Direct Oxidation Of Formic Acid Research Articles

Effect of Synchrotron X-ray Irradiation Time on the Particle Size and DFAFC Performance of Pd/CNT Catalysts.

Global energy sources are limited, and energy requirements are ever-increasing due to the demand for developments in human life and technology. The environmentally friendly direct formic acid fuel cell (DFAFC) is an attractive electronic device due to its clean energy. In a DFAFC, an anodic catalyst plays an important role concerning the oxidation pathway and activity. In the present study, palladium (Pd) was synthesized by synchrotron X-ray photoreduction using various irradiation times (0.5-4 min) to control the particle size. An acid-treated carbon nanotube (A-CNT) was used as the template for Pd deposition. The A-CNT and Pd/A-CNT were examined using scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and transmission electron microscopy to reveal the microstructural characteristics. Electrochemical evaluation, electrocatalytic activity, and the DFAFC performance of so-obtained Pd/A-CNT catalysts were investigated. The experiment's results showed that the Pd/A-CNT-2 (i.e., synchrotron photoreduction for 2 min) underwent a direct formic acid oxidation pathway and possessed a high ECSA value of 62.59 m2/gPd and superior electrocatalytic activity of 417.7 mA/mgPd. In a single DFAFC examination, the anodic Pd/A-CNT-2 catalyst had a power density of 106.2 mW/mgPd and a relatively long lifetime of 2.91 h. Pd/A-CNT-2 anodic catalysts synthesized by surfactant-free synchrotron X-ray photoreduction with a rapid processing time (2 min) are potential candidates for DFAFC applications.

Sub-Monolayer SbOx on PtPb/Pt Nanoplate Boosts Direct Formic Acid Oxidation Catalysis.

To promote the commercialization of direct formic acid fuel cell (DFAFC), it is vital to explore new types of direct formic acid oxidation (FAOR) catalysts with high activity and direct pathway. Here, we report the synthesis of intermetallic platinum-lead/platinum nanoplates inlaid with sub-monolayer antimony oxide surface (PtPb/Pt@sub-SbOx NPs) for efficient catalytic applications in FAOR. Impressively, they can achieve the remarkable FAOR specific and mass activities of 28.7 mA cm-2 and 7.2 A mgPt-1, which are 151 and 60 times higher than those of the state-of-the-art commercial Pt/C, respectively. Furthermore, the X-ray photoelectron spectroscopy and X-ray absorption spectroscopy results collectively reveal the optimization of the local coordination environment by the surface sub-monolayer SbOx, along with the electron transfer from Pb and Sb to Pt, driving the predominant dehydrogenation process. The sub-monolayer SbOx on the surface can effectively attenuate the CO generation, largely improving the FAOR performance of PtPb/Pt@sub-SbOx NPs. This work develops a class of high-performance Pt-based anodic catalyst for DFAFC via constructing the unique intermetallic core/sub-monolayer shell structure.

Focused microwave-assisted synthesis of activated XC-72R supported PdBi nanocatalyst for the enhanced electrocatalytic performance in formic acid oxidation

The present paper describes a rapid and straightforward synthesis technique called focused microwave-assisted synthesis (FMWS) for producing bimetallic carbon-based PdBi@C nanocomposites with desired monodispersity and uniformity and investigates their catalytic activity towards formic acid electro-oxidation reaction (FAOR). X-ray diffraction (XRD), transmission electron microscope (TEM), and energy dispersive X-ray (EDX) analysis confirmed that Pd atoms are embedded in the activated XC-72 R carbon support, and the resulting Pd@C surface shows excellent integration with Bi atoms via spontaneous chemisorption after FMWS. The synthesized Pd20Bi1@C nanocatalyst displayed optimal electrochemical performance for direct formic acid oxidation reaction (DFAOR), with uniform dispersity, a narrow size distribution (6.54 ± 1.03 nm), and a polydispersity index (PDI) of 16%, indicating high monodispersity achieved through FMWS. The influence of nanocomposite content on DFAOR was investigated, revealing that Pd20Bi1@C exhibited a significantly higher current density compared to salt Pd@C, with a 2.63-fold increase. The evaluated nanocatalysts ranked in descending order of final current densities (mAcm−2) as follows: Pd20Bi1@C (21.06) > Pd30Bi1@C (14.31) > Pd40Bi1@C (12.09) > Pd10Bi1@C (9.22) > Pd@C (8.02). Furthermore, chronoamperometry and cyclic voltammetry tests demonstrated that the addition of Bi to Pd@C enhanced the reaction of oxygenated species with CO-like poisonous intermediates, thereby facilitating the adsorption and oxidation of formic acid molecules by releasing Pd active sites in DFAOR. Notably, Pd20Bi1@C exhibited exceptional stability and improved CO tolerance. In summary, the current study highlights the potential of integrating FMWS with a chemisorption approach to achieve excellent electrochemical performance, enabling nanocomposites to demonstrate enhanced feasibility as prospective catalysts for FAOR.

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.

Tuning dehydrogenation behavior of formic acid on boosting cell performance of formic acid fuel cell at elevated temperatures

In high-temperature formic acid fuel cell (HT-FAFC), the dehydrogenation behavior of formic acid plays a significant role in boosting cell output performance by leading to a favorable and powerful hydrogen oxidation reaction (HOR) on the anode side instead of the direct formic acid oxidation reaction (dFAOR). The formic acid dehydrogenation mechanism of HT-FAFC at 200 °C is investigated by regulating concentration and flow rate. As a competitive path of dehydrogenation, unfavorable dehydration occurs simultaneously accompany by carbon monoxide (CO) release. It is found that high formic acid concentration is conducive to the dehydrogenation to produce more hydrogen, however, the reduction of water vapor content may promote the dehydration reaction and result in the inhibition of dehydrogenation. As the non-preferable alternative, the dehydration-caused total CO release remains under CO maximum tolerance (3%) of Pt catalyst at 200 °C which is unlikely to affect the power output of HT-FAFC. The permeation of formic acid can be considered as a barrier when the high concentration exceeds 12 mol L−1 or the flow rate exceeds 1 mL min−1. These findings may deepen understanding of formic acid consuming behavior of HT-FAFC anode, which helps to formulate strategies to improve cell performance in general.

Electronic Effect or Underpotentially Deposited Hydrogen? Insights into the effect of Pb on formic acid electro‐oxidation on Pt

AbstractFormic acid is a promising energy carrier. Electrochemical formic acid oxidation can serve as an important reaction within fuel cells. Although Pt remains the best‐known catalyst, surface adatoms like Pb have been known to promote formic acid electro‐oxidation significantly. We have carried out first principle‐based calculations, bonding analysis, and experiments to provide insights for this enhancement. Results show that upon adsorption of Pb on the Pt surface, an upshift of Pt energy levels above the Fermi energy is observed, which in general influences the binding energy of the adsorbates. Reaction free energy vs. electrochemical potential diagrams were constructed to understand the interaction of formic acid and water with Pt and Pb‐modified Pt surfaces. Electrochemical experiments indicating the underpotentially deposited hydrogen (Hupd) region and potential‐dependent apparent activation energies indicate that Hupd suppression has an important role to play in the formic acid oxidation reaction. The suppression of the Hupd region on Pb‐modified Pt surface results in free Pt sites that can carry out direct formic acid oxidation to CO2.

Electro-oxidation of formic acid on composites from polycarbazole and WO3

Direct oxidation of formic acid (FA) is reported in the present work on a low-cost, noble metal-free WO3 embedded polycarbazole nanocomposite (PCz-WO3) electrocatalyst. Nano WO3 component used herein is synthesized by a facile coprecipitation method and then various PCz nanocomposites are synthesized at the interface of two immiscible liquids by introducing different amounts of nano WO3 during the polymerization of an optimized amount of carbazole monomer. Further, these materials are used as an active material to modify commercially available glassy carbon electrodes (GCE) and then applied for the electro-oxidation of FA at ambient conditions. It is observed that due to optimal synergism between PCz and nano WO3, PCz-WO3/4 nanocomposite exhibits improved electro-activity with direct oxidation dominated FA oxidation at the lowest potential in comparison to other counterparts and earlier reported works.

Enhanced electrocatalytic activity of Cu-modified, high-index single Pt NPs for formic acid oxidation.

A key goal of nanoparticle-based catalysis research is to correlate the structure of nanoparticles (NPs) to their catalytic function. The most common approach for achieving this goal is to synthesize ensembles of NPs, characterize the ensemble, and then evaluate its catalytic properties. This approach is effective, but it excludes the certainty of structural heterogeneity in the NP ensemble. One means of addressing this shortcoming is to carry out analyses on individual NPs. This approach makes it possible to establish direct correlations between structures of single NPs and, in the case reported here, their electrocatalytic properties. Accordingly, we report on enhanced electrocatalytic formic acid oxidation (FAO) activity using individual Cu-modified, high-indexed Pt NPs. The results show that the Cu-modified Pt NPs exhibit significantly higher currents for FAO than the Pt-only analogs. The increased activity is enabled by the Cu submonolayer on the highly stepped Pt surface, which enhances the direct FAO pathway but not the indirect pathway which proceeds via surface-absorbed CO*.

Development of Advanced Electrode Materials on Porous Silicon for Micropower Formic Acid-Oxygen Fuel Cells

In this work, in order to create electrode materials for electrochemical energy converters, composites on porous silicon modified by palladium have been obtained. The functional characteristics of the electrodes have been studied by scanning electron microscopy, X-ray phase analysis, ex-situ and in-situ cyclic voltammetry. The electrode materials based on porous silicon had demonstrated high catalytic activity and specific characteristics in fuel cells with direct oxidation of formic acid. The fuel cell prototype with low palladium content showed the maximum specific power of about 30 mW/cm 2 at a current density of 95-100 mA/cm 2 . Copyright © VBRI Press.

Platinum Nanostructure Tailoring for Fuel Cell Applications Using Levitated Water Droplets as Green Chemical Reactors.

Tailoring of nanostructured materials with well-controlled morphologies and their integration into valuable applications in a facile, cheap, and green way remain a key challenge. Herein, platinum nanoparticles as well as Pt-polymer nanocomposites with unique shapes, including flower-, needle-, porous-, and worm-like structures, were synthesized and simultaneously deposited on a three-dimensional carbon substrate and carbon nanofibers in one step using a levitated, overheated water drop as a green, rotating chemical reactor. Sprinkling of a metal aqueous solution on a hot surface results in its sudden evaporation and creates an overheated zone along with the water self-ionization (i.e., charge separation) at the hot interface. These generated Leidenfrost conditions are believed to induce a series of chemical reactions involving the used solvent and counterions, resulting in the nanoparticles formation. Besides, the in situ generated basic conditions in the vicinity of the liquid-vapor interface due to the loss of hydronium ions into the vapor layer could also play a role in the mechanism of the nanoparticles formation, e.g., by discharging. The as-prepared Pt nanostructures exhibited a superior catalytic activity and stability toward the desired direct formic acid oxidation (essential anodic reaction in fuel cells) into CO2 without generating CO poisoning intermediates compared to the state-of-the-art commercial PtC electrode. The addressed nanotailoring technique is believed to be a promising, inexpensive, and scalable way for the sustainable manufacture of well-designed nanomaterials for future applications.

La0.80Sr0.20CoO3 as a noble-metal-free catalyst for the direct oxidation of formic acid under zero applied potential

Direct oxidation of formic acid to CO2 using noble-metal-free La0.80Sr0.20CoO3 is demonstrated in this study. The catalyst was able to oxidize HCOOH without any externally applied potential. The activity of La0.80Sr0.20CoO3 is compared with that of Pt nanoparticles. It is observed that the amount of CO2 generated using La0.80Sr0.20CoO3 is five times higher than that generated with Pt nanoparticles. The experimental observations are supported by DFT calculations, which reveal the role of the lattice oxygen in La0.80Sr0.20CoO3 in the catalytic effect. The Sr ions were not found to have any appreciable role in the dissociation step. Weak binding of CO2 involving energy changes of the order of −1 kcal/mol indicated the ease of CO2 desorption from the catalyst surface, thus making the catalyst highly active for electrochemical HCOOH oxidation.

Electrocatalytic enhancement of formic acid oxidation reaction by acetonitrile on well-defined platinum surfaces

The formic acid oxidation reaction has been studied on Pt(111), Pt(100) and Pt nanoparticles with preferential (111) surface structure in 0.1 M HClO4 in the presence of different concentrations of acetonitrile. An electrocatalytic enhancement towards the formic acid oxidation has been observed under these conditions, and it is proposed that this enhancement is due to two different effects of the adsorbed acetonitrile species: a third-body effect which hinders the formation of CO and a promoting effect of the direct oxidation of formic acid. This promoting effect is structure sensitive. The different enhancement between Pt(111) and Pt(100) indicates that the ratio of free Pt sites and sites occupied by adsorbed acetonitrile is important in order to have the better electrocatalytic activity. On-line mass spectrometry (OLEMS) measurements confirmed the preference for the direct oxidation of formic acid to CO2, which is almost complete below 0.3 V vs. RHE for Pt(111). Finally, chronoamperometric studies confirmed the lower poisoning rate in the presence of acetonitrile but they also pointed out a competition of formed CO for the Pt sites occupied by acetonitrile species. This work constitutes an example of electrocatalytic enhancement by using an organic molecule for surface modification, which is not as common as using metallic adlayers.

Significantly enhanced electrocatalytic activity of Au25 clusters by single platinum atom doping

The search for highly active catalysts with low-Pt content to advance the commercialization of fuel cells is continuing to receive ample attention. Herein, we report that by doping a single Pt atom into Au25 to form Pt1Au24 nanoclusters, the electrocatalytic activity for the direct formic acid oxidation (FAO) to carbon dioxide is enhanced significantly. The mass activity of Pt1Au24 (3.7 A mgPt+Au−1) is nearly 12 and 34 times greater than that of Pt nanoclusters and the commercial Pt/C catalyst, respectively. Density functional theory (DFT) calculations and potential-dependent thermodynamic analyses provide fundamental insights into the reaction mechanism illustrating that FAO proceeds through the carboxyl (COOH) intermediate on Pt1Au24. The present study not only develops a novel class of single-Pt atom doped Au nanocluster electrocatalysts for fuel cells with high utilization of Pt, but also provides insight into the mechanism of FAO on Pt-doped Au nanoclusters. Moreover, this study begins to shed light on the structure-activity relationship and helps to provide a strategy to design new catalysts by tuning their catalytic properties at the atomic level.

Impurity‐Induced Electrocatalysis: Unpredicted Enhancement Effect of Ammonia Impurity Towards Formic Acid Electro‐Oxidation

AbstractThis study addresses a noteworthy unexpected enhancement of the direct oxidation pathway of formic acid (FA) to CO2 at Pt nanoparticle‐modified GC (nano‐Pt/GC) electrode in the presence of ppm amounts of ammonia associated with suppressing the poisoning dehydration pathway of FA to CO, for the first time. This is reflected by a significant increase of the current intensity of the direct oxidation peak (Ipd) simultaneously with a significant decrease of the indirect oxidation peak current (Ipind) in the presence of a minute amount of ammonia compared to that observed in its absence. For instance, the ratio Ipd/Ipind increases from 0.2 in the absence of ammonia to 9.5 in the presence of 30 ppm of ammonia (i. e., 45 times higher) indicating that the direct pathway became the dominant oxidation pathway in the presence of ammonia. Ammonia is believed to favor the direct formic acid oxidation (FAO) to CO2 as it impedes the formation of CO by disturbing the geometry of Pt sites, which is necessary for CO adsorption as evident from CO stripping experiment (i. e., prevents non‐Faradic dissociation of FA). Additionally, it might induce the CH‐down adsorption orientation of FA thus favoring FAO directly to CO2 as evident from DFT calculations.

Palladium–platinum–porous silicon nanocatalysts for fuel cells with direct formic acid oxidation

An original technology for the controllable production of catalytically active functional electrode nanocomposites based on porous silicon with bimetallic palladium–platinum nanoparticles is proposed. The nanocomposites are studied by electron microscopy, X-ray phase analysis, and cyclic voltammetry. The synthesized materials demonstrate high electrocatalytic properties in the direct formic acid oxidation reaction.

Three-dimensional porous Au nanocoral structure decorated with Pt submonolayer via galvanic displacement of copper adatoms for electrooxidation of formic acid

Three-dimensional (3D) porous Au nanocoral network (GNN) structure was fabricated on glassy carbon (GC) electrode by one-step, template-free electrodeposition and decorated with ultrathin Pt film by combining the underpotential deposition (UPD) of copper adatoms and the galvanic displacement (GD) between PtCl62- and Cu. The thickness of Pt atomic layers can be controlled precisely by repeating the UPD–GD process. Scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) were employed to characterize the morphology of GNN and Ptn/GNN (n, the cycles of repeating the UPD–GD process). Cyclic voltammometric and chronoamperometric tests indicate that all Ptn/GNN samples effectively support the direct oxidation of formic acid and show higher electrocatalytic performance than the commercial Pt/C catalyst (Pt, 20 wt %, Johnson Matthey Co.), where Pt1/GNN completely eliminates the indirect oxidation of formic acid, exhibiting the best electrocatalytic activity and stability among all Ptn/GNN samples due to the optimal coverage and distribution of Pt atoms on GNN.

Probing the electrooxidation of weakly adsorbed formic acid on Pt(1 0 0)

Understanding the electrooxidation of formic acid on noble metal surfaces is both important for the insight it promises into a formic acid fuel cell and as a model for the electrooxidation of hydrocarbons more generally. As a result, this reaction has been studied for decades. Taken together this body of previous work suggests that on most noble metals the oxidation precedes both through an indirect, via adsorbed CO, and direct pathway via an intermediate that is controversial. In an attempt to rationalize large differences in electrooxidative activity as a function of metal, crystal surface, pH and the presence of other anions, a variety of intermediates in the direct pathway have been proposed. While differing in detail virtually all of the proposed mechanisms invoke a species that only weakly interacts with the metal surface and cannot be detected via conventional spectroscopic techniques. Here we overcome this challenge by characterizing the electrooxidation of formic acid on the Pt(100) surface using the surface selective nonlinear optical technique, vibrationally resonant sum frequency spectroscopy. We detect a weakly adsorbed form of formic acid and find by correlating its potential dependent spectral amplitude and oxidation peaks apparent in a simultaneously collected in situ cyclic voltammogram, that it is a reaction precursor in the direct oxidation of formic acid on this surface.

Promoting Effect of Hydrocarbon Impurities on the Electro-Oxidation of Formic Acid at Pt Nanoparticles Modified GC Electrodes

This paper addresses a systematic study of the unexpected enhancement of some hydrocarbon impurities towards formic acid oxidation (FAO) at Pt nanoparticles modified GC electrode, for the first time. That is, the oxidation current peak observed at ca. 0.25V (assigned for the direct FAO to CO2, Ipd) increases in the presence of a minute amount (∼ppm range) of Acetonitrile>Acrylonitrile>Acetamide>Pyridine∼vinyl acetate>Pyrrole>Methyl Acrylate>toluene with a concurrent decrease of the second oxidation peak current (assigned for the indirect oxidation of FA, Ipind) observed at ca. 0.65V. Moreover, the onset potential of FAO is favored by shifted towards the negative potentials together with a noticeable increase of the stability of the current transients measured during FAO in the presence of impurities. The enhanced activity is believed to originate from interrupting the contiguity of Pt sites by the pre-adsorption of the respective impurity at nano-Pt surface thus impedes/weakens the adsorption of the poisoning CO.

Enhanced Direct Oxidation of Formic Acid and Its Underlying Mechanism in the Ag-Pd Core-Shell Nanocatalyst: A First-Principles Study

Formic acid is an excellent in situ source of hydrogen for fuel cells, for it offers high energy density and remains as a liquid at standard temperature and pressure. So far, there has been a lack of reports regarding the underlying mechanism in enhancing the direct oxidation of formic acid on the bimetallic nano-catalyst. In this study, using spin-polarized density functional theory we examine the reactivity and selectivity of Ag-Pd core shell catalyst toward direct oxidation of formic acid. We find that the ligand effect in Ag-Pd core shell catalyst plays an important role in determining direct oxidation of formic acid rather than the strain effect. In particular, the thinnest Pd shell catalyst can boost the hydrogen production from direct oxidation of formic acid at room temperature and this result provides possibilities for the development of fuel cell devices.

Electrocatalysis by design: Enhanced electrooxidation of formic acid at platinum nanoparticles–nickel oxide nanoparticles binary catalysts

This study addresses the electrocatalytic oxidation of formic acid (FA) at binary catalysts composed of Pt nanoparticles (nano-Pt) and nickel oxide nanoparticles (nano-NiOx) electrodeposited onto glassy carbon (GC) electrodes. Pt electrode shows two oxidation peaks at ca. 0.25 and 0.65V vs. Ag/AgCl/KCl (sat.) corresponding to the direct (Ipd, favorable) and indirect (Ipind, unfavorable) oxidation pathways of FA, respectively. Nano-Pt/GC electrode shows a significantly higher catalytic activity toward FA oxidation than the bulk Pt electrode. Interestingly, further modification of the nano-Pt/GC electrode with nano-NiOx leads to a superb enhancement of Ipd with a concurrent suppression of Ipind. The catalytic activity of the various modified GC electrodes is probed by the ratio of Ipd/Ipind. This ratio increases from 0.2 at bulk Pt to 1.4 at nano-Pt/GC (i.e., ca. 7 times higher), and jumps up to more than 20 at the binary nano-NiOx/nano-Pt modified GC electrode, reflecting the superiority of the latter electrode toward FA oxidation to CO2. While nano-Pt furnishes a suitable base for FA adsorption, nano-NiOx acts as a catalytic mediator which facilitates the charge transfer during the direct oxidation of FA. The influence of the deposition sequence and the loading level of both species (i.e., Pt and NiOx) on the catalytic activity of the binary catalyst are investigated.