Formic Acid Electrooxidation Research Articles

Pt Nanoelectrodes Sealed in Quartz Capillaries Modified with Underpotential‐Deposited Bismuth for Formic Acid Electrooxidation

AbstractPlatinum disk nano‐ and micro‐electrodes with radii in the range 40 nm–12.5 μm were fabricated using quartz capillaries and the laser‐puller assisted approach. The hydrogen underpotential deposition (H‐UPD), performed in a 0.5 M H2SO4 aqueous solution, revealed that the nanoelectrodes, with radii of 160 nm and less, displayed extraordinarily large surface areas, which in terms of roughness factors (RFs, i. e., the ratio of the real surface areas to the geometric surface areas) were in the range 1030–3600. This finding was attributed to diffusion of adsorbed species at the Pt/quartz interface along portions of the Pt wires sealed within the glass. RFs between 2 and 3 were instead found at the microelectrodes. Similar results were also obtained with underpotential‐deposited metallic bismuth. In this case, diffusion of Bi adatoms onto the Pt surface was hindered to some extent, providing a RF value of 172. Bi‐modified Pt nano‐ and micro‐electrodes were employed to study the electrooxidation of HCOOH, which is of interest in the field of fuel cells. It was found that the nanoelectrode displayed higher activity towards the electrooxidation of HCOOH and tolerance to CO poisoning, compared to the microelectrode.

Promoting formic acid and ethylene glycol electrooxidation activity on Ga modified Pd based catalysts

Herein, carbon nanotube (CNT)-supported Ga@PdAgCo catalysts were synthesized by sodium borohydride (SBH) sequential reduction method. These catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma-mass spectrometry (ICP-MS). Characterization results revealed that these catalysts were succesfully preared at desired loading and atomic ratios. From the XRD pattern, the crystallite size of 0.5% Ga@PdAgCo(80:10:10)/CNT catalysts was found as 6.95 nm by utilizing the Scherrer equation. From TEM measurements, the average particle sizes of Pd/CNT, PdAgCo(80:10:10)/CNT, and 0.5% Ga@PdAgCo(80:10:10)/CNT catalysts were found to be 54 nm, 25 nm, and 7 nm, respectively. It is clear that particle sizes obtained from TEM and XRD were close to eachother. Electrochemical impedance spectroscopy (EIS), chronoamperometry (CA), and cyclic voltammetry (CV) measurements were realized to examine the formic acid and ethylene glycol electrooxidation performances of catalysts. 0.5% Ga@PdAgCo(80:10:10/CNT) and 7% Ga@PdAgCo(80:10:10/CNT) catalysts had the best specific activity and mass activity as 3.37 mA/cm2 (297.61 mA/mg Pd) and 4.95 mA/cm2 (462.59 mA/mg Pd) for ethylene glycol and formic acid electrooxidation, respectively. In addition, EIS results showed that Ga@PdAgCo(80:10:10/CNT) catalyst had a faster electron transfer rate via low charge transfer resistance. As a result, 0.5% Ga@PdAgCo(80:10:10/CNT) catalyst is a promising new anode catalyst for direct ethylene glycol fuel cells.

Electrocatalytic activity enhancement of palladium-manganese nanosheet assembled nanobuds by tuning electronic structure

Adding another transition metals into Pd lattice is demonstrated as an effective strategy to improve Pd utilization while enhancing its catalytic activity toward formic acid electrooxidation through the generated ligand and strain effects. However, it is still very challenging to identify the contributions from the two effects on activity enhancement, which restrains the rational design of Pd-based alloy electrocatalysts. Herein, we reported the synthesis of PdMn nanosheet assembled nanobuds using a facile polymeric surfactant-free method with eliminated strain effect essentially, which were demonstrated as advanced catalysts in the aspect of much better catalytic activity and stability compared with the-state-of-the-art Pd-C catalyst. The catalytic enhancement mechanism should be attributed to the generated ligand effect which originates from the modulated electronic structure and consequent charge redistribution.

Interface engineering of PtCuMn nanoframes with abundant defects for efficient electrooxidation of liquid fuels

Precise design and synthesis of advanced Pt-based catalysts through modulation of the surface coordination environment at the atomic level are crucial for the industrial application of fuel cells. However, conventional surface engineering approaches are generally multistage processes. Herein, we report a simple one-step method to precisely synthesize a set of ternary PtCuMn nanoframes (multiple-pin and external branch structures) with high-index facets (HIFs) and high defect density via change of alcohol species, structure-directing agent and heating mode. Owing to the high density of abundant coordinatively unsaturated sites and the unique electronic effect of ternary alloys, the prepared PtCuMn nanoframes present excellent performance for methanol electrooxidation (MOR) and formic acid electrooxidation (FAOR). Specifically, the area specific current densities of PtCuMn with multiple-pin nanoframe morphology for MOR and FAOR are approximately 7.76 and 6.68 times higher, respectively, than those of Pt/C. More importantly, the catalysts show more stability compared with Pt/C. This proposed surface engineering approach not only realizes efficient architecture- and defect-controlled PtCuMn nanoframe electrocatalyst, but also provides fundamental insights into the roles of architecture and defects in renewable energy electrocatalysis.

Surface engineering of Pt surfaces with Au and cobalt oxide nanostructures for enhanced formic acid electro-oxidation

A novel n-CoOx/n-Au/n-Pt nanocatalyst assembled onto a glassy carbon (GC) substrate is recommended for efficient formic acid electro-oxidation (FAEO), the principal anodic reaction in the direct formic acid fuel cells (DFAFCs). • A catalyst composed of Pt nanoparticles was engineered with Au and cobalt oxide nanostructures. • It showed a promising catalytic performance toward the formic acid electro-oxidation. • Adjusting its loading hierarchy drove the reaction mechanism to the desirable dehydrogenation pathway. • Geometric and electronic enhancements were elucidated and quantified. This study aims to mitigate the CO poisoning of platinum (Pt) surfaces during formic acid electro-oxidation (FAEO), the essential anodic reaction in the direct formic acid fuel cells (DFAFCs). For this purpose, a glassy carbon (GC) electrode was amended sequentially with Pt (n-Pt), gold (n-Au), and cobalt oxide (n-CoOx) nanostructures. Fascinatingly, the ternary modified n-CoOx/n-Au/n-Pt/GC catalyst (for which n-Pt, n-Au, and n-CoOx were sequentially and respectively assembled onto the GC surface) exhibited a remarkable electrocatalytic enhancement toward FAEO, which surpassed ca. 53 times that of the Pt/GC catalyst. Additionally, it exhibited a much (ca. 18 times) higher stability after 3000 s of continuous electrolysis. The observed enhancement was proven to originate from driving the reaction mechanism principally to the desirable direct dehydrogenation pathway on the expense of the poisoning dehydration path. The impedance and CO stripping measurements confirmed the prevailing of both the electronic and third body effects in the catalytic enhancement.

Electrical coupling of individual electrocatalytic oscillators.

The catalytic electro-oxidation of some small organic molecules is known to display kinetic instabilities, which reflect on potential and/or current oscillations. Under oscillatory conditions, those systems can be considered electrocatalytic oscillators and, therefore, can be described by their amplitude, frequency, and waveform. Just like mechanical oscillators, the electrocatalytic ones can be coupled and their dynamics can be changed by setting different coupling parameters. In the present work, we study the unidirectional coupling of electrocatalytic oscillators, namely, those comprehending the catalytic electro-oxidation of methanol and formic acid on polycrystalline platinum in acidic media under potentiostatic control. Herein, we explore two different scenarios (the coupling of compositionally identical and non-identical oscillators) and investigate the effects of the master's identity and of the coupling constant on the slave's dynamics. For the master (methanol)-slave (methanol) coupling, the oscillators exhibited phase lag synchronization and complete phase synchronization. On the other hand, for the master (formic acid)-slave (methanol) coupling, the oscillators exhibited complete phase synchronization with phase-locking with a 2:3 ratio, complete phase synchronization with phase-locking with a 1:2 ratio, phase lag synchronization, and complete phase synchronization. The obtained results suggest that both the master's identity and the coupling constant (sign and magnitude) are parameters that play an important role on the coupled systems, in such a way that even for completely different systems, synchronization could emerge by setting a suitable coupling constant. To the best of our knowledge, this is the first report concerning the electrical coupling of hidden N-shaped-negative differential resistance type systems.

Augmented formic acid electro-oxidation at a co-electrodeposited Pd/Au nanoparticle catalyst

In this study, the formic acid electro-oxidation reaction (FAEOR) was catalyzed on a Pd-Au co-electrodeposited binary catalyst. The kinetics of FAEOR were intensively impacted by changing the Pd2+:Au3+ molar ratio in the deposition medium. The Pd1-Au1 catalyst (for which the Pd2+:Au3+ molar ratio was 1:1) acquired the highest activity with a peak current density for the direct FAEOR (Ip) of 4.14 mA cm−2 (ca. 13- times higher than that (ca. 0.33 mA cm−2) of the pristine Pd1-Au0 catalyst). It also retained the highest stability that was denoted in fulfilling ca. 0.292 mA cm−2 (ca. 19-times higher than 0.015 mA cm−2 of the pristine Pd1-Au0 catalyst) after 3600 s of continuous electrolysis at 0.05 V. The CO stripping and impedance measurements confirmed, respectively, the geometrical and electronic enhancements in the proposed catalyst.

Two-Step Fabrication of Carbon-Supported Cu@Pd Nanoparticles for Electro-Oxidation of Formic Acid

Two-Step Fabrication of Carbon-Supported Cu@Pd Nanoparticles for Electro-Oxidation of Formic Acid

Catalyst Composites of Palladium and N-Doped Carbon Quantum Dots-Decorated Silica and Reduced Graphene Oxide for Enhancement of Direct Formic Acid Fuel Cells.

Pd-based catalysts consisting of Pd nanoparticles on nitrogen-doped carbon quantum dots (N-CQDs) modified silica (SiO2) and reduced graphene oxide have been synthesized through reduction for use as catalysts for improved formic acid oxidation. The structure, morphology, chemical composition, functional groups, and porosity of the synthesized catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy, and Brunauer–Emmett–Teller (BET) spectroscopy, respectively. Their electrocatalytic activities were also evaluated by electrochemical measurements. The differences in the average particle sizes found for Pd/N-CQDs-SiO2-rGO, Pd/N-CQDs-rGO, and Pd/rGO were 4.81, 5.56, and 6.31 nm, respectively. It was also found that the Pd/xN-CQDs-SiO2-yrGO composite catalysts (where x and y is 1 to 4) can significantly improve the activity and stability toward formic acid electrooxidation compared with Pd/rGO and commercial Pt/C. The mass activities of Pd/N-CQDs-SiO2-rGO, Pd/N-CQDs-rGO, and Pd/rGO were 951.4, 607.8, and 157.6 mA g–1, respectively, which was ca. 6–7 times compared with Pd/rGO and approximately 3–4 times compared with commercial Pt/C. With low potential for CO oxidation and high current intensity, the composites of rGO, SiO2, and N-CQDs into Pd-based catalysts improved the catalytic activity of the prepared catalyst for the oxidation of formic acid in acidic media. The value of the Tafel slope designated that the chief path of the prepared catalysts is the dehydrogenation process. These prepared catalysts exhibit promise toward the development of high-performance Pd-based electrocatalysts for formic acid oxidation.

Pt-based intermetallic compounds with tunable activity and selectivity toward hydrogen production from formic acid

Using first-principles methods, we studied formic acid dehydrogenation on the L11-type ordered Pt-based intermetallic compounds (i.e., X-Pt, X = Ag, Cu, Au, Pd, Ir, Rh, Tc, W, V). We found an adsorption-energy linear scaling relationship with positive slope between carbon monoxide (CO) and carboxyl (COOH) or hydrogen atom, but a weakly correlation with a negative slope for CO versus formate (HCOO) or CO versus hydroxyl (OH), which is attributed the beyond d-band-center model for the description of adsorption energies of HCOO and OH. And then, the selectivity of HCOOH dehydrogenation to HCOO (versus COOH) or COOH decomposition to CO2 (versus CO) on the Pt-based ordered alloys is regulated though breaking the adsorption-energy linear scaling relations of reaction intermediates. Our calculated results indicate that the L11-type CuPt is highly catalytic activity and selectivity toward formic acid decomposition and electrooxidation through the CO2 pathways of HCOOH→COOH+H→CO2+2H. This study underscores the importance of the unique adsorption-energy relations among reaction intermediates (e.g., CO versus OH) for screening high effective catalysts for hydrogen production of formic acid.

Tuning atomic Pt site surface on PtAu alloy toward electro-oxidation of formic acid

PtAu alloy is considered to be a promising catalyst for the formic acid (HCOOH) electro-oxidation reaction. Nevertheless, the mechanism of HCOOH electro-oxidation on various surface compositions of PtAu is still unclear. Here, a series of ∼5 nm PtAu catalysts from Pt50Au50 to atomically dispersed Pt surface is successfully prepared. We reveal that the electro-oxidation HCOOH mechanism depends on the surface Pt sites; i.e., when PtAu alloy surface tunes to surface atomic Pt site, their mechanisms will change from a dual pathway mechanism to a direct pathway. Therefore, PtAu alloy (Pt5Au95) with atomic Pt sites surface showed an excellent activity with 104.8 mA cm−2 at 0.24 V (normalized by the Pt active surface area), which is five times higher than that of Pt50Au50 (19.3 mA cm−2 at 0.24 V) toward HCOOH electro-oxidation. Significantly, external reflection in-situ Fourier transform infrared spectroscopy (FTIRS) results furtherly prove that the atomic Pt sites surface on PtAu alloy will prevent the formation of CO poisoning intermediate and undergo the direct pathway to form CO2. Moreover, attenuated total reflection (ATR) in-situ FTIRS results also demonstrate that the bridge formic acid anion on PtAu alloy is not a real intermediate for electro-oxidation HCOOH.

Formic acid electro-oxidation: Mechanism and electrocatalysts design

Formic acid electro-oxidation: Mechanism and electrocatalysts design

Novel Superaerophobic Anode with Fern‐Shaped Pd Nanoarray for High‐Performance Direct Formic Acid Fuel Cell

AbstractDirect formic acid fuel cells (DFAFCs) possess the advantages of high power density and theoretical cell potential. Exploring robust catalysts for electrochemical formic acid electro‐oxidation (FAO) is greatly essential for the wide spread uptake of DFAFCs. However, many electrodes with attractive catalysts suffer limited mass transport due to sluggish CO2 bubble growth and departure steps on its surface. In this study, a superaerophobic electrode is developed by depositing fern‐shaped palladium nanostructured arrays on the carbon paper (Pd‐nanoarray@CP). Its unique superaerophobic feature successfully facilitates the CO2 bubble releasing from the catalyst surface in a significantly small size. With the merits of specific nanoarray morphology, superior under water superaerophobicity, and rapid gas bubble release, the Pd‐nanoarray@CP shows fast charge/mass transport rate, high electrocatalytic activity, and great stability for FAO. A direct formic acid fuel cell equipped with the Pd‐nanoarray@CP anode is successfully fabricated on a microfluidic platform. A peak power density of 35.8 mW cm−2 and limiting current density of 173.3 mA cm−2 are obtained, respectively, which are 49.2% and 33.0% higher than that of conventional Pd‐black anodes. The electrode with superaerophobic interface allows deeper insight into the mechanism of FAO efficiency and holds promise for possible applications of commercially viable DFAFCs.

Effect of Palladium Loading on Catalytic Properties of Pd/GCE for the Electro-oxidation of Methanol, Formic Acid, and Ethylene Glycol

Effect of Palladium Loading on Catalytic Properties of Pd/GCE for the Electro-oxidation of Methanol, Formic Acid, and Ethylene Glycol

A new pathway for formic acid electro-oxidation: The electro-chemically decomposed hydrogen as a reaction intermediate

Formic acid electro-oxidation reaction (FAOR) is generally believed that follows a two-pathway mechanism. Herein, we resorted to in situ electrochemical mass spectrometry and successfully captured the trace of H2, as the new intermediate species, during the process of FAOR on both Pt based catalyst and two single atom catalysts (Rh-N-C and Ir-N-C). Inspired by this, we proposed a new reaction path named hydrogen oxidation pathway: at the oxidation potential, formic acid will break the C–H bond and combine with the protons in the solution to form H2 species, then hydrogen oxidation reaction (HOR) will occur to generate two protons. This process is accompanied by electron transfer and contributes currently to the whole reaction.

A Competent MWCNT-Grafted MnOx/Pt Nanoanode for the Direct Formic Acid Fuel Cells

A novel “MnOx/Pt/MWCNT-GC” nanocatalyst is recommended for the electrooxidation of formic acid (EOFA), the principal anodic reaction in the direct formic acid fuel cells (DFAFCs). The sequential (layer-by-layer) protocol was employed to prepare the catalyst through the electrodeposition of Pt (nano-Pt) and manganese oxide (nano-MnOx) nanoparticles onto the surface of a glassy carbon (GC) electrode supported with multiwalled carbon nanotubes (MWCNTs). The nano-MnOx could successfully mediate the mechanism of EOFA by accelerating the charge transfer, “electronic effect”. On the other hand, MWCNTs could enhance the catalytic performance by changing the surface geometry that inhibited the adsorption of poisoning CO, which is a typical intermediate in the reaction mechanism of EOFA that is responsible for the potential deterioration of the catalytic performance of DFAFCs. Interestingly with this modification, a significant enhancement in the catalytic activity and stability toward EOFA was achieved. Several techniques will be employed to evaluate the catalyst’s morphology, composition, crystal structure, and activity and further to understand the role of each of the nano-MnOx and MWCNTs in the catalytic enhancement.

Steady State Kinetic Study of the Formic Acid Electrooxidation Reaction on Iridium in a Flow Cell

Steady State Kinetic Study of the Formic Acid Electrooxidation Reaction on Iridium in a Flow Cell

2,2′-bipyridine palladium (II) complexes derived N-doped carbon encapsulated palladium nanoparticles for formic acid oxidation

Doping nitrogen (N) into the carbon support was widely applied to enhance the performance of Pd toward formic acid electro-oxidation (FAO). However, traditional nitrogen doping methods can only introduce a low content of nitrogen as well as a two-step complicated procedure to synthesize catalysts. In this study, a facile one-pot strategy is demonstrated to prepare N-doped carbon encapsulated palladium nanoparticles (Pd@NxC) via the pyrolysis of 2,2′-bipyridine palladium (II) complexes. A N-doped carbon layer with the thickness of about 4 nm is in-situ generated over Pd nanoparticles by only one pyrolysis procedure. Both XPS and in-situ XRD results suggest that metallic Pd is reduced from Pd2+ by the complexed N in bipyridine during the pyrolysis at high temperature. The physical characterizations prove that the in-situ formation of N-doped carbon shell can not only effectively prevent the agglomeration or dissolution of Pd nanoparticles, but also promote the charge donation from the carbon layer to Pd, and maintain the structure of Pd atom complexed to two pyridinic-N atoms (Pd-N). This in-situ synthesis strategy can be successfully applied to carbon supports with different geometry, such as reduced graphene oxide and Vulcan XC-72. Pd@N3C/rGO, which contains the highest amount of N (7.39 at.%) and Pd-N (33.15%), shows the highest specific activity (5.88 mA cm−2) and excellent durability toward FAO.

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.

Trends in Formic Acid Electro-Oxidation on Transition Metals Alloyed with Platinum and Palladium

Trends in Formic Acid Electro-Oxidation on Transition Metals Alloyed with Platinum and Palladium