Formic Acid Oxidation Reaction Research Articles

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.

Platinum-Lead-Bismuth/Platinum-Bismuth Core/Shell Nanoplate Achieves Complete Dehydrogenation Pathway for Direct Formic Acid Oxidation Catalysis.

Designing platinum (Pt)-based formic acid oxidation reaction (FAOR) catalysts with high performance and high selectivity of direct dehydrogenation pathway for direct formic acid fuel cell (DFAFC) is desirable yet challenging. Herein, we report a new class of surface-uneven PtPbBi/PtBi core/shell nanoplates (PtPbBi/PtBi NPs) as the highly active and selective FAOR catalysts, even in the complicated membrane electrode assembly (MEA) medium. They can achieve unprecedented specific and mass activities of 25.1 mA cm-2 and 7.4 A mgPt-1 for FAOR, 156 and 62 times higher than those of commercial Pt/C, respectively, which is the highest for a FAOR catalyst by far. Simultaneously, they show highly weak adsorption of CO and high dehydrogenation pathway selectivity in the FAOR test. More importantly, the PtPbBi/PtBi NPs can reach the power density of 161.5 mW cm-2, along with a stable discharge performance (45.8% decay of power density at 0.4 V for 10 h), demonstrating great potential in a single DFAFC device. The in situ Fourier transform infrared spectroscopy (FTIR) and X-ray absorption spectroscopy (XAS) results collectively reveal a local electron interaction between PtPbBi and PtBi. In addition, the high-tolerance PtBi shell can effectively inhibit the production/adsorption of CO, resulting in the complete presence of the dehydrogenation pathway for FAOR. This work demonstrates an efficient Pt-based FAOR catalyst with 100% direct reaction selectivity, which is of great significance for driving the commercialization of DFAFC.

Phase Engineering of Intermetallic PtBi2 Nanoplates for Formic Acid Electrochemical Oxidation.

Phase engineering of Pt-based intermetallic catalysts has been demonstrated as a promising strategy to optimize catalytic properties for a direct formic acid fuel cell. Pt-Bi intermetallic catalysts are attracting increasing interest due to their high catalytic activity, especially for inhibiting CO poisoning. However, the phase transformation and synthesis of intermetallic compounds usually occurring at high temperatures leads to a lack of control of the size and composition. Here, we report the synthesis of intermetallic β-PtBi2 and γ-PtBi2 two-dimensional nanoplates with controlled sizes and compositions under mild conditions. The different phases of intermetallic PtBi2 can significantly affect the catalytic performance of the formic acid oxidation reaction (FAOR). The obtained β-PtBi2 nanoplates exhibit an excellent mass activity of 1.1 ± 0.01 A mgPt-1 for the FAOR, which is 30-fold higher than that of commercial Pt/C catalysts. Moreover, intermetallic PtBi2 demonstrates high tolerance to CO poisoning, as confirmed by in situ infrared absorption spectroscopy.

Icosahedral Pd Nanocrystal Catalysts with Dispersed Bi Atoms via Photochemical Route for Enhanced Formic Acid Oxidation Reaction

AbstractThe decoration of noble metal catalysts with specific main group or transition metal atoms offers an effective way to improve the catalytic performance through electronic structure regulation and active site optimization without losing the active surface area. Herein, icosahedral Pd nanocrystals catalysts with highly dispersed Bi atoms decoration have been realized by a simple photochemical reduction approach. The decoration of Bi atoms maintains the original Pd cyclic penta‐twinned structure. The deposition amount of Bi atoms, which greatly affect the catalytic performance, is fundamentally regulated by the irradiation time. Compared with pure Pd, the Pd−Bi icosahedral nanocrystals show significant improvement in electrocatalytic activity towards formic acid oxidation. Besides, the catalytic performance is correlated with the content of Bi. The optimal performance is occurred at the Bi content of 2.86%.

Modulate the metallic Sb state on ultrathin PdSb-based nanosheets for efficient formic acid electrooxidation

Incorporation of oxophilic metals into Pd-based nanostructures has shown great potential in small molecule electrooxidation owing to their superior anti-poisoning capability. However, engineering the electronic structure of oxophilic dopants in Pd-based catalysts remains challenging and their impact on electrooxidation reactions is rarely demonstrated. Herein, we have developed a method for synthesizing PdSb-based nanosheets, enabling the incorporation of the Sb element in a predominantly metallic state despite its high oxophilic nature. Moreover, the Pd90Sb7W3 nanosheet serves as an efficient electrocatalyst for the formic acid oxidation reaction (FAOR), and the underlying promotion mechanism is investigated. Among the as-prepared PdSb-based nanosheets, the Pd90Sb7W3 nanosheet exhibits a remarkable 69.03% metallic state of Sb, surpassing the values observed for the Pd86Sb12W2 (33.01%) and Pd83Sb14W3 (25.41%) nanosheets. X-ray photoelectron spectroscopy (XPS) and CO stripping experiments confirm that the Sb metallic state contributes the synergistic effect of their electronic and oxophilic effect, thus leading to an effective electrooxidation removal of CO and significantly enhanced FAOR electrocatalytic activity (1.47 A mg−1; 2.32 mA cm−1) compared with the oxidated state of Sb. This work highlights the importance of modulating the chemical valence state of oxophilic metals to enhance electrocatalytic performance, offering valuable insights for the design of high-performance electrocatalysts for electrooxidation of small molecules.

Correction to: The effect of small silver inclusions on the palladium activity in formicacid oxidation reaction and corrosion stability

Correction to: The effect of small silver inclusions on the palladium activity in formicacid oxidation reaction and corrosion stability