Enhancing the durability of multi-walled carbon nanotube supported by Pt and Pt–Pd nanoparticles in gas diffusion electrodes

This work tries to improve the durability of electrocatalysts of gas diffusion electrodes (GDEs) by using multi-walled carbon nanotube supported Pt–Pd bimetallic (Pt–Pd/MWCNT). The durability investigation of multi-walled carbon nanotube supported metals was evaluated by a repetitive potential cycling (RPC) corrosion test and by extended constant potential (ECP) experiments. Potential cycling tests were performed from −0.3 to 1.2 V at 50 mV s⁻¹ in 1 mol L⁻¹ H₂SO₄. Extended constant potential (ECP) durability test were also carried out on the GDEs by 30 h of constant potential operation at 0.8 V vs. Ag/AgCl. The smaller performance loss was observed on the GDE using Pt–Pd/MWCNT as electrocatalyst compared with GDE using Pt/MWCNT during both durability tests. ICP analysis also suggests that the dissolution of Pt nanoparticles from the carbon nanotube surface is hindered when Pd is present.     

Synthesis and characterization of Cu core Pt–Ru shell nanoparticles for the electro-oxidation of alcohols

Cu@Pt–Ru core–shell supported electrocatalysts have been synthesized by a two-step process via a galvanic displacement reaction. XRD diffraction and EDX analysis, and cyclic voltammetry measurements revealed the presence of nanoparticles composed by a Cu-rich Pt–Cu core surrounded by a Pt-rich Pt–Ru shell. Cyclic voltammetry and chronoamperometric measurements showed that as-synthesized core–shell materials exhibit superior catalytic activity towards methanol and ethanol electro-oxidation compared to a commercial Pt–Ru/C catalyst with higher Pt loading. This behavior can be associated with the lattice mismatch between the Pt-rich shell and the Cu rich core, which in turn produces lattice-strain, surface ligand effects and a large amount of surface defect sites. In addition, the core–shell electrodes displayed a better catalytic activity and lower onset potentials for ethanol oxidation than for methanol oxidation.     

Electrodeposition of Pt–Ru and Pt–Ru–Ni nanoclusters on multi-walled carbon nanotubes for direct methanol fuel cell

A full-electrochemical method is developed to deposit three dimension structure (3D) flowerlike platinum-ruthenium (PtRu) and platinum-ruthenium-nickel (PtRuNi) alloy nanoparticle clusters on multi-walled carbon nanotubes (MWCNTs) through a three-step process. The structure and elemental composition of the PtRu/MWCNTs and PtRuNi/MWCNTs catalysts are characterized by transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray polycrystalline diffraction (XRD), IRIS advantage inductively coupled plasma atomic emission spectroscopy (ICP-AES), and X-ray photoelectron spectroscopy (XPS). The presence of Pt(0), Ru(0), Ni(0), Ni(OH)₂, NiOOH, RuO₂ and NiO is deduced from XPS data. Electrocatalytic properties of the resulting PtRu/MWCNTs and PtRuNi/MWCNTs nanocomposites for oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) are investigated. Compared with the Pt/MWCNTs, PtNi/MWCNTs and PtRu/MWCNTs electrodes, an enhanced electrocatalytic activity and an appreciably improved resistance to CO poisoning are observed for the PtRuNi/MWCNTs electrode, which are attributed to the synergetic effect of bifunctional catalysis, three dimension structure, and oxygen functional groups which generated after electrochemical activation treatment on MWCNTs surface. The effect of electrodeposition conditions for the metal complexes on the composition and performance of the alloy nanoparticle clusters is also investigated. The optimized ratios for PtRu and PtRuNi alloy nanoparticle clusters are 8:2 and 8:1:1, respectively, in this experiment condition. The PtRuNi catalyst thus prepared exhibits excellent performance in the direct methanol fuel cells (DMFCs). The enhanced activity of the catalyst is surely throwing some light on the research and development of effective DMFCs catalysts.     

Improvement on direct ethanol fuel cell performance by using doped-Nafion 117 membranes with Pt and Pt–Ru nanoparticles

Nafion^® 117 membranes doped with Pt (4 × 10⁻⁴ mol L⁻¹ or 8 × 10⁻⁴ mol L⁻¹ H₂PtCl₆ solution), and with Pt–Ru (4 × 10⁻⁴ mol L⁻¹ H₂PtCl₆ and 2 × 10⁻⁴ mol L⁻¹ RuCl₃ solutions) nanoparticles have been synthesized using a simple and scalable absorption-reduction method. The chemical integrity of the membranes was confirmed by ¹³C and ¹⁹F solid-state NMR. The pore microstructure of the membranes was preserved after the doping process, according to SAXS measurements. The tests of the direct ethanol fuel cells (DEFC) performance at 90 °C exhibited up to 38% and 56% increase at the maximum power densities for Pt doped-Nafion^® membrane from lower and higher concentration of H₂PtCl₆ solution, respectively, compared to bare Nafion^® membranes. Additionally, a Pt–Ru doped-membrane tested at 110 °C exhibited the highest power density. Such superior performances may be attributed to a synergistic effect between the extra amount of active catalytic sites inside the pore structure for the electrochemical oxidation of ethanol, thus preventing ethanol crossover, and the excellent proton migration properties conferred by the pore microstructure of Nafion^®. These results demonstrate that the doped-Nafion^® membrane has a good capacity to improve the performance of DEFC, and provided further clarification on the synthesis process of polymer electrolyte doped-membranes in fuel cell technology.     

Effect of carbon substrate materials as a Pt–Ru catalyst support on the performance of direct methanol fuel cells

The support effect of carbon nanotubes (CNTs) for direct methanol fuel cell (DMFC) was studied using CNTs with and without defect preparation, carbon black, and fishbone-type CNTs. The Pt–Ru/defect-free CNTs afforded the highest catalytic activity of methanol oxidation reaction (MOR) in rotating disk electrode experiments and the highest performance as the anode catalysts in DMFC single cell tests with the one-half platinum loading compared to Pt–Ru/VulcanXC-72R. CO stripping voltammograms with Pt–Ru/defect-free CNTs also revealed the lowest CO oxidation potential among other Pt–Ru catalysts using different carbon support. It is thus considered that the carbon substrates significantly affect the CO oxidation activity of anode electrocatalysts in DMFC. This is ascribed to the geometrical effect that the flat interface between CNTs and metal catalysts has a unique feature, at which the electron transfer occurs, and this interface would modify the catalytic properties of Pt–Ru particles.     

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.     

The Pt–Co alloying effect on the performance and stability of high temperature PEMFC cathodes

High temperature (HT) PEMFC technology offers a number of advantages over its low temperature counterpart, including high tolerance to fuel impurities, system simplifications and generation of high-quality waste heat. Nevertheless, the operating temperature and the presence of phosphoric acid necessitate the use of high amounts of platinum metal at the electrodes, especially the cathodic one. In this work, we report the facile preparation of a Pt–Co alloy supported on multi-wall carbon nanotubes. Using the rotating disk electrode method in HClO₄, the activity of this catalyst towards the oxygen reduction reaction, as well as its tolerance to phosphoric acid is evaluated. A comparison is made with two electrocatalysts with similar characteristics (support, nanoparticle size and spatial distribution), where one is based on Pt and the other is a physical mixture of the aforementioned metals (Pt and Co). The superior behavior of the alloyed electrocatalyst urged its electrochemical characterization in-situ, at the cathode of a HT-PEMFC, where performance and, very importantly, stability are thoroughly evaluated and discussed. A comparison with a commercial state-of-the-art electrocatalyst shows the potential to decrease the metal loading of HT-PEMFC electrodes without compromising performance.     

Silicotungstic acid stabilized Pt–Ru nanoparticles supported on carbon nanofibers electrodes for methanol oxidation

Silicotungstic acid stabilized Pt–Ru nanoparticles supported on Functionalized Carbon Nanofibers have been prepared by a microwave-assisted polyol process. The samples were characterized by XRD, SEM and TEM analysis. The electro-catalytic activities of the prepared composites (20% Pt–Ru/STA–CNF) were examined by using Cyclic Voltammetry (CV) for oxidation of methanol. The electro-catalytic activity of the carbon nanofiber based composite (20% Pt–Ru/STA–CNF) electrode for methanol oxidation showed better performance than that of commercially available Johnson Mathey 20% Pt–Ru/C and 20% Pt–Ru/STA–C catalyst. The results imply that carbon nanofiber based STA composite electrodes are excellent potential candidates for application in direct methanol fuel cells.     

Polyoxometallate-stabilized Pt–Ru catalysts on multiwalled carbon nanotubes: Influence of preparation conditions on the performance of direct methanol fuel cells

A novel catalyst, polyoxometallate-stabilized platinum–ruthenium alloy nanoparticles supported on multiwalled carbon nanotubes (Pt–Ru–PMo₁₂-MWNTs), was synthesized by a microwave-assisted polyol process. The effects of microwave reaction time, microwave reaction power, and pH value of the reaction solution on the electrocatalytic properties of Pt–Ru–PMo₁₂-MWNTs catalysts were also investigated. The polyoxometallate (PMo₁₂) formed a self-assembled monolayer on the surface of the Pt/Ru nanoparticles and MWNTs, which effectively prevented the agglomeration of Pt, Ru nanoparticles and MWNTs, due to the electrostatic repulsive interactions between the negatively charged PMo₁₂ monolayers. Energy dispersive spectroscopy examination and electrochemical measurements showed that the loading content of Pt/Ru and their electrochemical activity vary with the synthesis conditions, such as pH, reaction time, and microwave power. It was found that the a Pt–Ru–PMo₁₂-MWNTs electrocatalyst with high Pt loading content, small crystallite size, and good electrocatalytic activity could be synthesized using a long reaction time, intermediate microwave power, and a pH value of 7. The electrocatalysts obtained were characterized using X-ray diffraction, and scanning and transmission electron microscopy. Their electrocatalytic properties were also investigated by using the cyclic voltammetry technique.     

Electrochemical synthesis and characterization of carbon-supported Pt and Pt–Ru nanoparticles with Cu cores for CO and methanol oxidation in polymer electrolyte fuel cells

Pt and Pt–Ru shells on Cu cores supported on Vulcan carbon XC72R have been synthesized and tested as possible anode electrocatalysts for polymer electrolyte fuel cells. Pt(Cu)/C was prepared by Cu electrodeposition on the black carbon support at constant potential followed by Pt deposition on Cu by galvanic exchange, whereas Pt–Ru(Cu)/C was prepared by spontaneous deposition of Ru species on Pt(Cu)/C. The corresponding cyclic voltammograms in 0.5 M H₂SO₄ solution showed the hydrogen adsorption/desorption peaks and no Cu oxidation. The respective CO stripping peak potentials of Pt(Cu)/C and Pt–Ru(Cu)/C were about 0.1 and 0.2 V more negative than those corresponding to Pt/C and Ru-decorated Pt/C. The best conditions for CO oxidation were found for Cu deposition potentials between −0.2 and −0.4 V vs. Ag/AgCl/KCl(sat). The Pt economy of the Pt–Ru(Cu)/C system was proved for the methanol oxidation, with specific currents more than twice those obtained on the Ru-decorated commercial Pt/C catalysts.     

Metallic and carbonaceous –based catalysts performance in the solar catalytic decomposition of methane for hydrogen and carbon production

Solar catalytic decomposition of methane (SCDM) was investigated in a solar furnace facility with different catalysts. The aim of this exploratory study was to investigate the potential of the catalytic methane decomposition approach providing the reaction heat via solar energy at different experimental conditions. All experiments conducted pointed out to the simultaneous production of a gas phase composed only by hydrogen and un-reacted methane with a solid product deposited into the catalyst particles varying upon the catalysts used: nanostructured carbons either in form of carbon nanofibers (CNF) or multi-walled carbon nanotubes (MWCNT) were obtained with the metallic catalyst whereas amorphous carbon was produced using a carbonaceous catalyst. The use of catalysts in the solar assisted methane decomposition present some advantages as compared to the high temperature non-catalytic solar methane decomposition route, mainly derived from the use of lower temperatures (600–950 °C): SCDM yields higher reaction rates, provides an enhancement in process efficiency, avoids the formation of other hydrocarbons (100% selectivity to H₂) and increases the quality of the carbonaceous product obtained, when compared to the non-catalytic route.     

Boosting activity and stability by coupling Pt–Ni nanoparticles with La-modified flexible carbon nanofibers for hydrogen evolution reaction

Platinum (Pt) is considered as the most efficient catalyst for hydrogen evolution reaction (HER) with a nearly zero overpotential, but it is limited by the high cost and poor stability. Herein, we report an efficient electrocatalyst of Pt–Ni alloy nanoparticles (NPs) supported on the La-modified flexible carbon nanocomposite fibers (PtNi@La-CNFs) for HER. The rare earth metal oxide in the catalyst has a structure-effect relationship with the carbon fibers to form a flexible fiber membrane. Experimental results show that the macroscopic and microscopic properties of carbon nanocomposite fibers can be optimized by doping La₂O₃, and the Pt–Ni NPs can be anchored effectively. The Pt₁Ni₁@La-CNFs electrocatalyst exhibits a small overpotential of 32 mV to achieve current density of 10 mA cm^?2 with a low Tafel slope of 51 mV dec^?1 in alkaline medium, outperforming that of Pt@La-CNFs and the commercial Pt/C catalyst. This study reveals that the multiple coupling effect of rare earth compound, precious metal, and transition metal in composite catalyst can tailor its the electronic configuration, and results in an enhanced HER performance. This work opens up a novel approach to design high active and low cost Pt-based HER catalysts.     

Evaluation of Pt–Ru–Ni and Pt–Sn–Ni catalysts as anodes in direct ethanol fuel cells

In this study, the electrooxidation of ethanol on carbon supported Pt–Ru–Ni and Pt–Sn–Ni catalysts is electrochemically studied through cyclic voltammetry at 50 °C in direct ethanol fuel cells. All electrocatalysts are prepared using the ethylene glycol-reduction process and are chemically characterized by energy-dispersive X-ray analysis (EDX). For fuel cell evaluation, electrodes are prepared by the transfer-decal method. Nickel addition to the anode improves DEFC performance. When Pt₇₅Ru₁₅Ni₁₀/C is used as an anode catalyst, the current density obtained in the fuel cell is greater than that of all other investigated catalysts. Tri-metallic catalytic mixtures have a higher performance relative to bi-metallic catalysts. These results are in agreement with CV results that display greater activity for PtRuNi at higher potentials.     

Influence of the structural and surface characteristics of activated carbon on the catalytic decomposition of hydrogen iodide in the sulfur–iodine cycle for hydrogen production

Coal-based activated carbon (AC-COAL) catalysts subjected to acid treatment were tested to evaluate their performance on hydrogen-iodide (HI) decomposition for hydrogen production in sulfur-iodine (SI or IS) cycle. The effects of acid treatment on catalysts and the relations between sample properties and catalytic activities were discussed. The AC-COAL obtained by non-oxidative acid treatments had the best catalytic activity. However, the catalytic activity of AC-COAL decreased after the treatment of nitric acid. Higher surface area, higher carbon contents, lower ash contents and fewer surface oxidation groups contributed to the catalytic activity of ACs. HI decomposition on the AC surface itself may be due to high densities of unpaired electrons associated with structural defects and edge plane sites with similar structural ordering. Moreover, the oxygen-containing groups reduced the electron transfer capability associated with the basal plane sites.     

Kinetics of hydrogen evolution reaction on stabilized Ni,Pt and Ni–Pt nanoparticles obtained by an organometallic approach

Both (Ni, Pt) and bimetallic (Ni_xPt; x = 1, 2, 3) nanoparticles have been synthesized by hydrogenation of Ni(cod)₂ ad Pt₂(dba)₃ in the presence of a weak coordinating ligand, hexadecylamine (CH₃(CH₂)₁₅NH_2, HDA). These nanostructures were characterized by different techniques (Fourier Transform-Infrared Spectroscopy (FT-IR), High-Resolution Transmission Electron Microscopy (HRTEM)), and were evaluated as Hydrogen Evolution Reaction electrocatalysts in 0.5 M sulfuric acid. The effects of varying the platinum amount during the synthesis were systematically studied by Cyclic Voltammetry (CV), polarization measurements and electrochemical impedance spectroscopy (EIS) techniques. HRTEM shows that the bimetallic nanostructures display a different morphology compared to that observed for pure Ni and Pt ones. The process of hydrogen adsorption–desorption in the as-prepared electrodes seems to occur in (110) and (100) facets. It was found that the increase in the activity for the HER is due to an increased electrochemical active surface area (ECSA) and/or stabilization in the case of elemental electrode materials; and to the effect of Pt amount in the case of the Ni–Pt nanostructures (synergistic effect leads to lower overpotential). It has been established that the main pathway for the HER is Volmer–Heyrovsky.     

Pt and Pt–Ag nanoparticles supported on carbon nanotubes (CNT) for oxygen reduction reaction in alkaline medium

In this work, we investigated the effect of the carbon nanotubes (CNT) as alternative support of cathodes for oxygen reduction reaction (ORR) in alkaline medium. The Pt and Pt–Ag nanomaterials supported on CNT were synthesized by sonochemical method. The crystalline structure, morphology, particle size, dispersion, specific surface area, and composition were investigated by XRD, SEM-EDS, TEM, HR-TEM, N₂ adsorption-desorption and XPS characterization. The electrochemical activity for ORR was evaluated by cyclic voltammetry (CV), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS) in alkaline medium. The electrochemical stability was researched by an accelerated degradation test (ADT). Pt/CNT showed the better electrocatalytic activity towards ORR compared with Pt–Ag/CNT and Pt/C. Pt/CNT exhibited higher specific activity (1.12 mA cm^?2 _Pt) than Pt/C (0.25 mA cm^?2 _Pt) which can be attributed to smaller particle size, Pt-CNT interaction, and Pt load (5 wt%). The Pt monometallic samples supported on CNT and Vulcan showed higher electrochemical stability after ADT than Pt–Ag bimetallic. The ORR activity of all materials synthesized proceeded through a four-electron pathway. Furthermore, the EIS results showed that Pt/CNT exhibited the lower resistance to the transfer electron compared with conventional Pt/C and Pt–Ag/CNT.     

Characteristics of hydrogen production with carbon storage by CO2-rich hydrothermal alteration of olivine in the presence of Mg–Al spinel

Artificial control of olivine alteration has potential applications for both H₂ production and CO₂ reduction (by mineralization and hydrogenation). To explore methods to overcome the still-constrained olivine alteration problem, olivine + spinel alteration experiments were performed with the addition of Mg–Al spinel in CO₂-rich (0.5 M NaHCO₃) solution under hydrothermal conditions (300 °C and 10 MPa). Mg–Al spinel enhanced olivine serpentinization significantly (more than 2 times), and generation of both H₂ and CO₂ hydrogenation products was accelerated (up to 3 times) with ≥10 wt% Mg–Al spinel especially at the latter stage of the 72 h reaction.Mineral measurements revealed that more Al released from Mg–Al spinel was incorporated into Al-serpentine by the replacement of Fe with higher Mg–Al spinel content. Both Al and Fe incorporated into Al-serpentine were released as the reaction proceeded. Thus, H₂ production was elevated with the presence of a large amount Mg–Al spinel at the latter stage of the reaction. HCO₃⁻ played an important role in the promotion of Mg–Al spinel dissolution with the release of Al, which was stored in magnesite after being utilized. This study also suggests that the presence of Mg–Al spinel (5–20 wt%) in the starting mineral does not have significant influence on the total H₂ yield from olivine alteration over the entire operation period.     

Ni–Fe nanocubes embedded with Pt nanoparticles for hydrogen and oxygen evolution reactions

Electrochemical water-splitting is widely regarded as one of the essential strategies to produce hydrogen energy, while Metal-organic frameworks (MOFs) materials are used to prepare electrochemical catalysts because of its controllable morphology and low cost. Herein, a series of trimetallic porous Pt-inlaid Ni–Fe nanocubes (NCs) are developed with bifunctions of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In the process of prepare the electrochemical catalysts, Pt nanoparticles are uniformly embedded in the Fe–Ni PBA cube structure, and ascorbic acid is employed as a reducing agent to reduce Pt²⁺ to Pt nanoparticles. In this work, the cubic structure of Fe–Ni PBA is maintained and the noble metal Pt nanoparticles are embedded. Remarkably, the formation of PBA cubes, Pt inlay and reduction are completed in one step, and Pt nanoparticles are embedded by a simple method for the first time. By employing acid etching method, a porous structure is formed on the PBA cube, which increases the exposed area of the catalyst and provides more active sites for HER and OER. Due to the porous structure, highly electrochemical active surface area and the embedded of highly dispersed Pt nanoparticles, the porous 0.6 Ni–Fe–Pt nanocubes (NCs) exhibits excellently electrocatalytic performance and durable stability to HER and OER. In this work, for HER and OER, the Tafel slopes are 81 and 65 mV dec⁻¹, the overpotential η at the current density of 10 mA cm⁻² are 463 and 333 mV, and the onset potential are 0.444 and 1.548 V, respectively. And after a 12-h i-t test and 1000 cycles of cyclic voltammetry (CV), it maintained high stability and durability. This work opens up a new preparation method for noble metal embedded MOF materials and provided a new idea for the preparation of carbon nanocomposites based on MOF.     

Methanol,ethanol and ethylene glycol electro-oxidation at Pt and Pt–Ru catalysts electrodeposited over oxidized carbon nanotubes

Pt and Pt–Ru catalysts supported on oxidized multi-walled carbon nanotubes with different ruthenium content ranging from 19 to 30 at.% were prepared by pulse electrodeposition and tested for methanol, ethanol and ethylene glycol oxidation in H₂SO₄ electrolyte. The catalysts were mainly composed by small 3D irregular-shaped agglomerates of nano-sized particles.