Durability Of Pt Research Articles

Single Cell Performance and Durability of Pt and Pt-Based Catalysts Supported on Mesoporous Carbon

Introduction In Japan, an extremely high cell performance, i.e., 0.84 V at 0.2 A/cm2 and 0.70 V at 3.0 A/cm2, is required for polymer electrolyte fuel cells (PEFCs) used in fuel cell electric vehicles after 2030 [1]. In addition to high oxygen reduction reaction (ORR) activity of the Pt and the Pt-based cathode catalysts for increasing cell voltage in the low current density (LCD) region, high oxygen diffusivity is crucial for achieving the cell voltage in the high current density (HCD) region [2]. Therefore, it is considered that carbon supports for the catalyst NPs would play an important role for realizing the high cell performance. In this study, a mesoporous carbon (MPC) was selected as the support for Pt and Pd@Pt core-shell structured catalyst NPs and cell performance of the catalysts were compared with that of the catalyst supported on a conventional Ketjen Black (KB). Furthermore, durability of the MPC support against a high potential range was investigated. Experimental KB-600JD (SBET: 1,335 m2/g, LION) and MPC (CNovel MH-18, SBET 1,334 m2/g, TOYO TANSO [3]) were used as carbon supports. The Pt/MPC catalyst, Pt diameter of 2.5 nm and metal loading of 50 wt.%, was synthesized through impregnation of Pt(NO2)2(NH3)2 followed by thermal reduction in N2 at 400oC. Pt/Pd/KB and Pt/Pd/MPC core-shell catalysts were synthesized by a direct displacement reaction (DDR) method [4]. Diameter of Pd@Pt NPs was 5.8 nm and Pt and Pd metal loading were 20 wt.% and 30 wt.%, respectively. Cyclic voltammogram was recorded in Ar-saturated 0.1 M HClO4 at 25oC with a scan rate of 50 mV/s and ORR activity was evaluated in O2-saturated 0.1 M HClO4 at 25oC with a positive potential scan rate of 10 mV/s at 1,600 rpm. Fuel cell performance was evaluated by using a single cell with an active area of 1 cm2. Nafion DE2020 was used as an ionomer for the catalyst ink preparation (I/C ratio was set to 0.83-1.2) and Nafion NRE 211 with 25 µm in thickness was used as a membrane. Pt loading in the cathode catalyst layer was set to 0.1 mg/cm2. H2 and air were supplied to the anode and the cathode by 418 NmL/min. and 988 NmL/min., respectively, and pressurized to 150 kPa at gas outlets. The cell temperature was set to 80oC and humidified from 35% to 95% relative humidity (RH). H2 utilization was 5% at a current density of 3.0 A/cm2. Durability of the carbon supports was evaluated by using the single cell. H2 and N2 were fed to anode and cathode, respectively, and cathode potential was swept from 1.0 to 1.5 V vs. RHE with a scan rate of 500 mV/s for 1,000 cycles. Results and Discussion Pore size distribution of the carbon supports is shown in Figure 1. Both KB-600JD and MPC (CNovel MH-18) carbon supports have mesopores, and the MPC exhibits a narrower pore size distribution centered at 4 nm. Figure 2 demonstrates I-V performance of Pd@Pt core-shell catalysts, indicating that Pt/Pd/MPC catalyst shows a higher cell voltage in HCD region (> 2 A/cm2) than that of Pt/Pd/KB-600JD catalyst. Interconnectivity of the mesopores analyzed by 3D-TEM observation of the carbon supports is depicted in Figure 3. It is clear that density of interconnected mesopores is much higher in the MPC support, which is considered to contribute to the higher cell voltage in HCD region of the Pt/Pd/MPC catalyst. Figure 4 displays cross-sectional SEM image of the Pt/Pd/MPC catalyst. In addition to the well-interconnected mesopores (Figure 3), macropores coexist in the MPC support, which is also considered to contribute to the higher cell voltage in HCD region.A high potential durability test was performed by using potential cycling of 1.0-1.5 V vs. RHE for 1,000 cycles at 80oC. Thickness of Pt/MPC cathode catalyst layer was decreased by 36% after the durability test, while the decrease was mitigated to 14% with a heat treatment of the MPC support at 2,200oC in Ar. (Figures 5). As is well known, it was demonstrated that the high temperature heat treatment has a positive effect for durability improvement of the carbon support against the high potential range.This study was partly supported by NEDO, Japan.

Enhancement of Activity Low-Pt-Content O2-Reduction Catalysts through Formation of Hybrid Systems with Sub-Stoichiometric Cerium Oxide Nanostructures

Platinum is a main catalyst for the electroreduction of oxygen, a reaction of primary importance to the technology of low-temperature fuel cells. Due to the high cost of platinum, there is a need to significantly lower its loadings at interfaces. However, under such condition, O2-reduction reaction (ORR) often proceeds at a less positive potential, and produces higher amounts of undesirable H2O2-intermediate. Recent studies have demonstrated that the rational design of a catalytic system is based on nanostructures of platinum, or carbon-supported platinum (Pt/C), and metal oxide (MOx). By combining the catalytic properties of both components, such hybrid Pt-MOx catalysts are capable of tuning of the activity and durability of Pt. Due to strong interactions of MOx with Pt catalytic nanoparticles leading to the improved activity and durability during ORR, certain nanostructured metal oxides are considered as co-catalysts or active components of supports. The existence of specific interactions between MOx and noble metal (Pt) nanoparticles should improve the stability and activity of the metal catalytic sites due to modification of the Pt electronic structure and diminishing of the oxo (OH) species adsorption on Pt surface, thus promoting centers for the adsorption of oxygen and the cleavage of O=O bonds. The interactions mentioned above would also facilitate dispersion of Pt, inhibit their detachment and further aggregation, and, consequently, prevent or decrease their degradation during the fuel cell operation [1].The catalytic activity of substoichiometric ceria, CeOx (where x < 2) additive results from its unique structure, presence of oxygen vacancies, and other features resulting from the 4f-electronic configuration of cerium. While the oxygen defects are likely to serve as active oxygen adsorption sites, the mixed-valent CeIII/CeIV redox sites should permit the electron shuffling within the lattice of oxygen vacancies and enhancing the ORR activity. The formation of oxygen-defects is accompanied by the localization of electrons left behind in Ce 4f states, thus leading to the formation of CeIII species capable of elongating and reducing the O–O bond strength of the adsorbed O2 molecule; consequently, by increasing the relative ratio of CeIII-to-CeIV, the ORR electrocatalytic activity can be improved [1]. Therefore, in the present study, we consider the intentionally reduced CeOx nanostructured components through subjecting them to high-temperature pretreatment in the presence of argon gas admixed with hydrogen. It is reasonable to expect that, the increased population of CeIII sites on the surfaces of the pretreated ceria particles would stabilize the neighboring active Pt-metal centers, exhibit reductive interactions toward Pt-oxo species, and to improve durability of the catalytic materials. Thus the boundary formed between the Pt-metal and CeOx-metal oxide should facilitate inhibition of the Pt oxide formation by the CeOx layer. Furthermore, our recent studies clearly show that, in the presence of ceria, the oxidative degradation of carbon carriers is also largely decreased. Finally, cerium oxide is known to act as the oxidative scavenger for free radicals such as hydroxyl (HO•) and hydroperoxyl (HOO•), which, once generated, would otherwise lead to the formation of undesirable hydrogen peroxide. Sub-stoichiometric CeOx is capable of rapidly switching between CeIII and CeIV oxidation states, thus inducing the decomposition of both radicals and peroxides. The above observation seems to be very helpful when it comes to designing highly active and durable ORR catalysts containing low platinum loadings.[1] A.Kostuch, I.A. Rutkowska, B. Dembinska, A. Wadas, E. Negro, K. Vezzù, V. Di Noto, P.J. Kulesza, Molecules 26 (2021) 5147. Acknowledgements: This work was supported by the National Science Center (Poland) under Opus Project (2018/29/B/ST5/02627) and under auspices of the European Union EIT Raw Materials ALPE 19247 Project (Specific Grant Agreement No. EIT/RAW MATERIALS/SGA2020/1).

ZrO2 anchored core-shell Pt–Co alloy particles through direct pyrolysis of mixed Pt–Co–Zr salts for improving activity and durability in proton exchange membrane fuel cells

Highly active and durable Pt-based catalysts for oxygen reduction reaction (ORR) are very important and necessary for the proton exchange membrane fuel cells (PEMFCs). In this paper, we report the preparation and performance study of ORR catalysts composed of core-shell Pt–Co alloy nanoparticles (NPs) on multi-walled carbon nanotubes (MWCNTs) anchored with ZrO2 NPs (denoted as Pt–Co–ZrO2/MWCNTs). Thanks to the unique three-phase structure, the mass activity of Pt–Co–ZrO2/MWCNTs for ORR at 0.9 V versus reversible hydrogen electrode (RHE) is1577 mA mgPt−1, which is ∼6.6-fold higher than that of the commercial Pt/C (238 mA mgPt−1). After 50,000 cycles for durability test, the mass activity of Pt–Co–ZrO2/MWCNTs for ORR remained 88% of its initial value. In stark contrast, that of Pt/C kept only about 56.3% of its initial value. More importantly, its catalytic performance was fully observed/verified in a H2-air PEMFC single cell test. When the Pt loading of Pt–Co–ZrO2/MWCNTs loaded cathode was one fourth of that with commercial Pt/C as the cathode catalyst, comparable cell performance was achieved. More impressively, the MEA with Pt–Co–ZrO2/MWCNTs underwent only 24.5% degradation in maximum power density after 30,000 accelerated durability tests (ADTs). However, the MEA with Pt/C after 30,000 ADTs exhibited 39.6% performance loss in maximum power density. The enhanced mass activity and catalytic durability of Pt–Co–ZrO2/MWCNTs could be attributed to the core-shell Pt–Co alloy NPs with Pt-rich surface and the interface effect between Pt–Co alloy NPs and oxygen vacancy-rich ZrO2 NPs. In addition, this research also provided a solution to the durability issue of cathodes without sacrificing ORR mass activity, which would promote practical application of PEMFCs.

High-Current Density Durability of Pt/C and PtCo/C Catalysts at Similar Particle Sizes in PEMFCs

The durability of carbon supported PtCo-alloy based nanoparticle catalysts play a key role in the longevity of proton-exchange membrane fuel cells (PEMFC) in electric vehicle applications. To improve its durability, it is important to understand and mitigate the various factors that cause PtCo-based cathode catalyst layers (CCL) to lose performance over time. These factors include i) electrochemical surface area (ECSA) loss, ii) specific activity loss, iii) H+/O2-transport changes and iv) Co2+ contamination effects. We use a catalyst-specific accelerated stress test (AST) voltage cycling protocol to compare the durability of Pt and PtCo catalysts at similar average nanoparticle size and distribution. Our studies indicate that while Pt and PtCo nanoparticle catalysts suffer from similar magnitudes of electrochemical surface area (ECSA) losses, PtCo catalyst shows a significantly larger cell voltage loss at high current densities upon durability testing. The distinctive factor causing the large cell voltage loss of PtCo catalyst appears to be the secondary effects of the leached Co2+ cations that contaminate the electrode ionomer. A 1D performance model has been used to quantify the cell voltage losses arising from various factors causing degradation of the membrane electrode assembly (MEA).

Electrocatalytic Activity and Durability of Pt–Ni Nanowires for Oxygen Reduction

Oxygen reduction reaction (ORR) is a key reaction in future energy generation devices such as polymer electrolyte fuel cells (PEFCs) and metal–air batteries. To drive the ORR in PEFCs, Pt–M alloy nanoparticles (M = Ni) on carbon supports have been used as catalysts. Under electrocatalytic conditions, these electrocatalysts are known to degrade involving particle detachment, agglomeration and metal dissolution.[1] These phenomena can be suppressed by increase metal/support interactions: using heteroatom-doped carbon supports[2] and/or nanostructured Pt–M alloy catalysts.[3] Herein, we report synthesis, activity and durability of Pt–Ni nanowires (NWs) for the ORR in acidic media. The Pt–Ni NWs showed higher ORR electrocatalytic activity than Pt/C. The Pt–Ni NWs showed almost no activity loss even after 50,000 potential cycles in acidic media. Physicochemical measurements including in situ Pt L3-edge X-ray absorption spectroscopy [4] revealed that the Pt surface oxide formation under potential control was suppressed after potential cycles, relative to the initial state. This finding suggests that potential cycles could induce strong metal/support interactions, resulting in the formation of highly durable NW catalysts.References.[1] N. Hodnik, G. Dehm, K.J.J. Mayrhofer, Acc. Chem. Res., 49, 2015–2022 (2016).[2] M. Kato, K. Ogura, S. Nakagawa, S. Tokuda, K. Takahashi, T. Nakamura, I. Yagi, ACS Omega, 3, 9052–9059 (2018).[3] J. Li et al., Science, 354, 1414–1417 (2016).[4] K. Nagasawa et al., J. Am. Chem. Soc., 137, 12856 (2015).Acknowledgements.This work was supported by NEDO.

Rational Design of Single Atomic Co in CoNx Moieties on Graphene Matrix as an Ultra‐Highly Efficient Active Site for Oxygen Reduction Reaction

AbstractThe sharp increase in current energy consumption needs the development of fuel cells (FCs) as one of sustainable, renewable, efficient and eco‐friendly electrochemical conversion systems of energy. The performance of electrocatalysts is crucially important for commercialization of FCs. Commercial Pt based catalysts are used due to their high catalytic activity. However, widespread commercialization is impossible because of the scarcity and poor durability of Pt based catalysts. We are on our quest to find a more stable and affordable alternative catalyst of Pt based catalysts. In particular, single‐atom catalysts supported on graphene are greatly attractive because of their unique characteristic and high catalytic activity. In this work, graphene is hydrothermally treated by sulfuric acid to introduce the ion‐exchanging sites. Then, Co2+ ion‐exchanging, 2‐methylimidazole coordination and pyrolysis process are subsequently conducted to prepare highly‐dispersed single‐atom Co species catalyst with outstanding ORR activity and durability. This work presents a new direction for a rational design of single‐atom catalyst on carbon matrix.

On the durability of Pt coated Ti electrodes for the electro-oxidative dissolution of spent nuclear fuels

ABSTRACTThe main objective of this study is to assess the long-term performance of Pt nanoparticle coated anodised Ti coupons which are used for electrochemical dissolution of spent mixed-oxide nuclear fuels during reprocessing. In this work, electrodes were exposed to a simulated dissolver solution containing a representative fraction of low-activity actinides and fission products in 11.5 N nitric acid in a mock-up of the service dissolver vessel. Platinum nanoparticles were coated onto anodised titanium coupons through a seed-mediated hydrothermal method. The coated coupons were then exposed in the simulated dissolver solution for about 1185 h at 110°C. Morphological and compositional analyses confirmed the presence of metallic Pt nanoparticles on the electrode surface with some localised cracking. The electrochemically active surface area of the Pt-nanoparticle coated anodised titanium coupon after exposure was found to be twice that of polycrystalline platinum thus establishing the durability and efficiency of the coating on the electrode.

Bio Derived Electrocatalyst : Co2p Nanoparticles Supported on Heteroatom Doped Carbon for Highly Efficient Oxygen Reduction

The biggest issue in the fuel cell, which is believed to be the promising candidate as the next generation power source, is the oxygen reduction reaction (ORR). Due to the relatively high ORR activity, Pt-based catalysts are used predominantly, however, the scarcity, high cost and unsatisfactory durability of Pt make it difficult for commercialization of fuel cell. In this work, we developed a heteroatom doped carbon supported Co2P catalyst through the eco-friendly and simple method using bean sprouts. Final product exhibits excellent ORR activity and superior durability in alkaline media. The value of the half wave potential of NBSCo is 10 mV higher than that of commercial Pt/C. The excellent oxygen reduction activity is attributed to the synergistic effect of Co2P and N-doped carbon. NBSCo was applied in anion exchange membrane fuel cell (AEMFCs). At the optimized cathode composition, the NBSCo produce the max power density of 172 mW cm-2. It is considered to be competitive performance and it has demonstrated the potential for application to energy storage systems.

(Invited) Electrochemical Oxygen Reduction Catalyzed at Pt–Ni Nanostructured Electrocatalysts Immobilized on Nitrogen-Doped Carbon Supports

Oxygen reduction reaction (ORR) is the key reaction in future energy generation devices such as polymer electrolyte fuel cells (PEFCs) and metal–air batteries. To drive the ORR in state-of-the-art PEFCs, carbon-supported Pt–M alloys (M = Ni and Co) are used. Since platinum is rare and expensive, there is a need to develop ORR electrocatalysts with not only high catalytic activity but also high durability. Under electrocatalytic conditions, catalyst degradation mechanisms are known to involve many processes including particle detachment, agglomeration and metal dissolution.[1] These phenomena can be suppressed by increase metal/support interactions. Carbon black is typically used as the catalyst support and can be chemically modified by heteroatom-doping. Heteroatom-doped carbon supports can show strong metal/support interactions with Pt nanoparticles.[2] Herein, we report the enhancement of electrocatalytic ORR activity and durability of Pt–Ni alloy nanoframes by immobilization on nitrogen-doped carbon supports. Strong metal/support interactions between the nanoframe and the support caused the downshift of the d-band center position of the surface Pt, proved by X-ray photoelectron spectroscopy and surface-enhanced infrared absorption spectroscopy.[3] In situ X-ray absorption spectroscopy also revealed that the Pt surface oxide formation was suppressed by the immobilization on nitrogen-doped carbon supports. Our findings demonstrate that tuning the electronic structure of nanostructured Pt alloy electrocatalysts via strong metal/support interactions will allow the development of highly active and robust electrocatalysts for the ORR.

Facile synthesis of three-dimensional platinum nanoflowers on reduced graphene oxide – Tin oxide composite: An ultra-high performance catalyst for methanol electro-oxidation

Herein, we report platinum (Pt) nanoflowers decorated reduced graphene oxide (rGO)–tin oxide (SnO2) composite as an efficient electro-catalyst for direct methanol fuel cells (DMFCs). rGO-SnO2 composite is synthesized by a novel, eco-friendly hydrothermal method using lemon extract followed by electro-deposition of Pt to yield high density Pt nanoflowers uniformly distributed over rGO-SnO2 for superior catalytic performance and optimal utilization of Pt nanostructures. Whilst Pt nanoparticles (NPs)-rGO-SnO2 composite exhibits higher CO tolerance ability (If/Ib = 3) and poor catalytic stability, Pt nanoflowers-rGO-SnO2 composite shows comparable CO tolerance ability (If/Ib = 1.81) with excellent stability. At 3000 s, the current density of Pt nanoflowers-rGO-SnO2 has been found to be 2.1 folds higher than Pt NPs-rGO-SnO2 composite. Excellent durability of Pt nanoflowers-rGO-SnO2 is attributed to the high surface area of Pt nanoflowers which provides more active sites during methanol oxidation without any agglomeration, thus, facilitating diffusion of methanol to Pt for catalytic activity. As per our knowledge, this is the first report on Pt nanoflowers-rGO-SnO2 composite based electro-catalyst for DMFCs that yields superior performances in terms of catalytic efficiency, CO tolerance activity and stability. The composite shows enormous potential to be used as binder free, cost-effective, efficient and durable electro-catalyst for DMFCs applications.

Study on durability of Pt supported on graphitized carbon under simulated start-up/shut-down conditions for polymer electrolyte membrane fuel cells

The primary issue for the commercialization of proton exchange membrane fuel cell (PEMFC) is the carbon corrosion of support under start-up/shut-down conditions. In this study, we employ the nanostructured graphitized carbon induced by heat-treatment. The degree of graphitization starts to increase between 900 and 1300 °C as evidenced by the change of specific surface area, interlayer spacing, and ID/IG value. Pt nanoparticles are deposited on fresh carbon black (Pt/CB) and carbon heat-treated at 1700 °C (Pt/HCB17) with similar particle size and distribution. Electrochemical characterization demonstrates that the Pt/HCB17 shows higher activity than the Pt/CB due to the inefficient microporous structure of amorphous carbon for the oxygen reduction reaction. An accelerating potential cycle between 1.0 and 1.5 V for the carbon corrosion is applied to examine durability at a single cell under the practical start-up/shut-down conditions. The Pt/HCB17 catalyst shows remarkable durability after 3000 potential cycles. The Pt/HCB17 catalyst exhibits a peak power density gain of 3%, while the Pt/CB catalyst shows 65% loss of the initial peak power density. As well, electrochemical surface area and mass activity of Pt/HCB17 catalyst are even more stable than those of the Pt/CB catalyst. Consequently, the high degree of graphitization is essential for the durability of fuel cells in practical start-up/shut-down conditions due to enhancing the strong interaction of Pt and π-bonds in graphitized carbon.

One-pot synthesis of Pt/CeO2/C catalyst for enhancing the SO2 electrooxidation

SO2 is one of the critical poisoning species to Pt based catalysts of proton exchange membrane fuel cells (PEMFCs). Catalysts suffer severe performance degradation even trace amount of SO2 presenting in the hydrogen or air. To enhance the SO2 electrooxidation of Pt catalyst, we prepared Pt/CeO2/C composite catalysts via a one-pot synthesis method. The CeO2 nanoparticles initially deposited on carbon black, and followed by Pt nanoparticles selectively nucleating on CeO2 surface. The rich Pt-CeO2 interface facilitates the oxygen migration, enhancing SO2 electrooxidation and ORR activity. The catalysts containing 10 and 20wt.% CeO2 show the best performance, i.e., peak potentials of SO2 electrooxidation are 0.06 and 0.09V lower than Pt/C, respectively, ORR mass activity is over twofold greater, and area-specific activity is one fourth higher than Pt/C. Oxygen provided by CeO2 reduced the SO2 coverage on Pt surface and changed the dominant adsorbing state of SO2, hence, is vital to the SO2 electrooxidation. Besides, accelerated durability test confirmed that CeO2 could also improve the durability of Pt based catalysts.

Enhancement of ORR Activity and Durability of Pt Single Crystal Electrodes Modified with Alkylamines

1. Purpose Fuel cell is high-efficiency and clean energy system. However, high overpotential of oxygen reduction reaction (ORR) and large Pt loading in electrocatalyst are grave issues for the general use. Miyake et al. reported that platinum nanoparticles modified with octylamine (OA) and alkylamine with pyrene group (PA) give higher activity and durability at the molar ratio OA/PA=7/3 compared with bare Pt nanoparticles [1]. However, the platinum nanoparticles are not shape controlled or well-defined. We have investigated surface structures which enhance the ORR activity and durability using Pt single crystal electrodes modified with OA/PA. The surfaces examined are Pt(100), Pt(110), Pt(111), Pt(331)=3(111)-(111) that has the highest ORR activity [2] and Pt(775)=7(111)-(111). In the notation of high index planes such as n(hkl)-(mno), the value of n, Miller indices (hkl) and (mno) show the number of terrace atomic rows, the structures of terrace and step, respectively. 2. Experimental Linear sweep voltammograms of the ORR were measured with rotating disk electrode (RDE). Potential was scanned from 0.05 V (RHE) to 1.0 V (RHE) at scanning rate 0.010 V s-1 and rotation rate 2000 rpm. The activity for the ORR was estimated using the specific activity at 0.90 V (RHE) j k according to the Koutecky-Levich equation. Durability test was conducted using rectangular wave from 0.60 V step to 1.0 V. All the potentials were referred to RHE. 3. Result and Discussion The ORR activities of Pt(111) modified with OA/PA = 9/1, 8/2, 7/3 (molar ratio) were twice or three times higher than that of bare Pt(111). The ORR activity increases with the increase of the ratio of PA. The activity of Pt(775) = 7(111)-(111) modified with OA/PA=9/1 was also higher than that of bare Pt(775). Pt(100) and Pt(110) modified with OA/PA=9/1 gave lower ORR activity than bare electrodes. These results show that PA on wide (111) terrace enhances the ORR activity. The ORR activity of Pt(111) was enhanced after the durability test because active (110) type defects are formed on the surface. The ORR activity of Pt(111) modified with OA/PA was 1.8 mA/cm2 after 2000 cycles, higher than that of bare Pt(111) 1.0 mA/cm2. Adsorbed amines on wide (111) terrace preserved the high activity after the durability test. The activity after 2000 cycles decreased with the increase of the ratio of PA. This result differs from the previous study [1]. The ORR activity of Pt(775) modified with OA/PA was as high as that of bare Pt(775) after the durability test. Durability of Pt(775) was not improved by OA/PA modification. 4. Acknowledgement This work was supported by New Energy Development Organization. 5.

Durability of Pt Catalysts Supported on Graphitized Carbon-Black during Gas-Exchange Start-Up Operation Similar to That Used for Fuel Cell Vehicles

We investigated the durability of cathode catalysts during a start-up (SU) process similar to that used in actual polymer electrolyte fuel cell vehicle operation. The durability of Pt supported on graphitized carbon black (Pt/GCB) catalysts was evaluated in the practical SU process, i.e., the anode gas was successively cycled between air, hydrogen, and nitrogen. The effect of the SU process on the cell performance was evaluated using two types of catalysts (commercial Pt/GCB, and that prepared in house by the “nanocapsule-method,” n-Pt/GCB). The polarization curves and cyclic voltammetry were evaluated before and after the SU evaluation. The degradation of Pt nanoparticles and carbon supports was analyzed by transmission electron microscopy, scanning transmission electron microscopy, and micro-Raman spectroscopy. We also applied glancing incidence X-ray diffraction in order to observe the depth profiles of the Pt crystallite sizes in various interfacial regions. From these analyses, we found that the degradation of the Pt catalyst occurred not only in the gas outlet region but also the gas inlet region of the cathode. The degradation in the inlet region is ascribed to both the interim electrochemical evaluations and the potential fluctuations, which cause a dissolution of Pt nanoparticles used during the SU process.

Relating adatom emission to improved durability of Pt–Pd diesel oxidation catalysts

Sintering of nanoparticles is an important contributor to loss of activity in heterogeneous catalysts, such as those used for controlling harmful emissions from automobiles. But mechanistic details, such as the rates of atom emission or the nature of the mobile species, remain poorly understood. Herein we report a novel approach that allows direct measurement of atom emission from nanoparticles. We use model catalyst samples and a novel reactor that allows the same region of the sample to be observed after short-term heat treatments (seconds) under conditions relevant to diesel oxidation catalysts (DOCs). Monometallic Pd is very stable and does not sinter when heated in air (T⩽800°C). Pt sinters readily in air, and at high temperatures (⩾800°C) mobile Pt species emitted to the vapor phase cause the formation of large, faceted particles. In Pt–Pd nanoparticles, Pd slows the rate of emission of atoms to the vapor phase due to the formation of an alloy. However, the role of Pd in Pt DOCs in air is quite complex: at low temperatures, Pt enhances the rate of Pd sintering (which otherwise would be stable as an oxide), while at higher temperature Pd helps to slow the rate of Pt sintering. DFT calculations show that the barrier for atom emission to the vapor phase is much greater than the barrier for emitting atoms to the support. Hence, vapor-phase transport becomes significant only at high temperatures while diffusion of adatoms on the support dominates at lower temperatures.

Cr effect on the durability of Pt–TM catalysts for PEMFCs

Pt–TM–Cr/C alloy catalysts were produced by a polyol method. We investigated the improvement of durability by the addition of a small amount of Cr, which is expected to prevent dissolution of transition metals.

Study on the Oxygen Bonding Energy to Pt by Valence Band DOS Measurement of Pt Nano-Particle Catalysts

In order to improve the catalytic activity and durability of PEFC cathode Pt catalysts the particle size and ligand effects on the oxygen bonding energy of a Pt nano-particle catalyst were evaluated from the valence band DOS of Pt by using resonant inelastic X-ray scattering (RIXS). The RIXS measurement is suitable to probe changes of the valence band states by oxygen adsorption because it is element specific and compatible with ambient pressure. A hard X-ray whose photon energy is slightly lower than the Pt L 3 absorption edge was introduced on the sample to eliminate fluorescence component and subsequent emission by transition from the Pt valence states to the 2p core hole was detected as a function of energy transfer as shown in Fig. 1.The RIXS spectra of Pt nano-particle catalysts measured by 11.563 keV excitation are shown in Fig. 2. The mean particle diameters are evaluated from TEM images to be from 1.6 to 3.9 nm. The main peaks in the region between 2 and 4 eV can be assigned as X-ray Raman peak which comes from the bonding between platinum and oxygen. The X-ray Raman peak position decreases with increasing mean particle diameter as shown in Fig. 2.The energy transfer value of X-ray Raman peak position can be closely related to the oxygen bonding energy with Pt. Therefore Figure 2 suggests that the oxygen bonding energy to Pt decreases with the Pt particle size. Strong bonding between oxygen and Pt might reduce the catalytic activity and the durability of Pt nano-particles with diameters less than 3 nm. Alloying with transition metals also changes the bonding energy of oxygen to Pt. Based on these results, relationship between electronic structure and catalytic activity will be discussed. Acknowledgement This work was supported by New Energy and Industrial Technology Development Organization (NEDO). The RIXS experiments were approved by the Japan Atomic Energy Agency (JAEA) Proposal Review Committee (Proposal No. 2010B3575, 2011A3574 and 2013A3514).

Potentiality of Hydrocarbon Membrane for Durability Improvement of Pt and PtCo Alloy Catalyst and Pt Loading Reduction

One of the major cost drivers in polymer electrolyte fuel cells (PEFCs), particularly for automotive application, is the use of platinum-based electrodes to facilitate electrochemical reactions such as hydrogen oxidation and oxygen reduction. Improving the durability of Pt and PtCo alloy catalyst shall reduce total active area and/or Pt loading per unit active area without any sacrifice in performance of fuel cell stacks, and it can also significantly be beneficial to the reduction of total Pt usage on fuel cell vehicles (FCVs). Catalyst durability during fuel cell operation remains a key challenge to developing the fuel cell system with acceptable overall cost in automotive applications.Toray has been developing advanced hydrocarbon (HC) membranes to give a better total solution in terms of overall cost reduction of fuel cell systems, which includes i) the potentiality for durability improvement of Pt and PtCo alloy catalyst and Pt loading reduction due to less Pt particle dissolution, ii) no emission of super acids such as HF and perfluorosulfonic acids, iii) low gas crossover, and iv) environmental friendliness, in comparison with conventional PFSA membranes. We will describe in the meeting that Toray HC membrane would potentially improve the durability of PtCo alloy catalyst owing to less Pt particle dissolution, and thereby reduce total active area and/or Pt loading per unit active area by 45% ((1-0.24V/0.43V)x100) vs Nafion HP as a reference in case judging at 1000 hours in the accelerated chemical and mechanical durability test. We hope Toray HC membranes could help to form a pathway toward FCV wide commercialization.ACKNOWLEDGEMENTThis work was partially supported by the New Energy and Industrial Technology Development Organization (NEDO) of Japan.

Hydrogen evolution stability of platinum modified graphite electrode

Abstract A Platinum-modified alloy coating with high hydrogen evolution reaction (HER) durability activity was prepared by electrodeposition. The durability of this catalyst was determined with electrolysis technique for 120 h. The prepared electrode was characterized by energy dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM) and scanning electron microscopy (SEM). Long-term electrolysis was carried out in 1 M KOH solution by cathodic current–potential curves and electrochemical impedance spectroscopy (EIS). Experimental result showed that CoZn–Pt coating has a rough structure and presents good stability and high durability. Electrochemical activity increases slightly with increasing electrolysis time. High durability of Pt modified cathode was attributed to the high surface area and synergistic interaction between Co, Zn and Pt.

Remarkable durability of Pt–Ir alloy catalysts supported on graphitic carbon nanocages

Low durability is the major challenge hindering the large-scale implementation of proton exchange membrane fuel cell (PEMFC) technology. To improve the electrochemical activity and durability of conventional Pt catalyst used in PEMFCs, we prepare Pt–Ir alloy catalysts supported on homemade graphitic carbon nanocages (CNCs). Results from cyclic voltammetry (CV) and linear sweep voltammetry (LSV) show that the alloy catalyst with an atomic Pt/Ir ratio of 1:1 supported on CNCs with a high degree of graphitization exhibits an excellent electrocatalytic activity. Furthermore, this alloy catalyst shows a drastic improvement in durability and stability over the unalloyed Pt catalyst supported on the same CNCs and the catalyst from a commercial source (Johnson Matthey Co.). It is found that the concurrent uses of well-graphitized CNCs as the support material and Ir as the alloying element are critical for the observed improvement. Such a Pt–Ir alloy catalyst provides a new replacement for the conventional Pt catalyst with not only a drastic improvement in durability but also a reduction in Pt usage by 50% as well.