Formic Acid Electrooxidation Research Articles

Conformal Solution Deposition of Pt-Pd Titania Nanocomposite Coatings for Light-Assisted Formic Acid Electro-Oxidation.

Many nanofabrication processes require sophisticated equipment, elevated temperature, vacuum or specific atmospheric conditions, templates, and exotic chemicals, which severely hamper their implementation in real-world applications. In this study, we outline a fully wet-chemical procedure for equipping a 3D carbon felt (CF) substrate with a multifunctional, titania nanospike-supported Pt-Pd nanoparticle (Pt-Pd-TiO2@CF) layer in a facile and scalable manner. The nanostructure, composition, chemical speciation, and formation of the material was meticulously investigated, evidencing the conformal coating of the substrate with a roughened layer of nanocrystalline rutile spikes by chemical bath deposition from Ti3+ solutions. The spikes are densely covered by bimetallic nanoparticles of 4.4 ± 1.1 nm in size, which were produced by autocatalytic Pt deposition onto Pd seeds introduced by Sn2+ ionic layer adsorption and reaction. The as-synthesized nanocomposite was applied to the (photo)electro-oxidation of formic acid (FA), exhibiting a superior performance compared to Pt-plated, Pd-seeded CF (Pt-Pd@CF) and commercial Pt-C, indicating the promoting electrocatalytic role of the TiO2 support. Upon UV-Vis illumination, the performance of the Pt-Pd-TiO2@CF electrode is remarkably increased (22-fold), generating a current density of 110 mA cm-2, distinctly outperforming titania-free Pt-Pd@CF (5 mA cm-2) and commercial Pt-C (6 mA cm-2) reference catalysts. In addition, the Pt-Pd-TiO2@CF showed a much better stability, characterized by a very high poisoning tolerance for in situ-generated CO intermediates, whose formation is hindered in the presence of TiO2. This overall performance boost is attributed to a dual enhancement mechanism (∼30% electrocatalytic and ∼70% photoelectrocatalytic). The photogenerated electrons from the TiO2 conduction band enrich the electron density of the Pt nanoparticles, promoting the generation of active oxygen species on their surfaces from adsorbed oxygen and water molecules, which facilitate the direct FA electro-oxidation into CO2.

Efficient anchoring of nanoscale Pd on three-dimensional carbon hybrid as highly active and stable catalyst for electro-oxidation of formic acid

The commercialization of fuel cells requires the design and development of novel effective electrocatalysts. Thus, considerable efforts have been directed at the synthesis of supported electrocatalyst particles with an optimum size of <6 nm and controlled shape/size. To date, although most studies have focused on the exploitation of supports facilitating charge/mass transfer and capable of inhibiting catalyst sintering/detachment during the catalytic process, comprehensive and straightforward investigation of the anchoring effect and the stabilization mechanism of complex hybrid supports with tunable electronic properties and tuned morphologies remain challenging. Herein, we prepare nanoscale Pd supported by a three-dimensional hybrid of boron-doped graphene with carbon nitride (Pd/BG-CN). The results show that the mass (2215 mA mg−1) and specific (31.7 mA cm−2) activities of Pd/BG-CN for formic acid oxidation are 2.8- and 2.5-fold higher than those of commercial Pd/C, respectively. This enhanced activity was ascribed to the electronic effect of the BG-CN substrate and the high content of surface metallic Pd0 (55.2 at%). Moreover, identical-location transmission electron microscopy imaging show that the stabilization of Pd particles on BG-CN and the strong anchoring effect of this support reduced the extent of active Pd detachment, whereas the weakening of metal–carbon support interactions in commercial Pd/C resulted in remarkable performance degradation. Theoretical calculations of the intrinsic stabilization mechanism of Pd/BG-CN reveal that BG-CN could efficiently trap Pd atoms, which could accumulate and form Pd clusters at trapping (nucleation) sites.

Highly active PtAu alloy surface towards selective formic acid electrooxidation

Highly active PtAu alloy surface towards selective formic acid electrooxidation

Catalytic activity of extruded and annealed Au–Ag alloys for the electro-oxidation of CH3OH and HCOOH

The catalytic activities of Au5-xAgx (x = 0, 1, 2 and 5) alloys for the electro-oxidation of methanol (CH3OH) and formic acid (HCOOH), together with their structure and microhardness, are studied in extruded and annealed states. For the electro-oxidation of CH3OH, the catalytic activity of Au–Ag alloys increases continually with increasing x; for HCOOH, the catalytic activity of Au–Ag alloys reaches the maximum as x = 1, indicating that the Ag addition can apparently improve the catalytic activity of Au–Ag alloys. Meanwhile, the catalytic activity of annealed Au for the electro-oxidation of CH3OH and HCOOH is lower, but that of annealed Au3Ag2 is higher than the extruded counterpart, indicating that annealing treatment has a complex effect on the catalytic activity of Au–Ag alloys. This complex effect is due to the fact that the changes of texture and twin crystal fraction of Au after annealing are different from those of Au3Ag2.

Copper iodide nanoparticles within the organic matrix: an efficient catalyst for the electro-oxidation of formic acid

The synthesis of ultrafine copper (I) iodide (CuI) nanoparticles has been reported using a modified route of ‘in situ polymerization and composite formation (IPCF)’ method (Mallick et al 2007 J. Phys. Condens. Matter 19 196225, Mallick et al 2012 J. Macromol. Sci. B 51 134–141). The CuI nanoparticles with the average size of 10 nm are dispersed within the polyaniline matrix. The as-synthesized composite material was characterized by optical, surface and microscopic techniques. The polymer stabilized CuI nanoparticles has also been applied as a catalyst for the electrochemical detection of formic acid. The cyclic voltammetry and the square wave voltammetry techniques were used in this study for the efficient electro-oxidation of the analyte. The result shows the gradual increase of current intensity due to the increase of formic acid concentration. A moderately good stability and performance has shown by the CuI nanoparticles based device for the electrochemical oxidation of formic acid with the sensitivity and limit of detection values of 0.0197 μA. mM−1. cm−2 and 0.048 mM, respectively.

Towards more active and stable PdAgCr electrocatalysts for formic acid electrooxidation: The role of optimization via response surface methodology

Towards more active and stable PdAgCr electrocatalysts for formic acid electrooxidation: The role of optimization via response surface methodology

Cu5Pt Dodecahedra with Low-Pt Content: Facile Synthesis and Outstanding Formic Acid Electrooxidation.

Tailoring composition and structure are significantly important to improve the utilization and optimize the performance of the precious Pt catalyst toward various reactions, which greatly relies on the feasible synthesis approach. Herein, we demonstrate that Cu-rich Cu5Pt alloys with unique excavated dodecahedral frame-like structure (Cu5Pt nanoframes) can be synthesized via simply adjusting the amounts of salt precursors and surfactants under hydrothermal conditions. It is established that the presence of hexamethylenetetramine and cetyltrimethylammonium bromide, as well as the selection of a proper Pt/Cu ratio are key for the acquisition of the target product. The immediate appeal of this material stems from frame-like architecture and ultralow Pt content involved, which can be used to greatly improve the utilization efficiency of Pt atoms. When benchmarked against commercial catalysts, the developed Cu5Pt nanostructures display superior electrocatalytic performance toward formic acid oxidation, owing to unique electronic effect and ensemble effect. This work elucidates a promising methodology for the synthesis of Pt-based nanostructures while highlights the significance of composition and structure in electrocatalysis.

Flower-like carbon supported Pd–Ni bimetal nanoparticles catalyst for formic acid electrooxidation

It is crucial to developing high-performance anode electrocatalysts for the direct formic acid fuel cell (DFAFC). Herein, we successfully synthesize a novel catalyst with Pd and Ni nanoparticles dispersed on flower-like carbon (Pd–Ni/C), which exhibits high reactivity and stability to formic acid electrooxidation. The 3D flower-like structure of carbon matrix provides fast substances transport and expose large catalytic active sites. Density functional theory results further confirm the existence of Ni can eliminate significantly the CO poison of Pd. The special hybrid structures and the unique synergistic effect of Pd and Ni, enable the Pd–Ni/C electrocatalysts to exhibit good electrocatalytic performance. Our results demonstrate that Pd–Ni/C are a promising candidate for the anode electrocatalysts of DFAFC.

Catalytic electrooxidation of formic acid by noble metal nanoparticle catalysts on reduced graphene oxide

The noble metals (Pt and Pd) loaded on polydopamine (PDA) modified graphene oxide (GO) as catalysts were prepared by a reduction. The catalysts were characterized by Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The reduced graphene oxide (rGO) was prepared for use as a matrix to integrate alloyed metal catalysts. The results show that the dispersed small-catalyst nanoparticles are loaded on both GO and rGO supports and the PtxPdy catalysts on rGO are smaller than the PtxPdy catalysts on GO. Both cyclic voltammetry (CV) and chronoamperometry (CA) results reveal that bimetallic PtxPdy/PDA-GO catalysts have superior activity, CO tolerance, electron transfer and stability towards formic acid oxidation, compared to PtxPdy/GO and the commercial PtRu/C catalyst. The bimetallic PtxPdy and PDA loaded on GO could be capable of enhanced oxidation and hopefully used in direct formic acid fuel cells.

Ethanol/Formic Acid Blend As an Alternative Fuel for the Pd-Based Direct Formic Acid Fuel Cells

Sustainable energy production is necessary for the next generation. Therefore, it is important to develop/improve a new series of energy technologies that are clean and efficient. A major interest is given to low-temperature fuel cells as an energy conversion device for different applications such as portable devices and electric vehicles. Formic acid is being analyzed and considered to be one of the most promising fuels that could replace methanol in direct liquid fuel cells for portable power applications. The electro-oxidation of formic acid takes place through a dual reaction pathway, dehydrogenation (direct pathway) and dehydration (indirect pathway). In the indirect pathway, a strongly adsorbed CO is produced which blocks the surface, while in the direct pathway CO2 is directly produced. As the direct pathway requires fewer surface atoms than the indirect pathway,1 one of the strategies to enhance the catalytic activity and stability of the catalyst is to modify its surface with ad-atmos2 or adsorbed species, making the direct pathway more favorable (third body or ensemble effect).3

Synthesis and characterization of Co, Zn, Mn, V modified Pd formic acid fuel cell anode catalysts

In this study, carbon nanotube (CNT) supported Pd50Co50, Pd50V50, Pd50Mn50, and Pd50Zn50 bimetallic catalysts are prepared by using sodium borohydride (NaBH4) reduction method to investigate their formic acid electrooxidation (FAEO) activities. These catalysts are characterized by using X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Inductively Coupled Plasma-Optical Emission Spectrometer (ICP-OES), and X-ray Photoelectron Spectroscopy (XPS). The XRD results show that the electronic state of catalysts varied by second metal addition to Pd. TEM results reveal that Pd and Co are homogeneously distributed. The result of Pd43Co57/CNT obtained by ICP-OES analysis of Pd50Co50/CNT catalyst shows that the synthesis was successfully synthesized. XPS results of Pd50Co50/CNT and Pd50Zn50/CNT catalysts showed that Pd, Zn, and Co atoms used in the preparation of the catalysts were obtained mainly in their elemental state. In addition, FAEO activity and stability of these catalysts are examined by using cyclic voltammetry (CV) and chronoamperometry (CA). Pd50Co50/CNT indicated the highest specific and mass activities with 6.89 mA/cm2 and 649.69 mA/mg Pd, respectively. Direct formic acid fuel cell (DFAFC) performances are performed in different temperatures for Pd50Co50/CNT catalyst. The specific current for DFAFC performance of this catalyst was evaluated as 5.71, 6.87, and 2.43 mA/cm2 at 18 °C, 30 °C, and 60 °C cell temperature at 0.5 V, respectively.

Adsorption of Acetate on Au(111): An in-situ Scanning Tunnelling Microscopy Study and Implications on Formic Acid Electrooxidation.

The adsorption of acetate on an Au(111) electrode surface in contact with acetic acid at pH 2.7 was imaged in-situ using scanning tunnelling microscopy (STM). Two different ordered structures were imaged for acetate adsorbed in the bidentate configuration on the unreconstructed surface at 0.95 V (vs. the saturated calomel electrode, SCE). The first structure, , is metastable and transforms at constant potential within 20 minutes to a structure, which is thermodynamically more favourable. The acetate adlayer starts to form at step edges and propagates via nucleation and growth onto terraces. The findings from in-situ STM are in agreement with the electrochemical behaviour of acetate on Au(111) characterized by voltammetry. A comparison is made with formate adsorption on Au(111). While acetate is not reactive, in contrast to formate, it can act as a spectator species in formic acid electrooxidation.

Trimetallic Synergy in Intermetallic PtSnBi Nanoplates Boosts Formic Acid Oxidation.

Platinum is the most effective metal for a wide range of catalysis reactions, but it fails in the formic acid electrooxidation test and suffers from severe carbon monoxide poisoning. Developing highly active and stable catalysts that are capable of oxidizing HCOOH directly into CO2 remains challenging for commercialization of direct liquid fuel cells. A new class of PtSnBi intermetallic nanoplates is synthesized to boost formic acid oxidation, which greatly outperforms binary PtSn and PtBi intermetallic, benefiting from the synergism of chosen three metals. In particular, the best catalyst, atomically ordered Pt45 Sn25 Bi30 nanoplates, exhibits an ultrahigh mass activity of 4394 mA mg-1 Pt and preserves 78% of the initial activity after 4000 potential cycles, which make it a state-of-the-art catalyst toward formic acid oxidation. Density functional theory calculations reveal that the electronic and geometric effects in PtSnBi intermetallic nanoplates help suppress CO* formation and optimize dehydrogenation steps.

New Electrochemical Approach for the Synthesis of Pd‐PdO/C Electrocatalyst and Application to Formic Acid Electrooxidation

AbstractPd‐PdO/C catalyst for formic acid electrooxidation has been synthesized via electrochemical dispersion of Pd foil electrodes under pulse alternating current conditions in NaCl aqueous electrolyte. About 35 wt% of the as‐prepared Pd‐PdO/C specimen is PdO as revealed by X‐ray diffraction. The microstructural characteristics and catalytic activity of the synthesized Pd/C catalyst have been compared with those of a Pt/C catalyst prepared under the same conditions. Pd nanoparticles of Pd‐PdO/C catalyst exhibit smaller average dimensions and narrower particle size distribution – 7.4±0.5 nm and 1.9±0.5 respectively for Pd and PdO particles. The process of ethanol electrooxidation on the catalyst was characterized by high overvoltage (up to 800 mV). The overvoltage of the formic acid electrochemical oxidation on Pd/C is 590 mV less than on Pt/C.

Ternary CoPtAu Nanoparticles as a General Catalyst for Highly Efficient Electro-oxidation of Liquid Fuels.

Efficient electro-oxidation of formic acid, methanol, and ethanol is challenging owing to the multiple chemical reaction steps required to accomplish full oxidation to CO2 . Herein, a ternary CoPtAu nanoparticle catalyst system is reported in which Co and Pt form an intermetallic L10 -structure and Au segregates on the surface to alloy with Pt. The L10 -structure stabilizes Co and significantly enhances the catalysis of the PtAu surface towards electro-oxidation of ethanol, methanol, and formic acid, with mass activities of 1.55 A/mgPt , 1.49 A/mgPt , and 11.97 A/mgPt , respectively in 0.1 m HClO4 . The L10 -CoPtAu catalyst is also stable, with negligible degradation in mass activities and no obvious Co/Pt/Au composition changes after 10 000 potential cycles. The in situ surface-enhanced infrared absorption spectroscopy study indicates that the ternary catalyst activates the C-C bond more efficiently for ethanol oxidation.

Glycerol and formic acid electro-oxidation over Pt on S-doped carbon nanotubes: Effect of carbon support and synthesis method on the metal-support interaction

The effects of catalyst support and synthesis process on the interaction between Pt nanoparticles (NPs) and S-doped carbon nanotubes (SCNTs), and the resultant electro-oxidation catalytic performance of glycerol, formic acid and CO were systematically researched. Pt NPs on SCNTs had better electro-oxidation catalytic performances than that of Pt NPs on CNTs. The doped S in thiophene-like structure (C-S-C) activated the neighboring C atoms to interact with Pt NPs, improving the catalytic performance with stronger ability to remove poisonous intermediates. The formed C-S-C had a synergistic effect with the neighboring Pt-C, promoting the adsorption and activation of reactants. The improved metal-support interaction resulted in Pt with smaller nanoparticle size and more exposed active sites. In different synthesis process, Pt NPs were more likely to interact with activated C neighboring S in ethylene glycol reduction method. However, defects containing doped S preferred to interact with Pt NPs in impregnation method. The research results indicated that rationally regulating the surface properties of carbon support and choosing an appropriate catalyst synthesis strategy to intensify the required metal-support interaction can greatly improve the catalytic performance.

Carbon monoxide and formic acid electrooxidation study on Au decorated Pd catalysts prepared via microwave assisted polyol method

In this study, carbon supported Pd monometallic and PdAu bimetallic catalysts are prepared by using microwave assisted polyol method to investigate their carbon monoxide and formic acid electrooxidation activities. These catalysts are characterized by using Scanning Electron Micrsocopy (SEM-EDX) and N2 adsorption desorption measurements. EDX measurements reveal that catalysts are prepared at desired ratios. The electrochemical characterization was performed via cyclic voltammetry and CO stripping voltammetry. Electrochemical surface area (ECSA) was calculated thanks to CO oxidation peaks. It was reported that CO tolerance and ECSA of the PdAu/C catalysts were higher than that of the Pd/C, attributed to sweeping effect of Au particles in terms of CO adsorption. Furthermore, formic acid electrooxidation activity of these catalysts are examined by using cyclic voltammetry (CV). PdAu/CNT catalyst at prepared at 90:10 Pd:Au ratio exhibited the highest formic acid electroxidation activity. It is clear that PdAu/CNT catalyst is a promising catalyst for CO and formic acid electrooxidation.

Controlled organization of building blocks to prepare three-dimensional architecture of Pd–Ag aerogel as a high active electrocatalyst toward formic acid oxidation

Among self-assembled architectures, noble metal aerogels have emerged as state-of-the-art catalysts, and these unique architectures play a vital role in widespread applications. Until now, profuse ways have been introduced for the development and synthesis of noble metal aerogels, which suffer from long gelation time as well as complexity. In this work, a facile and efficient method is presented to create the Pd–Ag aerogel. This route offers advantages such as a surfactant-free route, short gelation time and a simple strategy. The Pd–Ag aerogel was prepared under controlled condition by using a galvanic displacement of sacrificial Ag nanoparticles with H2PdCl4 followed by supercritical CO2 drying. Porous three-dimensional architecture of Pd–Ag aerogel is confirmed by the TEM, FESEM, XRD, ICP-AES and N2 isotherm. The resultant aerogel displays exceptional catalytic activity and durability toward electro-oxidation of formic acid on account of two vital reasons: 1) the unique architecture of resultant aerogel reflects exceptional advantages such as meso-and macroporous properties, and 2) the combination of Ag with Pd, leading to the acceleration in the oxidation of formic acid (synergistic effects).

PdCu alloy nanoparticles supported on CeO2 nanorods: Enhanced electrocatalytic activity by synergy of compressive strain, PdO and oxygen vacancy

Metal oxides have been widely studied as promoter of catalytic performance of metal catalysts through the strong metal-support interactions. However, the mechanism behind it is still debating. Here a series of PdCu nanoparticles with size from 4.9 to 15.4 nm are prepared and loaded on CeO2 nanorods, which are further characterized by HRTEM, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electrochemical CO stripping. The coupling of PdCu nanoparticles and CeO2 nanorods induces compressive strain on PdCu nanoparticles, which is strongly dependent on the size of PdCu nanoparticles. The correlation among the compressive strain, down-shift of the d-band center, reduced CO binding energy and augmentation of PdO content for PdCu nanoparticles is further discussed in details. Based on comprehensive analyses, it is concluded that the reduced CO oxidation potential on PdCu nanoparticles upon CeO2 support is from enhanced PdO on PdCu, while the synergy of compressive strain, enhanced PdO and oxygen vacancy remarkably promotes the catalytic performance of PdCu towards electrooxidation of formic acid.

Layered Au-Pd-Au nanorod catalysts: Pd-layer thickness effects on catalyst performance

Au/Pd/Au and Au/Pd layered nanorods (NR) with different Pd thickness, down to 15 nm, are electrodeposited in Si-supported porous anodized aluminum thin film templates. These structures are, in contrast to Au-Pd core-shells, mechanically relaxed, so that chemical and electronic interaction effects between Au and Pd are expected to predominate in controlling their performance in the electrooxidation of formic acid. The XRD results are conclusive about the formation of pure metal layers, but a corrugated Au/Pd interface is revealed by scanning electron microscopy. The CV behavior of the different structures shows that the PdO reduction peak is shifted towards more noble values as the Pd thickness decreases. Regarding the electrocatalytic oxidation behavior there is a substantial increase in performance with decreasing Pd-layer thickness. It is further shown that the Au/Pd/Au nanostructures perform better than the Au/Pd bilayer structure for the same Pd layer thickness. Also the long term behavior is improved. Both CV and electrocatalytic behaviors are discussed in terms of interfacial intermixing between Pd and Au at the nanoscale and a higher interface contribution for thinner Pd layers.