Efficient method to obtain Platinum–Cobalt supported on graphene oxide and electrocatalyst development

We have prepared a highly efficient and stable platinum–cobalt catalyst supported on graphene oxide by using a one-step synthesis microwave-irradiation process. The structure and composition of two different compositions (Pt:Co(2.5:1)/rGO, Pt:Co(2:1)/rGO) have been investigated by Fourier infrared spectroscopy (FT-IR), X-ray Photoelectron spectroscopy (XPS), specific surface area (BET), Raman spectroscopy. Their electrocatalytic activity was investigated and the electrochemical response from cyclic voltammetry revealed the high efficiency and stability as well as the potential application as cathode electrode. The electrocatalysts exhibited a superior durability comparing with commercial Pt/C catalyst after accelerated stress test, indicating a lower loss of electrochemical surface area in the case of prepared samples. Moreover, this study extends the applicability of this synthesis method for the preparation of other noble or transitional metal nanoparticles decorated on reduced graphene oxide.     

Evaluation of electrochemical performance for surface-modified carbons as catalyst support in polymer electrolyte membrane (PEM) fuel cells

The electrochemical performance of platinum (Pt) catalyst deposited on various functionalized carbon supports was investigated and compared with that of a commercial catalyst, Pt on Vulcan XC-72 carbon. The supports employed were graphitic or amorphous with a wide range of surface areas. Cyclic voltammetry (CV) and rotating disk electrode (RDE) studies on the supported catalysts indicated equivalent platinum catalyst activities. Fuel cell performance was determined for membrane electrode assemblies (MEA) fabricated from the supported catalysts. The use of high surface area supports did not necessarily translate into a higher electrochemical utilization of platinum. Electrochemical impedance spectroscopy (EIS) measurements indicated lower ohmic losses for low surface area carbon MEAs. This is explained by the supported catalyst electrode microstructures and their intrinsic resistivities. Correlation of all data indicates that for low surface carbons, nature of the support does not significantly affect the Pt catalytic activity. The influence of the support is more critical when high surface area carbons are used because of the vastly different electrode morphology and resistivity.     

Platinum–Iron nanoparticles supported on reduced graphene oxide as an improved catalyst for methanol electro oxidation

Platinum–Iron nanoparticles supported on reduced graphene oxide powder are synthesized by chemical reduction method as an anode catalyst for the methanol electro oxidation. The characterization of the catalyst has been investigated using physical and electrochemical methods. Prepared catalyst was characterized by scanning electron microscopy (SEM), TEM (Transmission electron microscopy), FT-IR (Fourier-transform infrared spectroscopy), Raman spectroscopy and, X-ray diffraction (XRD) and energy dispersive analysis of X-ray (EDX). Pt and Pt-Fe nanoparticles are uniformly dispersed on the surface of reduced graphene oxide (rGO) powder nanocomposite support. The catalytic properties of the catalyst for methanol electro-oxidation were thoroughly studied by electrochemical methods that involved in the cyclic voltammetry, linear sweep voltammetry (LSV), chronoamperometry and electrochemical impedance spectroscopy (EIS). The Pt-Fe/rGo exhibits high electrocatalytic activity, catalyst tolerance for the CO poisoning and catalyst durability for electro-oxidation of methanol compared to the Pt/rGo and commercial Pt/C catalyst. Therefore, the Pt-Fe/rGo catalyst is a good choice for application in direct methanol fuel cells.     

The role of Pt loading on reduced graphene oxide support in the polyol synthesis of catalysts for oxygen reduction reaction

Common carbon-blacks have shown insufficient stability as cathodic catalyst supports for proton exchange membrane fuel cells (PEMFCs). In this regard, alternative supports have been proposed and, specifically graphene or reduced graphene oxide (rGO), have attracted special attention. Herein, a set of electrocatalysts using reduced graphene oxide (rGO) as support is synthetized by a modified polyol method. The influence of Pt loading on the support is studied and compared with conventional supports, considering Pt particle morphologies and oxygen reduction reaction (ORR) performance in rotating disk electrode (RDE). Despite Pt average particle size typically increases with the Pt loading, 30 wt% of Pt on rGO is the optimal Pt loading, yielding the highest ORR activity among the rGO-supported electrocatalysts. These results show that both Pt loading and type of support greatly impact on the morphology and electrochemical performance of Pt nanoparticles.     

Graphene nanoribbons as a novel support material for high performance fuel cell electrocatalysts

Graphene nanoribbons (GNRs) were first used as a novel support material for Pt nanoparticles (NPs) based catalyst for methanol electro-oxidation. Upon oxidation and cutting of multiwall carbon nanotubes (MWCNTs), highly dispersive graphene oxide nanoribbons (GONRs) were obtained, on which metal ions such as PtCl₆²⁻ can be homogenously deposited. The hybrid catalyst of GNRs supported Pt NPs (Pt/GNR) was further prepared through facile in-situ chemical co-reduction, with a homogeneous distribution of Pt NPs (2–3 nm) on the nanoribbons. Compared to Pt/MWCNT and commercial Pt/XC72R catalysts, Pt/GNR hybrids show much larger electrochemically active surface area, higher electrochemical stability, and better CO tolerance towards electro-oxidation of methanol. Therefore, GNR is a promising alternative two-dimensional support material for electrocatalysts in direct methanol fuel cells.     

Engineered catalyst layer design with graphene-carbon black hybrid supports for enhanced platinum utilization in PEM fuel cell

In this study, a new approach was applied to prepare platinum/reduced graphene oxide/carbon black (Pt/rGO/CB) hybrid electrocatalysts. Unlike literature firstly GO and CB in varying ratios are homogeneously mixed with a high shear mixer and then Pt was impregnated onto the hybrid support structure according to the polyol method. According to our approach CB was used as a spacer and intercalating agent in both Pt impregnation and electrode preparation to avoid restacking and increase the Pt utilization. Thus rGO/CB based hybrid support can ease the diffusion while it is promoting to the use of high electrical connectivity and surface area of graphene. The maximum power density of 645 mW cm^?2 with Pt utilization efficiency of 2.58 kW/gPt was achieved with the hybrid containing the smallest amount of CB. It seems that this small amount of CB effectively modifies the electrode structure. The enhanced fuel cell performance can be attributed to synergistic effects from graphene and CB providing better mass transport and Pt utilization in the catalyst layer.     

Effect of uniformity and surface morphology of Pt nanoparticles to enhance oxygen reduction reaction in polymer electrolyte membrane fuel cells

Platinum (Pt)-based electrocatalysts supported by reduced graphene oxide (rGO) is fabricated under microwave-assisted polyol method with various nucleation and growth conditions. The surface morphologies of the Pt nanoparticles (NPs) under various reaction conditions owing to different Pt NP sizes and inter-particle spacings are investigated by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, thermogravimetric analysis, cyclic and linear sweep voltammetry, and electrochemical impedance spectroscopy. The synthesized Pt/rGO catalyst under nucleation and growth times of 10 s and 50 s, respectively, exhibits excellent catalytic activity with increased electrochemical surface area, high density, good uniformity and surface morphology with a particle size and inter-particle spacing of 2.16 nm and 17.2 nm, respectively. These results elucidate the relationship between the Pt NP morphology distribution and oxygen reduction reaction of catalysts in polymer electrolyte membrane fuel cell systems. We also highlight the important role of size and inter-particle spacing on the Pt electrochemical catalystic performance.     

Reduced graphene oxide-supported nickel oxide catalyst with improved CO tolerance for formic acid electrooxidation

The superior catalytic activity along with improved CO tolerance for formic acid electrooxidation has been demonstrated on a NiO-decorated reduced graphene oxide (rGO) catalyst. The cyclic voltammetry response of rGO–NiO/Pt catalyst elucidates improved CO tolerance and follows direct oxidation pathway. It is probably due to the bene?cial effect of residual oxygen groups on rGO support which is supported by FT-IR spectrum. A strong interaction of rGO support with NiO nanoparticles facilitates the removal of CO from the catalyst surface. The chronoamperometric response indicates a higher catalytic activity and stability of rGO–NiO/Pt catalyst than the NiO/Pt and unmodified Pt electrode catalyst for a prolonged time of continuous oxidation of formic acid.     

Facile in-situ deposition of Pt nanoparticles on nano-pore stainless steel composite electrodes for high active hydrogen evolution reaction

Hydrogen is regarded as a clean and highly efficient renewable energy. The platinum catalytic electrode is widely used in hydrogen evolution reaction (HER), but it has affected its commercial application because of its high cost. Therefore, the study on cost-effective and high-active catalysts toward HER is required to realise large-scale hydrogen production. In this work, we present a novel Pt/NPSSF catalyst prepared by a one-step in-situ deposition of Pt precursor on a nano-porous stainless-steel film (NPSSF) substrate. The prepared catalyst was evaluated in acidic and alkaline conditions for its HER activities. The preliminary results demonstrate that the Pt/NPSSF electrodes have superior catalytic activity for HER. The hydrogen overpotential of Pt/NPSSF is ?70mV (RHE) in the alkaline solution, which is lower than the Pt electrode of ?184mV. At the same time, we also obtained ?71.2 mV of overpotential for the Pt/NPSSF electrode, which is similar to the ?73mV of Pt electrode in the acid solution. The Tafel graphs plotted from the LSV curves indicate the different HER mechanism in the alkaline and acid solution. The HER kinetics of the Pt/NPSSF were studied using EIS. Comparing Pt/NPSSF to Pt electrode, the multi-pore structures of NPSSF and the Pt nanoparticles active sites decrease the charge transfer-resistance for the HER process. The facile preparation, high efficiency and low value of the Pt/NPSSF composite electrodes demonstrate the promising applications in HER.     

Methanol electro-oxidation on Pt/C modified by polyaniline nanofibers for DMFC applications

In the present study, in order to achieve an inexpensive tolerable anode catalyst for direct methanol fuel cell applications, a composite of polyaniline nanofibers and Pt/C nano-particles, identified by PANI/Pt/C, was prepared by in-situ electropolymerization of aniline and trifluoromethane sulfonic acid on glassy carbon. The effect of synthesized PANI nanofibers in methanol electrooxidation reaction was compared by bare Pt/C by different electrochemical methods such as; cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometry. Scanning electron microscopy (SEM) was also employed to morphological study of the modified catalyst layer. The test results reveal that introduction of PANI nanofibers within catalyst layer improves the catalyst activity in methanol oxidation, hinders and prevents catalyst from more poisoning by intermediate products of methanol oxidation and improves the mechanical properties of the catalyst layer. SEM images also indicate that PANI nanofibers placed between platinum particles and anchor platinum particles and alleviate the Pt migration during methanol electrooxidation.     

One-step synthesis of graphene supported platinum nanoparticles as electrocatalyst for PEM fuel cells

Here in, we describe an ultrafast, single-step microwave irradiation route (MW) to prepare graphene supported Pt nanoparticles, during which the small Pt nanoparticles are distributed uniformly on a reduced graphene oxide surface. This route provides evident advantages namely low cost, easiness, low time consuming and high yield in comparison to actual chemical methods to develop efficient Pt/rGO catalyst with Pt content close to state-of-the-art commercial composition. The structure and composition of prepared samples have been studied by specific techniques, while the electrocatalytic stability has been studied using ex-situ and in-situ measurements. High performance and electrochemically stable catalyst for PEM fuel cells was developed using the sample with highest loading and good dispersion. The fabricated Pt-rGO-based MEA was investigated for durability under fuel starvation in comparison with commercial Pt/C-based MEA. The electrocatalytic activity was investigated and the electrochemical response revealed the higher stability during accelerated degradation test under fuel starvation in comparison with commercial Pt/C. This study promotes the applicability of described preparation method to noble or transition metal nanoparticles embedded on graphene-based materials.     

Electrochemical oxidation of CO over tin oxide supported platinum catalysts

Tin oxide supported platinum catalysts (Pt/SnO_x) for use in polymer electrolyte fuel cells were prepared, and their electrochemical oxidation of CO was investigated. From the XPS measurements of Pt/SnO_x catalysts, it was found that the binding energy of Pt showed no change compared to bulk Pt, regardless of tin oxide addition. In accordance with this result, CO-stripping voltammograms for Pt/SnO_x catalysts revealed that the peak potential for the pre-adsorbed CO oxidation was almost the same value of Pt/C catalyst. However, the onset potential of CO oxidation shifted negatively compared to PtRu/C catalyst, indicating an enhancement of CO tolerance of Pt/SnO_x catalysts.     

Preparation and electroactivity of polymer-functionalized graphene oxide-supported platinum nanoparticles catalysts

Polymer-functionalized graphene oxide or pristine graphene oxide supported platinum nanoparticles (Pt NPs) was prepared to study the surface modification effects. The catalysts were characterized by transmission electron microscopy, energy dispersive spectrometry, X-ray diffraction and thermogravimetric analysis. The electrochemical activities of Pt NPs were measured by cyclic voltammograms. The poly(diallyldimethylammonium chloride) (PDDA) was used as a modifier agent which formed a functionalized layer on graphene oxide (GO) sheets. As a result, the electrochemical active surface area (ESA) of PDDA functionalized GO supported Pt (Pt/PDDA–graphene) was shown to 66 m²/g that indicated higher hydrogen adsorption amount than 55 m²/g of the pristine Pt/graphene. In addition, an average particle size of Pt/PDDA–graphene NPs was measured to 1.8 nm slightly smaller than 2.0 nm of pristine Pt/graphene NPs.     

High performance electrocatalysts supported on graphene based hybrids for polymer electrolyte membrane fuel cells

In this study, new electrocatalysts for PEM fuel cells, based on Pt nanoparticles supported on hybrid carbon support networks comprising reduced graphene oxide (rGO) and carbon black (CB) at varying ratios, were designed and prepared by means of a rapid and efficient microwave-assisted synthesis method. Resultant catalysts were characterized ex-situ for their structure, morphology, electrocatalytic activity. In addition, membrane-electrode assemblies (MEAs) fabricated using resultant electrocatalysts and evaluated in-situ for their fuel cell performance and impedance characteristics. TEM studies showed that Pt nanoparticles were homogeneously decorated on rGO and rGO-CB hybrids while they had bigger size and partially agglomerated distribution on CB. The electrocatalyst, supported on GO-CB hybrid containing 75% GO (HE75), possessed very encouraging results in terms of Pt particle size and dispersion, catalytic activity towards HOR and ORR, and fuel cell performance. The maximum power density of 1090 mW cm^?2 was achieved with MEA (Pt loading of 0.4 mg cm^?2) based on electrocatalyst, HE75. Therefore, the resultant hybrid demonstrated higher Pt utilization with enhanced FC performance output. Our results, revealing excellent attributes of hybrid supported electrocatalysts, can be ascribed to the role of CB preventing rGO sheets from restacking, effectively modifying the array of graphene and providing more available active catalyst sites in the electrocatalyst material.     

Pt–Ni nanoparticles electrodeposited on rGO/CFP as high-performance integrated electrode for methanol oxidation

A novel carbon fiber paper loaded with reduced graphene oxide (rGO) was used as the substrate, on which Pt–Ni nanoparticles were electro-deposited as to prepare an integrated electrode by two electrochemical methods (cyclic voltammetry and square wave pulse). The electrochemical tests indicated two integrated electrodes had excellent performance towards methanol oxidation. Especially, Pt-Ni-CV(A)-rGO/CFP electrode showed the highest electrocatalytic activity, and mass activity reached 5.33 A·mg^?1_Pt, which was about 5.6 times that of the commercial Pt/C catalyst (JM). Further, after annealing under a reducing atmosphere, two electrodes exhibited completely different changes in the aspects of morphology and electrocatalytic performance. It can be attributed to the changes of element distribution and morphology of nanoparticles after annealing. The as-prepared Pt–Ni-rGO/CFPs composite electrode is promising for integrated electrode of proton exchange membrane fuel cells. This work opens an avenue for the preparation of high-performance integrated electrode.     

Heteroatom doped 3D graphene aerogel supported catalysts for formic acid and methanol oxidation

In this study, nitrogen (N) and boron (B) heteroatom doped graphene aerogel support materials have been employed for the dispersion of platinum (Pt) nanoparticles to improve their electrocatalytic activities for formic acid and methanol oxidation. Pt nanoparticles dispersed on the heteroatom doped graphene aerogel (GA) support materials by a microwave heating method. The as-prepared catalysts were characterized by a variety of means such as SEM, EDS, ICP-MS, TEM, XRD, BET and XPS. The electrocatalytic activities, stability and impedance of the synthesized catalysts were investigated for formic acid and methanol oxidation using electrochemical measurements. The 3D graphene aerogels have higher capacitive currents than the Vulcan XC-72 in the double layer region. The results of electrochemical chronoamperometry tests reveal that Pt/BGA shows the best stability for methanol oxidation and also exhibited superior electrocatalytic activity towards the oxidation of methanol in cyclic voltammetry. In addition to, heteroatom doped GA supported catalysts higher activity compared to the Vulcan XC-72 supported catalyst for formic acid oxidation.     

Sub-nano-Pt cluster supported on graphene nanosheets for CO tolerant catalysts in polymer electrolyte fuel cells

The carbon monoxide (CO) tolerance performance of polymer electrode fuel cells (PEFCs) was studied for a catalyst composed of graphene nanosheets (GNS) with sub-nano-Pt clusters. The Pt catalysts supported on the GNS showed a higher CO tolerance performance in the hydrogen oxidation reaction (HOR), which was significantly different from that of platinum on carbon black (Pt/CB). It is proposed that the presence of the sub-nano-Pt clusters promotes the catalytic activity and that the substrate carbon material alters the catalytic properties of Pt via the interface interactions between the graphene and the Pt.     

A promising negative electrode of asymmetric supercapacitor fabricated by incorporating copper-based metal-organic framework and reduced graphene oxide

A hybrid negative electrode was developed by combining a hydrothermally prepared copper-based metal-organic framework (Cu-MOF) and electrochemically synthesized reduced graphene oxide (rGO), which was labeled as MrGO. The MrGO composite was characterized using field emission scanning microscopy, Raman spectroscopy, Fourier transform infrared spectrometry and X-ray diffraction to confirm the presence of both Cu-MOF and rGO. Cyclic voltammetry, galvanostatic charge discharge and electrochemical impedance spectroscopy (EIS) were carried out to study the electrochemical properties of the MrGO negative electrode for asymmetric supercapacitor (ASC) application. The EIS analysis of the MrGO electrode revealed the lowest charge transfer resistance of 0.95 Ω compared to rGO (23.73 Ω) and Cu-MOF (10.23 Ω). The electrochemical measurements were performed on the MrGO electrode at a negative operating potential (−0.4 to 0 V) to emphasize the hybrid MrGO as a high-performance negative electrode. The novel ASC was then constructed utilizing the vanadium oxide/reduced graphene oxide (VrGO) as the positive electrode and the hybrid MrGO as the negative electrode. The VrGO//MrGO ASC device was successfully delivered a superior specific capacitance (483.9 F/g) and enormous specific energy (31.2 Wh/kg). The inclusion of incredibly conductive rGO in the MrGO electrode could synergistically enhance the cycling stability (92% over 4000 CV cycles) of the VrGO//MrGO ASC device.     

Utilization of the graphene aerogel as PEM fuel cell catalyst support: Effect of polypyrrole (PPy) and polydimethylsiloxane (PDMS) addition

In this study, three-dimensional (3D) graphene aerogel (GA) was synthesized by a self-assembly hydrothermal process as a PEM fuel cell catalyst support. The synthesized GA was also modified with the polypyrrole (PPy) by in-situ chemical oxidative polymerization of the pyrrole monomer (PPy-GA). The electrocatalytic performance of the platinum (Pt) nanoparticles (NPs) supported with both GA and PPy-GA materials towards oxygen reduction reaction (ORR) was investigated. In addition, the hydrophobic polydimethylsiloxane (PDMS) polymer was added to the catalyst ink media in order to enhance the hydrophobic property and durability of the synthesized GA and PPy-GA supported Pt catalysts. Pt NPs were decorated over the support materials with the microwave irradiation technique. Various characterization techniques such as FTIR, Raman Spectroscopy, BET, SEM, EDX, TEM, TGA, contact angle measurements, 3D topography images and four-point probe electrical conductivity measurements were performed in order to analyze the GA based support materials. Electrochemical characterizations were also carried out with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements. It was observed that PDMS addition to the catalyst ink media increased the electrocatalytic activity and durability of the GA supported Pt catalyst. Otherwise, the performance of the PPy modified GA supported Pt catalyst was negatively affected by the addition of PDMS to the catalyst media.