Formic Acid Oxidation Reaction Research Articles

Stabilizing Diluted Active Sites of Ultrasmall High-Entropy Intermetallics for Efficient Formic Acid Electrooxidation.

The poisoning of undesired intermediates or impurities greatly hinders the catalytic performances of noble metal-based catalysts. Herein, high-entropy intermetallics i-(PtPdIrRu)2FeCu (HEI) are constructed to inhibit the strongly adsorbed carbon monoxide intermediates (CO*) during the formic acid oxidation reaction. As probed by multiple-scaled structural characterizations, HEI nanoparticles are featured with partially negative Pt oxidation states, diluted Pt/Pd/Ir/Ru atomic sites and ultrasmall average size less than 2 nm. Benefiting from the optimized structures, HEI nanoparticles deliver more than 10 times promotion in intrinsic activity than that of pure Pt, and well-enhanced mass activity/durability than that of ternary i-Pt2FeCu intermetallics counterpart. In situ infrared spectroscopy manifests that both bridge and top CO* are favored on pure Pt but limited on HEI. Further theoretical elaboration indicates that HEI displayed a much weaker binding of CO* on Pt sites and sluggish diffusion of CO* among different sites, in contrast to pure Pt that CO* bound more strongly and was easy to diffuse on larger Pt atomic ensembles. This work verifies that HEIs are promising catalysts via integrating the merits of intermetallics and high-entropy alloys.

Ceria-modified palladium-based catalysts as high-performance electrocatalysts for oxygen reduction and formic acid oxidation

Recently, a primary challenge hindering the commercialization of direct fuel cells is the development of robust nonplatinum electrocatalysts to improve the performance of the oxygen reduction reaction (ORR) and formic acid oxidation reaction (FAOR). In this paper, polyol reduction and high temperature calcination carbonization were used to improve the conductivity of the catalyst by the modification of rare earth Ce. Pd has similar properties to Pt, with one-fifth of the properties of Pt, and the rare earth elements have low electronegativity, making it easy to supply electrons and fill Pd's antibonding orbitals. Rare Earth elements effectively enhance ORR activity by making palladium more metallic. The high-activity, low-cost and high-stability electrocatalytic ORR and FAOR catalysts PdxCe/C were designed. After a series of testing methods, the physical properties and electrochemical properties were characterized, and the optimum structure and composition were selected. The stability of the catalyst with the optimal structure and composition was assessed, and it was applied to various composite batteries to verify its capability in practical application.

Stabilizing Diluted Active Sites of Ultrasmall High‐Entropy Intermetallics for Efficient Formic Acid Electrooxidation

The poisoning of undesired intermediates or impurities greatly hinders the catalytic performances of noble metal‐based catalysts. Herein, high‐entropy intermetallics i‐(PtPdIrRu)2FeCu (HEI) are constructed to inhibit the strongly adsorbed carbon monoxide intermediates (CO*) during the formic acid oxidation reaction. As probed by multiple‐scaled structural characterizations, HEI nanoparticles are featured with partially negative Pt oxidation states, diluted Pt/Pd/Ir/Ru atomic sites and ultrasmall average size less than 2 nm. Benefiting from the optimized structures, HEI nanoparticles deliver more than 10 times promotion in intrinsic activity than that of pure Pt, and well‐enhanced mass activity/durability than that of ternary i‐Pt2FeCu intermetallics counterpart. In situ infrared spectroscopy manifests that both bridge and top CO* are favored on pure Pt but limited on HEI. Further theoretical elaboration indicates that HEI displayed a much weaker binding of CO* on Pt sites and sluggish diffusion of CO* among different sites, in contrast to pure Pt that CO* bound more strongly and was easy to diffuse on larger Pt atomic ensembles. This work verifies that HEIs are promising catalysts via integrating the merits of intermetallics and high‐entropy alloys.

Enhanced formic acid electro-oxidation reaction over Ir,N-doped TiO2-supported Pt nanocatalyst

In this work, we prepared an Ir,N-doped TiO2 nanomaterial via a facile HNO3-assisted hydrothermal process that was used as an advanced support for nano-sized Pt nanoparticles (NPs) for the formic acid oxidation reaction (FAOR). The physical and electrochemical behaviours of the as-made Pt/Ir,N-doped TiO2 catalyst were systemically investigated through X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), field emission scanning electron microscopes coupled with energy dispersive X-ray analysis (FE-SEM/EDX mapping), transmission electron microscopy (TEM), linear sweep voltammetry (LSV), Tafel slope, CO-stripping, and chronoamperometric (CA) test. The Pt NPs (ca. 3 nm) were anchored on the Ir,N-doped TiO2 support, being formed by a mixture of rutile and brookite with a particle size of several ten nanometers. Due to the small size and uniform distribution of Pt NPs, the Pt/Ir,N-doped TiO2 catalyst had an electrochemical surface area of 79.88 m2 g−1, which was greater than that of the commercial Pt/C (77.63 m2 g−1). In terms of the FAOR, the Pt/Ir,N-doped TiO2 catalyst showed a negative FAOR onset potential, high current density (11.85 mA cm−2), and superior CO-tolerance compared to the commercially available catalyst. Also, the as-made catalyst possessed high electrochemical durability after 3600 s for testing. The enhanced FAOR efficiency was assigned to the formation of a dual-doping effect and strong interplay between Pt and TiO2-based support, which not only improved the electron transfer but also weakened the adsorption of carbonaceous species, thereby boosting the reaction kinetics. This study could open up a facile but effective strategy to promote particular electrochemical applications.

Hollow cubic ternary PdCuB nanocage electrocatalysts with greatly enhanced catalytic performance for formic acid oxidation.

The prepared PdCuB Ngs/C catalysts exhibited outstanding catalytic activity and stability in the formic acid oxidation reaction (FAOR). The improvement in electrocatalytic performance is due to the introduction of Cu and B atoms and the hollow nanocage structure, which changes the electronic structures of Pd, increases the reactive sites, and accelerates the reaction mass transfer rates.

Disentangling pH Effects on Electrocatalytic Reactions

Electrocatalysis is the key discipline to enable breakthrough advances in electrochemical energy technology and in the conversion of CO2 into renewable fuels and value-added chemicals. However, crucial electrocatalytic reactions are afflicted with sluggish kinetics and low selectivity. The electrolyte plays a vital role for the course of an electrocatalytic reactions and, in this realm, understanding the impact of the local pH is crucial for electrocatalyst development and design. The high interest in this topic in the research community is well-reflected in the recent literature, cf., e.g., Science 2022, 375 (6579). Explanations of pH effects remain controversial, even for the simplest model reactions, i.e., the hydrogen evolution/oxidation reaction and the formic acid oxidation reaction (FAOR), since a complex interplay of multiple interacting factors, centered around the local reaction environment and kinetic effects, must be disentangled. Theory and modeling are indispensable in this context. We will present a hierarchical framework that self-consistently couples the impacts of the microkinetics, mass transport and double layer charging effects (going beyond Frumkin corrections).1,2 In our modelling work, we will assess the role of distinct phenomena and parameters at play in a step-by-step fashion. The developed framework will be demonstrated for the FAOR and other electrocatalytic reactions.

Epitaxial Ultrathin Pt Atomic Layers on CrN Nanoparticle Catalysts.

The construction of platinum (Pt) atomic layers is an effective strategy to improve the utilization efficiency of Pt atoms in electrocatalysis, thus is important for reducing the capital costs of a wide range of energy storage and conversion devices. However, the substrates used to grow Pt atomic layers are largely limited to noble metals and their alloys, which is not conducive to reducing catalyst costs. Herein, low-cost chromium nitride (CrN) is utilized as a support for the loading of epitaxial ultrathin Pt atomic layers via a simple thermal ammonolysis method. Owing to the strong anchoring and electronic regulation of Pt atomic layers by CrN, the obtained Pt atomic layerscatalyst (containing electron-deficient Pt sites) exhibits excellent activity and endurance for the formic acid oxidation reaction, with a mass activity of 5.17AmgPt -1 that is 13.6 times higher than that of commercial Pt/C catalyst. This novel strategy demonstrates that CrN can replace noble metals as a low-cost substrate for constructing Pt atomic layers catalysts.

Probing the Behavior of Composition‐Tunable Ultrathin PtNi Nanowires for CO Oxidation and Small‐Molecule Electrocatalytic Reactions

AbstractWe have successfully synthesized ultrathin nanowires of pure Pt, Pt99Ni1, Pt9Ni1, and Pt7Ni3 using a modified room‐temperature soft‐template method. Analysis of both methanol oxidation reaction (MOR) and ethanol oxidation reaction (EOR) results found that the Pt7Ni3 samples yielded the best performance with specific activities of 0.36 and 0.34 mA/cm2 respectively. Additionally, formic acid oxidation reaction (FAOR) tests noted that both Pt and PtNi nanowires oxidize small organic molecules (SOMs) via an indirect pathway. CO oxidation data suggests little measurable performance without any pre‐reduction treatment; however, after annealing in H2, we detected significantly improved CO2 formation for both Pt9Ni1 and Pt7Ni3 motifs. These observations highlight the importance of pre‐treating these nanowires under a reducing atmosphere to enhance their performance for CO oxidation. To explain these findings, we collected extended x‐ray adsorption fine structure (EXAFS) spectroscopy data, consistent with the presence of partial alloying with a tendency for Pt and Ni to segregate, thereby implying the formation of a Pt‐rich shell coupled with a Ni‐rich core. We also observed that the degree of alloying within the nanowires increased after annealing in a reducing atmosphere, a finding deduced through analysis of the coordination numbers and calculations of Cowley's short range order parameters.

Formic acid electrooxidation on palladium nanostructured electrodes in concentrated solutions

The formic acid oxidation reaction (FAO) was evaluated on palladium nanostructured films supported on glassy carbon in 0.5 M H2SO4 + x M HCOOH solutions, where 0.5 ≤ x ≤ 8.0, in the potential range 0.2 ≤ Es / V ≤ 0.6 vs. RHE at 25 °C. Measurements consisted in chronoamperometric experiments, which were followed by stripping voltammetry in order to evaluate the presence of COad. Open circuit potential (OCP) decay was also employed to analyse the formic acid spontaneous decomposition. The results of OCP experiments showed the formation of β-PdH hydride as well as the absence of COad for all HCOOH concentrations, evidencing that the spontaneous decomposition of HCOOH on palladium is the dehydrogenation reaction, which produces H2 and CO2. It was demonstrated that COad is not directly involved in the kinetic mechanism of the FAO on palladium, and it was also explained the controversy related to the detection of COad in previous studies. Additionally, the highest FAO electrocatalytic activity was observed at x = 2.0 M

N-Doped Mesoporous Carbon from Melamine-Modified Resorcinol-Formaldehyde Polymer Resin as Catalytic Support for Electrochemical Investigation of Formic acid Oxidation Reaction

N-Doped Mesoporous Carbon from Melamine-Modified Resorcinol-Formaldehyde Polymer Resin as Catalytic Support for Electrochemical Investigation of Formic acid Oxidation Reaction

Modulation of two-dimensional Pt-based intermetallic nanoplates for fuel cells

Recently, ultrathin two-dimensional (2D) noble-metal-based nanomaterials have gained a lot of attention due to their interesting physicochemical properties and widespread promising applications. In particular, 2D Pt-based intermetallic nanoplates (IMNPs) have been widely studied in cathodic oxygen reduction reaction (ORR), anodic methanol, formic acid, and ethanol oxidation reactions (MOR, FAOR, and EOR) of fuel cells (FCs). In this article, we first give a fundamental understanding of the FCs. Subsequently, several modulation strategies for 2D Pt-based IMNPs including alloying, doping, facet engineering, heterogeneous structure construction, defect and interface engineering, as well as their applications in ORR, MOR, FAOR, and EOR are briefly summarized. Finally, we discuss the current challenges and give our perspectives on the synthesis of high-performance 2D Pt-based IMNPs toward FCs.

PdMo Bimetallene Coupled with MXene Nanosheets as Efficient Bifunctional Electrocatalysts for Formic Acid and Methanol Oxidation Reactions.

In this study, we demonstrate a facile soft chemistry strategy for the in situ growth of two-dimensional (2D) ultrathin PdMo bimetallene tightly coupled with Ti3C2Tx MXene nanosheets (PdMo/Ti3C2Tx) using a robust stereoassembly process. The 2D PdMo bimetallene offers numerous unsaturated Pd atoms and simultaneously induces combined bimetallic alloy and strain effects, while the Ti3C2Tx matrix effectively optimizes the electronic structure of PdMo bimetallene via a face-to-face interface interaction and guarantees exceptional electrical conductivity. As a consequence, the newly designed PdMo/Ti3C2Tx nanoarchitecture expresses remarkable electrocatalytic properties for the formic acid and methanol electro-oxidation, in terms of large electrochemically active surface areas, ultrahigh catalytic activity, strong antipoisoning ability, and dependable long-term stability, all of which are better than those of conventional Pd nanoparticle catalysts supported by Ti3C2Tx and carbon matrices.

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.

Supercritical CO2 Mediated Multi‐scale Structural Engineering in PdCu/C for Boosting Electrocatalytic Formic Acid Oxidation

AbstractNowadays, PdCu alloy nanocatalyst with excellent performance in electrocatalytic formic acid oxidation reaction (FAOR) is believed to have great potential in application of direct formic acid fuel cells. Structural engineering has shown great success in achieving PdCu alloys with high catalytic performance, while achievement of multi‐scale structure engineering is still a great challenge. In this work, we found that supercritical carbon dioxide (SC CO2) could lead to multi‐scale structure engineering in PdCu/C nanocatalysts, including surface defect engineering, phase engineering, morphology engineering and substrate structure engineering. With the assistance of SC CO2, amorphous phase in surface, the transformation from face‐centered cubic (FCC) to body‐centered cubic (BCC) phase, the morphology of 2D nanoflakes and the curved carbon as substrate all contribute to the ultrahigh mass activity for electrocatalytic FAOR as 3624.3 mA/mgPd in PdCu/C nanocatalysts, which is the highest value in PdCu alloy reported up to now. Therefore, this work not only displays the great potential of SC CO2 in multi‐scale structure engineering, but also provides new inspiration of material design to achieve nanocatalysts with ultrahigh catalytic performance.

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.

Deterministic Synthesis of Pd Nanocrystals Enclosed by High-Index Facets and Their Enhanced Activity toward Formic Acid Oxidation.

Noble-metal nanocrystals enclosed by high-index facets are of growing interest due to their enhanced catalytic performance in a variety of reactions. Herein, we report the deterministic synthesis of Pd nanocrystals encased by high-index facets by controlling the rate of deposition (Vdeposition) relative to that of surface diffusion (Vdiffusion). For octahedral seeds with truncated corners, a reduction rate (and thus deposition rate) faster than that of surface diffusion (i.e., Vdeposition/Vdiffusion > 1) led to the formation of concave trisoctahedra (TOH) with high-index facets. When the reduction was slowed down, in contrast, surface diffusion dominated the growth pathway. In the case of Vdeposition/Vdiffusion ≈ 1, truncated octahedra with enlarged sizes were produced. When the reduction rate was between these two extremes, we obtained concave tetrahexahedra (THH) without or with truncation. Similar growth patterns were also observed for the cuboctahedral seeds. When the Pd octahedra, concave TOH, and concave THH were tested for electrocatalyzing the formic acid oxidation (FAO) reaction, those with high-index facets were advantageous over the conventional Pd octahedra enclosed by {111} facets. This work not only contributes to the understanding of surface diffusion and its role in nanocrystal growth but also offers a general protocol for the synthesis of nanocrystals enclosed by high-index facets.

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.

Formic acid oxidation on different coverages of Bismuth-modified Pt(1 0 0): A detailed voltammetric and FTIR study

The formic acid oxidation reaction (FAOR) on bismuth-modified Pt(100) is studied using electrochemical techniques and FITR spectroscopy at different bismuth coverages and formic acid concentrations. The results clearly show that: (1) The measured currents for the Bi-modified Pt(100) surface contain contributions from both the Pt-Bi ensembles and the Pt sites far from the Bi adatoms. (2) The catalytic effect of bismuth is not linked to the adsorption of formate on Pt sites. (3) The bismuth not only improves the activity of the FAOR through the active intermediate but also inhibits the CO poison by a third-body effect. (4) The experimental results indicate that the catalytic activity is linked to the Pt-Bi ensembles. The active species, formate, adsorbs on the Bi site and the neighboring Pt sites facilitate the cleavage of the C–H bond. (5) From the concentration dependence, the reaction order for formate on bismuth-modified Pt(100) is 1 at low potentials. In contrast, a reaction order of 0.5 is obtained at higher potentials. These results are in agreement with the proposed mechanism.

Electronic Modulation of Pd/C by Simultaneous Doping of Cu and Co Tendering a Highly Durable and Methanol-Tolerant Oxygen Reduction Electrocatalyst

Pd-based electrocatalysts are considered as suitable replacement for Pt-based ones owing to the similar electronic structure of Pd, relatively low cost, and superior catalytic performance. The activity and utilization efficiency of Pd in electrochemical reactions can be increased by alloying with transition metals, like Cu and Co. Herein, we report the synthesis of a homogeneously embedded Pd2CuCo alloy in the carbon matrix. Compared with the benchmark Pt/C, the as-synthesized Pd alloy electrocatalyst exhibited an improved limiting current density (Jm; −5.65 mA cm–2), a smaller Tafel slope (58.7 mV dec–1), and a comparable onset potential (Eonset; 0.91 V vs RHE). Comparatively, the optimized Pd2CuCo showed a current retention of ∼96% after a 6 h stability test and only a 4 mV loss in the half-wave potential (E1/2) after 10,000 redox cycles, while Pt/C showed a current retention of 72.5% and a loss of 5 mV in E1/2. Meanwhile, the Pd2CuCo alloy electrocatalyst also demonstrated excellent methanol tolerance compared to benchmark Pt/C. In addition, the electrocatalyst showed higher activity and long-term stability toward the formic acid oxidation reaction than Pd/C, signifying the potential for wide applicability.

Molybdenum-containing carbon nanofiber supported palladium catalyst for formic acid oxidation reaction

Numerous studies have reported the development of Pd-based catalyst for the anode direct formic acid fuel cell (DFAFC) that improves the electrocatalytic activities. We have now developed a carbon nanofiber embedded with carbon black (Vulcan) and molybdenum sulfide (MoS2) nanoparticles as the Pd support for the FAOR catalyst. The MoS2-Vulcan embedded carbon nanofiber (MoS-VECNF) was first prepared by electrospinning and heat treatment. The MoS-VECNF was prepared with different weight ratios of MoS2 to polyacrylonitrile (PAN). The prepared support was then loaded with 20 wt% Pd nanoparticles by the polyol method. The Pd/MoS-VECNF catalyst demonstrated a better FAOR activity and stability as compared to the Pd/VECNF catalyst with 0.10 as the optimum weight ratio. The achieved peak current density was 1.46 times higher than that of the Pd/VECNF catalyst. The presence of MoS2 nanoparticles in the carbon support produced a strong metal-support interaction which improved the FAOR activity and stability of the catalyst. Therefore, the Pd/MoS-VECNF catalyst is suggested to be promising for DFAFC applications.