Current Density For Methanol Oxidation Research Articles

A versatile non-precious metal based electrode material endowed by layer-on-layer structure for methanol oxidation and supercapacitor applications

A high-performance non-noble metal-based electrode is the need of the hour to resolve the challenge of huge energy demand. Energy conversion and storage devices are the two ways to tackle this challenge. In this context, porous and non-noble metal-based electrodes NiCo2O4 (NCO), NiCo2O4/NiO (CNO) and NiCo2O4/NiO/rGO (CNOG) are developed as a bifunctional electrode for supercapacitor and methanol fuel cell applications. The binary composite of NiCo2O4 with NiO increases the redox sites and enhances its electrochemical activity. The low conductivity and problem of aggregation of transition metal oxides are overcome by developing a hybrid nanocomposite of NiCo2O4/NiO with reduced graphene oxide (rGO). The layer-on-layer morphology of CNOG, and the interfacial interactions among NiCo2O4 nanoflakes, NiO nanoparticles and rGO nanosheets increase the specific surface area of the hybrid, which leads to enhanced ion penetration into the active sites. CNOG acts as a potential anode catalyst for methanol oxidation with excellent structural stability. It exhibits a high methanol oxidation current density with low onset potential and faster kinetics. Symmetric supercapacitor CNOG//CNOG delivers specific capacitance of 59.4989 F/g, energy and power density of 6.69 Wh/kg and 698 W/kg respectively at 3 M KOH aqueous electrolyte. The solid-state symmetric supercapacitor (SSSC) using PVA/KOH electrolyte allows broader potential window, thereby outperforming the aqueous electrolyte. The SSSC exhibits specific capacitance of 88.8 F/g, energy and power density 20.84 Wh/kg and 1003 W/kg respectively at the same current density.

Electrosynthesis of Superhydrophilic Nickel Nanosheets on a Three-Dimensional Microporous Template: Applicability toward MOR.

In this report, a nickel nanoscaled morphology was synthesized by two-step cathodic electrodeposition on a microporous copper template. The resulting morphology, nanosheets formed on 3D micropores, offers incredible cyclic stability of almost 100% and facilitates transport mechanisms while significantly preserving the active surface area. The origin of the nanosheets is assumed to be the presence of a small amount of iron cations in the electrolyte bath during the final deposition step. By altering the deposition current density of this step, three samples were prepared and compared in terms of the resulting morphology, chemical composition, surface area, wettability, and activation toward the methanol oxidation Reaction. Results show that an increase in the deposition current density in the range of this study produces finer and denser nanosheets, a higher content of reduced iron, a larger surface area, and greater activity toward MOR. The current density for methanol oxidation was exceptional among all other studies on nickel-containing electrocatalysts, yielding a steady-state current density of 135 mA cm-2 at 600 mV versus SCE. All samples offered superhydrophilicity.

Anodic TiO2 nanotube layers decorated by Pd nanoparticles using ALD: An efficient electrocatalyst for methanol oxidation

Herein, we report the performance of Pd nanoparticles (NPs) prepared by Atomic Layer Deposition (ALD) as a catalyst for methanol electro-oxidation. Pd NPs were decorated onto anodic TiO2 nanotube (TNT) layers as supporting material that possess a large available surface area and direct electrical contact via the underlying titanium foil. Different Pd loadings (150 – 300 – 450 – 600 ALD cycles) show different particles sizes ranging between 7 and 12 nm, as revealed by transmission electron microscopy. Coalescence dominated visibly from 450 ALD cycles, which led to a porous Pd layer all along the TNT walls rather than the growth of individual particles. Electrocatalytic performance was investigated by cyclic voltammetry (CV), where the catalytic activity increased proportional with Pd loading up to the highest values for 400 and 450 cycles, whereas a further increase in the number of ALD cycles (NALD) did not show any additional improvement in methanol oxidation current densities. TNT layers decorated with 400, 450 and 600 Pd ALD cycles show featureless curves suggesting complete anti-poisoning ability or possibly a proof of a direct conversion from CH3OH to CO2 (without any intermediate byproducts). The lack of an oxidation peak during the anodic scan and therefore a reduction peak during the cathodic scan, confirms Pd NPs (stabilized by TiO2) efficiently utilize OHads and chemisorbed CH3OH in a way that its CO poisoning was inhibited. As a result, the tuned high surface area TNT layers exhibited excellent performance as a supporting material for Pd NPs against formation of electrochemical poisoning species. Finally, the mechanism of the TNT layers interaction with Pd NPs, which led to the propelling methanol oxidation reaction without loss in performance over cycling is postulated.

Phase-dependent electrocatalytic activities of Pt-anchored rutile, anatase and mixed anatase-rutile TiO2 nano-composites for methanol oxidation in alkali

Anatase, rutile and mixed anatase-rutile TiO2 are synthesized using a single pot sol-gel technique followed by variation of calcination temperature. The Pt decorated synthesized catalysts have been characterized by diffraction, spectroscopic and microscopic analyses. The cyclic voltammetry (CV) study reveals the increase of forward peak current density of methanol oxidation in alkali on Pt-anchored mixed-phase TiO2 (Pt/ARTiO2) (324.8 A g−1) by 4 and 2.5 times than that on Pt-containing rutile and anatase phases. The charge transfer conductance of the former electrode (1/184 Ω−1) is 5.7 and 8.7 times greater compare to that of the laters. The phase-dependent electrocatalytic activity of the electrodes and large retention (95%) of maximum peak current density at 500th CV cycle for the best electrode, are analyzed by different product selectivity of the electrodes. Pt/ARTiO2 is found to be the best current provider and reliable as it accelerates the formation of formate instead of carbonate.

Physicochemical properties and antibacterial activity of Pt nanoparticles on TiO2 nanotubes as electrocatalyst for methanol oxidation reaction

TiO2 nanotubes were prepared electrochemically as pure Ti sheet in 0.5% HF anodized and annealed under nitrogen acquiring the TiO2 NTs-N2 support. By chemical deposition method using NaBH4 as reducing agent, platinum was deposited on TiO2 NTs-N2 support to gain the Pt NPs/TiO2 NTs-N2 electrocatalyst.Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were applied for the physicochemical characterization of TiO2 NTs-N2 and Pt NPs/TiO2 NTs-N2. The XRD exhibited the an existence of platinum nanoparticles with an average crystallite size of 12 nm, which was regularly combined with TiO2 nanotubes. The Pt NPs/TiO2 NTs-N2 catalyst indicated considerably high electrocatalytic activity and stability for methanol electrocatalytic oxidation reaction in basic medium of KOH. The catalyst Pt NPs/TiO2 NTs-N2 was electrochemically characterized in a basic solution of methanol using cyclic voltammetry (CV) measurement in the absence and an existence of light. The higher poison tolerance and higher methanol oxidation current density observed for the Pt NPs/TiO2 NTs-N2 catalyst suggest that this catalyst supported on TiO2 NTs-N2 has a promising potential applications in the electro catalyst reactions. In addition, the synthesized platinum nanoparticles deposited on TiO2 nanotubes revealed a tremendous antibacterial effects against pathogenic microorganismm.

Nitrogen‐doped graphene prepared by low‐temperature thermal treatment as an electrocatalyst support for methanol oxidation

AbstractIn this study, functionalized graphene is used as a carbon‐based material to support platinum–ruthenium bimetallic nanoparticles and to improve methanol oxidation reaction activity due to the enhanced physical and electrical properties of graphene. First, surface oxidation is used for creating oxygen functional groups, and then nitrogen doping by thermal treatment with ammonia as the nitrogen precursor. Platinum–ruthenium alloy nanoparticles are dispersed by the impregnation reduction method on the support materials. The final nanocomposite samples contain 8% of oxygen and 3% of nitrogen. Compared to PtRu/GNS and PtRu/CB, the PtRu/NO‐GNS catalyst indicates 1.25 and 1.3 times higher surface area, and 2.3 and 4 times higher electrochemical surface area, respectively. The highest methanol oxidation current density of 305 mA/mg and 262 mA/mg is obtained for platinum–ruthenium supported on nitrogen‐doped graphene and nitrogen‐doped oxidized graphene, which is 2.9 and 2.5 times higher than that for PtRu/GNS, respectively. It is revealed that the nitrogen‐doped samples have shown greater activity and long‐term stability than other electrocatalysts, including the widely used carbon black supported catalyst. Hence, this work reports the performance of an efficient alternative electrocatalyst with practical application in direct methanol fuel cells.

Pt-Ru/polyaniline/carbon nanotube composites with three-layer tubular structure for efficient methanol oxidation

Developing anode catalyst with highly active and CO tolerance of direct methanol fuel cells is of prime importance. In this work, the polyaniline/carbon nanotube composites were fabricated via in situ electrochemical method. The Pt–Ru alloy nanoclusters were well-distributed on polyaniline/carbon nanotubes supporting materials by co-electrodeposition method. SEM, HRTEM and XPS were employed to investigate the surface features of composites. The results indicated that Pt-Ru/polyaniline/carbon nanotubes composites were formed three-layer tubular structure. The Pt9.8Ru1/polyaniline/carbon nanotubes catalyst displayed good performance along with the lower peak potential of forward-scanning methanol oxidation, longer-term stability and higher current density compared to Pt/C, Pt-Ru/carbon nanotube composites and other Pt-Ru/polyaniline/carbon nanotube composites. The current density of the Pt9.8Ru1/PANI/CNTs catalyst for methanol oxidation was 8.9 folds higher than that for Pt/C and 2.4 folds higher for Pt9.8Ru1/CNTs catalyst, which indicated that this catalyst had a high number of active sites and surface Ru sites could effectively facilitate the removal of COad. Our data showed that the prepared Pt-Ru/polyaniline/carbon nanotubes composites are potential candidate as bimetallic electro-catalysts for methanol oxidation reaction.

Synthesis and Physicochemical Properties of Pt on TiO2 nanotubes as electro catalyst for Methanol Oxidation Reaction

In this paper, TiO2 nanotubes were synthesized electrochemically by anodization of pure Ti sheet in 0.5% HF and annealed in N2 atmosphere to obtain (TONTs-N2) then the platinum was deposited on the support TONTs-N2 by chemical deposition method using NaBH4 as reducing agents to obtain the electrocatalyst Pt-B/TONTs-N2.
 The physicochemical characterizations of Pt-B/TONTs-N2 were performed by scanning electron microscopy (SEM), X-ray diffraction (XRD analysis.
 The catalyst Pt-B/TONTs-N2 was electrochemically characterized in basic solution of methanol by cyclic voltammetry (CV) measurement. XRD characterization indicates the presence of platinum nanoparticles with diameter less than 54.8 nm and regularly combined into TiO2 nanotubes. Pt-B/TONTs-N2 catalyst exhibited a remarkably high electrocatalytic activity and has high electrocatalytic stability for methanol electrocatalytic oxidation reaction.
 In addition, the Pt-B/TONTs-N2 catalyst exhibits better poison tolerance and higher methanol oxidation current density than that reported for Pt/carbon catalyst.
 This suggests that the Pt-B/TONTs-N2 catalyst supported on TONTs-N2 has promising potential applications in electro catalyst reactions.
 Pt supported on the conductive support TONTs-N2 is used as electrocatalyst in alkaline fuel cells. Results showed best improvement in physico-chemical properties of these catalysts in comparison with previous studies.

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.

Decorated carbon nanofibers with mixed nickel−manganese carbides for methanol electro-oxidation in alkaline solution

Transition metal carbides were recently investigated in many vital applications due to their satisfactory thermal, mechanical and chemical characteristics. They showed a metallic architecture of the host lattice containing interstitial voids of carbon atoms. In this work, mixed nickel-manganese carbides were synthesized onto carbon nanofibers [NiC–MnC@CNFs] in different proportions using the electrospinning process with subsequent calcination at 800 °C. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) were employed to physically characterize the prepared nanomaterials. Homogeneous distribution of nanometallic particles over CNFs was clearly observed in SEM images. XRD charts detected the formation of mixed metallic carbides of Ni0.98C0.02 and (Mn9C)0.4 formulations in different nanomaterials. Excellent electrocatalytic behavior was displayed by NiC–MnC@CNFs nanocatalysts when methanol molecules were introduced into the alkaline solution. Methanol oxidation current density of 110.34 mA cm−2 was measured at the nanomaterial containing NiAc:MnAc ratio of 90:10 with a lowered Eonset value of 310 mV (Ag/AgCl). The effect of varying methanol concentration and the scan rate during the electro-oxidation reaction on the resultant nanomaterial activity was studied. Moreover, the feasibility of charge transfer step was significantly affected by the chosen potential value. Highly pronounced rate was measured at 450 mV. The chronoamperometric study revealed a promising stability trend with increased steady state oxidation current densities especially at nanopowders with lowered MnAc wt.%. The synergistic effect between mixed metallic carbides and CNFs could account for the improved electrocatalytic properties towards methanol molecules oxidation.

Development of CuAg/Cu2O nanoparticles on carbon nitride surface for methanol oxidation and selective conversion of carbon dioxide into formate

Herein we report a catalyst consisting of CuAg/Cu2O nanoparticles (NPs), synthesized on the two-dimensional carbon nitride (CN) surface via galvanic exchange route for electrocatalytic methanol oxidation and carbon dioxide reduction. The lower reduction potential of copper ([Cu+(aq) + e− → Cu(s)], + 0.52 eV) compared to Ag ([Ag+(aq) + e− → Ag(s)], +0.80 eV) makes Cu(0) easily exchangeable by Ag+ ions via galvanic exchange without applying any external bias. In a two-step process, the Cu NPs are synthesized first on CN surface by adsorbing Cu2+ precursors and reducing them by NaBH4. Due to unstable nature of Cu2+ in aqueous medium some Cu2O NPs (a mixed phase of Cu/CuO) were also formed. Thereafter in the second step, Ag+ precursors are brought in contact with the already synthesized Cu and Cu2O nanoparticles (NPs). The Cu and Cu2O NPs present on the surface of CN are partially exchanged by Ag atoms to generate bimetallic CuAg/Cu2O NPs. Two atoms of Ag are expected to be deposited for every Cu atom replaced. As galvanic replacement occurs on the solid surface of carbon nitride, there is only a partial replacement of Cu and Cu2O atoms. The catalysts CN/Cu/Cu2O and CN/CuAg/Cu2O were evaluated for their performance towards methanol oxidation and carbon dioxide reduction. CN/CuAg/Cu2O showed twice the current density for methanol oxidation than CN/Cu/Cu2O in a 0.5 M methanol solution. Probably the reason for high activity of Ag than Cu is related to the weak bond of oxygen on silver substrate for oxidation reactions and strong binding affinity on copper substrate. In case of carbon dioxide reduction (CO2 reduction) the product was identified to be formate by oxidizing the product (formate) on a Pt ring electrode. The results revealed CN/CuAg/Cu2O shows a better selectivity towards formic acid formation than CN/Cu/Cu2O using the rotating ring disc electrode (RRDE). A probable reason may be the strain induced by alloy formation which could favor a reduced coverage of adsorbed hydrogen and a decrease in oxophilicity of the compressively strained copper.

Enhanced Electrocatalytic Performance of Pt Nanoparticles Incorporated CeO2 Nanorods on Polyaniline-Chitosan Support for Methanol Electrooxidation (Experimental and Statistical Analysis)

Here, CeO2 nanorods (CeO2NRs) were successfully synthesized and characterized. Pt nanoparticles were synthesized in the presence of CeO2NRs and the matrix of polyaniline (PA) and chitosan (CH) as support to prepare the novel Pt-CeO2NRs/PA-CH nanocomposite. The electrocatalytic performance of Pt-CeO2NRs/PA-CH was investigated for methanol oxidation (MO) through chronoamperometry, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. Durability of the prepared catalyst was also evaluated. The effects of several factors such as temperature, methanol concentration and scan rate were also studied for MO experimentally and statistically. Pt-CeO2NRs/PA-CH had enhanced electrocatalytic activity, compared to Pt/PA-CH, revealing that it would be a promising catalyst for MO in fuel cells. The variations of anodic peak potential and current density of MO with three main factors (temperature, concentration and scan rate), their binary and triple interactions were investigated statistically. The results showed that both anodic peak potential and current density can be significantly affected by main factors and their interactions at 0.05 level of probability. Meanwhile, the proposed statistical models can accurately estimate the variation of peak potential and current density with studied factors. The results showed that increase in temperature and scan rate leads to the enhancement of both responses.

Platinum nanoparticles with TiO2–skin as a durable catalyst for photoelectrochemical methanol oxidation and electrochemical oxygen reduction reactions

Performance degradation of Pt nanoparticles is considered to be among the most severe problems for electrochemical reactions. Pt–TiO2 catalysts are widely studied due to the optical effect of TiO2, which is beneficial for electron transfer during methanol oxidation. However, different configurations of these catalysts are insufficient in research. Here, we report rationally designed Pt nanoparticles with TiO2-skin as electrocatalysts for methanol oxidations and oxygen reduction reactions. Methanol oxidation current densities of the Pt–TiO2 nanoparticles are largely improved under irradiation. When the catalysts are tortured successive at ultrahigh current up to 1.0 mA cm−2, the potential-increase is as small as 90 mV. It shows good stability with a peak current fades of 4% after 250 cycles under illumination, compared with 13% in the dark. It also exhibits a much better oxygen reduction durability compared with Pt/C. By mechanism analysis, we believe the excellence in photoelectrochemistry is attributed to the TiO2-skin. The electrons generated in TiO2 spontaneously migrate to Pt nanoparticles, which provide a partially reducing atmosphere to prevent Pt nanoparticles from ionization and dissolution.

Amorphous nickel coating on carbon nanotubes supported Pt nanoparticles as a highly durable and active electrocatalyst for methanol oxidation reaction

Multi-walled carbon nanotubes (CNTs) modified with amorphous nickel coating was reported as a novel support for platinum (Pt) for methanol oxidation reaction (MOR). First, an amorphous nickel coating on pristine CNTs (Ni/CNTs) via a simplified electroless deposition method without sensitization and activation is easily developed. Then, Pt nanoparticles (10 wt%) supported on Ni/CNTs (Pt/Ni/CNTs) were fabricated using a microwave-assisted reduction method. The as-prepared Pt/Ni/CNTs electrocatalyst exhibited higher electrocatalytic activity towards MOR in acidic solution, supported by the fact that its methanol oxidation current density was about 0.38 fold higher than that value of Pt/CNTs. Additionally, the proposed Pt electrocatalyst showed a little better electrocatalytic activity than the Pt/C catalyst containing Pt up to about 20%. Moreover, the Pt/Ni/CNTs also exhibited the best stability during the process of MOR. The improved activity and durability of Pt/Ni/CNTs electrocatalyst can be attributed to a more uniform distribution of Pt nanoparticles as well as the synergistic effect between Pt and amorphous nickel coating. Therefore, the as-prepared Pt/Ni/CNTs electrocatalyst is active and stable, which may be applied to the direct methanol fuel cells with high performance.

Low-Temperature Vapor-Phase Synthesis of Single-Crystalline Gold Nanostructures: Toward Exceptional Electrocatalytic Activity for Methanol Oxidation Reaction

Au nanostructures (Au NSs) have been considered promising materials for applications in fuel cell catalysis, electrochemistry, and plasmonics. For the fabrication of high-performance Au NS-based electronic or electrochemical devices, Au NSs should have clean surfaces and be directly supported on a substrate without any mediating molecules. Herein, we report the vapor-phase synthesis of Au NSs on a fluorine-doped tin oxide (FTO) substrate at 120 °C and their application to the electrocatalytic methanol oxidation reaction (MOR). By employing AuCl as a precursor, the synthesis temperature for Au NSs was reduced to under 200 °C, enabling the direct synthesis of Au NSs on an FTO substrate in the vapor phase. Considering that previously reported vapor-phase synthesis of Au NSs requires a high temperature over 1000 °C, this proposed synthetic method is remarkably simple and practical. Moreover, we could selectively synthesize Au nanoparticles (NPs) and nanoplates by adjusting the location of the substrate, and the size of the Au NPs was controllable by changing the reaction temperature. The synthesized Au NSs are a single-crystalline material with clean surfaces that achieved a high methanol oxidation current density of 14.65 mA/cm2 when intimately supported by an FTO substrate. We anticipate that this novel synthetic method can widen the applicability of vapor-phase synthesized Au NSs for electronic and electrochemical devices.

Free-standing nanoporous gold for direct plasmon enhanced electro-oxidation of alcohol molecules

Localized surface plasmon resonance (LSPR) excitation enhanced chemical and electrochemical reactions represent a promising pathway for solar-to-chemical energy conversion. However, plasmonic catalysts usually suffer from low collection efficiency of hot charge carries generated by LSPR excitation due to short lifetime of hot carriers and fast electron-hole recombination. Schottky barriers between plasmonic catalysts and semiconducting supports have been utilized to prevent the electron-hole recombination. However, the interfacial barriers also hinder low-energy hot charge collection and thus affect solar-to-chemical energy conversion efficiency. Here we report that bicontinuous nanoporous gold as a Schottky barriers-free direct plasmonic catalyst can significantly enhance electro-oxidation of alcohol molecules. A high energetic hole yield of 0.486% is achieved, which is 4 times higher than that of discrete plasmonic AuAg nanoparticles. The direct plasmonic catalyst offers the highest methanol oxidation current density of 531 µA cm−2 among all known Au catalysts. This work provides compelling evidence that higher hot carrier collection efficiency can be achieved from direct plasmonic electrocatalysis without the assistance of Schottky junctions and has important implications in developing high efficiency plasmonic catalysts for photo-enhanced electrochemical reactions.

Polyelectrolyte-assisted soft reduced process for Pt-Cu nanoclusters with enhanced electrocatalytic activity for the methanol oxidation reaction

Noble metal-based bimetallic alloy nanostructures became popular for methanol oxidation reaction (MOR) in order to lower the high cost of the Pt catalyst and improve the catalyst activity as well as their CO tolerance. Fabrication of the secondary structures of bimetallic alloy nanocrystal clusters is desired due to their abundant accessible active sites and enhanced stability. Herein, for the first time, we prepared novel Pt-Cu bimetallic alloy nanocrystal clusters (Pt-Cu BANCs) in the presence of poly(diallyldimethylammonium chloride) (PDDA). The selective use of PDDA and control of the amount of PDDA are critical to the controlled fabrication of secondary structures with nanograins assembled together. The Pt-Cu BANCs offered abundant active sites available and enhanced durable stability, and are investigated to be high-performance electrocatalysts for MOR (i.e. the ECSAs of Pt-Cu BANCs and the specific current density of methanol oxidation on Pt-Cu BANCs are 73.9 m2/g and 3.36 mA·cm-2, respectively), which are far better than those of commercial Pt/C and Pt black. Our results reported herein developed an effective strategy of polyelectrolyte-assisted soft reduced process for the creation of the secondary structures of bimetallic alloy nanocrystal clusters, which would be used as enhanced catalysts in the field of clean energy.

Multiwall carbon nanotubes loaded with MoS2 quantum dots and MXene quantum dots: Non–Pt bifunctional catalyst for the methanol oxidation and oxygen reduction reactions in alkaline solution

We synthesized a novel composite of multiwall carbon nanotubes (MWCNTs) decorated with MoS2 quantum dots (MoS2 QDs) and Ti3C2Tx QDs (denoted by MoS2QDs@Ti3C2TxQDs@MWCNTs), of which MoS2 QDs and Ti3C2Tx QDs were separately prepared by exfoliating MoS2 and Ti3C2Tx MXene nanosheets by the hydrothermal method. It showed that the as–prepared MoS2QDs@Ti3C2TxQDs@MMWCNTs composite was rich in functional groups and exhibited homogeneous nanotube nanostructure by coupling with good electrochemical activity. Of note, the MoS2QDs@Ti3C2TxQDs@MWCNTs composite exhibited outstanding bifunctional electrocatalytic performances for oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) in alkaline solution by combining the superior electrocatalytic activity of MoS2 QDs and Ti3C2Tx QDs and the excellent electrochemical performance of MWCNTs. The MoS2QDs@Ti3C2TxQDs@MMWCNTs catalyst exhibited a superior ORR activity to other non-Pt catalysts, giving a low Tafel slope (90 mV dec−1) and high half potential (E1/2, 0.75 V), which was close to those of the commercial Pt/C (20%) catalyst (Tafel slope of 89 mV dec−1, E1/2 of 0.80 V). Additionally, the MoS2QDs@Ti3C2TxQDs@MMWCNTs also possessed good electro–oxidation performance for methanol in alkaline solution, giving a maximum methanol oxidation current density at 2.2 V of 160 A·g−1. The results indicated that the combination of MoS2 and Ti3C2Tx QDs with MWCNTs can supply a potential for fabricating the bifunctional electrocatalysts for ORR and MOR.

Nickel-reduced graphene oxide composite foams for electrochemical oxidation processes: towards biomolecule sensing

Abstract

Synthesis of MCM-41 nanoparticles from stem of common reed ash silica and their application as substrate in electrooxidation of methanol

In this work, stem of common reed ash (SCRA) is introduced as a new source of silica in the preparation of mesoporous materials. Mesoporous silicate MCM-41 nanoparticles were synthesized hydrothermally using sodium silicate prepared from SCRA as a silica source. The characterization of MCM-41was carried out by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), N $$_{2}$$ adsorption/desorption (BET) and transmission electron microscopy (TEM). SEM shows that MCM-41 nanoparticles are sphere-like with size in the range of 30–50 nm with some degree of agglomeration. TEM image of the synthesized sample shows the open framework structure of MCM-41. A type IV isotherm can be observed from adsorption/desorption curves, which is the characteristic of mesoporous materials. The prepared MCM-41 nanoparticles were used as substrate to facilitate the oxidation of methanol through the modification with an electroactive species. The modification was achieved by impregnation of MCM-41 pores with $$\hbox {Ni}^{2+}$$ ions (Ni-doped MCM-41). A modified carbon paste electrode (CPE) was prepared by mixing Ni-doped MCM-41 with carbon paste (NiMCM-41CPE). Cyclic voltammetry of NiMCM-41CPE shows an increment in current density of methanol oxidation in comparison with CPE in alkaline solution. Moreover, a decrease in the overpotential of methanol oxidation occurred on the surface of modified electrode. The effects of some parameters such as scan rate and methanol concentration are also investigated on the behaviour of NiMCM-41CPE. Also, the heterogeneous electron transfer rate for the catalytic reaction (k) of methanol is calculated.