Electrochemical Oxidation Of Formic Acid Research Articles

Electrochemical Oxidation of Formic Acid on PdM (M=Cr, Mn, Fe, Co, Ni, and Ag) Alloy Nanoparticles with Low M Content: A Comparative Study

AbstractPdM (M=Cr, Mn, Fe, Co, Ni, and Ag) alloy nanoparticles with low M content were prepared using a chemical method and characterized by field emission scanning electron microscopy (FE‐SEM), energy dispersive X‐ray (EDX), EDX mapping, X‐ray diffraction (XRD), and transmission electron microscopy (TEM) analyses. The electro‐oxidation of formic acid on these samples was investigated by linear sweep voltammetry, cyclic voltammetry, and chronoamperometry in H2SO4 solution. The PdAg electrocatalyst demonstrated superior electrocatalytic activity toward the oxidation of formic acid with the mass activity of 1980 mA mg−1Pd which was significantly higher than the mass activity of commercial Pd/C electrocatalysts. Additionally, the PdAg electrocatalyst had the best CO poisoning tolerance as well as the best stability in the considered solution.

Pd-M (M = Ni, Co) Bimetallic Catalysts with Tunable Composition for Highly Efficient Electrochemical Formic Acid Oxidation

Bimetallic Pd-based catalysts for formic acid oxidation (FAO) are one of the most promising anode materials for the next generation of direct formic acid fuel cells (DFAFC). It is imperative to develop a simple strategy for preparing efficient, stable, and clean nanoparticle catalysts. Herein, we prepared a series of Pd, PdNi, and PdCo nanoparticle catalysts using the nanoparticle beam composite deposition system, which revealed good catalytic activity and stability in the process of FAO. The incorporation of Ni or Co prevents the adsorption of active intermediates and the accumulation of toxic intermediates in the process of FAO. Therefore, more Pd active centers can be used to decompose formic acid directly by dehydrogenation. The results indicate that PdNi-2 (Pd0.9Ni0.1) and PdCo-3 (Pd0.89Co0.11) catalysts exhibit the optimal catalytic performance, with the mass activity of 1491.5 A g−1Pd and 1401.7 A g−1Pd, respectively, which is 2.1 and 2 times that of the pure Pd sample. By optimizing the rate of Pd to transition metal M (Ni, Co), a high-performance Pd-based catalyst was obtained through their synergistic effect, which provides a new approach for designing efficient anode catalysts for DFAFCs.

Stabilizer-Free PdCu Nanoparticles Dispersed on Carbon Using Taylor Vortex Flow as Catalysts for Electrochemical Oxidation of Formic Acid

Stabilizers play a critical role in synthesizing small and well-dispersed nanoparticles with large catalytic surface areas. Simultaneously, they strongly bind to the surface of the nanoparticles and interfere with the catalytic reaction. In this study, we report that the effects of stabilizers can be replaced by the periodic and uniform fluid shear of Taylor vortex flow (TVF). Small PdCu alloy nanoparticles well-dispersed on carbon were synthesized in the Couette–Taylor reactor using TVF without the stabilizer. TVF could provide effective micromixing for a fast reaction and uniform fluid shear to prevent aggregation in nanoparticle synthesis, thus forming small and well-dispersed nanoparticles. In contrast, turbulent eddy flow generated by impeller agitation in a mixing tank reactor could only synthesize aggregates of nanoparticles seriously, indicating the importance of the periodic uniform flow. The synthesized stabilizer-free PdCu nanoparticles (Pd41Cu59/C) showed 1.4 times and 3 times higher mass activity than PdCu/C covered with a stabilizer (polyvinylpyrrolidone) and commercial Pd/C toward electrochemical formic acid oxidation, respectively.

Computational Study on the Catalytic Performance of Single-Atom Catalysts Anchored on g-CN for Electrochemical Oxidation of Formic Acid

The electrochemical formic acid oxidation reaction (FAOR) has attracted great attention due to its high volumetric energy density and high theoretical efficiency for future portable electronic applications, for which the development of highly efficient and low-cost electrocatalysts is of great significance. In this work, taking single-atom catalysts (SACs) supported on graphitic carbon nitrides (g-CN) as potential catalysts, their catalytic performance for the FAOR was systemically explored by means of density functional theory computations. Our results revealed that the strong hybridization with the unpaired lone electrons of N atoms in the g-CN substrate ensured the high stability of these anchored SACs and endowed them with excellent electrical conductivity. Based on the computed free energy changes of all possible elementary steps, we predicted that a highly efficient FAOR could be achieved on Ru/g-CN with a low limiting potential of −0.15 V along a direct pathway of HCOOH(aq) → HCOOH* → HCOO* → CO2* → CO2(g), in which the formation of HCOO* was identified as the potential-determining step, while the rate-determining step was located at the CO2* formation, with a moderate kinetic barrier of 0.89 eV. Remarkably, the moderate d-band center and polarized charge of the Ru active site caused the Ru/g-CN catalyst to exhibit an optimal binding strength with various reaction intermediates, explaining well its superior FAOR catalytic performance. Hence, the single Ru atom anchored on g-CN could be utilized as a promising SAC for the FAOR, which opens a new avenue to further develop novel catalysts for a sustainable FAOR in formic-acid-based fuel cells.

Leveraging Pd(100)/SnO2 interfaces for highly efficient electrochemical formic acid oxidation.

The electrocatalytic formic acid oxidation (FAO) is the crucial anodic reaction of direct formic acid fuel cells (DFAFCs), but its activity remains to be largely improved in order to be practically viable. The rational development of enhanced catalysts requires thorough consideration of various contributing factors that are possibly integrated in composite systems. Here, we demonstrate that, Pd(100)/SnO2 interfaces, provided being efficiently exploited, can significantly boost FAO activity by a factor of ∼10, compared with pure Pd(100) facets, with the mass activity reaching a record of 14.55 A mgPd-1 at a 40 mV-lower peak potential. Unique Pd/SnO2 nanocomposites with a myriad of Pd(100)/SnO2 interfaces were obtained by a newly developed successive seeded growth strategy, wherein pre-formed SnO2 nanospheres are used as seeds for two-round overgrowth of multitudinous Pd nanocubes. Using electron microscopic, electrochemical, spectroscopic and computational analyses, we found that the Pd(100)/SnO2 interfaces induce lattice contraction and electron loss on Pd nanocubes, which optimize intermediate binding during FAO. Moreover, we showed that the good cubicity of the Pd nanocubes and the presence of SnO2 nearby further promote the activity by facilitating the potential-determining step and the elimination of the poisoning CO intermediate, respectively. As such, the combined high intrinsic activity and number density of Pd(100)/SnO2 interfaces enabled the superior activity of the Pd/SnO2 nanocomposites. The composite material presented here holds promise for application in DFAFCs, but equally importantly, the insights regarding the structure-performance relationship would be beneficial for designing efficient metal/oxide composite catalysts for diverse electro- and photo-catalytic reactions.

Insights into the Effect of Pb on Formic Acid Electro-Oxidation on Pt

Formic acid is a promising energy carrier and electrochemical formic acid oxidation can serve as an important reaction within fuel cells. Although Pt remains the best-known catalyst, but the major currents contributing pathways is indirect oxidation pathways, which leads to poor activities at low potentials. The surface adatoms like Pb have been known to promote the direct oxidation pathways significantly. We have carried out theoretical calculations, and experiments to probe the reason for this enhancement. Theoretical results show an upshift of Pt energy levels above the Fermi energy upon adsorption of Pb on the Pt surface, which influences the binding energy of the adsorbates. Reaction free energy calculations of typical intermediates from water (H2O) and formic acid (HCOOH) molecule indicate that Pb adsorption suppresses the adsorption of Hydrogen atoms at potentials typical of underpotential deposition on Pt electrode. This results in larger number of vacant sites on the Pt surface which is now able to carry out formic acid oxidation to CO2. The calculations were supported by electrochemical experiments of underpotentially deposited hydrogen and potential dependent apparent activation energies. Figure 1

Determining the role of Pd catalyst morphology and deposition criteria over large area plasmonic metasurfaces during light-enhanced electrochemical oxidation of formic acid

The use of metal composites based on plasmonic nanostructures partnered with catalytic counterparts has recently emerged as a promising approach in the field of plasmon-enhanced electrocatalysis. Here, we report on the role of the surface morphology, size, and anchored site of Pd catalysts coupled to plasmonic metasurfaces formed by periodic arrays of multimetallic Ni/Au nanopillars for formic acid electro-oxidation reaction (FAOR). We compare the activity of two kinds of metasurfaces differing in the positioning of the catalytic Pd nanoparticles. In the first case, the Pd nanoparticles have a polyhedron crystal morphology with exposed (200) facets and were deposited over the Ni/Au metasurfaces in a site-selective fashion by limiting their growth at the electromagnetic hot spots (Ni/Au-Pd@W). In contrast, the second case consists of spherical Pd nanoparticles grown in solution, which are homogeneously deposited onto the Ni/Au metasurface (Ni/Au-Pd@M). Ni/Au-Pd@W catalytic metasurfaces demonstrated higher light-enhanced FAOR activity (61%) in comparison to the Ni/Au-Pd@M sample (42%) for the direct dehydrogenation pathway. Moreover, the site-selective Pd deposition promotes the growth of nanoparticles favoring a more selective catalytic behavior and a lower degree of CO poisoning on Pd surface. The use of cyclic voltammetry, energy-resolved incident photon to current conversion efficiency, open circuit potential, and electrochemical impedance spectroscopy highlights the role of plasmonic near fields and hot holes in driving the catalytic enhancement under light conditions.

Electrochemical formic acid oxidation catalyzed by graphene supported bimetallic Pd-Ni clusters: The role of Ni content and the hydrogen coverage effect

By means of periodic density functional theory calculations, we have investigated the electrocatalytic formic acid oxidation (FAO) on graphene supported Pd-Ni catalysts and elucidate the detail about the role of Ni content in different Pd-Ni atomic ratio and the hydrogen coverage effect. The FAO reaction often onsets at low oxidation potential range, where deposition of hydrogen is alive and affect the catalytic performance of Pd-Ni clusters, accordingly, the FAO reaction on varied H* ratio Pd-Ni clusters accompanying with enhanced external potential is also considered. In our calculation, the H* saturated situation would suppress the formation of COOH* much more than that of HCOO*, even controlling the reaction energy of HCOO* from HCOOH become moderate in FAO reaction. In addition, the potential requirements to proceed the FAO reaction on Pd10-gra and Pd8Ni2-graphene are similar but Ni content could also suppress formation of COOH* and enhance the interaction between Pd8Ni2-graphene and HCOO* species. Pd6Ni4-grahene model is another choice for FAO reaction, in which the HCOO* species on clean Pd6Ni4-graphene model has lowest onset potential of 0.18 V for HCOO* deprotonation to CO2 in all of our models. However, excess Ni content would cause Ni exposed on Pd2Ni8-grahene, where the HCOO* is downhill in energy with a larger onset potential of 0.59 V for the deprotonation of HCOO*, but the hydride formation of 8H* and 9H* Pd2Ni8-graphene could overcome the question.

Understanding the Effect of Blending Ethanol with Formic Acid on Pd Activity Towards Acidic Oxidation of Concentrated Formic Acid

Direct liquid fuel cells are among the most promising energy conversion devices for sustainable energy applications, especially as portable energy sources. The two most effective fuels are methanol and formic acid (FA), and even though methanol has higher energy content, it is toxic, non-renewable, and has high fuel crossover. However, FA can be produced easily from biomass and it is non-toxic and has a higher open circuit potential among other factors1. Usually, FA can be oxidized through two pathways, a direct pathway that is most desirable and directly produces CO2 2. While the indirect pathway produces CO as an intermedia that can adsorb to the catalyst surface deactivating it (poisoning effect)3. Palladium is known to be the most active catalyst for FA oxidation in acidic media4 but it is also easily poisoned by CO accumulation on its surface. The increase in FA concentration to get higher energy density would make the indirect oxidation pathway more favorable lowering the efficiency of the fuel cell. To overcome this problem low molecular weight organic additives were suggested to be used in combination with FA to suppress this poisoning effect by competing with CO molecules for the adsorption sites on the catalyst surface.In this work, the effect of using ethanol and FA blend fuels on the behavior of Pd/C towards FA oxidation was investigated. The preliminary cyclic voltammetry study showed promising results about ethanol's ability to inhabit the indirect FA oxidation pathway. However, the results obtained by the chronopotentiometry and by studying the first derivatives of the cyclic voltammetry data give more insightful results on the effect of ethanol in the fuel blend. It was found that ethanol will inhabit the indirect oxidation of FA up to specific concentration but it will also affect the direct oxidation after a giving time and that the applied potential will have an effect on the adsorption orientation of Ethanol molecules on the catalyst surface. References 1) Sun, J.; Luo, X.; Cai, W.; Li, J.; Liu, Z.; Xiong, J.; Yang, Z. Ionic-Exchange Immobilization of Ultra-Low Loading Palladium on a RGO Electro-Catalyst for High Activity Formic Acid Oxidation. RSC Adv. 2018, 8 (33), 18619–18625.2) Jiang, K.; Zhang, H.-X.; Zou, S.; Cai, W.-B. Electrocatalysis of Formic Acid on Palladium and Platinum Surfaces: From Fundamental Mechanisms to Fuel Cell Applications. Phys Chem Chem Phys 2014, 16 (38), 20360–20376.3) Gunji, T.; Matsumoto, F. Electrocatalytic Activities towards the Electrochemical Oxidation of Formic Acid and Oxygen Reduction Reactions over Bimetallic, Trimetallic and Core–Shell-Structured Pd-Based Materials. Inorganics 2019, 7 (3), 36.4) Gharib, A.; Arab, A. Improved Formic Acid Oxidation Using Electrodeposited Pd–Cd Electrocatalysts in Sulfuric Acid Solution. Int. J. Hydrog. Energy 2021, 46 (5), 3865–3875.

Electronic Effect or Underpotentially Deposited Hydrogen? Insights into the effect of Pb on formic acid electro‐oxidation on Pt

AbstractFormic acid is a promising energy carrier. Electrochemical formic acid oxidation can serve as an important reaction within fuel cells. Although Pt remains the best‐known catalyst, surface adatoms like Pb have been known to promote formic acid electro‐oxidation significantly. We have carried out first principle‐based calculations, bonding analysis, and experiments to provide insights for this enhancement. Results show that upon adsorption of Pb on the Pt surface, an upshift of Pt energy levels above the Fermi energy is observed, which in general influences the binding energy of the adsorbates. Reaction free energy vs. electrochemical potential diagrams were constructed to understand the interaction of formic acid and water with Pt and Pb‐modified Pt surfaces. Electrochemical experiments indicating the underpotentially deposited hydrogen (Hupd) region and potential‐dependent apparent activation energies indicate that Hupd suppression has an important role to play in the formic acid oxidation reaction. The suppression of the Hupd region on Pb‐modified Pt surface results in free Pt sites that can carry out direct formic acid oxidation to CO2.

Pt–Cu nanoalloy catalysts: compositional dependence and selectivity for direct electrochemical oxidation of formic acid

A PtCu3 nanoalloy catalyst showed much enhanced catalytic activity for the direct electrochemical oxidation of formic acid compared to a commercial platinum catalyst.

Pdm (M=Cr, Mn, Fe, Co, Ni, and Ag) Alloy Nanoparticles with Low M Content for Electrochemical Oxidation of Formic Acid: A Comparative Study

Pdm (M=Cr, Mn, Fe, Co, Ni, and Ag) Alloy Nanoparticles with Low M Content for Electrochemical Oxidation of Formic Acid: A Comparative Study

Separating kinetics and mass transfer in formic acid and formate oxidation on boron doped diamond electrodes

Abstract This paper describes the electrochemical oxidation of formic acid (pH 2) and formate (pH 6 and pH 10) on boron doped diamond electrodes and separates kinetic and mass transfer information using RDE and flow cell experiments. The voltammetry experiments show that the oxidation of formic acid and formate takes place before water oxidation, which indicates that the oxidation takes place via a direct electron transfer (DET) mechanism. The current densities measured in the linear sweep voltammograms were in line with the expected limiting current densities confirming mass transfer limitations. During chrono-amperometric experiments current densities were significantly lower, indicating a decrease in the kinetic rates. This is probably related to a surface modification at the electrode. This modification is reversible as bringing the electrode to low potentials restores the activity. The stable currents observed in the chronoamperometry experiments in the region before water oxidation indicate that there is probably a second DET mechanism, which has a much higher overpotential and a different pH dependency than the first DET mechanism. Koutecky-Levich plots showed clear mixed kinetic and mass transfer control and were used to deduce the Tafel slopes of this second mechanism. The observed high Tafel slopes of 240–300 mV/dec are in line with values reported for other reactions on BDD. Experiments in a parallel plate electrolyser show that the current efficiency is approximately 100% at 2.3 V for all pHs. At higher potentials current efficiency decreases due to the water oxidation. Interestingly at these potentials the formic acid oxidation exceeds the limiting current density, possibly related to the diffusion of ·OH radicals or other oxidation mediators to the bulk solution or the formation of oxygen bubbles on the electrode.

Bell shape vs volcano shape pH dependent kinetics of the electrochemical oxidation of formic acid and formate, intrinsic kinetics or local pH shift?

The interfacial pH at the electrode/electrolyte interface (pHs) and reaction kinetics of electrochemical oxidation of formic acid in the presence or absence of buffers are carried out. The transform from bell shape to volcano shape pH dependence of formic acid oxidation reaction (FOR) is clarified by considering both pHs drift and buffer effect. The Diagram of pHs as a function of FOR current density (j) in solutions with bulk pH (pHb) from 0 to 14 with/without buffers are constructed by numeral calculations, which are compared with experimental results of FOR on Pt and Au. Our study reveals that i) In solutions with 5< pHb <10 free of buffer or with limit buffer capability, there is significant pHs drop and drift of the thermodynamic equilibrium potential (Eeq); ii) FOR on both Pt and Au has a bell shape intrinsic pH dependence with maximum activity close to the pKa of HCOOH; iii) The observed volcano shape pH dependence of FOR activity with a plateau at 5<pHb<10 on top of the volcano is a coincidence related to pHs drift.

Electrocatalytic oxidation of low weight oxygenated organic compounds: A review on their use as a chemical source to produce either electricity in a Direct Oxidation Fuel Cell or clean hydrogen in an electrolysis cell

The electrocatalytic oxidation of low weight oxygenated compounds, such as formic acid and methanol, has been the subject of many investigations since nearly fifty years both for their use in a Direct Oxidation Fuel Cell or to produce clean hydrogen by their electrochemical reforming in an Electrolysis Cell. To optimize the energy efficiency of these processes it is very important to know the reaction mechanisms of their electro-oxidation on suitable and specific electrocatalysts. Andrzej Więckowski, together with Roger Parsons, were among the major scientists involved in the determination of the reaction mechanisms of their oxidation on noble metal electrodes both by electrochemical methods (such as linear and cyclic voltammetry) and physicochemical methods, e.g. radiometry, NMR and Infrared Spectroscopy. This review paper first presents the thermodynamics and kinetics of the electrocatalytic oxidation of low weight oxygenated compounds, together with the reaction mechanisms of the electrochemical oxidation of formic acid and methanol. Then their use, as basic feedstock in a Direct Oxidation Fuel Cell for electricity production with a relatively good efficiency (≈ 40%) or in a Proton Exchange Membrane Electrolysis Cell for the production of clean hydrogen able to feed low temperature fuel cells, is discussed.

Oxidation of Formic Acid, Methanol, and Ethanol at Surface-Modified Pt/C Catalysts

Pt-Bi/C and Pt-Pb/C catalysts were prepared by surface decoration of a commercial Pt/C catalyst, and their catalytic activities for electrochemical oxidation of formic acid, methanol and ethanol were compared. The electrocatalytic activity of these catalysts towards formic acid oxidation has been studied by both cyclic voltammetry and chronoamperometry. It was found that after addition of Bi or Pb, the catalytic activity of the Pt/C catalyst for formic acid oxidation increased greatly at low potentials. Bi in particular was found to greatly enhance oxidation of formic acid through the direct pathway in which absorbed CO is not formed, while it strongly inhibited methanol oxidation. It was found that the currents at 0 V vs SCE for formic acid oxidation at the Pt-Bi/C and Pt-Pb/C catalysts were ~ 6 and ~ 2 times higher, respectively compared to the unmodified Pt/C catalyst. In addition, the Pt-Bi/C catalyst showed more stable activity relative to Pt-Pb/C. The Pt-Bi/C catalyst also showed slightly higher activity for ethanol oxidation at low potentials compared to the unmodified Pt/C.

Mechanistic aspects of the comparative oscillatory electrochemical oxidation of formic acid and methanol on platinum electrode

The characteristics of the electrochemical oscillations that emerge along the catalytic oxidation of small organic molecules critically depend on the coverage and nature of adsorbates. Herein we report experimental results on the electro-oxidation of formic acid and methanol on platinum and platinum-modified electrodes, and under conventional, i.e., cyclic voltammetry, and oscillatory conditions. The investigation was focused on the role played by surface-free sites and the presence of a step with a short-lived specie adsorbed on electrode surface. In order to reduce the coverage of adsorbed species, and thus to increase the main reaction pathway, chronoamperometry in platinum oxide region followed by potential sweeps or the adsorption of ad atoms, like tin, to mitigate the surface poisoning was adopted. Overall, those strategies considerably improved the electrochemical oxidation of formic acid, but had no effect for methanol. Our results show that the efficiency of formic acid electro-oxidation is preferred powered, compared with methanol, on a less poisoned electrode surface, which is obtained through a self-cleaning process driven by the oscillatory electro-oxidation of organic molecules. These results are rationalized in terms of peculiarities of the reaction mechanisms of both systems.

Characterization of Formic Acid Oxidation at Surface-Modified Pt/C Catalysts

Over the last several decades, much attention has been given to low temperature fuel cells which provide energy based on electrochemical oxidation of fuels such as hydrogen and small organic molecules. Many researchers in the field of fuel cell technology have been focusing on the development of cost effective and durable catalysts. Among the small organic fuel molecules, electrochemical study of formic acid oxidation is being intensively investigated for two main reasons; formic acid can be used as a fuel in direct formic acid fuel cells and it can serve as a model reaction that can be used to understand more complex oxidation reactions, such as the oxidation of methanol and ethanol. Platinum is one of the most commonly used and effective catalysts for the oxidation of small organic molecules, despite the fact that it has significant disadvantages, such as high cost and loss of performance due to extreme susceptibility to poisoning by CO. To solve these problems several techniques have been applied, most of which are based on modifying the bulk and/or surface of Pt by a second metal. Heterogeneous bimetallic catalysts often show significantly enhanced catalytic performances because of their improved electronic and chemical properties that are different from their parent metals. Bimetallic catalysts provide opportunities to significantly improved catalytic selectivity, activity and durability. In order to improve the electrochemical oxidation of formic acid, addition of second metals such as Ru, Pb, Os, Sn, Cu, Pd, Rh, Bi has been widely applied. Among them, bismuth especially has received much attention as a Pt surface modifier. Various structures such as PtBi alloy, PtBi intermetallic, and surface modified systems have been reported. Co-deposited, carbon supported PtBi/C [1], under potential deposition [2] and irreversibly absorbed [3] Bi modified Pt surfaces were reported to be good catalysts for formic acid oxidation, in terms of onset potential, activity as well as stability and durability. The primary objective of this research is to obtain mechanistic information on the oxidation of formic acid, methanol and ethanol by comparing the effects of various modifying metals on voltammetric data at surface-modified Pt/C catalysts. For example, Bi was found to greatly enhance oxidation of formic acid through the direct pathway in which absorbed CO is not formed, while it strongly inhibits methanol oxidation. Data for Pb and Rh modified Pt will also be presented.

Bimetallic Pd-Based surface alloys promote electrochemical oxidation of formic acid: Mechanism, kinetics and descriptor

Palladium is well noted as anode catalyst for promoting electrochemical oxidation of formic acid (FAO) in direct formic acid fuel cell thanks to its high CO tolerance. Here, using combined approach of density-functional theory calculations and microkinetic modeling, we investigate the fundamental aspects of FAO catalyzed by bimetallic M@Pd(111) single-atom surface alloys (where M = Mo, Fe, Ru, Co, Ni, Cu, Zn, Ag, Au). Our results suggest that M@Pd(111) are highly stable and outperforms Pd(111) for FAO via primarily the direct mechanism: HCOOH → *HCOO (formate) → CO2 + 2H+ + 2e−. It is revealed that the decoordination of *HCOO from bidentate to monodentate adsorption mode (i.e., *bHuCOO → *mHdCOO) followed by the facile carbonyl-H abstraction forming CO2 + (H++e−) could be the potential-determining steps. Moreover, Mo@Pd(111) is predicted to be the most promising bimetallic Pd-based catalyst for FAO based on the weakest *CO binding and the strongest *OH binding with alloyed Mo, which therefore can be used as an effective descriptor for designing FAO catalysts with high activity. The simulated polarization curves of FAO on Pd(111) and Ru@Pd(111) agree reasonably well with the experiment, an indicative of the validity of mechanism and kinetics derived from this study.

Carbon supported palladium-copper bimetallic catalysts for promoting electrochemical oxidation of formic acid and its utilization in direct formic acid fuel cells

Carbon supported palladium-copper (Pd-Cu) bimetallic catalysts (PdxCuy/Cs) are fabricated by modified polyol method to enhance the reaction rate of formic acid oxidation reaction (FAOR) and the performance of direct formic acid fuel cell (DFAFC) through weakening the bond with the intermediate of formic acid. According to the evaluations, when the ratio of Pd and Cu is 3 : 1 (Pd3Cu1/C), catalytic activity is best. Its maximum current density is 1.68-times better than that of commercial Pd/C. Even from the optical and spectroscopic characterizations, such as TEM, EDS, XPS and XRD, Pd3Cu1/C shows an optimal particle size and a higher degree of alloying. This is because in Pd3Cu1/C catalyst, the d-band center that induces the weakening in adsorption of formate anion groups to Pd surface is most positively shifted, and this positive shift promotes the reaction rate of FAOR, which is the rate determining step. When the performance of DFAFCs using the PdxCuy/C catalysts is measured, the maximum power density (MPD) of DFAFC using Pd3Cu1/C catalyst is 158 mW cm−2, and this is the best MPD compared to that of DFAFCs using other PdxCuy/C catalysts. In addition, in a comparison with commercial Pd/C catalyst, when the same amount of catalyst is loaded, MPD of DFAFC using Pd3Cu1/C catalyst is 22.5% higher than that of DFAFC using commercial Pd/C.