For Formic Acid Oxidation Reaction Research Articles

In Situ Exfoliation and Pt Deposition of Antimonene for Formic Acid Oxidation via a Predominant Dehydrogenation Pathway.

Direct formic acid fuel cell (DFAFC) has been considered as a promising energy conversion device for stationary and mobile applications. Advanced platinum (Pt) electrocatalysts for formic acid oxidation reaction (FAOR) are critical for DFAFC. However, the oxidation of formic acid on Pt catalysts often occurs via a dual pathway mechanism, which hinders the catalytic activity owing to the CO poisoning. Herein, we directly exfoliate bulk antimony to 2D antimonene (Sb) and in situ load Pt nanoparticles onto antimonene sheets with the assistance of ethylenediamine. According to the Bader charge analysis, the charge transfer from antimonene to Pt occurs, confirming the electronic interaction between Pt and Sb. Interestingly, antimonene, as a cocatalyst, alters the oxidation pathway for FAOR over Pt catalyst and makes FAOR follow the more efficient dehydrogenation pathway. The density functional theory (DFT) calculation demonstrates that antimonene can activate Pt to be a lower oxidative state and facilitate the oxidation of HCOOH into CO2 via a direct pathway, resulting in a weakened intermediate binding strength and better CO tolerance for FAOR. The specific activity of FAOR on Pt/Sb is 4.5 times, and the mass activity is 2.6 times higher than the conventional Pt/C.

Promoting formic acid oxidation performance of Pd nanoparticles via Pt and Ru atom mediated surface engineering.

The alteration of surface functional properties via incorporation of foreign atoms is supposed to be a key strategy for the enhanced catalytic performance of noble-metal based nanocatalysts (NCs). In the present study, carbon-supported palladium (Pd)-based NCs including Pd, PdPt and PdRuPt have been prepared via a polyol reduction method under the same reduction conditions as for formic acid oxidation reaction (FAOR) applications. By cross-referencing the results of the microscopic, spectroscopic and electrochemical analysis we demonstrated that adding a small amount of platinum (Pt) into Pd NCs (i.e. PdPt NCs) significantly promotes the FAOR performance as compared to that of Pd NCs via weakening the COads bond strength at a lower voltage (0.875 V vs. NHE) than Pd (0.891 V vs. NHE). Of special relevance, the PdPt NC shows a mass activity (MA) of 1.0 A mg−1 and 1.9 A mg−1, respectively, in the anodic and cathodic scan. These values are ∼1.7-fold (0.6 A mg−1) and ∼4.8-fold (0.4 A mg−1) higher than those of Pd NC. Moreover, PdPt NC retains a higher MA (54 mA mg−1) than that of Pd NC (9 mA mg−1) after chronoamperometric (CA) stability tests over 2000 s. Meanwhile, further addition of ruthenium (Ru) (i.e. PdRuPt NCs) outstandingly enhances the CO tolerance during the CA test via removal of adsorbed COads and thus shows the highest MA (62 mA mg−1) after CA testing, which is higher than that of PdPt (54 mA mg−1) and Pd (9 mA mg−1) NCs. The intriguing results obtained in this study have great significance to provide further strategic opportunities for tuning the surface electronic properties of Pd-based NCs to design Pd-based NCs with improved electrochemical performance.

Electrocatalytic Performance of Palladium-Based Electrocatalysts Supported on Carbon Nanotubes for Formic Acid Oxidation

Recently, the study of carbon supports like carbon nanotubes (CNT) has intensified. The interaction between the support and nanoparticles improved the efficiency and durability of fuel cells (FCs), decreasing the electrocatalyst poisoning and in some cases it can modify the particle size. Palladium based nanostructured electrocatalysts, supported on glassy carbon [1], carbon black Vulcan [2] and CNT [3] are used in electrochemical energy storage devices such as FCs. In the present work, Pd and PdFe nanoparticles supported on CNT with and without functionalization (CNT and CNTox) were used for Formic Acid Oxidation Reaction (FAOR) in acid media. Electrocatalysts were synthesized by the borohydride reduction method with a metal loading of 20 wt.%. The CNTs were synthesized by the methane catalytic decomposition, and subjected to an oxidation treatment with nitric acid, named as CNTox. The morphology, composition and structural properties were studied by Transmission Electron Microscopy (TEM), Scanning Electron Microscopy-Energy Dispersive X-ray (SEM-EDX) and X-Ray Diffraction (XRD). The FAOR was evaluated in acid media in a conventional three-electrode cell by means of cyclic voltammetry and chronoamperometry. From the steady state current density it was found that that Pd and PdFe supported at CNTox allowed improving the catalytic activity in comparison with the non-oxidized support as shown in Figure and Table 1. Figure 1.Potentiostatic transients of the Pd base electrocatalysts supported at CNT and CNTox at 0.4 V for 900 seconds and Table 1. Comparison of steady-state current density of synthesized electrocatalysts to the potential of 0.4 V. I.E. Espino-López, M. Romero-Romo, M.G. Montes de Oca-Yemha, P. Morales-Gil, M.T. Ramírez-Silva, J. Mostany, M. Palomar-Pardavé. Journal of The Electrochemical Society 166 (2019) D3205.L. Juárez-Marmolejo, S. Pérez-Rodríguez, M.G. Montes de Oca-Yemha, M. Palomar-Pardavé, M. Romero-Romo, A. Ezeta-Mejía, P. Morales-Gil, M.V. Martínez-Huerta, M.J. Lázaro. International Journal of Hydrogen Energy 44 (2019) 1640.H. Yan, Z. Bai, S. Chao, Q. Cui, L. Niu, L. Yang, J. Qiao, K. Jiang, Ionics 20 (2014) 259. Figure 1

Electrocatalytic Performance of Palladium-Based Electrocatalysts Supported on Carbon Nanotubes for Formic Acid Oxidation

In the present work, Pd and PdFe nanoparticles supported on CNT with and without functionalization (CNT and CNTox) were used for Formic Acid Oxidation Reaction (FAOR) in acid media. Electrocatalysts were synthesized by the borohydride reduction method with 20 wt.% metal loading. The CNTs were synthesized by the methane catalytic decomposition, and subjected to an oxidation treatment with nitric acid, named as CNTox. Themorphology, composition and structural properties were studied by Transmission Electron Microscopy (TEM), Scanning Electron Microscopy-Energy Dispersive X-ray (SEM-EDX) and X-Ray Diffraction (XRD). The FAOR was evaluated in acid media in a conventional three-electrode cell by means of cyclic voltammetry and chronoamperometry. From the steady state current density, it was found that Pd and PdFe supported at CNTox allowed improving the catalytic activity in comparison with the nonoxidized support.

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.

One-pot controlled synthesis of AuPd@Pd core-shell nanocrystals with enhanced electrocatalytic performances for formic acid oxidation and glycerol oxidation

In this work, AuPd@Pd core–shell nanocrystals (AuPd@Pd NCs) were fabricated by a one-pot co-reduction approach, where theophylline-7-acetic acid (TAA) acted asa new structure-directing agent. The crystal structure and composition were mainly characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), X-ray diffraction (XRD), together with X-ray photoelectron spectroscopy (XPS). The growth mechanism of AuPd@Pd NCs was investigated in detail. The obtained AuPd@Pd NCs exhibited superior catalytic characters for formic acid oxidation reaction (FAOR) and glycerol oxidation reaction (GOR) in contrast with commercial Pd black in alkaline media.

Significant promotion effect of Fe3O4 on the mass catalytic activity of Pd nanocatalyst for the formic acid oxidation reaction

The catalytic activity of novel 20% PdFe3O4/C catalyst for Formic Acid Oxidation Reaction (FAOR) in 0.5 mol L−1 H2SO4 is reported. The evaluation has been carried out with several concentrations of the organic molecule (0.01, 0.1, 0.5 and 1 mol L−1). Electrochemical characterization shows lower specific current densities than those of a 20% Pd/C for the FAOR. Meanwhile, about a 2.6 increase in mass current density at PdFe3O4/C (441.67 mA mgPd−1) is observed compared to the monometallic with 1 mol L−1 FA. The onset potential (Eon-set) for the FAOR is also more negative (0.1 V) at PdFe3O4/C. Economic magnetite may improve the performance of Pd-based anodes for the FAOR in terms of mass catalytic activity, but there is necessity to enhance the specific activity.

Facile synthesis of flower-like Au@AuPd nanocrystals with highly electrocatalytic activity for formic acid oxidation and hydrogen evolution reactions

Herein, a one-pot co-reduction method was developed to prepare flower-like Au@AuPd core-shell nanocrystals (Au@AuPd NCs) under the guidance of 2,4-diamino-6-hydroxypyrimidine (DAHP). The product was mainly characterized by microscopic measurements, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analysis, and its formation mechanism was discussed in details. The architectures showed much larger electrochemical active surface area (62.68 m2 g−1Pd) than commercial Pd black (8.23 m2 g−1Pd), together with the higher mass activity (1250 mA mg−1) for formic acid oxidation reaction (FAOR). Besides, the catalyst displayed improved catalytic features for hydrogen evolution reaction (HER) relative to Pd black and Pt/C catalysts. These indicate the potential applications of the catalyst in energy storage and transformation.

Pd[sbnd]Bi bimetallic catalysts including polyvinylpyrrolidone surfactant inducing excellent formic acid oxidation reaction and direct formic acid fuel cell performance

PdBi bimetallic catalysts are synthesized while their catalytic activity and stability for formic acid oxidation reaction (FAOR) and direct formic acid fuel cell (DFAFC) performance are evaluated. According to investigations, Pd2Bi1/C catalyst including low Pd amount promotes oxygen desorption with enhancement in CO poisoning resistance. With that, indirect formic acid oxidation reaction (IFAOR) and its stability are improved. To further improve the FAOR, polyvinylpyrrolidone (PVP) surfactant is contained due to its amphiphilic property reducing Bi aggregation. To determine optimal amount of the PVP, analysis using TEM and XPS is performed and the results are verified by density functional theory (DFT). According to TEM, in 0.22 PVP-Pd2Bi1/C catalyst, PdBi has small size (∼5 nm) and is well-dispersed with widest Ed- EF of 3.85 eV, proving the catalyst induces effective CO-poisoning resistance and less Bi aggregation. These results are also compatible with trend in FAOR measured by cyclic voltammogram (CV). Even long-term stability, the catalyst maintains catalytic activity well. The best performance of DFAFC using the catalyst (32.7 mW cm−2·Pdg−1) indicates that 0.22 PVP- Pd2Bi1/C is excellent catalyst for FAOR and DFAFC performances.

Enhanced catalytic activity and stability for the electrooxidation of formic acid on lead modified shape controlled platinum nanoparticles

High catalytic activity for formic acid oxidation reaction (FAOR) is demonstrated in Pb modified shape-controlled Pt nanoparticles (NPs). Cyclic voltammetry is used to follow the effective modification of Pt NPs by Pb. Octahedral shaped Pt NPs (having a (111) preferential surface structure) modified by Pb are proved the most active electrocatalyst studied towards FAOR and display a catalytic activity of c.a. 7mAcm−2 at 0.5V in 0.1M formic acid solution. This current density represents an enhancement factor of 29.5 with respect to the unmodified Pt NPs and this is 2.7 and 2.3 times higher than that found on Tlθ/100-Pt NPs and Sbθ/111-Pt NPs, respectively, some of the most active electrocatalysts based on adatoms modified Pt NPs reported so far. This outstanding activity is displayed at maximum Pb coverage and also confers a wide electrocatalyst stability over the entire potential range studied. FAOR is also studied using scanning electrochemical microscopy (SECM) by the micropipette delivery/substrate collection (MD/SC) working mode as a preliminary rapid test to identify active electrocatalysts. In particular, the remarkable activity enhancement exhibited by a Pt ultramicroelectrode (100μm diameter) modified by Pb is rapidly imaged by SECM providing preliminary catalyst performance information. Thus, this technique emerges as a suitable and fast method to test, and in some cases quantify, catalyst activity for reactions of interest in fuel cell applications.

Synthesis of Pd/TiO2–C composite catalysts and investigation of its performance for the electrooxidation of formic acid

In this work, anatase-TiO2 is investigated as a catalyst support in Pd/TiO2–C composite to improve the electrocatalytic properties of Pd for formic acid oxidation reaction (FAOR). Pd/TiO2 has been synthesized by an impregnation-reduction method and then mixed with Vulcan XC-72R carbon black to obtain Pd/TiO2–C composite. Transmission electron microscopy (TEM) images show Pd nanoparticles (ca.3.5 nm in average diameter) in the Pd/TiO2–C (1:1) composite catalyst were dispersed on the surface of TiO2 with a narrow particle size distribution. Electrochemical tests demonstrate Pd/TiO2–C (1:1) composite has significantly increased catalytic activity and stability compared with Pd/C for FAOR. The proposed reasons for these observations are the excellent acid corrosion and oxidation resistance of TiO2 and the synergistic effect of Pd and TiO2 nanoparticles. The effect of mass ratios of TiO2 to C on the catalytic performance is also discussed. The best catalytic activity and stability for FAOR is found when the mass ratio of TiO2 to C is 1:1. It can be interpreted as the synergistic effects and conductivity reach balance at this point.

High Formic Acid Oxidation Activity and Stability of Pd Catalyst Supported by Nanoparticle-Embedded Carbon Nanofiber

A nanoparticle-embedded carbon nanofiber (PECNF) was proposed as a promising support of the Pd nanoparticle catalyst for formic acid oxidation reaction (FAOR). The nanofiber supports contained different weight and different nanoparticle were prepared by the electrospinning of polyacrylonitrile (PAN) by adding the nanoparticles, TiO2: TECNF, SiO2: SECNF and carbon black: CECNF, followed by carbonization and steam activation of the nanofiber. Cyclic voltammetry (CV) revealed a significantly high FAOR activity for the Pd/SECNF [1.00], which showed “muskmelon” like structure. Moreover, the chronoamperometory (CA) revealed a higher durability of the Pd/PECNF than that of Pd/CNF. Especially, Pd/SECNF [0.50] showed excellent durability. Based on these results, it was found that the SECNF is a promising support of the Pd for the DFAFC anode.

Graphene ribbon-supported Pd nanoparticles as highly durable, efficient electrocatalysts for formic acid oxidation

Graphene ribbon-supported Pd nanoparticles (Pd/GR) have been prepared by a simple, clean process in aqueous medium, involving only a Pd precursor and graphene ribbon (GR) as both a reducing agent and a catalyst support. A high density of Pd nanoparticles with a small average particle size (∼2.8±0.8nm) could be successfully deposited on graphene ribbons. The as-obtained Pd/GR electrocatalysts show increased electrochemical surface area and significantly enhanced catalytic activity for formic acid oxidation reaction (FAOR) compared to the conventional Pd/C electrocatalysts in terms of peak current density (1.4Amg−1 vs. 0.79Amg−1) and peak potential (−0.15V shift). Both the good dispersion and the relatively small particle size of the Pd nanoparticles on graphene ribbon and the synergetic effect between Pd and GR lead to high initial catalytic activity for FAOR. More importantly, a dramatic enhancement in durability is found with Pd/GR for FAOR due to the strong interaction between Pd and GR.

Carbon-supported PtAu alloy nanoparticle catalysts for enhanced electrocatalytic oxidation of formic acid

The understanding of the electrocatalytic activity of bimetallic nanoparticle catalysts requires the ability to precisely control the composition and phase properties. In this report, we describe a new strategy in the preparation of a series of carbon supported platinum–gold bimetallic nanoparticles with various bimetallic compositions which were loaded onto a carbon black support and subjected subsequently by thermal treatment (Pt100−mAum/C). The Pt100−mAum/C catalysts are characterized by X-ray diffraction (XRD), transmission electron spectroscopy (TEM), and induced coupled plasma-atomic emission spectroscopy (ICP-AES). The XRD pattern for the bimetallic nanoparticles shows single-phase alloy character. This ability enabled us to establish the correlation between the bimetallic composition and the electrocatalytic activity for formic acid (FA) electrooxidation. The electrocatalytic activities of the catalysts toward FA oxidation reaction are shown to strongly depend on the bimetallic PtAu composition. Within a wide range of bimetallic composition, the Pt50Au50/C catalyst shows the highest electrocatalytic activity for the FA oxidation, with a mass activity eight times higher than that of Pt/C. The high performance of the PtAu/C catalyst can be ascribed to the increased selectivity toward the FA dehydrogenation at the decreased availability of adjacent Pt atoms.