Catalyst In Acidic Medium Research Articles

High performance Fe and N-codoped graphene quantum dot supported Pd3Co catalyst with synergistically improved oxygen reduction activity and great methanol tolerance

Designing high-performance and durable non-platinum catalysts as oxygen reduction reaction (ORR) catalysts is still a major barrier of fuel cell commercialization. In this work, simple hydrothermal and impregnation routes were applied to prepare non-platinum Pd-Co bimetallic nano-catalysts such as Fe-N doped graphene quantum dot (Fe-N-GQD) supported Pd3Co (Pd3Co/Fe-N-GQD 10 wt%), carbon supported Pd3Co/C (10 wt%), graphene quantum dot supported Pd3Co/C (10 wt%). The synthesized catalysts were physico-chemically characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electronmicroscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The electrochemical investigation was carried out in three electrode half-cell system to evaluate the catalyst activity for oxygen reduction reaction (ORR), the tolerance to methanol crossover and durability. In comparison to commercial Pt/C (ETEK, 20 wt%), the Pd3Co/Fe-N-GQD with lower weight percentage catalyst (∼10 wt%) displayed comparable electrocatalytic activity toward ORR with even higher methanol-tolerance capability and durability. The fabricated Pd3Co/Fe-N-GQD with (10 wt %) metal loading exhibited only 20% lower activity than Pt/C (ETEK, 20 wt%) toward ORR. Nevertheless the durability study of the catalyst in acidic media showed that the Pd3Co/Fe-N-GQD preserve 40% of its activity while Pt/C (ETEK, 20 wt%) exhibited only 20% of its initial catalytic activity for ORR. Moreover the activity loss in the presence of methanol (0.1 M) was obtained for Pt/C (ETEK, 20 wt%) and Pd3Co/Fe-N-GQD 35% and 14%, respectively. To investigate the role of catalyst support, catalytic activities of Pd3Co/Fe-N-GQD, Pd3Co/C, Pd3Co/GQD and Pd/Fe-N-GQD were compared. The results demonstrated superior catalytic activity of Pd3Co/Fe-N-GQD which could be related to the cocatalytic role of Fe-N-GQD due to the presence numerous of active sites exposed to the reactants.

Characterization of Carboxylated Cellulose Nanocrytals Isolated through Catalyst-Assisted H2O2 Oxidation in a One-Step Procedure.

A green and facile method was designed to isolate a type of cellulose nanocrystal (CNC) with carboxylated surfaces from native cellulose materials. Because isolation and modification processes of cellulosic particles are generally performed separately using harmful chemicals and multiple steps, the one-pot approach employed in this work is interesting from both an economical and ecological point of view. The reaction is carried out by adding hydrogen peroxide as an oxidant and copper(II) sulfate as a catalyst in acidic medium under mild thermal conditions. The charge content of the carboxylated CNC is about 1.0 mmol g-1, measured by a conductometric titration. Fourier transform infrared spectroscopy also proved the presence of carboxyl groups on the CNC particles. Atomic force microscopy along with optical polarized microscopy readily showed a rod shape morphology for the cellulosic particles. An average length of 263 nm and width of 23 nm were estimated by transmission electron microscopy. Dynamic laser scattering on carboxylated CNC suspensions by adding salt confirmed that nanoparticles are electrostatically stable. Carboxylated CNCs were furthermore characterized by solid carbon-13 nuclear magnetic resonance and X-ray spectroscopy.

Pt[sbnd]CoN supported on TiN-modified carbon nanotubes (Pt[sbnd]CoN/TiN–CNT) as efficient oxygen reduction reaction catalysts in acidic medium

Herein, new catalysts for the oxygen reduction reaction (ORR) (PtCoN nanoparticles supported on TiN–carbon nanotubes (CNTs)) were successfully prepared via the simple polymerized complex method and heat treatment in NH3. Through this facile two-step synthesis, metal chlorides were first transformed to the corresponding oxides, then reduced to metal particles or nitrides. The synthesized PtCoN/TiN–CNT electrocatalysts showed excellent electrochemical activity for oxygen reduction and high tolerance against methanol in acidic medium. The ORR onset potential of Pt0.3CoN/TiN–CNT (0.812 V vs. RHE) is higher than that of 40 wt% commercial Pt/C (0.789 V vs. RHE) due to the synergistic effect between nano-platinum particles and metal nitrides. The TiN-coated CNT support provided high electron transfer rate and catalytic tolerance in methanol solution. The number of transferred electrons was examined by rotating ring-disk electrode measurements, which concurred with the result of the Koutecky–Levich equation for a four-electron mechanism.

(Invited) Hollow Doped Carbon Nanopolyhedra with Exclusive Fe–Nx Active Sites As Advanced Cathode Catalyst Achieving Ultra High Polymer Electrolyte Membrane Fuel Cells Performance

Developing high-efficiency and low-cost cathodic oxygen reduction reaction catalyst for large-scale application of proton exchange membrane fuel cell is highly significant but still full of challenges. Herein, well defined Fe–N co-doped hollow carbon nanopolyhedra catalyst, with exclusive Fe–Nx active sites derived from the addition of C3N4 in the precursor, have been prepared by a facile and effective strategy, where hollow ZIF-8 is first synthesized by a chemical etching process, followed by impregnating with ferric acetylacetonate and g-C3N4, and pyrolyzing in Ar atmosphere. The catalyst inherits the good polyhedra morphology from its precursor, and the resulting optimal catalyst exhibits superior ORR performance in both acidic and alkaline mediums, with a half-wave potential of 0.78 V comparable to that of commercial Pt/C catalysts in acidic medium, and a half-wave potential of 0.85 V, ca. 30 mV more positive than that of commercial Pt/C catalyst in alkaline medium, making it one of the best doped carbon catalysts in an acidic and alkaline medium up to now; It is important that our hollow nanopolyhedra catalyst exhibits superior stability both in acidic and alkaline mediums, superior to commercial Pt/C. Furthermore, in the H2-O2 single PEM cell test, the MEA with our optimal hollow nanopolyhedra catalysts as cathodeachieved a current density of 700 mA cm−2 @ 0.6 V and 400 mA cm−2 @ 0.7 V, which is one the best PEMFC’s performance reported for doped carbon cathode. Combining 57Fe Mössbauer spectroscopy and X-ray photoelectron spectroscopy results, we ascribe the outstanding performance of our catalyst to the homogeneous distributions of high-density of Fe–Nx active sites (D1: FeN4/C and D3: N–FeIIN2+2…Nprot/C) and pyridinic-N, caused by the addition of C3N4.

Microwave Reaction: A Facile Economic and Green Method to Synthesize Oxygen‐Decorated Graphene from Carbon Cloth for Oxygen Electrocatalysis

AbstractOxygen‐functionalized graphene is active for oxygen evolution reaction (OER). However, the high costs, complex instruments and pollution risks in the synthesis process make oxygen‐functionalized graphene difficult to be industrialized. The microwave reaction has originally been used to remove the oxygen groups on graphene structures. In this work, the microwave reaction is reversed to decorate oxygen groups on graphene from carbon cloth, by solely using a household microwave oven. After microwave treatment, the carbon cloth shows greatly improved OER performance with a much lower overpotential of 417 mV, in comparison with the pristine carbon cloth (627 mV), due to the decoration of oxygen groups on graphene, a higher electron conductivity and a higher specific surface area. Meanwhile, an overpotential of 542 mV at 10 mA cm−2 is obtained in an acidic electrolyte, which is one of the best values for non‐precious OER catalysts in acidic media. This work provides a facile, green and economic method for producing functionalized carbon catalysts for OER.

Ni2P Entwined by Graphite Layers as a Low-Pt Electrocatalyst in Acidic Media for Oxygen Reduction.

A simple and feasible strategy was reported to construct Ni2P nanostructures entwined by graphite layers (Ni2P/GC). In this process, a commercial amino phosphonic acid chelating resin was adopted as both the phosphorus and carbon resources. Then, Ni2+ was introduced into the resin framework via ionic exchange and chelation to form a resin-Ni2+ precursor. After carbonization, the highly dispersed Ni2P particles, coupled with thin graphite layers, were simultaneously synthesized in situ. A ternary 7.5% Pt-Ni2P/GC catalyst was further obtained by loading 7.5 wt % Pt on Ni2P/GC. For the oxygen reduction reaction in acidic media, the 7.5% Pt-Ni2P/GC catalyst exhibited even more positive onset (1.03 V) and half-wave (0.93 V) potentials, as well as a rather higher mass activity of 565.3 mA mgPt-1 and a better long-term stability than those of the commercial 20% Pt/C (JM) electrocatalyst. The improved reaction kinetics is mainly attributed to the synergistic effect between Pt and Ni2P/GC. This work not only provides a method for the synthesis of phosphides but also gives insight into the synergy between Pt and Ni2P, which is helpful for the development of more low-Pt catalysts in acidic media.

Recent development of methanol electrooxidation catalysts for direct methanol fuel cell

Direct methanol fuel cells (DMFCs) are very promising power source for stationary and portable miniature electric appliances due to its high efficiency and low emissions of pollutants. As the key material, catalysts for both cathode and anode face several problems which hinder the commercialization of DMFCs. In this review, we mainly focus on anode catalysts of DMFCs. The process and mechanism of methanol electrooxidation on Pt and Pt-based catalysts in acidic medium have been introduced. The influences of size effect and morphology on electrocatalytic activity are discussed though whether there is a size effect in MOR catalyst is under debate. Besides, the non Pt catalysts are also listed to emphasize though Pt is still deemed as the indispensable element in anode catalyst of DMFCs in acidic medium. Different catalyst systems are compared to illustrate the level of research at present. Some debates need to be verified with experimental evidences.

Nanosized Metal Phosphides Embedded in Nitrogen‐Doped Porous Carbon Nanofibers for Enhanced Hydrogen Evolution at All pH Values

Transition-metal phosphides (TMPs) have emerged as promising catalyst candidates for the hydrogen evolution reaction (HER). Although numerous methods have been investigated to obtain TMPs, most rely on traditional synthetic methods that produce materials that are inherently deficient with respect to electrical conductivity. An electrospinning-based reduction approach is presented, which generates nickel phosphide nanoparticles in N-doped porous carbon nanofibers (Ni2 P@NPCNFs) in situ. Ni2 P nanoparticles are protected from irreversible fusion and aggregation in subsequent high-temperature pyrolysis. The resistivity of Ni2 P@NPCNFs (5.34 Ω cm) is greatly decreased by 104 times compared to Ni2 P (>104 Ω cm) because N-doped carbon NFs are incorporated. As an electrocatalyst for HER, Ni2 P@NPCNFs reveal remarkable performance compared to other previously reported catalysts in acidic media. Additionally, it offers excellent catalytic ability and durability in both neutral and basic media. Encouraged by the excellent electrocatalytic performance of Ni2 P@NPCNFs, a series of pea-like Mx P@NPCNFs, including Fe2 P@NPCNFs, Co2 P@NPCNFs, and Cu3 P@NPCNFs, were synthesized by the same method. Detailed characterization suggests that the newly developed method could render combinations of ultrafine metal phosphides with porous carbon accessible; thereby, extending opportunities in electrocatalytic applications.

Nanosize water-soluble colloidal MnO2: an efficient oxidant for the ruthenium(III)-catalyzed degradation of metronidazole

The unrestricted use of drug has aroused researcher concern toward its removal from the environment. The present work is aimed to synthesize a highly stable water-soluble nanosize colloidal MnO2 and its application in the degradation of pharmaceuticals waste in aquatic environment. The as-synthesized colloidal MnO2 is systematically characterized by UV–vis, XRD, TEM, DLS, zeta potential and FTIR. The degradation of metronidazole (MTZ) by colloidal MnO2 was studied spectrophotometrically in the presence of ruthenium(III) catalyst in acidic medium under pseudo first-order condition. Our results show that nanosized colloidal MnO2 is an excellent oxidant for the degradation of MTZ catalyzed by ruthenium(III) in aqueous acidic medium. It was observed that the ruthenium(III) as catalyst significantly increases the reaction rate. The overall thermodynamic activation parameters were also calculated. The main oxidation product was identified as 5-nitro-1-(2-oxoethyl)-1H-imidazole-2-carboxylic acid and confirmed by GC–MS analysis. A plausible mechanism was also proposed.

Polyoxometalate electrocatalysts based on earth-abundant metals for efficient water oxidation in acidic media.

Water splitting is a promising approach to the efficient and cost-effective production of renewable fuels, but water oxidation remains a bottleneck in its technological development because it largely relies on noble-metal catalysts. Although inexpensive transition-metal oxides are competitive water oxidation catalysts in alkaline media, they cannot compete with noble metals in acidic media, in which hydrogen production is easier and faster. Here, we report a water oxidation catalyst based on earth-abundant metals that performs well in acidic conditions. Specifically, we report the enhanced catalytic activity of insoluble salts of polyoxometalates with caesium or barium counter-cations for oxygen evolution. In particular, the barium salt of a cobalt-phosphotungstate polyanion outperforms the state-of-the-art IrO2 catalyst even at pH < 1, with an overpotential of 189 mV at 1 mA cm-2. In addition, we find that a carbon-paste conducting support with a hydrocarbon binder can improve the stability of metal-oxide catalysts in acidic media by providing a hydrophobic environment.

Investigation of Chloride Poisoning Resistance for Nitrogen-Doped Carbon Nanostructures as Oxygen Depolarized Cathode Catalysts in Acidic Media

HCl electrolysis used to manufacture Cl2, a compound of high industrial value, suffers from its high energy requirements. Significant energy savings can be attained by an alternative oxygen depolarized cathode (ODC)-based process where oxygen is reduced at the cathode instead of protons. Though the ODC process is extremely attractive, the state of the art catalysts for oxygen reduction reaction (ORR) suffer from chloride ion poisoning and/or involve toxic chemicals such as hydrogen sulfide (H2S). In the present work, we demonstrate that non-metal containing CNx catalysts do not get deactivated upon exposure to chloride ion environment unlike Pt/C or RhxSy/C where significant chloride ion poisoning was observed. The synthesis of these CNx materials is also extremely facile and scalable. In addition, the performance of the synthesized CNx catalysts was found to be very stable in HCl environment. Thus, the results presented here demonstrate the promise of CNx materials as alternative catalysts for ODC-based HCl electrolysis process to manufacture Cl2 in a sustainable and safer way.

Kinetics of Oxygen Electroreduction on Me–N–C (Me = Fe, Co, Cu) Catalysts in Acidic Medium: Insights on the Effect of the Transition Metal

The influence of three different transition metals (Me = Fe, Co, Cu) on the oxygen reduction reaction (ORR) kinetics in acidic medium of Me–N–C catalysts synthesized using Me(II)-phthalocyanine as precursors is investigated in this work. Through a detailed electrochemical characterization using cyclic voltammetry and rotating ring-disk electrode, several kinetic parameters such as Tafel slope, reaction order for oxygen and proton, apparent activation energy, selectivity toward hydrogen peroxide production, and kinetics of reduction of adsorbed oxygen were determined. The behavior of these three catalysts is analyzed in detail. A comparison between each other of the catalysts, and with a Pt-based catalyst is done. The results obtained provide clear evidence of the important role played by each transition metal in the formation of more or less effective active sites. The ORR kinetics behavior can be well interpreted according to the occurrence of a redox-mediated coverage of the active sites at low overpote...

TiN Supported Cobalt and Molybdenum Nitrides as an Efficient Oxygen Reduction Reaction Catalyst in Acid Medium

TiN Supported Cobalt and Molybdenum Nitrides as an Efficient Oxygen Reduction Reaction Catalyst in Acid Medium

ENHANCING PHOTOCATALYTIC ACTIVITY OF BISMUTH FERRITE BY DOPING WITH COBALT AND ITS USE FOR DEGRADATION OF EVANS BLUE

An attempt has been made to enhance the photocatalytic activity of bismuth ferrite by doping it with cobalt, to prepare a catalyst to use in wide pH range for the photodegradation of Evans blue dye. The progress of the reaction has been monitored spectrophotometrically by measuring the absorbance of the reaction mixture at definite time intervals. Different parameters such as pH, the concentration of dye, amount of semiconductor and light intensity were varied to achieve the optimum rate of photodegradation. The results show that doping of bismuth ferrite by cobalt increases the rate of photocatalytic degradation due to narrowing of the band gap. Undoped bismuth ferrite has the highest catalytic activity in basic while the Co-doped catalyst in acidic medium. A tentative mechanism for the reaction has been proposed.

Fe, N, S-doped porous carbon as oxygen reduction reaction catalyst in acidic medium with high activity and durability synthesized using CaCl2 as template

Proton exchange membrane fuel cells suffer from the sluggish kinetics of the oxygen reduction reaction (ORR) and the high cost of Pt catalysts. In the present work, a high-performance ORR catalyst based on Fe, N, S-doped porous carbon (FeNS-PC) was synthesized using melamine formaldehyde resin as C and N precursors, Fe(SCN)3 as Fe and S precursors, and CaCl2 as a template via a two-step heat treatment without a harsh template removal step. The results show that the catalyst treated at 900 °C (FeNS-PC-900) had a high surface area of 775 m2/g, a high mass activity of 10.2 A/g in an acidic medium, and excellent durability; the half-wave potential decreased by only 20 mV after 10000 potential cycles. The FeNS-PC-900 catalyst was used as the cathode in a proton exchange membrane fuel cell and delivered a peak power density of 0.49 W/cm2. FeNS-PC-900 therefore has good potential for use in practical applications.

IrO2-TiO2: A High-Surface-Area, Active, and Stable Electrocatalyst for the Oxygen Evolution Reaction

The utilization and development of efficient water electrolyzers for hydrogen production is currently limited due to the sluggish kinetics of the anodic process—the oxygen evolution reaction (OER). Moreover, state of the art OER catalysts contain high amounts of expensive and low-abundance noble metals such as Ru and Ir, limiting their large-scale industrial utilization. Therefore, the development of low-cost, highly active, and stable OER catalysts is a key requirement toward the implementation of a hydrogen-based economy. We have developed a synthetic approach to high-surface-area chlorine-free iridium oxide nanoparticles dispersed in titania (IrO2-TiO2), which is a highly active and stable OER catalyst in acidic media. IrO2-TiO2 was prepared in one step in molten NaNO3 (Adams fusion method) and consists of ca. 1–2 nm IrO2 particles distributed in a matrix of titania nanoparticles with an overall surface area of 245 m2 g–1. This material contains 40 molM % of iridium and demonstrates improved OER activi...

An efficient and pH-universal ruthenium-based catalyst for the hydrogen evolution reaction.

The hydrogen evolution reaction (HER) is a crucial step in electrochemical water splitting and demands an efficient, durable and cheap catalyst if it is to succeed in real applications. For an energy-efficient HER, a catalyst must be able to trigger proton reduction with minimal overpotential and have fast kinetics. The most efficient catalysts in acidic media are platinum-based, as the strength of the Pt-H bond is associated with the fastest reaction rate for the HER. The use of platinum, however, raises issues linked to cost and stability in non-acidic media. Recently, non-precious-metal-based catalysts have been reported, but these are susceptible to acid corrosion and are typically much inferior to Pt-based catalysts, exhibiting higher overpotentials and lower stability. As a cheaper alternative to platinum, ruthenium possesses a similar bond strength with hydrogen (∼65 kcal mol-1), but has never been studied as a viable alternative for a HER catalyst. Here, we report a Ru-based catalyst for the HER that can operate both in acidic and alkaline media. Our catalyst is made of Ru nanoparticles dispersed within a nitrogenated holey two-dimensional carbon structure (Ru@C2N). The Ru@C2N electrocatalyst exhibits high turnover frequencies at 25 mV (0.67 H2 s-1 in 0.5 M H2SO4 solution; 0.75 H2 s-1 in 1.0 M KOH solution) and small overpotentials at 10 mA cm-2 (13.5 mV in 0.5 M H2SO4 solution; 17.0 mV in 1.0 M KOH solution) as well as superior stability in both acidic and alkaline media. These performances are comparable to, or even better than, the Pt/C catalyst for the HER.

Recent advances in Fe (or Co)/N/C electrocatalysts for the oxygen reduction reaction in polymer electrolyte membrane fuel cells

Exploring cheap and stable electrocatalysts to replace Pt for the oxygen reduction reaction (ORR) is significant for the large-scale application of fuel cells, especially in polymer electrolyte membrane fuel cells. In this paper, we have briefly reviewed the recent advances in the Fe (or Co)/N/C ORR catalysts in acidic medium including their preparation, structural characterization and related mechanism.

Activation of a Pt-based alloy by a Keggin-type cesium salt of heteropolytungstate towards electrochemical oxidation of ethylene glycol in acidic medium

This work reports the preparation and electrochemical characterization of PtSn/C and PtRh/C modified with a cesium salt of phosphotungstic acid, CsPTA, for use as electrochemical oxidation catalysts in acidic medium. The primary test system is the oxidation of ethylene glycol. Electrode with these modified nanoparticles confined as surface layers are used in studies not only on ethylene glycol but also on all side products of its oxidation in H2SO4 electrolyte. The experimental results reveal that films on carbon electrodes of nanoparticulate PtSn/C and PtRh/C modified with CsPTA enhance the catalytic activity relative to those lacking the CsPTA towards ethylene glycol oxidation. Higher anodic current densities are especially evident at low potentials, particularly below 0.35 V (vs. RHE). Additionally, a preliminary single fuel cell test with the CsPTA-modified PtSn/Vulcan anode shows a better performance than does the PtSn/Vulcan catalyst.

Oxygen Reduction Reaction Mechanisms on Al-Doped X-Graphene (X = N, P, and S) Catalysts in Acidic Medium: A Comparative DFT Study

Density functional theory (DFT) is applied to study the oxygen reduction reaction (ORR) mechanisms on Al-doped X-graphene (X = N, P, and S) electrocatalyst in acidic medium in a fuel cell cathode comparatively. In order to study the catalytic properties of Al-doped X-graphene (X = N, P, and S), we calculate the adsorption properties of the ORR intermediates O2, O, OOH, OH, H2O, and H2O2. We also examine 2e and 4e pathways during the ORR process in terms of adsorption energy of each ORR step. Our calculated results reveal that each Al-doped X-graphene (X = N, P, and S) catalyst follows a 4e transfer pathway with favorable (exothermic) reaction energies. We observe that both Al-doped N-graphene and Al-doped P-graphene are energetically more favorable than Al-doped S-graphene catalysts for enhanced and stable ORR via 4e pathways in an acidic environment. Such analysis is quite useful in choosing the appropriate catalyst in applications of a polymer electrolyte fuel cell cathode.