Formic Acid Oxidation Research Articles

Combined Role of {001} Facet-Enriched Morphology and Gold Nanoparticle Deposition on Anatase TiO2 Photoactivity.

The interplay on anatase TiO2 photoactivity between particle morphology and gold nanoparticles (NPs) deposition, via either deposition-precipitation (DP) or photodeposition (P), is here investigated by evaluating the photoactivity of Au modified anatase (Au/TiO2) nanocrystals with either a pseudospherical shape or a nanosheet structure in both reduction and oxidation test reactions. The presence of Au NPs on the anatase surface only slightly affects its photoactivity in Cr(VI) reduction, which is kinetically limited by the anodic half-reaction, whereas a larger exposure of highly oxidant {001} facets is beneficial for overcoming this rate-determining step. In the photocatalytic oxidation of both formic acid, proceeding through a direct mechanism, and rhodamine B (RhB) on surface fluorinated photocatalysts, occurring through a hydroxyl-radical-mediated mechanism, the presence of gold NPs produces a significant photoactivity increase only with spherically shaped photocatalysts, mainly exposing {101} facets. These results are rationalized in light of the preferential migration of photogenerated, oppositely charged carriers toward different crystal facets. In fact, when the Au/TiO2 material mainly exposes the more oxidant {001} facets, where photoproduced holes preferentially migrate, recombination between these latter and the electrons captured by Au NPs is favored. Instead, Au NPs on {101} facets efficiently capture photopromoted electrons, preferentially migrating toward such facets with a consequent improvement of photoproduced charge separation.

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

Empowering Tri-Functional Palladium's Catalytic Activity and Durability in Electrocatalytic Formic Acid Oxidation Reaction via Innovative Self-Caging and Alloying Strategies.

Direct formic acid fuel cells (DFAFCs) stand out for portable electronic devices owing to their ease of handling, abundant fuel availability, and high theoretical open circuit potential. However, the practical application of DFAFCs is hindered by the unsatisfactory performance of electrocatalysts for the sluggish anodic formic acid oxidation reaction (FAOR). Palladium (Pd) based nanomaterials have shown promise for FAOR due to their highly selective reaction mechanism, but maintaining high electrocatalytic durability remains challenging. In this study, a novel Pd-based electrocatalyst (UiO-Pd-E) is reported with exceptional durability and activity for FAOR, which can be attributed to the Pd nanoparticles encapsulated within a carbon framework where concurrent chemical alloying of Pd and Zr occurs. Further, the UiO-Pd-E demonstrates noteworthy multifunctionality in various electrochemical reactions including electrocatalytic ethanol oxidation reaction (EOR) and oxygen reduction reaction (ORR) in addition to the FAOR, highlighting its practical potentials.

Visualization of the Distance-Dependent Synergistic Interaction in Heterogeneous Dual-Site Catalysis.

Understanding the characteristics of interfacial hydroxyl (OH) at the solid/liquid electrochemical interface is crucial for deciphering synergistic catalysis. However, it remains challenging to elucidate the influences of spatial distance between interfacial OH and neighboring reactants on reaction kinetics at the atomic level. Herein, we visualize the distance-dependent synergistic interaction in heterogeneous dual-site catalysis by using ex-situ infrared nanospectroscopy and in situ infrared spectroscopy techniques. These spectroscopic techniques achieve direct identification of the spatial distribution of synergistic species and reveal that OH facilitates the reactant deprotonation process depending on site distances in dual-site catalysts. Via modulating Ir-Co pair distances, we find that the dynamic equilibrium between generation and consumption of OH accounts for high-efficiency synergism at the optimized distance of 7.9 Å. At farther or shorter distances, spatial inaccessibility and resistance of OH with intermediates lead to OH accumulation, thereby diminishing the synergistic effect. Hence, a volcano-shaped curve has been established between the spatial distance and mass activity using formic acid oxidation as the probe reaction. This notion could also be extended to oxophilic metals, like Ir-Ru pairs, where volcano curves and dynamic equilibrium further evidence the universal significance of spatial distances.

Cauliflower-like Pd/MoC||Mo2C/C heterostructure as an efficient trifunctional catalyst for formic acid oxidation, hydrogen evolution, and oxygen reduction reactions

The use of Pd-based catalytic materials as electrocatalysts for formic acid oxidation reaction (FAO), hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) has been well-established for some time. The incorporation of a second phase can markedly enhance the electronic properties of the composites. The combination of different compounds with superior electronic properties is crucial for the design and preparation of catalysts with optimal catalytic activity and stability. In this study, a novel cauliflower-like Pd/MoC||Mo2C/C composite with heterostructure is synthesised, which exhibits excellent catalytic activity and long-term stability against FAO, HER, and ORR. The high-temperature treatment results in the formation of small-sized Mo₂C and MoC nanoparticles on the carbonaceous substrate, thereby exposing a greater number of Mo and Mo-C active sites. The formation of heterostructures between Mo₂C and MoC optimises the electronic structure of the composite, thereby facilitating enhanced reaction processes. In terms of FAO, the mass activity of Pd/MoC||Mo2C/C is 1.87A mgPd-1, which is 2.75 times higher than that of Pd/C (0.68A mgPd-1). As for the HER, a much lower overpotential of 28mV is required to achieve a current density of 10mAcm-2 compared to Pd/C (40mV). Fortunately, Pd/MoC||Mo2C/C also shows excellent ORR activity with a half-wave potential of 0.798V and the maximum current density of approximately 5.73mAcm-2 in alkaline electrolyte. These findings may contribute to the development of other noble metal-based materials loaded on intermetallic compounds with stable and effective electrocatalytic performance.

Nanophase-separated ternary PdAgCu nanotubes with rich interfaces for enhanced formic acid oxidation reaction

Herein, a facile strategy for the preparation of PdAgCu ternary nanotubes (NTs) is introduced by using Cu nanowires (NWs) as sacrificial templates along with an acid-leaching treatment. Since the phase separation between Ag and Cu, the obtained PdAgCu NTs is made up of various nanosphases including pure Ag, Cu, bimetallic PdCu and PdAg nanoalloys, instead of PdAgCu trimetallic nanoalloys. By adjusting the types of solvents during synthesis, the surface morphology of PdAgCu NTs can be tuned from smooth (S-PdAgCu NTs) to rough (R-PdAgCu NTs). Both S-PdAgCu NTs and R-PdAgCu NTs exhibit excellent electrocatalytic performances for formic acid oxidation reaction (FAOR). Remarkably, the mass activity of S-PdAgCu NTs for FAOR can reach up to 4307 mA mgPd-1 at peak potential, which is 8.5 times higher than that of commercial Pd (506 mA mgPd-1). The impressively enhanced activity should be ascribed to the synergistic effect of Pd with Cu or Ag and the multi-phase interface engineering, which is resulting from the tight position relationships among different monometallic or bimetallic alloy nanophases.

Palladium-Embedded Laser-Induced Graphene for Efficient Formic Acid Oxidation

Palladium-Embedded Laser-Induced Graphene for Efficient Formic Acid Oxidation

Disentangling heterogeneous thermocatalytic formic acid dehydrogenation from an electrochemical perspective

Heterogeneous thermocatalysis of formic acid dehydrogenation by metals in solution is of great importance for chemical storage and production of hydrogen. Insightful understanding of the complicated formic acid dehydrogenation kinetics at the metal-solution interface is challenging and yet essential for the design of efficient heterogeneous formic acid dehydrogenation systems. In this work, formic acid dehydrogenation kinetics is initially studied from a perspective of electrochemistry by decoupling this reaction on Pd catalyst into two short-circuit half reactions, formic acid oxidation reaction and hydrogen evolution reaction and manipulating the electrical double layer impact from the solution side. The pH-dependences of formic acid dehydrogenation kinetics and the associated cation effect are attributed to the induced change of electric double layer structure and potential by means of electrochemical measurements involving kinetic isotope effect, in situ infrared spectroscopy as well as grand canonical quantum mechanics calculations. This work showcases how kinetic puzzles on some important heterogeneous catalytic reactions can be tackled by electrochemical theories and methodologies.

Bioinspired design of rhodium single-atom nanozymes enable a non-poisoning pathway for direct formic acid oxidation in enzymatic biofuel cells

Solving the dilemma of CO poisoning in electrocatalysts is the crucial step in the commercialization of direct formic acid fuel cells, however, it remains a challenge to design catalysts with high reaction tendency for the direct formic acid oxidation reaction (FAOR) as elaborately as natural enzymes. Herein, inspired by formate oxidase (FOD) with a delicate catalytic pocket, we report that rhodium single-atom nanozymes (Rh SAzymes) can catalyze direct FAOR without worrying about CO poisoning. Impressively, Rh SAzymes exhibit non-CO pathway for direct FAOR in both enzyme-like biocatalytic and electrocatalytic conditions. By combining docking studies and density functional theory calculations, we reveal that this striking reaction tendency mainly stems from thermodynamically unfavorable pathway in the generation and adsorption of CO, much more like that of natural FOD. Moreover, we successfully construct the membrane-less FA/O2 enzymatic biofuel with an open-circuit potential (OCP) of 0.68±0.01 V and a maximum power density (Pmax) of 0.41±0.01 mW cm−2. With 100 % selectivity toward direct anti-poisoning pathway and flexible configuration, the device realizes long-term stable operation and miniaturized goals. Our work not only provides a methodological template for exploring the CO-resilient reaction mechanism of enzyme-like biocatalysts as well as their homologous electrocatalysts in canonical reactions of fuel cells but also paves avenues for the integration of nanozymes in energy equipment.

The Deposition of Lead on a Pt(100) Electrode and the Effects on the Oxidation of Formic Acid

The electrodeposition of foreign metals on a platinum (Pt) electrode can be used to alter the electrochemical properties of the modified electrode. The current study employed in situ scanning tunneling microscopy (STM) to characterize the spatial structures of a monolayer and multilayer lead (Pb) electrodeposited on an ordered Pt(100) electrode in 0.1 M perchloric acid (HClO4) with and without formic acid under potential control. The Pt(100) bead crystal used in this study was pretreated by a modified annealing and quenching method, producing a long-range ordered, unreconstructed (1 × 1) surface. The underpotential deposition (UPD) of Pb on the Pt(100) electrode resulted in a pair of sharp and reversible peak at 0.5 V (vs. Ag/AgCl), prior to the bulk deposition at E < -0.45 V in 0.1 M HClO4 + 1 mM Pb(ClO4)2. Cyclic potential sweeping in the UPD regimes resulted in a stable voltammogram, but bulk Pb deposition led to varying morphologies of the profiles. Atomic resolution STM images were obtained to reveal a well-ordered Pt(100)-(√2 × √2)R45°-Pb structure and elongated rows of Pb aggregates and local (√2 × 2√2) R45° in the initial and final stages of Pb UPD, respectively. Bulk Pb deposition at E < -0.5 V led to a crystalline Pb film, but a roughened Pt(100) surface was imaged after the Pb deposit was anodically stripped. The activity of the Pt(100) electrode toward formic acid oxidation was nearly tripled after being modified with a sub-monolayer of Pb, and increased by another 20 % when it was loaded with multilayer Pb.

Molecular Iridium Catalyzed Electrochemical Formic Acid Oxidation: Mechanistic Insights.

Electrochemical formic acid oxidation reaction (FAOR) is a pivotal model for understanding organic fuel oxidation and advancing sustainable energy technologies. Here, we present mechanistic insights into a novel molecular-like iridium catalyst (Ir-N4-C) for FAOR. Our studies reveal that isolated sites facilitate a preferential dehydrogenation pathway, circumventing catalyst poisoning and exhibiting high inherent activity. In situ spectroscopic analyses elucidate that weakly adsorbed intermediates mediate the FAOR and are dynamically regulated by potential-dependent redox transitions. Theoretical and experimental investigations demonstrate a parallel mechanism involving two key intermediates with distinct pH and potential sensitivities. The rate-determining step is identified as the adsorption of formate via coupled or sequential proton-electron transfer, which aligns well with the observed kinetic properties, pH dependence, and hydrogen/deuterium isotope effects in experiments. These findings provide valuable insights into the reaction mechanism of FAOR, advancing our understanding at the molecular level and potentially guiding the design of efficient catalysts for fuel cells and electrolyzers.

Molecular Iridium Catalyzed Electrochemical Formic Acid Oxidation: Mechanistic Insights

Electrochemical formic acid oxidation reaction (FAOR) is a pivotal model for understanding organic fuel oxidation and advancing sustainable energy technologies. Here, we present mechanistic insights into a novel molecular‐like iridium catalyst (Ir‐N4‐C) for FAOR. Our studies reveal that isolated sites facilitate a preferential dehydrogenation pathway, circumventing catalyst poisoning and exhibiting high inherent activity. In‐situ spectroscopic analyses elucidate that weakly adsorbed intermediates mediate the FAOR and are dynamically regulated by potential‐dependent redox transitions. Theoretical and experimental investigations demonstrate a parallel mechanism involving two key intermediates with distinct pH and potential sensitivities. The rate‐determining step is identified as the adsorption of formate via coupled or sequential proton‐electron transfer, which aligns well with the observed kinetic properties, pH dependence, and hydrogen/deuterium isotope effects in experiments. These findings provide valuable insights into the reaction mechanism of FAOR, advancing our understanding at the molecular level and potentially guiding the design of efficient catalysts for fuel cells and electrolyzers.

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.

Direct Synthesis of Pd2+‐Rich Palladene Aerogels as Bifunctional Electrocatalysts for Formic Acid Oxidation Reaction and Oxygen Reduction Reaction

AbstractIn this work, we developed a direct strategy to fabricate Palladene (i. e. Palladium metallene) aerogels and propose a temperature‐dependent growth mechanism. Besides the typical three‐dimensional networks and wrinkled surface morphologies, the as‐prepared aerogel is endowed with abundant Pd2+. The as‐prepared aerogel exhibits an excellent mass activity in the formic acid oxidation reaction and a good half‐wave potential in the oxygen reduction reaction in comparison with Pd/C and a Pd aerogel. This work expands the range of metal aerogels from the perspective of the building block units and demonstrates a direct approach to fabricate highly promising bifunctional electrocatalysts for fuel cells.

Well-defined Pt-Fe alloy with enhanced catalytic performance for methanol oxidation and formic acid oxidation

Well-defined Pt-Fe alloy with enhanced catalytic performance for methanol oxidation and formic acid oxidation

Designing nanoporous Pd catalyst with dual enhancement of thermodynamics and kinetics for formic acid oxidation reaction

Conventional strategies for developing highly efficient electrocatalysts involve enhancing thermodynamics to minimize overpotential and improving kinetics to maximize reaction current. However, current research on Pd-based catalysts for formic acid oxidation reaction (FAOR) mainly focuses on accelerating its kinetics to increase the peak current. This study proposes a catalyst design that can simultaneously improve the kinetics and thermodynamics of FAOR. Specifically, the home-made catalyst (NPG-Pt1-Pd1) is obtained by sequentially depositing monolayer Pt and Pd shells on the surface of nanoporous gold (NPG) substrate. Compared with commercial Pd/C, this electrocatalyst exhibits a noticeable negative shift in onset potential (∼100 mV) and a significantly improved peak current (∼6 times). Experimental data and theoretical calculations demonstrate that NPG-Pt1-Pd1 exhibits a comparatively suitable adsorption energy for small molecules, not only reducing the overpotential but also accelerating the reaction rate of FAOR. Moreover, when applied in direct formic acid fuel cells (DFAFC), the NPG-Pt1-Pd1 anode with an exceptionally low Pd loading of 8.5 μg cm−2, achieves a remarkable power density of 141 mW cm−2. The power efficiency of Pd is 230 times that of Pd/C (1 mg cm−2, 73 mW cm−2). Therefore, this work provides a new methodology for developing efficient Pd-based FAOR electrocatalysts.

Mechanistic insights into the conversion of flavin adenine dinucleotide (FAD) to 8-formyl FAD in formate oxidase: a combined experimental and in-silico study

Formate oxidase (FOx), which contains 8-formyl flavin adenine dinucleotide (FAD), exhibits a distinct advantage in utilizing ambient oxygen molecules for the oxidation of formic acid compared to other glucose-methanol-choline (GMC) oxidoreductase enzymes that contain only the standard FAD cofactor. The FOx-mediated conversion of FAD to 8-formyl FAD results in an approximate 10-fold increase in formate oxidase activity. However, the mechanistic details underlying the autocatalytic formation of 8-formyl FAD are still not well understood, which impedes further utilization of FOx. In this study, we employ molecular dynamics simulation, QM/MM umbrella sampling simulation, enzyme activity assay, site-directed mutagenesis, and spectroscopic analysis to elucidate the oxidation mechanism of FAD to 8-formyl FAD. Our results reveal that a catalytic water molecule, rather than any catalytic amino acids, serves as a general base to deprotonate the C8 methyl group on FAD, thus facilitating the formation of a quinone-methide tautomer intermediate. An oxygen molecule subsequently oxidizes this intermediate, resulting in a C8 methyl hydroperoxide anion that is protonated and dissociated to form OHC-RP and OH−. During the oxidation of FAD to 8-formyl FAD, the energy barrier for the rate-limiting step is calculated to be 22.8 kcal/mol, which corresponds to the required 14-hour transformation time observed experimentally. Further, the elucidated oxidation mechanism reveals that the autocatalytic formation of 8-formyl FAD depends on the proximal arginine and serine residues, R87 and S94, respectively. Enzymatic activity assay validates that the mutation of R87 to lysine reduces the kcat value to 75% of the wild-type, while the mutation to histidine results in a complete loss of activity. Similarly, the mutant S94I also leads to the deactivation of enzyme. This dependency arises because the nucleophilic OH− group and the quinone-methide tautomer intermediate are stabilized through the noncovalent interaction provided by R87 and S94. These findings not only explain the mechanistic details of each reaction step but also clarify the functional role of R87 and S94 during the oxidative maturation of 8-formyl FAD, thereby providing crucial theoretical support for the development of novel flavoenzymes with enhanced redox properties.

Construction of H-Doped PdB Nanocrystals as Electrocatalysts to Modulate Formic Acid Oxidation.

The strong ligand effect in B-doped Pd-based (PdB) catalysts renders them a promising anode for constructing formic acid fuel cells (FAFCs) exhibiting high power density and outstanding stability. However, the enhancement of the oxidation barrier is unavoidable in this alloy system owing to the electron transfer (ET) from B to Pd. In this study, a hydrogen doping strategy is employed to open charge freedom in PdB compounds and boost their formic acid oxidation reaction (FAOR) activity by suppressing the ET process. The resulting hydrogen-doped PdB (PdBH) exhibits an ultrahigh mass activity of up to 1.2A mg-1 Pd, which is 3.23 times that of the PdB catalyst and 9.55 times that of Pd black. Detailed experimental and theoretical studies show that the interstitial hydrogen leads to enhanced orbital hybridization and reduced electron density around Pd. This optimized ligand effect weakens the carbon monoxide adsorption and increases the direct pathway preference of PdBH, resulting in its outstanding catalytic activity for the FAOR. The development of this high-performance hydrogen-doped PdB catalyst is an important step toward the construction of advanced light element co-doped metal catalysts.

Ultra-Large Two-Dimensional Metal Nanowire Networks by Microfluidic Laminar Flow Synthesis for Formic Acid Electrooxidation.

Despite the great research interest in two-dimensional metal nanowire networks (2D MNWNs) due to their large specific surface area and abundance of unsaturated coordination atoms, their controllable synthesis still remains a significant challenge. Herein, a microfluidics laminar flow-based approach is developed, enabling the facile preparation of large-scale 2D structures with diverse alloy compositions, such as PtBi, AuBi, PdBi, PtPdBi, and PtAuCu alloys. Remarkably, these 2D MNWNs can reach sizes up to submillimeter scale (~220 μm), which is significantly larger than the evolution from the 1D or 3D counterparts that typically measure only tens of nanometers. The PdBi 2D MNWNs affords the highest specific activity for formic acid (2669.1 mA mg-1) among current unsupported catalysts, which is 103.5 times higher than Pt-black, respectively. Furthermore, in situ Fourier transform infrared (FTIR) experiments provide comprehensive evidence that PdBi 2D MNWNs catalysts can effectively prevent CO* poisoning, resulting in exceptional activity and stability for the oxidation of formic acid.