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.     

Preparation and evaluation of a new hybrid support based on exfoliation of graphite by ball milling for Ni nanoparticles in hydrogen evolution reaction

A mixture of graphene/graphite as new support was prepared by ball milling procedure and was used for Nickel nanoparticles supported that was employed as a cathode catalyst for hydrogen evolution reaction (HER) in the KOH solution. The structure and electrocatalytic activity of electrocatalyst were investigated by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD) analysis, and electrochemical techniques. The results indicated that by raising the time of the ball milling from 0 to 270 min, the HER activity of electrocatalyst first increased, and then decreased according to the increase of active sites and then agglomeration of Ni nanoparticles. Ni nanoparticles supported on the mixture with 180 min ball milling exhibited the highest HER activity with a low overpotential (205 mV at 10 mA cm^?2), Tafel slope of 84 mV dec^?1, and remarkable durability.     

Carbon-ceramic supported bimetallic Pt–Ni nanoparticles as an electrocatalyst for electrooxidation of methanol and ethanol in acidic media

The electrooxidation of methanol and ethanol was investigated in acidic media on the platinum–nickel nanoparticles carbon-ceramic modified electrode (Pt–Ni/CCE) via cyclic voltammetric analysis in the mixed 0.5 M methanol (or 0.15 M ethanol) and 0.1 M H₂SO₄ solutions. The Pt–Ni/CCE catalyst, which has excellent electrocatalytic activity for methanol and ethanol oxidation than the Pt–Ni particles glassy carbon modified electrode (Pt–Ni/GCE), Pt nanoparticles carbon-ceramic modified electrode (Pt/CCE) and smooth Pt electrode, shows great potential as less expensive electrocatalyst for these fuels oxidation. These results showed that the presence of Ni in the structure of catalyst and application of CCE as a substrate greatly enhance the electrocatalytic activity of Pt towards the oxidation of methanol and ethanol. Moreover, the presence of Ni contributes to reduce the amount of Pt in the anodic material of direct methanol or ethanol fuel cells, which remains one of the challenges to make the technology of direct alcohol fuel cells possible. On the other hand, the Pt–Ni/CCE catalyst has satisfactory stability and reproducibility for electrooxidation of methanol and ethanol when stored in ambient conditions or continues cycling making it more attractive for fuel cell applications.     

Robust three dimensional N-doped graphene supported Pd nanocomposite as efficient electrocatalyst for methanol oxidation in alkaline medium

Pd nanoparticles (PdNPs) with the diameter of ～3.2 nm were successfully confined within a robust three dimensional (3D) N-doped porous graphene (R3DNG) via a polyol-assisted reduction strategy. The as-obtained PdNPs/R3DNG composite was characterized by SEM, TEM, XRD and XPS, and was conducted as electrocatalyst for methanol oxidation in alkaline medium. The results showed that PdNPs/R3DNG featured the remarkable electrocatalytic activity (2.71 A mg^?1 Pd) and outstanding cyclic stability (66.5% forward peak current retention after 1000 cycles), which is even superior to the state-of-the-art Pt/C catalyst. The synergistic effect between the support of R3DNG and PdNPs is believed to be responsible for the outstanding electrocatalytic performance.     

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.     

Pt/3D-graphene/FTO electrodes: Electrochemical preparation and their enhanced electrocatalytic activity

We report a facile, low-cost and green route to fabricate platinum nanoparticle (Pt NP) decorated three-dimensional (3D) graphene assembled on fluorine-doped tin oxide (FTO) electrodes (Pt/3D-G/FTO) with enhanced electrocatalytic activity. The fabrication process was accomplished by preparation of 3D graphene (3D-G/FTO) electrodes through electrochemical reduction of a graphene oxide suspension followed by electrodeposition of Pt NPs onto them. The Pt/3D-G/FTO electrode exhibits much higher catalytic activity and better stability for methanol oxidation compared with the electrodes prepared by electrodeposition of Pt NPs onto two-dimensional graphene sheets substrate (Pt/G/FTO) or bare FTO (Pt/FTO) under the same condition. These enhancements can be attributed to the high surface area, large void volume and high electrical conductivity as well as smaller size of Pt NPs in the hollows of the 3D architecture and a large amount of ridges on it.     

Electrodeposited Pd nanoparticles on polypyrole/nickel foam for efficient methanol oxidation

The present work describes the Ni foam (Ni–F)/polypyrrole (PPy)/palladium (Pd) (Ni–F/PPy/Pd) multilayered catalysts via a facile electrochemical technique. Potentiostatic deposition of PPy on the surface of Ni–F is followed by galvanostatic deposition of Pd nanoparticles on Ni–F/PPy acted as supports for electrochemical deposition of Pd nanoparticles. The produced catalysts are utilized for electrocatalytic methanol oxidation in alkaline media. Chronoamperometry (CA), cyclic voltammetry (CVs), and electrochemical impedance spectroscopy (EIS) techniques are used to examine the electrocatalytic performance of Ni–F/PPy/Pd based electrodes for methanol oxidation. The polypyrrole modification on Ni–F leads to an improvement in the electrocatalytic activity of the Ni-F/PPY-Pd catalysts toward methanol oxidation. As an open-pored, porous metal with high electrical conductivity, nickel foam produces a substantial amount of active area during the modification of Pd and polypyrrole, which results in significant catalytic activity and a rapid rate charge transfer reaction kinetics on methanol oxidation. The Ni–F/PPy/Pd10 catalyst exhibits enhanced specific activity than its counterparts and a reduced onset potential for methanol oxidation, as well as a low Tafel slope. Based on these results, Ni–F/PPy/Pd10 is suggested as a good material for the anode in the electrocatalytic oxidation of methanol.     

Performance and carbon deposition over Pd nanoparticle catalyst promoted Ni/GDC anode of SOFCs in methane,methanol and ethanol fuels

The electrochemical performance and carbon deposition on palladium catalyst promoted Ni/Gd_0.1C_0.9O_1.95 (Ni/GDC) anode in methane and alcohol fuels like methanol and ethanol are investigated at open circuit potential and under dc bias using electrochemical impedance spectroscopy technique. Presence of Pd nanoparticle catalyst significantly promotes the electrocatalytic activity of Ni/GDC for the electrooxidation reaction in methane and in particularly in methanol and ethanol fuels. For instance, in the case of methanol oxidation reaction, there is clear separation of the impedance arcs at high and low frequencies and activation energy for the reaction is reduced by ∼33% on a 0.15 mg cm⁻² PdO impregnated or infiltrated Ni/GDC anode. The transitional impedance response study when the inlet gas is switched from hydrogen to methane or alcohol fuels indicates that the oxidation reaction in methane and alcohol fuels is most likely dominated by adsorption, dissociation and diffusion steps of the reaction. Carbon deposition is also observed on Pd-infiltrated Ni/GDC in methanol and ethanol, but different from that observed in methane, there is no filament carbon fibers formation on the Pd-impregnated Ni/GDC surface in methanol fuel.     

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.     

Preparation and characterization of Pt supported on graphene with enhanced electrocatalytic activity in fuel cell

Pt nanoparticles are deposited onto graphene sheets via synchronous reduction of H₂PtCl₆ and graphene oxide (GO) suspension using NaBH₄. Lyophilization is introduced to avoid irreversible aggregation of graphene (G) sheets, which happens during conventional drying process. Pt/G catalysts reveal a high catalytic activity for both methanol oxidation and oxygen reduction reaction compared to Pt supported on carbon black (Pt/C). The performance of Pt/G catalysts is further improved after heat treatment in N₂ atmosphere at 300 °C for 2 h, and the peak current density of methanol oxidation for Pt/G after heat treatment is almost 3.5 times higher than Pt/C. Transmission electron microscope (TEM) images show that the Pt particles are uniformly distributed on graphene sheets. X-ray photoelectron spectroscopy (XPS) results demonstrate that the interaction between Pt and graphene is enhanced during annealing. It suggests that graphene has provided a new way to improve electrocatalytic activity of catalyst for fuel cell.     

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.     

Efficient electro-oxidation of methanol using PtCo nanocatalysts supported reduced graphene oxide matrix as anode for DMFC

Platinum – cobalt (PtCo) alloy based highly efficient nano electro-catalysts on reduced graphene oxide (rGO) matrix have been synthesized for the electro-oxidation of methanol, by chemical reduction method. Different molar ratio of Pt (IV) and Co (II) ions along with graphene oxide (GO) were reduced using ethylene glycol to obtain PtCo nanoparticles onto rGO sheets (Pt/rGO, PtCo (1:1)/rGO, PtCo (1:5)/rGO, PtCo (1:9)/rGO and PtCo (1:11)/rGO) with 20 wt. % metal and 80 wt. % rGO. The average particle size of PtCo nanoparticles onto rGO support was observed to be 2–5 nm using XRD and TEM analysis. The PtCo (1:9)/rGO nanocomposite catalyst exhibited ～23 times higher anodic current density compare to commercially available Pt/C catalyst (1.68 mA/cm²) for methanol oxidation reaction. The peak power density of 118.4 mW/cm² was obtained for PtCo (1:9)/rGO catalyst in direct methanol fuel cell (DMFC) at 100 °C, 1 bar, and 2 M methanol as anode feed, which is ～3 times higher than that of Pt/C catalyst. The results indicate the potential application of synthesized nanocomposite catalyst in commercial DMFCs.     

Investigation of the effect of carbonaceous supports on the activity and stability of supported palladium catalysts for methanol electro-oxidation reaction

In this study, nitrogen doped graphene (NG) and multi-walled carbon nanotubes (MWCNT) were used as supporting materials for palladium active phase to investigate their performance in direct methanol fuel cells (DMFCs). The facile and low temperature solvothermal method was used for the synthesis of NG. Palladium nanoparticles were deposited on the surface of NG and MWCNT by a modified polyol reduction method. The morphologies and microstructures of the prepared catalysts were characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. Also, cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy were carried out to evaluate the electrocatalytic activity and the durability of the obtained catalysts towards methanol oxidation reaction. Pd/NG catalyst had a better activity and durability of methanol electrocatalytic oxidation rather than Pd/MWCNT catalyst, which is related to good dispersion of Pd nanoparticles on the surface of nitrogen doped graphene and the physicochemical characteristics of NG.     

The effect of Sn on platinum dispersion in Pt/graphene catalysts for the methanol oxidation reaction

Sn-modified platinum catalysts are presently one of the most active catalysts for the room temperature electrooxidation of ethanol at low potentials. In this study, Pt–Sn/graphene catalysts containing different ratios of Pt and Sn were prepared by the solution-phase reduction. Microstructural characterization shows that metallic Pt, Pt–Sn alloy and tin dioxide (SnO₂) nanoparticles are distributed on the graphene sheets in the synthetic process. In terms of the electrocatalytic properties, graphene-supported Pt–Sn catalysts exhibit much higher current densities with increasing Sn proportions. It's proved that the addition of Sn not only decreases catalyst particles growth and agglomeration, but also promotes methanol electrooxidation by geometric effects on expanding Pt's lattice spacing, causing a synergistic effect between Pt and Sn nanoparticles.     

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.     

Cerium oxide-modified surfaces of several carbons as supports for a platinum-based anode electrode for methanol electro-oxidation

Catalyst composites based on Pt and CeO₂ on carbon for methanol oxidation were successively prepared for application in direct-methanol fuel cells (DMFCs). In this work, the catalyst was modified by decoration of CeO₂ onto several carbons, including carbon black (CB), carbon nanotubes (CNT), graphene oxide (GO), reduced graphene oxide (rGO) and mixed carbons, followed by the electrochemical deposition of Pt. The dispersal of CeO₂ and Pt nanoparticles onto the carbon surfaces was confirmed with a face-centred cubic structure. The use of single and mixed carbons takes admirable advantage of the coexisting CeO₂ and Pt nanoparticles, confirming the positive effect of various carbon structures for electrocatalytic enhancement towards methanol oxidation. The CeO₂ also improves the ability for CO oxidation, resulting in a reduction of CO poisoning. The outcomes show an enhancement of the activity and stability so that such alternative as-prepared materials can be introduced to improve the anodic oxidation in DMFCs.     

Pt nanoparticles modified Au dendritic nanostructures: Facile synthesis and enhanced electrocatalytic performance for methanol oxidation

A facile and simple method is presented for the synthesis of bimetallic composites, Pt nanoparticles modified dendritic Au nanostructures (PtNPs/DGNs), in which dendritic Au was deposited on a glassy carbon electrode via a potentiostatic method and sphere-like Pt nanoparticles were decorated on Au substrates through a chemical reduction reaction. The compositions, morphologies, and structures of the PtNPs/DGNs were characterized by X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and energy dispersive X-ray spectroscopy. Results indicated that bimetallic composites were successfully synthesized and spherical Pt nanoparticles were dispersed evenly on dendritic Au substrates. The number of Pt nanoparticles on Au surface was regulated by controlling the chemical reduction deposition time, allowing the electrocatalytic properties of the composite towards methanol oxidation to be tuned. Electrochemical measurements, including cyclic voltammetry and chronoamperometry, were performed to investigate the electrochemical properties and electrocatalytic behaviors of the PtNPs/DGNs towards methanol oxidation. Pt nanoparticles partially covered dendritic Au exhibited dramatically enhanced electrocatalytic activity (3.947 mA cm^?2), which was 2.65 times that of commercial carbon-supported Pt nanoparticles (1.487 mA cm^?2), along with much improved poisoning tolerance (current decline: 70.85% vs 99.36%). These enhanced performances were likely caused by the large active electrochemical area of the bimetallic nanocomposites and the change in the electronic structure of Pt when the Au surface was modified with fewer Pt nanoparticles.     

Synthesis and electrocatalytic alcohol oxidation performance of Pd–Co bimetallic nanoparticles supported on graphene

Magnetic Pd–Co bimetallic nanoparticles supported on reduced graphene oxide sheets (Pd–Co/RGO) with excellent electrocatalytic performance have been synthesized by a rapid reducing method, using sodium hypophosphite as the reducing agent. The loading and crystalline phase of cobalt in the Pd–Co/RGO hybrids varied as to the initial amount of cobalt salt and reducing agent. Transmission electron microscopy images show that the mean size of the Pd–Co bimetallic nanoparticles was about 10–13 nm and without significant agglomeration. At the same Pd loading on graphene, the current densities of the forward anodic peak of the different Pd–Co/RGO catalysts was decreased by about 25% when compared with that of the pure Pd nanoparticles supported on reduced graphene oxide for both methanol and ethanol oxidation. However, chronoamperometry tests confirmed that the stability was increased by up to 240% and 225% for methanol oxidation and ethanol oxidation, respectively. It is hypothesized that the Co layer on Pd partially blocks Pd sites sacrificing a small portion of the activity of the catalysts, but it leaves the remaining Pd more active and thus enhances alcohol oxidation kinetics and tolerance to poisoning intermediates. Catalytic performance of the Pd–Co/RGO hybrids for alcohol oxidation is primarily affected by the interaction among Pd, Co, and graphene.     

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.     

Synthesis of mesoporous silica (SBA-16) nanoparticles using silica extracted from stem cane ash and its application in electrocatalytic oxidation of methanol

In this work, a new catalyst based on modified mesoporous silica SBA-16 is proposed and used for electrochemical oxidation of methanol. Mesoporous silica SBA-16 nanoparticles are synthesized hydrothermally under the acidic medium using SiO₂/F127/BuOH/HCl/H₂O gel. Pure SiO₂ powder is prepared from inexpensive and environmentally friendly silica source of stem cane ash (SCA). The synthesized SBA-16 is characterized using X-ray diffraction, scanning electronic microscopy, transmission electron microscopy, Brumauer–Emmett–Teller (BET) and FT-IR techniques. The synthesized SBA-16 is modified with Ni(II) by dispersion in a 0.1 M nickel chloride solution. A modified carbon paste electrode (CPE) is prepared by mixing of NiSBA-16 to carbon paste (NiSBA-16CPE). The electrocatalytic oxidation of methanol was studied on modified electrode by cyclic voltammetry and chronoamperometry. From cyclic voltammetry, it is observed that the oxidation current is extremely increased by using NiSBA-16CPE compared to the nonmodified CPE. The incorporation of Ni²⁺ into SBA-16 channels provides the active sites for catalysis of methanol oxidation. Also, the rate constant for the catalytic reaction (k) of methanol is obtained.