Oxygen Electroreduction In Alkaline Media Research Articles

Chromium phosphide CrP as highly active and stable electrocatalysts for oxygen electroreduction in alkaline media

Catalysts for oxygen reduction reaction (ORR) are key components in emerging energy technologies such as fuel cells and metal-air batteries. Developing low-cost, high performance and stable electrocatalysts is critical for the extensive implementation of these technologies. Herein, we present a procedure to prepare colloidal chromium phosphide CrP nanocrystals and we test their performance as ORR electrocatalyst. CrP-based catalysts exhibited remarkable activities with a limiting current density of 4.94 mA cm−2 at 0.2 V, a half-potential of 0.65 V and an onset potential of 0.8 V at 1600 rpm, which are comparable to commercial Pt/C. Advantageously, CrP-based catalysts displayed much higher stabilities and higher tolerances to methanol in alkaline solution. Using density functional theory calculations, we demonstrate CrP to provide a very strong chemisorption of O2 that facilitates its reduction and explains the excellent ORR performance experimentally demonstrated.

Nitrogen-Doped Three-Dimensional Graphene-Supported Palladium Nanocomposites: High-Performance Cathode Catalysts for Oxygen Reduction Reactions

This study reports an effective strategy for fabricating three-dimensional nitrogen-doped graphene supports for palladium nanoparticles (Pd–N/3D-GNS) and studying the electrochemical activity of the synthesized nanocomposites toward oxygen electroreduction in alkaline media as well as implementing the nanocomposite as cathode catalysts in anion exchange membrane fuel cells (AEMFC). It was demonstrated that by embedding and etching an amorphous sacrificial silica template into the reduced graphene matrix, the as-prepared nanocomposites pyrolyzed into hierarchically porous 3D-nanosheets composed of interconnected nitrogen-doped graphene nanostacks, which was confirmed using transmission electron microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. Palladium nanoparticles were then deposited on the N/3D-GNS supports using a surfactant-free technique and characterized using various surface analysis and potentiodynamic techniques. By analyzing the linear sweep voltammograms obtained ...

Highly Active Transition Metal and Nitrogen Co-Doped Carbon Nanotube Based Cathode Catalysts for Anion Exchange Membrane Fuel Cells

Low cost and high durability are considered as the main challenges in mass scale commercialization of the low temperature fuel cells. Anion exchange membrane fuel cells (AEMFC’s) have attracted tremendous attention because of their promising characteristics to overcome some of the critical problems associated with proton exchange membrane fuel cells. The main advantages of AEMFC´s are possibility of using cheaper non-noble metal catalyst, lower crossover of cationic redox couples, facile reaction kinetics. In recent years, nitrogen-doping of carbon materials has been used to achieve active non-platinum catalyst.1,2 However it has been reported that the presence of transition metals such as Co or Fe can further enhances the electrocatalytic properties of N-doped carbons.3 The main goal of this study was to develop highly active transition metal-nitrogen co-doped catalyst as alternative cathode material to Pt/C in AMFC. A simple synthesis method was used to receive nitrogen doped multi-walled carbon nanotube supported CoCl2 catalyst material (Co/N-MWCNT). MWCNT treated in a concentrated HNO3-H2SO4 mixture were used as carbon support. MWCNTs were first dispersed in ethanol by sonication, after which dicyandiamide as the nitrogen source and Co salt were added along with a dispersing agent. The mixture was then heat-treated at 800 °C for 2 h in a tube furnace. Polished glassy carbon electrodes were modified with a dispersion containing the resulting materials and Tokuyama OH−ionomer AS-04. The rotating disk electrode (RDE) measurements were performed in 0.1 M KOH. The stability of the catalysts were also tested using RDE method. The structural and compositional properties of the catalyst material were defined by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The oxygen reduction reaction (ORR) has been studied on Co/N/MWCNT electrocatalyst modified GC electrodes in 0.1 M KOH using the RDE method. The fuel cell performance of Co/N/MWCNT cathode catalyst material was investigated by fabricating membrane-electrode assemblies (MEAs) using Tokuyama membrane (# A201). The RDE results indicated excellent electrocatalytic properties of Co/N-MWCNT material toward oxygen electroreduction in alkaline media. The comparative study of Co/N-MWCNT with commercial Pt/C catalyst showed fair catalytic activity of our non-platinum catalyst in 0.1M KOH and significant enhancement of the ORR was observed in comparison to unmodified MWCNTs. The number of electrons transferred per oxygen molecule (n) at different potentials for the Co/N-MWCNT modified GC electrode was calculated from the KouteckyLevich equation. The value of n for the Co/N-MWCNT material was 4 over the whole range of potentials studied. The fuel cell performance was investigated with Co/N-MWCNT cathode catalyst and Tokuyama A201 anion exchange membrane. AEMFC performance was evaluated and compared at different temperatures up to 50 ⁰C. Maximum power density with H2/O2 gases at ambient pressure was ~115 mWcm-2. The fuel cell perfomance of the Co/N-MWCNT catalyst was also compared with the perfomance of the commercial Pt/C and cobalt phthalocyanine modified MWCNT catalysts (Fig.1).

Ultrasmall Palladium Nanoclusters Encapsulated in Porous Carbon Nanosheets for Oxygen Electroreduction in Alkaline Media

AbstractUltrasmall noble‐metal nanoclusters have been gaining extensive attention because of their unique catalytic activity. Herein, we describe a facile in situ method for the preparation of palladium nanoclusters encapsulated in porous carbon nanosheets as effective catalysts for the oxygen reduction reaction (ORR) in alkaline media. Structural characterizations through X‐ray diffraction, X‐ray photoelectron spectroscopy, and transmission electron microscopy studies indicate that the Pd clusters were well incorporated into porous carbon nanosheets. The composition of the nanocomposites was manipulated by varying the initial loading ratio of Pd to carbon nanosheets (Pd/CNS). Among the series of samples tested, the sample at a Pd/CNS ratio of 1 : 4 (Pd/CNS‐20 %) exhibited the best ORR activity with the most positive onset potential and largest diffusion‐limited current density, which was even superior to that of commercial Pd black, along with remarkable long‐term durability. The findings highlight the unique advantages of employing ultrasmall ligand‐free palladium clusters as cost‐effective ORR catalysts with high efficiency and remarkable stability.

Shape and structural effects of R5-templated Pd nanomaterials as potent catalyst for oxygen electroreduction in alkaline media

Bio-inspired metal nanomaterials are receiving increasing research attentions in catalytic field recently, while peptide-based method represents new revenues to fabricate stable and reactive catalyst under mild and environmental friendly conditions. Among all kinds of noble metals, peptide-based palladium nanomaterials have demonstrated excellent catalytic capabilities in a variety of organic reactions. However, their electrocatalytic properties have not been systematically studied. Herein, R5-templated Pd nanomaterials have been fabricated and employed as potent catalysts for oxygen reduction reaction (ORR). The shape and morphology of these Pd nanomaterials were manipulated by tuning the metal-to-R5 ratio. The as-prepared Pd nanomaterials demonstrated excellent ORR activity in alkaline media. R5-Pd-90 exhibited the best activity which is superior than commercial Pt/C, in terms of onset potential, diffusion-limited current density as well as long-term stability. The correlation between the shape and/or morphology of the peptide-templated Pd nanomaterials and their ORR activity has been successfully established.

Peptide A4 based AuAg alloyed nanoparticle networks for electrocatalytic reduction of oxygen

Peptide based methods create new revenues to fabricate stable, multifunctional noble metal nanomaterials under mild and green synthesis conditions. Peptide sequence A4 stabilized AuAg alloyed nanomaterials were fabricated through a facile and straightforward approach. The as-prepared alloyed nanomaterials demonstrated effective catalytic activity toward oxygen electroreduction in alkaline media. Both the metal-to-A4 ratio and Au-to-Ag ratio were optimized to enrich the electrocatalytic performance, and the sample of Au:Ag:A4 = 10:30:1 exhibited the highest activity among the series. The performance of Au:Ag:A4 = 10:30:1 is comparable with that of commercial Pt/C, within the context of onset potential, diffusion-limited current density as well as long-term stability. The as-prepared samples were characterized by UV–visible absorbance, transmission electron microscopy (TEM), as well as X-ray photoelectron microscopy (XPS). The improved activity is probably attributed to the alloying induced ensemble effects and electronic effects. This discovery may shed light on fabricating peptide based alloys as highly efficient catalysts with enhanced stability for oxygen reduction reaction (ORR).

Co@Pt Core@Shell nanoparticles encapsulated in porous carbon derived from zeolitic imidazolate framework 67 for oxygen electroreduction in alkaline media

Abstract Nanocomposites based on Co@Pt core@shell nanoparticles encapsulated in nitrogen-doped porous carbons were prepared as a new type of high-performance electrocatalysts for oxygen reduction reaction (ORR). Controlled pyrolysis of zeolitic imidazolate framework 67 (ZIF-67) led to the formation of Co nanoparticles encapsulated in nitrogen-doped porous carbon (Co-NC), which underwent galvanic replacement reactions with K2PtCl4 forming Co@Pt core@shell nanoparticles. The surface microstructure and composition of the resulting Co@Pt-NC nanocomposite were examined by electron microscopic as well as X-ray photoelectron spectroscopic (XPS) measurements. With the Co@Pt particles encapsulated in nitrogen-doped porous carbon, the hybrids exhibited a high specific surface area and abundant catalytically active sites for ORR. Electrochemically, the specific activity and mass activity of the Co@Pt-NC composite at +0.85 V (0.145 mA cm−2 and 71.9 A g−1) were superior to those of commercial Pt/C (0.123 mA cm−2 and 38.4 A g−1). Furthermore, the Co@Pt-NC composite also exhibited remarkably higher durability and more robust tolerance against methanol crossover than commercial Pt/C.

Highly Active Transition Metal-Nitrogen Co-Doped Carbon Nanotube Based Cathode Catalyst for Anion Exchange Membrane Fuel Cells

Low cost and high durability are considered as the main challenges in mass scale commercialization of the low temperature fuel cells. Anion exchange membrane fuel cells (AEMFC’s) have attracted tremendous attention because of their promising characteristics to overcome some of the critical problems associated with proton exchange membrane fuel cells. The main advantages of AEMFC´s are possibility of using cheaper non-noble metal catalyst, lower crossover of cationic redox couples, facile reaction kinetics. In recent years, nitrogen-doping of carbon materials has been used to achieve active non-platinum catalyst.1,2 However it has been reported that the presence of transition metals such as Co or Fe can further enhances the electrocatalytic properties of N-doped carbons.3 The main goal of this study was to develop highly active transition metal-nitrogen co-doped catalyst as alternative cathode material to Pt/C in AMFC. A simple synthesis method was used to receive nitrogen doped multi-walled carbon nanotube supported CoCl2 catalyst material (Co/N-MWCNT). MWCNT treated in a concentrated HNO3-H2SO4 mixture were used as carbon support. MWCNTs were first dispersed in ethanol by sonication, after which dicyandiamide as the nitrogen source and Co salt were added along with a dispersing agent. The mixture was then heat-treated at 800 °C for 2 h in a tube furnace. Polished glassy carbon electrodes were modified with a dispersion containing the resulting materials and Tokuyama OH− ionomer AS-04. The rotating disk electrode (RDE) measurements were performed in 0.1 M KOH. The stability of the catalysts were also tested using RDE method. The structural and compositional properties of the catalyst material were defined by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The oxygen reduction reaction (ORR) has been studied on Co/N/MWCNT electrocatalyst modified GC electrodes in 0.1 M KOH using the RDE method. The fuel cell performance of Co/N/MWCNT cathode catalyst material was investigated by fabricating membrane-electrode assemblies (MEAs) using Tokuyama membrane (# A201). The RDE results indicated excellent electrocatalytic properties of Co/N-MWCNT material toward oxygen electroreduction in alkaline media. The comparative study of Co/N-MWCNT with commercial Pt/C catalyst showed fair catalytic activity of our non-platinum catalyst in 0.1M KOH and significant enhancement of the ORR was observed in comparison to unmodified MWCNTs. The number of electrons transferred per oxygen molecule (n) at different potentials for the Co/N-MWCNT modified GC electrode was calculated from the KouteckyLevich equation. The value of n for the Co/N-MWCNT material was 4 over the whole range of potentials studied. The fuel cell performance was investigated with Co/N-MWCNT cathode catalyst and Tokuyama A201 anion exchange membrane. AEMFC performance was evaluated and compared at different temperatures up to 50 ⁰C (Fig.1). Maximum power density with H2/O2 gases at ambient pressure was ~115 mWcm-2.

Oxygen electroreduction promoted by quasi oxygen vacancies in metal oxide nanoparticles prepared by photoinduced chlorine doping.

Quasi oxygen-deficient indium tin oxide nanoparticles (ITO NPs) were prepared by photoinduced chlorine doping, and exhibited much enhanced electrocatalytic activity for oxygen reduction reaction (ORR) in alkaline media, as compared with pristine ITO.

SnO 2–Au hybrid nanoparticles as effective catalysts for oxygen electroreduction in alkaline media

SnO 2 nanoparticles were synthesized by a facile electrochemical method based on anodic oxidation of a tin metal sheet. The resulting particles, with an average diameter of about 20 nm, were then loaded with varied amounts of HAuCl 4, forming SnO 2–Au( x) ( x = 0, 0.095, 0.38, 0.76, 1.9, 3.0, and 3.8 at.%) hybrid nanoparticles after calcination at elevated temperatures (700 °C). X-ray diffraction (XRD) and transmission electron microscopic (TEM) measurements showed that the SnO 2 particles exhibited high crystallinity with a rutile structure, and spherical Au nanoparticles were dispersed on the surface of the SnO 2 support. Based on the TEM images and the width of the Au(2 0 0) XRD diffraction peak, the size of the Au nanoparticles was found to be between 15 and 35 nm in diameter and decrease with increasing loading of the original HAuCl 4 precursor. The electrocatalytic activity of the resulting SnO 2–Au( x) composite nanoparticles toward oxygen reduction reactions (ORR) was then evaluated by cyclic and rotating disk voltammetric measurements in alkaline solutions. It was found that the incorporation of gold nanoparticles led to apparent improvement of the catalytic activity of SnO 2 nanoparticles. Moreover, the ORR electrocatalytic activity exhibited a strong dependence on the gold loading in the hybrid nanoparticles, and the most active catalyst was found with a gold loading of 1.9 at.%, based on the reduction current density and onset potential of ORR. Furthermore, at this gold loading, oxygen reduction was found to follow the efficient four-electron reaction pathway, whereas at other Au loadings, the number of electron transfer involved in oxygen reduction varied between 1 and 3. Additionally, Tafel analysis suggested that at low overpotentials, the first electron transfer might be the limiting step in oxygen reduction, whereas at high potentials, oxygen adsorption appeared to play the determining role at the SnO 2–Au hybrid electrodes. These results indicate that the SnO 2–Au composite nanoparticles might serve as effective catalysts for oxygen electroreduction in alkaline media.

Performance of Pt/C Doped with Ni for Oxygen Electro-Reduction in Alkaline Media

Abstract Carbon-supported Pt-Ni catalyst samples were prepared by the colloidal method and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopic (XPS) and transmission electron microscopy (TEM). Potentiodynamic was used to measure the performance of the electro-catalysts for the oxygen electro-reduction. The results indicate that the Pt-Ni alloy particles are distributed homogeneously on the carbon surface, and their particle sizes are 3−5 nm. In the same alkali concentration solution, the activity and methanol-tolerance of Pt nano-particle catalysts are greatly enhanced by doping Ni. For the catalyst, the optimum atom ratio of Pt to Ni is Pt 50 Ni 50 /C, and its methanol-tolerance is enhanced markedly as compared with Pt/C. The maximal current of the oxygen electro-reduction over Pt 50 Ni 50 /C reaches 106 mA/mg, and the onset over potential is 50 mV less than that over Pt/C in 0.1 mol/L KOH solution.

Synthesis of silver nanowires with different aspect ratios as alcohol-tolerant catalysts for oxygen electroreduction

The aqueous-phase synthesis of crystalline silver nanowires with different aspect ratios has been achieved by altering seeds. Cyclic voltammetry and tafel results showed that silver nanowires with high aspect ratio exhibited better activity and alcohol-tolerant stability for oxygen electroreduction in alkaline media than nanowires with low aspect ratio.

The beneficial effect of the addition of tungsten carbides to Pt catalysts on the oxygen electroreduction

Tungsten carbide nanocrystal modified Pt catalysts have been prepared by an intermittent microwave heating (IMH) method and show an improved activity for oxygen electroreduction in alkaline media.