Formic Acid Electrooxidation Research Articles

Bifunctional Tailoring of Platinum Surfaces with Earth Abundant Iron Oxide Nanowires for Boosted Formic Acid Electro-Oxidation

To expedite the marketing of direct formic acid fuel cells, a peerless inexpensive binary FeOx/Pt nanocatalyst was proposed for formic acid electro-oxidation (FAO). The roles of both catalytic ingredients (FeOx and Pt) were inspired by testing the catalytic performance of FAO at the FeOx/Au and FeOx/GC analogies. The deposition of FeOx proceeded electrochemically with a post‐activating step that identified the catalyst’s structure and performance. With a proper adaptation for the deposition and activation processes, the FeOx/Pt nanocatalyst succeeded to mitigate the typical CO poisoning that represents the principal element deteriorating the catalytic performance of the direct formic acid fuel cells. It also provided a higher (eightfold) catalytic efficiency than the bare Pt substrates toward FAO with a much better durability. Field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) were all employed to inspect, respectively, the surface morphology, bulk composition, and crystal structure of the catalyst. The electrochemical impedance spectra could correlate the charge transfer resistances for FAO over the inspected set of catalysts to explore the role of FeOx in mediating the reaction mechanism.

Fabrication of CuOx-Pd Nanocatalyst Supported on a Glassy Carbon Electrode for Enhanced Formic Acid Electro-Oxidation

Formic acid (FA) electro-oxidation (FAO) was investigated at a binary catalyst composed of palladium nanoparticles (PdNPs) and copper oxide nanowires (CuOxNWs) and assembled onto a glassy carbon (GC) electrode. The deposition sequence of PdNPs and CuOxNWs was properly adjusted in such a way that could improve the electrocatalytic activity and stability of the electrode toward FAO. Several techniques including cyclic voltammetry, chronoamperometry, field-emission scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction were all combined to report the catalyst’s activity and to evaluate its morphology, composition, and structure. The highest catalytic activity and stability were obtained at the CuOx/Pd/GC electrode (with PdNPs directly deposited onto the GC electrode followed by CuOxNWs with a surface coverage,Г, of ca. 49%). Such enhancement was inferred from the increase in the peak current of direct FAO (by ca. 1.5 fold) which associated a favorable negative shift in its onset potential (by ca. 30 mV). The enhanced electrocatalytic activity and stability (decreasing the loss of active material by ca. 1.5-fold) of the CuOx/Pd/GC electrode was believed originating both from facilitating the direct oxidation (decreasing the time needed to oxidize a complete monolayer of FA, increasing turnover frequency, by ca. 2.5-fold) and minimizing the poisoning impact (by ca. 71.5%) at the electrode surface during FAO.

Electrooxidation of formic acid enhanced by surfactant-free palladium nanocubes on surface modified graphene catalyst

Direct Formic Acid Fuel Cells (DFAFCs) have been extensively focused and rapidly growing as one of alternative energy systems for portable devices and automobiles. However, power energy requires the active and selective metal nanocatalysts to perform the highest electrochemical activity. Here, we propose a nanocubic shape of palladium nanoparticles (PdNPs) decorated on functionalized graphene (fG), where surface modification is obtained by surfactant free method. The 11 nm and high dispersion of Pd nanocubes (PdNCs), which are majorly enclosed with (1 0 0) indicated by XRD and HRTEM results, are successfully deposited on functionalized graphene (PdNCs/fG) and used as an enhanced electrocatalysts for formic acid oxidation. Our PdNCs/fG catalyst displays a remarkable mass activity towards formic acid oxidation (494.50 A/g, over 100 times) compared to commercial catalysts of Pd/C, and over 20 times to PdNPs on unmodified graphene or reduced graphene oxide (PdNPs/rGO). Moreover, our catalyst exhibits better stability and higher CO resistance. The PdNCs/fG catalyst also generates the superior specific activity towards formic acid oxidation to 20.37 A/m2. The study demonstrates the synergistic effect of high selective site enabled by {1 0 0} facet on PdNCs and a great potential from a support of modified graphene to Pd metal catalyst for the development of electrocatalysts in fuel cell applications.

A competent simultaneously co-electrodeposited Pt-MnOx nanocatalyst for enhanced formic acid electro-oxidation

Abstract In this paper, a new methodology replacing the typical sequential layer-by-layer immobilization, i.e., simultaneous co-electrodeposition protocol is proven eminent for assembling efficient binary nanoelectrocatalysts for formic acid (FA) electro-oxidation (FAO). This strategy is successful to integrate homogeneously Pt nanoparticles (nano-Pt; essential component for FA adsorption/oxidation) with manganese oxide nanowires (nano-MnOx; a CO poisoning alleviator) in a single blend avoiding the poisoning CO adsorption at the catalyst surface. The molar ratio of the catalyst's ingredients (Pt:Mn) in the deposition bath is critical in identifying the catalyst's composition of the prepared binary catalyst and thus, a molar ratio of (1:8) is optimum yielding the highest catalytic activity. It is believed that adjusting the catalyst's composition could preferably act against the adsorption of poisoning CO intermediate and/or providing an electronic support to the desired (low over potential) direct dehydrogenation pathway of FAO to CO2.

Twisted palladium-copper nanochains toward efficient electrocatalytic oxidation of formic acid

Twisted PdCu nanochains are synthesized successfully via a staged thermal treatment route, offering rich twin boundaries as catalytic “active sites” and modified electronic effects. Toward formic acid oxidation, the twisted PdCu nanochains hold the highest catalytic peak current density (1108.2 mA mg−1Pd) over previous reported PdCu alloy catalysts, and also much higher catalytic activity and durability comparing with Pd nanochains and commercial Pd/C. The catalytic enhancement mechanism to PdCu nanochains is proposed and discussed. Additionally, we found that the formation of PdCu nanochains follows a typical anisotropic growth approach, and the multiple steps of staged thermal treatment route displays a vital role in fabricating the unique PdCu nanochains while the introduced Cu precursors might affect the reduction rate of Pd species and act as deposition or nucleation sites for twisted structure in terms of rich twin boundaries. This work describes an efficient, low-Pd loading catalyst for electrooxidation of formic acid, and also demonstrates a universal method to fabricate other defect-rich catalysts for broad applications in energy conversion and storage systems and sensing devices.

Poly 1,5 diaminonaphthalene supported Pt, Pd, Pt/Pd and Pd/Pt nanoparticles for direct formic acid oxidation

Comparative studies were carried out on the direct electrooxidation of formic acid at palladium (Pd), platinum (Pt), Pt/Pd and Pd/Pt nanoparticles (NPs) supported on poly 1,5‑diaminonaphthalene (PDAN)-modified glassy carbon electrode. Metal electro-deposition was carried out using potentiodynamic technique. Cyclic voltammetry (CV), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) have been used to investigate the electrochemical behavior, surface morphology and chemical composition of the studied electrodes. Electrode's electroactive surface area has been determined by electrooxidation of pre-adsorbed CO monolayer using the coupling of the dual thin layer flow through cell with mass spectrometer. Electrooxidation of formic acid (FA) at different modified electrodes have been studied using the differential electrochemical mass spectroscopy (DEMS) protocol and the current efficiencies with respect to CO2 evolution were calculated. NPs incorporated PDAN polymer films improved the electrocatalytic efficiency towards the electrooxidation of FA. Among the studied electrodes, Pt/Pd/PDAN/GC shows the best metal dispersion and highest electrocatalytic activity towards formic acid oxidation (FAO).

Citrate-Coated, Size-Tunable Octahedral Platinum Nanocrystals: A Novel Route for Advanced Electrocatalysts.

The development of green and scalable syntheses for the preparation of size- and shape-controlled metal nanocrystals is of high interest in many areas, including catalysis, electrocatalysis, nanomedicine, and electronics. In this work, a new synthetic approach based on the synergistic action of physical parameters and reagents produces size-tunable octahedral Pt nanocrystals, without the use of catalyst-poisoning reagents and/or difficult-to-remove coatings. The synthesis requires sodium citrate, ascorbic acid, and fine control of the reduction rate in aqueous environment. Pt octahedral nanocrystals with particle size as low as 7 nm and highly developed {111} facets have been achieved, as demonstrated by transmission electron microscopy, X-ray diffraction, and electrochemical methods. The absence of sticky molecules together with the high quality of the surface makes these nanocrystals ideal candidates in electrocatalysis. Notably, 7 nm bismuth-decorated octahedral nanocrystals exhibit superior performance for the electrooxidation of formic acid in terms of both specific and mass activities.

Ir-Alloyed Ultrathin Ternary PdIrCu Nanosheet-Constructed Flower with Greatly Enhanced Catalytic Performance toward Formic Acid Electrooxidation.

Ternary metal-element alloys have been reported as efficient electrocatalysts toward various electrochemical reactions, but a unique three-dimensional (3D) Ir-alloyed ternary nanosheet-composed flower (NCF) structure has not been explored yet. Herein, an innovated 1.8 nm Ir-alloyed ultrathin ternary PdIrCu NCF structure is synthesized via one-pot solvothermal reduction without using any surfactant. The as-prepared PdIrCu/C NCF catalyst remarkably improves the stability than commercial Pd/C toward formic acid electrooxidation while resulting in significantly increased mass activity. The improvement of electrocatalytic properties depends on the introduction of Ir and Cu atoms, which greatly prevented poisoning from CO while modifying the electronic structure of Pd for increased reaction active sites and accelerated charge-transfer rate as well as facilitated mass transport by ultrathin NCF 3D structure. Therefore, this catalyst possesses a promising application prospect in electrochemical energy storage/conversion systems.

Facile synthesis and enhanced catalytic activity of electrochemically dealloyed platinum–nickel nanoparticles towards formic acid electro-oxidation

Abstract To obtain the electrocatalyst with an improved electrocatalytic performance towards formic acid electro-oxidation (FAEO), a simple impregnation method is used to prepare Pt3Ni nanoparticles loaded on carbon black, assisted with electrochemically dealloying process. The X-ray powder diffraction (XRD) results as well as transmission electron microscopy (TEM) analysis of as-synthesized electrocatalyst demonstrates that the reduction temperature has a great influence on the FAEO activity of the dealloyed Pt3Ni nanoparticles. X-ray photoelectron spectroscopy (XPS) analyses confirm the variation in the electronic structure of platinum by incorporation of nickel atoms which reduces chemisorption of toxic carbon monoxide and promotes the dehydrogenation pathway of FAEO. The size of the dealloyed Pt3Ni nanoparticles remains within the range of about 2.7 nm. All electrochemical results illustrate that the performance of the as-obtained electrocatalyst towards the FAEO is significantly enhanced. Moreover, the carbon black content, incorporation of Ni atoms, and reduction temperature conditions have been proven to be the key factors for modification of the crystal structure and morphology which leads to enhanced catalytic performance.

Composition-Controllable AuPt Alloy Catalysts for Electrooxidation of Formic Acid

AuPt alloy catalysts with various compositions have been successfully prepared simply by one-step co-reduction of Au and Pt precursors involving sodium citrate as stabilizer and reductant. XRD, TEM and EDX element mapping analysis confirmed that the resulting AuPt nanoparticles are single-phase alloys rather than random mixtures of tiny Au and Pt particles. Compared with Pt/C, alloying Au with Pt can effectively alter the kinetic process of formic acid oxidation, reducing the generation of CO-like intermediates. Au81Pt19 displays superior electrocatalytic activity and durability, ~11 times in the mass activity better than commercial Pt/C and may be of practical significance for the commercialization of direct formic acid fuel cell.

A complementary study on novel PdAuCo catalysts: Synthesis, characterization, direct formic acid fuel cell application, and exergy analysis

At present, Pd containing (10–40 wt%) multiwall carbon nanotube (MWCNT) supported Pd monometallic, Pd:Au bimetallic, and PdAuCo trimetallic catalysts are prepared via NaBH4 reduction method to examine their formic acid electrooxidation activities and direct formic acid fuel cell performances (DFAFCs) when used as anode catalysts. These catalysts are characterized by advanced analytical techniques as N2 adsorption and desorption, XRD, SAXS, SEM-EDX, and TEM. Electronic state of Pd changes by the addition of Au and Co. Moreover, formic acid electrooxidation activities of these catalysts measured by CV indicates that particle size changes in wide range play a major role in the formic acid electrochemical oxidation activity, ascribed the strong structure sensitivity of formic acid electrooxidation reaction. PdAuCo (80:10:10)/MWCNT catalyst displays the most significant current density increase. On the other hand, lower CO stripping peak potential obtained for PdAuCo (80:10:10)/MWCNT catalyst, attributed to the awakening of the Pd-adsorbate bond strength down to its optimum value, which favors higher electrochemical activity. DFAFCs performance tests and exergy analysis reveal that fuel cell performances increase with the addition of Au and Co which can be attributed to synergetic effect. Furthermore, temperature strongly influences the performance of formic acid fuel cell.

1, 10-Phenanthroline: A new highly effective promoter for formic acid electro-oxidation

Abstract 1, 10-Phenanthroline (Phen) as a new promoter has been found. Cyclic voltammetry, chronoamperometry and CO-stripping tests reveals the Phen modified Pt electrode exhibits remarkably enhanced electrocatalytic activity and durability towards electro-oxidation of formic acid (EOFA). Particularly, the EOFA on Phen modified Pt electrode only follows desired dehydrogenation step.

Enhanced formic acid electrooxidation reaction enabled by 3D PtCo nanodendrites electrocatalyst

The lack of high-performance anodic electrocatalysts for the electrooxidation of liquid fuel remains a prohibited challenge in realizing the large-scale application fuel cells technique. To this end, we herein demonstrated a simple wet-chemical approach for preparing the composition-tunable PtCo nanocatalysts with the three-dimensional (3D) dendrites structure and active surface composition. These unique properties have enabled them to exhibit superior electrocatalytic activity towards formic acid electrooxidation with the mass/specific activities of 1216.9 mA mg−1Pt and 3.36 mA cm−2, 4.3 and 8.2 times higher than that of the commercial Pt/C catalyst. Moreover, the Pt4Co1 nanodendrites can endure the durability test for at least 500 cycles with less decay, showing an advanced class of electrocatalysts for fuel cells. This work paves up a new avenue to promote the electrocatalytic performances of catalyst by designing their morphologies and pushes Pt-based nanocatalysts system much stronger for commercial application in fuel cells and beyond.

Formic Acid Electrooxidation on Platinum, Resolution of the Kinetic Mechanism in Steady State and Evaluation of the Kinetic Constants

A kinetic mechanism recently proposed for the formic acid oxidation (FAO) on platinum in acid solutions was analytically solved in order to verify its capability to correlate experimental measurements in steady state conditions. It involves three adsorbed reaction intermediates (COad, HCOOad, OHad) and two reaction pathways. The derived kinetic equations enabled the fitting of the experimental current-potential curves at three different formic acid concentrations, as well as the evaluation of the corresponding kinetic constants of the elementary steps involved in the mechanism. An expression for the variation of the COad surface coverage on potential was included in the calculations, obtained from measurements of the oxidation charges by voltammetric stripping. Finally, the dependences of the surface coverages of OHad and HCOOad on potential could be simulated, which are consistent with results obtained by other authors through spectroscopic techniques.

Catalytic investigation of PtPd and titanium oxide-loaded reduced graphene oxide for enhanced formic acid electrooxidation

Preparation, characterization, and electrocatalytic study of the electrodeposited Pt and Pd (e.g., Pt and PtPd) catalysts on titanium dioxide (TiO2) modified reduced graphene oxide (rGO) support for formic acid oxidation were performed. The catalyst composites are labeled as xPt/rGO-TiO2, xPtyPd/rGO-TiO2, and yPd/rGO-TiO2 where x and y are cycle numbers of metal electrodeposition (x and y = 2–6). The characterizations of the catalysts were performed by Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Small and dispersed metal nanoparticles are obtained on rGO-TiO2. The catalytic performances for formic acid oxidation were measured by cyclic voltammetry (CV) and chronoamperometry (CA). The electrocatalytic results reveal that the bimetallic 4Pt2Pd/rGO-TiO2 catalyst facilitates formic acid oxidations at the lowest potentials and generates the highest oxidation currents and also improves the highest CO oxidation compared to the monometallic 6Pt/rGO-TiO2 catalyst. According to the experimental data, the Pd and TiO2 enhance the electrocatalytic activity of the catalysts towards the formic acid oxidation; the improved catalytic performance of the prepared catalysts strongly relates to the high electrochemically active surface area (ECSA) investigated.

Shape-controlled metal nanoparticles for electrocatalytic applications

Abstract The application of shape-controlled metal nanoparticles is profoundly impacting the field of electrocatalysis. On the one hand, their use has remarkably enhanced the electrocatalytic activity of many different reactions of interest. On the other hand, their usage is deeply contributing to a correct understanding of the correlations between shape/surface structure and electrochemical reactivity at the nanoscale. However, from the point of view of an electrochemist, there are a number of questions that must be fully satisfied before the evaluation of the shaped metal nanoparticles as electrocatalysts including (i) surface cleaning, (ii) surface structure characterization, and (iii) correlations between particle shape and surface structure. In this chapter, we will cover all these aspects. Initially, we will collect and discuss about the different practical protocols and procedures for obtaining clean shaped metal nanoparticles. This is an indispensable requirement for the establishment of correct correlations between shape/surface structure and electrochemical reactivity. Next, we will also report how some easy-to-do electrochemical experiments including their subsequent analyses can enormously contribute to a detailed characterization of the surface structure of the shaped metal nanoparticles. At this point, we will remark that the key point determining the resulting electrocatalytic activity is the surface structure of the nanoparticles (obviously, the atomic composition is also extremely relevant) but not the particle shape. Finally, we will summarize some of the most significant advances/results on the use of these shaped metal nanoparticles in electrocatalysis covering a wide range of electrocatalytic reactions including fuel cell-related reactions (electrooxidation of formic acid, methanol and ethanol and oxygen reduction) and also CO2 electroreduction. Graphical Abstract:

PVF-PPy Composite as Support Material for Facile Synthesis of Pt@PVF-PPy Catalyst and Its Electrocatalytic Activity Towards Formic Acid Oxidation

Preparation and characterization of a Pt-based catalyst supported on poly(vinylferrocenium)-poly(pyyrole) conducting polymer composite (Pt@PVF-PPy) was described for electrocatalytic oxidation of formic acid. Pt precursor was aqueous solution of K2PtCl4 and electrochemical and chemical reduction methods were compared for optimum catalyst performance. Other experimental parameters such as polymer film thickness and Pt loading were also optimized with respect to the formic acid oxidation peak current values. Scanning electron microscopy, cyclic voltammetry and chronoamperometry methods were used for physical and electrochemical characterization of the catalyst system. When compared with similar Pt-based conducting polymer supported catalyst systems, the Pt@PVF-PPy catalyst revealed superior performance for formic acid electrooxidation.

Composition dependent activity of PdAgNi alloy catalysts for formic acid electrooxidation

In the present study, the carbon supported Pd, PdAg and PdAgNi (Pd/C, PdAg/C and PdAgNi/C) electrocatalysts are prepared via NaBH4 reduction method at varying molar atomic ratio for formic acid electrooxidation. These as-prepared electrocatalysts are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), inductively coupled plasma mass spectrometry (ICP-MS), N2 adsorption-desorption, and X-ray electron spectroscopy (XPS), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), chronoamperometry (CA), and lineer sweep voltammetry (LSV). While Pd50Ag50/C exhibits the highest catalytic activity among the bimetallic electrocatalyst, it is observed that Pd70Ag20Ni10/C electrocatalysts have the best performance among the all electrocatalysts. Its maximum current density is about 1.92 times higher than that of Pd/C (0.675 mA cm−2). Also, electrochemical impedance spectroscopy (EIS), chronoamperometry (CA) and lineer sweep voltammetry (LSV) results are in a good agreement with CV results in terms of stability and electrocatalytic activity of Pd50Ag50/C and Pd70Ag20Ni10/C. The Pd70Ag20Ni10/C catalyst is believed to be a promising anode catalyst for the direct formic acid fuel cell.

2D Materials for the Electro Oxidation of Formic Acid

In recent years Direct Formic Acid Fuel Cells (DFAFCs) have attracted interest as alternative energy sources. Formic acid is abundant as it is a by-product of multiple industrial processes and it can be obtained from the oxidation of biomass. In addition, due to the capacity to use high concentrations of fuel, DFAFCs are effective at room temperature which makes it an ideal candidate for portable energy applications and it has a low permeability, which clearly distinguishes it from other Proton Exchange Membrane Fuel Cells (PEMFCs). This allows it to generate higher power densities ~160 mW/cm2 at room temperature outperforming other liquid fuel cells such as Direct Methanol Fuel Cells (DMFCs) with power densities of ~50 mW/cm2. However, a few obstacles prevents its optimization, first the behaviour and loading of the catalytic material and second the proper selectivity of the proton exchange membrane. For this the synthesis of a new catalytic material has been carried out, by the deposition of palladium Nano-particles in graphene oxide and reduced graphene oxide, obtained by the electrochemical exfoliation of graphite in order to introduce doping agents in the graphene matrix such as nitrogen, sulphur and boron and with it improve its catalytically activity and reduce catalyst loadings in DFAFCs. To address the second obstacle hindering DFAFCs, a comparative analysis of proton exchange membranes of the Nafion family was carried out and the intrinsic conductivity, dimensional stability as well as its operational temperature was observed for its use in formic acid fuel cells. From the results obtained a high performance was observed using a polytetrafluoroethylene reinforce membrane (Nafion XL) at room temperature. The membrane displayed a higher resistance to dimensional change when exposed to a wide range of formic acid concentrations, showing a maximum increase of 10% of its planar dimension while other membranes such as Nafion 117,115 and 211 had a significantly higher increase up to 45%. Results indicated that a reinforced membrane could be more suitable for DFAFCs, not only by possessing a higher dimensional stability but also due to it having a higher hydrophobicity due to the reinforcement and the lower content of sulfonic groups present in the copolymer. These changes would address the dehydration of the membrane, a factor substantially affecting the performance of the cell.

PdAg@Pd core-shell nanotubes: Superior catalytic performance towards electrochemical oxidation of formic acid and methanol

The catalytic activity of alloy nanomaterials can be well modulated through the electrochemical dissolution of the more active component from alloy nanomaterials. In this paper, PdAg alloy nanotubes of diverse Pd to Ag ratio are prepared by galvanic displacement electrochemical reaction. The Ag-leached PdAg nanotubes are characterized by cyclic voltammetric scans, high-angle annular dark-field scanning transmission electron spectroscopy, energy dispersive X-ray elemental mapping and X-ray photoelectron spectroscopy measurements and demonstrate the formation of PdAg@Pd core-shell nanotubes structure with roughed surface and largely enhanced electrochemical surface area. The PdAg@Pd core-shell nanotubes show significantly enhanced catalytic activities and durability towards electro-oxidation of formic acid and methanol than the as-prepared PdAg nanotubes, with the mass activity and specific activity of 1.93 A mg−1 and 2.67 mA cm−2 towards formic acid respectively, which are 7.8 and 4.8 times that of Pd/C. The increased catalytic performance is ascribed to the unique surface and electronic structure of PdAg@Pd core-shell nanotubes.