Pd Adatoms Research Articles

Element-specific cluster growth on the two-dimensional metal–organic network

A porous two-dimensional metal–organic network (2D-MON) on a substrate captures deposited metal atoms and metal clusters growing in the pores of the 2D-MON. We found that the growth mechanisms of Ag, In, and Pd clusters in the 2D-MON synthesized from 1,3,5-tris(4-bromophenyl)benzene molecules on Ag(111) are different from each other, and the difference derives from the interaction of an adatom with the 2D-MON. Ag and Pd clusters grow from the 2D-MON since the interaction of Ag and Pd adatoms with the 2D-MON is attractive. In clusters grow inside of the pores of the 2D-MON since the interaction between an In adatom and the 2D-MON is repulsive. The growth process of metal clusters is determined by the element-specific behavior of metal adatoms in the pores, taking into account interactions with the 2D-MON.

Adsorption and sensing performances of transition metal (Pd, Pt, Ag and Au) doped MoTe2 monolayer upon NO2: A DFT study

Using density functional theory (DFT), the Pd, Pt, Ag and Au dopants are selected as the representatives to study the transition metal (TM)-doping behavior on the pristine MoTe2 monolayer and related NO2 sensing behavior. It is found that Pd and Pt adatoms prefer to be trapped through the TMo site, while Ag and Au dopants prefer to the TH site. The NO2 molecule behaves as electron-acceptor withdrawing charges from the TM-MoTe2 monolayer, based on the Hirshfeld analysis, and NO2 adsorption causes p-doping for Pd- and Pt-doped MoTe2 monolayer, and causes n-doping for Ag- and Au-doped MoTe2 monolayer, which decreases the bandgaps in the former two systems and increase the bandgaps in the latter two systems. Our calculations not only give an insight into the physicochemical property of TM-MoTe2 monolayer, but also elucidate their promising potential as novel NO2 sensors.

Adsorption of greenhouse gases (methane and carbon dioxide) on the pure and Pd-adsorbed stanene nanosheets: A theoretical study

We have examined the adsorption of methane (CH4) and carbon dioxide (CO2) molecules on the perfect and Pd-adsorbed stanene nanosheets using the first-principles computations. Since CH4 and CO2 molecules represent weak physisorption on the pure stanene, we have placed the Pd adatom on the hollow site of stanene sheet to enhance the interaction between stanene and methane molecule. The band structure diagram of the Pd-adsorbed stanene clearly reveals the semiconductor property of the system, being beneficial for gas sensing. Our calculations showed that CH4 adsorption on the Pd-adsorbed stanene is stronger than that on the perfect system. The Pd site of the Pd-stanene system strongly seizes the CH4 molecule. The electron accumulation was also observed along the Pd-Sn bonds, which represents the covalent character of the interaction between Pd and Sn atoms. Besides, after the adsorption of CH4 and CO2 molecules on the perfect and Pd-adsorbed stanene sheets, the systems still continue to be semiconductor with a little band gap. Hence, our theoretical results suggested an excellent potential for Pd-adsorbed stanene nanosheets as promising CH4 and CO2 sensing material.

A monolayer of Pd on ZrC(0 0 1) speeds up O2 dissociation: An ab initio study

We propose the Pd monolayer (ML) on ZrC(001) surface as an effective catalyst for the dissociation of oxygen by density functional theory calculations. We find that the coverage of Pd has a conspicuous impact on the adsorption and dissociation of O2. The strong interaction between the Pd atoms and the ZrC(001) support enhances the reactivity and stability of the electrocatalyst. By comparing the binding energies of Pd-Pd and Pd-C, we conclude that the Pd adatoms do not aggregate to form a cluster and prefer to form a monolayer when the coverage is low. With a monolayer of coverage, the C sites are fully saturated by adsorbed Pd atoms, which prevent the oxidation of the ZrC(001) surface. The dissociation activity of O2 on PdML/ZrC(001) is predicted to be a rival of or even surpass Pt(111). In addition, the high mobility of the dissociated oxygen atoms on PdML/ZrC(001) also benefits the later reaction step for ORR.

Anomalous versus Normal Room-Temperature Diffusion of Metal Adatoms on Graphene.

Fabrication of high-performance heterostructure devices requires fundamental understanding of the diffusion dynamics of metal species on 2D materials. Here, we investigate the room-temperature diffusion of Ag, Au, Cu, Pd, Pt, and Ru adatoms on graphene using ab initio and classical molecular dynamics simulations. We find that Ag, Au, Cu, and Pd follow Lévy walks, in which adatoms move continuously within ∼1–4 nm2 domains during ∼0.04 ns timeframes, and they occasionally perform ∼2–4 nm flights across multiple surface adsorption sites. This anomalous diffusion pattern is associated with a flat (<50 meV) potential energy landscape (PEL), which renders surface vibrations important for adatom migration. The latter is not the case for Pt and Ru, which encounter a significantly rougher PEL (>100 meV) and, hence, migrate via conventional random walks. Thus, adatom anomalous diffusion is a potentially important aspect for modeling growth of metal films and nanostructures on 2D materials.

Electrochemical Modification of Ni-Rich Bimetallic Ni1-x Mx (M= Bi, Pd and Au) Nanoparticles for Glycerol Electro-Oxidation in Alkaline Media

Glycerol partial electro-oxidation to produce various chemicals has attracted a great amount of attention in the decade [1]. Glycerol is the main by-product of biodiesel production and could be converted into high value-added chemicals. The control of catalyst selectivity and activity could be achieved through formulation of novel, nano-structured electrocatalysts. Nickel (Ni) is an attractive material for glycerol electro-oxidation (GEOR) in alkaline media [2], due to its natural abundance, anti-poising and good stability in alkaline media. Designing inexpensive nano-structured 3D Ni electrodes could improve the catalytic activity of Ni, whereas its selectivity could be modified by adding second metal [1].In the present work, GEOR was investigated on Ni-based mono and bi-metallic Ni x Au 1-x, Ni x Bi 1-x and Ni x Pd 1-x (x = 98, 95 and 90 at. %) nanoparticles in 1M KOH. Ni nanoparticles were synthesized by heatless chemical reduction in ethanol using sodium borohydride (NaBH4) as the reducing agent. Resulting Ni-based NPs were characterized using XRD, XPS, TEM, SEM, EDS mapping, HAADF imaging and EELS. Electrochemical measurements were carried out on Ni-based NPs using cyclic voltammetry (CV), chronoamperometry (CA) and linear sweep voltammetry (LSV) at room temperature. Results showed that Ni, NiAu and NiBi NPs are active for GEOR and that reaction proceeds through the formation of NiOOH active phase similar to bulk Ni electrodes [3]. Coupling CA with in-situ polarization modulation infrared-reflection absorption spectroscopy (PM-IRRAS) for the simultaneous analysis of products in the bulk electrolyte solution and on the Ni surface demonstrated that the main reaction products on Ni surface are glyceraldehyde, carbonyl and carboxylate ions. Whereas HPLC analysis reveals that Au, Bi and Pd adatoms strongly influence the reaction products by suppressing the pathways with C–C bond cleavage, hindering the formation of formate and enhancing the production of C2 and C3 products at different applied potentials (1.3, 1.4 and 1.55 V) and temperatures (25 and 50 oC).The correlation of electrocatalytic activity and selectivity with nanoparticle will be discussed in terms of mass activities and product distribution during GEOR.

First-principles study on the adsorption and diffusion properties of non-noble (Fe, Co, Ni and Cu) and noble (Ru, Rh, Pt and Pd) metal single atom on graphyne

Based on first-principles calculations, the adsorption and diffusion behavior of non-noble (Fe, Co, Ni and Cu) and noble (Ru, Rh, Pt and Pd) metal single atom on graphyne were performed. The hole formed by 12C-hexagon ring was found to be the most stable adsorption site. Strong interactions were also verified by bader charge analyses, charge difference density and density of states. Furthermore, the diffusion properties and growth modes of single metal adatoms were studied. With the adsorption on the most stable site getting stronger, the diffusion will get more difficult. The single adatoms diffuse difficultly at room temperature except Pd adatom. Moreover, results imply that Fe, Co, Cu, Ru, Rh, Pt and Pd adatoms present a tendency to grow 3D cluster while Ni adatom shows a tendency to grow 2D metal sheet at high concentration. Results imply graphyne could be a promise candidate substrate for most transition metal atoms.

DFT study of Ptn, Pdn, and Irn (n = 5, 6) clusters adsorbed on graphene: Structural and electronic properties

Adsorption of the transition metal (TM) clusters (Ptn, Pdn, and Irn; n = 5, 6) on the graphene (Gr) layer was investigated using the density functional theory (DFT). It was found that the bridge site between neighboring carbon atoms was the most stable one for the Pt, Pd, and Ir adatoms. The results obtained for the lowest energy configurations of the Gr/TMn systems showed that although the binding energy of the clusters increased with the number of their atoms (n), the energy of adsorption of the clusters to the Gr became weaker. The appending of the van der Waals corrections to the DFT increased the energy of adsorption of TMn clusters to the Gr. The electronic charge analysis showed that the charge was transmitted from the TM atoms to the C atoms. The results obtained showed that there was a peak at the Dirac point due to the TM:d states.

Strain Engineering of a Defect-Free, Single-Layer MoS2 Substrate for Highly Efficient Single-Atom Catalysis of CO Oxidation.

Single-atom catalysts (SACs) are of great scientific and technical importance due to their low cost, high site density, and high specificity to enhance chemical reactions. Nevertheless, a major issue that severely limits the practical exploration of SACs is their instability, i.e., the preference of sintering and clustering over a defect-free substrate during operation. Here, we employ first-principles calculations to investigate how substrate engineering can stabilize SACs by strain-tuning the electronic interactions between the metal and the substrate using two Pd adatoms on a defect-free, single-layer MoS2 as a typical example. It is identified that the Pd2 dimer is prone to dissociate and form highly efficient SACs for CO oxidation due to the enhanced charge transfer and orbital hybridization with the MoS2 substrate under a suitable tensile strain. The straining induces a semiconductive-to-metallic phase transition of the substrate. Moreover, low-cost elements, such as Ag, Ni, Cu, and Cr, can also be stabilized into high-performance SACs for CO oxidation with tunable reaction barriers by straining. The present findings offer a new avenue to inhibit the transition metal atoms from clustering into nanoclusters/particles and provide a clear guidance for the development of highly cost-efficient and stable SACs on defect-free substrates.

First principles investigation of growth of small Pd-Ga bimetallic clusters on MgO(100) surface

Adsorption and diffusion of small sized PdGa bimetallic clusters on the MgO(100) surface are studied by density functional theory, and the growth mechanism of these bimetallic clusters is studied by graph-theoretical kinetic Monte Carlo simulations. All the pure clusters except Ga tetramers are found to be mobile on the surface, and the slow kinetics of Ga tetramers is attributed to its planar shape. At 300 K, all these clusters are kinetically stable and the vacancy sites act as the trapping centers. Upon increasing the temperature, Ga2, Ga3, and Pd1Ga2 clusters tend to escape from the vacancy sites rather than decomposing, whereas all other clusters tend to decompose. The growth of the pure Pd and Ga clusters is heterogeneous, though the elementary reactions involved in the growth process for these two clusters are very different. For the bimetallic PdGa clusters, our simulations show that the thermodynamically more stable Pd adatoms trapped at the vacancy site act as nucleation centers for the cluster growth, and the freely mobile Ga adatoms significantly influence the kinetics of cluster formation. When bimetallic clusters are grown by depositing Pd and Ga adatoms with an equal deposition rate, the bimetallic clusters are formed in the large proportion, especially the clusters with 1:1 atomic ratio are found in the highest fraction. Further, the clusters with the desired stoichiometric ratios can be obtained in a large fraction by varying the deposition rates of the Pd and Ga adatoms on the surface.

Controlling morphology and texture of sputter-deposited Pd films by tuning the surface topography of the (Ti) adhesive layer

In this work, the effect of the deposition parameters of a magnetron sputtered Ti adhesive intermediate layer on the morphology and hydrogen absorption properties of thin Pd films of about 100 nm was investigated. The insertion of an adhesive layer between a Pd film and a rigid substrate usually suppresses or reduces hydrogen absorption. In this study, it is shown that by tuning the surface topography of the intermediate layer the morphology, crystallographic texture and hydrogen absorption properties of the Pd film can be controlled. The surface topography of the Ti layer was characterized using atomic force microscopy. The surface topography strongly depends on the Ti deposition conditions and can vary from widely spread large islands to densely packed small-grained islands depending on thickness (between 1 and 6 nm) and sputter pressure (0.4 and 3 Pa). TEM and XRD analysis led to the conclusion that rough Ti intermediate layers result in Pd films with an open columnar structure with small voids, and a weak and broad (111) texture. Smooth Ti intermediate layers promote the formation of Pd films with a dense columnar structure with fewer voids, and a strong and sharp (111) texture. Changes in the Pd adatom surface diffusion and shadowing effects are the main cause of the observed differences. Pd films with an open columnar morphology and weaker texture show better hydrogen absorption properties with respect to absorption capacity and kinetics of the films with dense columnar morphology. By tuning the surface topography of the Ti adhesive layer, Pd films with controlled morphology and texture can be prepared such that no delamination from the substrate occurs without compromising on absorption properties.

In Situ Atomic-Level Tracking of Heterogeneous Nucleation in Nanocrystal Growth with an Isocyanide Molecular Probe.

We report the use of 2,6-dimethylphenyl isocyanide (2,6-DMPI) as a spectroscopic probe to study the heterogeneous nucleation and deposition of Pd on Ag nanocubes under different conditions by surface-enhanced Raman scattering. As a major advantage, the spectroscopic analysis can be performed in situ and in real time with the nanoparticles still suspended in the reaction solution. The success of this method relies on the distinctive stretching frequencies (νNC) of the isocyanide group in 2,6-DMPI when it binds to Ag and Pd atoms through σ donation and π-back-donation, respectively. Significantly, we discovered that νNC was sensitive to the arrangement of Pd adatoms on the Ag surface. For example, when the isocyanide group bound to one, two, and three Pd atoms, we would observe the atop, bridge, and hollow configurations, respectively, at different νNC frequencies. As such, the νNC band could serve as a characteristic reporter for the Pd adatoms being deposited onto different types of facets on Ag nanocubes with atomic-level sensitivity. When 2,6-DMPI molecules were introduced into the reaction solution, we further demonstrated in situ tracking of heterogeneous nucleation and early stage deposition of Pd on Ag nanocubes by monitoring the evolution of νNC bands for both Ag and Pd surface atoms as a function of reaction time. This in situ technique opens up the opportunity to investigate the roles played by reaction temperature and the type of Pd(II) precursor in influencing the heterogeneous nucleation and growth of bimetallic nanocrystals. The sensitivity of isocyanide group to Pd atoms helps elucidate some of the details on the reduction, deposition, and diffusion processes involved in heterogeneous nucleation.

Self-assembly of bimetallic AuxPd1-x alloy nanoparticles via dewetting of bilayers through the systematic control of temperature, thickness, composition and stacking sequence

Bimetallic alloy nanoparticles (NPs) are attractive materials for various applications with their morphology and elemental composition dependent optical, electronic, magnetic and catalytic properties. This work demonstrates the evolution of AuxPd1-x alloy nanostructures by the solid-state dewetting of sequentially deposited bilayers of Au and Pd on sapphire (0001). Various shape, size and configuration of AuxPd1−x alloy NPs are fabricated by the systematic control of annealing temperature, deposition thickness, composition as well as stacking sequence. The evolution of alloy nanostructures is attributed to the surface diffusion, interface diffusion between bilayers, surface and interface energy minimization, Volmer-Weber growth model and equilibrium configuration. Depending upon the temperature, the surface morphologies evolve with the formation of pits, grains and voids and gradually develop into isolated semi-spherical alloy NPs by the expansion of voids and agglomeration of Au and Pd adatoms. On the other hand, small isolated to enlarged elongated and over-grown layer-like alloy nanostructures are fabricated due to the coalescence, partial diffusion and inter-diffusion with the increased bilayer thickness. In addition, the composition and stacking sequence of bilayers remarkably affect the final geometry of AuxPd1−x nanostructures due to the variation in the dewetting process. The optical analysis based on the UV–vis-NIR reflectance spectra reveals the surface morphology dependent plasmonic resonance, scattering, reflection and absorption properties of AuxPd1−x alloy nanostructures.

Investigation on the morphological and optical evolution of bimetallic Pd-Ag nanoparticles on sapphire (0001) by the systematic control of composition, annealing temperature and time.

Multi-metallic alloy nanoparticles (NPs) can offer additional opportunities for modifying the electronic, optical and catalytic properties by the control of composition, configuration and size of individual nanostructures that are consisted of more than single element. In this paper, the fabrication of bimetallic Pd-Ag NPs is systematically demonstrated via the solid state dewetting of bilayer thin films on c-plane sapphire by governing the temperature, time as well as composition. The composition of Pd-Ag bilayer remarkably affects the morphology of alloy nanostructures, in which the higher Ag composition, i.e. Pd0.25Ag0.75, leads to the enhanced dewetting of bilayers whereas the higher Pd composition (Pd0.75Ag0.25) hinders the dewetting. Depending on the annealing temperature, Pd-Ag alloy nanostructures evolve with a series of configurations, i.e. nucleation of voids, porous network, elongated nanoclusters and round alloy NPs. In addition, with the annealing time set, the gradual configuration transformation from the elongated to round alloy NPs as well as size reduction is demonstrated due to the enhanced diffusion and sublimation of Ag atoms. The evolution of various morphology of Pd-Ag nanostructures is described based on the surface diffusion and inter-diffusion of Pd and Ag adatoms along with the Ag sublimation, Rayleigh instability and energy minimization mechanism. The reflectance spectra of bimetallic Pd-Ag nanostructures exhibit various quadrupolar and dipolar resonance peaks, peak shifts and absorption dips owing to the surface plasmon resonance of nanostructures depending on the surface morphology. The intensity of reflectance spectra is gradually decreased along with the surface coverage and NP size evolution. The absorption dips are red-shifted towards the longer wavelength for the larger alloy NPs and vice-versa.

High performance material for hydrogen storage: Graphenelike Si2BN solid

Recently, two dimensional graphenelike i.e. Si2BN solid monolayer have attracted much attention for the use of hydrogen developments. The work is based on first principles calculations using density functional theory with long range van der Waal (vdW) interactions. The optimized structure is energetically more stable due to high formation energy 45.39 eV with PBE and 50.82 eV with HSE06 functionals, respectively. Our ab-initio studies show that Pd (palladium) adatoms secured graphenelike Si2BN solid via two types of interactions; physisorption and chemisorptions reactions, which engrossing up to 3H2 molecules signifying gravimetric limits of ≈6.95–10.21 wt %. The absorption energies vary from −0.31 eV to −1.93 eV with Pd-adatom and without Pd-adatom respectively, and it varies up to −1.24 eV. The work function of pure Si2BN is 5.36 eV while metal-adatom on monolayer Si2BN with (1 to 6)H2 molecules is 3.53 eV–4.99 eV and reaches up to 5.85 eV. The theoretical study suggests that the functionalized graphenelike Si2BN is efficient for hydrogen storage and propose a possible improvement for advantageous storage of hydrogen at ambient conditions.

First-principles study of CO catalytic oxidation on Pd-doped single wall boron nitride nanotube

The carbon monoxide (CO) catalytic oxidation reaction is a model reaction which is important in serials of technical and industrial applications. In this study, density functional theory (DFT) is employed to explore the catalytic oxidation of CO on Pd-doped boron nitride nanotube (BNNT). The electronic structures and thermodynamic parameters of CO and O2, which are adsorbed on BNNT substrate with Pd embedded at the N- and B- vacancy, are examined in detail. It is revealed that the BNNT substrate with vacancy strongly stabilizes the Pd adatom. Benefit from the B vacancy defect, the Pd atom binds strongly with BNNT. The interaction energy of 3.74eV is strong enough to prevent the aggregation of Pd atom. With B vacancy, Pd atom accepts extra electron from the substrate, causing O2 to bind stronger than CO molecule. An additional charge is transferred to O2 when CO and O2 are co-adsorbed on the substrate. This additional charge thus strengthens the O2 and CO adsorption and changes the electronic structure properties of the tube. Four proposed CO oxidation mechanisms (Eley–Rideal (ER), Langmuir–Hinshelwood (LH), termolecular Eley–Rideal (TER), and termolecular Langmuir–Hinshelwood (TLH)) are studied by calculating the reaction energy barriers along the minimum-energy pathway. It is found that a large reaction barrier exists in the rate-limiting step of the ER mechanism. It is then suggested that the most probable mechanisms for CO oxidation on Pd doped boron vacancy BNNT (Pd-Bv/BNNT) could be the LH mechanism and the new TER and TLH mechanisms under experimental circumstances.

Nanoscale structure of submicron-thick sputter-deposited Pd films: Effect of the adatoms diffusivity by the film-substrate interaction

Pd films were deposited, at room temperature, on Ti and SiO2 substrates by normal (0°) and oblique (36° and 48°) incidence sputtering processes. Scanning electron microscopy was used to analyze the surface and cross morphology of the Pd films so to study the effect of the Pd adatoms surface diffusivity on the films nanostructure. In fact, even if the low homologous temperature (0.17) prescribes that the Pd film grows on both substrates in the Zone I of the structure zone model, some differences are observed: in normal incidence condition, the Pd film on the Ti substrate was found to be formed by tapered grains, while on the SiO2 substrate the Pd film exhibited a columnar morphology with the columns showing a cauliflower shape. Also in the oblique deposition configurations, notable differences in the nanoscale morphology of the Pd films grown in the same conditions are observed on the basis of the supporting substrate. These data suggest that, during depositions, the Pd adatoms diffusivity on the substrate, as determined by the film-substrate interaction both in normal and oblique deposition conditions, is crucial in determining the final film nanostructure. This aspect is semi-quantitatively discussed on the basis of the adsorption energy of the Pd atoms on Ti (0.69eV) and on SiO2 (0.27eV).

Compositional effect on the fabrication of AgxPd1−x alloy nanoparticles on c-plane sapphire at distinctive stages of the solid-state-dewetting of bimetallic thin films

The bilayer composition effect on the evolution of AgxPd1–x nanoparticles is thoroughly investigated by the thermal activation, diffusion and inter-mixing of Ag–Pd adatoms with respect to the growth conditions on c-plane sapphire.

Adsorption of transition metal adatoms on h-BN/Rh(111): Implications for nanocluster self-assembly

The hexagonal boron nitride (h-BN) nanomesh is a promising 2D material for driving the self-assembly of metal nanoparticles with potential catalytic applications. Herein the adsorption of Au, Pt, Ag, Pd, Cu, and Ni adatoms on h-BN/Rh(111) is investigated using density functional theory (DFT) calculations to determine the ability of this pore-wire structure to facilitate the formation of size-limited, monodisperse metal nanoparticles. While all six metal atoms exhibit covalent coupling and negative charging following their adsorption in the pore region, only Au and Pt have sufficiently large barriers (>1.2eV) to prevent pore-to-pore diffusion at room temperature. In contrast, Ag and Cu have pore-to-pore diffusion barriers of only ∼0.5eV, while Pd and Ni show no special affinity for any specific region of the nanomesh. For verification, we have imaged Au, Pt, and Ag on h-BN/Rh(111) at room temperature and submonolayer depositions using STM. Au and Pt form numerous small nanoparticles confined to the pore regions, whereas Ag only forms a few large particles. The difference is fully consistent with the DFT predictions, indicating that our approach has qualitatively predictive power for nanoparticle nucleation and growth behavior on the h-BN/Rh(111) nanomesh.

A Hybrid of Palladium-Graphitic Carbon Nitride-Reduced Graphene Oxide for Methanol and Formic Acid Electrooxidation

A novel nitrogen-rich support material (CNNF-G) consisting of graphitic carbon nitride (g-C3N4) nanoflakelets (CNNF) and reduced graphene oxide (rGO) is designed and fabricated for loading Pd nanoparticles. Structural characterizations indicates that the CNNF is formed via splitting decomposition of the g-C3N4 polymer on rGO at higher temperatures and the resulting CNNF is intimately coupled to the rGO sheets. The CNNF can provide more exposed edge sites and active nitrogen species for the high dispersion of Pd NPs. It is found that the Pd NPs with an average diameter of 3.92 nm are uniformly dispersed on CNNF-G sheets. DFT computations reveal that CNNF can trap Pd adatom and thus act as a Pd nucleation site at which Pd atoms tend to accumulate to form Pd clusters. The Pd-CNNF-G nanocatalyst exhibits excellent electrocatalytic activity for both formic acid and methanol oxidation reactions, including large electrochemically active surface area (ECSA) values, significantly high forward peak current densities, and reliable stability and durability, far outperforming the Pd-graphene, commercial activated carbon-supported Pd catalyst or Pd-carbon nanotubes. Such a stable Pd/CNNF-G nanocatalyst may bring new design opportunities for high-performance direct formic acid fuel cell (DFAFC) and direct methanol fuel cell (DMFC) in the future. Figure 1