Commercial Carbon Support Research Articles

Macroporous Structures of Nb-SnO2 Particles as a Catalyst Support Induce High Porosity and Performance in Polymer Electrolyte Fuel Cell Catalyst Layers.

Macroporous niobium-doped tin oxide (NTO) is introduced as a robust alternative to conventional carbon-based catalyst supports to improve the durability and performance of polymer electrolyte fuel cells (PEFCs). Metal oxides like NTO are more stable than carbon under PEFC operational conditions, but they can compromise gas diffusion and water management because of their denser structures. To address this tradeoff, we synthesized macroporous NTO particles using a flame-assisted spray-drying technique employing poly(methyl methacrylate) as a templating agent. X-ray diffraction analysis and scanning electron microscopy confirmed the preservation of crystallinity and revealed a macroporous morphology with larger pore volumes and diameters than those in flame-made NTO nanoparticles, as revealed by mercury porosimetry. The macroporous NTO particles exhibited enhanced maximum current density and reduced gas diffusion resistance relative to commercial carbon supports. Our findings establish a foundation for integrating macroporous NTO structures into PEFCs to optimize durability and performance.

Ag-NP-Decorated Carbon Nanostructures: Synthesis, Characterization, and Antimicrobial Properties.

As the global urgency for effective antimicrobial agents intensifies, this work harnesses the widely demonstrated antimicrobial activity of silver nanoparticles (Ag-NPs) and proposes alternative synthesis approaches to metal-organic hybrid systems with antimicrobial activity. In this study, the proposed synthesis route involves decorating metallic nanoparticles into organic substrates without previous doping. The synthesis simultaneously uses polyethylene glycol for three crucial purposes: (1) acting as a mild reducing agent to generate Ag-NPs with a spherical shape and diameters ranging from 10 to just over 20 nm, (2) functioning as a dispersing agent for flakes of commercial nanostructured carbon supports, including reduced graphene oxide (rGO, ID-nano), and commercial carbon nanoplatelets from Sigma-Aldrich (GNPs, Sigma-Aldrich), and (3) serving as a promoter for the homogeneous anchoring of Ag-NPs in the carbon lattice without altering the conformation of the carbon lattice. This intricate interaction involves the π-orbitals from the sp2 hybridization honeycomb and the d-orbitals from the Ag-NPs, leading to the constructive rehybridization of rGO and GNPs. In our study, Ag-NPs/rGO are compared with a support lacking oxygenated groups in the lattice, such as commercial GNPs (Sigma-Aldrich), to produce Ag-NPs/GNPs. This comparison maintains constructive sp2 rehybridization, preserving the characteristic properties of rGO (ID-nano) and graphene nanoplatelets, including commercial GNPs (Sigma-Aldrich). Notably, oxygenated groups from rGO exhibit greater availability for exchanging oxo and hydroxy defects for Ag-NPs compared with GNPs (Sigma-Aldrich). The resulting Ag-NPs/rGO and Ag-NPs/GNP systems are thoroughly physicochemically characterized, employing techniques such as Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy, high-resolution transmission electron microscopy, and scanning transmission electron microscopy, revealing the successful integration of Ag-NPs with minimal alteration to the carbon lattice. Subsequent antimicrobial evaluation against Escherichia coli (E. coli) demonstrates significant activity, with Ag-NPs/rGO and Ag-NPs/GNPs registering similar minimum inhibitory concentrations of 50 μg mL-1. This study underscores the potential of our metal-organic hybrid systems as antimicrobial agents and provides insights into the constructive rehybridization process, paving the way for diverse applications in the biomedical and environmental fields.

Optimizing the Performance of Low-Loaded Electrodes for CO2-to-CO Conversion Directly from Capture Medium: A Comprehensive Parameter Analysis.

Gas-fed reactors for CO2 reduction processes are a solid technology to mitigate CO2 accumulation in the atmosphere. However, since it is necessary to feed them with a pure CO2 stream, a highly energy-demanding process is required to separate CO2 from the flue gasses. Recently introduced bicarbonate zero-gap flow reactors are a valid solution to integrate carbon capture and valorization, with them being able to convert the CO2 capture medium (i.e., the bicarbonate solution) into added-value chemicals, such as CO, thus avoiding this expensive separation process. We report here a study on the influence of the electrode structure on the performance of a bicarbonate reactor in terms of Faradaic efficiency, activity, and CO2 utilization. In particular, the effect of catalyst mass loading and electrode permeability on bicarbonate electrolysis was investigated by exploiting three commercial carbon supports, and the results obtained were deepened via electrochemical impedance spectroscopy, which is introduced for the first time in the field of bicarbonate electrolyzers. As an outcome of the study, a novel low-loaded silver-based electrode fabricated via the sputtering deposition technique is proposed. The silver mass loading was optimized by increasing it from 116 μg/cm2 to 565 μg/cm2, thereby obtaining an important enhancement in selectivity (from 55% to 77%) and activity, while a further rise to 1.13 mg/cm2 did not provide significant improvements. The tremendous effect of the electrode permeability on activity and proficiency in releasing CO2 from the bicarbonate solution was shown. Hence, an increase in electrode permeability doubled the activity and boosted the production of in situ CO2 by 40%. The optimized Ag-electrode provided Faradaic efficiencies for CO close to 80% at a cell voltage of 3 V and under ambient conditions, with silver loading of 565 μg/cm2, the lowest value ever reported in the literature so far.

Ag nanoparticles on mesoporous carbon support as cathode catalyst for anion exchange membrane fuel cell

Silver nanocatalyst (40 wt%) is deposited on commercial mesoporous carbon support material (Ag/C) using two different wet chemical methods, to obtain high electrochemically active surface area. The catalyst materials are characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, thermogravimetric analysis and are evaluated toward the oxygen reduction reaction (ORR) in alkaline media employing the rotating disk electrode method. It is worth noting that the Ag/C leads to oxygen reduction through a direct four-electron pathway in alkaline medium. The silver catalyst on mesoporous carbon exhibits relatively higher mass activity for ORR (38 A g−1) compared to that with Vulcan carbon (32 A g−1) at −0.2 V vs SCE at room temperature. Anion exchange membrane fuel cell shows maximum power density of 310 mW cm−2 with Ag/C cathode catalyst using H2 and O2 gases at 65% RH conditions at 65 °C.

Continuous Production of Carbon-Supported and Surfactant-Free Pt-M (M=Fe, Co, Ni, and Cu) Nanocrystals for Catalyzing Oxygen Reduction

Scalable production of carbon-supported Pt-M (M=Co, Ni, and Fe) alloy nanocrystals is of great importance for their practical application as catalysts towards the oxygen reduction reaction (ORR), a process key to the operation of proton-exchange membrane fuel cells. Here we report the use of a fluidic device for the in situ nucleation and growth of Pt-M nanocrystals on a commercial carbon support in a continuous and scalable fashion. The use of dimethylformamide not only enables well dispersion of the carbon powders for the creation of a homogeneous reaction mixture but also helps reduce metal precursors for the heterogeneous nucleation and growth of nanocrystals on the carbon surface. The size, shape, and composition of the nanocrystals can all be tuned by changing the metal precursors added into the reaction mixture, resulting in Pt-M nanocrystals uniformly distributed across the surface of the carbon support. Among the nanocrystals, the carbon-supported Pt-Co nanocrystals show the highest ORR specific and mass activities at 0.9 V, demonstrating 11.4- and 8.8-fold enhancements over the state-of-the-art commercial Pt/C catalyst.

Microstructure and activity of Pd catalysts prepared on commercial carbon support for the liquid phase decomposition of formic acid

In this work, a series of Pd catalysts supported on commercially available activated carbon (Norit ®) were prepared by employing different metal precursors (Pd(NO3)2 and Na2PdCl4) by the impregnation-reduction method at different pH. Catalysts were tested for the liquid phase decomposition of formic acid to generate hydrogen. The best results, in terms of small particle size and high catalytic activity were achieved for the Pd/C sample prepared by using Pd(NO3)2 salt impregnated at pH = 2.5, and reduced with sodium borohydride. The particle size of the best Pd/C catalyst is (4.1 ± 1.4) nm with initial TOFs of 2929 and 683 h−1 at 60 and 30 °C respectively and an apparent activation energy of 40 kJ mol−1. Samples prepared by using Na2PdCl4 precursor, consisted of particles with higher size and thus lower activity than the ones prepared with Pd(NO3)2. Regardless the Pd precursor employed, the best results in terms of particle size and activity were achieved at the point of zero charge of the support when the Pd species and the carbon surface were both neutral. The impregnation pH not only determines the particle size, but also the nature of the reducing agent does. The catalytic activity was shown to be size-dependent and it was shown that a mixture of surface Pd0 and PdII oxidation states is beneficial for the activity. When comparing with literature catalysts with similar composition, we found that our best catalyst is competitive enough and that Norit ® support could be promising for future studies on this reaction.

Correlative Electrochemical-TEM Study: Probing the Pt Stability of Mesoporous N-Doped Carbon Supported Pt Nanoparticle ORR Electrocatalyst

In recent years, hydrogen proton exchange membrane fuel cells have gained growing attention in the heavy duty vehicle (HDV) sector due to lower cost with increased driving range and lower refueling time compared to Li ion battery systems.[1] However, special requirements apply to HDV fuel cells such as long lifetime (25000 – 30000 h) at low Platinum loadings. Additionally, future Pt cathode loadings should be reduced from ≥ 0.4 mgPt/cm² (i.e. the current benchmark) to 0.25 mgPt/cm² by 2050, while a constant power density of 840 mW/cm² at 0.769 V should be achieved as defined by the US Department of Energy.[2]Despite Pt nanoparticles finely dispersed on carbon supports are considered the benchmark catalysts, the cathode is yet suffering from several degradation processes such as carbon corrosion, Pt nanoparticle detachment, agglomeration, dissolution and Pt redeposition, hindering the achievement of the aforementioned goals.[3, 4] Therefore, in-depth understanding of the electrocatalyst degradation mechanisms by which Pt losses its catalytic activity is required to develop optimized synthesis methods for stable materials. Recently, we developed novel mesoporous N-doped carbon (MPNC) supports with improved stability against carbon corrosion in comparison to a commercial reference carbon support.[5] Utilizing the advantage of such enhanced stability, we designed Pt/MPNC catalysts for oxygen reduction reaction (ORR) with an extended stability reaching over 10000 cycles in comparison to the commercial Pt/C catalyst, as revealed by the accelerated stress tests (AST) in acidic media and within the carbon corrosion potential range between 1 V and 1.5 V vs RHE.In the present study, we synthesized Pt/MPNC-T catalysts under different reduction temperatures to control the Pt nanoparticle size distribution. We then investigated the impact of the various sizes of the Pt nanoparticles on the stability of Pt/MPNC-T after AST cycles. Therefore, Rotating disc electrode measurements with an established Pt AST protocol using a square wave potential between 0.6 V and 0.95 V vs. RHE over 30000 cycles was applied.[1] The ORR activity, the electrochemical active surface area by HUPD and CO stripping experiments were measured at the beginning of the cycle life test, then after 10000 AST cycles and finally after 30000 AST cycles. The electrochemical measurements before and after AST of the Pt/MPNC-T catalysts were correlated with ex-situ TEM and aberration corrected (AC) STEM data. Experimentally, lower reduction temperature synthesis leads to broader Pt size distributions. Thereby, we noticed the presence of Pt nanoparticles with a diameter between 1 and 3 nm, and smaller Pt entities such as Pt atom clusters and single sites of Pt (i.e. Pt single atoms) at the beginning of cycling. By imaging the surface after 30000 AST cycles, the Pt nanoparticle size substantially increased and the amount of smaller Pt entities was drastically reduced. Such findings indicate that the major degradation process follows the Ostwald ripening mechanism.In conclusion such results reveal the importance of determining the structure-function correlations, which contributes to the general understanding of catalyst degradation processes and allows a knowledge-based optimization of these Pt/MPNC materials in future works.

Carbon materials functionalized by nitrogenous ligands for dual application in energy storage and production: Fuel cells and supercapacitors

Dual-purpose fuel cell/supercapacitor materials were made by covalent embedding of phenazin-iron adducts into various commercial carbon supports (Vulcan XC-72, Black Pearls 2000, Ketjen Black 600). The diazonium coupling reaction allows for controlled deposition of nitrogen functionalities to the carbon supports via the formation of the strong carbon-carbon bond between the nitrogenous ligand and carbon surface. The novel phenazin-functionalized carbon supports were prepared and fully characterized using thermogravimetric analysis, Raman spectroscopy, and BET pore size determination. Notably, the micro-and macrostructure and the porosity of the carbon support drastically affected the catalytic activity of the system in oxygen reduction reaction (ORR). The KB-phenazin-Fe-700 showed the highest activity for the ORR in both basic and acidic media. Interestingly, the heat treatment of the phenazin-based materials resulted in a significant increase in the ORR activity that is different from the trend we previously observed for terpyridine-based catalysts on Vulcan carbon that were demonstrating a significant decrease in the activity after heat treatment. Furthermore, the potential of the same materials to be used for energy storage was explored and their performance as supercapacitors was studied. The modification of the carbon surfaces by phenazin ligand shows significant improvement of the specific capacitance when examined in acidic media. Coordination of iron to the surface results in a further increase of the specific capacitance due to the additional Faradaic contributions. Drastic increases were seen in the capacitance when Fe was added to the BP-phenazin system. Interestingly, the heat treatment process was found to decrease the energy storage ability of the materials with a significant decrease of the specific capacitance. Thus, for phenazin-based materials, the heat treatment is a necessary step for the production of effective ORR catalysts but is undesirable for materials targeting mainly energy storage applications.

Hybrid Supercapacitor Electrode Materials via Molecular Imprinting of Nitrogenous Ligands and Iron Complexes into Carbon Support

Novel hybrid supercapacitor materials were made by the covalent immobilization of nitrogenous ligands onto the surface of commercial carbon support (Vulcan XC-72), then coordinated to iron. The covalent attachment of the nitrogenous ligands allows for the controlled deposition of nitrogen functionalities on the surface of the carbon. The supercapacitor tests in acidic media showed significant growth of the capacitance as a result of the nitrogenous ligands on the support. Notably, the increase of the capacitance values directly correlates with the molecular loading on the surface. Following coordination of iron to the ligands on the surface further elevated the capacitance via Faradaic reactions of the metal center. Remarkably, the overall capacitance of materials significantly increased after the course of long-term cycling tests (ca. 110% or higher). At the beginning of durability studies, a small decline in capacitance was observed, due to some extent of molecular decomposition on the surface of the electrode. However, the intense cycling further propagates a steady growth of the overall capacitance of the materials. This could be attributed to the process of polymerization of physisorbed molecules/ radicals that result in the formation of a 3D network structure that eventually boosts the overall capacitance and the charge storage of the electrode.

In Situ Growth of Pt-Co Nanocrystals on Different Types of Carbon Supports and Their Electrochemical Performance toward Oxygen Reduction.

Carbon-supported Pt-M (M = Co, Ni, and Fe) alloy nanocrystals are widely used as catalysts toward oxygen reduction, a reaction key to the operation of proton-exchange membrane fuel cells. Here we report a colloidal method for the in situ growth of Pt-Co nanocrystals on various commercial carbon supports. The use of different carbon supports resulted in not only variations in size and composition for the nanocrystals but also their catalytic activity and durability toward oxygen reduction in acidic media. Among the nanocrystals, those grown on Vulcan XC72 and Ketjenblack EC300J showed the highest specific and mass activities in the 0.1 M HClO4 and 0.05 M H2SO4 electrolytes, respectively. Additionally, the catalysts also showed different durability depending on the strength of the interaction between the nanocrystals and the carbon support. Our analysis demonstrated that the difference in catalytic performance could be ascribed to the distinct effects of carbon support on both the synthetic and catalytic processes.

Electrocatalysts for Direct CO2 to C2+ Chemical Conversions with High Selectivity and Energy Efficiency

Carbon dioxide emission from fossil fuel combustion has generated an on-going debate on its impact to the global environmental and ecological systems. New carbon capture, sequestration and conversion technologies are widely pursued as potential solutions to mitigate the concerns. The electrochemical CO2 reduction reaction (CO2RR) to hydrocarbon fuels and chemicals using renewable electricity offers an attractive “carbon-neutral” or even “carbon-negative” mitigation strategy. CO2 is an inexpensive carbon source and can be used as a feedstock for producing high value chemicals. Key challenges facing the current CO2RR electrocatalysis include improving energy efficiency by reducing the overpotentials; increasing the process selectivity by enhancing a single-product Faradaic efficiency (FE); and lowering the system operating cost by prolonging the catalyst stability.The U.S. produced 5.1 billion metric tons of CO2 in 2018 from industrial processes, posing a major concern on its impact to the climate.[1] The CO2 can be captured and used as raw material to produce to value-added chemicals. According to DOE’s “Bandwidth Study on Energy Use and Potential Energy Saving Opportunities in U. S. Chemical Manufacturing”,[2] C2+ chemicals such as ethanol (C2H5OH), acetic acid (CH3CO2H) and acetone (C3H6O) are among top 74 major chemicals produced in the US. Making these chemicals using sequestrated CO2 represents a huge opportunity for US manufacturing while improving the environment. Techno-economic analysis (TEA) of low-temperature electrochemical conversion of CO2 to C2+ chemical, particularly ethanol, has been conducted by several studies. All analyses indicate that profitable manufacturing of C2+ chemicals by electrochemical CO2 reduction reaction (CO2RR) depend strongly on conversion selectivity (Faradaic efficiency, or FE) and the difference between the actual and theoretical operating potentials (overpotential).Argonne National Laboratory, through collaboration with Northern Illinois University, recently prepared a series of highly active and durable electrocatalysts for CO2RR over commercial carbon support using a novel amalgamated lithium metal (ALM) synthesis technique.[3] The new electrocatalysts offer the several advantages in direct conversion to C2+ chemicals, including a) high FEs (all with peak FE > 90%) with one-step conversion to C2 (C2H5OH and CH3COOH) and C3 (C3H6O) chemicals; b) low voltage with the onset potential as low as -0.4 V and approaching to the theoretic limit; c) low cost catalysts made of earth-abundant transition metal; d) low operating temperature (< 80 °C) and pressure (one bar). including > 90% single-product FE, low onset potential (-0.4 V RHE for ethanol conversion) and excellent durability.In this presentation, we will report discuss the new electrocatalyst performance in terms of FE, onset potential and durability. The structure-function relationship with particular emphasis on CO2 to ethanol conversion and the mechanistic insight gained from operando X-ray absorption spectroscopy and computational modeling will also be reported. Acknowledgement: This work was supported by Argonne National Laboratory LDRD office. The works performed at Argonne National Laboratory’s Center for Nanoscale Materials, an U.S. Department of Energy Office of Science User Facility, is supported by Office of Science, U.S. Department of Energy under Contract DE-AC02-06CH11357.[1] https://www.eia.gov/environment/emissions/carbon/pdf/2019_co2analysis.pdf[2] https://www.energy.gov/sites/prod/files/2015/08/f26/chemical_bandwidth_report.pdf[3] Xu, H. P. et al.; Highly selective electrocatalytic CO2 reduction to ethanol by metallic clusters dynamically formed from atomically-dispersed copper, Nature Energy, 2020, 5, 623-632.

Enhancing Methanol Oxidation Reaction with Platinum‐based Catalysts using a N‐Doped Three‐dimensional Graphitic Carbon Support

AbstractNitrogen‐doped graphitic carbon materials have been widely used as a catalyst support in the methanol oxidation reaction (MOR). In this study, we report the role of three‐dimensionally architectured in‐situ N‐doped vertically aligned carbon nanofibers (VACNF) as a catalyst support for MOR in acidic and alkaline media. The abundant graphitic edge sites at the sidewall of N‐doped VACNF strongly anchor the deposited platinum group metal (PGM) catalysts and induce a partial electron transfer between the PGM catalysts and support. Density Functional Theory (DFT) calculations reveal that the strong metal‐support interaction substantially increases the adsorption energy of OH, particularly near the N‐doping sites, which helps to compete and remove the adsorbed intermediate species generated during MOR. The PGM catalysts on N‐doped VACNF support exhibits CO stripping at lower potentials comparing to the commercial Vulcan carbon support and presents an enhanced electrocatalytic performance and better durability for MOR.

Direct Electrocatalytic Conversion of CO2 to Chemicals over Single Atom Catalysts

Carbon dioxide emission from fossil fuel combustion has generated an on-going debate on its impact to the global environmental and ecological systems. New carbon capture, sequestration and conversion technologies are widely pursued as potential solutions to mitigate the concerns. The electrochemical CO2 reduction reaction (CO2RR) to hydrocarbon fuels and chemicals using renewable electricity offers an attractive “carbon-neutral” or even “carbon-negative” mitigation strategy. CO2 is an inexpensive carbon source and can be used as a feedstock for producing high value chemicals. Key challenges facing the current CO2RR electrocatalysis include: a) how to improve energy efficiency by reducing the overpotentials; b) how to increase the process selectivity by enhancing a single-product Faradaic efficiency (FE); and c) how to lower the system operating cost by prolonging the catalyst stability. Argonne National Laboratory through collaboration with Northern Illinois University recently developed a series of highly active and durable single atom catalysts (SACs) for CO2RR prepared using a robust synthesis method over the commercial carbon support. The new electrocatalysts offer the several advantages including: a) direct conversion to C2 (C2H5OH and CH3CO2H) and C3 (C3H6O) chemicals in one-step electro-catalytic reaction without secondary upgrading; b) higher than 90% FE by suppressing the byproduct formation; c) high energy efficiency with the onset potential as low as 0.4 V observed for ethanol conversion; and d) good stability with no sign of activity loss during extended hours of chronoamperometry measurement. In this presentation, we will discuss the structure-function relationship of the new SACs with particular emphasis on CO2 to ethanol conversion. We will also share the mechanistic insight on catalysis as the catalyst transitioning from SAC to metal cluster. The catalyst performance in terms of FE, onset potential and durability will also be reported, combined with the catalyst structural properties obtained from various conventional and advanced characterization tools. Acknowledgement: The work performed at Argonne National Laboratory is supported by Office of Science, U.S. Department of Energy under Contract DE-AC02-06CH11357.

Catalytic System Based on Sub-2 nm Pt Particles and Its Extraordinary Activity and Durability for Oxygen Reduction.

Carbon-supported Pt nanoparticles are used as catalysts for a variety of reactions including the oxygen reduction reaction (ORR) key to proton-exchange membrane fuel cells, but their catalytic performance has long been plagued by detachment and sintering. Here we report the in situ growth of sub-2 nm Pt particles on a commercial carbon support via the galvanic reaction between a Pt(II) precursor and a uniform film of amorphous Se predeposited on the support. The residual Se could serve as a linker to strongly anchor the Pt nanoparticles to the carbon surface, leading to a catalytic system with extraordinary activity and durability toward ORR. Even after 20 000 cycles of accelerated durability test, the sub-2 nm Pt particles were still dispersed well on the carbon support and maintained a mass activity more than three-times as high as the pristine value of a commercial Pt/C catalyst.

Insight into the alternative metal oxide modified carbon-supported PtCo for oxygen reduction reaction in proton exchange membrane fuel cell

The aim of this work was to prepare the metal oxides modified carbon (C-MOx) that was used as the support for a PtCo catalyst. Effect of C-MOx support on the oxygen reduction reaction activity and stability of the PtCo catalysts in acid electrolyte and in proton exchange membrane fuel cell was explored at ambient pressure. It was found that the use of respective C-MOx support changed the morphologies (degree of alloying and particle sizes) as well as the electrochemical properties (electrode resistance and electrochemical surface area) of the obtained PtCo catalyst. In addition, it enhanced the formation of Pt atoms with a small d-electron occupancy, which consequently affected positively the ORR activity of the PtCo catalysts. Among the three utilized C-MOx support (C-TiOx, C-CeOx, C-MoOx), the C-MoOx exhibited the highest ORR activity in an acid electrolyte monitored in terms of kinetic current density and the highest current density of 570 mA/cm2 at 60 °C and 1 atm (abs) in a proton exchange membrane (PEM) fuel cell. In addition, it also achieved a comparable stability of PtCo catalyst to that of C-TiOx support, which were higher than that of the commercial carbon support.

Stability of carbon-supported iron catalysts for catalytic wet peroxide oxidation of ionic liquids

The stability of two carbon-supported Fe catalysts in the catalytic wet peroxide oxidation (CWPO) of 1-Butyl-3-methylimidazolium acetate (BmimAc) was examined. One catalyst (Fe/AS) was obtained by chemical activation of dried sewage sludge with iron chloride at a FeCl3:sewage sludge mass ratio of 3 and the other (Fe/HTCS) by hydrothermal carbonization of the sludge in the presence of FeCl3 at a mass ratio of also 3. Fe/AS catalyst exhibited a well-developed porosity, whereas Fe/HTCS one did not show porosity. The carbon content was high in both catalysts, with a total Fe content of 5.2 and 6.6% (w/w) for Fe/AS and Fe/HTCS catalysts, respectively. An aditional Fe catalyst prepared by incipient wetness impregnation on a commercial active carbon support (Fe/AC) was used for comparison with the previous two. All catalysts were active in experiments of H2O2 decomposition and long-term CWPO runs (0.133 kgFe h molBmimAc–1 at 80 °C). Whereas Fe/AC catalyst lost activity largely due to Fe leaching (90% of FeBulk), Fe/AS and Fe/HTCS catalysts exhibited virtually no Fe leaching and hence fairly good stability. Fe/AS catalyst, which afforded complete removal of Bmim+ and TOC conversion values around 30%, proved the most efficient catalyst.

Control of the Interfacial Wettability to Synthesize Highly Dispersed PtPd Nanocrystals for Efficient Oxygen Reduction Reaction.

Highly dispersed PtPd bimetallic nanocrystals with enhanced catalytic activity and stability were prepared by adjusting the interfacial wettability of the reaction solution on a commercial carbon support. This approach holds great promise for the development of high-performance and low-cost catalysts for practical applications.

Enhanced vanadium redox flow battery performance using graphene nanoplatelets to decorate carbon electrodes

Rotating Disk Electrode (RDE) measurements on model glassy carbon (GC) substrates and Cyclic Voltammetry on more practical commercial carbon supports are used to demonstrate that the kinetics of the positive VO2+/VO2+ redox reaction can be substantially enhanced by using electrostatic layer-by-layer assembly (LbL) to decorate their surface with graphene nanoplatelets (GNPs). An exchange current density, i0, is obtained that is more than two orders of magnitude greater than that observed with standard carbon supported Pt nanocatalyst with the deposition of only 20 GNP layers. Tafel slope analysis is compared to electron microscopy imaging to conclude that while faster redox kinetics is associated with an increase in the available active area, the prevalence of smaller GNPs and associated edge sites the can attenuate activity gains with increasing number of layers. Practical implementation to existing Vanadium Redox Flow Battery (VRFB) configurations was demonstrated through the application of a 370 nm (20 layer) LbL GNP coating on carbon felt (CF). The GNP coating yielded a 5% increase relative in voltage and overall efficiency of charge discharge curves obtained under typical VRFB cell operating conditions at 40 mA cm−2. Furthermore, a substantial increase in the discharge time is observed with this GNP coating on CF.

Importance of non-intrinsic platinum dissolution in Pt/C composite fuel cell catalysts.

The dissolution of different platinum-based nanoparticles deposited on a commercial high-surface area carbon (HSAC) support in thin catalyst films is investigated using a highly sensitive electrochemical flow cell (EFC) coupled to an inductively coupled plasma mass spectrometer (ICP-MS). The previously reported particle-size-dependent dissolution of Pt is confirmed on selected industrial samples with a mean Pt particle size ranging from 1 to 4.8 nm. This trend is significantly altered when a catalyst is diluted by the addition of HSAC. This indicates that the intrinsic dissolution properties are masked by local oversaturation phenomena, the so-called confinement effect. Furthermore, by replacing the standard HSAC support with a support having an order of magnitude higher specific surface area (a micro- and mesoporous nitrogen-doped high surface area carbon, HSANDC), Pt dissolution is reduced even further. This is due to the so-called non-intrinsic confinement and entrapment effects of the (large amount of) micropores and small mesopores doped with N atoms. The observed more effective Pt re-deposition is presumably induced by local Pt oversaturation and the presence of nitrogen nucleation sites. Overall, our study demonstrates the high importance and beneficial effects of porosity, loading and N doping of the carbon support on the Pt stability in the catalyst layer.

Performance of Pd/Graphene Nanocomposite Catalysts in H2/O2 Anion Exchange Membrane Fuel Cells

With the recent developments of high-performance anion-exchange membranes (AEM), there has been an increased interest towards studying various electrochemical reactions such as ethanol electrooxidation, hydrogen oxidation reactions and oxygen reduction reactions in AEM fuel cells (AEMFC). This increased attention has been attributed to the faster electro oxidation kinetics, increased stability and lower poisoning of the catalysts in alkaline media. And since AEMFCs are not limited to platinum - unlike in proton exchange membrane fuel cells (PEMFCs) with highly acidic environments - intensive efforts towards developing alternatives such as palladium (Pd) and Pd-based alloys are currently underway.1 , 2 Various studies have shown the enhanced stability and higher activities of Pd-based catalysts compared to Pt in alkaline medium using potentiodynamic and potentiostatic techniques. However, there are only a limited number of studies that have investigated the performance of Pd-based electrocatalysts in AEMFCs. Also, majority of these studies have demonstrated relatively low performances in AEMFCs, mainly due the complications associated with forming the triple-phase boundary (TPB) structure in the membrane layer, where reactions are taking place in the electrolyte, gaseous fuel and electrode interface. The density of the TPB, along with the intrinsic activities of the catalysts can play an important role in determining the overall performance of AEMFCs. Moreover, Pd-based are usually synthesized using surfactants, organic stabilizers or reducing agents, that can get adsorbed onto the surface of Pd and inhibit ionomer-catalyst-fuel interactions in the TPB. To mitigate the limitations associated with TPB structure and subpar catalyst activities, macroporous three-dimensional Graphene nanosheet (3D-GNS) supports with controlled morphologies and porosities were fabricated by utilizing silica sacrificial templates.3 The sacrificial templates were then etched to leave a network of porous channels within its matrix, and utilized as supports for Pd nanoparticles. The porous structure of these highly graphitized 3D-GNS supports can facilitate mass-transport kinetics by enabling the ionomer and polymer electrolyte getting the reactants to get catalyzed by Pd nanoparticles. Also, to enhance ionomer-nanoparticle interactions, the Pd nanoparticles of an average size of 3-5 nm were synthesized using a previously established surfactant-free soft alcohol reduction method.4 In this study, anion exchange catalyst-coated membranes (CCMs) were prepared using Pd nanoparticles supported on both commercial carbon blacks (Vulcan) and 3D-Graphene supports as both cathode and anode catalyst in H2/O2 fed AEMFCs. The Pd catalyst inks were prepared by mixing the dispersed Pd-catalyst in an optimized solution of isopropyl alcohol and quaternary ammonium-functionalized AS4 ionomer. The inks were then applied onto an anion exchange membrane (A201, Tokuyama) with an active area of 5 cm2. The CCMs was then hydrated in 0.5 M KOH for 24 hours, followed by rinsing in de-ionized water for 24 hours. It was then sandwiched between gas diffusion layers and annealed with gaskets by pressing under 500 psi for 5 minutes. The cell was then assembled and activated by operating at 0.3V at 60ºC for 10 minutes under humidified O2 and H2, followed by the measuring the polarization curves. Preliminary results show that Pd nanoparticles synthesized using surfactant-free method SARM and deposited on commercial carbon supports have and OCV of 0.95 V and a peak power output of 200 mWcm-2. These results already show the promising potential of using surfactant-free non-alloyed monometallic Pd nanoparticles. Further tests will also be performed to show the effect of porous 3D-Graphene supports towards modifying the TPB interphase and its effects on MEA performance in both Ethanol/O2 and H2/O2 fed AEMFCs. The results from this study will not only contribute towards the development of Pt-free oxidative and reductive electrocatalysts, but also lead to further advancements in AEMFC technology that will enable it to operate with other fuels such as methanol and hydrazine.