Vulcan XC-72R Carbon Research Articles

Assessing the Electrochemical Performance of a Novel Low‐Cost Screen‐Printed Electrode Based on Apis mellifera Beeswax Modified with Vulcan@Chitosan Used for Acetominophen Detection

AbstractThe present work reports the development of a highly sensitive electrochemical platform, constructed using screen printed electrode based on Apis mellifera beeswax (SPWE) – employed as substrate, and its application for acetaminophen (AC) detection. The sensor was produced using graphite ink and varnish glass solubilized in acetone. The SPWE was modified with a dispersion of chitosan (0.5% m/v) − functionalized Vulcan XC72R carbon black (Vulcan@Chitosan). Electrochemical characterization was performed using cyclic voltammetry (−0.7 to +0.8 V vs. pseudo‐graphite) and chronoamperometry in 0.1 mol L−1 KCl in the presence of 1.0 mmol L−1 [Fe(CN)6]3−/[Fe(CN)6]4−. Through the application of differential pulse voltammetry (DPV) using 0.1 mol L−1 PBS at pH 6.5, the proposed SPWE/Vulcan@Chitosan sensor was found to exhibit significant improvements in current response relative to the AC electrochemical detection. The sensor exhibited linear dynamic range of 0.05 to 4.0 μmol L−1 (n= 3), with R2= 0.992 and theorical LOD of 0.013 μmol L−1 (RSD= 3.80%). The AC detection was conducted in real matrices of river water, synthetic urine and synthetic saliva using the DPV technique yielded a mean recovery rate of 103% (RSD= 3.52%), exhibiting a high degree of accuracy. The SPWE/Vulcan@Chitosan electrochemical platform demonstrated high stability, good reproducibility and satisfactory repeatability; the current responses were not affected by the reutilization of the beeswax substrate for the production of new electrode. The findings of this study show that the proposed modified electrode is a simple, low‐cost sensing device which has proven to be highly efficient when applied for the AC detection in different matrices.

Fabrication of highly conductive VXC-72R carbon nanoparticles decorated Zr (IV)-based metal-organic framework for highly sensitive detection of methyl parathion

A simple and efficient ultrasonic-assisted strategy was used to prepare the nanocomposite of Vulcan XC-72R carbon (VXC-72R) nanoparticles and Zr(IV)-based metal-organic framework (UIO-66) nanoparticles. For the multifunctional VXC-72R@UIO-66 nanocomposite, VXC-72R nanoparticles possessed good conductivity property and good dispersion, which were conductive to form the interconnected carbon conductive channels; UIO-66 nanoparticles could improve the accumulation ability of methyl parathion (MP) because of the high affinity of Zr-O groups with phosphoric groups. Moreover, the introduction of VXC-72R nanoparticles could effectively make up the conductivity property of UIO-66 nanoparticles. The VXC-72R@UIO-66/GCE sensor presented good MP detection performance with limit of detection (LOD) of 1.35 nM (Linear MP concentration range: 0.01–10 μM). When used for the detection of MP in juice samples, the VXC-72R@UIO-66/GCE sensor showed acceptable recoveries of 96.00–104.67 %.

Rotating Disk Slurry Electrodeposition of Trimetallic Nickel-Cobalt-Iron Nanoparticles Electrocatalyst on Vulcan Xc-72R for the Oxygen Reduction Reaction in Alkaline Media

Although platinum and platinum group metals (PGMs) catalysts are the most efficient for oxygen reduction reaction, the cost and scarcity of the metals are the reason to look for alternative electrocatalysts. Transition metals, such as cobalt, iron, and nickel, have shown promise as an alternative catalyst to oxygen reduction reactions (ORR). In this work, we electrochemically synthesized nickel-cobalt-iron trimetallic alloy nanoparticles dispersed on carbon Vulcan using Rotating Disk Slurry Electrodeposition (RoDSE). This technique is an energy-efficient green method to synthesize well-dispersed catalysts on carbon and oxide supports for various applications including the oxygen reduction reaction (ORR) for fuel cell applications. Cobalt-nickel iron nanoparticles have been well dispersed in 20 mg carbon Vulcan XC-72R using a negative potential (-1.05V vs Ag/AgCl-sat KCl) in a saturated Argon environment. The electrodeposition potential was obtained from cyclic voltammetry analysis of the metal salts in 0.1m KClO4 solution with an electrochemically cleaned glassy carbon electrode. The starting material precursors were iron chloride, nickel acetate, and cobalt acetate in 0.1 M KClO4 aqueous solution. A 500 micromolar metal salt solution aliquot was added for the electrodeposition every 20 minutes, with a total of 12 aliquots.Compared with commercially available 20% Pt/Vulcan, the synthesized catalyst shows comparable mass activity and durability with an onset potential of 0.78V vs RHE(@0.01mA/cm2), limiting current density of 5.56mA/cm2 and half wave potential of 0.66V vs RHE.The X-ray diffraction (XRD) studies and transmission electron microscopy showed that trimetallic nanoparticles are formed and deposited on the carbon Vulcan support. Moreover, scanning electron microscopy, X-ray fluorescence studies, and transmission emission microscopy show the presence of trimetallic nanoparticles. The RDE and RRDE studies show that the synthesized material is active and may lead to a good and inexpensive catalyst for ORR.

Lithium-Mediated Nitrogen Reduction in a Flow Electrolyzer Cell Using Gas Diffusion Electrodes with Carbon-Based Electrocatalysts

Due to the sluggish kinetics in activating the chemically stable dinitrogen (N2) and the competing hydrogen evolution reaction in aqueous media, recent attention in the field of direct ammonia (NH3) electrosynthesis has been increasingly drawn to the lithium-mediated N2 reduction reaction (LNRR) in tetrahydrofuran (THF)-based non-aqueous electrolyte. In particular, near 100% faradaic efficiency (FE) and/or a current density (j) of 100 mA cm-2 has been demonstrated with unique electrolyte (proton-shuttle additive) and/or electrode designs (expansive electrochemical surface area) in single-compartment cells at elevated N2 pressure (5 – 20 bar).[1,2]A submerged electrode leads to electrolyte flooding and restricts to N2 mass transfer to the electrode surface where electrodeposited Li as an electron mediator is available.[3] However, flow cell electrolyzers containing gas-diffusion electrodes can improve this technology to practical relevance, which features the LNRR on the cathode and hydrogen oxidation reaction (HOR) on the anode. Differing from single-compartment cells, the HOR supplements the ethanol additive (<1 vol%) as the proton source, which not only prevents the oxidative electrolyte degradation but also reduces the energy consumption due to a lower equilibrium anode potential (E0 = 0 VRHE). Gas-diffusion electrodes (GDEs) are used in the few LNRR studies with flow cell configurations, which are prepared by electro- or electroless depositing electrocatalysts (e.g., Pt [4] or PtAu alloy [5]) onto a porous substrate.In this work, carbon-based electrocatalysts (Vulcan XC72R carbon black, battery-grade conductive carbon SUPER C45, and graphitic carbon SFG6L) as low-cost alternatives to previously studied precious metals are assessed for their LNRR performance in flow cells using an HOR anode. In comparison to Vulcan-supported Pt, XC72R and C45 can obtain similar NH3 production rates (rNH3 )and FE at the same . Continuous LNRR at -3 mA cm-2 was demonstrated with linearly increased NH3 production for over 8 h without catalyst layer detachment, which was also verified with open circuit and Ar control experiments (Fig. 1). By presenting the LNRR activity with GDEs spray-coated with carbon-based electrocatalysts, opportunities for future research are suggested, such as novel carbon materials and porous substrates other than SSC for facile N2 mass transfer and Li deposition.

Fabrication of β-cyclodextrin decorated Vulcan XC-72R carbon nanoparticles for electrochemical sensing analysis of methyl parathion

ABSTRACT In this work, we prepared a sensing platform by utilising the nanocomposite of Vulcan XC-72 R carbon nanoparticles and β-cyclodextrin (β-CD/VXC-72 R) to decorate glassy carbon electrode for detecting MP sensitively. For the β-CD/VXC-72 R composite, VXC-72 R possesses high electroactive area and exceptional electrical conductivity, which is conducive to the generation of interwoven carbon conductive structures. β-CD can effectually facilitate the homogeneous dispersion of VXC-72 R and also enhance the accumulate of MP at the sensing interface. Furthermore, the presence of VXC-72 R compensates for the inherent inferior conductivity of β-CD. The collaborative interaction of VXC-72 R and β-CD enabled the prepared sensor to obtain excellent MP detection properties with a low limit of detection (LOD) of 6.7 nM in MP concentration range of 0.1–10 μM. In addition, the β-CD/VXC-72 R modified glassy carbon electrode (GCE) displayed satisfactory repeatability and reproducibility.

Mn3O4/Vulcan XC-72R composites: preparation, physicochemical characterization and electrochemical study for purification of organic contaminants

The microwave-assisted technique was applied to the preparation of composites from manganese(II) acetate and Carbon-supported (Vulcan XC-72R). Composites were prepared by chemical deposition of manganese(II) acetate nanoparticles onto Vulcan XC-72R carbon black (catalytic mass) using microwave irradiation. The new composites were physicochemically characterized by Energy-dispersive X-ray spectroscopy (EDX) with scanning electron microscopy (SEM), BET surface area, pore size distribution and X-ray diffraction (XRD). BET analysis of Mn3O4/Vulcan XC-72R composites obtained by alkali method has shown specific surface area of 1135 m2/g. Novel composites were electrochemically studied as catalysts for the remediation of organic contaminants in industrial waters. From novel catalytic mass, double-sided coated electrodes on a Nickel mesh conductor were made by pressing and heating at 250 °C. The prepared electrodes have geometric area of 2.5 cm2. The electrodes were fabricated and studied regarding the amount of catalyst and 35 % Teflonized Vulcan XC-72R. Electrochemical studies were carried out for phenol oxidation in an aqueous solution in model electrolyte: phenol solution 200 mg.L-1 and supporting electrolyte: 18 g.L-1 NaCl and 2.6 mg.L-1 Na2SO4.

Cu@PtRu Core–Shell Nanostructured Electrocatalysts Anchored on Reduced Graphene Oxide toward Methanol Oxidation

This work reports the influence of a reduced graphene oxide (rGO) support on the catalytic performance of Cu@PtRu/rGO electrocatalysts toward methanol oxidation in an acidic medium. These electrocatalysts are synthesized via a two-step reduction method; the first step utilizes ethylene glycol for the reduction of Cu2+ ions, forming Cu/rGO. In the second step, spontaneous redox reactions take place, in a process known as galvanic displacement, where the Pt2+ and Ru3+ species are reduced to form PtRu layers, and the copper is partially oxidized to the solution. Then, the Cu@PtRu/rGO core–shell is produced, comprising Cu in the inner structure (core) and PtRu on the outer part (shell). To compare the catalytic performance of the prepared nanocatalysts (NCs), Pt/C, PtRu/C, and Cu@PtRu/C are also synthesized on Vulcan XC-72R carbon. All catalysts are characterized via X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Cyclic voltammetry (CV) and chronoamperometry (CA) are employed to measure the electrochemical performance. The core–shell/rGO combination is superior in catalytic activity to the traditional Pt/C, PtRu/C, and Cu@PtRu/C catalysts for the methanol oxidation reaction. These results suggest that Cu@PtRu/rGO exhibits a high bulk activity for methanol electrooxidation, a high stability, and a high tolerance to CO poisoning, meaning it is possible to reduce the platinum loading in proton-exchange membrane fuel cells (PEMFCs).

The Effect of Heteroatom-Doped Graphene Supports on the PtNPs Electrocatalytic Activity for ORR

There has been a global shift in energy production emphasizing the reduction of fossil fuels by the augmentation of more renewable energy. Proton-exchange membrane fuel cells (PEMFC) and anion-exchange membrane fuel cells (AEMFC) can mitigate a need for fossil fuels and provide an alternative route of hydrogen-based energy production. Fuel cells utilize a catalyst at both the cathode and anode to increase the overall kinetics of the redox reactions and enhance the cell performance.1 Current fuel cell technology employs a platinum based catalyst due to its efficiency and robust performance in both alkaline and acidic environments.1,2 The drawbacks associated with Pt-based catalysts are centered around its economic viability and its affinity towards surface poisoning.1 A catalyst using platinum nanoparticles (PtNPs) loaded onto a graphene support can address some of the aforementioned drawbacks.1 To maximize the electrocatalytic activity of the PtNPs – all aspects of the PtNPs catalyst must be optimized, which includes the optimization of the support material. The effect that the different commercially available heteroatom-doped graphene had on the activity of the PtNPs was investigated during this study. The PtNPs were synthesized using the citrate method, which produces ≤ 5 nm size particles. Our study confirmed that the choice of doped graphene support has an effect on the overall activity of PtNPs. The results were confirmed via a comparison with PtNPs supported on Vulcan XC-72R carbon. All Pt catalysts supported on the doped graphene showed an improvement in the oxygen reduction reaction (ORR) half-wave potentials (E 1/2) over PtNPs on Vulcan XC-72R carbon (Fig. 1A); with the nitrogen-doped graphene exhibiting the greatest improvements in the half-wave potential with the E 1/2 value of 0.85 V vs. RHE as compared to the 0.77 V of the Pt/C. A comparison of the Tafel slopes (Fig. 1B) confirmed that the transfer of the first electron was the rate-determining step for all of the Pt catalysts supported on doped graphene as all Tafel slopes were around -120 mV per decade. This has been confirmed in literature with Pt on various carbon supports.2 Figure 1. A) Comparison of RDE polarization curves for oxygen reduction on Pt/NGr (pink), Pt/SGr (green) and Pt/N-PGr (blue) with Pt/C (black) at 1900 rpm in a O2-saturated 0.1 M HClO4 solution (v= 10 mV s−1). B) Mass transfer corrected Tafel plots derived from A

Electrochemical advanced oxidation processes using PbO2 anode and H2O2 electrosynthesis cathode for wastewater treatment

The assessments of a novel electrochemical advanced oxidation process are presented, where PbO2 anode and H2O2 electrosynthesis cathode are simultaneously used in one system. The anode is β-PbO2 coated on a titanium substrate. The cathode is fabricated by rolling the activated Vulcan XC-72R carbon catalyst and PTFE binder on the titanium current collector as the catalyst layer and water-repellent layer, according to different carbon/PTFE ratios. Different electrolysers are used to evaluate the synergistic contributions of the PbO2 anode and H2O2 generated cathode on the pollutant degradation process. The contributions of both direct anodic oxidation and indirect oxidation can be observed. The synergy of the PbO2 anode and H2O2 on-site generated cathode can significantly enhance the oxidation ability and COD removal. Almost all COD in the real pesticide wastewater and dye wastewater can be removed using a PbO2-H2O2 batch electrolyser, which is run at a cell voltage of 3.0 V and at room temperature. The reaction mechanisms in both chloride-containing and sulfate-containing wastewater are discussed particularly.

Design of Pt-Sn-Zn Nanomaterials for Successful Methanol Electrooxidation Reaction.

This work highlights the potential for the synthesis of new PtSnZn catalysts with enhanced efficiency and durability for methanol oxidation reaction (MOR) in low-temperature fuel cells. In this research, PtZn and PtSnZn nanoparticles deposited on high surface area Vulcan XC-72R Carbon support were created by a microwave-assisted polyol method. The electrochemical performances of synthesized catalysts were analyzed by cyclic voltammetry and by the electrooxidation of adsorbed CO and the chronoamperometric method. The physicochemical properties of obtained catalysts were characterized by transmission electron microscopy (TEM), thermogravimetric (TGA) analysis, energy dispersive spectroscopy (EDS) and by X-ray diffraction (XRD). The obtained findings showed the successful synthesis of platinum-based catalysts. It was established that PtSnZn/C and PtZn/C catalysts have high electrocatalytic performance in methanol oxidation reactions. Catalysts stability tests were obtained by chronoamperometry. Stability tests also confirmed decreased poisoning and indicated improved stability and better tolerance to CO-like intermediate species. According to activity and stability measurements, the PtSnZn/C catalyst possesses the best electrochemical properties for the methanol oxidation reaction. The observed great electrocatalytic activity in the methanol oxidation reaction of synthesized catalysts can be attributed to the beneficial effects of microwave synthesis and the well-balanced addition of alloying metals in PtSnZn/C catalysts.

Solubility Considerations for Cloud Condensation Nuclei (CCN) Activity Analysis of Pure and Mixed Black Carbon Species

Black carbon (BC) is an aerosol that is released into the atmosphere due to the incomplete burning of biomass and can affect the climate directly or indirectly. BC commonly mixes with other primary or secondary aerosols to undergo aging, thereby changing its radiative properties and cloud condensation nuclei (CCN) activity. The composition of aged BC species in the atmosphere is difficult to measure with high confidence, so their associated CCN activity can be uncertain. In this work, the CCN activity analysis of BC was performed using laboratory measurements of proxy aged BC species. Vulcan XC72R carbon black was used as the representative of BC, and three structural isomers of benzenedicarboxylic acid─phthalic acid (PTA), isophthalic acid (IPTA), and terephthalic acid (TPTA)─were mixed with BC to generate three different proxies of aged BC species. Most studies related to CCN activity analysis of BC aerosols use the traditional Köhler theory or an adsorption theory (such as the Frenkel-Halsey-Hill adsorption theory). PTA, IPTA, and TPTA fall in the sparingly water-soluble range and therefore do not fully obey either of the aforementioned theories. Consequently, a novel hybrid activity model (HAM) was used for the CCN activity analysis of the BC mixtures studied in this work. HAM combines the features of adsorption theory via the adsorption isotherm with the features of Köhler theory by incorporating solubility partitioning. The results in this work showed that HAM improves the representation of CCN activity of pure and mixed BC aerosol species with high certainty, evident from generally better goodness of fit, R2 > 0.9. This work implies that the hygroscopicity parameterization based on HAM captures the size-dependent variability in the CCN activity of the pure and aged BC species.

Autonomous electrochemical system for ammonia oxidation reaction measurements at the International Space Station

An autonomous electrochemical system prototype for ammonia oxidation reaction (AOR) measurements was efficiently done inside a 4'' x 4'' x 8'' 2U Nanoracks module at the International Space Station (ISS). This device, the Ammonia Electrooxidation Lab at the ISS (AELISS), included an autonomous electrochemical system that complied with NASA ISS nondisclosure agreements, power, safety, security, size constrain, and material compatibility established for space missions. The integrated autonomous electrochemical system was tested on-ground and deployed to the International Space Station as a “proof-of-concept” ammonia oxidation reaction testing space device. Here are discussed the results of cyclic voltammetry and chronoamperometry measurements done at the ISS with a commercially available channel flow-cell with eight screen-printed electrodes, including Ag quasi-reference (Ag QRE) and carbon counter electrodes. Pt nanocubes in Carbon Vulcan XC-72R were used as the catalyst for the AOR and 2 μL drop of Pt nanocubes/ Carbon Vulcan XC-72R, 20 wt%, ink was placed on the carbon working electrodes and allowed to dry in air. After the AELISS was prepared for launch to the ISS, a 4 days delayed (2 days in the space vehicle Antares and 2 days space transit to the ISS) cause a slight shift on the Ag QRE potential. Nevertheless, the AOR cyclic voltametric peak was observed in the ISS and showed ca. 70% current density decrease due to the buoyancy effect in agreement with previous microgravity experiments done at the zero-g aircraft.

Effects of H2/O2 and H2/O3 gases on PtMo/C cathode PEMFCs performance operating at different temperatures

This study reported the activity of catalysts synthesized from platinum and molybdenum alloys in different atomic ratios and used as cathode electrocatalysts in the PEMFC. The structural properties of PtMo/C and Pt/C catalysts were analyzed by XRD analysis. The composition and distribution of these alloys in Vulcan XC-72R Carbon were determined by SEM and EDX techniques. CV studies assessed electrochemical properties such as ORR and ECSA activity. The performance of PEMFC cathodes that supplied pure hydrogen and oxygen was examined using polarization curves at different temperatures. Another way to improve the cathodic reaction is to use ozone as a potent oxidizing agent. It was measured that the OCV of the H2/O3 PEM fuel cell was 1.60 V, much greater than the open circuit voltage of the traditional H2/O2 PEM fuel cell. The PtMo/C catalyst achieved its highest power density of 137 mWcm−2 at 70 °C, 128 mWcm−2 at 60 °C, 101 mWcm−2 at 50 °C, and 85 mWcm−2 at 40 °C when exposed to H2/O2. As the temperature of the cell was raised, it was seen that the catalyst's catalytic activity increased.The maximum power density was detected to be inversely related to the rise in temperature when ozone was used. At low current densities, however, ozone was observed to greatly boost activation polarization.

A novel approach to pulsed laser deposition of platinum catalyst on carbon particles for use in polymer electrolyte membrane fuel cells.

The research undertaken aimed to develop an efficient Pt-based catalyst for polymer electrolyte membrane fuel cells (PEMFCs) by using a cost-effective and efficient physical method to deposit platinum nanoparticles (PtNPs) on carbon supports directly from the platinum target. The method developed avoids the chemical functionalization of the carbon substrate and the chemical synthesis of PtNPs during catalyst fabrication. Platinum was deposited on carbon particles at room temperature using a pulsed laser deposition (PLD) system equipped with an ArF excimer laser (λ = 193 nm). The uniform deposition of PtNPs on carbon supports was achieved thanks to a specially designed electromechanical system that mixed the carbon support particles during platinum deposition. In the studies, Vulcan XC-72R carbon black powder, a popular material used as support in the anodes and cathodes of PEMFCs, and a porous carbon material with a high degree of graphitization were used as carbon supports. The best electrochemical measurement results were obtained for Pt deposited on Vulcan XC-72R. The peak power density measured for this material in a membrane electrode assembly (MEA) of a PEMFC (fed with H2/Air) was 0.41 W/cm2, which is a good result compared to 0.57 W/cm2 obtained for commercial 20% Pt Vulcan XC-72R. This result was achieved with three times less Pt catalyst on the carbon support compared to the commercial catalyst, which means that a higher catalyst utilization factor was achieved.

Synthesis of a carbon-wrapped microsphere MoO2/Mo2C heterojunction as an efficient electrocatalyst for the oxygen reduction reaction and the hydrogen evolution reaction.

The development of non-noble metal catalysts for the optimization of conversion and storage devices is an important research topic. Hence, the microsphere MoO2/Mo2C/C heterojunction composites, which play an important role in the oxygen reduction reaction (ORR) and the hydrogen evolution reaction (HER), were synthesized using the solvothermal-sintering method. The results revealed that the as-prepared composite exhibited better ORR and HER catalytic performances than those of MoO2/Mo2C and Vulcan XC-72R (carbon black), and approaching that of commercial Pt/C. At the same time, it has a superior methanol tolerance and electrochemical stability than that of the commercial Pt/C. The excellent performance may be attributed to the synergistic effect of the MoO2/Mo2C heterostructure, highly conductive Vulcan XC-72R, and oxygen vacancies (Ov). This research offers new insights into the design and synthesis of cost-effective, environmentally friendly heterojunction composite catalysts used as a high-performance cathode material in fuel cells and water splitting.

Physical and Electrochemical Effect of Bimetallic Pd–Mo Nanoalloys Supported on Vulcan XC-72R Carbon as Cathode Catalysts for Proton Exchange Membrane Fuel Cell

Physical and Electrochemical Effect of Bimetallic Pd–Mo Nanoalloys Supported on Vulcan XC-72R Carbon as Cathode Catalysts for Proton Exchange Membrane Fuel Cell

Electrochemical production of extremely high concentrations of hydrogen peroxide in discontinuous processes

This work reports the development and application of a gas diffusion electrode based on Printex L6 carbon for the production of high concentrations of hydrogen peroxide (H2O2) using a flow-by electrochemical reactor in discontinuous operation mode. With the application of current densities ranging between 75 and 200 mA cm−2, the use of Printex L6 carbon-based GDE generated H2O2 concentrations in the range of 4,000–5,000 mg/L, despite the formation of scavengers. The proposed technique also promoted the production of ozone and persulfate species though at low concentrations. The application of the Printex L6 carbon-based GDE led to a roughly 3.4–3.9-fold increase in H2O2 concentrations ​​compared to Vulcan XC-72R carbon-based GDE which was used for comparison purposes (Vulcan XC-72R carbon is currently-one of the most widely employed carbon materials in electrochemical processes). In addition, the Printex L6 carbon-based GDE exhibited high stability with a lifetime of 36 Ah (7,5 days) of uninterrupted use at 200 mA cm−2. The improvements observed in the Printex L6 carbon-based GDE can be attributed to the presence of higher amounts of carboxyl oxygenated functional groups in the material and its greater electrochemically active surface area compared to the Vulcan XC-72R-based GDE.

Influence of Shell Thickness on Durability of Ru@Pt Core-Shell Catalysts for Reformate PEM Fuel Cells

For the use of polymer electrolyte membrane fuel cells (PEMFCs) in heavy duty applications, on-site generation of hydrogen rich gas by reforming hydrocarbons or methanol are a suitable alternative to pure H2 due to higher availability and higher energy density of hydrocarbon fuels [1]. The so-called reformate contains in addition of H2 also CO, which is a catalyst poison. PtRu alloys are the most promising catalysts for PEM fuel cells operated with reformate due to their high CO-tolerance [2]. It is known that the less noble Ru is unstable in acidic PEMFC conditions and is lowering the durability of the membrane electrode assembly (MEA) by dissolution and crossing over through the membrane to the cathode [3]. Ru dissolution and crossover result in a decreased CO-tolerance on the anode and a lower activity of the cathode towards oxygen reduction due to Ru blocking the Pt surface of the cathode catalyst [4]. To prolong the lifetime and CO-tolerance of reformate PEMFCs, the stability of the anode catalysts must be improved. One approach is nano-structuring the catalysts by encapsulating the less noble Ru-core with a Pt-shell. In doing so, the corrosion resistant Pt-shell supposes to protect the Ru-core from dissolution and thus mitigates the Ru crossover phenomenon.In this work, the influence of the Pt-shell thickness on the stability and performance of the Ru@Pt catalysts is investigated. Two catalysts with varying Pt-shell thicknesses were synthesized on Vulcan XC72R carbon via a two-step polyol. The catalyst with the thinner Pt-shell is called Ru@1Pt and with the thicker shell Ru@2Pt. The as-synthesized catalysts were physically characterized by XRD, ICP-OES, TEM and EDS. A representative EDS map of Ru@1Pt is shown in fig. 1a. The physical characterization of the obtained catalysts unveils a Ru@Pt core-shell structure with crystalline hcp Ru and fcc Pt. To further investigate the catalysts electrochemically, MEAs were manufactured using Ru@Pt catalysts as anodes and commercial membranes and cathode catalysts. An accelerated stress test (AST) was developed to target Ru dissolution by potential cycling and was applied to investigate and compare the stability of the catalysts. The MEAs were electrochemically characterized by cyclic voltammetry, CO-stripping and U-I curves before, during and after the AST. Post-mortem cross-section STEM analysis of the stressed cells were performed to evaluate the elemental composition and morphology of the anode and cathode after the stress test.During the AST, CO-stripping on the Ru@1Pt anode showed a peak shift to higher potentials, indicating a decrease in CO-tolerance due to Ru loss. By contrast, on the Ru@2Pt anode, the peak shifted to lower potentials implying a stronger promoting influence of Ru. On the cathode side, CV measurements before and after the AST revealed a double layer increase and a decrease in the HUPD. This change implies the poisoning of Pt with Ru and were more pronounced for Ru@1Pt compared to Ru@2Pt. As seen by the CO-stripping and CV results, the Ru dissolution and crossover was more severe for Ru@1Pt than for Ru@2Pt. Hence, a higher fuel cell performance loss was observed for the cell with Ru@1Pt in H2, as can be seen in fig. 1b. In addition, further U-I curves were measured under varying reformate conditions to identify the influence of CO on the cell performance. Cross-section EDS maps of the stressed MEAs were used to evaluate the Ru dissolution and its distribution in the different layers of the MEA. A higher Ru:Pt ratio was found on the cathode for the cell with Ru@1Pt compared to a cell with Ru@2Pt, which further verifies a higher degree of Ru crossover for the catalyst with the thinner Pt-shell. The above findings could evidence that the shell thickness plays a significant role in the corrosion resistance of core-shell reformate anode fuel cell catalysts.

Oxygen reduction reaction on PdM/C (M = Pb, Sn, Bi) alloy nanocatalysts

In this work three PdM/C bimetallic catalysts were prepared with a second metal being either Bi, Pb or Sn. The synthesised Pd-alloy nanoparticles were supported on Vulcan carbon XC-72R. These catalysts were studied using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HR-TEM) and electrochemically using the rotating disk electrode (RDE) technique. The prepared Pd-based electrocatalysts were compared to pure Pd/C catalyst synthesised using the citrate method. The oxygen reduction reaction (ORR) kinetics on Pd-alloy catalysts in alkaline solution was systematically investigated. Pd content was determined by microwave plasma atomic emission spectroscopy, which was used to calculate the mass activities (MA) for ORR. Mass activities revealed that BiPd had two-fold higher and PbPd showed 1.6-times increase in MA as compared to Pd/C, however SnPd showed lower MA than Pd/C. BiPd/C catalyst showed around 45% increase in specific activity (SA) for ORR, PdSn catalyst showed around 25% increase and PbPd no increase in SA in comparison to the Pd/C catalyst. Methanol tolerance was also studied for the PdM/C alloy catalysts and a higher tolerance was observed for BiPd/C losing 17 mV in the half-wave potential value and even better methanol tolerance was in evidence with the other two catalysts that lost only ∼10 mV in 0.1 M KOH + 0.5 M MeOH.

Synthesis of Anti-poisoning Spinel Mn-Co-C as Cathode Catalysts for Low-Temperature Anion Exchange Membrane Direct Ammonia Fuel Cells.

Low-temperature anion exchange membrane direct ammonia fuel cells (AEM-DAFCs) have emerged as a potential power source for transportation applications with the recognition that liquid ammonia is a carbon-free hydrogen carrier and facilitates storage, refill, and distribution. However, ammonia crossover from the cell anode to cathode can decrease the fuel efficiency, drop the voltage, and poison the cathode catalysts. In this work, the Mn-Co spinel on three different carbon supports [BP2000, Vulcan XC-72R, and multiwalled carbon nanotubes (MWCNTs)] has been successfully synthesized and demonstrated a high oxygen reduction reaction (ORR) activity with good ammonia tolerance. The structure and composition of the obtained Mn-Co-C catalysts were characterized by high-angle annular dark-field scanning transmission electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. All three catalysts exhibit superb ammonia tolerance, and Mn-Co-BP2000 demonstrates the highest ORR activity, even better than the commercial Pt-C in the presence of ammonia. When paired with the commercial PtIr-C anode, the Mn-Co-BP2000 cathode improved the peak power density of single cells from 100.1 mW cm-2 for the Pt-C cathode to 128.2 mW cm-2 under a 2 bar backpressure in both electrodes at 80 °C. All the results have manifested that Mn-Co-BP2000 is a good cathode catalyst for low-temperature AEM-DAFCs.