Reaction In Acid Medium Research Articles

Effect of template, reaction time and platinum concentration in the synthesis of PtCu/CNT catalyst for PEMFC applications

Ultra-low PtCu loading on carbon nanotubes (CNT) catalysts were synthesized by a novel galvanic displacement (GD) method under sonication conditions. The influence of the type of copper template, reaction time, and Pt concentration in the galvanic displacement bath and their correlation to electrocatalytic activity of the catalysts for oxygen reduction reaction in acidic media were studied. Among the catalysts synthesized, the best catalyst identified through electrochemical analysis was used to prepare Membrane Electrode Assembly and evaluated in a hydrogen fuel cell. The maximum power density of the PtCu/CNT and commercial catalyst (20% Pt/C) in the fuel cell were 452 mW cm−2 at 0.424 V and 358 mW cm−2 at 0.475 V, respectively, clearly showing the superior electrocatalytic capability of the PtCu/CNT catalyst synthesized in this study when compared with the commercial catalyst.

Carbon coated nickel - Nickel oxide composites as a highly efficient catalyst for hydrogen evolution reaction in acid medium

Carbon coated nickel - nickel oxide composites (Ni/NiO@C/GR-t-w) was synthesized from the direct carbonization of the composites composed of Ni-MOF-74 and graphene oxide (GO). Due to the synergetic effects of Ni, NiO and graphene, Ni/NiO@C/GR-t-w all exhibited the electrocatalytic performance to HER in acidic medium. When the GO content was 8% and the carbonization temperature was 900 °C, the composites (Ni/NiO@C/GR-900-8) showed the best electrocatalytic properties with an lower overpotential of 108 mV (vs. RHE) at 10 mA cm−2, a smaller Tafel slope of 44 mV dec−1 and a good stability in a 0.5 M H2SO4 solution. The excellent electrocatalytic performance enabled Ni/NiO@C/GR composites to be a favorable HER catalyst to replace the expensive Pt-based materials in the applications of the hydrogen production.

Cobalt nitride nanoparticle-modified nitrogen-doped graphene aerogel used as an efficient catalyst for oxygen reduction reaction in acidic medium

A promising cobalt nitride nanoparticle-modified nitrogen-doped graphene aerogel (CoN–NGA) has been prepared by chemical reduction and thermal treatment for oxygen reduction reaction (ORR). X-ray diffractometry result reveals the presence of cobalt nitride (CoN) nanoparticles on aerogel. X-ray photoelectron spectroscopy analyses reveal that nitrogen atoms have been doped into framework of graphene sheet and nitrogen-doped graphene sheets have been modified with cobalt nitride nanoparticles through CoN–C moieties. Analyses of scanning electron microscopy and Brunauer–Emmett–Teller show that CoN–NGA catalyst displays a various and interconnected pore structure. Because of a huge synergistic effect of the nitrogen-doped graphene, the three-dimensional porous structure and cobalt nitride nanoparticles, the prepared CoN–NGA catalyst displays comparable electrocatalytic activity and the similar onset potential as commercial Pt/C (20% loading). CoN–NGA catalyst exhibits superior stability and excellent methanol tolerance in acidic solution. Nitrogen-doped graphene has been provided positive potential and excellent methanol tolerance through functionalizing with cobalt nitride nanoparticles, because there are strong interactions between N-doped graphene and CoN nanoparticles through CoN–C moieties. It is found that CoN–C moieties are actual ORR active sites rather than CoN nanoparticles themselves. The possible mechanism of ORR on CoN–C moieties has been involved. This study demonstrates a feasible strategy to design non-precious metal nitride-modified heteroatom-doped graphene electrocatalyst for ORR in acidic electrolyte.

Urchin-like Mo2S3 prepared via a molten salt assisted method for efficient hydrogen evolution.

Urchin-like Mo2S3 crystals, prepared via a molten salt assisted solid-state method, have been explored as novel electro-catalysts for hydrogen evolution reactions for the first time. Because of their unique three-dimensional structure and superior electrical conductivity, Mo2S3 exhibits better catalytic activity and stability in acidic media compared with the well-known two-dimensional 2H-MoS2 and 1T'-MoS2.

Interfacial proton enrichment enhances proton-coupled electrocatalytic reactions

PdNi alloy nanostructures–polyethyleneimine inorganic–organic nanocomposites exhibit enhanced catalytic activity for the oxygen reduction reaction and hydrogen evolution reaction in acidic media due to interfacial proton enrichment.

Electrocatalytic activity of electrochemically dealloyed PdCu3 intermetallic compound towards oxygen reduction reaction in acidic media

A structurally ordered phase of PdCu3 nanoparticles (NPs)/carbon black (CB), in which PdCu3 has a Cu3Au-type structure, was prepared by co-reduction of Pd and Cu precursors using ethylene glycol as a reducing agent and an annealing procedure.

Phosphonium-Based Ionic Liquid: A New Phosphorus Source toward Microwave-Driven Synthesis of Nickel Phosphide for Efficient Hydrogen Evolution Reaction

Employing phosphonium-based ionic liquid, tetrabutylphosphonium chloride [P4444]Cl as novel phosphorus source and reaction medium, a facile approach for fabricating nanostructured Ni2P and Ni12P5 was developed upon microwave heating in 1–2 min or conventional heating at 350 °C for 3 h. In a microwave-driven approach, controlling counteranions of various nickel salts could conveniently tune the phase of as-synthesized nickel phosphides. Ni(acac)2 and Ni(OAc)2·4H2O as Ni source could yield Ni2P nanoparticles, while NiCl2·6H2O and NiSO4·7H2O offered Ni12P5 nanocrystals. The synthesized products were characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. Their electrocatalytic behavior toward hydrogen evolution reaction in acidic medium was investigated. The as-synthesized Ni2P nanoparticles presented more excellent catalytic efficiency than Ni12P5. Ni2P nanoparticles from Ni(acac)2 require overpotentials of only 102 mV to reach 10 mA cm–2 with a sma...

Mesoporous Ag-doped Co3O4 nanowire arrays supported on FTO as efficient electrocatalysts for oxygen evolution reaction in acidic media

Abstract In acidic media, benchmark electrocatalysts for oxygen evolution reaction (OER) are mainly restricted to noble metal oxides like IrO2 and RuO2. Herein, a facile electrodeposition-hydrothermal process has been used to fabricate mesoporous Ag-doped Co3O4 nanowire arrays supported on FTO (Ag Co/FTO) for water oxidation in 0.5 M H2SO4. The role of electrodeposited Ag includes: 1) Ag film on FTO can direct the vertical growth of Co3O4 to form nanowire arrays; 2) Ag2O in Ag Co hydroxides precursors contribute to the formation of mesoporous nanostructure owing to the pyrolysis of Ag2O in calcination process. XRD confirms the diffraction peaks of metal Ag and Co3O4. SEM and TEM images display that mesoporous nanowire arrays of Ag-doped Co3O4 are uniformly distributed on FTO, which introduces more exposed active sites and shorter electron transfer paths. Ag Co/FTO show excellent OER activity with the onset potential of 1.91 V at the current density of 10 mA cm−2. Besides, Ag Co/FTO shows high stability at a constant overpotential of 370 mV for 10 h. So Ag-doping greatly enhances not only the conductivity but also the stability of electrocatalyst in acidic media. Therefore, Ag-doped transition metal oxides may be promising alternative mesoporous nanostructures for efficient OER in acid.

Nitrogen-doped porous carbon derived from surface-attached polymer layers for oxygen reduction reaction under acidic conditions

We reported the synthesis of nitrogen-doped carbon using surface-attached polyelectrolyte layers as precursors. The synthesized material has a large surface area of 800 m2·g-1 with uniformed pore distribution. Benefitfed from the high pyridinic nitrogen content, the synthesized nitrogen-doped porous carbon material exhibits promising electrocatalytic activity toward oxygen reduction reactions in acidic medium and very high stability against continuous cyclic voltammetry scans. The experimental results demonstrate that surface-attached polyelectrolyte layers are promising carbon and nitrogen sources for the formation of heteroatom-doped porous carbon materials.

Anion-Regulated Selective Generation of Cobalt Sites in Carbon: Toward Superior Bifunctional Electrocatalysis.

The introduction of active transition metal sites (TMSs) in carbon enables the synthesis of noble-metal-free electrocatalysts for clean energy conversion applications; however, there are often multiple existing forms of TMSs, which are of different natures and catalytic models. Regulating the evolution of distinctive TMSs is highly desirable but remains challenging to date. Anions, as essential elements involved in the synthesis, have been totally neglected previously in the construction of TMSs. Herein, the effects of anions on the creation of different types of TMSs are investigated for the first time. It is found that the active cobalt-nitrogen sites tend to be selectively constructed on the surface of N-doped carbon by using chloride, while metallic cobalt nanoparticles encased in protective graphite layers are the dominant forms of cobalt species with nitrate ions. The obtained catalysts demonstrate cobalt-sites-dependent activity for oxygen reduction reaction and hydrogen evolution reaction in acidic media. The remarkably enhanced catalytic activities approaching that of benchmark Pt/C in an acidic medium have been obtained on the catalyst dominated with cobalt-nitrogen sites, confirmed by the advanced spectroscopic characterization. This finding demonstrates a general paradigm of anion-regulated evolution of distinctive TMSs, providing a new pathway for enhancing performances of various targeted reactions related with TMSs.

Electrodeposited Ni-W nanoparticles: Enhanced catalytic activity toward hydrogen evolution reaction in acidic media

Electrocatalytic production of hydrogen through non-precious metals is of great importance. While Ni and its alloys show a good catalytic activity in alkaline solutions, their poor response and stability in acidic electrolytes is yet a challenge. Herein, we report on the electrodeposition of Ni-W nanoparticles (NPs) with the aim of electrocatalytic enhancement of nickel material in acidic media for hydrogen evolution reaction (HER). The catalyst showed a high current density of 10 mA.cm−2 at −205 mV (vs. RHE) for HER and an improved stability compared to that of tungsten-free Ni NPs. The high catalytic activity of Ni-W NPs stems from incorporation of the tungsten atoms into the nickel structure. The results are promising for developing of highly efficient, earth-abundant and inexpensive Ni-based cathodes for HER.

Low temperature synthesis of copper manganese oxide – polyaniline composite: Electrochemical characterizations for oxygen reduction reaction in acid media

ABSTRACTCopper manganese mixed oxide with polyaniline based composite is electrodeposited by chronoamperometric method on Vulcan XC72 carbon paper used as a backing layer in proton exchange membrane fuel cell. The electro deposited catalyst characterized by XRD and SEM shows the formation of Cu1.5Mn1.5O4 with polyaniline coating during the process of polymerization under constant potential in acidic medium. Oxygen reduction reaction (ORR) activity of the catalyst evaluated by linear sweep voltammetry, rotating ring disk electrode voltammetry and scanning electrochemical microscopy measurements established ∼2 e transfer process and significant catalytic surface roughness with promising activity towards ORR.

Molybdenum oxide and molybdenum carbide coated carbon black as an electrocatalyst for hydrogen evolution reaction in acidic media

Molybdenum oxide and molybdenum carbide coated carbon black (MoO2–Mo2C/C) non-noble metal hybrid electrocatalyst for hydrogen evolution reaction (HER) was synthesized from a mixture of metal molybdenum (Mo) powders and carbon black particles by a spark plasma coating (SPC) method. After the SPC process, the MoO2–Mo2C coating can anchor strongly on carbon black with the help of intermediate products Mo2C. The MoO2–Mo2C/C electrocatalyst exhibited a good HER performance with an onset overpotential of −121 mV, a high exchange current density of 6.8 × 10−2 mA cm−2 and a Tafel slope of −69 mV dec−1 in 0.5 M H2SO4 solution. In addition, the MoO2–Mo2C/C showed much higher stability than Pt/C (20 wt% Pt supported on Vulcan XC-72 carbon black) after 3000 cycles of accelerated durability tests. The enhanced electrocatalytic activity and stability of MoO2–Mo2C/C electrocatalyst toward HER may originate from the Mo2C active sites formed in the process of SPC, and the effectively anchoring effect of MoO2–Mo2C coating on carbon black.

Synergistic Effects between Atomically Dispersed Fe-N-C and C-S-C for the Oxygen Reduction Reaction in Acidic Media.

Various advanced catalysts based on sulfur-doped Fe/N/C materials have recently been designed for the oxygen reduction reaction (ORR); however, the enhanced activity is still controversial and usually attributed to differences in the surface area, improved conductivity, or uncertain synergistic effects. Herein, a sulfur-doped Fe/N/C catalyst (denoted as Fe/SNC) was obtained by a template-sacrificing method. The incorporated sulfur gives a thiophene-like structure (C-S-C), reduces the electron localization around the Fe centers, improves the interaction with oxygenated species, and therefore facilitates the complete 4 e- ORR in acidic solution. Owing to these synergistic effects, the Fe/SNC catalyst exhibits much better ORR activity than the sulfur-free variant (Fe/NC) in 0.5 m H2 SO4 .

Synergistic Effects between Atomically Dispersed Fe−N−C and C−S−C for the Oxygen Reduction Reaction in Acidic Media

AbstractVarious advanced catalysts based on sulfur‐doped Fe/N/C materials have recently been designed for the oxygen reduction reaction (ORR); however, the enhanced activity is still controversial and usually attributed to differences in the surface area, improved conductivity, or uncertain synergistic effects. Herein, a sulfur‐doped Fe/N/C catalyst (denoted as Fe/SNC) was obtained by a template‐sacrificing method. The incorporated sulfur gives a thiophene‐like structure (C−S−C), reduces the electron localization around the Fe centers, improves the interaction with oxygenated species, and therefore facilitates the complete 4 e− ORR in acidic solution. Owing to these synergistic effects, the Fe/SNC catalyst exhibits much better ORR activity than the sulfur‐free variant (Fe/NC) in 0.5 m H2SO4.

Secondary Impact of Manganese on the Catalytic Properties of Nitrogen‐Doped Graphene in the Hydrogen Evolution Reaction

AbstractCatalysts play a key role in hydrogen production as green energy carriers. We show herein for the first time that manganese impurities in graphene can improve the catalytic activity of synthesized N‐doped graphene (NG) for the hydrogen evolution reaction in acid media by influencing the ratio of different N‐functionalities. A 122 mV improvement in the overpotential was found following the Mn impregnation of graphene. Transmission electron microscopy images confirmed the formation of manganese oxide nanoparticles on the NG sheets. X‐ray photoelectron spectroscopy revealed structural alteration in favor of higher quantities of quaternary and pyrrolic nitrogen functionalities, from approximately 37 % in NG to 84 % in the Mn‐inserted‐doped graphene catalyst. This enhanced catalytic performance, based on density functional theory calculations in the literature, was attributed to an increase in the number of active sites with higher activity.

Induced changes of Pt/C in activity and durability through heat-treatment for oxygen reduction reaction in acidic medium

In this study, the Pt/C catalysts systematically heat-treated from 200 to 800 °C are characterized physically and chemically to investigate the induced properties for the activity and durability. The relative intensity of Pt0 increases from approximately 40 to 70% and the mean Pt particle size mildly increases as the temperature increases from 200 to 600 °C. However, the Pt/C heat-treated at 800 °C sharply increases and shows poor Pt particle size distribution resulting in the poor electrochemical performance. Catalysts prepared at between 200 and 600 °C exhibit similar electrocatalytic properties. Durability tests using sweeping potential between 0.6 and 1.0 V show that the durability of catalysts heat-treated at 400–600 °C significantly increases since the Pt oxide can be readily dissolved under potential cycling as compared to the Pt0. We strongly believe that the induced changes by heat-treatment play an important role in the challenges for fuel cells.

An efficient Sb-SnO2-supported IrO2 electrocatalyst for the oxygen evolution reaction in acidic medium

Polymer (acidic) electrolyte membrane water electrolysis suffers from insufficient catalyst activity, high cost of noble metal, and unsatisfactory durability, due to the sluggish reaction kinetics of oxygen evolution reaction and poor stability of catalysts under harsh operating environments. Aiming to enhance the utilization and durability of noble metals, a mesoporous Sb-doped SnO2 material with high surface area and conductivity was synthesized via soft-template method to support IrO2 catalyst. Physical characterization reveals that the as-prepared composite exhibits a rough morphology with the weak crystallinity IrO2 upper layer covering the rutile SnO2 crystalline phase. Electrochemical test for the IrO2-loading-dependant activity finds that both the area-free activity and mass-specific current on the 31 wt% sample are the optimal, meaning the excellent dispersion effect coming from the mesoporous Sb-SnO2 support and the synergy between the catalytic particles and Sb dopant. In addition, the enhancement in mass transfer efficiency and conductivity coming from the porous, IrO2-covered cross-linked morphology and the support-active component interaction, the supported IrO2 with 50 wt% loading marks the maximum normalized charge (227 C g−1 IrO2) and the highest apparent current at 1.75 V. What is more, this composite catalyst with the noble metal oxide coating is much more durable during continuous oxygen evolution procedure under a constant potential of 1.6 V because of the anchor effect from the carrier on the catalyst and a protective effect from the noble metal layer on the non-acid-tolerant support.

Carbon Supported Mono- and Bi-Metallic Dispersed Thin Film Catalysts for Oxygen Electro-Reduction Reaction in Acid Medium

Carbon Supported Mono- and Bi-Metallic Dispersed Thin Film Catalysts for Oxygen Electro-Reduction Reaction in Acid Medium

Tungsten diselenide/porous carbon with sufficient active edge-sites as a co-catalyst/Pt-support favoring excellent tolerance to methanol-crossover for oxygen reduction reaction in acidic medium

Developing an acid-stable, highly active and methanol-tolerant electrocatalyst towards the oxygen reduction reaction (ORR) is crucial for commercialization of direct methanol fuel cells (DMFCs). In this study, via a simultaneous synthesis method, tungsten diselenide/porous carbon (WSe2/C) composites are prepared as the supports/ORR co-catalysts to support Pt with a low loading of 5wt.%. Varied WSe2/C supports are obtained by tuning the carbonization temperature (600–1000°C) to investigate the relationships between structural characteristics and ORR performance. Pt-WSe2/C (800°C) exhibits a considerably higher specific activity (4.57mAcm−2) for ORR than those of WSe2/C (2.45mAcm−2) and commercial Pt/C (10wt.%, 2.69mAcm−2), owing to the high ORR co-catalytic activity of WSe2/C for Pt. The robust contacts among Pt, WSe2 and porous carbon with high surface area can significantly improve the exposure of Pt active sites, which correspondingly promote the charge transfer efficiency and the fast adsorption, activation and reduction of oxygen molecules. Moreover, Pt-WSe2/C (800°C) catalyst exclusively exhibits a four-electron pathway for ORR. With the intimate cooperation among Pt, WSe2 and porous carbon skeleton, more available Pt active sites are exposed to improve the ORR kinetics and durability. The tolerance to methanol-crossover on Pt-WSe2/C are remarkably enhanced, which should be attributed to the synergistic effects between the exposed edge sites of embedded WSe2 and the porous carbon skeleton with abundant oxygen-containing functional groups. The use of WSe2/C supports with low-cost, high co-catalytic/catalytic activity and strong methanol-tolerance provides a promising way to enhance ORR activity in DMFCs.