Construction of carboxyl functional groups and their enhancement effect for methanol electrocatalytic oxidation reaction

In this paper, we investigated the effect of ozone oxidation on properties of commercial carbon black supported platinum (Pt) nanoparticles for the methanol electro-oxidation reaction. The results indicated that the oxygenated functional groups could be introduced on the carbon black evenly with the increase of processing time. Apparently, mainly introduced oxygenated functional group is carboxyl. Platinum nanoparticles could be uniformly immobilized on the surfaces of carbon black treated with ozone, which has significant high electro-catalytic activity and stability for methanol electrooxidation. This phenomenon is attributed to the fact that oxygen-containing groups (mainly for carboxyl functional groups) produced by ozone oxidation are good for improving the dispersion and strengthening the interaction between support and platinum nanoparticles. The ozone oxidation conditions had significant effects on the defects properties of carbon black which showed a positive correlation between the defect levels and methanol electro-oxidation performances. This paper also fully demonstrated the positive relationship between carboxyl functional groups and the performance of methanol electrocatalytic oxidation.     

The formation of wrapping type Pt–Ni alloy on three-dimensional carbon nanosheet for electrocatalytic oxidation of methanol

In this paper, the PtNi alloy was embedded into the surface layer of three-dimensional carbon nanosheets (CNSs) with a special layered structure. We controllably adjusted the ratio of Pt/Ni to form large particle alloy with Pt coating Ni and a small number of hollow PtNi alloy pellets. The electro-catalytic methanol oxidation activity and durability of the catalysts were estimated by cyclic voltammetry and chronoamperometric techniques. The results indicated that the doping of Ni effectively improved the activity and anti-poisoning of the catalyst in the methanol electrocatalytic oxidation reaction (MOR). Transmission electron microscopy (TEM), Raman spectroscopy, nitrogen adsorption-desorption techniques, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to explore the composition, morphology and structure of these catalysts. It is discovered that the Pt–Ni/CNSs (2:1) sample exhibits the best MOR activity with a peak current density of 15.03 mA cm^?2 at the forward scan due to the excellent lamellar structure, good crystallinity and abundant pore structure of CNSs, which is benefit to form ultrahigh specific surface area, superb electron and ionic conductivity.     

Carbon supported PtPdCr ternary alloy nanoparticles with enhanced electrocatalytic activity and durability for methanol oxidation reaction

In this work, the trimetallic PtPdCr nanoparticles with low platinum loading (~5 wt%) supported on Vulcan carbon (PtPdCr/C) were synthesized through a facile two-step co-reduction method and showed superior methanol oxidation activity. The particle size distribution, morphology and elemental composition of the PtPdCr/C were investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis. The electrochemical performance for methanol oxidation of the PtPdCr/C was found to be higher with the mass activity of 969 mA·mg⁻¹_Pt compared to Pt/C (581 mA·mg⁻¹ _Pt) and PtRu/C (725 mA·mg⁻¹ _Pt). Moreover, the stability studies confirmed the enhanced durability of PtPdCr/C over Pt/C and PtRu/C catalysts after the accelerated durability test (ADT) and chronoamperometry (CA) analysis. The increased methanol oxidation activity and durability of the trimetallic PtPdCr/C in acid medium can be attributed to the change in binding energy of Pt and the induced synergistic effect from Pd and Cr atoms to Pt, which demonstrated a promising strategy for the preparation and utilization of ternary alloy catalysts towards methanol electrooxidation.     

Investigating the addition of silicon oxide to carbon: Effects of amount and heat treatment on anti-aggregation and electrochemical performance of Pt catalysts

Small nanoparticles offer high surface areas and are certainly desirable for electrocatalytic reactions and fuel cells. However, the drawback of using small nanoparticles is their tendency towards particle aggregation. This paper aims to inhibit platinum agglomeration by adding silicon oxide to a carbon support for enhanced catalytic activity in low-temperature fuel cells. The catalysts are characterized by X-ray diffraction and transmission electron microscopy. Physical characterization and cyclic voltammetry techniques at room temperature are used to assess the effects of silicon oxide amount, post-heating temperature, and holding time on particle size and dispersion of active components, and the catalysts’ activity towards the methanol oxidation and oxygen reduction reactions. It is found that using a support of carbon powder with 3 wt.% silicon oxide can enhance the electrochemically active surface area of Pt catalysts and their activity towards the anodic oxidation of methanol and reduction of oxygen. The active components are also more resistant than Pt/C to agglomeration upon heating.     

Platinum-antimony doped tin oxide nanoparticles supported on carbon black as anode catalysts for direct methanol fuel cells

Antimony doped tin oxide supported on carbon black (ATO/C) has been synthesized using an in situ co-precipitation method, and platinum-ATO/C nanoparticles have been prepared using a consecutive polyol process to enhance the catalyst activity for the methanol oxidation reaction. The Pt-ATO/C electrocatalyst is characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microcopy (SEM), energy dispersive X-ray spectroscopy (EDS) and cyclic voltammetry. The Pt-ATO/C catalyst exhibits a relatively high activity for the methanol oxidation reaction compared to Pt-SnO₂/C or commercial Pt/C catalyst. This activity can be attributed to the high electrical conductivities of the Sb-doped SnO₂, which induces the electronic effects with Pt catalysts. Pt-ATO/C is a promising methanol oxidation catalyst with high activity for the reaction in direct methanol fuel cells.     

One-step synthesis in deep eutectic solvents of PtV alloy nanonetworks on carbon nanotubes with enhanced methanol electrooxidation performance

We report a simple one-step chemical reduction strategy in deep eutectic solvents (DESs) for the fabrication of a PtV alloy nanonetwork (ANN)/multiwalled carbon nanotube (MWCNT) nanohybrid, which exhibits excellent electrocatalytic performance in both activity and stability for the methanol oxidation reaction (MOR). The as-synthesized nanohybrid was characterized by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy, confirming the formation of a porous nanonetwork structure composed of smaller PtV alloy nanoparticles (~3.8 nm) and the presence of strong electronic transfer interactions between Pt and alloyed V. The electrochemical properties of catalysts for the MOR were evaluated by using cyclic voltammetry and chronoamperometry techniques. The electrocatalytic activity, durability and CO tolerance ability of PtV ANNs/MWCNTs toward the MOR are found to be considerably higher than those of the Pt/MWCNT and commercial Pt/C catalysts. This investigation of the effect of several reaction parameters (e.g., scan rate and methanol concentration) indicates that the electrocatalytic oxidation of methanol on PtV ANNs/MWCNTs is a diffusion-controlled electrochemical process. The performance enhancement mechanism of MOR on the PtV ANN/MWCNT catalyst is analyzed based on the structure and electrochemical studies.     

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.     

A new durable and high performance platinum supported on Ag–Ni-porous coordination polymer as an anodic DMFC nano-electrocatalyst: DFT and experimental investigation

Due to the poor performance and intermediates poisoning of available catalysts in direct methanol fuel cells (DMFC), the researcher is confronted with a considerable challenge for obtaining modified electrocatalyst. Ag–Ni porous coordination polymer (ANP) as a new electrocatalyst supporter was synthesized by a hydrothermal method. To achieve favorable electrocatalyst for DMFC systems, platinum nanoparticles was deposited upon ANP by an electrochemical method and platinum supported on Ag–Ni porous coordination polymer (Pt-ANP) was formed. Fourier transform infrared spectroscopy (FTIR) analysis ensured correct synthesized of ANP and Pt-ANP. In addition, the morphologies investigation of ANP and Pt-ANP were carried out by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The FE-SEM images indicate that the platinum nanoparticles have been greatly deposited on ANP surface. Electrochemical behaviors of prepared catalyst for methanol oxidation were evaluated by cyclic voltammetry (CV), linear sweep voltammetry (LSV), and chronoamperometry (CA) techniques. Electrochemical cyclic voltammetry tests (CV) indicate that the forward peak current density of Pt-ANP is about 105 mA/cm² which it is 33% more than the forward peak current density of pure Pt catalyst (70.21 mA/cm²). Moreover, electrochemical surface area (ECSA) of Pt-ANP is 26.42 m²/g_Pt. In addition, density functional theory (DFT) computations show that with the deposition of Pt upon ANP, the HOMO-LOMO energy gap of ANP has been decreased which they are suitable for electrochemical reactions. Theoretical results are greatly in accordance with the experiments. Based on the results, Pt-ANP could be a superior electrocatalyst for methanol oxidation.     

A proper amount of carbon nanotubes for improving the performance of Pt-Ru/C catalysts for methanol electro-oxidation

This study aims to improve the performance of the anode catalyst in a direct methanol fuel cell by using carbon black (XC) and mesoporous carbon (MC) as supporting materials for preparing Pt-Ru/XC and Pt-Ru/MC catalysts. This study investigates the effect of adding different amounts of bare carbon nanotubes (CNTs) or carbon nanotubes impregnated with Pt and Ru (abbreviated as Pt-Ru/CNT, containing 10 wt.% Pt and Ru) to the prepared catalysts. Experimental results reveal that 10 wt.% Pt-Ru/C with carbon black and mesoporous carbon prepared by the multiple impregnation method had smaller Pt-Ru grain sizes and a better dispersion or carbon supports due to low precursor concentrations in each impregnation. These, in turn, achieved better electro-catalytic performance for methanol oxidation. Adding CNTs or Pt-Ru/CNT to Pt-Ru/XC and Pt-Ru/MC obviously improves their electro-catalytic characteristics. The appropriate amounts of bare CNT and Pt-Ru/CNT added to Pt-Ru/XC and Pt-Ru/MC catalysts are 5% and 20%, respectively. The resulting catalysts (both containing 10 wt.% Pt and Ru) produce activities similar to those of the E-TEK Pt-Ru/C catalyst containing 20 wt.% Pt and Ru.     

Electrochemical synthesis,characterization and electro-oxidation of methanol on platinum nanoparticles supported poly(o-phenylenediamine) nanotubes

The electrochemical synthesis and the characterization of Pt nanoparticles dispersed poly(o-phenylenediamine) (PoPD) nanotube electrodes, employing alumina membrane as templates are reported. The morphology of the electrodes was characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and transmission electron microscopy (TEM). Catalytic activity and stability for the oxidation of methanol were studied by using cyclic voltammetry and chronoamperometry. The results show that poly(o-phenylenediamine) nanotubes electrodes significantly enhance the catalytic activity of platinum nanoparticles for oxidation of methanol. The results obtained affirm that the dispersion of the platinum particles is connected with catalytic response to a higher activity. The chronoamperometric response confirms the better activity and stability of the nanotube-based electrode compared to the commercial 20 wt.% Pt/C (E-TEK) and template-free electrode. The nanotubular morphology of poly(o-phenylenediamine) helps in the effective dispersion of Pt particles facilitating the easier access of methanol to the catalytic sites. The poly(o-phenylenediamine) nanotubes modified with platinum nanoparticles cause a great increase in electroactivity and the electro-catalytic oxidation of methanol.     

Enhanced electrocatalytic activity of high Pt-loadings on surface functionalized graphene nanosheets for methanol oxidation

Here we report a simple one-pot microwave-polyol reduced method to anchor platinum nanoparticles on graphene with the aid of poly (diallyldimethylammonium chloride) (PDDA), forming a Pt/PDDA–G hybrid (Pt/PDDA–G). High Pt metal loadings, up to 85 wt.% with a mean size of 1.4 nm, were densely in situ decorated on PDDA-modified graphene surfaces. The electrochemical tests showed that the activity and stability of Pt supported on PDDA–graphene hybrid substrates for methanol oxidation were better than that of Pt supported on graphene sheets, also better than the widely used Pt/carbon black electrocatalysts with the same Pt content on the electrode. This improved activity indicates that PDDA plays a crucial role in the highly dispersion and stabilization of Pt nanoparticles on graphene and PDDA–G are able to an alternative support for Pt immobilization in direct methanol fuel cells.     

Platinum supported on hydroxyl-grafted poly (3,4-ethylenedioxythiophene)-modified RuCo,N-tridoped bamboo-like carbon nanotubes for direct methanol fuel cell

The development of highly active and efficient heterogeneous catalytic oxidation system has become an attractive research field. In this paper, a catalyst (RuCo/N-CNT@PEDOT-OH/Pt) from platinum nanoparticles (Pt NPs) supported on hydroxyl-grafted poly(3,4-ethylenedioxythiophene) (PEDOT–OH)-modified RuCo, N-tridoped bamboo-like carbon nanotubes (RuCo/N-CNT) are used for direct methanol fuel cell (DMFC). The electrocatalytic activity of RuCo/N-CNT@PEDOT-OH/Pt is systematically compared with RuCo/N-CNT/Pt (Pt NPs supported on RuCo/N-CNT without PEDOT-OH) in the methanol oxidation reaction (MOR). The growth mechanism of carbon nanotubes and the role of heteroatom doping in the electrocatalytic process is explored. The catalysts show excellent electrocatalytic performance with high stability for MOR. It is found that the mass activity (MA) of the RuCo/N-CNT@PEDOT-OH/Pt (1961.3 mA mg^?1_Pt) for MOR was higher than that of RuCo/N-CNT/Pt (1470.1 mA mg^?1_Pt) and the commercial Pt/C catalysts (281.0 mA mg^?1_Pt), indicating the positive effect of the PEDOT-OH in the electrocatalytic MOR. In addition, density functional theory (DFT) calculations verify the possible mechanism pathways of the obtained RuCo/N-CNT@PEDOT-OH/Pt catalyst. This presented catalyst offers new inspiration for designing efficient electrocatalysts for methanol oxidation.     

Methanol-tolerant carbon aerogel-supported Pt-Au catalysts for direct methanol fuel cell

Pt-Au nanoparticles supported on carbon aerogel, namely 2:1 has been synthesized by the microwave-assisted polyol process. The structure of Pt-Au nanoparticles is characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The electrochemical property of Pt-Au catalysts for methanol oxidation is evaluated by cyclic voltammetry (CV). The results show that Au-modified Pt catalysts exhibit a high methanol tolerance and improved electrochemical catalytic activity, suggesting that carbon aerogel supported Pt-Au catalysts are better catalysts for the electrochemical oxidation of methanol than conventional Pt catalysts.     

Electrocatalytic oxidation of methanol on Pt modified single-walled carbon nanotubes

Platinum nanoparticles on modified single-walled carbon nanotubes (SWNT) were investigated by a completely new electrochemical method. A Pt(IV) complex was formed on the SWNT surface through coordination to the oxygen atom of an oxide functional group on the SWNT surface and then converted to platinum nanoparticles by a potential pulse method. The structure and chemical nature of Pt nanoparticles on SWNTs have been investigated by transmission electron microscopy and X-ray diffraction, the mean diameter of Pt nanoparticles was 5–8 nm. The electrocatalytic properties of the Pt/SWNT electrode for methanol oxidation and its kinetic characterization were investigated by cyclic voltammetry (CV) and excellent electrocatalytic activity was observed.     

Electrocatalytic activity of nanostructured Ni and Pd–Ni on Vulcan XC-72R carbon black for methanol oxidation in alkaline medium

Ni and Pd–Ni nanoparticles were chemically deposited on Vulcan XC-72R carbon black by impregnation method using NaBH₄ as a reducing agent. The prepared electrocatalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX). The electrocatalytic activity of Ni/C and Pd–Ni/C electrocatalysts towards methanol oxidation in 0.5 M KOH solution was examined using cyclic voltammetry and chronoamperometry. Two methanol oxidation peaks were observed on the Pd–Ni/C at 0 and +860 mV. Their current density values are higher than those at Pd/C and Ni/C electrocatalysts by 1.92 and 1.68 times, respectively. The catalytic rate constant of methanol oxidation reaction at Ni/C and Pd–Ni/C electrocatalysts in (0.2 M MeOH + 0.5 M KOH) solution was estimated using double-step chronoamperometry as 5.64 × 10³ and 6.25 × 10³ cm³ mol⁻¹ s⁻¹, respectively. Pd–Ni/C is more stable than Pd/C and Ni/C electrocatalysts. Therefore, Pd–Ni/C is a suitable as a less expensive electrocatalyst for methanol oxidation in alkaline medium.     

Core shell like behavior of PdMo nanoparticles on multiwall carbon nanotubes and their methanol oxidation activity in alkaline medium

Core–shell like behavior has been shown by the nanoparticles comprised of Pd and Mo that have been synthesized on multiwall carbon nanotubes (Mo@Pd/MWCNT or Pd@Mo/MWCNT) by hydrothermal technique in different pH. The synthesized catalysts are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The formation mechanism of the core–shell like PdMo nanoparticles has been explained with the consequences of reduction potential and surface segregation properties of Pd and Mo. The activity of the catalysts towards methanol oxidation is investigated by cyclic voltammetry (CV), chronoamperometry and impedance spectroscopy. The primary electrochemical analysis indicates that the electrochemical activity of this Pd@Mo/MWCNT along with Mo@Pd/MWCNT is better than that of Pd/MWCNT.     

Pt and PtRu nanoparticles deposited on single-wall carbon nanotubes for methanol electro-oxidation

Platinum (Pt) and platinum–ruthenium (PtRu) nanoparticles supported on Vulcan XC-72 carbon and single-wall carbon nanotubes (SWCNT) are prepared by a microwave-assisted polyol process. The catalysts are characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The PtRu nanoparticles, which are uniformly dispersed on carbon, have diameters of 2–6 nm. All the PtRu/C catalysts display the characteristic diffraction peaks of a face centred cubic Pt structure, excepting that the 2θ values are shifted to slightly higher values. The results from XPS analysis reveal that the catalysts contain mostly Pt(0) and Ru(0), with traces of Pt(II), Pt(IV) and Ru(IV). The electrooxidation of methanol is studied by cyclic voltammetry, linear sweep voltammetry, and chronoamperometry. Both PtRu/C catalysts have high and more durable electrocatalytic activities for methanol oxidation than a comparative Pt/C catalyst. Preliminary data from a single direct methanol fuel cell using the SWCNT supported PtRu alloy as the anode catalyst delivers high power density.     

Pd nanoparticles supported on HPMo-PDDA-MWCNT and their activity for formic acid oxidation reaction of fuel cells

A novel Pd electrocatalyst is developed by self-assembly of Pd nanopartilces on phosphomolybdic acid (HPMo)-poly(diallyldimethylammonium chloride) (PDDA)-functionalized multiwalled carbon nanotubes supports (Pd/HPMo-PDDA-MWCNTs). The as-synthesized Pd/HPMo-PDDA-MWCNTs were characterized by TEM, EDS mapping, Raman spectra, X-ray photoelectron spectroscopy, electrochmeical CO stripping and cyclic voltammetry techniques. Pd nnaoparticles deposited on HPMo-PDDA-MWCNTs are in the range of 3.1 nm with uniform distributon. Pd/HPMo-PDDA-MWCNT catalysts have lower overpotential for CO_ad oxidation manifested as lower peak and onset potentials as compared to acid-treated MWCNTs supported Pd (Pd/AO-MWCNTs) and carbon supported Pd catalysts (Pd/C). Pd/HPMo-PDDA-MWCNTs catalysts also exhibit a much higher electrocatalytic activity and stability for formic acid oxidation reaction as compared to that on Pd/AO-MWCNTs and Pd/C. The high electrocatalytic activities of Pd/HPMo-PDDA-MWCNTs catalysts are most likely related to highly dispersed and fine Pd nanoparticles as well as synergistic effects between Pd and HPMo immobilized on PDDA-functionalized MWCNTs.     

MOF-derived N-doped carbon coated CoP/carbon nanotube Pt-based catalyst for efficient methanol oxidation

Designing rational nanostructures of metal-organic frameworks to speed up the methanol oxidation reaction and promote their application in methanol oxidation is highly desired but still remains a great challenge. In this study, we report a novel N-doped carbon coated CoP nanoparticles/carbon nanotube Pt-based catalyst (Pt–CoP-NCZ/CNT). This composite is produced through in situ growth of CoZn-ZIF on carbon nanotubes, subsequent carbonization and phosphorization treatment and microwave-assisted Pt supporting synthesis. The high specific surface area and N-doped structure endow the prepared catalysts with ideal conditions for supporting of Pt as well as good electrical conductivity. In addition, the evaporation of Zn²⁺ in CoZn-ZIF not only makes a contribution to a higher specific surface area of the material but also is favorable for uniform distribution of CoP nanoparticles, which gives CoP nanoparticles an excellent co-catalysis effect. Thus, the composite exhibits wonderful mass activity in both acid (930 mA mg⁻¹) and alkaline (3622.5 mA mg⁻¹) environments. Furthermore, the Pt–CoP-NCZ/CNT catalyst also shows better CO tolerance and long-time stability compared with other catalysts in this study. Thereby, the fabrication of the composite catalyst makes wider application of metal-organic frameworks in methanol oxidation possible and provides inspiration for designing efficient catalysts for methanol oxidation.