Electrocatalysts For Formic Acid Oxidation Research Articles

N-doped hollow carbon nanospheres embedded in N-doped graphene loaded with palladium nanoparticles as an efficient electrocatalyst for formic acid oxidation

N-doped hollow carbon nanospheres embedded in N-doped graphene loaded with palladium nanoparticles as an efficient electrocatalyst for formic acid oxidation

N-doped hollow carbon nanospheres embedded in N-doped graphene loaded with palladium nanoparticles as an efficient electrocatalyst for formic acid oxidation

Efficient electrocatalysts with a low cost, high activity and good durability play a crucial role in the use of direct formic acid fuel cells. Pd nanoparticles supported on N-doped hollow carbon nanospheres (NHCNs) embedded in an assembly of N-doped graphene (NG) with a three-dimensional (3D) porous structure by a simple and economical method were investigated as direct formic acid fuel cell catalysts. Because of the unique porous configuration of interconnected layers doped with nitrogen atoms, the Pd/NHCN@NG catalyst with Pd nanoparticles has a large catalytic active surface area, superior electrocatalytic activity, a high steady-state current density, and a strong resistance to CO poisoning, far surpassing those of conventional Pd/C, Pd/NG, and Pd/NHCN catalysts for formic acid electrooxidation. When the HCN/GO mass ratio was 1:1, the Pd/NHCN@NG catalyst had an outstanding performance in the catalytic oxidation of formic acid, with an activity 4.21 times that of Pd/C. This work indicates a way to produce superior carbon-based support materials for electrocatalysts, which will be beneficial for the development of fuel cells.

Constructing a Triangle Ensemble of Pt Clusters for Enhanced Direct-Pathway Electrocatalysis of Formic Acid Oxidation

The pursuit of operational advancements in direct formic acid fuel cells (DFAFCs) necessitates the development of high-performance platinum (Pt)-based catalysts for formic acid electrooxidation (FAOR). However, FAOR on Pt-based catalysts follows a dual pathway mechanism, in which the direct pathway is a preferred route due to its efficient dehydrogenation process. Conversely, the indirect pathway results in the generation of adsorbed CO species, a process that deleteriously poisons the active sites of the catalyst, with CO species only being oxidizable at higher potentials, causing a significant compromise in catalyst performance. Herein, we have successfully synthesized Pt-C3N4@CNT, where three Pt clusters are precisely dispersed in a triplet form within the C3N4 by virtue of the unique structure of C3N4. The mass activity for the direct pathway (0.44 V) delivered a current density of 1.91 A mgPt−1, while the indirect pathway (0.86 V) had no obvious oxidation peak. The selectivity of Pt-C3N4@CNT catalysts for the direct pathway of FAOR was improved due to the special structure of C3N4, which facilitates the dispersion of Pt tri-atoms in the structure and the electronic interaction with Pt. In this study, we provide a new strategy for the development of highly active and selective catalysts for DFAFCs.

A Facile Preparation of Sandwich-Structured Pd/Polypyrrole-Graphene/Pd Catalysts for Formic Acid Electro-Oxidation.

Direct formic acid fuel cells (DFAFCs) are one of the most promising power sources due to its high conversion efficiency; relatively low carbon emissions, toxicity, and flammability; convenience; and low-cost storage and transportation. However, the key challenge to large-scale commercial applications is its poor power performance and the catalyst's high preparation cost. In this study, a new sandwich-structured Pd/polypyrrole-graphene/Pd (Pd/PPy-Gns/Pd)-modified glassy carbon electrode (GCE) was prepared using a simple constant potential (CP) electrodeposition technique. On the basis of the unique synthetic procedure and structural advantages, the Pd/PPy-Gns/Pd shows a fast charge/mass transport rate, high electrocatalytic activity, and great stability for formic acid electro-oxidation (FAO). The mass activity of Pd/PPy-Gns/Pd electrode reaches 917 mA·mg-1Pd. The excellent catalytic activity is mainly due to the uniform embedding of Pd nanoparticles on the polypyrrole-graphene (PPy-Gns) support, which exposes more active sites, and prevents the shedding and inactivation of Pd nanoparticles. At the same time, the introduction of graphene (Gns) in the PPy further improved the conductivity of the catalyst and accelerated the transfer of electrons.

Enhanced Performance of Bimetallic Pd-based Electrocatalysts for Formic Acid Oxidation

Enhanced Performance of Bimetallic Pd-based Electrocatalysts for Formic Acid Oxidation

Sm2O3 promoted Pd/rGO electrocatalyst for formic acid oxidation

Herein, we report the synthesis of Sm2O3 incorporated palladium based electrocatalyst, supported over reduced graphene oxide (rGO). PdxSmy nanoparticles (20 wt %) are distributed over rGO surface by using sodium borohydride reduction technique. Different physicochemical analyses are used to characterize the PdxSmy/rGO electro-catalysts (x = 2,4,6 and y = 8,6,4). The synthesized materials (PdxSmy/rGOs) are investigated for their catalytic capabilities toward electro-oxidation of formic acid. The results show that adding Sm2O3 to the Pd/rGO electrocatalyst boosts electrochemical activities of the materials toward formic acid oxidation. The optimized catalyst (Pd6Sm4/rGO) shows excellent activity towards formic acid oxidation with current density of 46.70 mA/cm2 compared to reference catalysts i.e., Pd/rGO (28.78 mA/cm2) and Pd/C (22.22 mA/cm2). The optimized catalyst also demonstrates high CO tolerance and great stability during formic acid oxidation reaction. The enhanced activity and stability are attributed to the synergistic interaction between Sm2O3, and palladium nanoparticles supported over reduced graphene oxide.

Sn-doped PdCu alloy nanosheet assemblies as an efficient electrocatalyst for formic acid oxidation.

A ternary alloy catalyst has been confirmed to be an effective catalyst for anode catalysis in direct formic acid fuel cells, which can improve the electrocatalytic performance of the fuel cell by introducing commonly used metal elements to change the Pd electronic structure and can reduce the use of precious metals and the cost of catalyst production. In this study, PdCuSn Ns/C with a special 3D structure was synthesized by a simple two-step wet chemical method. The PdCuSn Ns/C catalyst prepared exhibits excellent catalytic activity and stability for the formic acid oxidation reaction (FAOR). The mass activity of 2420.1 mA mg-1Pd is 3.94 times that of the Pd/C catalyst. The improvement in the electrocatalytic performance stems from the introduction of Cu and Sn atoms and the unique 3D nanosheet structure, which changes the electronic structure of Pd to increase the reactive active site and accelerates the reaction mass transfer rate, and also reduces the content of precious metals, while improving the electrocatalytic performance. Therefore, the PdCuSn Ns/C catalyst has a promising future in the field of electrocatalysis.

Electrocatalysts for Formic Acid-Powered PEM Fuel Cells: Challenges and Prospects

In view of the drawbacks of rechargeable batteries, such as low mass and volumetric energy densities, as well as slow charging rate, proton exchange membrane fuel cells (PEMFCs) are reckoned to be promising alternative devices for energy conversion. Currently, commercial PEMFCs mainly use H 2 as the fuel, but the challenges in generation, storage, and handling of H 2 limit their further development. Among the liquid fuels, formic acid possesses the merits of low flammability, low toxicity, slow crossover rate, faster reaction kinetics, and high volumetric H 2 storage capacity, thus being considered as the most promising energy carrier. It can be used as the energy source for direct formic acid fuel cells (DFAFCs) and formic acid-based H 2 -PEMFCs, which are also called indirect formic acid fuel cells (IFAFCs). A common issue hindering their commercialization is lacking efficient electrocatalysts. In DFAFCs, the anodic electrocatalysts for formic acid oxidation are suffering from stability issue, whereas the cathodic electrocatalysts for oxygen reduction are prone to poisoning by the permeated formic acid. As for IFAFCs, CO and CO 2 impurities generated from formic acid dehydrogenation will cause rapid decay in the catalytic activity. High working temperature can improve the CO and CO 2 tolerance of catalysts but will accelerate catalyst degradation. This review will discuss the mitigation strategies and recent advances from the aspect of electrocatalysts to overcome the above challenges. Finally, some perspectives and future research directions to develop more efficient electrocatalysts will be provided for this promising field.

Facile synthesis of PdCu nanocluster-assembled granular films as highly efficient electrocatalysts for formic acid oxidation

Facile synthesis of PdCu nanocluster-assembled granular films as highly efficient electrocatalysts for formic acid oxidation

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.

Galvanic replacement-mediated synthesis of Pd–Cu alloy nanospheres as electrocatalysts for formic acid oxidation

Rational synthesis of bimetallic electrocatalysts with the special geometric structure for direct formic acid fuel cells remains yet challenging. Herein, a facile synthetic strategy is presented to prepare the bimetallic Pd–Cu alloy nanospheres (Pd–Cu ANSs) catalysts based on the galvanic replacement and high-temperature reconstruction. The formation mechanism of Pd–Cu ANSs is studied thoroughly from comprehensive characterizations and control experiments. The optimized Pd–Cu ANSs with unique nanosphere structure as well as regulated electronic structure provide excellent electrocatalytic performance for formic acid oxidation reaction (FAOR) with a specific activity of 6.11 mA cm-2Pd and mass activity of 1569.48 mA mg-1Pd, which are 2.7 times and 3.5 times as high as these of the Pd/C catalyst. This synthetic method outlined here could provide a new pathway for noble metal-based alloy nanomaterials for diverse applications.

Pd nanoparticles anchored on porous boron nitride nanofibers as highly active and stable electrocatalysts for formic acid oxidation

Direct formic acid fuel cells (DFAFCs) are promising power generation technologies for various electronic devices. The design of efficient and stable electrocatalysts for the formic acid oxidation reaction (FAOR) plays an important role for the commercial applications of the DFAFCs. Herein, porous boron nitride (BN) supported Pd nanoparticles (NPs) have been developed as unique and effective composite catalysts for FAOR. Porous BN nanofibers (BNNFs) has been utilized as a functional support to anchor of Pd NPs. The high specific surface area and rich porosity of BNNFs play a key role for the well-dispersion and stabilization of Pd NPs with uniform ultra-small size (~2.32 nm) on their surface. The developed Pd/BNNFs composite catalyst exhibits excellent catalytic activity for FAOR with the mass activity of 725 mA mg−1Pd and a very low onset potential (about −0.12 V). Comparative experiments confirm that the microstructure of porous BN carrier greatly affects the electrocatalytic behaviors of the composite catalyst in FAOR. As compared with the composite catalyst using BN microfibers (BNMFs) as a support, the developed Pd/BNNFs catalyst shows superior catalytic activity and long-term stability owing to the larger specific surface area of BNNFs and stronger interaction between Pd NPs and support. This study not only illustrates that porous BN is a desirable catalyst carrier for catalytic FAOR but also provides new ideas for the design of novel BN-based catalysts.

Rational design of defect-rich tungsten-molybdenum oxide modified carbon supported Pd as superior performances electrocatalyst for formic acid oxidation

A novel defect-rich tungsten-molybdenum oxide modified carbon support (WMOx-C) is prepared by adsorption and calcination of mixed heteropolyacids on Vulcan XC-72 carbon. The Pd/WMOx-C and Pd/C catalysts are fabricated by the liquid reduction method. Results show that the Pd/WMOx-C exhibits a more even distribution and smaller particle size. Electrochemical measurements demonstrate that the Pd/WMOx-C presents superior electrocatalytic performances and stability than that of Pd/C. The mass activity and specific oxidation activity of Pd/WMOx-C are 3.04 and 1.89 times as those of Pd/C, respectively. In addition, the negatively shifted CO-stripping peak (59 mV than Pd/C), enhanced stability and lower charge transfer resistance value are observed for Pd/WMOx-C. The improvement of electrocatalytic performances of Pd/WMOx-C catalyst may be assigned to the uniformly dispersed Pd with smaller particle size, electronic tuning of Pd by WMOx, rapid change of the oxidation state of molybdenum with the redox couples Mo5+/Mo6+ and resultant defects of Pd/WMOx-C.

Tailor-Made Iron and Nickel Nanowire Oxides at Platinum Catalyst for Formic Acid Electro-Oxidation

Tailor-Made Iron and Nickel Nanowire Oxides at Platinum Catalyst for Formic Acid Electro-Oxidation

Tailor-designed nanowire-structured iron and nickel oxides on platinum catalyst for formic acid electro-oxidation.

This investigation is concerned with designing efficient catalysts for direct formic acid fuel cells. A ternary catalyst containing iron (nano-FeOx) and nickel (nano-NiOx) nanowire oxides assembled sequentially onto a bare platinum (bare-Pt) substrate was recommended for the formic acid electro-oxidation reaction (FAOR). While nano-NiOx appeared as fibrillar nanowire bundles (ca. 82 nm and 4.2 μm average diameter and length, respectively), nano-FeOx was deposited as intersecting nanowires (ca. 74 nm and 400 nm average diameter and length, respectively). The electrocatalytic activity of the catalyst toward the FAOR depended on its composition and loading sequence. The FeOx/NiOx/Pt catalyst exhibited ca. 4.8 and 1.6 times increases in the catalytic activity and tolerance against CO poisoning, respectively, during the FAOR, relative to the bare-Pt catalyst. Interestingly, with a simple activation of the FeOx/NiOx/Pt catalyst at −0.5 V vs. Ag/AgCl/KCl (sat.) in 0.2 mol L−1 NaOH, a favorable Fe2+/Fe3+ transformation succeeded in mitigating the permanent CO poisoning of the Pt-based catalysts. Interestingly, this activated a-FeOx/NiOx/Pt catalyst had an activity 7 times higher than that of bare-Pt with an ca. −122 mV shift in the onset potential of the FAOR. The presence of nano-FeOx and nano-NiOx enriched the catalyst surface with extra oxygen moieties that counteracted the CO poisoning of the Pt substrate and electronically facilitated the kinetics of the FAOR, as revealed from CO stripping and impedance spectra.

Pd(1 1 1)/SnO2(1 0 1) heterostructure on porous N-carbon material as enhanced catalyst for formic acid electrooxidation

High specific surface area carbon materials act as a critical factor of fuel cell catalyst carriers. In this study, the PtxPdy/SnO2/GC nanocatalysts were successfully synthesized at different molar ratios of Pt and Pd to conduct the formic acid oxidation. In addition, the N-doped porous carbon carrier (GC) was prepared with graphene oxide and gelatin through the solvated volatilization/nanometer SiO2 template/KOH activation, and the prepared carrier GC took up a large specific surface area (SBET = 1104.5 m2/g). The fine-tuning of the atomic ratio of Pt and Pd was demonstrated to further guide the growth of ultra-small nanocrystals that achieved an average size of 2.52 nm and displayed uniform distributions on the prepared GC carrier. Compared with PtPd/GC, PtSnO2/GC and Pt/GC catalysts, Pt1Pd1/SnO2/GC took up a larger electrochemical activity area of 528.93 cm2/mg, and the positive sweep peak current density reached 2258.45 mA/mgPt at 0.75 V. As confirmed by the DFT analysis, the heterojunction structure formed between the Pt-Pd (111) and SnO2 (101) surfaces would contribute to the electron transport. The optimal electrochemical performance was reasonably attributed to the synergistic effect exerted by PtPd alloy and SnO2, as well as N-doped porous carbon carrier.

Nitrogen and Phosphorus Self-Doped Carbon Supported Palladium as Highly Efficient Electrocatalysts for Formic Acid Oxidation

Nitrogen and Phosphorus Self-Doped Carbon Supported Palladium as Highly Efficient Electrocatalysts for Formic Acid Oxidation

PdRu Nanoparticles Supported on Functionalized Titanium Carbide—a Highly Efficient Catalyst for Formic Acid Electro-Oxidation

PdRu Nanoparticles Supported on Functionalized Titanium Carbide—a Highly Efficient Catalyst for Formic Acid Electro-Oxidation

Bimetallic Pd–Fe Supported on Nitrogen-Doped Reduced Graphene Oxide as Electrocatalyst for Formic Acid Oxidation

This study was conducted to exploit the properties of nitrogen-doped reduced graphene oxide (N-rGO) as support material for formic acid fuel cell. Nitrogen-doped reduced graphene oxide was synthesized by the hydrothermal synthesis method using graphene oxide (GO) flakes and urea as a nitrogen source. Palladium and iron with controllable atomic ratio were used as the active metals. Graphene oxide and carbon nanotube-supported PdFe nanoparticles were synthesized for comparison. The structure, morphology, and chemical composition of the synthesized catalysts were ascertained by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The average particle sizes for Pd3Fe/N-rGO and Pd/N-rGO were 4.65 and 3.95 nm, respectively. The electrochemical characterizations (CO stripping, cyclic voltammetry, and chronoamperometry) showed that the Pd3Fe/N-rGO electrocatalyst had higher electrocatalytic activity and stability compared with that of Pd3Fe/rGO and Pd3Fe/CNT. The mass activity of Pd3Fe/N-rGO in 0.5 M of HCOOH and 0.5 M of H2SO4 solutions was 1463.9 mAmg−1 Pd, which was 3.3 and 1.35 times that of the activity obtained with graphene oxide and carbon nanotubes with the same composition, respectively. The superior performance of the Pd3Fe/N-rGO catalyst was ascribed to the presence of nitrogen functionalities in the nitrogen-doped reduced GO and the synergistic interaction between Pd and Fe nanoparticles. Nitrogen-doped reduced GO promoted the formation of smaller and narrowly distributed nanoparticles and exerted favorable electronic effects because of electron transfer from N to Pd. Therefore, Pd3Fe/N-rGO can serve as a potential electrocatalyst for the oxidation of formic acid.

Robust and Efficient Pd–Cu Bimetallic Catalysts with Porous Structure for Formic Acid Oxidation and a Mechanistic Study of Electrochemical Dealloying

To obtain highly efficient and robust electrocatalysts for formic acid oxidation, PdxCuy/C binary catalysts with porous structures were successfully prepared via electrochemical dealloying. Catalysts with different Pd/Cu atomic ratios were characterized through transmission electron microscopy, inductively coupled plasma atomic emission spectroscopy, and X-ray diffraction. The optimized dealloyed Pd1Cu4/C catalyst with a porous structure displayed a catalytic activity of 2611 A g−1 and high stability (30.5% activity retention under repeated cyclic voltammetric (CV) patrol), whereas a commercial Pd/C-Aldrich benchmark showed a catalytic activity of 785 A g−1 and retained 16.5% activity. A detailed mechanistic study of electrochemical dealloying was performed. Under repeated CV patrol, Pd-enriched porous architectures evolved from Pd-poor surfaces, accompanied by successive Cu dissolution.