Three dimensional assembly of electrocatalytic platinum nanostructures on reduced graphene oxide – An electrochemical approach for high performance catalyst for methanol oxidation

By means of co-electrodeposition, we fabricated 3D assembly of Pt nanostructures with dominant (100) plane on reduced graphene oxide (rGO) modified graphite electrode. The strong metal-support interaction at the atomic level makes the nanostructure highly durable and this modified electrode exhibited high electrocatalytic activity towards methanol oxidation. It has been found that the morphology, active site and the electrochemical activity of Pt are highly dependent on the substrate and the number of electrochemical cycling used for the deposition. rGO-Pt composite deposited using one cycle showed a high mass activity of 2.54 A/mg at 0.67 V for methanol oxidation in acidic condition and 1.84 A/mg at ?0.03 V in alkaline medium. This simple and single step approach using electrodeposition to grow the morphology controlled Pt nanostructure on rGO, will aid in the development of active and stable catalyst for fuel cell applications.     

Hierarchical reduced graphene oxide supported dealloyed platinum–copper nanoparticles for highly efficient methanol electrooxidation

Exploiting highly efficient electrocatalysts through simple methods is very critical to the development of energy conversion technologies. Herein, we develop a hierarchical reduced graphene oxide supported dealloyed platinum–copper nanoparticle catalyst (Pt–Cu/RGO) by a facile one-step electrodeposition of graphene oxide in the presence of H₂PtCl₆ and copper ethylenediamine tetraacetate. The nanostructure and composition were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. Meanwhile, the electrocatalytic performance was investigated by cyclic voltammetry and chronoamperometry, showing that the Pt–Cu/RGO catalyst not only equips with an outstanding electrocatalytic activity for the methanol oxidation reaction (2.3 times that of commercial Pt/C catalyst), but also shows a robust durability and superior tolerance to CO poisoning. The excellent electrocatalytic performance could be attributed to the three-dimensional hierarchical structure, porous dealloyed nanoparticles and synergistic effect between each component.     

Reduction of carbon dioxide to methanol on the surface of adenine functionalized reduced graphene oxide at a low potential

In this study, the surface of reduced graphene oxide (rGO) was modified with adenine via diazonium reaction. Then, to prepare Pt@Adenine-rGO, Pt was deposited on the surface of adenine-rGO, using cyclic voltammetry in the range of ?0.30 to +1.30 V at a scan rate of 100 mV s^?1 in a solution containing Pt salt. Afterward, it was characterized by various techniques such as scanning electron microscopy, X-ray photoelectron spectroscopy, and infrared spectroscopy. Electrochemical studies showed the efficient electrocatalytic behavior of Pt@Adenine-rGO for the reduction of CO₂ to methanol at ?0.30 V. The products formed on the surface of Pt@Adenine-rGO were monitored using different techniques including Raman spectroscopy, gas chromatography, gas chromatography-mass spectrometry, and ¹³C NMR spectroscopy. Our findings indicated that methanol with a reasonably high Faradaic efficiency up to 85% and a current density of 0.5 mA cm^?2 as the main product of CO₂ reduction on the surface of Pt@Adenine-rGO.     

Polyaniline decorated MoO3 nanorods: Synthesis,characterization and promoting effect to Pt electrocatalyst

The promoting effect of metal oxides to Pt catalysts toward methanol oxidation reaction (MOR) has attracted widespread attention in recent years. In this communication, we report the promoting effect of MoO₃ to Pt catalyst by rationally designing and tuning the nanostructure of the catalysts. MoO₃ nanorods are firstly synthesized through hydrothermal method and used as the substrate for the deposition of polyaniline (PANI) layer. The PANI-MoO₃ composite nanostructures are then used as the support for Pt catalyst. Depending on the preparation method of Pt nanoparticles, the nanostructure can be PANI nanotube supported Pt (Pt/PANI) through etching MoO₃ nanorods with NaBH₄ and PANI-MoO₃ composite nanorods supported Pt (Pt/PANI-MoO₃). The catalytic properties of the two catalysts toward MOR are investigated. Results show that the current of methanol oxidation on Pt/PANI-MoO₃ catalyst is comparable to that on Pt/PANI, while the peak potential of MOR on the former is lowered by 180 mV as compared with the latter, suggesting a much higher catalytic activity of Pt/PANI-MoO₃. The presence of MoO₃ may be responsible for the improvement of the catalytic properties through the co-synergistic effects of PANI and MoO₃.     

Comparison study of electrocatalytic activity of reduced graphene oxide supported Pt–Cu bimetallic or Pt nanoparticles for the electrooxidation of methanol and ethanol

Pt–Cu bimetallic nanoparticles supported on reduced graphene oxide (Pt–Cu/RGO) were synthesized through the simple one-step reduction of H₂PtCl₆ and CuSO₄ in the presence of graphene oxide (GO) at room-temperature. The Pt–Cu/RGO was characterized with UV–vis spectrophotometer, X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy and its catalytic behavior for the direct oxidation of methanol was investigated. Compared to Pt/RGO and Pt/C catalysts, Pt–Cu/RGO hybrids exhibited markedly superior catalytic activity for the electrocatalytic oxidation of methanol and ethanol. This improved catalytic activity can be attributed to the dendritic structure of the Pt–Cu bimetallic nanoparticles.     

In situ growth of Ni0·85Se on graphene as a robust electrocatalyst for hydrogen evolution reaction

Seeking the efficient and robust electrocatalysts necessarily enhances performance of hydrogen evolution reaction (HER). Increasing the surface active sites is a means to improve the performance. Herein, we use the Ni_0·85Se anchored on reduction of graphene oxide (Ni_0·85Se/rGO) hybrid material skillfully established by one-step facile hydrothermal method as a robust and stable electrocatalyst applying to hydrogen evolution reaction (HER). In terms of morphology, Ni_0·85Se nanospheres composed of many nanosheets are uniformly distributed on the graphene sheet layer. We also detailedly analyze its properties. Based on the interaction between Ni_0·85Se and rGO, and the roles of graphene are as a substrate to heighten conductivity, possesses more active surface area by limiting growth of Ni_0·85Se, and increases dispersion for exposing more active surface area and enlarge ion/electron transfer rate. In HER, the Ni_0·85Se/rGO catalyst displays the overpotential of 128 mV with a common current density of 10 mA cm⁻², a small Tafel slope of 91 mV dec⁻¹, an extremely low onset potential of 37 mV, outstanding stability that a high current retention of 97.7% after 1000 cycles and well long-term stability for 18 h, outperforming the capability of Ni_0·85Se nanospheres in alkaline solution for HER. The above results indicate that the Ni_0·85Se/rGO hybrid material is a good HER ability and non-noble metal electrocatalyst has potential value in HER.     

Electrochemical layer-by-layer fabrication of a novel three-dimensional Pt/graphene/carbon fiber electrode and its improved catalytic performance for methanol electrooxidation in alkaline medium

Here, we report a novel method for assembling reduced graphene oxide (RGO) and Pt nanoparticles on a carbon fiber (CF) electrode successively to form a stable Pt nanoparticle-RGO-Pt nanoparticle-RGO/CF multiple junction for electrocatalysis application. As the SEM imaging exhibited, Pt nanoparticles are uniformly deposited on the surface of each RGO sheet, performing an alternative covering structure of RGO and Pt nanoparticle multi-layer on the CF electrode. Thus, a novel three-dimensional (3D) multi-layered Pt/RGO modified CF electrode (N–Pt/RGO/CF) is obtained. Experimental results demonstrate that the prepared N–Pt/RGO/CF electrode shows good electrochemical properties and enhanced electrocatalytic activity toward methanol electrooxidation in alkaline medium as compared with the Pt/RGO/CF electrode without layer-by-layer structure or the Pt/CF electrode without RGO. It is due to the unique 3D pore structure of N–Pt/RGO/CF and the good electron transport property of RGO in the composite electrode.     

Hollow hexagonal NiSe–Ni3Se2 anchored onto reduced graphene oxide as efficient electrocatalysts for hydrogen evolution in wide-pH range

Integrating transition metal complexes with carbon-based materials, especially graphene, is a useful strategy for synthesizing effective hydrogen evolution catalysts. Herein, we report a design of hollow hexagonal NiSe–Ni₃Se₂ nanosheets grown on reduced graphene oxide (NiSe–Ni₃Se₂/rGO) by a simple hydrothermal method as an effective catalyst for hydrogen evolution reaction (HER) in the full pH range. In 0.5 M H₂SO₄, the NiSe–Ni₃Se₂/rGO possesses 112 mV to achieve 10 mA cm^?2 and a small Tafel slope (61 mV dec^?1). In 1.0 M PBS and 1.0 M KOH, the overpotentials are 261 and 188 mV at 10 mA cm^?2, and Tafel slopes are 103 and 92 mV dec^?1, respectively. Meanwhile, it owns good cycle stability and durability over 20 h in the whole pH range (0-14). In all solutions, the HER performance of NiSe–Ni₃Se₂/rGO is better than that of NiSe–Ni₃Se₂. This is because the rGO substrate accelerates the electron transfer and improves the electrical conductivity, increasing HER activity of catalyst.     

One-step solution-induced impregnation synthesis of strongly coupled platinum–molybdenum/silicon carbide quantum dots heterostructures encapsulated on reduced graphene oxide sheet as electrocatalyst for hydrogen evolution reaction

Strongly coupled platinum-based transition-metal oxide/carbon hybrids and the development of quantum-dot structures of hybrid catalysts are cost-effective and maximize accessible active sites. However, a significant obstacle still exists for the rational proposal and simple synthesis of hybrid quantum-dot material catalysts. Herein, novel Pt_xMo_1-xSiC quantum dots encapsulated in reduced graphene oxide (rGO) (Pt_xMo_1-xSiC QDs @rGO) for catalyzing the hydrogen evolution reaction (HER) were fabricated through a simple solution-induced impregnation method. The optimized Pt₅Mo₉₅SiC QDs @rGO catalyst only require overpotentials of 18 mV and 25 mV to deliver current densities of 10 mA cm⁻² and 250 mA cm⁻² in acidic media, respectively. The synergistic effects of the inner Pt_xMo_1-xSiC QDs networks and outer conductive rGO sheets that promote electron transfer are responsible for the outstanding HER performance. This work presents a novel method for producing an extremely effective HER catalyst for applications on large-scale.     

Ni nanoparticles intercalated LTA-type nanozeolite (KZ) supported on reduced graphene oxide for 4-nitrophenol reduction

We present a novel nanocomposite catalyst, Ni nanoparticles (NPs) intercalated LTA-type nanozeolite (KZ) on reduced graphene oxide (RGO), abbreviated as KZ-Ni/RGO for the reduction of environmental pollutant 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). The structure, composition and morphology of the catalyst were characterized by using the X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) techniques. The presence of Ni inside the nanocomposite was confirmed by the elemental mapping analysis. 4-NP reduction reaction shows the high catalytic activity (30 min) to KZ-Ni/RGO nanocomposite compared to the KZ-Ni (75 min) with excellent stability up to 5 cycles.     

Multichelate-functionalized carbon nanospheres used for immobilizing Pt catalysts for fuel cells

We have developed a covalent/coordinate strategy to immobilize Pt nanocrystals (average diameter 3.5 nm) on multichelate-functionalized carbon nanospheres (CNS). The method involves the covalent grafting of triethylenetetramine onto the CNS’ surface and the coordination of well-structured ethylenimine chains to Pt ions or atoms. The Pt-CNSs interface is probed with X-ray photoelectron spectroscopy to elucidate the nature of the chemical binding of ethylenimine to Pt. The Pt particle deposition can be easily controlled; to form separated and uniform Pt nanocrystals, or densely loaded Pt particles, depending on the molar ratio of Pt to amine groups. The Pt particle layer covered carbon exhibits significantly higher activity toward methanol oxidation (0.75 A mg⁻¹ cm⁻²) than commercial E-TEK 40% Pt loaded carbon with the corresponding data of 0.51 A mg⁻¹ cm⁻².     

Electrocatalytic hydrogen production on GCE/RGO/Au hybrid electrode

We have prepared a nanocomposite hybrid film to produce a collaborative network of gold (Au) nanoparticles that are highly dispersed on reduced graphene oxide (RGO) sheets, and tested it for electrocatalytic hydrogen production. The RGO/Au nanocomposite film synthesized on glassy carbon electrode (GCE) allows significant improvements to the electron-transfer process. The Au nanoparticles decorated on the surface of graphene increases the electron density, which synergistically promote the adsorption of hydrogen atoms on the graphene sheets and consequently enhance the hydrogen evolution reaction (HER) activity. The surface properties of the composite was characterized by field-emission scanning electron microscopy (FE-SEM) and the electrocatalytical performances evaluated as-prepared electrocatalyst toward (HER) by linear sweep voltammetry (LSV), Tafel polarization curves and electrochemical impedance spectroscopy (EIS) analyses. The GCE/RGO/Au nanohybrid electrode exhibited good catalytic activity for HER with an onset potential of ?0.3 V and a Tafel slope of 136 mV dec^?1, achieving a current density of 10 mA cm^?2 at an overpotential of ?0.43 V.     

Remarkable electrocatalytic activity of Ni-nanoparticles on MOF-derived ZrO2-porous carbon/reduced graphene oxide towards methanol oxidation

In the present work, a porous carbonaceous platform containing zirconium oxide was used for spreading Ni nanoparticles, and applied to methanol oxidation. The platform was obtained by calcination of a metal-organic framework (MOF) attached to graphene oxide. Nickel nanoparticles were then deposited on the nanocomposite by chemical reduction from a Ni²⁺ solution. The obtained electrocatalyst was characterized by different methods. An excellent electrocatalytic behavior was observed towards methanol oxidation in alkaline medium (j ~ 240 mA cm^?2 or ~ 626 mA mg^?1 in 1.0 M methanol). The results of methanol oxidation by various electrochemical studies (cyclic voltammetry, electrochemical impedance spectroscopy, chronoamperometry and chronopotentiometry) revealed the effective synergy between reduced graphene oxide, porous carbon material, ZrO₂ metal oxide and Ni nanoparticles. Good durability and stability of the proposed electrocatalyst and significantly increased current density of methanol oxidation suggest it as a potential alternative for Pt-based electrocatalysts in direct methanol fuel cells.     

Carbon nanotube-supported Pt-HxMoO3 as electrocatalyst for methanol oxidation

Carbon nanotube (CNT)-supported platinum modified with H_xMoO₃ (Pt-H_xMoO₃/CNT) was prepared and used as an electrocatalyst for methanol oxidation. In the preparation of this electrocatalyst, a platinum precursor was loaded on CNTs and reduced by sodium borohydride in ethylene glycol, resulting in CNT-supported platinum without modification (Pt/CNT), and then the Pt/CNT was modified with H_xMoO₃ that was formed by hydrolysis and subsequent reduction of ammonium molybdate. The surface morphology, structure and composition of Pt-H_xMoO₃/CNT and Pt/CNT as well as their activity toward methanol oxidation were investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), energy-dispersive spectrometry (EDS), Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV), chronoamperometry (CA), chronopentiometry (CP), and electrochemical impedance spectroscopy (EIS). The results, obtained from TEM, XRD, EDS, and FTIR, indicate that the platinum loaded on CNTs has a face-centered cubic structure with particle sizes of 2–5 nm, and the modification of H_xMoO₃ on platinum with an atom ratio of Pt:Mo = 2:1 has little effect on the particle size, distribution and structure of the platinum. The results, obtained from CV, CA, CP, and EIS, show that the Pt-H_xMoO₃/CNT exhibits higher electrocatalytic activity toward methanol oxidation and better carbon monoxide tolerance than Pt/CNT.