beam irradiated Pt25Ni75(111) substrate surfaces by using molecular beam epitaxy (MBE) and discuss the ORR activity and the durability. Experimental Model catalyst sample surfaces are fabricated as follows. First, Pt25Ni75(111) single crystal substrate was cleaned by Ar+ sputtering and annealing at 1173 K in ultra–high vacuum (UHV). Next, neutralized N2–beam (≤ 100eV) was irradiated onto the cleaned Pt25Ni75(111) at room temperature by using low–energy neutralized nitrogen ion beam gun. Then, 3ML–thick–Pt was deposited on the N2–beam irradiated Pt25Ni75(111) substrate by an electron–beam evaporation method at room temperature, followed by annealing at 673 K for 10 minutes in UHV to flatten the topmost surfaces. The resulting surface structure was verified by scanning tunneling microscopy (STM). The sample thus fabricated was transferred to electrochemical evaluation systems set in a N2–purged glove box without air exposure [2]. CV and LSV measurements were conducted in N2–purged and O2–saturated 0.1 M HClO4, respectively, and ORR activity was evaluated from j k values at 0.9 V vs. RHE by using Koutecky–Levich equation. The electrochemical stability of the sample was investigated by applying potential cycles between 0.6 V (3s) and 1.0 V (3s) in O2–saturated 0.1 M HClO4. Results and Discussion UHV–STM images of the as–prepared 3ML–Pt/Pt25Ni75(111) and 3ML–Pt/100eV–N2–beam irradiated Pt25Ni75(111) (3ML–Pt/N2–beam–Pt25Ni75(111)) surfaces are shown in Fig. 1(a). The line profiles of white arrows are depicted below the corresponding STM images. The STM images clearly show that atomically flat surfaces can be obtained through the UHV–process, irrespective of the 100eV–N2–beam irradiation. Furthermore, the both surfaces exhibited moiré–like height modulations (line profiles) that derived from lattice mismatches between the topmost Pt–shell layers and corresponding substrates. The results suggest that compressive surface strain should be induced for both the shell layers. Corresponding CV curves of the 3ML–Pt/Pt25Ni75(111) (blue), 3ML–Pt/N2–beam–Pt25Ni75(111) (red) and Pt(111) (black–dashed) are summarized in Fig. 1(b). Compared with the clean Pt(111), the total Hupd charges for the 3ML–thick–Pt surfaces considerably decreased and the onset of Oads positively shifted. Such CV features are common for highly–active Pt skin–type surfaces [2, 3]. Furthermore, the oxidation of the Pt shell layers for the latter N2–beam irradiated sample is suppressed in comparison to the former. ORR activities evaluated before and after 1000 potential cycles loading are summarized in Fig. 1(c). As for the initial activity enhancement factor, the 3ML–Pt/Pt25Ni75(111) andthe N2–beam irradiated one reveals ×15 and ×8 vs. Pt(111), respectively. The results suggest that the nitrogen atoms located at the Pt–shell/Pt25Ni75(111) interface should release the surface strain of the Pt–shell layers, leading to decrease in pristine ORR activity. In contrast, N2–beam irradiated sample is relatively stable against the potential cycle loading, indicating that the interface nitrogen atoms dominate not only activity but also durability of the Pt– shell/nitride–core type catalysts. At the PRiME 2016, I will discuss ORR activity and durability for various–thick Pt shells prepared on N2–beam–Pt25Ni75(111). Acknowledgement This study was supported by new energy and industrial technology development organization (NEDO) of Japan.

Oxygen Electrocatalysis on Dealloyed Pt Nanocatalysts

We review the fundamental principles, the preparation and catalytic performance of dealloyed Pt core–shell electrocatalysts for the electroreduction of molecular oxygen. This reaction is key to the efficiency of all fuel cell cathodes, as the oxygen electrocatalysis exhibits much larger kinetic overpotentials compared to typical fuel cell anode reactions. We discuss structural surface lattice strain in metal overlayers and show that they serve as models for nanostructured core–shell catalysts. We address preparation pathways with particular emphasis on the dealloying routes. Trends in reactivity of different dealloyed Pt core–shell catalysts are compared with a focus on the dealloyed Pt–Ni alloy system. Size effects are discussed. Practical catalytic performance data in automotive fuel cells and under automotive fuel cell conditions is provided and contrasted to other state-of-art catalyst concepts. This review concludes that dealloyed Pt core–shell cathode catalysts are currently the most attractive commercialization candidate for automotive applications.

Increasing Stability and Activity of Core-Shell Catalysts by Preferential Segregation of Oxide on Edges and Vertexes: Oxygen Reduction on Ti-Au@Pt/C.

We describe a new class of core-shell nanoparticle catalysts having edges and vertexes covered by refractory metal oxide that preferentially segregates onto these catalyst sites. The monolayer shell is deposited on the oxide-free core atoms. The oxide on edges and vertexes induces high catalyst stability and activity. The catalyst and synthesis are exemplified by fabrication of Au nanoparticles doped by Ti atoms that segregate as oxide onto low-coordination sites of edges and vertexes. Pt monolayer shell deposited on Au sites has the mass and specific activities for the oxygen reduction reaction about 13 and 5 times higher than those of commercial Pt/C catalysts. The durability tests show no activity loss after 10 000 potential cycles from 0.6 to 1.0 V. The superior activity and durability of the Ti-Au@Pt catalyst originate from protective titanium oxide located at the most dissolution-prone edge and vertex sites and Au-supported active and stable Pt shell.

ORR activity and electrochemical stability for well-defined topmost and interface structures of the Pt/Pd(111) bimetallic system

We investigated oxygen reduction reaction (ORR) activity and electrochemical stability of Pt/Pd(111) model electrocatalysts having well-defined topmost and sub-surface structures. The Pt/Pd(111) bimetallic surfaces were prepared by vacuum-deposition of Pt on clean Pd(111) at substrate temperatures of x (x-Ptynm/Pd(111), where x=573K or 673K, y=0.6 or 1.2) in ultra-high vacuum (UHV). Reflection high-energy electron diffraction patterns and UHV scanning tunneling microscopy images revealed that Pt grew epitaxially on the Pd(111) substrate under the aforementioned Pt deposition conditions. High substrate temperatures resulted in thermal diffusion of deposited Pt with substrate Pd atoms. The Pt atomic ratio at the topmost surface of 573K-Pt0.6nm/Pd(111) is estimated to be 95% using He-ion scattering spectroscopy (ISS), which is 8% greater than that of 673K-Pt0.6nm/Pd(111). ORR activities of the 573K-Pt0.6nm/Pd(111) and 673K-Pt0.6nm/Pd(111) surfaces were 6.3 and 3.6 times higher than that of clean Pt(111), respectively, indicating that the activity is sensitive to the topmost surface Pt atomic ratios. Moreover, electrochemical stability of 573K-Pt0.6nm/Pd(111) evaluated under potential cycle loadings (0.6V–1.0V) is better than that of 673K-Pt0.6nm/Pd(111). Depth profiles of the surfaces judged by corresponding ISS spectra suggest that the stability stems not only from the topmost Pt atomic ratios but also effective Pt-shell thickness determined by thermal diffusion of Pt and Pd. Furthermore, an increase in Pt-thickness from 0.6nm to 1.2nm improved the electrochemical stability: 573K-Pt1.2nm/Pd(111) retained 5 times more activity vs. clean Pt(111) even after 2000 potential cycles, at which the activity of 573K-Pt0.6nm/Pd(111) was the same as that for initial activity of clean Pt(111). The results obtained in this study demonstrate that atomic-level structures Pt-Pd bimetallic alloy surfaces determine the ORR activity and electrochemical stability of practical Pd@Pt core–shell catalysts.

Design of a core–shell Pt–SiO2 catalyst in a reverse microemulsion system: Distinctive kinetics on CO oxidation at low temperature

The mechanism of formation of Pt@SiO2 as a model of core–shell nanoparticles via water-in-oil reverse microemulsions was studied in detail. By controlling the time of growth of Pt precursors, Pt(OH)x, after hydrolysis in NH3 aq. before adding SiO2 precursor (TEOS), Pt nanoparticles with a narrow size distribution were produced, from ultrafine metal nanoparticles (<1nm) to 6nm nanocrystals. Separately, the thickness of SiO2 was controllably synthesized from 1 to 15nm to yield different Pt@SiO2 materials. The Pt@SiO2 core–shell catalysts exhibited a higher rate of CO oxidation by one order of magnitude with a positive order regarding CO pressure. The SiO2 shell did not perturb the Pt chemical nature, but it provided different coverage of CO in steady-state CO oxidation.

Controlled one-pot synthesis of RuCu nanocages and Cu@Ru nanocrystals for the regioselective hydrogenation of quinoline

RuCu nanocages and core–shell Cu@Ru nanocrystals with ultrathin Ru shells were first synthesized by a one-pot modified galvanic replacement reaction. The construction of bimetallic nanocrystals with fully exposed precious atoms and a high surface area effectively realizes the concept of high atom-efficiency. Compared with the monometallic Ru/C catalyst, both the RuCu nanocages and Cu@Ru core–shell catalysts supported on commercial carbon show superior catalytic performance for the regioselective hydrogenation of quinoline toward 1,2,3,4-tetrahydroquinoline. RuCu nanocages exhibit the highest activity, achieving up to 99.6% conversion of quinoline and 100% selectivity toward 1,2,3,4-tetrahydroquinoline.

Core–shell structured Cu@m-SiO2 and Cu/ZnO@m-SiO2 catalysts for methanol synthesis from CO2 hydrogenation

The core–shell catalysts with Cu and Cu/ZnO nanoparticles coated by mesoporous silica shells are prepared for CO2 hydrogenation to methanol. With the confined effect of silica shell, the size of Cu nanoparticles is only about 5.0nm, which results in high activity for CO2 conversion. The CH3OH selectivity is enhanced significantly with the introduction of ZnO. The core–shell structured catalysts endow the Cu nanoparticles trapped inside with excellent anti-aggregation and no deactivation is observed with time-on-stream. Therefore, the core–shell Cu/ZnO@m-SiO2 catalyst exhibits the maximum CH3OH yield with high stability.

Doped Carbon Shell Catalysts for Oxidation of Alkanes

Doped Carbon Shell Catalysts for Oxidation of Alkanes

Preparation of PtRu/C core–shell catalyst with polyol method for alcohol oxidation

Carbon supported PtRu core–shell catalyst is prepared by a facile and efficient method, in which the Ru nanoparticles are prepared with microwave-assisted method followed by in-situ reduction of Pt on Ru nanoparticles forming the PtRu core–shell structure. The catalyst is characterized by energy-dispersive X-ray spectroscope (EDX) analyzer attached to scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and electrochemical measurements. The TEM results show that the synthesized PtRu/C catalysts have small particle size and narrow size distribution. The PtRu/C catalyst shows higher electrochemical performance toward ethanol oxidation reaction (EOR) compared with methanol oxidation reaction (MOR). Notably, the PtRu/C catalysts exhibit higher mass activity and stability than that of the commercial PtRu/C (JM) catalyst for ethanol electrooxidation.

Biodiesel production from waste cotton seed oil using low cost catalyst: Engine performance and emission characteristics

Summary Production of fatty acid methyl esters from waste cotton seed oil through transesterification was reported. The GC–MS analysis of WCCO oil was studied and the major fatty acids were found to be palmitic acid (27.76%) and linoleic acid (42.84%). The molecular weight of the oil was 881.039 g/mol. A maximum yield of 92% biodiesel was reported when the reaction temperature, time, methanol/oil ratio and catalyst loading rate were 60 °C, 50 min, 12:1 and 3% (wt.%), respectively. The calcined egg shell catalyst was prepared and characterized. Partial purification of the fatty acid methyl esters was proposed for increasing the purity of the biodiesel and better engine performance. The flash point and the fire point of the biodiesel were found to be 128 °C and 136 °C, respectively. The Brake thermal efficiency of WCCO B10 biodiesel was 26.04% for maximum load, specific fuel consumption for diesel was 0.32 kg/kW h at maximum load. The use of biodiesel blends showed a reduction of carbon monoxide and hydrocarbon emissions and a marginal increase in nitrogen oxides (NO x ) emissions improved emission characteristics.

Clam shell catalyst for continuous production of biodiesel

ABSTRACTContinuous flow transesterification of waste frying oil (WFO) with methanol for the biodiesel production was tested in a laboratory scale jacketed reactive distillation (RD) unit packed with clam shell based CaO as solid catalyst. The physiochemical properties of the clam shell catalysts were characterized by X-ray Diffraction (XRD), Brunauer–Emmett–Teller (BET), Scanning Electron Microscopy (SEM), and Energy Dispersive Atomic X-ray Spectrometry (EDAX). The effects of the reactant flow rate, methanol-to-oil ratio, and catalyst bed height were studied to obtain the maximum methyl ester conversion. Reboiler temperature of 65°C was maintained throughout the process for product purification and the system reached the steady state at 7 hr. The experimental results revealed that the jacketed RD system packed with clam shell based CaO showed high catalytic activity for continuous production of biodiesel and a maximum methyl ester conversion of 94.41% was obtained at a reactant flow rate of 0.2 mL/min, methanol/oil ratio of 6:1, and catalyst bed height of 180 mm.

Palladium–Platinum Core–Shell Electrocatalysts for Oxygen Reduction Reaction Prepared with the Assistance of Citric Acid

Core–shell structure is a promising alternative to solid platinum (Pt) nanoparticles as electrocatalyst for oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). A simple method of preparing palladium (Pd)–platinum (Pt) core–shell catalysts (Pd@Pt/C) in a gram-batch was developed with the assistance of citric acid. The Pt shell deposition involves three different pathways: galvanic displacement reaction between Pd atoms and Pt cations, chemical reduction by citric acid, and reduction by negative charges on Pd surfaces. The uniform ultrathin (∼0.4 nm) Pt shell was characterized by in situ X-ray diffraction (XRD) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images combined with electron energy loss spectroscopy (EELS). Compared with state-of-the-art Pt/C, the Pd@Pt/C core–shell catalyst showed 4 times higher Pt mass activity and much better durability upon potential cycling. Furthermore, both the mass activity and durability were compara...

Highly Active and Thermally Stable Supported Pd@SiO2 Core–Shell Catalyst for Catalytic Methane Combustion

AbstractA series of Pd‐based core–shell catalysts (Pd@SiO2, Pd@CeO2, and Pd@ZrO2) supported on Si‐modified Al2O3 were prepared for the catalytic combustion of lean methane. Pd@SiO2 exhibited slightly lower catalytic activity than Pd@CeO2 and higher catalytic activity than Pd@ZrO2 in dry conditions; however, Pd@SiO2 had the highest catalytic activity among the three catalysts in the presence of high concentrations of water vapor. Furthermore, the Pd@SiO2 catalyst showed good thermal stability and resistivity to water poisoning. CO chemisorption and TEM results demonstrated that the core–shell structure could help in the stabilization of the active phase compared to the uncoated Pd/Si‐Al2O3 catalyst. XRD and X‐ray photoelectron spectroscopy results indicated that a balanced mixed phase of PdOx/Pd0 is the main active phase of these Pd‐based catalysts.

Mixed and ground KBr-impregnated calcined snail shell and kaolin as solid base catalysts for biodiesel production

Mixed and ground activated snail shell and kaolin catalysts impregnated with KBr were investigated. The snail shell and kaolin were calcined, mixed, and ground prior to immersion with KBr solution and subsequent activation at 500 °C for 3 h. The precursor and catalysts were characterized by thermal gravimetric analysis, Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and Brunauer–Emmett–Teller surface area. The catalytic performance of the prepared catalysts was evaluated by transesterification of soybean oil with methanol. The effects of various parameters on biodiesel yield were investigated. A biodiesel yield of 98.5% was achieved using the catalyst prepared by 40% KBr-immersed, mixed, and ground snail shell and kaolin, which were activated at 500 °C. The transesterification conditions were as follows: reaction temperature, 65 °C; reaction time, 2 h; methanol-to-soybean oil molar ratio, 6:1; and catalyst amount (relative to the weight of soybean oil), 2.0 wt%. The solid catalyst could be reused for four times, and biodiesel yield remained over 73.6% for the fourth time.

Electrochemical Study of Oxygen Reduction on a Carbon‐Supported Core–Shell Platinum–Gold Electrocatalyst with Tuneable Gold Surface Composition

AbstractThe presence of gold on the surface of platinum nanoparticles can have profound effects on the activity in the electrochemical oxygen reduction reaction (ORR). In this work, the ORR activity is studied at different surface coverage of gold on two types of core–shell platinum–gold catalysts. Surface‐limited redox reaction and redox transmetalation methods are used to synthesize core–shell catalysts with varying degrees of gold coverage on their surface. Experimental results indicate that the presence of gold on the surface intrinsically decreases the ORR activity. Furthermore, the effect of the core on the activity for ORR has been studied.

MnO2 coated Fe2O3 spindles designed for production of C5+ hydrocarbons in Fischer–Tropsch synthesis

Manganese served as promoter for the Fe-based catalysts has been considered to have great potential in Fischer–Tropsch (FT) synthesis. However, many previous researchers mainly focus on the enhancement of lower olefins, primarily because the previous reported Fe–Mn spinel oxide hindered its wide applications. In this article, Fe2O3@MnO2 spindles were fabricated by coverage of hematite with MnO2 via a hydrothermal reaction and applied in FT synthesis reaction. Different from the conventional Fe–Mn catalysts, the synthesized core–shell catalysts exhibited enhanced catalytic performance, especially in C5+ hydrocarbons selectivity. It demonstrated that Mn promoter could accelerate the dissociation of CO and thus enhanced the concentration of active intermediates for chain growth. Compared with the pure Fe2O3 (Mn-free) catalyst, the selectivity toward C5+ hydrocarbons over Fe2O3@MnO2 (Mn-9) catalyst was increased from 44.6 to 66.6wt%. Meanwhile, the undesired CH4 was decreased from 16.8 to 8.9wt%.

Pt deposited Pt–Pd/C electrocatalysts with the enhanced oxygen reduction activity

Reducing the cost of state-of-the-art Pt electrocatalysts while maintaining their oxygen reduction performance is always a hotspot in fuel cell research owing to their significant economic benefit for the commercialization of polymer electrolyte membrane fuel cells. Herein, we report a simple and cost-effective synthesis of Pt–Pd catalysts and a systematic study of their characteristics and catalytic performances for the oxygen reduction reaction (ORR). Pt–Pd bimetallic catalysts were prepared by a simple chemical deposition of Pt on the surface of Pd particles using a commercial Pd/C catalyst. During the synthesis, Pt precursor was reduced, and Pt layers were preferentially overgrown on the surface of the preexisting Pd particles resulting in Pd@Pt core–shell particles, which are favorable for ORR. By varying Pt precursors and the amount of Pt deposited, the physicochemical and electrochemical properties of the Pt–Pd catalysts were optimized. The formation of a thin Pt layer on Pd surface is more favorable, when using Pt(NH3)4Cl2·xH2O rather than H2PtCl6·xH2O. As the amount of Pt increased from 0 to 10%, the surface properties of metal particles changed to similar to that of Pt, and the resulting catalysts mainly consist of a Pt-rich layer with a Pd core such as the Pd@Pt core–shell configuration. Pt(10%)Pd/C catalyst prepared by using Pt(NH3)4Cl2·xH2O exhibited a significant improvement in the ORR with the mass activities of 221 and 53mA/mgPGM at 0.85 and 0.9V, respectively, which are beatable values compared to those (219 and 59mA/mgPt at 0.85 and 0.9V) of commercial Pt/C catalysts. The performance improvement of our bimetallic Pt–Pd/C catalysts mainly originate from the formation of an active Pt surface on the Pd core. In addition, considering that Pd is generally less expensive than Pt, these catalysts should have much better ORR performance and more feasibility of decreasing the total cost of fuel cells. In this study, the characteristics, electrochemical behaviors, and ORR performance improvements of the simply prepared Pt(x)–Pd/C core–shell catalysts were systemically investigated and are discussed.

Achieving High-Power PEM Fuel Cell Performance with an Ultralow-Pt-Content Core–Shell Catalyst

The high-power performance of proton exchange membrane fuel cells (PEMFC) decreases as the Pt loading or Pt surface area decreases due to oxygen transport constraints. This has limited the Pt reduction of a fuel cell below the current ∼0.2 mgPt/cm2MEA. In this paper, the performance of a Pt-monolayer core–shell catalyst (PtML/Pd/C) was studied with a particular focus on high-current-density operation. Although conventional Pt/C electrodes with low Pt loading showed a substantial voltage falloff at high current densities, PtML/Pd/C showed superior performance due to its greater Pt surface area. We show that Pt loading can be reduced to a level as low as 0.025 mgPt/cm2 without noticeable transport-related losses. This suggests considerable potential for further fuel cell cost reduction. The performance and microscopic properties of the catalyst were also studied after accelerated stability tests. The degradation mechanism and pathways for future development are also discussed.

ChemInform Abstract: Synthesis and Characterization of Iron—Nitrogen‐Doped Graphene/Core—Shell Catalysts: Efficient Oxidative Dehydrogenation of N‐Heterocycles.

AbstractThe catalyst, which consists of iron oxides surrounded by nitrogen‐doped‐graphene shells immobilized on carbon, is obtained via pyrolysis of iron acetate and phenanthroline followed by a selective leaching process.