Synthesis and characterization of Pd-La(OH)3/C electrocatalyst for direct ethanol fuel cell

The composite nanomaterial of Pd-La(OH)₃/C was successfully synthesized via intermittent microwave heating–glycol reduction method and characterized with X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. The TEM photograph shows that Pd-La(OH)₃ is well polymerized and dispersed on the carbon support. The performance of the prepared material for ethanol oxidation was evaluated by cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry (CA), and chronopotentiometry (CP) measurements in alkaline media. The results reveal that Pd-La(OH)₃/C has significantly higher activity and stability than that of Pd/C with the same Pd loading of 0.1 mg cm^?2. The stable potential reaches to ?0.38 V vs. Hg/HgO at 20 mA cm^?2 on the Pd-La(OH)₃/C electrode in CP curve. Single direct ethanol fuel cell (DEFC) was constructed using Pd-La(OH)₃/C electrode and MnO₂/C electrode as the ethanol anode and air cathode respectively, where the cell voltage can stay at 0.4 V under the current density of 20 mA cm^?2 by discharge test at room temperature.     

Graphitic C<Subscript>3</Subscript>N<Subscript>4</Subscript>@MWCNTs supported Mn<Subscript>3</Subscript>O<Subscript>4</Subscript> as a novel electrocatalyst for the oxygen reduction reaction in zinc–air batteries

A series of catalysts (g-C₃N₄@MWCNTs/Mn₃O₄) were prepared from g-C₃N₄, MWCNTs, and Mn₃O₄ for oxygen reduction reaction (ORR) in zinc–air batteries. From the half-cell tests, the loading of 35 % Mn₃O₄ (sample GMM35) presents an excellent activity toward ORR in alkaline condition. Rotating ring-disk electrode (RRDE) studies reveal that 3.6～3.8 electrons are transferred with a H₂O₂ yield of 11.4 % at ?0.4 V. Meanwhile, the GMM35 nanocomposite exhibits the same durability as commercial 20 wt% Pt/C in alkaline condition, but it shows lower peak power density (192.4 mW cm^?2 at 229.1 mA cm^?2) and cell voltage than those with a commercial Pt/C catalyst (260.9 mW cm^?2 at 285.4 mA cm^?2).     

Hydrogen evolution reaction and formic acid oxidation by decorated nanostructural Pt/Pd on a copper-filled nanoporous stainless steel

In this work, a 304 stainless steel (SS) was anodized to prepare nanoporous SS (NPSS) with an average size of about 75 nm and then filled with copper (Cu/NPSS) using pulsed electrodeposition method. Afterward, a nanostructural Pt and Pd film was deposited by galvanic replacement (GR) on the Cu/NPSS to prepare modified electrode (PtPd/Cu/NPSS) for hydrogen evolution reaction (HER) and formic acid electrooxidation (FAO). The electrocatalytic activity of the modified electrode and its structural characterization have been studied by voltammetric methods, electrochemical impedance spectroscopy (EIS), inductively coupled plasma optical emission spectrometry (ICP-OES), and field emission scanning electron microscopy (FESEM). The results show that the nanostructural Pt₁Pd₁/Cu/NPSS composition, with low Pt loading and suitable stability, has a good electrocatalytic performance toward HER (E_Onset = + 12 mV vs. NHE) and FAO (E_Onset = ?180 mV vs. NHE). For HER observed a high mass activity of noble metals (87.54 mA cm^?2μg _Pd+Pt ^?1 ) in comparison with Pt deposited Cu/NPSS (41.5 mA cm^?2 μg _Pt ^?1 ) at the same applied potential of ? 0.25 V versus NHE. Also, the fabricated electrocatalysts with more electrochemically active surface area in comparison with Pd/Cu/NPSS and Pt/Cu/NPSS revealed more resisting to the poisoning components and good stability for FAO.     

Electrochemical degradation of tetracycline in artificial urine medium

The electrochemical degradation of tetracycline hydrochloride (TeC) was comparatively investigated in artificial urine and chloride-containing media using a one-compartment filter-press flow cell composed of a Ti/Ru_0.3Ti_0.7O₂ dimensionally stable anode. The effect of the current density (10–40 mA cm^?2) on the removal levels attained for TeC and total organic carbon (TOC) (in both media), as well as for urea and creatinine in artificial urine medium, was assessed. The TeC removal rate in the artificial urine medium was much lower than in chloride-containing medium, probably due to the higher consumption of the electrogenerated active chlorine species by the urea and creatinine in the artificial urine medium. Moreover, the obtained removal levels for the urea and creatinine were negligible at current densities lower than 30 mA cm^?2. As TOC abatement was also very small, it is possible that TeC oxidation leads to intermediate compounds. Thus, if current densities less than 20 mA cm^?2 are applied, TeC can be selectively removed.     

Electrocatalytic oxidation of methanol on Pt-Pd nanoparticles supported on honeycomb-like porous carbons in alkaline media

Honeycomb-like porous carbons (PCs) were synthesized using a facile self-assembly method with phenolic resin as the carbon source and tetraethyl orthosilicate (TEOS) as the silica source. The PCs were found to have a large BET surface area of 458 m² g^?1 and a partially graphitized structure. The obtained PCs were used as a support for various Pt-Pd bimetallic alloy catalysts employed for methanol oxidation in alkaline media. Compared with Pt supported on commercial Vulcan XC-72R carbon (Pt/C) and with the other Pt-Pd bimetallic alloy catalysts on PCs, Pt₃Pd₁ on PCs displayed the most negative onset potential for methanol oxidation and the highest steady-state current (2.04 mA cm^?2). This may be because the Pt₃Pd₁/PCs catalyst has the largest electrochemical active surface area (ESA), and because adding Pd to the catalyst improves the ability of the intermediate species to tolerate oxidation. The results show that the prepared Pt-Pd/PCs is a potential candidate for application as a catalyst in alkaline direct methanol fuel cells.     

Investigation of carbon-supported Ni@Ag core-shell nanoparticles as electrocatalyst for electrooxidation of sodium borohydride

Carbon-supported Ni@Ag core-shell nanoparticles were synthesized and used as the anode electrocatalyst for direct borohydride-hydrogen peroxide fuel cell (DBHFC). The morphology, structure, and composition of the as-prepared electrocatalysts are characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and energy dispersive spectroscopy (EDS). Electrochemical characterizations are performed by cyclic voltammetry (CV), chronoamperometry (CA), linear scan voltammetry with rotating disk electrode (LSV RDE), and fuel cell test. The catalytic behaviors and main kinetic parameters (e.g., Tafel slope, number of electrons exchanged, exchange current density, and apparent activation energy) toward BH ₄ ^‐ oxidation on Ag/C and Ni@Ag/C electrocatalysts are determined. Results show that the as-prepared nanoparticles have a core-shell structure with the average size approximately 13 nm. The kinetics of NaBH₄ oxidation is faster for Ni@Ag/C than that for Ag/C. Among the as-prepared catalysts, the highest transition electron value and the lowest apparent activation energy are obtained on Ni₁@Ag₁/C; the values are 4.8 and 20.23 kJ mol^?1, respectively. The DBHFC using Ni₁@Ag₁/C as anode electrocatalyst and Pt mesh (1 cm²) as cathode electrode obtains the maximum anodic power density as high as 8.54 mW cm^?2 at a discharge current density of 8.42 mA cm^?2 at 25 °C.     

Effects of humidity and temperature on the electrochemical activities of H2/O2 PEMFCs using hybrid membrane electrolytes

Electrochemical characteristics of single cell performances at various humidity conditions and constant temperatures of 40?100 °C using membrane electrode assemblies (MEAs) were studied. The MEAs consist of alternative proton-conducting hybrid membrane electrolyte and noble Pt/C catalyst for the H₂/O₂ proton exchange membrane fuel cells (PEMFCs). The function of humidity on the cell performances was investigated at larger current density values of 501 mA cm^?2 and constant cell temperatures of 80 and 90 °C and the relative humidity of 100 %. The power density value of 400 mW cm^?2 was obtained when the same MEA at similar operating conditions was used. The effects of temperature on the single cell performances were investigated at various temperature ranges of 40–100 °C and constant relative humidity of 50, 70, and 100 %. The maximum current density and power density values of about 600 mA cm^?2 and 160 mW cm^?2, respectively, were obtained at 90 °C with 100 % RH. The results were compared with the reported results of Nafion membrane and similar hybrid membranes operating at low temperatures for H₂/O₂ fuel cells. Finally, the results provided an alternative proton-conducting electrolyte as promising candidate for low/intermediate temperature operating H₂/O₂ fuel cells.     

Performance studies of electrolyte-supported solid oxide fuel cell with Ni–YSZ and Ni–TiO2–YSZ as anodes

Redox cycling of Ni-based anode induces cell degradation which limits the cell's lifetime during solid oxide fuel cell operation. In the present study, the redox testing of electrolyte-supported cells has been investigated with TiO₂-added NiO–YSZ anode matrix. Button cells were fabricated by die-pressing YSZ powder as electrolyte, and onto which NiO–YSZ or NiO–TiO₂–YSZ anode and LSM–YSZ composite cathode were painted. The electrochemical performance and stability have been evaluated by measuring current–voltage characteristics followed by impedance spectroscopy after each redox cycling. Anode matrices before and after cell operation have been characterized by X-ray diffraction (XRD), elemental dispersive X-ray (EDX), and scanning electron microscopy (SEM). During cell operation the peak power density decreases from 111 mW cm^?2 (239 mA cm^?2) to 84 mW cm^?2 (188 mA cm^?2) between 23 and 128 h with five redox cycles for cell having NiO–YSZ (40:60) anode. But for cell with NiO–TiO₂–YSZ (30:10:60), the anode peak power density was constant and stable around 85 mW cm^?2 (194 mA cm^?2) throughout the cell run of 130 h and five redox cycles. No loss in the open circuit voltage was observed. SEM and XRD studies of NiO–TiO₂–YSZ (30:10:60) anodes revealed formation of ZrTiO₄, which may be responsible for inhibition of Ni coarsening leading to stable cell performance.     

Cyclohexene Hydroconversion Using Monometallic and Bimetallic Catalysts Supported on γ‐Alumina

The hydroconversion of cyclohexene (CHE) using monometallic catalysts containing 0.35wt% of Pt, Pd, Ir or Re on a γ‐alumina support, as well as bimetallic catalysts containing combinations of 0.35wt% Pt with 0.35wt% of either Pd, Ir or Re on γ‐alumina, were investigated in a plug flow‐type fixed‐bed reactor. The Cyclohexene (CHE) feed was injected continuously with a rate of 8.33 × 10^?3mole h^?1 on 0.2 g of catalyst using a simultaneous hydrogen gas flow of 20 cm³ min^?1 throughout a broad reaction temperature range of 50–400 °C. The dispersion of the metals in the catalysts was determined via H₂ or CO chemisorption. The activities of the monometallic catalysts were found to be in the order: Pd > Pt > Ir > Re, whereas those of the bimetallic catalysts were in the order: PtPd > PtIr > PtRe. Cyclohexene hydrogenation and dehydrogenation reactions using the current mono‐ and bimetallic catalysts were kinetically investigated applying the absolute reaction rate theory, whereby reaction rate constant, activation energy, enthalpy and entropy of activation were computed to explain surface variations on these catalysts.     

碳黑预处理对Pt/C催化剂对甲醇氧化电催化活性的影响

直接甲醇燃料电池(DMFC)由于具有较多的优点而受到广泛的关注. 但是碳载Pt (Pt/C)阳极催化剂电催化活性低是限制其应用的一个主要问题. 为了提高Pt/C催化剂对甲醇氧化的电催化性能, 分别用CO₂, 空气, H₂O₂或HNO₃对常用作为载体的Vulcan XC-72碳黑进行预处理. 结果表明, 在用CO₂, 空气, HNO₃, H₂O₂处理的及未处理的碳黑作载体制得的Pt/C催化剂电极上, 甲醇氧化峰的峰电流密度顺序为39, 33, 32, 20和18 mA•cm^－2, 表明用CO₂处理的碳载体制备的Pt/C催化剂对甲醇氧化有最好的电催化活性和稳定性. 其主要原因是用CO₂处理能减少碳黑表面的含氧基团和增加石墨化程度, 而使碳黑的电阻降低及Pt粒子在碳黑上的分散性变好.     

Bimetallic Cu–Pt/nanoporous carbon composite as an efficient catalyst for methanol oxidation

A novel bimetallic Cu–Pt nanoparticle supported onto Cu/indirectly carbonized nanoporous carbon composite (Cu–Pt/ICNPCC) was prepared through a two-step process: first, carbonization of furfuryl alcohol-infiltrated MOF-199 [metal–organic framework Cu₃(BTC)₂ (BTC?=?1,3,5-benzene tricarboxylate)], without removing the Cu metal with HF aqueous solution; second, the partial galvanic replacement reaction (GRR) of Cu nanoparticles by Pt^IV upon immersion in a platinum(IV) chloride solution. The synthesized materials characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy (EDS), and electrochemical methods. The EDS result revealed that part of Cu nanoparticles have been substituted by Pt nanoparticles after GRR. The methanol oxidation at the surface of Cu–Pt/ICNPCC was investigated by cyclic voltammetry method in 0.5 M H₂SO₄ and indicated good electro-catalytic activity towards methanol oxidation (E_p?=?0.85 V vs. NHE and j_f?=?1.00 mA cm^?2). It is suggested that this improvement is attributed to the effect of proper Cu/ICNPCC for fine dispersion, efficient adhesion, and prevention of Pt coalescing.     

Synthesis of palladium nanoparticles supported on reduced graphene oxide-tungsten carbide composite and the investigation of its performance for electrooxidation of formic acid

Palladium (Pd) nanoparticles are uniformly distributed on tungsten carbide (WC)-reduced graphene (RGO) oxide composite to synthesize a new electrocatalyst Pd-WC/RGO. The catalysts prepared with various amounts of tungsten carbide are characterized by transmission electron microscopy, energy dispersive spectrometry, and X-ray diffraction. The electrocatalytic performance of the prepared materials toward formic acid oxidation reaction is tested to evaluate the effect of adding WC. The results show that Pd-WC/RGO electrocatalyst with a 25 wt% WC (Pd-WC(25)/RGO) presented a narrow Pd particle size distribution both on the surface of RGO and WC nanocrystallites. Its current density of the positive main anodic peak of formic acid electrooxidation is up to 42.35 mA cm^?2. Compared with the other catalysts, especially the Pd/RGO, the Pd-WC(25)/RGO demonstrate better electrocatalytic activity and higher stability toward the formic acid oxidation reaction. It is attributed to the small size and uniform dispersion of Pd NPs on both RGO sheets and WC nanocrystallines, and to the stronger synergistic effect between Pd NPs and WC nanocrystallines, which result from the proper mass percentage of 25 % WC in the Pd-WC(25)/RGO composite. The present work reveals that WC could be a good additive component, and the composite WC/RGO could be a better support in preparing Pd-based catalysts.     

Low temperature carbon monoxide catalytic oxidation at the Pd/Ce–Zr–Al–Ox catalyst

The homogeneous chemical composition ceria–zirconia–alumina (Ce–Zr–Al–O_x) nano-alloy were successfully synthesized by surfactant-assisted parallel flow co-precipitation method and applied as supports for low temperature CO oxidation. The experiment conditions were studied in detailed. At 0.92 wt% Pd loading, 30,000 ppm CO could be completely oxidized to CO₂ at 30 °C at a WHSV of 4,380 ml g^?1 h^?1 over the Pd/Ce–Zr–Al–O_x (n_Ce:n_Zr = 3:1) catalyst. Pd/Ce–Zr–Al–O_x catalysts were systematical studied by mean of BET, XRD and TEM analysis. XRD characterization showed that zirconium element entered into cubic structure of ceria and leaded to structure distortion. Addition of aluminum increased specific surface area of ceria–zirconia solid solution substantially. The average pore diameter of Ce–Zr–Al–O_x support palladium catalysts were the key impact factor for CO oxidation. When the Pd/Ce–Zr–Al–O_x catalysts had highly dispersed palladium nanoparticles, large average pore diameter, suitable surface area and pore volume, the activity of CO oxidation was the best.     

Kinetics of ethylene glycol electrooxidation on the noble metal-based nano-catalysts

A comparative electrooxidation of Eg in the alkaline solution was investigated over Pt, Pd and Au nanoparticle-modified carbon-ceramic electrode. The kinetic parameters of Eg oxidation, i.e., Tafel slope and activation energy (E _a), were determined on the modified electrodes. The lowest E _a value of 8.9 kJ mol^?1 was calculated on Pt|CCE. In continuation, the reaction orders with respect to the Eg and NaOH concentrations on Pd|CCE were found to be 0.4–0.2 and 0.6, respectively. An adsorption equilibrium constant (b) of 22.36 M^?1 and the adsorption Gibbs energy change (ΔG°) of ?7.7 kJ mol^?1 were obtained on Pd|CCE. The chronopotentiometry (CP) and chronoamperometry (CA) results showed that Pd|CCE and then Au|CCE have better performance stability than Pt|CCE for Eg electrooxidation. Additionally, the electrochemical impedance spectroscopy (EIS) suggested faster electron-transfer kinetics on Pt than that on the Pd and Au electrocatalysts.     

Evaluation of gamma irradiation effect on physico-chemical properties of a mixed beverage based in soy milk and grape juice

The effects of the main operation variables on the electrochemical oxidation of simulated tributyl phosphate (TBP) waste by a boron-doped diamond anode are individually studied. The optimum operating conditions are obtained as follows: 4 g L^?1 initial TBP concentration, 180 min degradation time, 40 mA cm^?2 current density, 0.5 mol L^?1 Na₂SO₄ as the supporting electrolyte, and unadjusted pH of the aqueous phase. Under such conditions, a chemical oxygen demand (COD) removal ratio of 82.3% is achieved, and the energy consumption is 26.16 kWh m^?3. A degradation mechanism of TBP is tentatively proposed.     

Proton conductivity and structural properties of precursors mixed PVA/PWA-based hybrid composite membranes

A new class of hybrid nanocomposite membranes containing poly(vinyl alcohol) (PVA), phosphotungstic acid (PWA), 3-glycidyloxypropyltrimethoxysilane (GPTMS), 3-mercaptopropyltrimethoxysilane (MPTMS) and glutaraldehyde (GA) were prepared by a sol–gel method. The aim of this research study was to investigate these novel and highly proton-conducting membranes including their properties, and performances for proton exchange membrane fuel cells (PEMFCs) operating at low temperature. 'Swelling' was observed at room temperature for all the composites. The manner in which the conductivity depended on temperature and humidity was determined and a maximum conductivity value of 2.5?×?10^?2 S cm^?1 was found at a 140°C and 30 % relative humidity (RH) for the PVA/PWA/GPTMS/MPTMS/P₂O₅/GA (50/5/15/10/10/10 wt.%) hybrid composite membrane. It was suggested that the conductivity depended strongly on the nature of the organic/inorganic components as well as on the acid concentration. X-ray diffraction (XRD) results demonstrated that this membrane had an amorphous phase, and Fourier transform infrared spectroscopy (FTIR) results confirmed the composite formation. Finally, membrane-electrode assemblies with a loading of 0.1 mg cm^?2 of Pt/C on a prepared electrode gave rise to a current density of 309 mA cm^?2 at 0.5 V.     

Hybrid materials utilizing polyelectrolyte-derivatized carbon nanotubes and vanadium-mixed addenda heteropolytungstate for efficient electrochemical charging and electrocatalysis

Preparation and electrochemical behavior of new hybrid materials composed of multi-walled carbon nanotubes (CNTs) that were derivatized with poly(diallyldimethylammonium) chloride and modified with vanadium-mixed addenda Dawson-type heteropolytungstate, [P₂W₁₇VO₆₂]^8?, is described here. These nanostructured composite systems exhibited fast dynamics of charge propagation. They were characterized by the transport (effectively diffusional) kinetic parameter of approximately 8?×?10^?8 cm^?2 s^?1/2 and the specific capacitance parameter of 82 F g^?1 (at the charging/discharging current of 200 mA g^?1). The latter parameter for bare CNTs was found to be only 50 F g^?1 under analogous conditions. These observations were based on the results of galvanostatic charging–discharging, cyclic voltammetric, and AC impedance spectroscopic measurements. The improved capacitance properties were attributed to the systems’ pseudocapacitive features originating from the fast redox transitions of the [P₂W₁₇VO₆₂]^8? polyanions. In addition to the fast redox conduction, the proposed organic–inorganic hybrid materials exhibited interesting electrocatalytic activity toward reduction of bromate in the broad concentration range (sensitivity, 0.24 mA cm^?2 mmol^?1 dm³).     

Synthesis and electrochemical evaluation of La<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>MnO<Subscript>3</Subscript> catalysts for zinc-air batteries

La_1-x Sr _x MnO₃ (x?=?0.1～0.4) catalysts for primary and rechargeable zinc-air batteries have been successfully synthesized by the citrate method and their electrochemical properties measured. The materials can catalyze both ORR and OER, and the one with ideal composition of La_0.8Sr_0.2MnO₃ catalyst exhibits the highest catalytic activity and durability in alkaline medium. The resulting primary zinc-air cell shows a peak power density of 146 mW cm^?2 at 235 mA cm^?2. The secondary cell exhibits a charge-discharge voltage gap of 1.0 V at 10 mA cm^?2, which is highly stable over many charge-discharge cycles.     

Folded nanosheet-like Co<Subscript>0.85</Subscript>Se array for overall water splitting

Active, stable, and earth-abundant bifunctional electrocatalyst for overall water splitting is pivotal to actualize large-scale water splitting via electrolysis. In this work, the hierarchical folded nanosheet-like Co_0.85Se array on Ni foam is constructed by liquid-phase chemical conversion with cobalt precursor nanorod array. It can serve as an efficient bifunctional electrocatalyst for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline electrolyte, with a current density of 10 mA cm^?2 at overpotential of 232 mV for OER and 129 mV for HER and Tafel slope of 78.9 mV dec^?1 for OER and 95.0 mV dec^?1 for HER, respectively. The two-electrode alkaline water electrolyzer utilizing this folded nanosheet-like Co_0.85Se array as both anode and cathode toward overall water splitting offered a current of 10 mA cm^?2 at a cell voltage of 1.60 V. This work explores an efficient and low-cost electrocatalyst for overall water splitting application in alkaline electrolytes.     

Preparation and characterization of sulfonated polyimide/TiO2 composite membrane for vanadium redox flow battery

A sulfonated polyimide (SPI)/TiO₂ composite membrane was fabricated by a blend way to improve its performance in vanadium redox flow battery (VRB). Both EDS and XRD results verify the successful preparation of the SPI/TiO₂ composite membrane. The surface SEM image shows its homogeneous structure. TG analysis identifies its thermal stability. The SPI/TiO₂ composite membrane possesses much lower permeability of VO²⁺ ions (2.02?×?10^?7 cm² min^?1) and favorable proton conductivity (3.12?×?10^?2 S cm^?1). The VRB single cell with SPI/TiO₂ composite membrane shows higher coulombic efficiency (93.80–98.00 %) and energy efficiency (83.20–67.61 %) at the current density ranged from 20 to 80 mA cm^?2 compared with that with Nafion 117 membrane. And the operational stability of the as-prepared composite membrane is good after 50 times of cycling tests. Therefore, the low-cost SPI/TiO₂ composite membrane with excellent battery performance exhibits a great potential for application in VRB.