Performance For Formic Acid Oxidation Research Articles

Hollow cubic ternary PdCuB nanocage electrocatalysts with greatly enhanced catalytic performance for formic acid oxidation.

The prepared PdCuB Ngs/C catalysts exhibited outstanding catalytic activity and stability in the formic acid oxidation reaction (FAOR). The improvement in electrocatalytic performance is due to the introduction of Cu and B atoms and the hollow nanocage structure, which changes the electronic structures of Pd, increases the reactive sites, and accelerates the reaction mass transfer rates.

Synthesis of new Pd@NDG electrocatalyst by using g-C3N4/GO hydrogel toward formic acid electrooxidation reaction in direct formic acid fuel cell

In this research, the new Pd@NDG electrocatalyst was evaluated for the formic acid oxidation reaction. The nitrogen-doped graphene nanosheets (NDG) support was obtained by heating the g-C3N4/GO hydrogel in an inert atmosphere. The Pd@NDG electrocatalyst was prepared by combined use of NDG and palladium chloride via a one-stage reduction using ascorbic acid. The as-prepared Pd@NDG electrocatalyst displayed high catalytic activity in formic acid oxidation. The significant electrocatalytic performance stems from the presence of the NDG support in the structure of the electrocatalyst. The NDG support improved the physicochemical properties of the catalyst. The NDG support acts as an excellent ligand and leads to increase dispersion of Pd. The number of active metal sites is enhanced by increasing dispersion and exposing the surface area of the electrocatalyst and improving electronic properties, which lead to improving the catalytic performance of the catalyst. Furthermore, the formic acid electrocatalytic activity and the durability of Pd@NDG electrocatalyst as compared to the Pd/C commercial benchmark catalyst. The results displayed that the Pd@NDG electrocatalyst has better performance for formic acid oxidation.

Electrochemical synthesis of dendritic Pd-CoO/PW10V2/rGO and its electrocatalytic performance for formic acid oxidation

The preparation of Pd-CoO/TMSP/rGO modified electrodes is reported.

Pd12Ag1 nanoalloy on dendritic CNFs catalyst for boosting formic acid oxidation

In this study, dendritic carbon nanofibers (CNFs) loaded with Pd12Ag1 nanoalloy were prepared as a catalyst using a one-pot method. The average particle size of the Pd12Ag1 nanoalloy is 4.2 nm, which is uniformly dispersed over the surface of the CNFs. The Pd12Ag1/CNFs catalyst has the best performance for formic acid oxidation (FAO), with catalytic activity (2825.0 mA mgPd−1) and durability after 7200 s (70.6 mA mgPd−1) up to 5.25 and 10.87 times, respectively, compared with commercial Pd/C. The improved electrocatalytic performance of the Pd12Ag1/CNFs catalyst is attributed to the appropriate Ag doping, which changes the electronic state around the Pd atom, forming two new active sites (Pd-Pd and Pd-Ag); on the other hand, the special structure and rough surface of CNFs expose more active sites to enhance the dehydrogenation process of FAO. Furthermore, Pd13, Ag13, and Pd12Ag1 clusters loaded on the surface of defect-free graphene (DG) and single vacancy defective graphene (SVG) were simulated using density functional theory (DFT) to confirm the effect of different carbon materials and doped metals on the overall catalyst at the atomic level.

Double-Base Plate Cooperative Assembly Strategy for the Construction of Ordered Macro-/Mesoporous Noble-Metal Materials for Enhanced Electrochemical Oxidation of Formic Acid

Herein, we propose a general and mild double-base plate cooperative assembly strategy to synthesize the three-dimensional ordered macro-/mesoporous (3DOM/m) noble-metal materials (including Pd, Pt, and Ru), in which the unique double-base plate can play the role of restricting growth area and effectively stabilizing the porous structure of the noble-metal material. In this synthesis process, poly(styrene-b-acrylic acid) (PS-b-PAA) micelles and polymer colloidal crystals are used as templates for the construction of mesopores and macropores, respectively. By adjusting the particle size of polymer colloidal nanospheres, the size of three-dimensional ordered macropores can be precisely adjusted from 160 to 320 nm. Benefiting from the synergistic effect of hierarchical pore structures, the as-prepared 3DOM/m Pd film exhibits outstanding electrocatalytic performance for formic acid oxidation. These results provide an effective and universal method for the designed synthesis of the three-dimensional hierarchical architecture of high-catalytic-activity noble-metal materials.

Microporous Sulfur-Doped Carbon Atoms as Supports for Sintering-Resistant Platinum Nanocluster Catalysts

Carbon (C)-supported metal nanoclusters consisting of a few dozen atoms are highly attractive for a wide range of important catalytic processes with optimal reactivity and selectivity, yet they suffer from metal sintering and consequent deactivation because of the weak interaction between metals and inert C surface. Here, we report a microporous sulfur-doped carbon (S–C) as a support for sintering-resistant metal nanoclusters based on the strong interaction between metal and doped sulfur (S) atoms. The S–C support is prepared by carbonization of microporous conjugated poly(3,3′-bithiophene), which has a robust three-dimensional cross-linked network structure. The structural features of the conjugated polymer-derived S–C support, including high S contents of up to ∼26.9 wt % and large specific surface areas of 708–1019 m2 g–1, make it capable of anchoring ∼1 nm platinum (Pt) clusters even with a high Pt loading of 20 wt %. Remarkably, the S–C-supported Pt nanocluster catalysts can tolerate high-temperature treatments up to 700 °C in a reductive atmosphere or harsh hydrothermal treatments (alkaline water, 2 M bar of H2, and 200 °C for 12 h). Moreover, the S–C-supported Pt nanocluster catalysts exhibit a much enhanced catalytic performance for formic acid oxidation compared to the commercial Pt/C catalyst owing to the small-size effects.

Palladium Particles Modified by Mixed-Frequency Square-Wave Potential Treatment to Enhance Electrocatalytic Performance for Formic Acid Oxidation

Palladium catalysts have attracted widespread attention as advanced electrocatalysts for the formic acid oxidation (FAO) due to their excellent electrocatalytic activity and relatively high abundance. At present, electrodeposition methods have been widely developed to prepare small-sized and highly-dispersed Pd electrocatalysts. However, the customary use of surfactants would introduce heterogeneous impurities, which requires complicated removal processes. In this work, we reported a two-step electrochemical method that employed square-wave potential treatment (SWPT) to modify electrodeposited Pd particles without the use of capping agents. Under the SWPT with a mixed frequency, Pd particles show significantly reduced size and more dispersed distribution, exhibiting a high mass activity of 1.43 A mg−1 toward FAO, which is 4.6 times higher than the counterpart of commercial Pd/C. The increase in electrocatalytic activity of FAO is attributed to the highly developed surface of palladium particles uniformly distributed over the support surface.

Pt Deposits on Bi-Modified Pt Electrodes of Nanoparticle and Disk: A Contrasting Behavior of Formic Acid Oxidation

This work presents a contrasting behavior of formic acid oxidation (FAO) on the Pt and Bi deposits on different Pt substrates. Using irreversible adsorption method, Bi and Pt were sequentially deposited on Pt electrodes of nanoparticle (Pt NP) and disk (Pt disk). The deposited layers of Bi and Pt on the Pt substrates were characterized with X-ray photoelectron spectroscopy, transmission microscopy and scanning tunneling microscopy. The electrochemical behaviors and FAO enhancements of Pt NP and Pt disk with deposited Bi only (i.e., Bi/Pt NP and Bi/Pt disk), were similar to each other. However, additional deposition of Pt on Bi/Pt NP and Bi/Pt disk (i.e., Pt/Bi/Pt NP and Pt/Bi/Pt disk) changed the electrochemical behavior and FAO activity in different ways depending on the shapes of the Pt substrates. With Pt/Bi/Pt NP, the hydrogen adsorption was suppressed and the surface oxidation of Pt was enhanced; while with Pt/Bi/Pt disk, the opposite behavior was observed. This difference was interpreted as a stronger interaction between the deposited Bi and Pt on Pt NP than that on Pt disk. The FAO performance on Pt/Bi/Pt NP is much better than that on Pt/Bi/Pt disk, most likely due to the difference in the interaction between the deposited Pt and Bi depending on the shapes of Pt substrates. In designing FAO electrochemical catalysts using Pt and Bi, the shape of a Pt substrate was concluded to be critically considered.

PdAg Nanoparticles with Different Sizes: Facile One-Step Synthesis and High Electrocatalytic Activity for Formic Acid Oxidation.

Recently, direct formic acid fuel cells (DFAFCs) which possess superior advantages such as a low operating temperature, light environmental pollution and high energy density, have been considered as one of the power generation technologies with a bright prospect. Herein, bimetallic PdAg nanoparticles (NPs) with different particle sizes were successfully produced via an easy one-pot solvothermal co-reduction synthetic route and their electrocatalytic performance for formic acid oxidation (FAO) were further investigated. In our strategy, the size of PdAg NPs can be easily controlled by only varying the concentration of precursors. The larger sized PdAg alloy (9.5 nm, noted as PdAg-L) was obtained at a low concentration of precursors, while the smaller PdAg alloy (3.7 nm, named as PdAg-S) was separated from the reaction system with higher solubility by centrifugation. The electrocatalytic activity and stability of the obtained PdAg NPs could be well optimized when incorporated with carbon (C), which is owing to a synergetic effect. The PdAg-S/C exhibits the highest mass activity with around 1.6 times that of PdAg-L/C and 2 times that of commercial Pd/C, which can be attributed to its larger ECSA and lower adsorption energy of the intermediate to facilitate the direct oxidation of HCOOH molecule.

Enhanced Formic Acid Oxidation over SnO2-decorated Pd Nanocubes

The formic acid oxidation reaction (FAOR) is one of the key reactions that can be used at the anode of low-temperature liquid fuel cells. To allow the knowledge-driven development of improved catalysts, it is necessary to deeply understand the fundamental aspects of the FAOR, which can be ideally achieved by investigating highly active model catalysts. Here, we studied SnO2-decorated Pd nanocubes (NCs) exhibiting excellent electrocatalytic performance for formic acid oxidation in acidic medium with a SnO2 promotion that boosts the catalytic activity by a factor of 5.8, compared to pure Pd NCs, exhibiting values of 2.46 A mg–1Pd for SnO2@Pd NCs versus 0.42 A mg–1Pd for the Pd NCs and a 100 mV lower peak potential. By using ex situ, quasi in situ, and operando spectroscopic and microscopic methods (namely, transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray absorption fine-structure spectroscopy), we identified that the initially well-defined SnO2-decorated Pd nanocubes maintain their structure and composition throughout FAOR. In situ Fourier-transformed infrared spectroscopy revealed a weaker CO adsorption site in the case of the SnO2-decorated Pd NCs, compared to the monometallic Pd NCs, enabling a bifunctional reaction mechanism. Therein, SnO2 provides oxygen species to the Pd surface at low overpotentials, promoting the oxidation of the poisoning CO intermediate and, thus, improving the catalytic performance of Pd. Our SnOx-decorated Pd nanocubes allowed deeper insight into the mechanism of FAOR and hold promise for possible applications in direct formic acid fuel cells.

Interfacial Pd-O-Ce Linkage Enhancement Boosting Formic Acid Electrooxidation.

Metal-support interaction enhancement is critical in the fuel cell catalyst design and fabrication. Herein, taking the Pd@CeO2 system as an example, we revealed the substrate morphology coupling effect and the thermal annealing-induced Pd-O-Ce linkage enhancement in the improved catalytic capability for formic acid electrooxidation. Three well-defined CeO2 nanocrystals were employed to support Pd nanoparticles, and the best catalytic performance for formic acid oxidation and anti-CO poisoning ability was found on CeO2 plates because of the high oxygen vacancy, Ce3+, and more Pd-O-Ce linkages resulting from the more edge/corner defects. This interaction of Pd-O-Ce linkages could be largely enhanced by thermal annealing in the N2 atmosphere, as confirmed by a series of crystal structures, surface chemical state, and Raman analysis because the oxygen vacancies and lattice oxygen resulting from the oxygen atoms leaching from the CeO2 lattice would trap the mobile Pd nanocrystals by forming strengthened Pd-O-Ce linkages. Due to the high oxygen vacancy and strong Pd-O-Ce linkages, largely increased catalytic activity and stability, catalytic kinetics, and rapid charge transfer were found for all the thermal annealed Pd@CeO2 catalysts. A nearly 1.93-fold enhancement in the mass activity was achieved on the Pd@CeO2-plate catalysts demonstrating the significance of Pd-O-Ce linkage enhancement. The formation mechanism of Pd-O-Ce linkage was also probed, and a valid Pd-O-Ce linkage can only be formed in the inert atmosphere because of the reaction between metallic Pd and CeO2. This finding sheds some light on the more efficient catalyst interface construction and understanding for the fuel cell catalysis via metal-support interaction enhancement.

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 mgPd−1, and residual current of 69.93 mA mgPd−1 at 3000 s was achieved with our Pd3Cu1/rGO catalyst in the electrocatalytic FAO process.

Formation of conformal NiO underlayer on carbon for strong metal-support interactions effects on electrocatalytic performance of supported Pd nanoparticles

Enhancing the performance of noble metal electrocatalysts is regarded as an urgent issue for the commercialization of fuel cells in the near future. In this study, we demonstrate that the electrocatalytic performance of Pd nanoparticles (NPs) supported on carbon can be enhanced by introducing NiO coating on carbon. We further demonstrate that a uniform thin layer of NiO coating on carbon support can be readily achieved by using a sonochemical reaction (ultrasound-assisted polyol synthesis, UPS) method. NiO-modified carbon (NiO/C) supports were synthesized by two different methods, atomic layer deposition (ALD) and UPS methods, and Pd NPs were formed on them. Compared with Pd NPs on carbon support, Pd NPs on NiO/C supports showed 3–5 fold enhanced electrocatalytic performance for formic acid oxidation and oxygen reduction reactions. Between the two NiO/C supports, the one synthesized by UPS method outperforms the one by ALD by up to 2 times. Detailed structural analysis data show that the NiO/C synthesized by UPS is composed of uniform and continuous thin (0.42 nm) NiO coating on the external surface of carbon while the NiO/C by ALD has thicker (1.13 nm) NiO islands to form patch-like coating on the carbon surface. The enhanced electrocatalytic performance of Pd NPs on NiO/C supports can be explained by the change of the electronic structure of strong metal-support interaction between Pd and NiO and the bifunctional mechanism enabled by the NiO surface around Pd NPs.

Surfactant-free fabrication of porous PdSn alloy networks by self-assembly as superior freestanding electrocatalysts for formic acid oxidation

Porous PdSn networks synthesized by self-assembly at 60 °C for the first time with high electrocatalytic performance for formic acid oxidation.

Extraordinary electrocatalytic performance for formic acid oxidation by the synergistic effect of Pt and Au on carbon black

Improving catalyst performance and understanding reaction mechanism of formic acid electrooxidation (FAO), a typical anodic reaction in fuel cells, are of technological and scientific importance. Here, Pt-Au/C catalysts were designed and synthesized for catalyzing the FAO reaction. An ultrasound-assisted method was developed to enable the uniform and dense loading of Pt and Au on carbon black without any surfactant. The Pt-Au/C sample with a Pt/Au atomic ratio of 32:68 exhibits an FAO catalytic activity of 14.5 A mgPt−1, which is 153 times higher than that of Pt/C. The extraordinary performance is attributed to the optimized synergistic effect of Pt and Au. Density functional theory calculations disclose that the neighboring Au decreases the reaction energy barriers of the direct pathway on Pt. This work demonstrates a promising FAO catalyst and an effective strategy to obtain supported catalysts.

Facile Synthesis of Porous Pd3 Pt Half-Shells with Rich "Active Sites" as Efficient Catalysts for Formic Acid Oxidation.

Exploring highly efficient electrocatalysts is greatly important for the widespread uptake of the fuel cells. However, many newly generated nanocrystals with attractive nanostructures often have extremely limited surface area or large particle-size, which leads them to display limited electrocatalytic performance. Herein, a novel anode catalyst of hollow and porous Pd3 Pt half-shells with rich "active sites" is synthesized by using urea as a guiding surfactant. It is identified that the formation of Pd3 Pt half-shells involves the combination of bubble guiding, in situ deposition of particles and bubble burst. The obtained Pd3 Pt half-shells demonstrate a rich edge area with abundant exposed active sites and surface defects, indicating great potential for the electrocatalysis. When used as an electrocatalyst, the Pd3 Pt half-shells exhibit remarkably improved electrocatalytic performance for formic acid oxidation (FAO), where it promotes the dehydrogenation process of FAO by suppressing the formation of poisonous species COads via the electronic effect and ensemble effect.

Effect of thermal treatment of Pd decorated Fe/C nanocatalysts on their catalytic performance for formic acid oxidation.

The thermal treatment of bimetallic nanocatalysts plays an important role in determining their catalytic performance. Here tuning the surface oxidized metal species of bimetallic Pd–Fe electrocatalysts for the formic acid (FA) oxidation reaction is reported and a correlation between the surface oxidized metal species of the Pd–Fe nanoparticles and their catalytic activities is proposed. The structural details of the Pd–Fe/C catalysts are characterized by X-ray diffraction, X-ray photoelectron spectroscopy and high-sensitivity low-energy ion scattering (HS-LEIS). Cyclic voltammetry measurements demonstrated that the mass activity of the Pd–Fe nanoparticles with a molar ratio of Pd/Fe = 1/15 is about 7.4 times higher than that of Pd/C. This enhancement could be attributed to the synergistic effect between Pd(0) and Pd oxidized species on the surface of the Pd–Fe/C treated sample and electronic effects. This finding demonstrates the importance of surface oxidized metal species at the nanoscale in harnessing the true electrocatalytic potential of bimetallic nanoparticles and opens up strategies for the development of highly active bimetallic nanoparticles for electrochemical energy conversion.

Core–shell CuPd@Pd tetrahedra with concave structures and Pd-enriched surface boost formic acid oxidation

Concave CuPd@Pd tetrahedra are synthesized via a facile l-proline-mediated strategy, exhibiting remarkably improved electrocatalytic performance for formic acid oxidation.

The role of surface functionalities in fabricating supported Pd-P nanoparticles for efficient formic acid oxidation

In the present work, O–functionalized carbon nanotubes (OCNTs) supported Pd–P nanoparticles (Pd–P/OCNTs) were prepared by using sodium hypophosphite (NaH2PO2) as the P source and the reducing agent. The presence of O-functionalities on the carbon surface provide a microenvironment of the reaction system which favors the anchorage of P precursors and Pd salt ions through the electrostatic interaction and the formation of chemical bonds on the carbon support. Thus, Pd nanoparticles supported on the OCNTs could be efficiently incorporated with P. Pd with the modified outer electron structure enhanced the electrocatalytic performance for formic acid oxidation (FAO).

Yolk-Shell Fe3O4-Polyaniline Decorated Pd-Ni Nanoparticles with Enhanced Performance for Direct Formic Acid Fuel Cell

The yolk-shell Fe3O4-polyaniline for decoration of Pd-Ni nanoparticles (yolk-shell Fe3O4-PANI/Pd-Ni) were synthesized and used as a new electrocatalyst for oxidation of formic acid. The yolk-shell Fe3O4-PANI/Pd-Ni catalyst provided superior catalyst performance for formic acid oxidation in H2SO4 aqueous solution. These yolk-shell Fe3O4-PANI/Pd-Ni catalysts were found to be more resistant to deactivation in the oxidation of formic acid than yolk-shell Fe3O4-PANI/Pd and Pd/C and to consistently show better long-term performances. The enhanced catalytic performance may arise from the unique structure and surface properties of the yolk-shell Fe3O4-PANI and bi-functional effect, which process extraordinary promotional effect on Pd catalyst.