Reduced graphene oxide-supported Pd@Au bimetallic nano electrocatalyst for enhanced oxygen reduction reaction in alkaline media

Rational design and synthesis of core-shell bimetallic nanoparticles with tailored structural and functional properties is highly sought to realize clean and energy-efficient fuel cell systems. Herein, PdAu bimetallic nanoparticles (NPs) with core-shell morphology (Pd_Core–Au_Shell) were fabricated on the surface of reduced graphene oxide (RGO) support by a facile two-step protocol. In the first step, Pd_Core–Ag_Shell bimetallic NPs were synthesized on RGO support by reducing Pd²⁺and Ag⁺ ions with methyl ammonia borane (MeAB). Later, Pd_Core–Au_Shell bimetallic NPs were conveniently fabricated on RGO support via a galvanic replacement strategy involving sacrificial oxidation of metallic silver and reduction of gold ions. The resulting core/shell bimetallic NPs were characterized by X-ray diffraction (XRD), High-resolution transmission electron microscopy (HR-TEM), Energy dispersive X-ray spectroscopy (EDS), Fourier-Transform Infrared Spectroscopy (FT-IR) and cyclic voltrammetry (CV). The electrocatalytic performance of core/shell nanostructures for the room temperature oxygen reduction reaction (ORR) in alkaline media were systematically performed by CV. The electrode-area-normalized ORR activity of RGO-supported Pd_Core–Au_Shell NPs was higher than the corresponding commercially available carbon-supported Pt nanoparticles (Pt/C) at ?0.8 V vs Ag/AgCl (satd. KCl) (6.24 vs 5.34 mA cm^?2, respectively). Further, methanol-tolerant ORR activities of as-synthesized catalysts were also studied. The Au-on-Pd/RGO bimetallic NPs presented enhanced ORR activity both in presence and in the absence of methanol in comparison with a commercial Pt/C catalyst and as-synthesized Pd/RGO and Au/RGO catalysts. The enhanced catalytic activities of core/shell structures might be resulted owing to the optimized core/shell structure comprising of a small Pd core and a thin Au shell and synergistic effects offered by Pd and Au. The present synthesis protocol demonstrated for two-layer structure can be extended to multi-layered structures with desired functions and activities.     

High-yield, size-controlled synthesis of silver nanoplates and their applications as methanol-tolerant electrocatalysts in oxygen reduction reaction

A novel method for the synthesis of as-prepared Ag nanoplates in high yield and the control of their dimensions has been developed. In this method, hexadecyltrimethyl ammonium ions (CTA⁺) are used as a trace additive in a seed solution for blocking the seed surface to govern the growth direction on nanoplate in the growth pathway, leading to a high-yield production of the Ag nanoplates with mixed morphologies, mainly triangular nanoplates and nanodisks. The spectra of the obtained nanoplate solution showed a high-intensity peak attributed to the in-plane dipole resonance and a low-intensity peak at 400 nm. By decreasing the amount of CTA⁺, the mean edge length of triangular nanoplates could be changed from ∼78.7 nm-∼124.8 nm. The in-plane dipole resonance peak corresponding to change in the mean edge length shifted from 630 nm to 785 nm, respectively. The mean edge length of triangular nanoplates could also be controlled from 70 nm to 148 nm by decreasing the CTA⁺-adsorbed seed amount. To investigate the practical feasibility of application of the proposed method, the prepared nanoplates were used as a methanol-tolerant electrocatalyst in an oxygen reduction reaction (ORR). An analysis conducted using a rotating ring-disk electrode showed that these nanoplates have high activity towards the ORR and that the electron transfer numbers (n) were 3.85, 3.83, 3.81, and 2.94 for 70 nm, 124 nm, 148 nm nanoplates, and macroscopic Ag electrode, respectively. If the present of methanol, the corresponding n values of 3.82, 3.81, 3.78, and 2.30 were detected. Despite working in the methanol-tolerant solution, the prepared Ag nanoplates still exhibited high electroactivity and their ORR proceeded via an approaching 4-electron pathway.     

Simple preparation of Pd–Pt nanoalloy catalysts for methanol-tolerant oxygen reduction

Carbon-supported Pd–Pt bimetallic nanoparticles of different atomic ratios (Pd–Pt/C) have been prepared by a simple procedure involving the complexing of Pd and Pt species with sodium citrate followed by ethylene glycol reduction. As-prepared Pd–Pt alloy nanoparticles evidence a single-phase fcc disordered structure, and the degree of alloying is found to increase with Pd content. Both X-ray diffraction and transmission electron microscopy characterizations indicate that all the Pd–Pt/C catalysts possess a similar mean particle size of ca. 2.8 nm. The highest mass and specific activity of the oxygen reduction reaction (ORR) using the Pd–Pt/C catalysts are found with a Pd:Pt atomic ratio of 1:2. Moreover, all Pd–Pt alloy catalysts exhibit significantly enhanced methanol tolerance during the ORR than the Pt/C catalyst, ensuring a higher ORR performance while diminishing Pt utilization.     

Pd9Au1@Pt/C core-shell catalyst prepared via Pd9Au1-catalyzed coating for enhanced oxygen reduction

The scarcity and poor long-term stability of Pt has greatly hindered its commercial application as oxygen reduction reaction (ORR) catalyst. In this work, carbon-supported Pd₉Au₁ alloy particles with a Pd/Au molar ratio of 9:1 synthesized by using an ethylene glycol-based reduction method were used to catalyze ethanol oxidation to coat Pd₉Au₁ core with Pt atomic layers to synthesize Pd₉Au₁@Pt/C catalyst. Physical characterization shows that the as-synthesized Pd₉Au₁@Pt/C catalysts present a well-defined core-shell structure and the surface Pt layers can be well controlled by tuning the amount of Pt precursor added during synthesis. Electrochemical characterization shows that among the synthesized catalysts Pd₉Au₁@Pt₂/C with 2 atomic Pt layers exhibits the best activity and excellent stability for ORR, as evidenced by its even increased half-wave potential after 10000 potential cycles between 0.6 and 1 V in O₂-saturated 0.1 M HClO₄ solution. This enhanced ORR activity and stability of Pd₉Au₁@Pt₂/C catalyst can be attributed to the compressive strain and stabilizing effect of Pd₉Au₁ core on Pt shell.     

Carbon-supported Pd-Co bimetallic nanoparticles as electrocatalysts for the oxygen reduction reaction

Carbon-supported Pd-Co bimetallic nanoparticle electrocatalysts of different Pd/Co atomic ratios were prepared by a modified polyol reduction. Electrocatalytic activities of the catalysts for the oxygen reduction reaction (ORR) have been investigated based on the porous rotating disk and disk-ring electrode techniques. As-prepared Pd-Co bimetallic nanoparticles evidence a single-phase fcc disordered structure, and the mean particle size is found to decrease with increase in Co content. A typical TEM image of the Pd₂Co/C catalyst, heat-treated at 500 °C, reveals a mean particle diameter is ca. 8.3 nm with a relatively narrow size distribution. For synthesized Pd-Co catalysts, the highest catalytic activity for the ORR, when supported on carbon (i.e., Pd-Co/C) was found for a Pd:Co atomic ratio of 2:1 and heat treatment at ca. 500 °C, corresponding to a Pd–Pd mean interatomic distance of ca. 0.273 nm. Kinetic analysis based on the rotating disk and disk-ring electrode measurements reveals that the ORR on Pd-Co/C catalysts undergoes a four-electron process in forming water. Because the Pd-Co/C catalyst is inactive for the adsorption and oxidation of methanol, it may function as a methanol-tolerant ORR catalyst in a direct methanol fuel cell.     

Electrocatalysis of oxygen reduction when varying the mass ratio of metal nanoparticles to carbon support for catalysts with a 10 to 10 to 80 mol% of Pt and Pd on Ag

The reduction of total Pt-loading in a cathode catalyst without sacrificing performance is one of the key objectives for the large-scale commercialization of proton exchange membrane fuel cell (PEMFC) technology. A core-shell type nanostructured catalyst with a Pt-loading 20 times lower than a commercial catalyst is demonstrated herein to be more active for the electrocatalysis of the oxygen reduction reaction (ORR) in acid electrolyte. The weight ratio of metal nanoparticles on carbon support is the key to achieving the highest ORR activity in a series of silver-based catalysts, all with 10 mol percent of Pt and 10 mol percent of Pd over 80 mol percent of silver (Ag) and supported on untreated Vulcan carbon to form an electrocatalyst (Ag@Pt₁₀Pd₁₀/C) with either 5, 10, 20 or 30 wt% of total metals on carbon; which correspond to a Pt concentration around 1, 2, 3 and 5 wt%, respectively. All metal nanostructures on carbon show a similar morphology, size and structure. Thin films of these four Ag@Pt₁₀Pd₁₀/C catalysts on rotating disk electrodes (TF-RDEs) all shown a 4-electrons pathway for the ORR and give higher exchange current densities (j_o > 3.8 mA/cm²) than a commercial Etek Pt₂₀/C catalyst (j_o = 2.4 mA/cm²). The Ag@Pt₁₀Pd₁₀/C catalyst with 5 wt% of total metals (1 wt% of Pt) on carbon gives the best electrocatalysis; reducing molecular oxygen to water two times faster and generating 25% higher current per milligram of platinum (mass activity) than the commercial catalyst (Pt₂₀/C). Therefore, the Ag@Pt₁₀Pd₁₀/C catalyst with 5 wt% of total metals is a new catalyst for ORR for a PEMFC with a lower Pt loading and cost.     

Pre-deposited Co nanofilms promoting high alloying degree of PdxAu nanoparticles as electrocatalysts in alkaline media

High alloyed and well dispersed Pd_xAu nanoparticles are deposited on pre-deposited Co nanofilm substrates (Pd_xAu/Co-nanofilms/C) by using an immiscible ionic liquid (IL)/water interface. However, low alloyed Pd_xAu/C catalysts are formed without pre-deposited Co nanofilms through the same synthesis method. The high-alloyed Pd_xAu/Co-nanofilms/C catalysts demonstrate significantly increased activity for ethanol oxidation reaction (EOR) than low-alloyed Pd_xAu/C of the same Pd/Au composition, with the catalysts of low Pd/Au atom ratio (Pd:Au = 1:1) demonstrating the optimal activity. Notably, high alloyed degree of the Pd_xAu nanoparticles in the Pd_xAu/Co-nanofilms/C catalysts brings the lattice expansion of Pd, causing an up-shift of the d-band center, which results in the enhancement of OH⁻ adsorption and correspondingly promotes electro-oxidation of ethanol excluding the effect of Co nanofilm substrates. Differently, the enhancement activities of the Pd-Au bimetallic system for oxygen reduction reaction (ORR) are almost not affected by the alloying degree and only dependent on Pd/Au atom ratios, with the catalysts of low Pd/Au atom ratio (Pd:Au = 1:1) displaying the highest ORR mass activity, respectively. These results exhibit the specific dependence between the different electrochemical process and the physical parameters for the Pd-Au bimetallic system.     

Promotion of palladium catalysis by silver for ethanol electro-oxidation in alkaline electrolyte

Bimetallic Pd_mAg alloy nanostructures (m being the atomic Pd/Ag ratio, m = 0.1–1.5), prepared through a simple co-reduction process, are employed as the catalysts toward ethanol electro-oxidation reaction (EOR). XPS results show that the electronic structure of Pd can be modified due to the presence of Ag, which is crucial for the enhancement of the catalytic performance of the Pd_mAg/C catalysts. It is found that the catalytic activity of Pd was strongly dependent on the composition of the Pd_mAg/C catalysts, with the best performance found with the Pd_0.5Ag/C. The mass-specific activity (MSA) and intrinsic activity (IA) data of Pd_0.5Ag/C is 3.6 and 2.4 times higher than that of the monometallic Pd/C catalyst, respectively, which might be ascribed to the electronic and synergistic effect. These findings would be promising in understanding the mechanism of EOR on Pd-based catalysts and designing the bimetallic catalysts for direct ethanol fuel cells and other applications.     

Carbon nanotubes-supported colloidal Ag-Pd nanoparticles as electrocatalysts toward oxygen reduction reaction in alkaline electrolyte

Ag-Pd nanoparticles with compositional ratios of 1:1 (Ag₁Pd₁), 2:1 (Ag₂Pd₁), and 4:1 (Ag₄Pd₁) and supported on multiwall carbon nanotubes (CNTs) were prepared by the self-regulated reduction of sodium dodecyl sulfate, and then, they were used as catalysts for oxygen reduction reactions (ORRs) in 1 M NaOH solution. Polarization curves showed that, among the prepared nanocatalysts, Ag₄Pd₁/CNT nanocatalysts showed higher activity. During the ORRs, two types of oxygen coverages given by the Temkin isotherm and Langmuir isotherm were observed for low and high overpotentials, respectively. Koutecky-Levich plots showed that the number of electrons involved in the ORRs catalyzed by Ag₁Pd₁/CNT, Ag₂Pd₁/CNT, and Ag₄Pd₁/CNT were 2.11, 1.88, and 2.25, respectively. These ORRs proceeded through a two-electron pathway. Polarization curve in the electrolyte with methanol revealed that Ag₄Pd₁/CNT has high methanol tolerance during ORRs.     

Power source research at USC: Development of advanced electrocatalysts for polymer electrolyte membrane fuel cells

This paper provides an overview on the development of advanced fuel cell cathode catalysts at University of South Carolina (USC) with the emphasis on the stability of non-precious metal and Pt alloy catalysts. Nitrogen-modified carbon composite (NMCC) catalysts were developed for the oxygen reduction reaction (ORR) through the pyrolysis of cobalt (iron)-nitrogen chelate followed by the treatment combination of pyrolysis, acid leaching, and re-pyrolysis. A promising stability was observed for 1050 h fuel cell operation under current density of 200 mA cm⁻² as evidenced by a potential decay rate as low as 40 μV h⁻¹. The performance degradation mechanism of the NMCC-based fuel cell is discussed. Pt and PtPd hybrid catalysts are developed that use a NMCC, which is itself active for the ORR, instead of a conventional carbon black support. The stability test at 1 A cm⁻² indicated that the Pt/NMCC hybrid catalyst (new Pt-Co/C) is more stable than the conventional Pt-Co/C without the Co leaching out. The PEM fuel cell accelerated stress test (AST) for supports and catalysts demonstrated that their stability changes in the order: Pt₃Pd₁/NMCC hybrid catalyst > Pt/NMCC hybrid catalyst > conventional Pt/C catalyst. Moreover, the hybrid catalysts exhibit higher mass activity than the Pt/C catalysts.     

Catalytic activities of Ag/C decorated with small amounts of Au and Pt for glycerol oxidation

The two-step decoration of the Ag nanoparticles supported on carbon black (Ag/C) with Au and Pt, the electrooxidation of glycerol on the Pt/Au/Ag/C catalysts in alkaline solution, and the effect of the amounts of Au and Pt on the catalytic activity of Pt/Au/Ag/C are investigated. The decoration of Ag/C is performed by electrochemically depositing a small amount of Au and then Pt on Ag/C, and the Pt_x/Au_y/Ag₁₀₀/C catalysts with different x:y:100 ratios (0.15 ≤ x ≤ 1.9 and 0.2 ≤ y ≤ 1.5) are obtained. Physical and electrochemical characterizations reveal that small parts of the Ag surfaces are covered by the deposited Au and Pt. Pt_x/Au_y/Ag₁₀₀/C mainly shows Pt-relevant behaviors in glycerol oxidation, and Pt_1.3/Au_y/Ag₁₀₀/C exhibits high catalytic activities. The results reveal that the surface decoration is a useful method of fabricating efficient ternary catalysts at low cost.     

Study of isotope effect on dehydrogenation kinetics of Pd based alloys using differential scanning calorimetry

Owing to the large hydrogen isotope effect, palladium and palladium based alloy are of great technological importance for their application in separation of hydrogen isotopes. The present study deals with the investigation of isotope effect on hydrogen desorption kinetics of Pd, Pd_0.77Ag_0.23 and Pd_0.77Ag_0.10Cu_0.13 alloys, using non-isothermal method by employing Differential Scanning Calorimetry (DSC). Pd_0.77Ag_0.23 and Pd_0.77Ag_0.10Cu_0.13 alloys were prepared by arc melting method and characterised by XRD, TXRF and EDS. Both the alloys are found to have FCC phase similar to Pd lattice. Prior to kinetic measurements, samples were activated by hydriding-dehydriding method. Hydrogen/deuterium desorption kinetic measurements were carried out at four different heating rates (8, 12, 16 and 20 K/min) and Kissinger plots were constructed from peak temperature of DSC curves. Activation energies for hydrogen/deuterium desorption from the corresponding hydride/deuteride were calculated from the slope of Kissinger plot which follows the order; Pd > Pd_0.77Ag_0.23 > Pd_0.77Ag_0.10Cu_0.13. Activation energy for deuterium desorption was found to be lower than that of hydrogen desorption and significant isotope effect was observed for the Pd_0.77Ag_0.10Cu_0.13 alloy which makes it a favorable candidate material for its application in hydrogen isotope separation, employing self-displacement gas chromatography.     

Methanol-tolerant cathode electrode structure composed of heterogeneous composites to overcome methanol crossover effects for direct methanol fuel cell

A methanol-tolerant cathode electrode composed of heterogeneous composites was developed to overcome CO poisoning and large O₂ mass transfer overpotential generated by methanol crossover as well as the limitation of a single alloy catalyst with methanol-tolerance in direct methanol fuel cells (DMFCs). Two additives, PtRu black and PTFE particles, were well distributed in the Pt/C matrix of the cathode electrode, and had significant effects upon open circuit voltage (OCV) and performance. A small amount of PtRu black protected the Pt surface during the oxygen reduction reaction (ORR) by decreasing CO poisoning. In addition, hydrophobic PTFE particles reduced the O₂ mass transfer overpotential induced by water and permeated methanol in the cathode. Despite only 0.5 mg cm⁻² of metal catalysts in the cathode, the membrane electrode assembly (MEA) with 3 M methanol showed high performance (0.117 W cm⁻²), which was larger than that of the traditional MEA (0.067 W cm⁻²).     

Methanol and ethanol oxidation on carbon supported nanostructured Cu core Pt–Pd shell electrocatalysts synthesized via redox displacement

Six different carbon-supported Cu core Pt–Pd shell (Cu@Pt–Pd) catalysts have been successfully synthesized by the galvanic replacement of Cu atoms by Pt⁴⁺ and Pd²⁺ ions at room temperature and their electrocatalytic activity for methanol and ethanol oxidation have been evaluated in acid media. Cu@Pt–Pd core shell nanoparticles with a narrow size distribution and an average diameter in the range of 3.1–3.5 nm were generated onto the carbon support. The compositional and the structural analysis of the as-prepared materials pointed out that the nanoparticles are formed by a Cu rich core covered by a Pt–Pd rich shell due to the interdiffusion of the metals after the galvanic replacement reaction. The electrocatalytic properties of the Cu@Pt–Pd electrodes in the electro-oxidation of methanol and ethanol was found to be dependent on the electrochemical surface area, lattice strain of the surface, composition and thickness of the Pt–Pd shell surrounding the Cu core. The optimum catalyst composition to obtain the best performance for methanol and ethanol electro-oxidation was determined to be Pt_0.59Pd_0.324Cu_0.167/C (6.2 wt.% Pt, 2.2 wt.% Pd and 0.7 wt.% Cu). This catalyst has a greatly enhanced mass activity, lower onset potential and poisoning rate, and higher turnover number in the MOR and EOR reactions compared to a commercial Pt_0.51Ru_0.49/C (20 wt.% Pt and 10 wt.% Ru). Consequently, this simple preparation method is a viable approach to making a highly active catalyst with low platinum content for application in direct alcohol fuel cells (DAFCs).     

Pd5Cu4Pt oxygen reduction nanocatalyst for PEM fuel cells

Carbon dispersed Pd₅Cu₄Pt nanocatalyst synthesized by chemical reduction with NaBH₄ for the oxygen reduction reaction (ORR) in acid media is investigated. Nanocatalyst is physically characterized by transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (DRX). Results demonstrate the formation of conglomerate nanometric particles ranging from 2 to 10 nm in size. Electrochemical activity is demonstrated by cyclic voltammetry (CV) and rotating disk electrode (RDE) techniques. The results show that the onset potential for the ORR on Pd₅Cu₄Pt is shifted by ca. 50 mV to more positive values and enhanced catalytic current densities are observed in comparison to carbon dispersed PdCu and Pd catalysts. The Pd₅Cu₄Pt tested as cathode electrode in a membrane-electrode assembly (MEA) shows a power density of 330 mW cm⁻² at 0.5 V and 80 °C, resulting an attractive low Pt content cathode nanocatalyst for PEM fuel cells.     

Facile fabrication and electrocatalytic activity of Pt0.9Pd0.1 alloy film catalysts

A nano-thickness porous Pt_0.9Pd_0.1 alloy film with a greatly enhanced surface area were firstly synthesized at a glassy carbon electrode (GCE) using a facile cyclic voltammetry (CV) method. The atomic ratio of the alloy can be controlled by controlling the composition of the electrodeposition solution. We found that small amount of alloying Pd is an excellent catalytically enhancing agent for the Pt catalyst, and 10% Pd is the optimal. The structures of the Pt_0.9Pd_0.1 alloy film were characterized by FE-SEM, XPS, XRD and electrochemical techniques. It was found that the Pt_0.9Pd_0.1 film was in nanoporous structure and consisted of crystallites of 10.1 nm on average, leading to the modified electrode (Pt_0.9Pd_0.1/GCE) has an effective surface area as large as 790 times that of a corresponding bare Pt disk electrode. The Pt_0.9Pd_0.1/GCE exhibited significantly higher stability and catalytic activity for both of the methanol electro-oxidation reaction (MOR) and the oxygen electro-reduction reaction (ORR) than the correspondingly electrodeposited Pt modified GCE. The advantage can be attributed to the CV-prepared nano-porous structure on the electrode surface. This method and the prepared electrode can be expected to have promising applications in biosensors and fuel cells, etc.     

Fabrication and evaluation of passive alkaline membraneless microfluidic DMFC

The fabrication and evaluation of a passive, air-breathing, membraneless microfluidic direct methanol fuel cell (ML-μDMFC) using a methanol-tolerant Ag/Pt/CP cathode is presented here. We previously proposed that due to its high tolerance to methanol and the good activity towards the oxygen reduction reaction in alkaline medium, this catalyst could be useful to reduce the methanol crossover effect in direct methanol fuel cells. Therefore, in order to demonstrate it, we designed and fabricated a microfluidic device that allowed the evaluation of the cathode in a high fuel concentration environment, using up to 5 M MeOH in 0.5 M KOH in passive mode. The results confirmed the high tolerance to MeOH and the ORR selectivity of the Ag/Pt/CP cathode, in contrast with a Pt/CP cathode, where performance decreased severely due to the methanol crossover. Employing the methanol-tolerant cathode, it was possible to obtain a power density of 2.4 mW cm⁻². Additionally, the durability studies revealed more stability for the ML-μDMFC using the bimetallic catalyst, compared with Pt/CP.     

Synergistic catalytic activity of palladium–silver alloy nanoparticle for anodic oxidation of ethanol in alkali

Palladium and palladium-silver alloy nano catalysts were synthesized from aqueous precursor at room temperature via a single vessel chemical reduction and co-reduction methods in absence of capping agent. XPS analysis confirms the presence of Pd and Ag in the catalyst matrix. Microscopic analyses reveal spherical morphology of the catalyst in the nanoscale dimension. The electro-analytical investigation of the catalyst loaded on carbon electrode shows that the Pd₄Ag nano alloy catalyst demonstrates marked improvement in electro-catalytic efficiency among all prepared catalysts for ethanol oxidation in alkali. The Pd₄Ag/C catalyst shows the mass normalized peak current density of 522 mA mg^?1_Pd in cyclic voltammetric (CV) study, which is 1.97 times greater than that of similarly synthesized Pd/C (264.2 mA mg^?1_Pd) catalyst. Chronoamperometric and impedance analyses further establish the superiority of Pd₄Ag/C catalyst. To discover the plausible mechanism, the CV study is typically extended to the intermediates like sodium acetate which reveals that though Pd is better for catalytic oxidation of intermediate than the best catalyst but the optimal OH^? adsorption on the surface of the metal, favours catalytic oxidation of ethanol more on Pd₄Ag catalyst. The mechanistic path of the reaction is anticipated by evaluating the ex-situ FTIR and chromatographic studies which explain the promotion of the formation of carboxylate in comparison to carbonate by Ag.     

Nanoporous PdCu alloys as highly active and methanol-tolerant oxygen reduction electrocatalysts

Nanoporous (NP) PdCu alloys with three different bimetallic ratios are fabricated by selectively dealloying PdCuAl ternary alloys in sulfuric acid solution. Electron microscopy and X-ray diffraction characterizations demonstrate that selective etching of Al from ternary PdCuAl source alloys in acid medium generates three-dimensional bicontinuous ligament-pore nanostructures with a single-phase face-centered-cubic crystalline structure. NP-PdCu alloys show superior electrocatalytic activity and structure stability toward oxygen reduction reaction (ORR) compared with the commercial Pt/C catalyst. The specific and mass activities for ORR follow the order of NP-Pd₅₀Cu₅₀ > NP-Pd₇₅Cu₂₅ > NP-Pd₃₀Cu₇₀ > Pt/C. It is found that among three PdCu samples NP-Pd₅₀Cu₅₀ exhibits the highest methanol tolerance and catalytic durability for ORR. These experimental observations indicate that incorporation of 50 at.% Cu into Pd accompanied with the network nanoarchitecture is beneficial to maximize the ORR performances of Pd.     

Synthesis of ultrafine low loading Pd–Cu alloy catalysts supported on graphene with excellent electrocatalytic performance for formic acid oxidation

Here, surfactant free composite catalysts (Pd–Cu/rGO) with Pd–Cu alloy nanoparticles uniformly distributed on graphene sheets are successfully prepared via a facile hydrothermal approach. Compared with pure Pd/rGO catalyst, the introduction of copper could dramatically enhance the performance of the catalyst in the electrocatalytic formic acid oxidation (FAO) due to the strain effect and the ligand effect. With the optimized atomic ratio of 3:1 between palladium and copper, the alloy nanoparticle shows the smallest size of 2.12 nm, thus endowing the composite catalyst with highest catalytic efficiency. With Pd load as low as 14.5%, a maximum mass current density of 1580 mA mg_Pd⁻¹, and residual current of 69.93 mA mg_Pd⁻¹ at 3000 s was achieved with our Pd₃Cu₁/rGO catalyst in the electrocatalytic FAO process.