Electrocatalysts For Formic Acid Oxidation Research Articles

Composition dependent activity of PdAgNi alloy catalysts for formic acid electrooxidation

In the present study, the carbon supported Pd, PdAg and PdAgNi (Pd/C, PdAg/C and PdAgNi/C) electrocatalysts are prepared via NaBH4 reduction method at varying molar atomic ratio for formic acid electrooxidation. These as-prepared electrocatalysts are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), inductively coupled plasma mass spectrometry (ICP-MS), N2 adsorption-desorption, and X-ray electron spectroscopy (XPS), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), chronoamperometry (CA), and lineer sweep voltammetry (LSV). While Pd50Ag50/C exhibits the highest catalytic activity among the bimetallic electrocatalyst, it is observed that Pd70Ag20Ni10/C electrocatalysts have the best performance among the all electrocatalysts. Its maximum current density is about 1.92 times higher than that of Pd/C (0.675 mA cm−2). Also, electrochemical impedance spectroscopy (EIS), chronoamperometry (CA) and lineer sweep voltammetry (LSV) results are in a good agreement with CV results in terms of stability and electrocatalytic activity of Pd50Ag50/C and Pd70Ag20Ni10/C. The Pd70Ag20Ni10/C catalyst is believed to be a promising anode catalyst for the direct formic acid fuel cell.

Facile synthesis based on novel carbon-supported cyanogel of structurally ordered Pd3Fe/C as electrocatalyst for formic acid oxidation

A novel carbon-supported cyanogel (C@cyanogel)-derived strategy is used to synthesize an intermetallic Pd3Fe/C compound of the desired ordered Pd3Fe phase with a small particle size. The novelty of this work lies in using carbon-supported K2PdIICl4/K4FeII(CN)6 cyanogel as a reaction precursor, generated through the substitution of two chloride ligands by the nitrogen ends of the cyanide ligands on the metal center. The inherent nature of cyanogels can effectively suppress the movement of Pd0 and Fe0 nuclei in the crystal, benefiting the formation of the intermetallic, which is otherwise challenging via traditional synthesis techniques. The ordered Pd3Fe/C catalyst exhibits excellent catalytic activity and good cycle stability for the formic acid oxidation (FAO) reaction relative to the properties of disordered Pd3Fe/C and commercial Pd/C catalysts, demonstrating that the ordered Pd3Fe/C is a promising replacement for commercial Pd-based catalysts. The outstanding performance can be ascribed to the full isolation of active sites in the ordered Pd3Fe structure and the modified electronic structure of the active components. This work provides an effective and novel route to obtain Pd-based intermetallic compounds with potential applications in a wide range of electrocatalysis.

Poly-l-lysine mediated synthesis of palladium nanochain networks and nanodendrites as highly efficient electrocatalysts for formic acid oxidation and hydrogen evolution

The morphology- and size-tunable synthesis of nanocatalysts has attracted substantial research interest especially in catalysis. In this work, we synthesized free-standing Pd nanochain networks (Pd NCNs) and Pd nanodendrites (Pd NDs) through a direct poly-l-lysine (PLL)-mediated one-pot aqueous method. The presence of PLL and its concentrations were critical in this regard, showing PLL as the structure-directing and capping agents during the nucleation and crystal growth procedures. The synthesized architectures exhibited improved catalytic activity and enhanced durability towards formic acid oxidation and hydrogen evolution reactions relative to commercial Pd black catalyst. Moreover, the electrochemical active surface area and the electrocatalytic performance of Pd NCNs were dramatically enhanced in comparison to Pd NDs mainly owing to the unique network-like structure of Pd NCNs.

Hyperbranched PdRu nanospine assemblies: an efficient electrocatalyst for formic acid oxidation

A very simple one-step synthetic method is developed for the fabrication of PdRu nanospine assemblies for electrocatalytic formic acid oxidation.

A general strategy to the synthesis of carbon-supported PdM (M = Co, Fe and Ni) nanodendrites as high-performance electrocatalysts for formic acid oxidation

Rational synthesis of a new class of electrocatalysts with high-performance and low-cost is of great significance for future fuel cell devices. Herein, we demonstrate a general one-step simultaneous reduction method to prepare carbon-supported PdM (M = Co, Fe, Ni) alloyed nanodendrites with the assistance of oleylamine and octadecylene. The morphology, structure and composition of the obtained PdM nanodendrites/C catalysts have been fully characterized. The combination of the dendritic structural feature and alloyed synergy offer higher atomic utilization efficiency, excellent catalytic activity and enhanced stability for the formic acid oxidation reaction (FAOR). Strikingly, the as-synthesized PdCo nanodendrites/C catalyst could afford a mass current density of 2467.7 A g−1, which is almost 3.53 and 10.4 times higher than those of lab-made Pd/C sample (698.3 A g−1) and commercial Pd/C catalyst (237.6 A g−1), respectively. Furthermore, the PdCo nanodendrites/C catalyst also exhibit superior stability relative to the Pd/C catalysts, make it a promising anodic electrocatalyst in practical fuel cells in the future. Additionally, the present feasible synthetic approach is anticipated to provide a versatile strategy toward the preparation of other metal alloy nanodendrites/carbon nanohybrids.

Effect of OMC and MWNTC support on mass activity of Pd[sbnd]Co catalyst for formic acid electro-oxidation

The electrochemical evaluation of PdCo catalyst supported on Ordered Mesoporous Carbon (PdCo/OMC) synthesized by the polyol method is reported in this work. OMC is synthesized via self-assembly in aqueous solution, as an alternative route to conventional preparation methods. The electrocatalytic performance of PdCo/OMC is evaluated for Formic Acid Oxidation Reaction (FAOR). The results are compared with those of PdCo on Multi-Walled Carbon Nanotubes (PdCo/MWCNT) and Pd/OMC, prepared by the same procedure, with the aim to evaluate the effect of support and the Co contribution during the FAOR. The catalysts are characterized by scanning and transmission electron microscopy (SEM and TEM), X-ray diffraction (XRD) and small-angle X-ray scattering (SAXS). Cyclic voltammetry (CV) and chronoamperometric studies are carried out in acid media with different formic acid concentrations (0.1, 0.5 and 1 mol L−1). According to TEM results, PdCo/OMC exhibits smaller particle size (∼3.5 nm) and enhanced distribution of nanoparticles compared with PdCo/MWCNT. At 0.5 mol L−1 HCOOH, PdCo/OMC delivers a higher anodic mass current density (185 mA mg−1Pd) of the FAOR than PdCo/MWCNT (94.3 mA mg−1 Pd). Moreover, at 1 mol L−1 HCOOH the jf/jb ratio for PdCo/OMC is 1.09 mA mg−1Pd, higher than the ratios determined for PdCo/MWCNT (0.76) and Pd/OMC (0.85). The improvement of the mass catalytic activity of PdCo/OMC is attributed to the combination of the mesoporous structure of the support, which promotes the catalyst-support interaction facilitating the mass transfer process during the reaction, and to the incorporation of Co in the Pd structure.

Mass-transport-limited oxidation of formic acid on a PdMLPt(100) electrode in perchloric acid

In this communication, we study the electrocatalytic formic acid oxidation process on an epitaxially grown Pd monolayer on a Pt(100) single crystal in perchloric acid. The formic acid oxidation activity on this PdMLPt(100) electrode in perchloric acid is significantly enhanced compared to the same electrode in sulfuric acid and compared to unmodified Pt(100), with a low onset potential of around 0.14 VRHE. The absence of hysteresis between the positive and negative scan during formic acid oxidation indicates the remarkable resistance to CO poisoning of the Pd monolayer surface. Most importantly, we report, for the first time, a mass-transport-limited formic acid oxidation rate on the PdMLPt(100) rotating electrode in perchlorate acid, setting a catalytic benchmark for future electrocatalysts for formic acid oxidation.

Ultrathin AgPt alloy nanowires as a high-performance electrocatalyst for formic acid oxidation

To address the insufficient electrocatalytic activity and stability of formic acid oxidation reaction (FAOR) electrocatalysts, as well as their high cost, we herein demonstrate the facile hydrothermal synthesis of ultrathin AgPt alloy nanowires using amine-terminated poly(N-isopropylacrylamide) (PNIPAM-NH2) as a structure-directing agent. The initial generation of AgCl precipitates, subsequent formation of AgPt nanoparticles, and their oriented attachment account for the formation of ultrathin AgPt alloy nanowires. Benefiting from their unique 1D anisotropy and alloyed composition, the prepared ultrathin AgPt nanowires exhibit a superior electrocatalytic activity and better CO tolerance for the FAOR, reaching a 1.6-fold and 3.7-fold higher specific current density than AgPt nanoparticles and a commercial Pt black catalyst, respectively. Additionally, the ultrathin AgPt alloy nanowires manifest a superior electrochemical stability and structural robustness during electrocatalysis, making them a promising FAOR electrocatalyst. This work not only provides a reliable strategy for the synthesis of noble metal-based ultrathin nanowires, but also opens an avenue towards the rational design of efficient electrocatalysts for fuel cell systems.

Synthesis of Ultrathin PdCu Alloy Nanosheets Used as a Highly Efficient Electrocatalyst for Formic Acid Oxidation.

Inspired by the unique properties of ultrathin 2D nanomaterials and excellent catalytic activities of noble metal nanostructures for renewable fuel cells, a facile method is reported for the high-yield synthesis of ultrathin 2D PdCu alloy nanosheets under mild conditions. Impressively, the obtained PdCu alloy nanosheet after being treated with ethylenediamine can be used as a highly efficient electrocatalyst for formic acid oxidation. The study implicates that the rational design and controlled synthesis of an ultrathin 2D noble metal alloy may open up new opportunities for enhancing catalytic activities of noble metal nanostructures.

Remarkable catalytic activity of electrochemically dealloyed platinum–tellurium nanoparticles towards formic acid electro-oxidation

Aiming to improve the activity of Pt-based catalysts for formic acid electro-oxidation, dealloyed PtxTey/C catalysts were prepared via electrochemical leaching process. The dealloyed-Pt3Te/C catalyst presented superior activity and stability for formic acid electro-oxidation. The mass activities of dealloyed-Pt3Te/C at 0.25 V and 0.4 V vs. SCE were about 10.6 and 16.5 times as high as that of commercial Pt/C, respectively. It is found that the FAEO on D-Pt3Te/C is mainly through dehydrogenation pathway. The weak CO adsorption, increased electrochemical specific area and ensemble effect are suggested as reasons for the remarkable enhancement.

Surfactant‐Free Synthesis of Graphene‐Supported PdCu Nanocrystals with High Alloying Degree as Highly Active Catalyst for Formic Acid Electrooxidation

In recent years, graphene/metal nanocrystal hybrids have attracted tremendous attention in catalysis and electrocatalysis. This work demonstrates a surfactant‐free coprecipitation/coreduction method to synthesize graphene‐supported nanocrystalline PdCu (PdCu/GN) hybrids with high alloying degree. The strong interaction between graphene oxide and metal hydrates results in uniform precipitation on the graphene oxide surface, which plays a critical role in excellent dispersion and high alloying degree of PdCu nanocrystals. Cyclic voltammetry and chronoamperometry measurements show that nanocrystalline PdCu/GN hybrids have higher activity and durability than commercial Pd/C catalyst for the formic acid oxidation reaction.

Highly active Aucore@Ptcluster catalyst for formic acid electrooxidation

This work attempts to enhance platinum utilization in a Pt-based electrocatalyst by the tuned covering of gold nanoparticles with small Pt entities. Reductive deposition of platinum (donated as Pt) on gold (donated as Au) nanoparticles with different atomic Pt:Au ratios was used to prepare a series of samples named Aucore@Ptcluster particles. UV–vis spectrum, TEM and XRD were used to characterize the core-cluster samples. The electrochemical tests (cyclic voltammerty (CV)) showed that the core-cluster structure could significantly improve the catalytic activity of Au-Pt towards electrooxidation of formic acid, in comparison to commercial Pt/C electrocatalyst. The improvement of activity is ascribed to the interaction between Au core and Pt cluster.

Catalytic Stability Study of a Pd‐Ni2P/C Catalyst for Formic Acid Electrooxidation

AbstractIn this work, the catalytic stability of Pd‐Ni2P/C, a highly efficient anode catalyst for direct formic acid fuel cells, was studied by using electrochemical and physical techniques. The dynamic stability was probed in an accelerated stability test (AST) by using cyclic voltammetry for 1000 cycles, and a very low performance decay rate was observed on the Pd‐Ni2P/C catalyst compared with a homemade Pd/C catalyst. About 60 % of the initial peak current density, three times higher than that of the homemade Pd/C catalyst, was retained after the AST on the Pd‐Ni2P/C catalyst. There were no obvious structure and morphology changes in the Pd‐Ni2P/C catalyst revealed by X‐ray diffraction, X‐ray photoelectron spectroscopy, or transmission electron microscopy characterization. However, largely increased Pd particle sizes that appear on the Pd/C catalyst might lead to serious performance decay. The strong interaction of Pd and Ni2P in the catalyst system might increase the anchoring of Pd nanoparticles on the support surface, thus less Pd was lost during electrocatalysis. Steady‐state stability tests further confirmed the high stability of the Pd‐Ni2P/C catalyst, and the high anti‐poisoning ability to CO‐like intermediates would maintain the high stability. The results are important for an in‐depth understanding of the contribution of Ni2P in the catalyst system.

Polymer-assisted formation of 3D Pd nanoassemblies: highly active catalysts for formic acid electrooxidation

Three-dimensional (3D) Pd nanoassemblies were synthesized by a facile hydrothermal procedure, in which polyallylamine hydrochloride (PAH) was simultaneously used as a cross-linking and scaffold molecule in order to construct the 3D interconnected nanoassemblies.

Branched PdAu nanowires with superior electrocatalytic formic acid oxidation activities

Branched PdAu nanowires supported on graphene were prepared as catalysts for formic acid electro-oxidation, and they exhibited higher catalytic activity and durability than Pd/graphene and commercial Pd/C catalysts.

La2O3 Promoted Pd/rGO Electro-catalysts for Formic Acid Oxidation.

High activity, a low rate of CO poisoning, and long-term stability of Pd electro-catalysts are necessary for practical use as an anode material in direct formic acid fuel cells. Achieving a high degree of Pd nanoparticle dispersion on a carbon support, without agglomeration, while maintaining a facile electron transfer through the catalyst surface are two challenging tasks to be overcome in fulfilling this aim. Herein, we report the effect of addition of La/La-oxides on the efficiency of Pd nanoparticles supported on reduced graphene oxide (rGO) for formic acid electro-oxidation reaction. A series of electro-catalysts with different Pd-La molar ratios were successfully synthesized and characterized using a range of techniques including PXRD, XPS, TEM, FTIR, and Raman spectroscopy and then tested as anode materials for direct formic acid fuel cells. We explore that the lanthanum species (La/La-oxide) significantly promote the activity and stability of Pd catalyst toward electrocatalytic oxidation of formic acid. The metallic ratio is found to be critical, and the activity order of various catalysts is observed as follows; Pd30La70/rGO > Pd80La20/rGO > Pd70La30 rGO. The obtained mass specific activity for Pd30La70/rGO (986.42 A/g) is 2.18 times higher than that for Pd/rGO (451 A/g) and 16 times higher than that for Pd/C (61.5 A/g) at given onset peak potentials. The high activity and stability of the electro-catalysts are attributed to the uniform dispersion of Pd nanoparticles over the rGO support, as evidenced from TEM images. It is believed that the role of La species in promoting the catalyst activity is to disperse the catalyst particles during synthesis and to facilitate the electron transfer via providing a suitable pathway during electrochemical testing.

One‐Pot Synthesis of Freestanding Porous Palladium Nanosheets as Highly Efficient Electrocatalysts for Formic Acid Oxidation

Freestanding ultrathin 2D noble metal nanosheets have drawn enormous attention due to their potential applications in various fields. However, the synthesis of 2D noble metal nanosheets still remains a great challenge due to the lack of an intrinsic driving force for anisotropic growth of 2D structures. Here, a facile one‐pot synthesis of ultrathin freestanding porous Pd nanosheets (≈2.5 µm in lateral size and 10 nm in thickness) flexibly knitted by interweaved ultrathin nanowires with the assistance of poly(diallyldimethylammonium chloride) is presented. Nanoparticles attachment and subsequent self‐assembly in the synthetic process are responsible for the formation of such intriguing nanostructures. Moreover, finely controlling the pH value of the precursor solution leads to yield different Pd nanostructures with tunable dimensionalities, including 3D nanoflowers, 2D nanosheets, and 1D nanochains. Owing to the unique structural features, the obtained freestanding porous Pd nanosheets exhibit excellent electrocatalytic activity and stability towards formic acid oxidation compared to those of other dimensional counterparts and commercial Pd black.

Pt/C Spontaneously Decorated with Citrate As a Catalyst for Formic Acid Electro-Oxidation

Efficient direct electro-oxidation of liquid fuels, such as methanol and formic acid for low-temperature portable fuel cell applications, remains a challenge limiting commercialization. The major performance detractors are: (1) the formation of strongly adsorbed reaction intermediates, (2) fuel crossover through the membrane depolarizing the cathode, and (3) mass transport for fast fuel delivery into the anode catalyst layer and gaseous product removal. Direct formic acid fuel cells (DFAFCs) have the advantage over direct methanol fuel cells in that it is possible for formic acid to be electro-oxidized via a direct non-strongly adsorbed reaction intermediate pathway.[1] In addition to being less susceptible to fuel crossover due to electrostatic repulsion of the polarized formic acid dipole by the negatively charged sulfonic groups in the proton exchange membrane (PEM).[2] However, the catalyst selection is pivotal for enhanced performance. Previous research from our group has shown highly active carbon-supported platinum (Pt/C) catalyst layers spontaneously decorated with bismuth exhibiting low overpotential for formic acid electro-oxidation, shown in Fig 1. This enhancement of catalytic ability has been attributed to promotion of the direct oxidation pathway by the ‘third-body’ as well as an electronic effect to promote CH-down adsorption of formic acid on the unoccupied Pt/C surface.[3] However, adsorbed Bi is unstable under oxidizable potentials, as demonstrated in our previous studies, Figure 2.[4] Pore-former was incorporated into the catalyst layer to increase formic acid mass transport. During open potential acid wash removal of the pore-former the Bi was lost from the Pt surface and performance was also lost. Research by Antaño-López et al. has shown that the spontaneous adsorption of citrate, a common nanoparticle capping agent, suppresses the formation of platinum oxide.[5] This implies that citrate is a stable surface adsorbate in the oxide region. It is predicted that citrate will exhibit a similar ‘third-body’ effect as Bi with an optimal surface coverage fraction yet to be determined due to the chelation effect of citrate that Bi does not exhibit.

Hydrogen co-reduction synthesis of PdPtNi alloy nanoparticles on carbon nanotubes as enhanced catalyst for formic acid electrooxidation

A novel electrocatalyst of PdPtNi ternary alloy nanoparticles supported on multi-walled carbon nanotubes (MWCNTs) for formic acid oxidation (FAO) reaction is synthesized by a simple hydrogen co-reduction process. The as-synthesized catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray (EDX) spectroscopy and X-ray photoelectron spectroscopy (XPS). It is found that highly dispersed PdPtNi alloy nanoparticles of ca. 2.56 nm are homogeneously deposited on the MWCNT surface, and the alloying with Pt and Ni alters the electronic structure of Pd atoms with the downshift of Pd d-band center. Studies of cyclic voltammetry and chronoamperometry indicate that the electrocatalytic activity and durability of the PdPtNi/MWCNT for FAO are significantly enhanced as compared with the PdPt/MWCNT and commercial Pd/C catalysts. This study implies that the prepared PdPtNi/MWCNT composite is a promising anode electrocatalyst of direct formic acid fuel cells.

Palladium nanoparticles supported on hollow mesoporous Tungsten carbide microsphere as electrocatalyst for formic acid oxidation

Hollow tungsten carbide and cobalt spheres (HTCCS) with cobalt concentration of 6% were prepared by spray conversion and reduction carbonization methods. The HTCCS with diameters of about 8–18 μm were covered with 0.3–1.0 μm microporous. The Pd/WC catalyst was prepared through the replacement reaction between Co nanoparticles on the surface of HTCCS and PdCl4. The electro-catalytic performances for formic acid electro-oxidation were investigated by cyclic voltammetry and chronoamperometry. It exhibited the low onset potential, excellent catalytic activity and stability compared with Pd/C due to the larger electrochemical surface area (ECSA) and the synergistic effect between Pd and WC.