Activity For Formic Acid Oxidation Research Articles

Electrodeposited Pt–Pd dendrite on carbon support as anode for direct formic acid fuel cells

The activity of bimetallic catalyst is predominantly determined by its composition and its shape. In this work, Pt–Pd bimetallic catalysts were codeposited using cyclic voltammetry on a carbon black-coated carbon paper at two different potential ranges (0 to 1.3 V and − 0.2 to 1.3 V vs. SHE) and with two different Pt precursors (H2PtCl6 and K2PtCl4). SEM analysis revealed that the deposit obtained from both K2PtCl4 and H2PtCl6 precursor resembled the shape of a flower-like dendrite when the deposition potential window was in the range of 0 to 1.3 V. However, shifting the lower potential limit from 0 to − 0.2 V resulted in a leaf-like dendritic structure, irrespective of the Pt precursor used. Leaf-like dendritic structures showed enhanced formic acid oxidation activity with high mass activity and superior stability compared to flower-like structures. The superior performance of the leaf-like structure was clearly evident from fuel cell polarization studies carried out at 70 °C, which showed a maximum power density of 49 mW cm−2, whereas flower-like structures showed a power density of 20 mW cm−2.

Pd and polyaniline nanocomposite on carbon fiber paper as an efficient direct formic acid fuel cell anode

Direct formic acid fuel cells are advantageous as portable power generating devices. In the present work, an anode catalyst for direct formic acid fuel cell (DFAFC) is presented which has good catalytic activity for formic acid oxidation. The catalyst is composed of Pd and conducting polymer polyaniline (Pd-PANI) nanocomposite. The catalyst was prepared by using a single step galvanostatic electrochemical deposition method. The Pd-PANI catalyst was electrodeposited at different time durations and a comparison of the catalytic activity at each deposition time was carried out and optimized.

Enhanced Electrocatalytic Oxidation of Formic Acid on Au(111) in the Presence of Pyridine

The adsorption of pyridine on Au(111) single crystal electrodes has been systematically studied in a broad range of pH values between 1 and 13. From the voltammetric features of Au(111) in 0.1 M pyridine a potential/pH diagram has been derived, which classifies various phases for adsorbed pyridine. At sufficiently high concentrations of unprotonated pyridine in solution, a significantly enhanced activity for formic acid oxidation on Au(111) is observed in a narrow potential region, where strongly bound formate has not yet reached its saturation coverage. The various pyridine structures exhibit different enhancement factors. At positive potentials, the typical features of formic acid oxidation on Au(111) are present, pointing toward complete replacement of adsorbed pyridine by formate.

PtAu katalizator sa poboljšanom aktivnošću za reakciju oksidacije mravlje kiseline

PtAu systems are recognized as good catalysts for the oxidation of formic acid electrooxidation, which is investigated as a possible anodic reaction in low-temperature fuel cells. In this research, bimetallic PtAu nanoparticles, supported on high area carbon Vulcan XC-72R, were synthesized by water in oil microemulsion method. The precursor reduction process took place in a single microemulsion, simultaneously, in the presence of 35% of HCl in the water phase, as a capping agent. Electrochemical behavior of the PtAu/C catalyst was investigated at as prepared electrodes by cyclic voltammetry in 0.5M H2SO4 as a supporting electrolyte, and also in the oxidation of adsorbed CO. The results were compared to the Pt/C catalyst prepared by the same synthesis procedure. PtAu/C catalyst powder was also characterized by X-Ray Diffraction (XRD), High Resolution Transmission Electron Microscopy (HRTEM) and Energy Dispersive X-Ray Spectroscopy (EDS). Average particle diameter, of 2nm, was calculated from XRD data, which is close to the value of 2.82 nm obtained from TEM images. Compared to identically synthesized Pt nanoparticles, the bimetallic ones are significantly smaller. EDS maps of PtAu/C sample confirm the presence of both elements, and indicate a very fine distribution of Au in the sample. Elemental composition of about 20% Au and 80% Pt was also determined from these maps. Prepared catalyst was tested for formic acid electro-oxidation in terms of its activity and stability over the long term cycling. The voltammograms recorded indicate the change of reaction mechanism and better utilization of the catalyst surface in comparison to Pt/C.

Pd–Zn nanocrystals for highly efficient formic acid oxidation

Highly uniform Pd–Zn nanocrystals were facilely fabricated with coexisting noble metals and ascorbic acid, which exhibited superior electrocatalytic activity for formic acid oxidation.

Efficient Direct Formic Acid Fuel Cells (DFAFCs) Anode Derived from Seafood waste: Migration Mechanism

Commercial Pt/C anodes of direct formic acid fuel cells (DFAFCs) get rapidly poisoned by in-situ generated CO intermediates from formic acid non-faradaic dissociation. We succeeded in increasing the Pt nanoparticles (PtNPs) stability and activity for formic acid oxidation (DFAFCs anodic reaction) by embedding them inside a chitosan matrix obtained from seafood wastes. Atop the commercial Pt/C, formic acid (FA) is predominantly oxidized via the undesired poisoning dehydration pathway (14 times higher than the desired dehydrogenation route), wherein FA is non-faradaically dissociated to CO resulting in deactivation of the majority of the Pt active-surface sites. Surprisingly, PtNPs chemical insertion inside a chitosan matrix enhanced their efficiency for FA oxidation significantly, as demonstrated by their 27 times higher stability along with ~400 mV negative shift of the FA oxidation onset potential together with 270 times higher CO poisoning-tolerance compared to that of the commercial Pt/C. These substantial performance enhancements are believed to originate from the interaction of chitosan functionalities (e.g., NH2 and OH) with both PtNPs and FA molecules improving FA adsorption and preventing the PtNPs aggregation, besides providing the required oxygen helping with the oxidative removal of the adsorbed poisoning CO-like species at low potentials. Additionally, chitosan induced the retrieval of the Pt surface-active sites by capturing the in-situ formed poisoning CO intermediates via a so-called “migration mechanism”.

Selective Surface Engineering of Heterogeneous Nanostructures: In Situ Unraveling of the Catalytic Mechanism on Pt–Au Catalyst

Heterogeneous nanostructures hold substantial promise in many fields including energy conversion and catalysis, and their functionality is largely determined by the interactive surface features of respective architectural components. Herein, we report the facile preparation of a Pt–Au heterogeneous nanostructure, which as a model exhibits not only the enhanced electrocatalysis for oxygen reduction reaction (ORR) and ethanol oxidation reaction (EOR), but also an unprecedented activity for formic acid oxidation (FAO). Further, selective under-potential deposition coupled with CO adsorption is employed to probe the electrocatalytic mechanism of the Pt–Au heterogeneous nanostructure. The electronic effect is clarified for the ORR and EOR mechanisms on the Pt–Au nanostructure. A synergetic mechanism in that Pt ruptures the C–H bond of HCOOH and Au converts the resulted −COOH into CO2 is revealed for FAO. This strategy provides a versatile and powerful tool for the selective surface engineering and in-depth ana...

Deposition of Pt Nanoclusters on Au and Their Catalytic Activity

Electrocatalytic studies of Pt nanoclusters (Pt-nc) distributed on foreign metals have shown to exhibit different and often much higher activity than the bulk Pt. In recent years, 2D Pt sub-ML catalysts designed using surface limited redox replacement reaction (SLRR) of an underpotentially deposited (UPD) monolayer of Cu have been used as model systems in studies of the coverage-dependant behaviour during formic acid, methanol, ethanol and hydrogen oxidation reactions.1-4 The effects of the substrate (ligand effect) as well as the size-dependant strain (geometric effect) have been suggested to play an important role in the Pt-nc activity. However, studies on single layered and multilayer Pt-nc suggests that there is an important correlation between the nanoclusters size (2D and 3D) and coverage (controlling the methods of deposition) that needs to be understood better.5 Formic acid oxidation (FAO) is an ideal reaction to study as a function of size and coverage of Pt-nc as many studies recently reported the low-coverage Pt-nc on Au as the ‘most active’ bimetallic system configurations for this reaction.2, 6-8 Here in this talk we will present a study of FAO activity and stability dependence on the size and coverage of 2D and 3D Pt-nc designed by two different methods: spontaneous deposition and the SLRR via Pb UPD. SD is a method that produces uniformly distributed multi-layered Pt-nc by reduction of the spontaneously adsorbed [PtCl4]2- complex.9A systematic study of Pt-nc coverage and distribution included the time of the Pt-complex adsorption and the number of the applied SD cycles on the evolution of the 3D nature of Pt-nc as well as the distribution i.e. on Au substrate coverage. A particular attention was given to the different surface processes used as analytical tools for the determination of Pt coverage: 1) oxidation/reduction of AuO and PtO surface oxides and 2) adsorption processes such as H-UPD and CO. The discrepancies in the values of Pt coverage obtained by different methods requires better understanding of these processes on Pt-nc/Au. The study has shown that up to 5 SD cycles the Pt-nc size and coverage increases up to ~ 60% of Au substrate coverage. Subsequent cycles results in the growth of exiting Pt-nc height but not in the formation of new clusters. The SLRR deposition of 2D Pt-nc using Pb UPD has been controlled by galvanic replacement of electrodeposited Pb-sub ML layer on Au. The study of isolated Pt-nc of comparable coverage (0.23 ±0.02) created by SD and SLRR methods showed the differences in their FAO behaviour that can be attributed to the clusters size (2D and 3D) and coverage. The analysis showed that SD Pt-nc with smaller diameter but larger variation of height than SLRR Pt-nc exhibit 5 times higher activity for FAO. Stability of SD and SLRR Pt-nc during FAO cycling showed that both Pt-nc structures follow a similar trend of changes that can be correlated with the dissolution of Pt. The SD Pt-nc however, showed higher (longer) stability during FAO that could be attributed to their size and larger percentage of 2ML height clusters compared to the SLRR Pt-nc.

A facile synthesis of high activity cube-like Pt/carbon composites for fuel cell application

High activity catalyst with simple low-cost synthesis is essential for fuel cell commercialization. In this study, a facile procedure for the synthesis of cube-like Pt nanoparticle (PtCube) composites with high surface area carbon supports is developed by mixing precursor of Pt with carbon supports in organic batches, hence, one pot synthesis. The PtCube grow with Vulcan XC-72 or Ketjen black, respectively, and then treated for 5.5 h at 185oC (i.e., PtCube5.5/V and PtCube5.5/K). The resulting particle sizes and shapes are similar; however, PtCube5.5/K has a larger electrochemical active surface area (EASA) and a remarkably better formic acid (FA) oxidation performance. Optimization of the PtCube/K composites leads to PtCube10/K that has been treated for 10 h at 185oC. With a larger EASA, PtCube10/K is also more active in FA oxidation than the other PtCube/K composites. Impedance spectroscopy analysis of the temperature treated and asprepared (i.e., untreated) PtCube/K composites indicates that PtCube10/K is less resistive, and has the highest limiting capacitance among the PtCube/K electrodes. Consistently, the voltammetric EASA is the largest for PtCube10/K. Furthermore, PtCube10/K is compared with two commercial Pt/C catalysts, Tanaka Kikinzoku Kogyo (TKK), and Johnson Matthey (JM)Pt/C catalysts. The TKK Pt/C has a higher EASA than PtCube10/K, as expected from their relative particles sizes (3–4 nm vs. 6–7 nm for PtCube10/K), however, PtCube10/K has a significantly better FA oxidation activity.

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

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

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.

Electrocatalytic Oxidation of Formate and Formic Acid on Platinum and Gold: Study of pH Dependence with Phosphate Buffers

The effect of electrolyte pH on the electrooxidation of formic acid/formate is studied using cyclic voltammetry on polycrystalline rotating disk and single-crystalline Pt and Au electrodes in phosphate-based solutions over a wide range of pH (1–12). A non-linear relationship between oxidation current and pH at constant overpotential is identified for both metals. Surface structure influences the reaction for both Pt and Au electrodes. The results in terms of pH dependence are in agreement with those reported in literature. However, experimental evidence shows that adsorbed phosphates cause dramatic changes in the behaviour of the oxidation of formic acid on Pt and Au electrodes due to site blocking and competitive adsorption. The pH dependence on the catalytic activity for formic acid oxidation on Pt is more complex, due to the poisoning of the electrodes by adsorbed CO in addition to intricate anion adsorption effects. The role of the phosphates in the electrocatalyzed reaction is more than maintaining the pH of the system. Rather, various phosphate anions strongly adsorb on the surface, block reactive surface sites and quantitatively decrease oxidation currents. The blocking effect of the phosphate anions increases with increasing pH value. A more considerable blocking effect is established for Au. In addition, a strong pH dependence on overpotential is identified for Pt. In general, oxidation kinetics of formic acid depends strongly on pH, the nature of the adsorbed phosphate species and the electrode potential.

Highly active carbon nanotube-supported Ru@Pd core-shell nanostructure as an efficient electrocatalyst toward ethanol and formic acid oxidation

Herein, we report the facile synthesis of core-shell structured Ru@Pd/multi-walled carbon nanotube (MWCNT) catalyst via a two-step chemical reduction process without any surfactant and its electro-catalytic performance for ethanol and formic acid oxidation. X-ray diffraction (XRD) and transmission electron microscopy (TEM) results revealed that the Ru@Pd nanoparticles are quite uniformly distributed on the surface of MWCNT with an average particle size of 2.3nm. X-ray photoelectron spectroscopy (XPS) analysis showed the strong charge transfer interaction between Pd and Ru atoms on catalytic surface. The electrochemical studies demonstrated that the Ru@Pd/MWCNT catalyst exhibits higher peak current density and significantly enhanced long-term stability toward the anodic oxidation of ethanol in alkaline medium. Its electro-catalytic activity for ethanol oxidation is 1.8 and 2.7 times higher than that of Pd/MWCNT and commercial Pd/C catalysts, respectively, indicating the high utilization of Pd in as-prepared Ru@Pd/MWCNT catalyst. Moreover, the Ru@Pd/MWCNT also presents the enhanced electro-catalytic activity for formic acid oxidation (FAO) in acidic medium. This study opens up a new way for the fabrication of Pd-based electrocatalysts with high performance and low cost.

A rapid synthesis of high surface area PdRu nanosponges: Composition-dependent electrocatalytic activity for formic acid oxidation

Here, PdRu nanoparticle networks (NPNs) with various compositions were synthesized through an inexpensive method in water as a green solvent, at different ratios of the H2PdCl4 and RuCl3 precursors. This is a fast, room temperature and surfactant free strategy which is able to form high surface area metal nanosponges with a three-dimensional (3D) porous structure. The structure of as-prepared nanosponges was characterized using the techniques of field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS) and cyclic voltammetry (CV). Then, the electrocatalytic activities of PdRu NPNs towards formic acid oxidation were examined by electrochemical measurements including CV, chronoamperometry, and electrochemical impedance spectroscopy (EIS). Based on studies, it was found that the current density of formic acid oxidation (FAO) is strongly dependent on the composition of PdRu NPNs. The best performance was realized for Pd4Ru1 NPNs compared to monometallic Pd counterpart and other bimetallic NPNs which might be ascribed to the role of Ru in the decrease of CO adsorption strength on the catalyst and consequently the priority of formic acid oxidation through the direct pathway. The Pd4Ru1 NPNs also showed the maximum current density and stability in chronoamperometric measurements. In addition, comparative studies were performed between as-prepared NPNs and CNTs-supported Pd nanoparticles (Pd NPs/CNTs). The present results demonstrated the unique structural advantages of NPNs compared to individual Pd NPs supported on the CNT which leads to the promising performance of NPNs as supportless catalysts for the oxidation of formic acid.

Preparation of carbon-supported Pd-decorated PtCu nanoparticles towards formic acid oxidation reaction

This work reports the synthesis of a novel carbon-supported Pd-decorated PtCu nanocatalyst for formic acid oxidation. Without using surfactants or polymers, PtCu alloy was firstly prepared through simply co-reduction of Pt and Cu ions using ethylene glycol and sodium citrate as the reducing and stabilizing reagents. Then, Pd was decorated on the surface of PtCu through spontaneous replacement of Cu by Pd. XRD results suggest that the lattice parameters of the PtCu and Pd-decorated PtCu nanoparticles are smaller than that of Pt. TEM images show that all metallic nanoparticles are well dispersed on the carbon surface. The average particle size of the Pd-decorated PtCu nanoparticles is 2.9 nm. Electrochemical analysis suggests that the carbon-supported Pd-decorated PtCu nanocatalyst exhibits an enhanced activity for formic acid oxidation in comparison with the carbon-supported Pt and carbon-supported PtCu, as well as a high stability in acidic medium.

Pt-Au Film Catalyst for Formic Acid Oxidation

Direct formic acid fuel cells (DFAFCs) have shown promise as efficient and renewable power sources for portable electronics. However, pure Pt catalysts exhibit poor activity for the formic acid oxidation reaction (FAOR) due to the formation of poisoning species, which slow down the rate of oxidation. Here, we report on the novel synthesis of a bimetallic, Pt-Au film electrocatalyst for the oxidation of formic acid (HCOOH). A bilayer stack composed of individual Pt and Au metal layers was deposited using magnetron sputtering, resulting in a smooth surface consisting of tightly packed nanocrystallites. At room temperature, the bilayer stack shows the electrochemical characteristics of a pure Pt surface. A post-synthesis heat treatment was carried out to form a bimetallic film consisting of the two metals. As a result, the heat-treated film showed electrochemical characteristic of both metals, indicating a mixed metal surface. The Pt-Au catalyst surface exhibited greatly enhanced activity for formic acid oxidation compared to a commercial bulk Pt catalyst. The presence of Au on the catalyst surface promotes the oxidation of formic acid through the direct dehydrogenation pathway, via the ensemble effect. Therefore, the heat treatment of a sputtered bilayer stack provides a simple method for forming stable bimetallic Pt-Au catalysts with high activity for the oxidation of formic acid.

Branched PdAu nanowires with superior electrocatalytic formic acid oxidation activities

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

PdCu alloy nanoparticle-decorated copper nanotubes as enhanced electrocatalysts: DFT prediction validated by experiment

In order to combine the advantages of both 0D and 1D nanostructured materials into a single catalyst, density functional theory (DFT) calculations have been used to study the PdCu alloy NP-decorated Cu nanotubes (PdCu@CuNTs). These present a significant improvement of the electrocatalytic activity of formic acid oxidation (FAO). Motivated by our theoretical work, we adopted the seed-mediated growth method to successfully synthesize the nanostructured PdCu@CuNTs. The new catalysts triple the catalytic activity for FAO, compared with commercial Pd/C. In summary, our work provides a new strategy for the DFT prediction and experimental synthesis of novel metal NP-decorated 1D nanostructures as electrocatalysts for fuel cells.

Composition–controlled Synthesis of PtCuNPs Shells on Copper Nanowires as Electrocatalysts

AbstractPtCuNPs‐shells with adjustable composition on copper nanowires (CuNWs) are synthesized in an organic solvent. Transmission electron microscopy, X‐ray diffraction, energy dispersive spectroscopy, and X‐ray photoelectron spectroscopy (XPS) measurement techniques are used to analyze the structure and surface composition of the as‐prepared PtCuNPs‐coated CuNWs (PtCu/CuNWs). The XPS results verify that the incorporation of Cu in the PtCuNPs‐shells modified electronic state of Pt, which could further tune the formic acid oxidation (FAO) activity. Electrochemical measurements show that their FAO activities are strongly dependent on the PtCuNPs‐shells composition. Our results show that PtCu/CuNWs with atom Pt:Cu ratio of 2:15 (PtCu/CuNWs‐(2:15)) have the optimal shell composition and show the best FAO performance, with a specific activity of 0.92 mA cmPt−2 and a mass activity of 0.54 A mgpt−1 at 0.5 V (vs. RHE), which are 6.6‐ and 6.0‐fold enhancements over those of the commercial Pt/C (0.14 mA cmPt−2 and 0.09 A mgpt−1) catalyst.

Ultra-low Pt decorated PdFe Alloy Nanoparticles for Formic Acid Electro-oxidation

Palladium (Pd), has demonstrated promising electro-catalytic activity for formic acid oxidation, but suffers from extremely low abundance. Recently alloying with a transition metal has been considered as an effective approach to reducing the loading of Pd and enhancing the activity of Pd-based catalysts simultaneously. Herein, carbon supported PdFe nanoparticles (NPs) are synthesized at room temperature by using sodium borohydride as reducing agent and potassium ferrocyanide as Fe precursor. The Pd50Fe50 alloy sample annealed at 900°C for 1h shows the best catalytic activity among PdxFe1-x (x=0.2, 0.4, 0.5, 0.6, and 0.8) towards formic acid oxidation. To further improve both catalytic activity and stability, the ultra-low Pt (0.09wt %) decorated Pd50Fe50 NPs (PtPd/PdFe) are prepared via the galvanic replacement reaction. Compared with Pd50Fe50/C, the PtPd/PdFe/C Exhibits 1.52 times higher catalytic activity and lower onset potential (−0.12V). The significant enhancements of formic acid oxidation can be attributed to the accelerated dehydrogenation reaction of formic acid by Pt atomic clusters. Moreover, the PtPd/PdFe/C also demonstrates better tolerance to poisons during formic acid oxidation.