Pd–Ni–Cu–P metallic glass nanowires for methanol and ethanol oxidation in alkaline media

We demonstrate that Pd₄₃Ni₁₀Cu₂₇P₂₀ bulk metallic glass (BMG) nanowires, prepared by a facile, scalable top-down nanomolding approach, can be used as high surface area electrocatalysts for alkaline alcohol fuel cell applications. These nanowires exhibit higher activity for methanol and ethanol oxidation in alkaline media compared to pure Pd, quantified by cyclic voltammetry. Furthermore, the Pd-BMG nanowire electrocatalyst has a 300 mV lower onset potential for CO oxidation suggesting improved poisoning resistance beyond pure Pd. The Pd-BMG electrocatalyst activation energies for methanol and ethanol oxidation of 22 and 17 kJ mol⁻¹ are lower than the pure Pd values of 38 and 30 kJ mol⁻¹, respectively. Unique properties of BMGs (homogeneity, viscosity, surface tension) facilitate the formability into high surface area electrocatalysts at low processing temperatures. The high electrical conductivity and chemical/physical stability suggest that these materials are ideal candidates for widespread commercial use including energy conversion/storage, hydrogen production, and sensors.     

Electrocatalytic activity of nanostructured Ni and Pd–Ni on Vulcan XC-72R carbon black for methanol oxidation in alkaline medium

Ni and Pd–Ni nanoparticles were chemically deposited on Vulcan XC-72R carbon black by impregnation method using NaBH₄ as a reducing agent. The prepared electrocatalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX). The electrocatalytic activity of Ni/C and Pd–Ni/C electrocatalysts towards methanol oxidation in 0.5 M KOH solution was examined using cyclic voltammetry and chronoamperometry. Two methanol oxidation peaks were observed on the Pd–Ni/C at 0 and +860 mV. Their current density values are higher than those at Pd/C and Ni/C electrocatalysts by 1.92 and 1.68 times, respectively. The catalytic rate constant of methanol oxidation reaction at Ni/C and Pd–Ni/C electrocatalysts in (0.2 M MeOH + 0.5 M KOH) solution was estimated using double-step chronoamperometry as 5.64 × 10³ and 6.25 × 10³ cm³ mol⁻¹ s⁻¹, respectively. Pd–Ni/C is more stable than Pd/C and Ni/C electrocatalysts. Therefore, Pd–Ni/C is a suitable as a less expensive electrocatalyst for methanol oxidation in alkaline medium.     

Electrocatalytic activity of Pd–Au nanoalloys during methanol oxidation reaction

Methanol fuel cells are very promising power source due to its high efficiency and low emissions of pollutants but their commercialization is hindered by development of the effective catalysts. Bimetallic nanostructured catalysts have been used to increase the effectiveness of methanol electrooxidation. Their high electrocatalytic activity can be accounted largely by the difference in electronegativity of two metals (e.g. Pd and Au), that resulting in gradual Au^δ+→Au^δ– transition with the increase in Pd content. Therefore, gold-enriched bimetallic Pd-Au_nano were recommended as catalysts for oxidation processes since they are characterized by the presence of Au^δ+ on their surface. Deposition of Pd, Au and Pd–Au nanoparticles (~50–350 nm) were carried out in dimethyl sulfoxide by pulsed mode of electrolysis directly on electrode surface. Cyclic voltammetry was the main method to study catalytic properties of the modified electrode in the anode oxidation process of methanol. It was found that oxidation rate on the electrode surface modified by bimetallic Pd–Au nanoparticles is ~1.5 times higher as compared to that in the case of electrodes modified by Pd or Au monometallic nanoparticles individually. In order to find highly active, selective, and stable catalysts for methanol electrocatalytic oxidation reaction additional studies are needed to understand the role of electrode surface charge and local OH⁻ ions concentration from alkali solution.     

Cell performance of Pd–Sn catalyst in passive direct methanol alkaline fuel cell using anion exchange membrane

Direct methanol alkaline fuel cell (DMAFC) using anion exchange membrane (AEM) was operated in passive condition. Cell with AEM exhibits a higher open circuit voltage (OCV) and superior cell performance than those in cell using Nafion. From the concentration dependences of methanol, KOH in fuel and ionomer in anode catalyst layer, it is found that the key factors are to improve the ionic conductivity at the anode and to form a favorable ion conductive path in catalyst layer in order to enhance the cell performance. In addition, by using home-made Pd–Sn/C catalyst as a cathode catalyst on DMAFC, the membrane electrode assembly (MEA) using Pd–Sn/C catalyst as cathode exhibits the higher performance than the usual commercially available Pt/C catalyst in high methanol concentration. Therefore, the Pd–Sn/C catalyst with high tolerance for methanol is expected as the promising oxygen reduction reaction (ORR) catalyst in DMAFC.     

Facile aqueous phase synthesis of 3D-netlike Pd–Rh nanocatalysts for methanol oxidation

The structure-activity relationship between the morphology and composition of Pd-based nanocatalysts is an important fundamental issue in direct methanol fuel cells (DMFC). Three dimensional (3D) netlike Pd–Rh bimetallic catalysts with different atomic ratios (Pd₁Rh₃, PdRh, Pd₃Rh₁) are synthesized through a simple wet chemical way using P123 as a reducing agent and KBr as morphological regulator. The morphology, structure and composition of the catalysts are proved by a series of physicochemical test technology. It is shown that the 3D-netlike structure is composed of short self-assembly nanochains. Electrochemical results display that their application towards methanol oxidation reaction (MOR) in alkaline solution. The MOR activity of the optimized Pd₃Rh₁ nanocatalyst is improved to about 4.0 mA cm⁻², which is much higher than that of the commercial Pd/C catalyst.     

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.     

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.     

Fe–N–Si tri-doped carbon nanofibers for efficient oxygen reduction reaction in alkaline and acidic media

The most ideal substitute for Pt/C to catalyze the oxygen reduction reaction (ORR) is the transition metal and nitrogen co-doped carbon-based material (TM-N-C). However, large particles with low catalytic activity are formed easily for the transition metals during high-temperature carbonization. Herein, PAN nanofibers uniformly distributed with FeCl₃ were coated with SiO₂ and then carbonized to obtain Fe–N–Si tri-doped carbon nanofibers catalyst (Fe–N–Si-CNFs). The SiO₂ can further anchor the Fe atoms, thus preventing agglomeration during the carbonization process. Meanwhile, Si atoms have been doped in CNFs during this process, which is conducive to the further improvement of catalytic performance. The Fe–N–Si-CNFs catalyst has a 3D network structure and a large specific surface area (809.3 m² g⁻¹), which contributes to catalyzing the ORR. In alkaline media, Fe–N–Si-CNFs exhibits superior catalytic performance (E_1/2 = 0.86 V vs. RHE) and higher stability (9.6% activity attenuation after 20000s) than Pt/C catalyst (20 wt%).     

The formation of wrapping type Pt–Ni alloy on three-dimensional carbon nanosheet for electrocatalytic oxidation of methanol

In this paper, the PtNi alloy was embedded into the surface layer of three-dimensional carbon nanosheets (CNSs) with a special layered structure. We controllably adjusted the ratio of Pt/Ni to form large particle alloy with Pt coating Ni and a small number of hollow PtNi alloy pellets. The electro-catalytic methanol oxidation activity and durability of the catalysts were estimated by cyclic voltammetry and chronoamperometric techniques. The results indicated that the doping of Ni effectively improved the activity and anti-poisoning of the catalyst in the methanol electrocatalytic oxidation reaction (MOR). Transmission electron microscopy (TEM), Raman spectroscopy, nitrogen adsorption-desorption techniques, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to explore the composition, morphology and structure of these catalysts. It is discovered that the Pt–Ni/CNSs (2:1) sample exhibits the best MOR activity with a peak current density of 15.03 mA cm^?2 at the forward scan due to the excellent lamellar structure, good crystallinity and abundant pore structure of CNSs, which is benefit to form ultrahigh specific surface area, superb electron and ionic conductivity.     

Preparation of three-dimensional Fe–N co-doped open-porous carbon networks as an efficient ORR electrocatalyst in both alkaline and acidic media

It is of significant importance to construct the low-cost, efficient, and stable carbon-based non-noble metal to replace the noble metal electrocatalyst for oxygen reduction reaction in both alkaline and acidic media. In this work, a straightforward and cost-efficient strategy is reported to synthesize the Fe–N co-doped open-porous carbon materials with three-dimensional (3D) carbon networks structure, high surface areas and multiple actives sites including iron carbide nanoparticles, pyridinic N, and graphitic N using a new kind of Fe-Imace coordinated complex as the precursor and melamine as nitrogen sources by direct pyrolysis. The obtained Fe–N–C 900 catalyst shows excellent oxygen reduction performance in both alkaline (E_onset, 1.014 vs. RHE) and acidic (E_onset, 0.982 V vs. RHE) media, which are better than those of the Pt/C in alkaline (E_onset, 0.986 vs. RHE) and acidic media (E_onset, 0.979 V vs. RHE). Even more important, the stability and methanol tolerance of the Fe–N–C 900 catalyst are much better than that of the Pt/C catalyst in both alkaline and acidic media. All the results demonstrate that the present facile and universal one-step pyrolytic strategy can be used to synthesize catalyst materials as one of the superior non-precious cathode electrocatalysts for fuel cells.     

An improved Stӧber method towards iron and nitrogen co-doped porous carbon spheres for oxygen reduction reaction in alkaline media

The significant progress of non-precious metal cathodic electrocatalytic materials is impressive in electrochemical energy conversion application. Here, iron and nitrogen co-doped porous carbon spheres (Fe/N-PCS) have been designed via 3-aminophenol/formaldehyde (APF) resin spheres as carbon precursor, ferric nitrate as iron source, colloidal silica as template and tetramethylguanidine as catalyst by the improved Stöber method. Fe/N-PCS possesses uniform spherical morphology, abundant mesoporous shape and high surface area and exhibits higher oxygen reduction reaction (ORR) electrocatalytic activity (E_1/2, 0.838 V vs. RHE) compared with the Pt/C (E_1/2, 0.827 V vs. RHE) in alkaline media. In addition, the methanol tolerance and catalytic stability of Fe/N-PCS are greater than commercial Pt/C catalyst. The outstanding ORR behavior of Fe/N-PCS mainly benefits from the iron and nitrogen elements synergistic effect, pyridinic N and the spherical porous structure enabling plenty of active sites exposed. This method is prospective for preparation of highly efficient cathodic ORR electrocatalyst.     

Optimization of the Pd–Sn–GNS nanocomposite for enhanced electrooxidation of methanol

Highly dispersed Pd nanoparticles with varying loadings (15–40 wt%) and (20 − x)%Pd–x%Sn (where x = 1, 2, 3 and 5) nanocomposites are obtained on graphene nanosheets (GNS) by a microwave-assisted ethylene glycol (EG) reduction method for methanol electrooxidation in alkaline solution. The electrocatalysts were characterized by XRD, SEM, TEM, cyclic voltammetry, and chronoamperometry. The study shows that the Pd nanoparticles on GNS are crystalline and follow the face centered cubic structure. Introduction of a small amount of Sn (1–5 wt%) shifts the characteristic diffraction peaks for Pd slightly to a lower angle. The electrocatalytic performance of the Pd/GNS electrodes has been observed to be the best with 20 wt% Pd loading; a higher or lower loading than 20 wt% Pd produces an electrode with relatively low catalytic activity. The apparent catalytic activity of this active electrode at E = −0.10 V is found to improve further by 79% and CO poisoning tolerance by 40% with introduction of 2 wt% Sn. Among the electrodes investigated, the 18%Pd–2%Sn/GNS exhibited the greatest electrocatalytic activity toward methanol electrooxidation.     

Efficient electrocatalyst of Pt–Fe/CNFs for oxygen reduction reaction in alkaline media

Transition metal iron-based catalysts are promising electrocatalysts for oxygen reduction reaction (ORR), and they have the potential to replace noble metal catalysts. The one-dimensional of carbon nanofibers with tubular structure can effectively promote the electrocatalytic activity, which facilitates electron transport. Herein, the Pt–Fe/CNFs were synthesized by electrospinning and subsequent calcination. Benefiting from the advantages of one-dimensional structure, Pt–Fe/CNFs-900 with fast electrochemical kinetics and excellent stability for ORR with excellent onset of 0.99 V, a low Tafel slope of 62 mV dec⁻¹ and high limiting current density of 6.00 mA cm⁻². Long-term ORR testing indicated that the durability of this catalyst was superior to that of commercial Pt/C in alkaline electrolyte. According to RRDE test, the ORR reaction process of Pt–Fe/CNFs-900 was close to four-electron transfer routes.     

The capacitive characteristics of supercapacitors consisting of activated carbon fabric–polyaniline composites in NaNO3

A sandwich-type supercapacitor consisting of two similar activated carbon fabric–polyaniline (ACF–PANI) composite electrodes was demonstrated to exhibit excellent performance (i.e., highly reversibility and good stability) in NaNO₃. Polyaniline with the charge density of polymerization less than or equal to 9 C cm⁻² synthesized by means of a potentiostatic method showed a high specific capacitance of 300 F g⁻¹. Influences of the polymerization charge density (i.e., the polymer loading) on the capacitive characteristics of ACF–PANI composites were compared systematically. The capacity of an ACF–PANI electrode reach ca. 3.4 F cm⁻² (a 100% increase in total capacity) when the charge density of polymerization is equal to 9 C cm⁻². The surface morphology of these ACF–PANI composites was examined by a scanning electron microscope (SEM).     

Use of Pd–MnMoO4–graphene hybrids as efficient and CO poisoning tolerant electrocatalysts for methanol oxidation

40 wt%Pd-x wt%MnMoO₄/Graphene (GNS) (0 ≤ x ≤ 20) hybrids have been synthesized for use as efficient and CO poisoning tolerant anode materials in methanol fuel cells. Investigations revealed that the addition of MnMoO₄ increases the electrocatalytic activity of the base electrode (40 wt%Pd/GNS) towards the methanol oxidation reaction (MOR) in 1 M KOH significantly. The catalytic activity of the electrode is found to be the greatest with 8 wt%MnMoO₄. The addition of MnMoO₄ also improves CO poisoning tolerance of the base electrode by 11–73%. The MOR activity and CO poisoning tolerance of the 40 wt%Pd-8 wt%MnMoO₄/GNS hybrid electrode were superior to other electrodes of the investigation.     

A comparative study on the performance of mesoporous SBA-15 supported Pd–Zn catalysts in partial oxidation and steam reforming of methanol for hydrogen production

Using mesoporous SBA-15 (Santa Barbara Amorphous No. 15, a mesoporous material) as support, Pd–Zn nanocatalysts with varying Pd and Zn content were tested for hydrogen production from methanol by partial oxidation and steam reforming reactions. The physico-chemical characteristics of the synthesized SBA-15 support were confirmed by XRD, N₂ adsorption, SEM and TEM analyses. The PdZn alloy formation during the reduction of Pd–Zn/SBA-15 was revealed by XRD and DRIFT study of adsorbed CO. Also, the correlation between Pd and Zn loadings and PdZn alloy formation was studied by XRD and TPR analyses. The metallic Pd surface area and total uptakes of CO and H₂ were measured by chemisorption at 35 °C. The metallic Pd surface area values are in linear proportion with the Pd loading. The formation of PdZn alloy during high temperature reduction was confirmed by a shift in absorption frequency of CO on Pd sites to lower frequency due to higher electron density at metal particles resulted from back-donation. The reduced Pd–Zn/SBA-15 catalysts were tested for partial oxidation of methanol at different temperatures and found that catalyst with 4.5 wt% Pd and 6.75 wt% Zn on SBA-15 showed better H₂ selectivity with suppressed CO formation due to the enhanced Pd dispersion as well as larger Pd metallic surface area. The O₂/CH₃OH ratio is found to play a significant role in CH₃OH conversion and H₂ selectivity. The performance of 4.5 wt% Pd–6.75 wt% Zn/SBA-15 catalyst in steam reforming of methanol was also tested. Comparatively, the H₂ selectivity is significantly higher than that in partial oxidation, even though the CH₃OH conversion is less. Finally, the long term stability of the catalyst was tested and the nature of PdZn alloy after the reactions was found to be stable as revealed from the XRD pattern of the spent catalysts.     

In-situ investigation on hydrogenation-dehydrogenation of Pd–Ag alloy films

The present work reports on synthesis of Pd–Ag nano-composite films by magnetron co-sputtering and the structural changes in the alloy film during hydrogenation and dehydrogenation. Synchrotron X-ray diffraction is employed in-situ to reveal subtle structural changes occurring during hydrogenation and dehydrogenation processes, an aspect not investigated so far. It is revealed that the nanocomposite film having 88 at% Pd shows the formation of α-phase as an intermediate phase, however, completion of the hydrogenation process yields only β-phase. No β-phase formation is observed in nanocomposite thin film containing 54 at% of Pd, suggesting the suppression of formation of β-phase with increase in Ag concentration. On dehydrogenation, the peak returns to its original position i.e. the value before hydrogenation. The data also demonstrated that the addition of Ag in Pd results in complete removal of dissolved hydrogen thereby eliminates the problem of hysteresis. The study shows that the lower concentrations of Ag in Pd are better in terms of extent of peak-shift on hydrogenation/dehydrogenation and faster response/recovery kinetics.     

Autothermal reforming of ethanol in a Pd–Ag/Ni composite membrane reactor

The main objective of this project is to study the hydrogen production reaction from oxidative steam reforming of bio-ethanol in the pertinent characteristics of a palladium–silver alloy membrane reactor. The enhancements of hydrogen permeation and of H₂/N₂ permselectivity were studied in a Ni–Pd–Ag ternary alloy membrane, which was fabricated by successive electroless plating of palladium and silver on stainless steel (PSS) supports modified with nickel electroplating. XRD, SEM, and EDS were used to characterize the surface morphology of the membranes. Ethanol–water mixture (n_water/n_ethanol = 1 or 3) and oxygen (n_oxygen/n_ethanol = 0.2 or 0.7) were fed concurrently into the membrane reactor packed with Zn–Cu commercial catalyst (MDC-3). The reaction temperatures were set at temperatures of 593–723 K and pressures of 3–10 atm. The amount of oxygen added in the feed has a significant effect on the steam reforming reaction of ethanol. At high pressures, autothermal reaction of ethanol with no need for external heating to the composite membrane reactor to produce high purity hydrogen was easily processed.     

Si–CN for the oxygen reduction reaction in alkaline media,the effect of synthesis temperature

The electrocatalytic properties of silicon-doped carbon nanotubes (Si–CN) for oxygen reduction reaction (ORR) in alkaline media are reported. The Si-CNs were obtained by a modified chemical vapor deposition method. The Si–CN showed good activity towards ORR since most of the process was carried out efficiently by the four-electron transfer pathway, and it exhibited a low Tafel slope of 84.28 mV dec^?1 indicating that the material has a good kinetic activation response for ORR. This favorable response was attributed to 0.29 at. % silicon intercalated in the carbon lattice enhancing electrons transport at neighboring silicon sites. In addition, its mechanical robustness and thermodynamic stability influenced by the synthesis temperature contributed favorably to the energetic activation of Si–CN to the adsorption and reduction of oxygen. Therefore, Si–CN could be considered a potential metal-free and low-cost material for the ORR in alkaline fuel cells.