Synthesis and characterization of GO-PpPDA/Ni–Mn nanocomposite as a novel catalyst for methanol electrooxidation

The graphene oxide-poly (p-phenylene diamine) (GP) composite is synthesized through in-situ polymerization of p-phenylene diamine on GO sheets and used as an efficient support material for electrodeposition of Ni and Mn. The resulting GP/Ni–Mn catalyst shows high catalytic activity, stability and durability for methanol electrooxidation. The surface area of GP composite is calculated to be about 28% and 36% higher than GO and PpPDA, respectively. In addition, combining Ni and Mn demonstrated some synergetic effect for methanol electrooxidation. The electrochemical active surface area of GP/Ni–Mn is about 1.625 cm², which is much higher than GP/Ni and GP/Mn. GP/Ni–Mn nanocomposite presented 87.3% of the peak current after 5 h and almost 83.16% of the maximum current for 500 cycles. The excellent characteristics of this composite are attributed to high surface area, high electrochemical active surface area and fine distribution of metallic particles on the support material.     

CO tolerant PtRu–MoOx nanoparticles supported on carbon nanofibers for direct methanol fuel cells

Novel nanostructured catalysts based on PtRu–MoO_x nanoparticles supported on carbon nanofibers have been investigated for CO and methanol electrooxidation. Carbon nanofibers are prepared by thermocatalytic decomposition of methane (NF), and functionalized with HNO₃ (NF.F). Electrocatalysts are obtained using a two-step procedure: (1) Pt and Ru are incorporated on the carbon substrates (Vulcan XC 72R, NF and NF.F), and (2) Mo is loaded on the PtRu/C samples. Differential electrochemical mass spectrometry (DEMS) analyses establish that the incorporation of Mo increases significantly the CO tolerance than respective binary counterparts. The nature of the carbon support affects considerably the stabilization of MoO_x nanoparticles and also the performance in methanol electrooxidation. Accordingly, a significant increase of methanol oxidation is obtained in PtRu–MoO_x nanoparticles supported on non-functionalized carbon nanofiber, in parallel with a large reduction of the Pt amount in comparison with binary counterparts and commercial catalyst.     

Effect of decreasing platinum amount in Pt–Sn–Ni alloys supported on carbon as electrocatalysts for ethanol electrooxidation

Literature describes the influence of morphological and structural electrocatalysts characteristics, on the catalytic activity toward ethanol electrooxidation. Thus, in this work Pt and ternary Pt–Sn–Ni alloys nanoparticles, supported on Vulcan carbon, were obtained by impregnation/reduction method. The aim of this work was to evaluate the influence of the decrease of platinum and increase of nickel content of the electrocatalysts obtained. The electrocatalysts were characterized by Rutherford backscattering spectroscopy, X-ray diffraction, transmission electronic microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. The results obtained showed that it was possible to obtain Pt–Sn–Ni nanoparticles with a uniform size distribution in a narrow particle size range with a composition control. Moreover, the simultaneous addition of Sn and Ni to Pt did not affect reticular lattice a value, but the crystallite size decreases significantly. Besides, electrochemical results suggest that the substitution of platinum by nickel, in the electrocalatyst alloys studied, does not compromise the catalytic activity toward ethanol eletrooxidation.     

Enhanced solar hydrogen generation using Cu–Cu2O integrated polypyrrole nanofibers as heterostructured catalysts

Nanostructured conducting polymeric materials are beneficial for electron conduction and mass transport, showing high photocatalytic performance under visible light. Herein, we report a colloidal synthesis of copper and copper oxides (Cu₂O) modified polypyrrole nanofibers (PPy) heterostructures, which demonstrates significantly high photocatalytic H₂ generation under visible light. The presence of Cu nanoparticles (NPs) of 50 nm and cubic shaped Cu₂O nanoparticles of size 200 nm endows the heterostructures with a large specific surface area as well as good dispersion of nanoparticles on PPy nanofibers allows the migration of electron during catalysis. Cu₂O/PPy exhibits excellent H₂ production (67 mmol h⁻¹) which is 12 times higher than pure PPy (5.7 mmol h⁻¹). The high catalytic activity of Cu₂O/PPy heterostructure provides a fervent alternative to noble metal-based catalysts for the hydrogen generation and water splitting.     

Study of bimetallic Cu–Ni/γ-Al2O3 catalysts for carbon dioxide hydrogenation

The effect of the Cu/Ni ratio on CO₂ hydrogenation at 773 K and 873 K was studied by XRD, TPR, H₂ and CO₂–TPD. There exists strong interaction between Cu and Ni components. At high temperature (773 K and 873 K), the products are CO, CH₄ and H₂O without CH₃OH formation. The Cu/Ni ratio has a significant effect on the conversion and selectivity. Cu favors CO formation while Ni is of benefit in CH₄ formation.     

Carbon supported bifunctional Rh–Ni(OH)2/C nanocomposite catalysts with high electrocatalytic efficiency for alkaline hydrogen evolution reaction

Pt group metals display lower HER activity in alkaline solution than in acidic solution, because they are inefficient in the water dissociation step (Volmer step). Compared with Pt, the activity difference of Rh in alkaline and acidic media is much smaller. Meanwhile, Ni(OH)₂ is proved to be an effective catalyst for water dissociation. Therefore, Rh–Ni(OH)₂/C nanocomposites with different Rh:Ni(OH)₂ ratios were synthesized by a co-deposition/partial reduction method, and their microstructures as well as electrocatalytic properties were studied. The results show that Rh and Ni(OH)₂ display synergistic effect in Rh–Ni(OH)₂/C nanocomposites. The Rh–Ni(OH)₂/C nanocomposite with a molar ratio of Rh to Ni(OH)₂ of 1:1 exhibits the highest activity. It shows an overpotential of 36 mV at 10 mA cm^?2 and a Tafel slope of 32 mV dec^?1 for HER in alkaline media, which is superior to commercial Pt/C. In addition, the Rh–Ni(OH)₂/C (1:1) nanocomposite shows excellent durability in alkaline media as well.     

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.     

Synthesis and characterisation of platinum–cobalt–manganese ternary alloy catalysts supported on carbon nanofibers: An alternative catalyst for hydrogen evolution reaction

A systematic method for obtaining a novel electrode structure based on PtCoMn ternary alloy catalyst supported on graphitic carbon nanofibers (CNF) for hydrogen evolution reaction (HER) in acidic media is proposed. Ternary alloy nanoparticles (Co0.6Mn0.4 Pt), with a mean crystallite diameter under 10 nm, were electrodeposited onto a graphitic support material using a two-step pulsed deposition technique. Initially, a surface functionalisation of the carbon nanofibers is performed with the aid of oxygen plasma. Subsequently, a short galvanostatic pulse electrodeposition technique is applied. It has been demonstrated that, if pulsing current is employed, compositionally controlled PtCoMn catalysts can be achieved. Variations of metal concentration ratios in the electrolyte and main deposition parameters, such as current density and pulse shape, led to electrodes with relevant catalytic activity towards HER. The samples were further characterised using several physico-chemical methods to reveal their morphology, structure, chemical and electrochemical properties. X-ray diffraction confirms the PtCoMn alloy formation on the graphitic support and energy dispersive X-ray spectroscopy highlights the presence of the three metallic components from the alloy structure. The preliminary tests regarding the electrocatalytic activity of the developed electrodes display promising results compared to commercial Pt/C catalysts. The PtCoMn/CNF electrode exhibits a decrease in hydrogen evolution overpotential of about 250 mV at 40 mA cm⁻² in acidic solution (0.5 M H₂SO₄) when compared to similar platinum based electrodes (Pt/CNF) and a Tafel slope of around 120 mV dec⁻¹, indicating that HER takes place under the Volmer-Heyrovsky mechanism.     

Effect of sulfur–carbon interaction on sulfur poisoning of Ni/Al2O3 catalysts for hydrogenation

The poisoning effects of two types of carbon-containing sulfides (CS₂ and CH₃SSCH₃) on Ni/Al₂O₃ catalysts for the hydrogenation of benzene and cyclohexene were systematically investigated via experiments and DFT calculations. The toxicity of CH₃SSCH₃ is two and three times greater than that of CS₂ for the hydrogenation of cyclohexene and benzene, respectively. The characterization and DFT results reveal that CH₃SSCH₃ dissociates easily during hydrogenation and releases CH₄, allowing sulfur atoms to poison the Ni sites. However, the presence of CS₂ in the hydrogenation step slows the decline in the catalytic performance, because of resistance to the direct dissociation of the strong CS bond of CS₂. The chemisorbed CS₂ molecules and their incomplete dissociation weaken the strength of NiS bond and decrease the poisoning effect of sulfur. The poisoning processes of two sulfides are also discussed following a DFT study. This work opens up promising possibilities for the industrial study of S-poisoning resistance in supported Ni catalysts.     

Enhanced activity of Pt(HY) and Pt–Ru(HY) zeolite catalysts for electrooxidation of methanol in fuel cells

The investigation describes the synthesis of Pt and Pt–Ru catalysts by a new method using a HY zeolite support. The catalysts are used to study the anodic oxidation of methanol in an acidic medium to investigate their suitability for use in direct methanol fuel cells (DMFCs). The catalysts prepared in a HY zeolite support display significantly enhanced electrocatalytic activity in the order: HY<Pt/C<Pt(HY)<Pt–Ru/C<Pt–Ru(HY). The enhanced electrocatalytic activity is explained on the basis of the formation of specific CO clusters in zeolite cages.     

A straightforward one-pot synthesis of Pd–Ag supported on activated carbon as a robust catalyst toward ethanol electrooxidation

Direct Ethanol Fuel Cells (DEFCs) have fascinated remarkable attention on account of their high current density and being environmentally friendly. Developing efficient and durable catalysts with a simple and fast method is a great challenge in the practical applications of DEFCs. To this end, the bimetallic Pd–Ag with adjustable Pd:Ag ratios were synthesized via a simple and one-pot strategy on activated carbon as a support in this study. The Pd–Ag/C catalysts with different molar ratios were synthesized by simultaneous reduction of Pd and Ag ions in the presence of the ethanolic sodium hydroxide as a green reducing agent for the first time. Several different methods, including FE-SEM, HR-TEM, XRD, XPS EDX, ICP-OES, and BET were used to confirm the structure and morphology of the catalysts. The performance of catalysts was also examined in ethanol oxidation. Obtained results of electrochemical experiments revealed that the Pd₃–Ag₁/C catalyst had superior catalytic activity (2911.98 mAmg^?1_Pd), durability, and long-stability compared to the other catalysts. The excellent catalytic characteristic can be attributed to the synergistic effect between Pd and Ag. We presume that our simple method have the chance to be utilized as a proper method for the synthesis of fuel cell catalysts.     

Titanium compounds TiC–C and TiO2–C supported Pd catalysts for formic acid electrooxidation

In this work, Pd nanoparticles supported on TiC–C and TiO₂–C as novel and efficient supports for formic acid electrooxidation are investigated. The Pd/TiC–C and Pd/TiO₂–C catalysts have been synthesized by microwave-assisted polyol process. The Pd nanoparticles in the Pd/TiC–C and Pd/TiO₂–C catalysts are found to disperse more uniformly and have smaller sizes on the TiC–C and TiO₂–C supports than that on carbon support alone. The addition of titanium compounds (TiC and TiO₂) significantly increases catalytic activity and stability of Pd for formic acid electrooxidation because of outstanding oxidation and acid corrosion resistance of titanium compounds (TiC and TiO₂), and metal-support interaction between Pd nanoparticles and titanium compound (TiC or TiO₂). The Pd/TiC–C catalyst displays the best performance among all the samples. The effect of TiC:C mass ratio on the catalytic activity is also investigated. It is found that the maximal catalytic activity and stability for formic acid electrooxidation is observed at the Pd/TiC–C catalyst with TiC:C mass ratio of 1:2.     

Thermo-photo synergic effect on methanol steam reforming over mesoporous Cu/TiO2–CeO2 catalysts

Methanol steam reforming (MSR) is considered as an effective method for hydrogen storage and generating high-quality hydrogen for fuel cells. In this work, mesoporous Cu/TiO₂–CeO₂ catalysts are proposed to achieve efficient MSR based on synergetic effects of thermal and photon energies. Optimal Ti/Ce molar ratio is found to be 2:1, for which excellent methanol conversion of 100% and extremely low CO selectivity of 2.2% are achieved for thermal catalysis. Further applying UV light (280–400 nm) irradiation while keeping the same temperature, the hydrogen production rate is enhanced to be 78.8 mmol/h/g from 58.6 mmol/h/g. The underlying mechanism is attributed to photogenerated electron hole pairs promoting the REDOX reaction of intermediate product methyl formate based on in situ diffuse reflectance infrared fourier transform spectra (DRIFTS). This work provides a new method to enhance methanol steam reforming performance via thermo-photo synergic effects, and paves a way for the development of direct solar driven MSR techniques.     

Comparison study of electrocatalytic activity of reduced graphene oxide supported Pt–Cu bimetallic or Pt nanoparticles for the electrooxidation of methanol and ethanol

Pt–Cu bimetallic nanoparticles supported on reduced graphene oxide (Pt–Cu/RGO) were synthesized through the simple one-step reduction of H₂PtCl₆ and CuSO₄ in the presence of graphene oxide (GO) at room-temperature. The Pt–Cu/RGO was characterized with UV–vis spectrophotometer, X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy and its catalytic behavior for the direct oxidation of methanol was investigated. Compared to Pt/RGO and Pt/C catalysts, Pt–Cu/RGO hybrids exhibited markedly superior catalytic activity for the electrocatalytic oxidation of methanol and ethanol. This improved catalytic activity can be attributed to the dendritic structure of the Pt–Cu bimetallic nanoparticles.     

Amorphous NiFe–OH/Ni–Cu–P supported on self-supporting expanded graphite sheet as efficient bifunctional electrocatalysts for overall water splitting

With the serious intensification of energy shortage and greenhouse effect, people begin to look for the sustainable energy sources to replace fossil energy sources. Herein, self-supporting expanded graphite sheet (SSEGS) was developed as an ideal catalyst support through electrochemically intercalating flexible graphite sheet in alkaline solution. Electroless deposition was employed to synthesize Ni–Cu–P alloy on SSEGS and then an amorphous NiFe hydroxide/Ni–Cu–P/SSEGS (NiFe–OH/Ni–Cu–P/SSEGS) composite catalyst was further constructed through electrodeposition. Benefitting from the unique structural advantage of SSEGS and the synergistic effect between two amorphous Ni-based materials (Ni–Cu–P alloy and NiFe–OH), the resulting electrode exhibited superior bifunctional electrocatalytic performance in 1 M KOH. For H₂ evolution reaction and O₂ evolution reaction, the NiFe–OH/Ni–Cu–P/SSEGS composite catalyst could reach 10 mA cm⁻² at low overpotentials of 75 and 240 mV, respectively. Remarkably, the two-electrode system driven by NiFe–OH/Ni–Cu–P/SSEGS as the anode and cathode could afford 10 mA cm⁻² at a low cell voltage of 1.56 V vs. RHE. And after the 12 h stability test, the cell voltage at 10 mA cm⁻² increased by only 7 mV, indicating that the two-electrode system had excellent stability. The preparation of NiFe–OH/Ni–Cu–P/SSEGS material with superior bifunctional electrocatalytic performance has a significance influence to the development and expansion of hydrogen production technology.     

Characterization and performance evaluation of Pt–Ru electrocatalysts supported on different carbon materials for direct methanol fuel cells

The paper addresses the effect of the carbon support on the microstructure and performance of Pt–Ru-based anodes for direct methanol fuel cells (DMFC), based on the study of four electrodes with a carbon black functionalized with HNO₃, a mesoporous carbon (CMK-3), a physical mixture of TiO₂ and carbon black and a reference carbon thermally treated in helium atmosphere (HeTT). It is shown that CMK-3 hinders the growth of the electrocatalyst nanoparticles (2.7 nm) and improves their distribution on the support surface, whereas the oxidized surfaces of HNO₃ carbon and TiO₂+carbon lead to larger (4–4.5 nm), agglomerated particles, and the lowest electrochemical active areas (54 and 26 m² g⁻¹, in contrast with 90 m² g⁻¹ for CMK-3), as determined from CO stripping experiments. However, HNO₃ and TiO₂ are characterized by the lowest CO oxidation potential (0.4 V vs. RHE), thus suggesting higher CO tolerance for the se electrodes. Tests in DMFC configuration show that the three modified electrodes have clearly better performance than the reference HeTT. The highest power density attained with electrodes supported on carbon treated with HNO₃ (65 mW cm⁻²/300 mA cm⁻² at 90 °C) and the equally interesting performance of the TiO₂-based electrodes (53 mW cm⁻²/300 mA cm⁻²), is a strong indication of the positive effect of the presence of oxygenated groups on the methanol oxidation reaction. The results are interpreted in order to identify separate microstructural (electrocatalyst particle size, porosity) and compositional (oxygenated surface groups, presence of oxide phase) effects on the electrode performance.     

Novel palladium–lead (Pd–Pb/C) bimetallic catalysts for electrooxidation of ethanol in alkaline media

Carbon-supported bimetallic palladium–lead (Pd–Pb/C) catalysts with different amounts of lead are prepared using a co-reduction method. The catalysts are characterized by various techniques, which reveal the formation of an alloy nanoparticle structure. The electrochemical activities of the catalysts towards ethanol oxidation in alkaline media are examined by cyclic voltammetry, linear sweep voltammetry and chronoamperometry methods. The results show that the Pd–Pb(4:1)/C catalyst exhibits a better catalytic activity than the Pd/C catalyst. From carbon monoxide (CO) stripping results, the addition of lead also facilitates the oxidative removal of adsorbed CO. The promoting effect of lead is explained by a bi-functional mechanism and d-band theory.     

Novel MoSe2–Ni(OH)2 nanocomposite as an electrocatalyst for high efficient hydrogen evolution reaction

Nowadays, there is a great demand for low-cost and highly active electrocatalyst for the production of clean renewable energy. However, most of the electrocatalysts are noble metal-based which are very costly and unstable. To counter this, electrochemical water splitting in energy storage systems is been widely applied, using non-noble metal-based nanostructured electrocatalysts. In this work, a novel noble metal-free MoSe₂–Ni(OH)₂ nanocomposite electrocatalyst is synthesized using a multi-step hydrothermal technique for efficient hydrogen evolution reaction (HER). The morphology, structural, chemical composition, and functional features of the synthesized nanomaterials were characterized using different techniques that include scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), X-ray photoelectron spectroscopy (XPS), and Raman analysis. The new developed MoSe₂–Ni(OH)₂ nanocomposite combines a high active surface area with a high chemical stability, generating a novel material with a synergistic effect that enhances water splitting process performance. Thus, an outstanding low Tafel slope of 54 mV dec⁻¹ is accomplished in the hydrogen evolution reaction.     

Pt–rGO–TiO2 nanocomposite by UV-photoreduction method as promising electrocatalyst for methanol oxidation

Pt/TiO₂-decorated reduced graphene oxide composite as catalyst for methanol electro-oxidation with three phase junction structure has been synthesized by UV-photoreduction (denoted as p-Pt/rGO@TiO₂). The obtained p-Pt/rGO@TiO₂ has been detailedly characterized by transmission electron microscope (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV) and chronoamperometry (CA). XRD and TEM characterizations indicate that photoreduction is favorable to anchoring Pt nanoparticles (NPs) (ca. 2.2 nm) at the interface between TiO₂ and reduced graphene oxide (rGO), and forming the Pt, TiO₂ and rGO three phase junction structure. P-Pt/rGO@TiO₂ exhibits a higher activity for methanol electro-oxidation than m-Pt/rGO and m-Pt/rGO@TiO₂ (prepared by microwave-assisted polyol process). Lifetime tests demonstrate that the electrochemical durability of p-Pt/rGO@TiO₂ is improved by a factor of 2 or more as compared with m-Pt/rGO and m-Pt/rGO@TiO₂. XPS characterizations of p-Pt/rGO@TiO₂ reveal stronger interaction between Pt and support hybrid compared with m-Pt/rGO@TiO₂, which facilitates poisoning species removal and prevents Pt nanoparticles from migrating/agglomerating on or detaching from carbon support. This provides a facile and promising strategy to improve both the activity and durability of electrocatalysts for DMFCs.