Stability For Formic Acid Electrooxidation Research Articles

A Facile Preparation of Sandwich-Structured Pd/Polypyrrole-Graphene/Pd Catalysts for Formic Acid Electro-Oxidation.

Direct formic acid fuel cells (DFAFCs) are one of the most promising power sources due to its high conversion efficiency; relatively low carbon emissions, toxicity, and flammability; convenience; and low-cost storage and transportation. However, the key challenge to large-scale commercial applications is its poor power performance and the catalyst's high preparation cost. In this study, a new sandwich-structured Pd/polypyrrole-graphene/Pd (Pd/PPy-Gns/Pd)-modified glassy carbon electrode (GCE) was prepared using a simple constant potential (CP) electrodeposition technique. On the basis of the unique synthetic procedure and structural advantages, the Pd/PPy-Gns/Pd shows a fast charge/mass transport rate, high electrocatalytic activity, and great stability for formic acid electro-oxidation (FAO). The mass activity of Pd/PPy-Gns/Pd electrode reaches 917 mA·mg-1Pd. The excellent catalytic activity is mainly due to the uniform embedding of Pd nanoparticles on the polypyrrole-graphene (PPy-Gns) support, which exposes more active sites, and prevents the shedding and inactivation of Pd nanoparticles. At the same time, the introduction of graphene (Gns) in the PPy further improved the conductivity of the catalyst and accelerated the transfer of electrons.

Self-catalytic induced interstitial C-doping of Pd nanoalloys for highly selective electrocatalytic dehydrogenation of formic acid

Light-metalloid-atom-doped Pd interstitial nanoalloy is promising candidate for electrocatalysis because of the favorable electronic effect. Herein, an innovative method was developed to synthesize C-doped Pd interstitial nanoalloy using palladium acetate both as metal precursor and C dopant. Elaborate characterizations demonstrated that C atoms were successfully doped into the Pd lattice via self-catalytic decomposition of acetate ions. The as-synthesized C-doped Pd catalysts showed excellent activity and durable stability for formic acid electrooxidation. The mass activity and specific activity at 0.6 V of C-doped Pd were approximately 2.59 A/mg and 3.50 mA cm−2, i.e., 2.4 and 2.6 times of Pd, respectively. DFT calculations revealed that interstitial doping with C atoms induced differentiation of Pd sites. The strong noncovalent interaction between the Pd sites and the key intermediates endowed Pd with high-selectivity to direct routes and enhanced CO tolerance. This work presents a sites-differentiation strategy for metallic catalysts to improve the electrocatalysis.

Hydrogen evolution reaction and formic acid oxidation by decorated nanostructural Pt/Pd on a copper-filled nanoporous stainless steel

In this work, a 304 stainless steel (SS) was anodized to prepare nanoporous SS (NPSS) with an average size of about 75 nm and then filled with copper (Cu/NPSS) using pulsed electrodeposition method. Afterward, a nanostructural Pt and Pd film was deposited by galvanic replacement (GR) on the Cu/NPSS to prepare modified electrode (PtPd/Cu/NPSS) for hydrogen evolution reaction (HER) and formic acid electrooxidation (FAO). The electrocatalytic activity of the modified electrode and its structural characterization have been studied by voltammetric methods, electrochemical impedance spectroscopy (EIS), inductively coupled plasma optical emission spectrometry (ICP-OES), and field emission scanning electron microscopy (FESEM). The results show that the nanostructural Pt1Pd1/Cu/NPSS composition, with low Pt loading and suitable stability, has a good electrocatalytic performance toward HER (EOnset = + 12 mV vs. NHE) and FAO (EOnset = −180 mV vs. NHE). For HER observed a high mass activity of noble metals (87.54 mA cm−2μg Pd+Pt −1 ) in comparison with Pt deposited Cu/NPSS (41.5 mA cm−2 μg Pt −1 ) at the same applied potential of − 0.25 V versus NHE. Also, the fabricated electrocatalysts with more electrochemically active surface area in comparison with Pd/Cu/NPSS and Pt/Cu/NPSS revealed more resisting to the poisoning components and good stability for FAO.

Nitrogen-doped carbon black supported Pd nanoparticles as an effective catalyst for formic acid electro-oxidation reaction

Pd nanoparticles supported on nitrogen doped carbon black (Vulcan XC-72R) with two different levels of doping were prepared by the microwave-assisted ethylene glycol reduction process and used as catalyst for the formic acid electro-oxidation (FAEO). The results indicate that the different nitrogen doping contents in Pd/N-C catalysts have a significant effect on the performance of FAEO. A higher N content facilitates the uniform dispersion of Pd nanoparticles on carbon black with narrow particle size distribution. Furthermore, the electrochemical results show that the catalyst with a higher N-doping content possesses a higher catalytic activity and a long-term stability for FAEO. The peak current density of the Pd/N-C (high) catalyst is 1.27 and 2.31 times that of the Pd/N-C (low) and homemade Pd/C-H catalyst. The present paper may provide a simple method for preparation of high-performance anode catalyst for direct formic acid fuel cells (DFAFCs).

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.

A Pd/PW12/RGO Composite Catalyst Prepared by Electro-Codeposition for Formic Acid Electro-Oxidation

A highly active Pd based catalyst for direct formic acid fuel cells (DFAFCs), Pd/Na3PW12O40 (PW12)/reduced graphene oxide (RGO), was prepared by a facile and green preparation strategy based on electrochemical-codeposition. The composite was investigated by SEM, TEM, XPS, Raman spectroscopy and XRD. The GO and PdCl42− can be reduced simultaneously and the mass of Pd is measured to be ca. 18.7 μg for Pd/PW12/RGO composite. The PW12 can facilitate the deposition of more uniform and smaller Pd nanoparticles. Notably, the Pd/PW12/RGO catalyst exhibits higher specific activity ranging from 0.15 V to 0.30 V toward formic acid electro-oxidation as compared with the Pd/RGO and Pd/C catalyst. The specific activity for Pd/PW12/RGO catalyst (5.98 mA cm−2Pd at 0.2 V vs. Ag/AgCl) is enhanced by a factor of 2.4 in comparison with Pd/RGO catalyst (2.49 mA cm−2Pd at 0.2 V vs. Ag/AgCl). Moreover, Pd/PW12/RGO catalyst displays an improved stability for formic acid electro-oxidation and a better tolerance toward CO poisoning than Pd/RGO and Pd/C catalyst. The enhanced performance of Pd/PW12/RGO catalyst can be contributed to the synergistic effect of better dispersion of Pd nanoparticles, and high protonic conductivity and superior oxidation power of PW12.

Preparation of graphene and graphene supported Pd catalysts for formic acid electrooxidation

Two kinds of graphene GN-1 and GN-2 with significantly increased specific surface area were obtained from nano graphite by different methods. The morphology and pore size distribution of GN-1 and GN-2 also have great differences. Using these two kinds of graphene as supports, Pd catalysts were prepared and designed as Pd/GN-1 and Pd/GN-2. The electrochemical specific surface area of Pd/GN-1 and Pd/GN-2 catalysts are 34.66 and 71.25 m2/g. The catalytic activities of Pd/GN-1 and Pd/GN-2 during the formic acid electrooxidation reaction are greatly improved compared with the Pd catalyst supported by nano graphite. The peak current densities of formic acid oxidation on Pd/GN-1 and Pd/GN-2 are 66.0 and 95.8 mA/cm2. The Pd/GN-1 and Pd/GN-2 catalysts also have good stability for formic acid electrooxidation.

An efficient antimony doped tin oxide and carbon nanotubes hybrid support of Pd catalyst for formic acid electrooxidation

We report on a mixture of antimony doped tin oxide (ATO) and carbon nanotubes as a novel support of Pd catalyst (Pd/ATO-CNTs) with the aims to enhance electron and proton conductivity of hybrid support, and catalytic activity and stability for formic acid electrooxidation. The surface content, morphology and structure of the as-prepared Pd/ATO-CNTs catalysts with different CNTs contents have been characterized by X-ray diffraction (XRD), energy dispersive analysis of X-ray (EDAX), inductively coupled plasma-optical emission spectroscopy (ICP-OES), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and high angle annular dark field STEM (HAADF-STEM), respectively. The electrocatalytic properties of the samples for formic acid electrooxidation reaction are investigated by cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy. The results show that the activity and stability of Pd/ATO-CNTs catalyst is obviously higher than that of Pd/CNTs catalyst for formic acid electrooxidation due to unique physical and chemical properties of ATO and metal-support interaction between Pd nanoparticles and ATO. Moreover, the Pd/ATO-CNTs10 (CNTs content is 10 wt.% of ATO-CNTs support mass) with smaller Pd particle size and narrower size distribution on surface of the hybrid support exhibits the best performance for formic acid electrooxidation among all the samples.

Remarkable activity of PdIr nanoparticles supported on the surface of carbon nanotubes pretreated via a sonochemical process for formic acid electro-oxidation

It was reported for the first time that the surface treated multi-walled carbon nanotubes supported PdIr (PdIr/CNT-SCP) catalyst presents remarkable electrocatalytic activity and stability for formic acid electro-oxidation (FAEO). The surface of CNTs was functionalized by a sonochemical process for the deposition of PdIr nanoparticles (NPs). The XRD and TEM characterizations show that the prepared PdIr/CNT-SCP catalyst has small mean size and good dispersion of PdIr NPs on CNTs. The electrochemical measurements show that the onset and anodic peak potentials of FAEO on PdIr/CNT-SCP catalyst are 60 and 50mV more negative than that on the commercial Pd/C catalyst. The mass-normalized peak current density of PdIr/CNT-SCP is 3365mAmg−1Pd, which is 4.5, 1.4 and 2.7 times higher than that of PdIr/CNT-Untreated, PdIr/C-SCP and commercial Pd/C, respectively. It demonstrates the promotion of Ir and functionalized CNTs to Pd for FAEO.

ZrC–C and ZrO2–C as Novel Supports of Pd Catalysts for Formic Acid Electrooxidation

AbstractThe Pd/ZrC–C and Pd/ZrO2–C catalysts with zirconium compounds ZrC or ZrO2 and carbon hybrids as novel supports for direct formic acid fuel cell (DFAFC) have been synthesized by microwave‐assisted polyol process. The Pd/ZrC–C and Pd/ZrO2–C catalysts have been characterized by X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), energy dispersive analysis of X‐ray (EDAX), transmission electron microscopy (TEM), and electrochemical measurements. The physical characteristics present that the zirconium compounds ZrC and ZrO2 may promote the dispersion of Pd nanoparticles. The results of electrochemical tests show that the activity and stability of Pd/ZrC–C and Pd/ZrO2–C catalysts show higher than that of Pd/C catalyst for formic acid electrooxidation due to anti‐corrosion property of zirconium compounds ZrC, ZrO2, and metal–support interaction between Pd nanoparticles and ZrC, ZrO2. The Pd/ZrC–C catalyst displays the best performance among the three catalysts. The peak current density of formic acid electrooxidation on Pd/ZrC–C electrode is nearly 1.63 times of that on Pd/C. The optimal mass ratio of ZrC to XC‐72 carbon is 1:1 in Pd/ZrC–C catalyst with narrower particle size distribution and better dispersion on surface of the mixture support, which exhibits the best activity and stability for formic acid electrooxidation among all the samples.

Efficient anchorage of highly dispersed and ultrafine palladium nanoparticles on the water-soluble phosphonate functionalized multiwall carbon nanotubes

A facile noncovalent approach is proposed to graft phosphonate groups onto the surface of the multiwall carbon nanotubes (MWCNTs) by π–π stacking interaction between naphthalen-1-ylmethylphosphonic acid (NYPA) and MWCNTs. Noncovalently attachment of phosphonate groups on the MWCNTs surface is confirmed by Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and zeta potential analysis. The water-soluble phosphonate functionalized MWCNTs are further deposited with Pd nanoparticles (Pd-NPs) as electrocatalyst for formic acid oxidation. The morphology and structure of Pd-MWCNTs nanocomposites are characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and XPS measurements. It is observed that Pd-NPs are highly dispersed and effectively anchored on the side walls of the phosphonate functionalized MWCNTs. The Pd-MWCNTs nanocomposites exhibit better electrocatalytic activity and long-term stability for formic acid electrooxidation than the un-phosphonated counterpart.

Titanium compounds TiC–C and TiO2–C supported Pd catalysts for formic acid electrooxidation

In this work, Pd nanoparticles supported on TiC–C and TiO2–C as novel and efficient supports for formic acid electrooxidation are investigated. The Pd/TiC–C and Pd/TiO2–C catalysts have been synthesized by microwave-assisted polyol process. The Pd nanoparticles in the Pd/TiC–C and Pd/TiO2–C catalysts are found to disperse more uniformly and have smaller sizes on the TiC–C and TiO2–C supports than that on carbon support alone. The addition of titanium compounds (TiC and TiO2) significantly increases catalytic activity and stability of Pd for formic acid electrooxidation because of outstanding oxidation and acid corrosion resistance of titanium compounds (TiC and TiO2), and metal-support interaction between Pd nanoparticles and titanium compound (TiC or TiO2). The Pd/TiC–C catalyst displays the best performance among all the samples. The effect of TiC:C mass ratio on the catalytic activity is also investigated. It is found that the maximal catalytic activity and stability for formic acid electrooxidation is observed at the Pd/TiC–C catalyst with TiC:C mass ratio of 1:2.

Electrooxidation of formic acid catalyzed by Pd Nanoparticles supported on multi-walled carbon nanotubes with sodium oxalate

This paper repots a highly catalytic palladium nanoparticle catalyst dispersed on the purified multi-walled carbon nanotubes (P-MWCNTs) for the electrooxidation of formic acid, in which sodium oxalate is employed as both a dispersant and a coordination agent. The nanostructured catalysts have been characterized by X-ray diffraction technique and transmission electron microscopy. It is found that the as-prepared face-centered cubic crystal Pd nanoparticles are uniformly dispersed on the surface of MWCNTs with an average particle size of 5.6 nm. Fourier transform infrared spectroscopy and thermogravimetric analysis revel that sodium oxalate is a tractable ligand with the aid of a suitable solution. Cyclic voltammetry and chronoamperometry tests demonstrate that the obtained Pd/P-MWCNT catalyst from typical experiment has better catalytic activity and stability for formic acid electrooxidation than acid-oxidation treatment MWCNT (AO-MWCNT)-supported Pd catalyst from the control experiment. Therefore, the as-prepared Pd/P-MWCNTs would be a potential candidate as an anode electrocatalyst in direct formic acid fuel cells.

Electronic effect on oxidation of formic acid on supported Pd–Cu bimetallic surface

Vapor deposition method is used to prepare layered Pd–Cu bimetallic model catalytic surfaces, with different thickness of Pd, supported on glassy carbon. Charge transfer from Pd to Cu produces a positive binding energy (BE) shift for the overlayer Pd 3d and an opposite shift for Cu 2p as measured by X-ray photoelectron spectroscopy (XPS). Similarly, the d-band center moves away from the Fermi level as the thickness of Pd decreased for these bimetallic materials. This electronic perturbation of the Pd–Cu systems results in a drastic increase in current density and an improved stability for formic acid electro-oxidation. Our findings indicate that layered Pd–Cu bimetallic surfaces with Pd layers thicker than 1nm do not form a surface alloy at room temperature and are better electrocatalytic materials than Bulk Pd and could be used to enhance direct formic acid fuel cell (DFAFC) performance.

Electrodeposited Pd–MoOx catalysts with enhanced catalytic activity for formic acid electrooxidation

Pd–MoOx catalysts supported on glassy carbon electrode were co-deposited using cyclic voltammetry. The influence of two key deposition parameters (i.e. scanning potential range and concentration of sodium molybdate in the electrolyte) on the catalysts was investigated by X-ray diffraction, energy dispersive X-ray spectroscopy, element analysis mapping, scanning electron microscopy, X-ray photoelectron spectroscopy and typical electrochemical measurements, respectively. It was found both of the parameters had great effect on the morphology, chemical states, composition and electrochemical performance of the catalysts. By tuning the electrodeposition parameters, we found the optimal condition to prepare the catalysts. The as-prepared catalysts showed much improved catalytic activity and stability for formic acid electrooxidation. The enhanced performance can be attributed to the fine porous structure composed of small particles, hydrogen spillover effect and unique element distribution (different composition between surface and bulk).

Pd nanotube electrodes with improved electrocatalytic stability for formic acid electrooxidation

We report Pd nanotube electrodes fabricated by means of electrodeposition method as a function of applied current density. Transmission electron microscopy and scanning electron microscopy images show that the higher applied current density results in the rougher surface structure. From the X-ray diffraction patterns, it is observed that the smaller grain size of the Pd nanotube electrodes may be attributed to the higher applied current density. In the electrochemical data, it is found that the Pd nanotube electrode with the smaller grain size results in much higher electrocatalytic properties for formic acid electrooxidation. The Pd nanotube electrode electrodeposited under the highest applied current density exhibits the improved electrocatalytic stability in comparison with Pd catalyst supported by carbon black (Pd/C, E-TEK, Co.).

Controllable synthesis of carbon nanofiber supported Pd catalyst for formic acid electrooxidation

Carbon nanofiber (CNF) supported Pd nanoparticles are synthesized with sodium citrate and sodium borohydride served as stabilizing agent and reducing agent, respectively. The size and distribution of the supported Pd nanoparticles are controlled by adjusting the pH value of the synthesis solution. Analyses of the obtained Pd/CNF catalysts indicate that the supported Pd nanoparticles become more uniform in size and the average particle size is decreased from 5.85 to 3.62 nm with pH value of the synthesis solution increasing from 3.2 to 6.0. However, the further increasing of the pH value to 6.5 leads to an increased particle size and the formation of PdO phase in the synthesized Pd/CNF catalyst. The Pd/CNF catalyst synthesized at the pH value of 6.0 exhibits superior catalytic activity and stability for formic acid electrooxidation due to its small particle size and uniform size distribution.

Enhanced electroactivity of Pd nanocrystals supported on H3PMo12O40/carbon for formic acid electrooxidation

The preparation of highly dispersed precious metal catalysts is an important subject for fuel cell applications. Here, using a phosphomolybdic acid (PMo12)-assisted method, a Pd-PMo12/C catalyst with uniform Pd nanoparticles is prepared. The TEM results show that the presence of PMo12 facilitates the formation of uniform Pd particles with an average particle size of 3.2nm. More importantly, the Pd-PMo12/C catalyst displays an enhanced activity and stability for formic acid electro-oxidation and a better tolerance toward CO poisoning than Pd nanocatalysts prepared with sodium citrate as a stabilizer. A combination of the composition and structure analyses show that the reasons for the improved electro-catalytic activity of the Pd-PMo12/C catalyst involve the metal–support interaction, the richer Pd oxide/hydrous oxide content and the inherent properties of PMo12.

Mixed-phase PdRu bimetallic structures with high activity and stability for formic acid electrooxidation

Aiming at investigating the effect of structure on electrocatalytic properties, Pd(50)Ru(50) nanoparticles (NPs) with three different structures were carefully designed in a one-pot polyol process for application in formic acid electrooxidation. The three structures are: (1) single-phase PdRu nanodendrites (denoted as PR-1), (2) a mixed-phase mixture of PdRu nanodendrites and monometallic Ru NPs (denoted as PR-2), and (3) a mixed-phase mixture of monometallic Pd and Ru NPs (denoted as PR-3). From PR-1 to PR-3, the structure was varied from single-phase to mixed-phase. The relative position of Ru was altered from completely Pd-connected (PR-1), to a mixture of Pd-connected and monometallic (PR-2), and completely monometallic (PR-3). All PdRu NPs outperform the commercial Pd/C. PR-2 exhibits the highest peak current density, but its stability is slightly lower than that of PR-3. When both the current density and the durability are taken into consideration, PR-2 is the best choice of catalyst for formic acid oxidation. It indicates that both the Pd-connected Ru NPs and monometallic Ru NPs in the mixed-phase PR-2 are essential to improve the electrocatalytic properties. Our study also illustrates that the electrochemical active surface area (ECSA) and hydrogen storage capacity of the as-prepared PdRu NPs are greatly enhanced after several hundred scans in formic acid, indicating the possibility for highly restorable catalysts in direct formic acid fuel cells.

Investigation on performance of Pd/Al2O3–C catalyst synthesized by microwave assisted polyol process for electrooxidation of formic acid

A Pd/Al2O3–C catalyst with α-Al2O3 and Vulcan XC-72 carbon black as a mixture support for direct formic acid fuel cell (DFAFC) has been prepared by a microwave-assisted polyol process for the first time. The as-prepared Pd/Al2O3–C catalysts with different mass ratios of α-Al2O3 to XC-72 carbon have been characterized by XRD, EDAX, XPS, TEM, HRTEM, and electrochemical measurements in this study. The results show that the activity of the catalyst with α-Al2O3 as the support is lower than that of the catalyst with carbon black as the support, owing to α-Al2O3 having poor electrical conductivity. However, the activity of the catalyst with α-Al2O3 and Vulcan XC-72 carbon black as a mixture support is evidently enhanced. The Pd/Al2O3–C catalyst with a mass ratio of α-Al2O3 to XC-72 carbon of 1 : 2 presents the narrowest particle size distribution on the surface of the mixture support, which exhibits the best activity and stability for formic acid electrooxidation among all the samples. Its current density of the positive anodic peak of formic acid electrooxidation is up to 36.97 mA cm−2. Pd/Al2O3–C catalyst with a suitable ratio of α-Al2O3 to XC-72 carbon shows a better catalytic activity for formic acid electrooxidation and a higher stability than Pd/C, resulting from the addition of α-Al2O3 improving its electrooxidation ability for formic acid due to an anti-corrosion property of α-Al2O3 and a metal–support interaction between the Pd nanoparticles and the α-Al2O3.