Synthesis of Au-NiOx/ultrathin graphitic C3N4 nanocomposite for electrochemical non-platinum oxidation of methanol

The Au-NiO_x/g-C₃N₄ (graphitic C₃N₄) nanocomposite is synthesized and utilized as catalyst for the electrochemical oxidation of methanol in the alkaline electrolyte. Au and Ni nanoparticles are uniformly dispersed on ultrathin g-C₃N₄ nanosheets by in-situ synthesis with nickel nitrate and chloroauric acid as Ni and Au resource respectively. The structure, morphology and component of the prepared nanocomposites are characterized by different techniques like transmission electron microscopy, X-ray diffraction, elemental mapping image and X-ray photoelectron spectroscopy. The results prove that the nanoparticles are well-distributed and embedded in g-C₃N₄ nanosheets. The electrochemical performance of different nanocomposite for methanol oxidation reaction (MOR) is tested under alkaline conditions via electrochemical technologies. Compared to the pure g-C₃N₄ and Au/g-C₃N₄, the NiO_x/g-C₃N₄ exhibits electrochemical catalytic effect toward methanol electro-oxidation with the existence of Ni. This electrochemical catalytic performance is enhanced significantly for the Au-NiO_x/g-C₃N₄, whose oxidation peak current density is 2.32 times higher than NiO_x/g-C₃N₄. The slope value drew from the Tafel plots shows that the Au-NiO_x/g-C₃N₄ owns the lowest Tafel slope (67.00 mV/dec). After the 7200 s stability test, the Au-NiO_x/g-C₃N₄ catalyst can still maintain a high current density. Long-term stability and good anti-poisoning ability promise Au-NiO_x/g-C₃N₄ a competitive non-Pt catalyst for the methanol oxidation.     

Recent progress of anode catalysts and their support materials for methanol electrooxidation reaction

This review paper summarizes the recent progress of anode catalysts for methanol oxidation reaction (MOR) in direct methanol fuel cells (DMFCs). The electrocatalytic activities of the noble and noble-free catalysts in different electrolyte media are compared and discussed. Noble-free catalysts exhibit high activity in alkaline medium, whereas Pt-based catalysts are the most active MOR catalysts in acidic medium. The types of catalyst support materials for DMFC anodes are also discussed and further divided into carbonaceous and non-carbonaceous materials. The ion and electron transport through the support materials and their effects on the overall performance are elaborated. Lastly, this paper highlights the major challenges in achieving the optimum DMFC performance from the aspect of tailoring the properties of MOR electrocatalysts to pave its way for commercialisation.     

Fabrication and characterization of gold nanoparticles and fullerene-C60 nanocomposite film at glassy carbon electrode as potential electro-catalyst towards the methanol oxidation

Development of low cost anodic materials and high efficient electro-kinetics of methanol in direct methanol fuel cell (DMFC) has been a promising approach. However it has not been successfully reached to market from laboratory due to its high cost and low kinetic oxidation. Both issues encounter from one of its main components, the catalyst. Therefore, present work focuses upon the development of new catalyst material and optimization of various most significant influencing parameters of a high performance DMFC. We have developed a nanocomposite material employing gold nanoparticles and fullerene-C₆₀ at glassy carbon electrode (AuNP@reduced-fullerene-C₆₀/GCE) as anode for high performance oxidation of methanol. Fullerene-C₆₀ was manually dropped on pre treated GCE and partially electro-reduced in KOH to make it more conductive. Gold nanoparticles (AuNPs) were deposited on reduced-fullerene-C₆₀ modified electrode using cyclic voltammetry (CV). Electrochemical characterization techniques such as CV, electrochemical impedance spectroscopy (EIS) and chronocoulometry were used to characterize modified electrode. Modified electrode was also characterized by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) for morphological properties. The electrochemical behavior of methanol was performed in alkaline medium using CV and chronoamperometry methods. The results revealed good electrocatalytic performance and better stability than previously reported catalysts using AuNP@reduced-fullerene-C₆₀ catalyst, suggesting making promising anodic material for direct methanol oxidation fuel cell.     

High-performance core–shell PdPt@Pt/C catalysts via decorating PdPt alloy cores with Pt

A core–shell structured low-Pt catalyst, PdPt@Pt/C, with high performance towards both methanol anodic oxidation and oxygen cathodic reduction, as well as in a single hydrogen/air fuel cell, is prepared by a novel two-step colloidal approach. For the anodic oxidation of methanol, the catalyst shows three times higher activity than commercial Tanaka 50 wt% Pt/C catalyst; furthermore, the ratio of forward current I_f to backward current I_b is high up to 1.04, whereas for general platinum catalysts the ratio is only ca. 0.70, indicating that this PdPt@Pt/C catalyst has high activity towards methanol anodic oxidation and good tolerance to the intermediates of methanol oxidation. The catalyst is characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The core–shell structure of the catalyst is revealed by XRD and TEM, and is also supported by underpotential deposition of hydrogen (UPDH). The high performance of the PdPt@Pt/C catalyst may make it a promising and competitive low-Pt catalyst for hydrogen fueled polymer electrolyte membrane fuel cell (PEMFC) or direct methanol fuel cell (DMFC) applications.     

Direct methanol–air fuel cells with membranes plus circulating electrolyte

A new approach for direct methanol–air fuel cells (DMFC), with the advantage of reduced methanol crossover is discussed in this paper. Methanol traces in the circulated electrolyte are recovered and CO₂ bubbles in the cells are removed due to the forced methanol–electrolyte stream through the cell.Degradation of the catalyst is reduced since fuel cell electrodes degrade on activated stand without load to a higher extent than under load because high voltage on open circuit promotes carbon oxidation, catalyst changes, etc. Therefore, life expectancy increases with circulating electrolyte by removing the electrolyte from the cells between operating periods.     

PtRu/C-Au/TiO2 electrocatalyst for a direct methanol fuel cell

Au/TiO₂ is added to a PtRu/C electrode to improve the performance of a direct methanol fuel cell (DMFC). A high-throughput-screening test is performed for the fast screening of the loading of Au/TiO₂ on PtRu/C. The electrochemically-active surface area of PtRu/C-Au/TiO₂ and PtRu/C is determined from cyclic voltammetry. In CO-stripping and methanol oxidation voltammetry, PtRu/C-Au/TiO₂ exhibits better activity for CO and methanol oxidation than PtRu/C. The performance of the DMFC is also improved by addition of Au/TiO₂ to the PtRu/C electrode. The CO adsorbed on Pt may move to the surface of the Au/TiO₂ by the interaction between PtRu/C and Au/TiO₂. The improved performance of the PtRu/C-Au/TiO₂ catalyst is explained in terms of preferential oxidation of CO or CO-like poisoning species that are generated during the oxidation of methanol on PtRu/C.     

Electrochemical study of platinum deposited by electron beam evaporation for application as fuel cell electrodes

Platinum is the most used catalyst in electrodes for fuel cells due to its high catalytic activity. Polymer electrolyte and direct methanol fuel cells usually include Pt as catalyst in their electrodes. In order to diminish the cost of such electrodes, different Pt deposition methods that permit lowering the metal load whilst maintaining their electroactivity, are being investigated. In this work, the behaviour of electron beam Pt (e-beam Pt) deposited electrodes for fuel cells is studied. Three different Pt loadings have been investigated. The electrochemical behaviour by cyclic voltammetry in H₂SO₄, HClO₄ and in HClO₄ + MeOH before and after the Pt deposition on carbon cloth has been analysed. The Pt improves the electrochemical properties of the carbon support used. The electrochemical performance of e-beam Pt deposited electrodes was finally studied in a single direct methanol fuel cell (DMFC) and the obtained results indicate that this is a promising and adequate method to prepare fuel cell electrodes.     

Platinum nanoparticles decorated on graphitic carbon nitride-ZIF-67 composite support: An electrocatalyst for the oxidation of butanol in fuel cell applications

In the present study, we report an eco-friendly and simple route to design and synthesize novel nanocomposite catalyst based on platinum nanoparticles anchored on binary support of graphitic carbon nitride (g-C₃N₄) and cobalt-metal-organic framework (ZIF-67). For this purpose, ZIF-67 was prepared by precipitation method and g-C₃N₄ was prepared through thermal polymerization method. Later, ZIF-67 and g-C₃N₄ were hybridized through sonication to get homogeneous g–C₃N₄–ZIF-67 nanocomposite support material. Platinum nanoparticles (PtNPs) were uniformly deposited on g–C₃N₄–ZIF-67 by an electrochemical method. The as-developed nanocatalyst was characterized by morphological, structural and electrochemical techniques. The electrocatalytic activity of PtNPs@g–C₃N₄–ZIF-67 nanocatalyst towards butanol oxidation was evaluated via CV, CA, LSV and EIS in an alkaline medium. Results revealed that the proposed catalyst showed greatly enhanced electrooxidation of butanol in terms of high magnificent current density, lower oxidation potential, excellent long-term stability, large surface area, low charge transfer resistance and less toxic ability. Enhanced catalytic performance of the proposed catalyst could be ascribed to the synergistic effect of g–C₃N₄–ZIF-67 nanocomposite and PtNPs. The PtNPs@g–C₃N₄–ZIF-67 catalyst holds promising potential applications to be used as an anodic electrocatalyst for the development of high-performance alkaline fuel cells.     

Effect of carbon black additive in Pt black cathode catalyst layer on direct methanol fuel cell performance

Vulcan XC-72R, Ketjen Black EC 300J and Black Pearls 2000 carbon blacks were used as the additive in Pt black cathode catalyst layer to investigate the effect on direct methanol fuel cell (DMFC) performance. The carbon blacks, Pt black catalyst and catalyst inks were characterized by N₂ adsorption and scanning transmission electron microscopy (STEM) with Energy dispersive X-ray (EDX) spectroscopy. The cathode catalyst layers without and with carbon black additive were characterized by scanning electron microscopy, EDX, cyclic voltammetry and current-voltage curve measurements. Compared with Vulcan XC-72R and Black Pearls 2000, Ketjen Black EC 300J was more beneficial to increase the electrochemical surface area and DMFC performance of the cathode catalyst layer. The cathode catalyst layer with Ketjen Black EC 300J additive was kept intimately binding with the Nafion membrane after 360 h stability test of air-breathing DMFC.     

New RuO2 and carbon–RuO2 composite diffusion layer for use in direct methanol fuel cells

A RuO₂ diffusion layer is examined for use in direct methanol fuel cells (DMFC) by comparison with acetylene black and Vulcan XC-72R. In the test with a DMFC unit cell, the RuO₂ diffusion layer is superior to the other two materials. The difference in performance is interpreted in terms of structural and electrical properties which are evaluated by porosity, scanning electron microscopy and resistance measurements. The RuO₂ diffusion layer displays different behaviors at the anode and cathode sides. These characteristics can be attributed to a reduced loss of catalyst in the active catalyst layer, which leads to increased methanol diffusion at the anode and prevention of water flooding in the cathode. The effect of the RuO₂ diffusion layer on cell performance becomes more pronounced at lower temperatures and during operation in the presence of air. Finally, a carbon–RuO₂ composite is evaluated as a diffusion layer material for a DMFC.     

The significant promotion of g-C3N4 on Pt/CNS catalyst for the electrocatalytic oxidation of methanol

This article reported a series of g–C₃N₄–CNS (g-C₃N₄ and carbon nanosheets) composite carriers formed by the hydrothermal method, and then the ethylene glycol reduction method was used to anchor Pt nanoparticles on the g–C₃N₄–CNS carrier to form the Pt/g–C₃N₄–CNS catalysts. The electrochemical test for the electrocatalytic oxidation of methanol (MOR) shown that the Pt/20%g–C₃N₄–CNS catalyst has the best catalytic performance and stability. These Pt/g–C₃N₄–CNS catalysts were analyzed by TEM, XRD, XPS, and BET characterization. It is discovered that the amount of g-C₃N₄ greatly influenced the structure and chemical properties of Pt/CNS precursor. As the content of g-C₃N₄ increases, the content of pyridine nitrogen and pyrrole nitrogen also increases, and N species can enhance the interaction between Pt nanoparticles and CNS, promote Pt dispersion, and increase the specific surface area of the catalyst. Similarly, an excessive addition of g-C₃N₄ will cause a sharp decline in the conductivity of the catalyst, and then led to the decline of MOR activity.     

Electrodeposited graphene hybridized graphitic carbon nitride anchoring ultrafine palladium nanoparticles for remarkable methanol electrooxidation

Exploiting high performance electrocatalysts is crucial for the effective electrooxidation of methanol, although some barriers exist. Herein, we develop a hybrid support composed of graphitic carbon nitride (g-C₃N₄) and reduced graphene oxide (rGO) synergistically anchoring sufficient ultrafine palladium (Pd) nanoparticles via a simple one-step electrodeposition technique. The morphology and structure were characterized by scanning/transmission electron microscopy, X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy, which confirmed that the Pd nanoparticles were massively and uniformly dispersed on the support of g-C₃N₄@rGO with a the average particle size of 5.87 nm, deriving from the nitrogen in g-C₃N₄ contributing to the electron transport highway on the rGO nanosheet layer surface. Furthermore, electrochemical results suggested that the Pd/g-C₃N₄@rGO showed a high electrocatalytic efficiency for methanol oxidation with a high current density reached 0.131 mA cm⁻². Based on a novel approach to the g-C₃N₄@rGO hybrid nanostructure, this work offers a promising method for the design and synthesis for the superior performance methanol electrocatalyst.     

Frustrated Lewis pair engineering on ceria to improve methanol oxidation activity of Pt for direct methanol fuel cell applications

Practical application of direct methanol fuel cell (DMFC) technology is greatly hindered by the strong dependence of anodic methanol oxidation reaction (MOR) on precious Pt based catalyst and the unsatisfying performance of Pt. Therefore, increasing the utilization and the catalytic performance of Pt toward MOR in DMFC is urgent. Here in this work, CeO₂ is modified via a plasma-phosphating combing strategy and is invited as Frustrated Lewis Pair to assist the catalytic MOR process on Pt sites. Simultaneously, the plasma-phosphating combing strategy leads to negatively charged sites on CeO₂ surface, which can be functioned as host for Pt anchoring, facilitating the even dispersion of Pt nanocrystals. Besides, this strategy also has an effect on the Ce³⁺/Ce⁴⁺ ratio and vacancy oxygen ratio on CeO₂ surface, which are critical to the adsorbed OH generation and anti-CO poisoning ability, thus boosting the MOR catalytic activity of Pt. DMFC device therefore exhibits ca. 30% maximum power density enhancement compared with the commercial Pt/C based DMFC.     

Effect of conditioning method on direct methanol fuel cell performance

We investigated the effect of the conditioning methods on improving the direct methanol fuel cell (DMFC) performance. The DMFC performance after the conditioning was measured using a newly developed single cell having an Ag/Ag₂SO₄ reference electrode, which is not influenced by methanol. As a result, we succeeded in developing an original two-step conditioning method in which the conditioning by fueling H₂ gas is conducted prior to a conventional DMFC conditioning. The anode and cathode characteristics after the two-step conditioning were measured with respect to a reference electrode. Based on the obtained i-E curves, the two-step conditioning is found to improve the methanol oxidation performance at the anode and also suppress the decline of the O₂ reduction performance at the cathode. The high DMFC performance based on the two-step conditioning is well explained by the anode and cathode characteristics.     

Defect configuration of ceria for Pt anchoring toward efficient methanol oxidation

As a potential next-generation power source for portable electronic devices, commercialization process of direct methanol fuel cell (DMFC) technology is hindered by the high dependence of anode methanol oxidation reaction (MOR) on precious Pt catalyst. In order to improve the efficiency of Pt toward MOR catalysis, a Ni doping strategy is proposed for defect engineering on ceria substrate to achieve uniform dispersion of Pt nanoparticles. Besides, Ni could also act as electron donor for Pt and hence favor the removal of CO intermediate on Pt and act as a co-catalyst toward MOR. Superior MOR activity and great stability is therefore achieved for the as-prepared Pt/CeO₂@Ni catalyst with 3 times higher peak MOR current density compared with Pt/C catalyst. Due to the evenly anchored Pt and enhanced CO oxidation ability caused from Ni doped ceria substrate, Pt utilization of the Pt/CeO₂@Ni catalyst is calculated to be 3.24 times higher than that of the commercial Pt/C catalyst. By considering the significantly improved stability, the Pt/CeO₂@Ni catalyst has the potential for application in DMFC devices.     

Design of PdxIr/g-C3N4 modified FTO to facilitate electricity generation and hydrogen evolution in alkaline media

In current work, the performance of Pd_xIr hybridized with g-C₃N₄ (Pd_xIr/g-C₃N₄) onto a fluorine-doped tin oxide (FTO) glass was investigated for alcohols oxidation reaction and hydrogen evolution reaction in alkaline media. The nanostructures were synthesized with convenient one-step solvothermal method and characterized with ICP-AES, EDX, XRD and TEM techniques. For comparison, Pd/g-C₃N₄ and Pt/C catalyst-coated FTO were also investigated. Higher current densities of 250 for methanol oxidation and 2570 mA mg⁻¹ for glycerol oxidation and better stability in the presence of Pd₃Ir/g-C₃N₄ compared to the other catalysts were proven by cyclic voltammetry and chronoamperometry. Electro-oxidation mechanism was investigated using linear sweep voltammetry method. Also, Pd₃Ir/g-C₃N₄ showed the Tafel slope of 72 mV dec⁻¹ and good stability in alkaline media which is comparable to that of other catalysts for hydrogen evolution reaction.     

A latest overview on photocatalytic application of g-C3N4 based nanostructured materials for hydrogen production

Photocatalytic H₂ production is a hopeful technology to solving the environment problems and global energy. Consequently, it is essential to develop high efficient, nonprecious and stable photocatalysts. Graphitic carbon nitride (g-C₃N₄) was fascinated much concentration owed to this metal free n-type semiconductor possesses appropriate bandgap, unique two dimensional (2D) layered structures, low toxicity, high thermal and chemical stability, lowcost, facile preparation and visible light response. Moreover, the g-C₃N₄ composites are having huge promise on photocatalytic H₂ production but, the efficiency of pure g-C₃N₄ is at present limited by its poor visible light absorption and suffers from high recombination rate of g-C₃N₄ photogenerated electron/hole pairs resulting in low photocatalytic performance. Furthermore, the g-C₃N₄ has unique electronic structure, therefore renowned candidates have been coupled with different functional components to improve photocatalytic activity. In this contribution, we review the recent research progresses of transition metals, non metals, noble metals, semiconductor compounds, graphene, carbon nanotubes (CNTs), carbon dots and quantum dots, supported on g-C₃N₄ nanosheets, which were applied to photocatalytic H₂ production. In addition, different techniques used to synthesis the g-C₃N₄ based photocatalyst including with their corresponding examples have been described. We hope that this review will encourage the readers to extend the applications of g-C₃N₄ based heterostructure in the field of H₂ production in a green manner.     

Two-step conditioning method for high power-generating direct methanol fuel cells

Power-generation improvement of a direct methanol fuel cell (DMFC) has been investigated through the enhancements of the anode and cathode characteristics using a newly developed “two-step conditioning method”, in which the conditioning is conducted by supplying H₂ gas before the conventional DMFC conditioning. By using the two-step conditioning, the DMFC performances are enhanced. From the polarization curves measured during the DMFC operation using a single cell having an Ag/Ag₂SO₄ reference electrode, the methanol oxidation performance of the anode is proven to be improved with an increase in the methanol concentration. In addition, a decline in the O₂ reduction performance at the cathode due to the methanol crossover is suppressed by our original conditioning method. These results are also supported by the linear sweep voltammetry, and the superior DMFC performances after the two-step conditioning are related to the high speed cleaning of the electrocatalysts. Note that the optimum two-step conditioning leads to 1.4–2.2 times higher maximum power densities than those for the conventional DMFC conditioning even for a shorter conditioning time.     

An effective layout of polyaniline nanofibers incorporated in membrane-electrode assembly as methanol transport regulator for direct methanol fuel cells

This study reports a novel strategy by using polyaniline nanofibers (PANFs) to modify membrane-electrode assembly (MEA) for improving direct methanol fuel cell (DMFC) performance. First of all, a series of PANFs emeraldine salt was synthesized and characterized. Then, we investigated the effect of PANFs layout in MEA on DMFC performance. Three different placements to incorporate the as-synthesized PANFs in anodes include (1) placing a layer of PANFs between catalyst layer (CL) and proton exchange membrane (PEM), (2) mixing with catalyst slurry and coating onto gas diffusion layer (GDL), and (3) placing a layer of PANFs between CL and GDL. Polarization curves indicate that the third method is superior to the others and is adopted as the incorporation layout thereafter. Both methanol transport resistance and methanol crossover of the PANFs-modified MEA are studied further. The DMFC incorporated with H₂SO₄-doped PANFs obtained after the re-doping process with 2 mol L⁻¹ H₂SO₄ performs a power density as high as 53 mW cm⁻², about 20% higher than that of the pristine one without PANFs incorporation. However, an excessive doping level may result in a higher methanol transport resistance due to PANFs aggregation and thus deteriorate DMFC performance. This study provides a simple and effective way by placing a layer of PANFs between CL and GDL in anode to act as methanol transport regulator and improve DMFC performance consequently.     

Palladized dysprosium fluoride nanorods as a new performance catalyst in direct methanol fuel cell

Fuel cells are a new type of batteries that produce electricity from a continuous source of alcohols as long as fuel is inserted. In this study, decorated palladium nanoparticles (PdNPs) on dysprosium fluoride (DyF₃) nanorods (DyFNRs)‐multiwalled carbon nanotubes (MWCNTs) were used for electrooxidation of methanol. DyFNRs were synthesized by the hydrothermal method, and the proposed multifunctional catalyst (DyFNRs/MWCNT‐PdNPs) was identified by several methods such as X‐ray diffraction, elemental mapping images, field emission scanning electron microscopy, energy dispersive analysis of X‐rays, and transmission electron microscopy which demonstrated a uniform distribution and high dispersion of the PdNPs on the supports. The electrocatalytic activity toward methanol electrooxidation on glassy carbon electrode (GCE) with DyFNRs/MWCNT‐PdNPs (DyFNRs/MWCNT‐PdNPs/GCE) was investigated by cyclic voltammetry (CV) and chronoamperometry (CA). Experimental results showed a high improvement in oxidation potential and peak current of methanol electrooxidation by DyFNRs/MWCNT‐PdNPs in comparison to DyFNRs and PdNPs. The values of the catalytic rate constant (k) and physical dimension (D_s) for methanol oxidation on the DyFNRs/MWCNT‐PdNPs/GCE catalyst were calculated 0.008 s^?1 and 1.43, respectively. Moreover, the order of reaction was determined to be 0.43 and 0.13 for CH₃OH and NaOH, repectively. Finally, the synthesized catalyst was evaluated in direct methanol fuel cell (DMFC). The single DMFC with proposed anodic catalyst, DyFNRs/MWCNT‐PdNPs, indicated a power density of 4.4 mW·cm^?2 at a current density of 18 mA·cm^?2 in alcohol (1 M) and NaOH (1 M).