Activity For Formic Acid Oxidation Research Articles

Construction of PtAg‐on‐Au Heterostructured Nanoplates for Improved Electrocatalytic Activity of Formic Acid Oxidation

AbstractDirect formic acid fuel cells have attracted significant attention due to their low fuel crossover, high safety, and high theoretical power density among all proton‐exchange membrane fuel cells. Numerous efforts have been dedicated to studying formic acid oxidation, particularly in the fabrication of high‐performance electrocatalysts with economical utilization of Pt metal. In this work, we report a synthetic strategy to create PtAg dots supported on plate‐like Au nanoparticles and explore their applications in electrocatalytic formic acid oxidation. The highly dispersed nature of the catalytic Pt centers and the successful construction of PtAg−Au trimetallic interfaces makes the current nanostructure an ideal system to allow for a synergetic effect between Pt, Au, and Ag, leading to improved electrocatalysis. Compared with commercial Pt/C, our PtAg‐on‐Au heterogenous nanoplates exhibit superior mass activity, along with enhanced reaction kinetics and long‐term durability for FAOR in an acidic medium. Density functional theory (DFT) simulation results indicate that AgPtAu(111) exhibits a relatively high activity for HCOOH oxidation into CO2 among the various Au‐based catalysts. This work provides a viable strategy for constructing Pt‐based electrocatalysts with controlled Pt ensembles, offering insights into the development of fuel cell catalysts that make highly efficient use of costly noble metals.

Lattice-mismatch-induced formation of defect-rich Pd–Cu alloy nanocages for enhanced formic acid oxidation activity

Lattice-mismatch-induced formation of defect-rich Pd–Cu alloy nanocages for enhanced formic acid oxidation activity

Optimization of Pd–Co–M (M= Cu, Au, Ni) Catalysts for the Oxidation of Formic Acid Using Scanning Electrochemical Microscopy

Formic acid, a versatile substance with applications as both a fuel and hydrogen storage material, emerges as a promising energy source. When utilized as a hydrogen storage material, a single liter of formic acid yields an impressive 590 liters of hydrogen gas under ambient conditions. Furthermore, as a fuel, the Direct Formic Acid Fuel Cell (DFAFC) stands out as a potential energy solution due to its elevated open-circuit voltage, low toxicity, and reduced permeability of high molecular weight membranes. Efficient catalysts play a pivotal role in enhancing the formic acid oxidation reaction, thereby diminishing the anode overpotential and amplifying the hydrogen production efficiency of DFAFC. The conventional method of manually testing each catalyst for optimal formic acid oxidation performance is both time-consuming and resource-intensive. Consequently, this study employs a substrate collection method based on a scanning electrochemical microscope (SECM) microelectrode for catalyst screening. A ternary catalyst array, primarily comprising PdCo with supplementary elements (Au, Cu, Ni), was crafted using the innovative concept of compositional assembly. The SECM facilitated the determination of the catalyst's surface morphology, energy-dispersive spectroscopy gauged the catalyst composition, and X-ray diffraction, along with X-ray photoelectron spectroscopy, confirmed the crystalline structure composition. To delve into the kinetic aspects of the catalyst for formic acid oxidation, a comprehensive analysis was carried out using cyclic voltammetry, stripping voltammetry, electrochemical impedance spectroscopy, and Tafel slope analysis. The outcomes unveiled that the optimal proportions for the ternary catalysts were Pd2Co6Au2, Pd2Co6Cu2, and Pd2Co6Ni2, with Pd2Co6Au2 exhibiting superior attributes such as lower overpotential, heightened resistance to CO poisoning, and enhanced catalytic activity for formic acid oxidation.

Synthesis of platinum-nickel nanoparticles supported by carbon and titanium oxide structures for efficient and enhanced formic acid oxidation

In this study, Platinum Nickel (PtNi) nanoparticles was synthesized using the chemical reduction method and functionalized multi-walled carbon nanotube (f-MWCNT) was synthesized by handling multi-walled carbon nanotube (MWCNT) with weak acid using the arc discharge method. To be evaluated in formic acid oxidation, f-MWCNT supported by PtNi (PtNi@f-MWCNT) and titanium oxide (TiO2) supported by PtNi (PtNi@TiO2) catalysts were synthesized using chemical reduction method. The comparison of PtNi, PtNi@f-MWCNT, and PtNi@TiO2 catalysts obtained in the study for formic acid oxidation is presented and their characterizations were carried out by X-ray Diffraction (XRD), Transmission Electron Microscope (TEM), and Fourier Transform Infrared Spectrometer (FTIR). According to TEM results; PtNi, PtNi@f-MWCNT, and PtNi@TiO2 particle sizes were found to be 12.00 nm, 7.37 nm, and 5.38 nm, respectively. According to the CV results obtained for formic acid oxidation, the anodic peak peaks for PtNi, PtNi@f-MWCNT, and PtNi@TiO2 were 61.20 mA.cm−2, 80.17 mA.cm−2 and 65.07 mA.cm−2, respectively. These results showed that the addition of f-MWCNT and TiO2 support exhibited 1.30 and 1.06 times higher electrocatalytic activity for formic acid oxidation and higher resistance to CO poisoning with If/Ib ratios of 0.97 and 1.48, respectively. With the long-term stability tests obtained, it was observed that the f-MWCNT-supported catalyst showed approximately 9 times more current at the end of 5000 s and provided faster charge transfer with EIS. These findings demonstrated that a more cost-effective catalyst with high electrocatalytic activity was synthesized by obtaining f-MWCNTs from MWCNTs using the arc discharge method. It has also been revealed that TiO2 and f-MWCNT supports exhibit very high potential for fuel cell applications.

Synthesis of new Pd@NDG electrocatalyst by using g-C3N4/GO hydrogel toward formic acid electrooxidation reaction in direct formic acid fuel cell

In this research, the new Pd@NDG electrocatalyst was evaluated for the formic acid oxidation reaction. The nitrogen-doped graphene nanosheets (NDG) support was obtained by heating the g-C3N4/GO hydrogel in an inert atmosphere. The Pd@NDG electrocatalyst was prepared by combined use of NDG and palladium chloride via a one-stage reduction using ascorbic acid. The as-prepared Pd@NDG electrocatalyst displayed high catalytic activity in formic acid oxidation. The significant electrocatalytic performance stems from the presence of the NDG support in the structure of the electrocatalyst. The NDG support improved the physicochemical properties of the catalyst. The NDG support acts as an excellent ligand and leads to increase dispersion of Pd. The number of active metal sites is enhanced by increasing dispersion and exposing the surface area of the electrocatalyst and improving electronic properties, which lead to improving the catalytic performance of the catalyst. Furthermore, the formic acid electrocatalytic activity and the durability of Pd@NDG electrocatalyst as compared to the Pd/C commercial benchmark catalyst. The results displayed that the Pd@NDG electrocatalyst has better performance for formic acid oxidation.

CeO2 promotes electrocatalytic formic acid oxidation of Pd-based alloys

Engineering metal/oxide interface and controlling composition are the important strategies that aim towards obtaining efficient Pd-based electrocatalysts (ECs). Rationally designed ECs for dehydrogenation of formic acid play a dynamic role in the proper utilization of its chemical energy. Herein, we report Pd3M alloy nanoparticles anchored on CCeO2 (Pd3M/CCeO2, M = Cu, Ni, Co) which shows significant performance towards formic acid oxidation (FAO). Interestingly, Pd3M/CCeO2 (M = Cu, Ni, Co) ECs displayed the best FAO activity via the “dehydrogenation” pathway. The remarkable performance can be mainly attributed to the proper electronic and synergistic effects between Pd and the alloyed metal, which leads to Pd lattice contraction and downshift of d-band center. It was also observed that the FAO activity of Pd3Cu/CCeO2 is superior to that of Pd3Co/CCeO2 and Pd3Ni/CCeO2. The oxygen vacancies in CeO2 and strong Pd/CeO2 interactions established by computational and experimental studies contribute towards the overall electrocatalytic behaviour.

Hydrogen Intercalation‐Induced Crystallization of Ternary PdNiP Alloy Nanoparticles For Direct Formic Acid Fuel Cells

AbstractDirect formic acid fuel cells (DFAFCs) are among the promising energy sources in the future low‐carbon economy. A key challenge hindering their scale‐up and commercialization is the lack of efficient electrocatalysts for anodic formic acid oxidation (FAO). Very recently, the FAO performance of palladium hydrides (PdHx) has been found to be superior to the pristine Pd that is well known for its high intrinsic FAO activity. However, there is enormous space for the controlled synthesis and electrocatalytic behaviors of PdHx‐based nanomaterials awaiting to be explored. Herein, the hydrogen intercalation‐induced crystallization of PdNiP alloy nanoparticles is reported, and the obtained PdNiP‐H nanoparticles exhibit excellent FAO performance. Of particular note, the FAO stability of PdNiP‐H is much better than that of pristine Pd‐H. Furthermore, the PdNiP‐H nanoparticles are used as the anode catalyst in a prototype DFAFC, which demonstrate much higher power density than commercial Pd/C. Density functional theory calculations show that the synergistic effect of alloying Ni and P endows the PdNiP‐H with a higher preference toward FAO via the direct pathway and better anti‐CO* poisoning capability. This work shines new light on the development of PdHx‐based nanoalloys with good activity and stability for DFAFC applications.

CO2-Assisted Synthesis of Amorphous and Crystal PdCu Nanodots for Enhanced Photothermal and Catalytic Application

Metallic nanomaterials with an amorphous structure and unique properties have received increasing attention. However, the formation of the amorphous structure is strictly limited by the preparation method, and at the same time, the control of the proportion of amorphous regions is difficult to realize. Here, for the first time, we report that PdCu nanodots with an amorphous or crystal structure can be successfully modulated with the assistance of supercritical carbon dioxide (SC CO2), including their thickness, crystallinity, and valence state. In addition, the corresponding applications of the as-prepared PdCu nanodots are also demonstrated; amorphous PdCu nanodots can realize efficient photothermal conversion, while crystal PdCu nanodots can help realize excellent electrocatalytic activity for formic acid oxidation. The mass activity is 1502.6 mA/mgPd, which is 3.7 times higher than that of the commercial Pd/C catalyst. More importantly, this study sheds light on the amorphization mechanism of a pure metal material system in SC CO2 and provides inspiration for preparing more amorphous nanomaterials with fascinating structures and properties.

Pulsed laser-driven green synthesis of trimetallic AuPtCu nanoalloys for formic acid electro-oxidation in acidic environment

The process of hydrogen energy storage via water electrolysis is challenging because of the highly explosive nature of hydrogen gas. To circumvent this issue, the formic acid aqueous solution is being intensively investigated in the field of fuel cells as of its excellent stability and no hazard of combustion or explosion. In formic acid oxidation (FAO), a formic acid solution is decomposed into CO2, thus generating hydrogen ions and electrons. This process can occur via two pathways, i.e., with or without CO generation. In this study, we prepared AuPtCu alloys as a catalyst for formic acid fuel cell (FAFC) usage employing an ecofriendly pulsed laser without requiring a reducing agent or surfactant. The FAO process catalyzed by the AuPtCu alloys was found to ensue via a direct path, i.e., dehydrogenation in the existence of Pt and Au. Formic acid was directly oxidized to CO2 while CO was removed by Cu. The optimal Au1Pt1Cu0.5 catalyst exhibited the best electrochemical FAO activity, outperforming traditional Pt/C, most likely because of the Cu content enhancing the amount of active surface sites. This research demonstrates the potential of AuPtCu for application in direct FAFCs as a power source for transportable devices.

The Ways for Bi on Pt to Enhance Formic Acid Oxidation

This work presents a correlation between the behavior of formic acid oxidation (FAO) on various Bi-modified Pt(poly) disk electrodes and their morphologies observed on Bi-modified Pt(111) disk electrodes using electrochemical scanning tunneling microscopy (EC-STM) to understand the effects of Bi on Pt. To distinguish the FAO activities of Bi on Pt and plain Pt around Bi, additional Pt was intentionally deposited using two different routes: direct route and iodine route. In direct route, Pt was directly deposited on Bi islands and plain Pt sites around Bi islands, while in iodine route, Pt was exclusively deposited on Bi islands by protecting plain Pt sites with adsorbed iodine. Thus, a comparison of FAO performances on the two Bi-modified Pt electrodes with additional Pt (deposited in the different ways) disclosed a difference in FAO performances on plain Pt sites and Bi islands. When Bi coverage was ~0.04, the Bi deposits were scattered Bi islands enhancing FAO on Pt(poly). The additional Pt deposits using direct route increased FAO efficiency, while the ones using iodine route slightly decreased FAO current. The EC-STM observations indicated that Pt deposits around Bi islands, not on Bi islands, were responsible for the FAO current increase on Bi-modified Pt(poly). The FAO efficiency on Bi-modified Pt(poly) with a Bi coverage of ~0.25 increased by a factor of 2. However, the additional Pt deposits using the two Pt deposition routes notably decreased the FAO current. The dependency of FAO on Bi coverage was discussed in terms of electronic effect and ensemble effect.

Reduced graphene oxide (RGO)-supported AuCore–PdShell nanocomposite electrocatalyst for facile formic acid oxidation

CO tolerant anode electrocatalysts with promising formic acid oxidation activities are necessary to develop DFACs (direct formic acid fuel cells) as viable renewable energy sources. Here, we report capabilities of bimetallic AuCore–PdShell nanoparticles with an average particle size of 5.7 nm strewn across a carbonaceous support made of RGO (reduced graphene oxide), i.e.. for formic acid electrochemical oxidation were elaborated. The microstructural details of as-prepared electrocatalysts were assessed by X-ray diffraction of (XRD), low and high resolution transmission electron microscopy (TEM & HR-TEM) patterns, along with energy dispersive X-ray spectroscopy (EDS) and selected area electron diffraction (SAED) patterns, as well as cyclic voltammetry. At room temperature, nanoparticles' electrocatalytic activity towards formic acid oxidation reaction (FAOR) was measured in a solution made up of N2-saturated 0.5 M H2SO4 and 0.5 M HCOOH. AuCore–PdShell/RGO catalyst showed higher catalytic performance and more stability towards the FAOR unlike in-house synthesized electrocatalysts like Pd/RGO, Au-Pd/RGO and multi-walled carbon nanotubes (MWCNT)-supported Au-Pd (Au-Pd /MWCNT).

Chemically prepared Pd-Cd alloy nanocatalysts as the highly active material for formic acid electrochemical oxidation

In this research, different Pd-Cd alloy electrocatalysts (Pd6.3Cd, Pd2.6Cd, Pd1.1Cd, PdCd1.7, and PdCd5.6) were synthesized by a simple chemical method. The field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), EDX mapping, and X-Ray diffraction (XRD) techniques were employed for the characterization of the prepared samples. These electrocatalysts were deposited on the surface of the glassy carbon electrode and the obtained electrodes were employed for formic acid oxidation in sulphuric acid solution using electrochemical methods. Our results demonstrated that in comparison with the Pd sample, the prepared Pd-Cd alloys possessed higher electrocatalytic activity for formic acid oxidation. It was also found that the Pd6.3Cd sample was the best electrocatalyst with a mass activity of 597.06 mA mg−1Pd among all studied samples. This mass activity was significantly higher compared to the commercial Pd sample. Additionally, the Pd6.3Cd sample was the best sample against poisoning with adsorbed CO intermediate.

Ligand‐Mediated Self‐Terminating Growth of Single‐Atom Pt on Au Nanocrystals for Improved Formic Acid Oxidation Activity

AbstractDecreasing the ensemble size of Pt to isolated single atoms is the key to enhance the electrocatalytic formic acid oxidation reaction (FAOR) by bypassing the indirect reaction path that involves the poisoning by the CO intermediate. However, it is challenging to construct isolated Pt single atoms on a foreign metal substrate, especially at high Pt loadings, because Pt tends to form large ensembles due to the high Pt–Pt bond energy. Herein, a ligand‐mediated self‐terminating growth strategy is reported for reliably controlling the ensemble size of Pt on an Au substrate. The key is to introduce a ligand of sulfite (SO32−) into the synthesis, which preferentially adsorbs at Pt sites, thus substantially increasing the kinetic barrier toward Pt–Pt bond formation. This strategy enables reliable formation of isolated Pt single atoms even at high Pt loadings (up to 26% coverage on Au), which is difficult to achieve by regular syntheses. The resulting catalyst exhibits a high FAOR activity of 38.6 A mgPt−1 in 0.5 m H2SO4+0.25 m HCOOH, 370 times greater than that of the commercial Pt/C. It is believed this strategy is general and potentially applicable to the fabrication of a wide range of noble metal catalysts with tailored ensemble sizes for energy conversion.

Electrosynthesis of palladium nanocatalysts using single droplet reactors and catalytic activity for formic acid oxidation

The synthesis of nanosized palladium (Pd) catalyst from a Pd2+ emulsion is performed using the emulsion nanodroplet-mediated electrodeposition method. In this method, aqueous emulsion droplets act as tiny reactors for the inner precursor (e.g., Pd2+) to reduce and generate the corresponding metal products while they are discretely colliding on the working ultramicroelectrode surface, which is biased at a suitable constant potential. The utilized volume of each reactor (with a given concentration of the Pd2+ precursor) and the monitored total number of deposition (i.e., droplet collision) events, being the critical factors, can facilitate the controllable (or quantifiable) synthesis of Pd nanocatalysts where the amount of Pd per deposition event and the generated product amount are determinable. In this research, individual Pd nanocatalysts nucleate from droplet collisions and become uniformly distributed on the substrate surface. The electrocatalytic activities of the synthesized Pd nanocatalysts for formic acid electrooxidation are higher than ca. 10 A mg(Pd)−1.

Irradiance-Controlled Photoassisted Synthesis of Sub-Nanometre Sized Ruthenium Nanoparticles as Co-Catalyst for TiO2 in Photocatalytic Reactions.

Photoassisted synthesis is as a highly appealing green procedure for controlled decoration of semiconductor catalysts with co-catalyst nanoparticles, which can be carried out without the concourse of elevated temperatures, external chemical reducing agents or applied bias potential and in a simple slurry reactor. The aim of this study is to evaluate the control that such a photoassisted method can exert on the properties of ruthenium nanoparticles supported on TiO2 by means of the variation of the incident irradiance and hence of the photodeposition rate. For that purpose, different Ru/TiO2 systems with the same metal load have been prepared under varying irradiance and characterized by means of elemental analysis, transmission electron microscopy and X-ray photoelectron spectroscopy. The photocatalytic activity of the so-obtained materials has been evaluated by using the degradation of formic acid in water under UV-A light. Particles with size around or below one nanometer were obtained, depending on the irradiance employed in the synthesis, with narrow size distribution and homogeneous dispersion over the titania support. The relation between neutral and positive oxidation states of ruthenium could also be controlled by the variation of the irradiance. The obtained photocatalytic activities for formic acid oxidation were in all cases higher than that of undecorated titania, with the sample obtained with the lowest irradiation giving rise to the highest oxidation rate. According to the catalysts characterization, photocatalytic activity is influenced by both Ru size and Ru0/Ruδ+ ratio.

Palladium Particles Modified by Mixed-Frequency Square-Wave Potential Treatment to Enhance Electrocatalytic Performance for Formic Acid Oxidation

Palladium catalysts have attracted widespread attention as advanced electrocatalysts for the formic acid oxidation (FAO) due to their excellent electrocatalytic activity and relatively high abundance. At present, electrodeposition methods have been widely developed to prepare small-sized and highly-dispersed Pd electrocatalysts. However, the customary use of surfactants would introduce heterogeneous impurities, which requires complicated removal processes. In this work, we reported a two-step electrochemical method that employed square-wave potential treatment (SWPT) to modify electrodeposited Pd particles without the use of capping agents. Under the SWPT with a mixed frequency, Pd particles show significantly reduced size and more dispersed distribution, exhibiting a high mass activity of 1.43 A mg−1 toward FAO, which is 4.6 times higher than the counterpart of commercial Pd/C. The increase in electrocatalytic activity of FAO is attributed to the highly developed surface of palladium particles uniformly distributed over the support surface.

Pt Deposits on Bi-Modified Pt Electrodes of Nanoparticle and Disk: A Contrasting Behavior of Formic Acid Oxidation

This work presents a contrasting behavior of formic acid oxidation (FAO) on the Pt and Bi deposits on different Pt substrates. Using irreversible adsorption method, Bi and Pt were sequentially deposited on Pt electrodes of nanoparticle (Pt NP) and disk (Pt disk). The deposited layers of Bi and Pt on the Pt substrates were characterized with X-ray photoelectron spectroscopy, transmission microscopy and scanning tunneling microscopy. The electrochemical behaviors and FAO enhancements of Pt NP and Pt disk with deposited Bi only (i.e., Bi/Pt NP and Bi/Pt disk), were similar to each other. However, additional deposition of Pt on Bi/Pt NP and Bi/Pt disk (i.e., Pt/Bi/Pt NP and Pt/Bi/Pt disk) changed the electrochemical behavior and FAO activity in different ways depending on the shapes of the Pt substrates. With Pt/Bi/Pt NP, the hydrogen adsorption was suppressed and the surface oxidation of Pt was enhanced; while with Pt/Bi/Pt disk, the opposite behavior was observed. This difference was interpreted as a stronger interaction between the deposited Bi and Pt on Pt NP than that on Pt disk. The FAO performance on Pt/Bi/Pt NP is much better than that on Pt/Bi/Pt disk, most likely due to the difference in the interaction between the deposited Pt and Bi depending on the shapes of Pt substrates. In designing FAO electrochemical catalysts using Pt and Bi, the shape of a Pt substrate was concluded to be critically considered.

Preparation and characterization of hybrid Pd/C nanocomposites and their application in electrocatalytic activity

An environment-friendly oxidation–reduction method was used to prepare Pd/C hybrid nanocomposites (NCs) using carbon as host and Pd nanoparticles (NPs) as surface loading, and sodium citrate was used as a reducing agent. The structures and morphologies of the Pd/C hybrid NCs were characterized by X-ray diffraction, transmission (high-resolution) electron microscopy (TEM, HRTEM), X-ray photoelectron spectroscopy and so on. The results demonstrated that the Pd NPs were deposited on the surface of the C sphere beads, and the Pd NPs were homogeneous and monodispersed. The results also indicated that the diameter of the Pd NPs was 3 ± 0.5 nm and the Pd/C NCs were 197 ± 6.5 nm. In addition, the Pd/C NCs showed improved electrocatalytic activity for formic acid oxidation in comparison with commercial Pd NPs through controlling the surface structures. So, the environment-friendly preparation method provided developmental direction to fabricate all kinds of metal/C hybrid NCs architectures.

Enhancement of anodic oxidation of formic acid on Pd–Fe bimetallic nanoparticles by thermal treatment

The surface composition and catalytic properties of Pd–Fe bimetallic catalysts with identical bulk composition can be continuously tuned by treatment at different temperatures. The activity of these catalysts in formic acid oxidation was related to the treatment temperature. The thermal treatment temperatures ranged from 400 to 600 °C. The Pd–Fe nanoparticles are characterized by an array of analytical techniques including TEM (transmission electron microscopy), XRD (X-ray diffraction), ICP (inductively coupled plasma) and HS-LEIS (low energy ion scattering spectroscopy). The electrocatalytic activity is examined using cyclic voltammetric and chronoamperometric measurements. The Pd–Fe/C catalyst with 500 °C shows the highest electrocatalytic activity for formic acid oxidation, with a current activity 3 times higher than that of before treated Pd–Fe/C catalyst, 5.6 times higher than that of commercial Pt/C catalyst. The migration of Pd to the surface on the nanoparticle catalysts as well as the electrochemical active surface area of the PdFe–H catalysts was shown to play a major role in enhancing the electrocatalytic activity for catalyst. These findings provided important insights into the correlation between the electrocatalytic activity and the treatment temperature of the nanoengineered bimetallic catalysts.

Construction of AuPdPt spherical nanodendrites with a multilayered structure by manipulating etching and regrowth in seeded growth

Size-tunable gold–palladium–platinum nanodendrites with a multilayered structure are successfully prepared via etching–regrowth-involved seeded growth, exhibiting superb electrochemical activity for formic acid oxidation.