Electrochemically Active Surface Area Values Research Articles

Synergistic Effect of Electrocatalyst for Enhanced Oxygen Reduction Reaction: Low Pt-Loaded CuPt Alloy Nanoparticles Supported on N-Doped Hierarchical Porous Carbon.

It is challenging to synthesize oxygen reduction reaction (ORR) electrocatalysts that are highly efficient, affordable, and stable for use in proton exchange membrane fuel cells. To address this challenge, we developed a low platinum-loading (only 6.68% wt) ORR catalyst (PtCu1-NC), comprising CuPt nanoparticles (average size: 1.51 nm) supported on the N-doped carbon substrates. PtCu1-NC possesses a high specific surface area of 662 m2 g-1 and a hierarchical porous structure, facilitating efficient mass transfer. The synergistic effect from introduced copper and the electron effect from nitrogen modify the electronic structure of platinum, effectively accelerating the ORR reaction and enhancing stability. Density functional theory calculations demonstrate the catalytic mechanism and further verify the synergistic effect. Electrochemical assessments indicate that PtCu1-NC exhibits specific activity and mass activity 5.3 and 5.6 times higher, respectively, than commercial Pt/C. The half-wave potential is 27 mV more positive than that of commercial Pt/C. The electrochemical active surface area value is 104.3 m2 g-1, surpassing that of Pt/C. Approximately 78% of current is retained after 10,000 s chronoamperometry measurement. These results highlight the effectiveness of alloying in improving the catalyst performance.

Electrosynthesis of deep eutectic solvent assisted NiFe nanoparticles on stainless steel mesh for electrocatalytic water splitting reactions

This work focuses on the use of a deep eutectic solvent mixture to deposit nanoparticles of nickel and iron onto a surface of stainless steel (SS) mesh. The study was used to assess the performance of NiFe@SS nanoparticles in hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and overall water splitting (OWS) reactions in a 1.0 M KOH solution. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) were the materials characterization techniques that were used to examine the structure and physical properties of the NiFe@SS alloy deposited on the SS mesh. Electrochemical active surface area (ECSA) calculations were used for estimating the surface area of the electrode actively participating in the electrochemical reactions. The stability and durability of NiFe@SS nanoparticles were investigated through chronopotentiometry, chronoamperometry, and cyclic voltammetry. The results of the HER, OER, and OWS reactions brought out the significant electrocatalytic performance of NiFe@SS. The benchmark catalyst afforded overpotential values of −0.138 V and 0.234 V towards the HER and OER, respectively. The overall water-splitting cell voltage was about 1.56 V. The outperformed catalyst of NiFe@SS had an ECSA value of 32.75 mF/cm2 and showed more activity in HER, OER, and OWS reactions.

(Digital Presentation) The Utilization of Platinum Catalysts Deposited on Carbon Support Synthesized from Coffee Grounds in a Polymer Electrolyte Membrane Fuel Cell

Exploring alternative sources for platinum catalyst carbon support material is vital for the further development of polymer electrolyte membrane fuel cells (PEMFC).1 The support material and the method of depositing Pt nanoparticles are crucial for defining the catalytic properties of the catalyst. In this study, carbon support material, derived from coffee grounds was used in the preparation of Pt catalysts for PEMFC application. The carbon material was synthesized using ZnCl2 activated pyrolysis method2 and the Pt nanoparticles were deposited onto carbon support by two methods: using ethylene glycol3 or hydrogen4 as a reducing agent.The physical properties of the support material, as well as catalysts were analysed through thermogravimetric analysis (TGA), dynamic light scattering, X-ray diffraction (XRD), N2 sorption analysis and high-resolution scanning electron microscopy (HR-SEM) methods. The electrochemical activity, as well as the electrochemically active surface area (ECSA) of the catalysts were determined in a completed PEMFC. The properties and performance of catalysts synthesised were compared with the catalyst which was deposited onto commercial carbon (Ketjenblack, EC-300J).TGA displayed that carbon derived from coffee grounds contained 6.9 % of impurities by mass in the form of metal oxides and that the coffee carbon Pt catalyst contained 60 wt% of Pt. The Pt crystallite size was determined through XRD and it was 1.4 nm. HR-SEM analysis displayed that the average particle size of Pt nanoparticles on the coffee carbon catalyst was 4.7±2.5 nm. Results from N2 sorption analysis showed that all materials were micro-mesoporous, with coffee ground carbon having a specific surface area of 590 m2 g-1. The coffee carbon Pt catalyst produced smaller results of 370 m2 g-1 compared to the carbon support, due to the Pt nanoparticles depositing in the micropores, however still had a larger specific surface area than the commercial carbon catalyst with a specific surface area of 300 m2 g-1.Catalysts deposited on coffee ground carbon produced comparable electrochemical results to catalysts deposited on commercially available carbon. The coffee carbon catalyst produced a higher ECSA of 64 mPt 2 gPt -1, compared to the commercial carbon catalyst with an ECSA of 51 mPt 2 gPt -1. The current density of the Pt catalyst deposited onto coffee carbon was 0.68 A cm-2 at 670 mV, whilst in the same conditions commercial carbon peaked at 0.70 A cm-2. Both coffee and commercial carbon Pt catalysts produced similar power density maximums with the coffee Pt catalyst producing 0.56 W cm-2 and the commercial Pt catalyst producing 0.60 W cm-2.Physical and electrochemical characterizations displayed that higher ECSA values were strongly correlated to smaller Pt crystallite size. Other techniques to increase fuel cell performance were also experimented with, such as covering the gas diffusion layer with catalyst instead of Nafion membrane and adding additional Nafion layers, with both methods producing promising results.This study displays that there is a lot of potential in improving the catalytic performance of Pt catalysts by depositing on support materials derived from alternative sources. The methods of boosting PEMFC performance could be further investigated for catalysts deposited on different carbon supports. Acknowledgements This work was supported by the EU through the European Regional Development Fund TK141 “Advanced materials and high-technology devices for energy recuperation systems” (2014-2020.4.01.15-0011), Personal Research Grant PRG676 and by private limited company AuVe Tech LLTKT20148 “Production of Polymer Electrolyte Membrane Fuel Cells”. The SEM measurements were conducted using the NAMUR+ core facility funded by the Estonian Research Council (TT 13). References S. Shahgaldi and J. Hamelin, Carbon, 94, 705-728 (2015). M. Härmas, PhD thesis, University of Tartu, Tartu, Estonia (2020). Y. Shao, S. Zhang, R. Kou, X. Wang, C. Wang, S. Dai, V. Viswanathan, J. Liu, Y. Wang, Y. Lin, J. Power Sources 195, 1805-1811 (2010). Y. Zheng, Z. Dou, Y. Fang, M. Li, X. Wu, J. Zeng, Z. Hou, S. Liao, J. Power Sources, 306, 448-453 (2015).

Synthesis of PtRe electrocatalysts supported on mesoporous carbon for the ethanol oxidation reaction

Mesoporous carbon was synthesized to be employed as support in PtRe anodic electrocatalysts. The catalysts were prepared by the polyol method with the following Re loadings: 1, 3, 5, and 10 wt.%. The N2 adsorption-desorption isotherms, thermogravimetric measurements, temperature programmed desorption and temperature programmed reduction of the support were performed and the catalysts were structurally characterized by temperature programmed reduction, H2 chemisorption, X-ray diffraction, X-ray photoelectron spectroscopy, benzene hydrogenation reaction, and transmission electron microscopy. Furthermore, the electrochemical characterization of the catalysts was carried out by cyclic voltammetry, chronoamperometry, and CO stripping techniques. The addition of Re leads to a decrease in the CO oxidation onset potential value. The PtRe(3)/MC catalyst exhibited the best electrocatalytic activity, showing an electrochemical active surface area value of 82.5 m2 gPt−1. Moreover, the potential and anodic current values for ethanol oxidation reaction were 889 mV vs Ag/AgCl and 648 mA mgPt−1, respectively. This result is consistent with electronic effects and the smallest particle size found for this catalyst.

Insight into the Evolution of Ordered Mesoporous sp2 Carbonaceous Material Derived from Self-Assembly of a Block Copolymer.

Block-copolymer-derived ordered mesoporous carbon (OMC) materials have great potential in many applications, such as adsorption, catalysis, and energy conversions; however, their formation process and the kinetic mechanism remain unclear. Herein, a N-doped OMC (N-OMC) with sp2-bonded C atoms is developed via self-assembly of the polystyrene-block-poly(4-vinyl pyridine) block copolymer. By correlating the external morphologies with the internal chemical states, the formation process can be concluded as follows: (1) pore evolution via polystyrene domain degradation and (2) regularization and graphitization of the residual carbon via the removal of sp3 C atoms. In addition, the thickness of the N-OMC shows a power function relationship with the spin-coating rate, and the N content can be incredibly increased up to 26.34 at. % in an NH3 carbonization atmosphere. With the as-prepared N-OMC as the support for loading of the pseudo-atomic-scale Pt (Pt/N-OMC), a high electrochemical active surface area value of 99.64 m2·g-1 and a half-wave potential (E1/2) of 0.850 VRHE are achieved, showing great potential in developing single-atom electrocatalysts.

Development and performance of A-site rich perovskite-type material for enhanced oxygen evolution reaction in alkaline electrolyte

A-site rich perovskites Ba2xCoMoO6 (x = 1, 1.1, 1.2, and 1.3) were synthesised by a solid-state reaction method. The as-prepared Ba2.4CoMoO6 catalyst showed good catalytic activity towards oxygen evolution reaction (OER) activity with an overpotential of 420 mV at 10 mA cm−2, which was enhanced by 100 mV compared with that of Ba2CoMoO6, with a low Tafel slope of 79 mV dec−1, an obviously enhanced electrochemical active surface area value, and sharply improved mass and specific activities. The enhanced OER activity even surpassed the precious metal oxide IrO2 and perovskite benchmark Ba0.5Sr0.5Co0.8Fe0.2O3-δ activities.

Self-Supported Nanocolumnar Platinum Thin Film Catalysts for Oxygen Reduction Reaction

Nanocolumnar platinum thin films (Pt-TFs) were produced by high pressure sputtering (HIPS) and investigated as oxygen reduction reaction electrocatalysts for polymer electrolyte membrane fuel cells. Conventional high-density Pt-TF by low pressure sputtering was also studied for comparison. Pt-TFs were deposited on a microporous layer (MPL)-like surface composed of carbon particles in order to mimic the catalyst coated gas diffusion layer in a membrane electrode assembly (MEA). Scanning electron microscopy and transmission electron microscopy images revealed that HIPS Pt-TFs developed a cauliflower-like columnar microstructures, which originated from a shadowing effect. At high working gas pressure conditions of HIPS, sputtered Pt atoms go through several gas phase collisions, lose their directionality, and can arrive at the substrate surface at oblique angles that results in the formation of columnar islands that shadow the gaps among them from incident flux of atoms. This shadowing effect is believed to be enhanced on the rough surface of MPL-like carbon particles that leads to the formation of nano-cauliflower structures. Electrochemical characterization of the samples was performed by cyclic voltammetry and rotating disk electrode measurements on Pt-TF/MPL-like-layer/glassy-carbon-insert samples in aqueous perchloric acid electrolyte. With this approach, we also aimed to relate the catalyst performance obtained by benchtop tests directly to MEA results. Electrochemically active surface area (ECSA) of PT-TFs were found to be ranging from 10 m2/g to 19 m2/g with increasing sputter pressure, which was determined from the charge for hydrogen adsorption and desorption in the cyclic voltammograms. In addition, carbon monoxide (CO)-stripping of Pt-TF coated gas diffusion electrodes were performed in a fuel cell station and similar ECSA values were recorded (ranging from 11 to 15 m2/g). This indicated that successful mimicking of a gas diffusion electrode in an MEA can be achieved by utilizing an MPL-like substrate surface for benchtop tests in aqueous electrolyte environment as opposed to directly depositing Pt-TFs on glassy carbon inserts. Specific activity (SA) values for conventional high-density and nanocolumnar films were similar that was approximately ~600 μA/cm2, which is believed to correspond to grain sizes of >5 nm as obtained from TEM and XRD analysis. On the other hand, mass-specific (MA) activity values increased from 0.06 A/mgPt for conventional Pt-TF to 0.13 A/mgPt for HIPS Pt-TFs. Higher MA agrees with the columnar microstructure of HIPS thin films that increases the surface to volume ratio of the Pt layer that provides a better catalyst utilization compared to conventional Pt-TFs.

Porous molybdenum trioxide as a bifunctional electrocatalyst for oxygen and hydrogen evolution

Hierarchically porous molybdenum trioxide (MoO3) electrocatalyst is controllably synthesized by the facile hydrothermal method with the assistance of soft template (polyethylene oxide-polypropylene oxide-polyethylene oxide, P123). The as-prepared porous MoO3 material works as a highly efficient and bifunctional electrocatalyst for oxygen and hydrogen evolution. In oxygen evolution reaction (OER), the porous MoO3 electrode shows an overpotential reduction of 52mV compared with precious RuO2, which is also superior to that of commercial MoO3. Besides, the electrochemical active surface area (ECSA) of porous MoO3 (2.8cm2) which is three times higher than that of commercial MoO3 (0.8cm2). For hydrogen evolution reaction (HER), porous MoO3 electrode exhibits a reduction of 113mV overpotential at −10mAcm−2 compared with commercial MoO3. Furthermore, the ECSA value of porous MoO3 (1.4cm2) is four times higher than that of commercial MoO3 (0.3cm2). The bifunctional MoO3 material displays Tafel slopes of 0.44 and 0.75 times for OER and HER than those of commercial MoO3. Besides, bifunctional MoO3 material exhibits high durability for both reactions in 24h.

Amorphous Ni x Co y P-supported TiO2 nanotube arrays as an efficient hydrogen evolution reaction electrocatalyst in acidic solution.

Bimetallic phosphides have been attracting increasing attention due to their synergistic effect for improving the hydrogen evolution reaction as compared to monometallic phosphides. In this work, NiCoP modified hybrid electrodes were fabricated by a one-step electrodeposition process with TiO2 nanotube arrays (TNAs) as a carrier. X-ray diffraction, transmission electron microscopy, UV–vis diffuse reflection spectroscopy, X-ray photoelectron spectroscopy and scanning transmission electron microscopy/energy-dispersive X-ray spectroscopy were used to characterize the physiochemical properties of the samples. The electrochemical performance was investigated by cyclic voltammetry, linear sweep voltammetry, and electrochemical impedance spectroscopy. We show that after incorporating Co into Ni–P, the resulting NixCoyP/TNAs present enhanced electrocatalytic activity due to the improved electron transfer and increased electrochemically active surface area (ECSA). In 0.5 mol L−1 H2SO4 electrolyte, the NixCoyP/TNAs (x = 3.84, y = 0.78) demonstrated an ECSA value of 52.1 mF cm−2, which is 3.8 times that of Ni–P/TNAs (13.7 mF cm−2). In a two-electrode system with a Pt sheet as the anode, the NixCoyP/TNAs presented a bath voltage of 1.92 V at 100 mA cm−2, which is an improvment of 79% over that of 1.07 V at 10 mA cm−2.

Novel nanorod Ti0·7Ir0·3O2 prepared by facile hydrothermal process: A promising non-carbon support for Pt in PEMFCs

Late transition metal doped TiO2 has been exploited for generating efficient catalyst support by enhancing electrical conductivity and modifying properties of TiO2. The Ti0·7Ir0·3O2 nanorod (NRs), a novel catalyst support for Pt nanoparticles, was prepared for the first time via single-step hydrothermal process at low temperature using IrCl3·3H2O and TiCl4 as starting materials. We found that the Ti0·7Ir0·3O2 NRs with 70–80 nm in length and 25–30 nm in width is successful prepared at 210 °C for 12 h without utilizing surfactants or stabilizers. In addition, the Ti0·7Ir0·3O2 NRs was presented principally as a single-phase solid with the TiO2 is in the rutile form with high crystallinity without using further treatment after synthesis. More importantly, we found that the Ti0·7Ir0·3O2 NRs possesses high electrical conductivity (0.028 S cm−1) dealing the intrinsically non-conducted drawback of TiO2. The Pt nanoparticles were then deposited on the support of Ti0·7Ir0·3O2 NRs via chemical reduction method. The properties of 20 wt % Pt/Ti0·7Ir0·3O2 NRs electrocatalyst were characterized by X-ray diffraction (XRD), Transmission electron microscopy (TEM), the cyclic voltammetry (CV). The uniformly distributed small Pt nanoparticles (3–4 nm diameter) were well adhered to the Ti0·7Ir0·3O2 NRs. The electrochemically active surface area (ECSA) of 20 wt % Pt/Ti0·7Ir0·3O2 NRs was higher than that of the commercial 20 wt % Pt/C (E-TEK) due to the small size and good dispersion of Pt nanoparticles on the surface of Ti0·7Ir0·3O2 NRs. Moreover, the ECSA value of the Pt/Ti0·7Ir0·3O2 NRs retained up to 88% after 2000 cycles of cyclic voltammetry, suggesting the high stability of catalyst resulted from strong metal support interaction (SMSI) of Titania-based materials with the noble metals. More importantly, the onset potential of Pt/Ti0·7Ir0·3O2 NRs catalyst towards oxygen reduction reaction is more positive (∼80 mV) compared to commercial Pt/C, indicating the high catalytic activity of the Pt/Ti0·7Ir0·3O2 NRs catalyst. The results of this research suggested that novel Ti0·7Ir0·3O2 NRs could be applied as promising robust non-carbon support for Pt. This research also creates a preliminary step for investigating systematically promising Iridium doped Titania materials.

Electrochemical and Chemical Synthesis of Platinum Hierarchical Nanostructures Using Bicontinuous Microemulsions

Fabrication of hierarchical noble metal nanostructures is of interest due to the unique structural arrangement of nanoscale building blocks: nanocrystals or nanoparticles, composition and size are important in taking the physical and chemical usefulness of metal nanomaterials to a macroscopic scale. Various methods have been employed in achieving nanostructures of unique morphological arrangement. Amongst which are chemical and electrochemical reduction, or electrodeposition. In this research, platinum hierarchical nanostructures (PtHNs) were prepared using bicontinuous microemulsion (BC-ME) as soft templates. The PtHNs were synthesized using electrodeposition method as well as chemical reduction method. PtHNs was electrodeposited on Au macroelectrode from the bicontinuous microemulsion as well as from aqueous solution of chloroplatinic acid. Linear sweep voltammetry and chronopotentiometry was employed to achieve the deposition of Pt0 from the aqueous and bicontinuous platinum microemulsion electrolytic media. In the chemical method, sodium borohydride was used to reduce the hexachloroplatinic ions present in the bicontinuous microemulsion to platinum nanomaterial. In using bicontinuous microemulsions as a soft templates, the channels serve as continuous vessels for the converging growth of structures, which are dimensionally restricted by the diameter of the channels. PtHNs were characterized by SEM, EDX, TEM, XRD and cyclic voltammetry. The SEM images obtained, showed that the structure was unique, hierarchical with a regular morphology. From the SEM images, it was observed that the chemically synthesized PtHNs, were made up of interconnected spheres and self-assembled nanoneedles forming a nanocoral shape. The PtHNs XRD patterns confirm the polycrystalline nature of the platinum nanomaterials. Cyclic voltammetry (CV) of PtHNs synthesized through chemical reduction and electrodeposition method was conducted in degassed 0.5 M H2SO4. CV measurements (current voltage curve) essentially provide information about the electrochemical reactions that occurs on a working electrode surface. Electrochemical active surface area (ECSA) values of 35.1 m2/g and 20.9 m2/g were recorded for PtHNs synthesized by chemical reduction of 2% and 4% water soluble Pt precursor respectively. The highest ECSA value of 35.1 m2/g recorded from the PtHNs is higher than Pt dendritic tubes (23.3 m2/g) reported by Zhang et al. [1]. This clearly shows that the catalytic ability of the nanostructures synthesized in this work are highly desirable. The electrochemical surface area (ECSA) of 14.6 m2/g was recorded for the PtHNs electrodeposited on Au macroelectrode from aqueous Pt electrolyte while 12.2 m2/g was obtained when bicontinuous microemulsion of Pt was used as the platinum electrodeposition media. The PtHNs synthesized by the chemical method exhibited larger surface area than the platinum nanomaterial synthesized by electrodeposition. Broadly, this report presents a novel study of different synthetic methods for obtaining platinum nanostructures demonstrating the “template effect” of bicontinuous microemulsions towards the synthesis of metallic superstructures. Reference [1] Zhang, G., Sun, S., Cai, M., Zhang, Y., Li, R., and Sun, X., 2013, Porous dendritic platinum nanotubes with extremely high activity and stability for oxygen reduction reaction: Sci. Rep., 3, 1526. Figure 1

Conformal deposition of Pt on titania nanotubes to produce a bio-electrode for neuro-stimulating applications

We develop an alkaline electroless bath for deposition of a conformal Pt layer 40 nm thick on titania nanotubes 800 nm long. The charge storage capacity (CSC) and electrochemically active surface area (ECSA) of this Pt-coated titania nanotube array have been studied to evaluate its potential as a bio-electrode for implantable bio-electronic devices. Images from electron microscopes confirm the formation of a uniform Pt film on both the internal and external surfaces of the nanotubes. The X-ray diffraction pattern indicates a preferred (111) orientation. Analysis from X-ray absorption spectroscopy on the plating bath suggests a reduction sequence of Pt4+ → Pt2+ → Pt. The Pt-coated titania nanotube array has large CSC and ECSA values, attributed to the hollow tubular nanostructure with a conformal Pt coating.

Effective size-controlled synthesis and electrochemical characterization of ordered Pt nanopattern arrays from self-assembling block copolymer template

This work offers an effective size-controlled synthesis of platinum nanoparticle (Pt NP) arrays for electrocatalyst through self-assembled nanopatterns of block copolymers on titanium (Ti) wafers. Size, spacing and uniformity of Pt NP with loading of Pt to a minimum were investigated to be controlled and adjusted in order to improve the electrochemically active surface area (ECSA) and ECSA stability, and Pt concentration in copolymer/chloroplatinic acid (H2PtCl6) solution was verified to be one of the most important factors to control the arrays’ structure. In our case, the Pt NPs with predictable size of 5–16.5 nm could be obtained when the Pt concentration is larger than 0.05 mg ml−1, which the dominant diameter is proved to be proportional to one-third power of the Pt concentration according to the linear relation of templates’ Pt/N mass ratio versus Pt concentration, and the Pt NPs remain highly ordered arrays with predictable spacing when the Pt concentration is larger than 0.125 mg ml−1. Decrease in Pt concentration from 2 to 0.125 mg ml−1 is an effective method to improve the ECSA and durability simultaneously. The Pt NP arrays exhibit not only a remarkable initial ECSA value of 106.2 m2 g−1, but also a pseudo-zero particle aggregation possibility during 3000-cycle voltammetry, which is attributed to the high Pt NP dispersion and the ordered arrays that improve the Pt utilization and lower the possibility of aggregation.

Evaluation of the Durable Performance of the Pt/Marimo Carbon Catalyst in PEFC

1.IntroductionImproving the durability of polymer electrolyte fuel cell (PEFC) has been a challenge. The deterioration of carbon can be cited as a cause of reduced durability. Carbon black is considered to be easily oxidized and deteriorated, because of the low crystallinity of amorphous carbon. We applies Marimo carbon, a new carbon material comprising entangled carbon fibers.(1) There is a cavity of several hundred nanometers in Marimo carbon. The diffusion of water and fuel gas is expected to be improved compared with conventional carbon catalysts. The fibers of Marimo carbon are arranged in a cup stack structure. It is possible to easily loading platinum. We study an improvement in the power generation performance of PEFCs using Marimo carbon.(2) In this study, an accelerated degradation test of a catalyst employing Marimo carbon was performed using electrochemical measurements to evaluate changes in catalyst performance. 2.ExperimentalMarimo carbon was synthesized by chemical vapor deposition. The loading of Marimo carbon with Pt was performed using the nano colloid solution method.(3) Marimo carbon and NaOH were added to distilled water, and the mixture was stirred during ultrasonication. Citric acid and chloroplatinic acid were then added, and the mixture was stirred during ultrasonication. Next, sodium borohydride was added as a reducing agent, and the mixture was stirred during ultrasonication. Finally, centrifugation and drying were performed to prepare a Pt/Marimo carbon. Accelerated degradation tests were performed with a scan speed of 500 mV s-1, and a potential range of 1.0 - 1.5 V vs. RHE. After each test cycle, the catalyst performance was evaluated by cyclic voltammetry (CV) and linear sweep voltammetry (LSV) with a rotating ring disc electrode (RRDE). Catalyst performance was also evaluated by I-V testing using a single cell. For comparison, similar measurements were performed using a Pt/carbon black catalyst. 3.Results and discussionLSV results before and after the accelerated degradation test are presented. The number of cycles ranged from 0 to 7200, and RRDE rotation speed was 3600 rpm. In the case of carbon black, the value of the diffusion limited current density after 7200 cycles was confirmed to become small. However, in the case of Marimo carbon, the value of the diffusion limited current density was not changed even after 7200 cycles. The lowering of the catalytic activity due to the oxidation of carbon or elimination of the catalyst from the electrode. The resistance overvoltage was compared using Tafel plots. Prior to the accelerated degradation test, no difference was found in the slopes of both catalysts. After the accelerated degradation test, the slope for Marimo carbon did not change. However, the slope for carbon black increased, and thus, the resistance increased. The electrochemically active surface area (ECSA) was calculated CV of each accelerated degradation test. The ECSA of carbon black after 7200 cycles was reduced to 34 % of its initial value. However, Marimo carbon exhibited a high ECSA value, i.e., 80 % of its initial value after 7200 cycles and 63 % of its initial value after 23400 cycles. For Marimo carbon, there was no change in the oxidation peak of carbon, before and after the accelerated degradation test. In the case of carbon black, the oxidation peak of the carbon after the accelerated degradation test increased. From these results, carbon black is easily oxidized because of its amorphous nature and low crystallinity. Marimo carbon is not easily oxidized because Marimo carbon fibers comprise laminated graphite of higher crystallinity. The durability of Marimo carbon is higher than its of carbon black.Reference (1) K. Nakagawa et al., J. Mater. Sci. 44,221-226 (2009). (2) M. Eguchi et al., Trans. Mat. Res. Soc. Japan 38, 349-352 (2013). (3) K. Baba et al., Jpn. J. Appl. Phys. 52, 06GD06 (2013).

Accelerated Durability Tests for Pt-Nanoclusters Modified Carbide Derived Carbons Catalysts in Acidic Solution

Pt-nanoparticles activated porous carbon composite catalysts are widely used in PEMFC applications. The instability of these catalysts in harsh fuel cell working conditions is the main problem hindering the large-scale application of the fuel cell technology in commercial and energy recuperation systems [1]. Hierarchical microporous-mesoporous carbon supports C(Mo2C) were prepared from molybdenum carbide using high temperature chlorination method at different synthesis temperatures from 600 °C to 1000 °C. The Pt-nanoparticles were deposited onto the carbon support using the NaHB4method [2,3]. The X-ray diffraction, low temperature nitrogen sorption, thermogravimetric analysis (TGA) and high-resolution scanning electron microscopy (HRSEM) methods were used to characterize the catalysts materials. The medium size of the Pt-nanoparticles deposited was 4.5±0.6 nm. Corrosion of the Pt-C(Mo2C) catalysts were evaluated using an accelerated durability test (ADT) method (in oxygen (99.999%, AGA) saturated 0.5 M H2SO4 aqueous solution, from 0.58 V to 0.98 V vs SHE, at potential scan rate 50 mV s−1) [4]. The oxygen electroreduction reaction kinetics and the value of electrochemically active surface area (ECA) of the catalysts were determined after 10, 100, 1000, 3000, 10 000, 20 000 and 30 000 cycles. Electrochemical impedance spectra were obtained at 0.9 V vs SHE within ac frequencies from 0.01 to 10 000 Hz to determine the changes of the electrolyte resistance and capacitance values during the ADT. The results show that only 20% decrease in electrode capacitance and 15% increases in series resistance takes place during 30,000 potential cycles. The values of ECA were estimated in the solution saturated with nitrogen (99.999%, AGA) using the cyclic voltammetry at different potential scan rates from 30 to 1000 mV s−1. The rotating disc electrode method was used to evaluate the oxygen electroreduction kinetics in solution saturated with oxygen at rotation rate 1600 rev min−1 and at potential scan rate 20 mV s−1within the region of potentials from 1.03 V to 0.03 V vs SHE. Based on the cyclic voltammetry and rotating disk electrode data the main decrease in ECA took place during the first 1000 cycles and thereafter the ECA value stabilized. The half wave potential values depend weakly on the number of cycles (up to 30,000) measured. The content of Pt in the catalyst was determined before and after the ADT using the electrochemical dissolution of platinum from the electrode in 6 M HCl solution. The average weight percentage of Pt in different catalyst materials was 71.8±1.7. The content of Pt in the catalysts before the ADT was in a good agreement with the TGA data.

The Oxygen Reduction Reaction Activity of Pt-Co Catalysts Supported on Ta-Doped SnO2 for Polymer Electrolyte Fuel Cells

Pt and Pt alloy nanoparticles supported on carbon were applied as cathode catalysts for polymer electrolyte fuel cells (PEFCs). The carbon support is appropriate for the support due to its high electrical conductivity and high surface area, although it corrodes under high potential conditions. Carbon corrosion leads to aggregation and detachment of the catalyst and reduces the performance of the PEFC. In our group, a highly durable Pt/Ta-SnO2 catalyst was developed for the cathode of PEFCs1). In this study, we synthesized Pt-Co alloy particles supported on Ta-SnO2 (PtCo/Ta-SnO2) in order to improve the activity while maintaining high durability. The Ta-SnO2 support was synthesized by the flame spray synthesis method. Pt67Co33, Pt75Co25 and Pt80Co20 catalysts were loaded on the Ta-SnO2 by the colloidal method. After heat treatment, the crystal phases, Pt/Co content, and microstructure were evaluated by X-ray diffractometry (XRD), inductively coupled plasma mass spectrometry (ICP-MS), and scanning transmission electron microscope (STEM), respectively. The electrochemical measurements were carried out by the half-cell method using the rotating disk electrode (RDE). The electrochemically active surface area (ECA) of each catalyst was estimated by cyclic voltammetry (CV). The kinetically controlled current density (j k) and mass activity (MA k ) at 0.85 V were also estimated from linear sweep voltammetry (LSV) with Koutecky-Levich plots. The Pt:Co composition ratios (mol%) of the catalysts were 67.1:32.9(Pt67Co33), 74.6:25.4(Pt75Co25), and 80.9:19.1(Pt80Co20), which were well controlled to the desired ratios. The metal loading amounts (wt%) of the catalysts were 17.9, 17.4 and 15.4, respectively. The particle diameters (nm) were 2.7 ± 0.9, 2.8 ± 0.9, and 3.1 ± 0.8, respectively. The catalysts were highly dispersed on the support with hemispherical shape (Fig. 1 (a)). Based on the HAADF-STEM image, it was confirmed that the lattice planes of the catalyst particles were oriented parallel to those of the support. This is expected to suppress the agglomeration of the catalyst particles during startup/shutdown. The Ta-SnO2 support particles formed a fused aggregated network structure, which is able to function as a pathway for both gas diffusion and electrical conduction2). The ECA values of the catalysts, estimated from the CV, were 56.2, 70.6, and 71.3 m2g-1. The LSV values of these catalysts (1750 rpm, Fig. 1 (a)) showed the same limiting current density of that of commercial Pt/carbon black (Pt/CB, TEC10E50E). The jk values at 0.85 V (Fig. 1 (b)) showed that the Pt75Co25/Ta-SnO2 catalyst had the highest oxygen reduction reaction (ORR) activity, which reached 2.5 times larger than that for commercial Pt/CB. Acknowledgement This work was supported by funds for the SPer-FC project from the New Energy and Industrial Technology Development Organization (NEDO) of Japan. References 1) Y. Senoo, K. Taniguchi, K. Kakinuma, M. Uchida, H. Uchida, S. Deki, M. Watanabe, Electrochem. Commun. 51, 37 (2015). 2) K. Kakinuma, Y. Chino, Y. Senoo, M. Uchida, T. Kamino, H. Uchida, S. Deki, M. Watanabe, Electrochemica Acta 110, 316 (2013). Figure 1

High-Performance Pt Catalysts Supported on Polybenzimidazole-Grafted XC72 for Pemfcs

The performance of a polymer electrolyte membrane fuel cell (PEMFC) is limited by the sluggish oxygen reduction reaction (ORR) and the poor durability of the catalyst. Typically, most common catalysts are chemically deposited Pt nanoparticles on the surface of carbon nanoparticles (XC-72). A functionalized carbon support allows better dispersion of the catalyst nanoparticles, which can reduce the aggregation of metal nanoparticles and, consequently, improve the catalyst performance.1 Polybenzimidazole (PBI) is one kind of conducting polymer with excellent thermal stability and proton conductivity upon acid doping.2 Therefore, polybenzimidazole has been widely studied as proton conducting membrane in high-temperature fuel cells.3Recently, several studies have been reported the use of physically-adsorbed polybenzimidazole on carbon as the stable Pt catalyst support. In this work, covalently-functionalized carbon black XC-72 with polybenzimidazole was prepared as the catalyst support. The Pt nanoparticles were uniformed deposited onto PBI/XC-72 due to a strong interaction between PBI and Pt. Such Pt catalyst supported on the PBI grafted XC-72 will be expected to possess better proton conductivity, higher stability and better mass transport. The synthesized catalysts were characterized using rotating disk electrode (RDE) as well as membrane electrode assembly (MEA). The Cyclic voltammetry (CV) curves of PBI-grafted XC-72 supported Pt catalyst at a scan rate of 20 mV/s in N2-saturated 0.1 M HClO4 is shown in Figure 1. The electrochemical active surface area (ECSA) was calculated to be about 74 m2 Pt/gPt, which is much higher with that of commercial E-TEK Pt/C catalyst (58 m2 Pt/gPt). This high ECSA value suggests the uniform distribution of Pt on the surface of PBI/XC-72. Accelerated degradation tests (ADT) were also evaluated by monitoring the changes in electrochemical surface area during voltage cycling between 0.6 V and 1.2 V at a scan rate of 20 mV/s in N2-saturated 0.1 M HClO4. After 1000 cycles, a relatively surface area loss of more than 34% was observed in commercial catalyst. In comparison, the relative surface area loss of graphene/PBI supported Pt catalyst was only 14%. The increase in the stability of catalyst may result from the strong binding of Pt nanoparticles on PBI and the electrochemical stability of PBI-grafted XC-72. This catalyst was further compared with commercial Pt/C catalyst in MEA. It is shown that the peak power density of MEA made with was about 1400 mW/cm2, much higher than that of the commercial Pt/C catalyst (970 mW/cm2). Besides, the IR-drop of Pt/PBI-grafted XC-72 was lower than Pt/XC-72 mainly due to an enhanced proton transport. It is known that the MEA performance at high current densities is limited by the proton and mass transport. It is believed that the proton transport can be signifantly improved at the triphase interface (PBI-grafted XC-72 surfaces, Pt nanoparticles, and Nafion). Proton conducitivity tests are current being carried out in our group to elucidate our assumptions. In conclusion, the excellent electrochemical performance and better durability of PBI-grafted XC72 supported Pt catalyst illustrates the advantage of polybenzimidazole-grafted XC-72 as a catalyst support in PEMFCs. Figure 1. (a) CV curves of PBI/XC72 supported Pt catalyst between 0 and 1 V vs RHE at a scan rate of 20 mV/s in N2-saturated 0.1 M HClO4; (b) ECSA retention during ADT; and (c) MEA performance. Reference (1) Xu, F.; Wang, M.-x.; Sun, L.; Liu, Q.; Sun, H.-f.; Stach, E. A.; Xie, J. Electrochim. Acta 2013, 94, 172-181. (2) He, R.; Li, Q.; Xiao, G.; Bjerrum, N. J. Journal of Membrane Science 2003, 226, 169-184. (3) Xiao, L.; Zhang, H.; Scanlon, E.; Ramanathan, L. S.; Choe, E.-W.; Rogers, D.; Apple, T.; Benicewicz, B. C. Chem. Mater. 2005, 17, 5328-5333. Figure 1

Trimetallic (aurod-pdshell-ptcluster) catalyst used as amperometric hydrogen peroxide sensor.

Bimetallic nanostructured core-shell structures are commonly used as catalysts in a wide variety of reactions. We surmised that the addition of an additional metal would potentially allow catalytic tailoring with the possibility of an increase in activity. Here a tri-metallic catalytic structure, consisting of clustered catalytic Pt on the surface of a Pd shell supported on a rod shaped Au core was fabricated. The significance of the additional metallic component is shown by comparative electrochemically active surface area (ECSA) analysis results for the trimetallic Aurod-Pdshell-Ptcluster, bimetallic Aurod-Ptcluster and monometallic JM-Pt (used as a reference), which have respective ECSA values (cm2/mgPt) of 1883.0, 1371.7 and 879. The potential utility of the trimetallic catalysts was shown in a hydrogen peroxide sensing protocol, which showed the catalyst to have a sensitivity of 604 ìA/mMcm2 within a linear range of 0.0013–6.191 mM.

Electrochemical behavior of platinum nanoparticles on a carbon xerogel support modified with a [(trifluoromethyl)-benzenesulfonyl]imide electrolyte.

A monoprotic [(trifluoromethyl)benzenesulfonyl]imide (SI) superacid electrolyte was used to covalently modify a mesoporous carbon xerogel (CX) support via reaction of the corresponding trifluoromethyl aryl sulfonimide diazonium zwitterion with the carbon surface. Electrolyte attachment was demonstrated by elemental analysis, acid-base titration, and thermogravimetric analysis. The ion-exchange capacity of the fluoroalkyl-aryl-sulfonimide-grafted carbon xerogel (SI-CX) was ∼0.18 mequiv g(-1), as indicated by acid-base titration. Platinum nanoparticles were deposited onto the SI-grafted carbon xerogel samples by the impregnation and reduction method, and these materials were employed to fabricate polyelectrolyte membrane fuel-cell (PEMFC) electrodes by the decal transfer method. The SI-grafted carbon-xerogel-supported platinum (Pt/SI-CX) was characterized by X-ray diffraction and transmission electron microscopy to determine platinum nanoparticle size and distribution, and the findings are compared with CX-supported platinum catalyst without the grafted SI electrolyte (Pt/CX). Platinum nanoparticle sizes are consistently larger on Pt/SI-CX than on Pt/CX. The electrochemically active surface area (ESA) of platinum catalyst on the Pt/SI-CX and Pt/CX samples was measured with ex situ cyclic voltammetry (CV) using both hydrogen adsorption/desorption and carbon monoxide stripping methods and by in situ CV within membrane electrode assemblies (MEAs). The ESA values for Pt/SI-CX are consistently lower than those for Pt/CX. Some possible reasons for the behavior of samples with and without grafted SI layers and implications for the possible use of SI-grafted carbon layers in PEMFC devices are discussed.

Pt Catalysts Supported on Polybenzimidazole-Grafted Graphene for PEMFCs

The performance of a PEMFC is dominated by its catalyst performance, which depends on the size and distribution of the catalyst on the surface of the carbon support. A functionalized carbon support allows better dispersion of the catalyst nanoparticles, which can reduce the aggregation of metal nanoparticles and, consequently, improve the catalyst performance.1 Graphene is single-atomic-layer-thick carbon atoms arranged in a hexagonal lattice, which is the thinnest catalyst support for Pt catalyst nanoparticles. Graphene has many advantages over conventional carbon black catalyst support, like high electronic conductivity, surface area, mechanical strength, and excellent stability.2 All of these unique properties make the graphene as an ideal candidate for Pt catalyst support in polymer electrolyte fuel cells (PEFCs).3 In this work, covalently-functionalized graphene with polybenzimidazole (PBI) was employed as the catalyst support. The Pt nanoparticles were uniformed deposited onto graphene/PBI due to a strong interaction between PBI and Pt. Such Pt catalyst supported on the PBI grafted graphenes will benefit the MEA for PBI membrane based PEMFCs. The synthesized catalysts were characterized using rotating disk electrode (RDE) for their elctrocatalytic performance. The Cyclic voltammetry (CV) curves of graphene/PBI supported Pt catalyst at a scan rate of 20 mV/s in N2-saturated 0.1 M HClO4 is shown in Figure 1. The electrochemical active surface area (ECSA) was calculated to be about 55 m2 Pt/gPt, which is comparable with that of commercial E-TEK Pt/C catalyst (58 m2 Pt/gPt). The high ECSA value suggests the uniform distribution of Pt on the surface of graphene/PBI. Accelerated degradation tests (ADT) were also evaluated by monitoring the changes in electrochemical surface area during voltage cycling between 0.6 V and 1.2 V at a scan rate of 20 mV/s in N2-saturated 0.1 M HClO4. After 1000 cycles, a relatively surface area loss of more than 81% was observed in commercial catalyst. In comparison, the relative surface area loss of graphene/PBI supported Pt catalyst was 57%. The increase in the stability of catalyst may result from the strong binding of Pt nanoparticles onto PBI-grafted graphene. In conclusion, the high ECSA and excellent durability of graphene/PBI supported Pt catalyst illustrates the advantage of polybenzimidazole-grafted graphene as a catalyst support in PEMFCs.