Activity For Formic Acid Oxidation Reaction Research Articles

A Biphasic Strategy to Synergistically Accelerate Activation and CO Spillover in Formic Acid Oxidation Catalysis.

Developing highly efficient and carbon monoxide (CO)-tolerant platinum (Pt) catalysts for the formic acid oxidation reaction (FAOR) is vital for direct formic acid fuel cells (DFAFCs), yet it is challenging due to the high energy barrier of direct intermediates (HCOO* and COOH*) as well as the CO poisoning issues associated with Pt alloy catalysts. Here we present a versatile biphasic strategy by creating a hexagonal/cubic crystalline-phase-synergistic PtPb/C (h/c-PtPb/C) catalyst to tackle the aforementioned issues. Detailed investigations reveal that h/c-PtPb/C can simultaneously facilitate the adsorption of direct intermediates while inhibiting CO adsorption, thereby significantly improving the activation and CO spillover. As a result, h/c-PtPb/C showcases an outstanding FAOR activity of 8.1 A mgPt-1, which is 64.5 times higher than that of commercial Pt/C and significantly surpasses monophasic PtPb. Moreover, the h/c-PtPb/C-based membrane electrode assembly exhibits an exceptional peak power density of 258.7 mW cm-2 for practical DFAFC applications.

Highly Selective Synthesis of Monoclinic-Phased Platinum-Tellurium Nanotrepang for Direct Formic Acid Oxidation Catalysis.

Designing efficient formic acid oxidation reaction (FAOR) catalysts with remarkable membrane electrode assembly (MEA) performance in a direct formic acid fuel cell (DFAFC) medium is significant yet challenging. Herein, we report that the monoclinic-phased platinum-tellurium nanotrepang (m-PtTe NT) can be adopted as a highly active, selective, and stable FAOR catalyst with a desirable direct reaction pathway. The m-PtTe NT exhibits the high specific and mass activities of 6.78 mA cm-2 and 3.2 A mgPt-1, respectively, which are 35.7/22.9, 2.8/2.6, and 3.9/2.9 times higher than those of commercial Pt/C, rhombohedral-phased Pt2Te3 NT (r-Pt2Te3 NT), and trigonal-phased PtTe2 NT (t-PtTe2 NT), respectively. Simultaneously, the highest reaction tendency for the direct FAOR pathway and the best tolerance to poisonous CO intermediate can also be realized by m-PtTe NT. More importantly, even in a single-cell medium, the m-PtTe NT can display a much higher MEA power density (171.4 mW cm-2) and stability (53.2% voltage loss after 5660 s) than those of commercial Pt/C, demonstrating the great potential in operating DFAFC device. The in-situ Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy jointly demonstrate that the unique nanostructure of m-PtTe NT can effectively optimize dehydrogenation steps and inhibit the CO intermediate adsorption, as well as promote the oxidation of noxious CO intermediate, thus achieving the great improvement of FAOR activity, poisoning tolerance, and stability. Density functional theory calculations further reveal that the direct pathway is the most favorable on m-PtTe NT than r-Pt2Te3 NT and t-PtTe2 NT. The higher activation energy to produce CO and the relatively weaker binding with CO of m-PtTe NT result in the better CO tolerance. This work achieves remarkable FAOR and MEA performances of advanced Pt-based anodic catalysts for DFAFCs via a phase engineering strategy.

Asymmetric Coordination of Iridium Single‐atom IrN3O Boosting Formic Acid Oxidation Catalysis

AbstractRational design of the proximal coordination of an active site to achieve its optimum catalytic activity is the ultimate goal in single‐atom catalysis, but still challenging. Here, we report theoretical prediction and experimental realization of an asymmetrically coordinated iridium single‐atom catalyst (IrN3O) for the formic acid oxidation reaction (FAOR). Theoretical calculations reveal that the substitution of one or two nitrogen with more electronegative oxygen in the symmetric IrN4 motif splits and downshifts the Ir 5d orbitals with respect to the Fermi level, moderating the binding strength of key intermediates on IrN4−xOx (x=1, 2) sites, especially that the IrN3O motif shows ideal activity for FAOR with a near‐zero overpotential. The as‐designed asymmetric Ir motifs were realized by pyrolyzing Ir precursor with oxygen‐rich glucose and nitrogen‐rich melamine, exhibiting a mass activity of 25 and 87 times greater than those of state‐of‐the‐art Pd/C and Pt/C, respectively.

Asymmetric Coordination of Iridium Single-atom IrN3 O Boosting Formic Acid Oxidation Catalysis.

Rational design of the proximal coordination of an active site to achieve its optimum catalytic activity is the ultimate goal in single-atom catalysis, but still challenging. Here, we report theoretical prediction and experimental realization of an asymmetrically coordinated iridium single-atom catalyst (IrN3 O) for the formic acid oxidation reaction (FAOR). Theoretical calculations reveal that the substitution of one or two nitrogen with more electronegative oxygen in the symmetric IrN4 motif splits and downshifts the Ir 5d orbitals with respect to the Fermi level, moderating the binding strength of key intermediates on IrN4-x Ox (x=1, 2) sites, especially that the IrN3 O motif shows ideal activity for FAOR with a near-zero overpotential. The as-designed asymmetric Ir motifs were realized by pyrolyzing Ir precursor with oxygen-rich glucose and nitrogen-rich melamine, exhibiting a mass activity of 25 and 87 times greater than those of state-of-the-art Pd/C and Pt/C, respectively.

Platinum-Tellurium Alloy Metallene Toward Formic Acid Oxidation Reaction

Open AccessRenewablesRESEARCH ARTICLES14 Jan 2023Platinum-tellurium alloy metallene towards formic acid oxidation reaction Ya-Nan Li, Qing-Ling Hong, Bo-Qiang Miao, Tian-Jiao Wang, Yu Ding and Yu Chen Ya-Nan Li Google Scholar More articles by this author , Qing-Ling Hong Google Scholar More articles by this author , Bo-Qiang Miao Google Scholar More articles by this author , Tian-Jiao Wang Google Scholar More articles by this author , Yu Ding Google Scholar More articles by this author and Yu Chen Google Scholar More articles by this author https://doi.org/10.31635/renewables.022.202200005 SectionsSupplemental MaterialAboutPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Engineering the composition and/or morphology is highly effective strategy for enhancing the electrocatalytic performance of noble metal nanocrystals. Recently, metallenes with specific chemical and physical properties have attracted increasing attention in electrocatalysis field. In this work, two-dimensional ultrathin platinum-tellurium alloy metallene (PtTe A-ML) is synthesized by using a conventional liquid-phase chemical reduction method. The high atom utilization as well as alloy effect endow PtTe A-ML with preeminent electrocatalytic activity for the formic acid oxidation reaction (FAOR). Specifically, the direct oxidation pathway of FAOR can be completely achieved at PtTe A-ML, which suppresses the production of toxic carbon monoxide (CO) intermediates and improves the reaction kinetics of FAOR. Accordingly, the FAOR activity of PtTe A-ML in acidic media is 43 and 5.6 times higher than that of commercial Pt and Pd nanocrystals, respectively. Meanwhile, PtTe A-ML exhibits also excellent electrocatalytic activity for CO oxidation reaction because of the introduction of oxygenophilic Te atoms and electron transfer between Pt and Te, which elevates the durability of PtTe A-ML for FAOR. The study provides a simple synthesis strategy of PtTe A-ML and shows PtTe A-ML has a promising practical prospect in direct formic acid fuel cells. Download figure Download PowerPoint Next article FiguresReferencesRelatedDetails Issue AssignmentNot Yet AssignedSupporting Information Copyright & Permissions© 2023 Chinese Chemical Society Downloaded 4 times PDF downloadLoading ...

Intermetallic PtTe metallene for formic acid oxidation assisted electrocatalytic nitrate reduction

Development of highly efficient electrocatalysts for selective electroreduction of nitrate is of great significance. In this work, the ultrathin intermetallic platinum-tellurium metallene (PtTe-ML) with atomic thickness is synthesized by simple liquid-phase chemical reduction. The introduction of Te atoms can sharply weaken the catalytic activity of Pt for the hydrogen evolution reaction. And, PtTe-ML exhibits superior catalytic activity for the nitrate reduction reaction (NO3−-ERR) than Pt black. In 0.5 M H2SO4 solution, PtTe-ML achieves an effective ammonia (NH3) production rate of 2.32 mg h−1 mgcat−1 and a Faradic efficiency of 95.5% at −0.04 V potential for NO3−-ERR. Meanwhile, the entry of Te atom isolates the continuous Pt active site and increases the proportion of the direct dehydrogenation pathway of the formic acid oxidation reaction (FAOR). Therefore, PtTe-ML also exhibits excellent FAOR activity due to the optimization of FAOR pathway. Then, anodic FAOR with low anodic oxidation potential is used to replace the oxygen evolution reaction with slow kinetic, so that the total electrolytic voltage of conventional electrochemical NH3 production can be effectively reduced. Consequently, the bifunctional PtTe-ML electrocatalyst requires only 0.4 V total voltage for FAOR assisted NH3 electroproduction. This work demonstrates a reaction coupling strategy to significantly improve the utilization rate of electric energy in electrochemical synthesis.

Atomic Pt clusters on Au dendrite for formic acid oxidation

The minimization of Pt loadings on Au via facile fabrication methods remains a grand challenge in the development of commercially viable electrodes for direct formic acid fuel cells. Herein, we report a simple electrochemical strategy to prepare atomic Pt clusters on Au dendrites supported by carbon paper (CP) as a gas diffusion electrode. At highly negative deposition potentials, Pt deposition is autonomously quenched by immediate adsorption of discharged proton (H) on Pt surface, while highly roughened Au dendrites lead to resistance–capacitance delay for the transient cathodic current. As a result, the suppressed Pt nucleation and self-terminated Pt growth allows for the formation of isolated Pt sites on Au dendrites. The Pt/Au/CP with an ultra-low Pt loading of 5.0 μgPt/cmgeo2 demonstrates high selectivity for direct pathway of formic acid oxidation reaction (FAOR), owing to the ensemble effect. A gradual increase of FAOR activity is observed during cycling test and then, the 20 cycled Pt/Au/CP shows remarkable FAOR activity in half-cell test, exceeding state-of-the-art Pt-Au catalysts. Theoretical calculation indicates that the stabilized intermediate on Pt clusters accelerates the direct FAOR pathway. CO chemisorption analysis reveals that the isolated Pt sites remain stable throughout the reaction. Single cell test for direct formic acid fuel cell with 20 cycled Pt/Au/CP anode demonstrate two-order higher Pt mass activity and mass power density, compared with values reported in recent literature.

Nanocomposite Concept for Electrochemical In Situ Preparation of Pt-Au Alloy Nanoparticles for Formic Acid Oxidation.

Herein, we report a straightforward approach for the in situ preparation of Pt–Au alloy nanoparticles from Pt + xAu/C nanocomposites using monometallic colloidal nanoparticles as starting blocks. Four different compositions with fixed Pt content and varying Pt to Au mass ratios from 1:1 up to 1:7 were prepared as formic acid oxidation reaction (FAOR) catalysts. The study was carried out in a gas diffusion electrode (GDE) setup. It is shown that the presence of Au in the nanocomposites substantially improves the FAOR activity with respect to pure Pt/C, which serves as a reference. The nanocomposite with a mass ratio of 1:5 between Pt and Au displays the best performance during potentiodynamic tests, with the electro-oxidation rates, overpotential, and poisoning resistance being improved simultaneously. By comparison, too low or too high Au contributions in the nanocomposites lead to an unbalanced performance in the FAOR. The combination of operando small-angle X-ray scattering (SAXS), scanning transmission electron microscopy (STEM) elemental mapping, and wide-angle X-ray scattering (WAXS) reveals that for the nanocomposite with a 1:5 mass ratio, a conversion between Pt and Au from separate nanoparticles to alloy nanoparticles occurs during continuous potential cycling in formic acid. By comparison, the nanocomposites with lower Au contents, for example, 1:2, exhibit less in situ alloying, and the concomitant performance improvement is less pronounced. On applying identical location transmission electron microscopy (IL-TEM), it is revealed that the in situ alloying is due to Pt dissolution and re-deposition onto Au as well as Pt migration and coalescence with Au nanoparticles.

Pd nanoparticles anchored on porous boron nitride nanofibers as highly active and stable electrocatalysts for formic acid oxidation

Direct formic acid fuel cells (DFAFCs) are promising power generation technologies for various electronic devices. The design of efficient and stable electrocatalysts for the formic acid oxidation reaction (FAOR) plays an important role for the commercial applications of the DFAFCs. Herein, porous boron nitride (BN) supported Pd nanoparticles (NPs) have been developed as unique and effective composite catalysts for FAOR. Porous BN nanofibers (BNNFs) has been utilized as a functional support to anchor of Pd NPs. The high specific surface area and rich porosity of BNNFs play a key role for the well-dispersion and stabilization of Pd NPs with uniform ultra-small size (~2.32 nm) on their surface. The developed Pd/BNNFs composite catalyst exhibits excellent catalytic activity for FAOR with the mass activity of 725 mA mg−1Pd and a very low onset potential (about −0.12 V). Comparative experiments confirm that the microstructure of porous BN carrier greatly affects the electrocatalytic behaviors of the composite catalyst in FAOR. As compared with the composite catalyst using BN microfibers (BNMFs) as a support, the developed Pd/BNNFs catalyst shows superior catalytic activity and long-term stability owing to the larger specific surface area of BNNFs and stronger interaction between Pd NPs and support. This study not only illustrates that porous BN is a desirable catalyst carrier for catalytic FAOR but also provides new ideas for the design of novel BN-based catalysts.

Electrochemically Dealloyed Cu–Pt Nanostructures for Oxygen Reduction and Formic Acid Oxidation

Surface engineering of catalysts by dealloying is a promising strategy to fine-tune the catalytic activity. Rational electrochemical surface engineering significantly improves the electrocatalytic performance. Herein, we demonstrate the synthesis of a surface-engineered CuxPty bimetallic electrocatalyst of low Pt content by solvothermal and subsequent electrochemical dealloying approaches for the electrocatalytic reduction of oxygen and oxidation of formic acid. The electrochemically dealloyed electrocatalysts have enhanced activity toward the oxygen reduction reaction and formic acid oxidation reaction (FAOR) due to the dealloying-induced increase in the electrochemically active surface area and lattice strain. Among the electrochemically dealloyed catalysts (Cu11Pt89, Cu17Pt83, and Cu23Pt77), Cu17Pt83 shows excellent ORR activity in acidic medium with an onset potential of 0.98 V. It delivers a limiting current density and mass specific activity of 5.4 mA/cm2 and 0.157 A/mgPt, respectively. The mass specific activity of Cu17Pt83 is 2–12 times higher than that of 20% Pt/C and monometallic Pt nanoparticles. The dealloying-induced lattice strain on Pt modifies the d-band structure. Such modification weakens the chemisorption of oxygenated species (OHads and OOHads) and improves the electron transfer kinetics. Among all dealloyed CuxPty catalysts, the low-Pt content Cu23Pt77 catalyst exhibits high FAOR activity. The Cu23Pt77 catalyst has good tolerance toward in situ generated CO, and the CO-stripping potential is significantly less positive compared to that of the other catalysts.

Ligand‐Mediated Self‐Terminating Growth of Single‐Atom Pt on Au Nanocrystals for Improved Formic Acid Oxidation Activity

AbstractDecreasing the ensemble size of Pt to isolated single atoms is the key to enhance the electrocatalytic formic acid oxidation reaction (FAOR) by bypassing the indirect reaction path that involves the poisoning by the CO intermediate. However, it is challenging to construct isolated Pt single atoms on a foreign metal substrate, especially at high Pt loadings, because Pt tends to form large ensembles due to the high Pt–Pt bond energy. Herein, a ligand‐mediated self‐terminating growth strategy is reported for reliably controlling the ensemble size of Pt on an Au substrate. The key is to introduce a ligand of sulfite (SO32−) into the synthesis, which preferentially adsorbs at Pt sites, thus substantially increasing the kinetic barrier toward Pt–Pt bond formation. This strategy enables reliable formation of isolated Pt single atoms even at high Pt loadings (up to 26% coverage on Au), which is difficult to achieve by regular syntheses. The resulting catalyst exhibits a high FAOR activity of 38.6 A mgPt−1 in 0.5 m H2SO4+0.25 m HCOOH, 370 times greater than that of the commercial Pt/C. It is believed this strategy is general and potentially applicable to the fabrication of a wide range of noble metal catalysts with tailored ensemble sizes for energy conversion.

Formic acid oxidation reaction on Au(111) electrodes modified with 4-mercaptopyridine SAM

The formic acid oxidation reaction (FAOR) on Au(111) electrodes modified by a 4-mercaptopyridine self-assembled monolayer (SAM) was studied with electrochemical techniques and surface-enhanced Raman spectroscopy (SERS). The adsorption of 4,4’-dithiodipyridine on Au(111) leads to a tremendous enhancement (up to 31-48 times) in electrocatalytic activity for FAOR, which is unique compared to other SAM molecules. The influence of 4,4’-dithiodipyridine and similar aromatic SAM molecules on Au(111) towards formic acid oxidation was studied systematically as a function of coverage and electrolyte composition. Several parameters such as position and availability of the pyridine nitrogen, adsorption and configuration of the SAM molecules, and the number of free gold sites exert a distinct effect on the formic acid oxidation on SAM-modified Au(111) electrodes and result in different enhancement of electrocatalytic activity. While various coverages of 4-mercaptopyridine enhance the activity towards FAOR on Au(111), the striped (5×3) SAM shows a tremendous activating effect after the addition of HCOOH to HClO4. In this way, 4-mercaptopyridine efficiently prevents the adsorption of strongly bound, non-reactive formate. The unique enhancement of this specific striped 4-mercaptopyridine adlayer renders FAOR a convenient test reaction to monitor self-assembly processes on Au(111).

The Origins of the High Performance of Pd Catalysts Supported on Carbon Black-Embedded Carbon Nanofiber for Formic Acid Oxidation

In this study, we developed a carbon black (CB)-embedded carbon nanofiber (CNF) as a Pd support, which showed a high level of formic acid oxidation reaction (FAOR) activity. For the support preparation, heat treatment involving calcination at 1000 °C in a nitrogen atmosphere (carbonization) followed by calcination at 850 °C in water vapor (steam activation) was conducted to form a CB, which contained carbon nanofibers made from a polyacrolynitrile (PAN) fiber prepared by electrospinning. This catalyst showed a high level of FAOR activity. In this situation, the CB was also heat-treated, therefore, it was unclear whether the origin of the high FAOR activity of the CB-embedded CNF was caused by the CNF itself or the heat treatment of the CB. In order to establish the cause of the high FAOR activity of the CB-embedded CNF, the CBs underwent several heat treatments; i.e., stabilization, carbonization, and steam activation. Two types of carbon black with different pore structures, i.e., Ketjen black and Vulcan XC-72, were used to investigate the FAOR activity. The appropriate heat treatment of the CB promotes the improved FAOR activity; however, excessive heat treatment caused a deterioration in the FAOR activity, especially for Ketjen due to the presence of numerous micropores. However, by embedding the CB into the CNF, the FAOR activity improved, especially in the case of Ketjen, even though the embedded CB underwent several heat treatments. The optimum ratio of CB/PAN in the CB-embedded CNF was also investigated. The highest FAOR activity was observed at 0.25 CB/PAN for both the Vulcan and Ketjen. The electronic state of Pd3d in which the binding energy of the metallic Pd shifted to a lower binding energy suggested that the metal–support interaction is strong at the CB/PAN ratio of 0.25. On the basis of these results, it was found that heat treatment of the CB by embedding it in the CNF is a promising way to achieve a metal–support interaction without destroying its structure.

Bi-modified Pt supported on carbon black as electro-oxidation catalyst for 300 W formic acid fuel cell stack

Formic acid is a chemical with a simple molecular structure containing hydrogen. This liquid at room temperature is easy to handle and has a low toxicity, and is thus in the spotlight as a fuel. In particular, formic acid is an excellent fuel candidate because it can be operated at low temperatures when applied as a fuel in fuel cells with a high theoretical open-circuit voltage (1.48 V). However, it has a drawback in that the electrode catalyst is deactivated due to the generation of CO intermediates when formic acid is oxidized during cell operation. Therefore, to prevent this, an irreversibly adsorbed Bi on Pt catalyst is applied to a direct formic acid fuel cell (DFAFC) anode because it is easy to synthesize and economical. Physical analyses such as transmission electron microscopy (TEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA) were conducted, and electrochemical evaluations were performed through half-cell and single-cell level tests. The results revealed that the formic acid oxidation reaction activity of the Bi-modified Pt/C was 13 times higher than that of the conventional catalyst at 0.58 V. Further, a DFAFC stack was fabricated using the Bi-modified Pt/C, which yielded a power of 300 W. These results suggest that a simple synthesis method can be applied to fabricating industrially available DFAFC stacks.

Atoms diffusion-induced phase engineering of platinum-gold alloy nanocrystals with high electrocatalytic performance for the formic acid oxidation reaction

Bimetallic noble metal nanocrystals have been widely applied in many fields, which generally are synthesized by the wet-chemistry reduction method. This work presents a purposely designed atoms diffusion induced phase engineering of PtAu alloy nanocrystals on platy Au substrate (PtAu-on-Au nanostructures) through simple hydrothermal treatment. Benefitting from the synergistic effects of component and structure, PtAu-on-Au nanostructures remarkably enhance the dehydrogenation pathway of the formic acid oxidation reaction (FAOR), and thus exhibit much higher FAOR activity and durability compared with Pt nanocrystals on platy Au substrate (Pt-on-Au nanostructures) and commercial Pd black due to an excellent stability of platy Au substrate and a high oxidation resistance of PtAu alloy nanocrystals. The atoms diffusion-induced phase engineering demonstrated in this work builds a bridge between the traditional metallurgy and modern nanotechnologies, which also provides some useful insights in developing noble metals based alloyed nanostructures for the energy and environmental applications.

Intriguing Catalytic Activity of Surface Active Gold‐Platinum Islands on Nano‐Porous Au in Determining Efficient Direct Formic Acid Oxidation Pathway

AbstractGold‐platinum nano‐porous structures (Au100‐xPtx NPoS) with unique surface enriched Au−Pt islands are synthesised through a galvanic replacement strategy from Au100‐xAg2x nano‐alloys with ultra‐low platinum loading (x=1.25, 2.5 and 5). Formic acid oxidation reaction (FAOR) on Au100‐xPtx/C NPoS shows a distinct peak at around 0.5 V related to CO2 formation. A characteristic peak at around 1.5 V increases with increasing FA concentration owing to the direct FAOR by nano‐porous Au centers. FAOR peaks and If/Ib peak current ratios indicates that, Au100‐xPtx/C NPoS facilitates direct FAOR pathway unlike HiSPEC Pt/C (dehydration pathway). Based on the enhanced chrono‐amperometric response, Tafel behaviour and mass activity values, Au97.5Pt2.5/C NPoS (5.5 A/mgPt) reflects as the optimal catalyst for efficient FAOR. The intriguing catalytic role of surface enriched Au−Pt islands present on nano‐porous Au greatly helps in determining the superior FAOR activity in Au97.5Pt2.5/C NPoS towards direct dehydrogenation pathway at ultra‐low Pt content compared to other NPoS and HiSPEC Pt/C catalysts.

Power Generation Characteristics of the Direct Formic Acid Fuel Cell Using Silica Containing Carbon Nanofiber as the Anode Supports

Direct formic acid fuel cells, DFAFCs, have received considerable attention due to their higher power density in the direct liquid fuel cells. Recently, 550 mW/cm2 of power density at 30 oC was reported by Chan et al. using Pd–Ni2 P/C catalyst for DFAFC anode [1]. In order to obtain the higher power density, the operation temperature of DFAFC should be elevated since anode and cathode reaction kinetics increases with the increasing operation temperature, however, it has been known that the power density of DFAFC above 50 oC showed plateau with the increasing temperature. As a reason of the plateau in the power desnity above 50 oC, the increase of the mass transport loss was considered [2]. Therefore, controlling the mass transport in the catalyst layer is one of the key factor to obtain high power density. In this context, the silica embedded carbon nanofiber, SECNF, support for DFAFC anode have been suggested in this study. By using SECNF as a catalyst support, both of the high porosity catalyst layer which can enhance the mass transport rate in the catalyst layer and the high catalystic activity due to the support metal effect of the silica have been expected. It was found that the formic acid oxidation reaction activity significantly increased by using SECNF as a support of Pd comparing to conventional Pd/CNF and Pd/C due to the support effect of the SiO2. Moreover, the high porosity anode electrode could be successfully fabricated by using Pd/SECNF. On the other hand, the power density of DFAFC was not enhanced due to thick catalyst layer. In the presentation, the effect of the porosity and thickness of catalyst layer on the anode mass transport loss and power generation characteristics will be discussed in detail. Reference [1] J. Chang, L. Feng, C. Liu, W. Xing, and X. Hu, Angew. Chemie Int. Ed., 53, 122–126 (2014). [2] T. Tsujiguchi, F. Matsuoka, Y. Hokari, Y. Osaka, and A. Kodama, Electrochim. Acta, 197, 32–38 (2016)

Power Generation Characteristics of the Direct Formic Acid Fuel Cell Using Silica Containing Carbon Nanofiber as the Anode Supports

In order to prepare high Pd containing Pd/SECNF (SiO2 containing carbon nanofiber) catalyst, which showed high formic acid oxidation reaction activity, the effect of the time and frequency on the ultrasonication before the chemical reduction process was investigated. It was found that 45 kHz and 45 min was the optimum condition. Based on this condition, Pd/SECNF containing 80 wt% of Pd was successfully prepared. Using this catalyst for the DFAFC anode, power generation characteristics was investigated. It was found that the performance was similar to the conventional DFAFC using Pd/C for anode catalyst although the catalytic activity of Pd/SECNF was higher than that of Pd/C. This is due to the high anode mass transport resistance in the anode catalyst layer in the case of Pd/SECNF.

Morphological impact onto organic fuel oxidation of nanostructured palladium synthesized via carbonyl chemical route

Nanostructured palladium (Pd) supported on carbon (Vulcan XC-72) substrate, prepared via carbonyl chemical route, showed Pd-mass depending morphology, reflected on the surface electrochemistry via cyclic, CO-stripping voltammograms, and performance in direct formic acid and direct methanol micro laminar flow fuel cell arrangement. Comparison was done with commercial Pd/C (30wt.%, ETEK) catalyst. The formic acid oxidation reaction (FAOR) studied in different acid media (0.1M HClO4, 0.5M H2SO4 and 0.5M H3PO4), indicated an enhanced FAOR activity on nanowire-like as compared to nanoparticles and nanorods as well as the commercial one in each electrolyte. Besides, the nanowire-like Pd/C catalyst also favored methanol (MOR) in 0.1M KOH. These facts confirm favorable morphological effect of nanowires for organic fuel oxidation in both acid and alkaline media.

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

1. Introduction Direct formic acid fuel cells, DFAFCs, have attracted as the alternative electric power source for the hydrogen fuel cells with a polymer electrolyte, PEFCs, due to the easy handling of the liquid fuel and the low operating temperatures. However, the power density of the DFAFCs are half or a forth comparing to that of PEFCs. Therefore, the enhancement of the catalyst activity is required in order to improve the power density of DFAFC. Ito et.al reported that PtRu nanoparticles supported on TiO2-embedded carbon nanofibers, PtRu/TECNF, showed a grate methanol electro- oxidation activity [1]. In this study, nanoparticle- embedded carbon nanofibers, PECNF, were proposed as a promising support of the Pd catalyst for the formic acid oxidation reaction. We prepared the PECNFs which contained three different nanoparticles (TiO2, SiO2, Vulcan XC-72R) as a support of the Pd catalyst and compared the formic acid oxidation reaction (FAOR) activities. 2. Experiment The nanofiber supports were prepared by the electrospinning of polyacrylonitrile (PAN) with nanoparticles followed by carbonization and steam activation of nanofiber as same as previous report [1]. The TiO2-emmbedded carbon nanofiber, SiO2-emmbedded carbon nanofiber and Vulcan carbon-emmbedded carbon nanofiber were denoted TECNF, SECNF and CECNF, respectively. 20 wt% of Pd nanoparticles were deposited on the prepared supports by the reduction of the Pd Cl2. The FAOR activities of the prepared catalysts were evaluated by the cyclic voltammetry, CV, in a three-electrode cell with a fixed glassy carbon electrode (GCE) (3-mm diameter) at room temperature. The electrolyte solution was a 3 M formic acid containing 0.5 M H2SO4. The CV measurements were conducted in the potential range from 0 to 1.2 V vs.NHE at the scan rate of 20 mV s-1 with N2 bubbling at room temperature. 3. Result and discussion Figure 1 shows the SEM images for the PECNFs obtained after steam activation. The surface of CNFs is flat, on the other hand, that of SECNFs is bumpy. We also confirmed that the surfaces of TECNF and CECNF were bumpy. The average diameter of fiber is approximately 300 nm in all the samples irrespective of with or without nanoparticles. Figure 2 shows the effect of the nanoparticles embedded in the CNF on the CV profile. For the comparisons, Pd/CNF and Pd/C were also shown in Fig.2. The highest FAOR activity of 3151 mA mg-Pd -1, which is 12.6 times higher than that of Pd/C, was obtained in the case of Pd/SECNF. Pd/TECNF and Pd/CECNF also showed higher FAOR activity, 618 mA mg-Pd and 1010 mA mg-Pd, respectively, than that of Pd/C. On the other hand, Pd/CNF showed lower FAOR activity than that of Pd/C. Therefore, it is found that the fiber structure was not contributed to the high FAOR activity. It has been reported that SiO2 and TiO2 showed strong metal-support interaction. Due to this, SECNF and TECNF showed higher FAOR activity. In case of CECNF, Vulcan contained in the CNF was carbonized and activated by steam with CNF. There is a possibility that Vulcan embedded in the CNF showed stronger metal-support than the Vulcan used in Pd/C by doing these treatments. Moreover, it is considered that the high activity of the PECNF is influenced by not only metal-support interaction but also the electrical conductivity. Based on these results, it was confirmed that the PECNF is the promissing support of the Pd for the FAOR. The highest catalyst activity was obtained using Pd/SECNF. This might be mainly attributed to the metal-support interaction between SiO2 and Pd 4. Conclusion Using PECNF, the FAOR activity was enhanced irrespective of the nanoparticles. Pd/SECNF showed the highest FAOR activity comparing to that of the other catalysts prepared in this study. Acknowledgement This work was supported by JST, PRESTO. Reference [1] Y.Ito et al,J.Power Sources 242(2013)280-288. Figure 1