Low-coordinated Surface Atoms Research Articles

Ultrathin two-dimensional photocatalysts for carbon dioxide reduction into fuels and chemicals

The extensive burning of fossil fuels has caused energy shortages and worsened the greenhouse effect, posing a significant threat to human survival and development. The use of solar energy as a renewable source to reduce CO2 emissions and produce green fuels and high-value chemicals is seen as a promising solution to the ongoing energy crisis. Ultrathin two-dimensional photocatalysts have large surface areas and numerous low-coordination surface atoms, giving them substantial potential for highly efficient photocatalytic performance. These materials can reduce carrier transmission distance, enhance reactant adsorption and activation (e.g., CO2 and H2O), lower energy barriers, facilitate specific reactions, inhibit competing reactions, and regulate catalytic efficiency and selectivity. This article provides a concise overview of ultrathin two-dimensional semiconductor synthesis, clarifies catalytic mechanisms, explores various photocatalytic applications, and outlines strategies to enhance photoconversion performance. It also emphasizes the primary challenges and opportunities faced by ultrathin photocatalysts. We anticipate that this review will offer valuable insights for further research in two-dimensional photocatalysis and encourage the practical application of these unique materials in energy conversion.

SERS Reveals the Presence of Au–O–O–H and Enhanced Catalytic Activity of Electrochemically Dealloyed AgAu Nanoparticles

Due to their high surface-to-volume ratio and large proportion of low coordinated surface atoms, dealloyed nanoparticles have gained increasing attention as porous catalysts for the electrochemical oxygen evolution reaction (OER). Here, we characterize and rationalize the physical and chemical properties of operando gold-enriched porous nanoparticles fabricated by electrochemical dealloying of citrate-capped silver gold alloy nanoparticles in 250 mM KNO3. We combine surface-enhanced Raman spectroscopy (SERS) with electrochemistry for catalyst tracking. With SERS, we observe at 1.05 V (vs platinum quasi-reference electrode) the formation of Au–O–O–H species, a known intermediate of OER, while this is not observed for monometallic gold nanoparticles or bare electrodes. In agreement, qualitative measurements of the catalytic activity prove that appreciable OER currents are detected at lower potentials for gold-enriched porous nanoparticles compared to gold nanoparticles of the same size. Our results pave the way for the application of dealloying-derived nanoparticles as promising catalyst materials.

Intermetallic Pd3Pb nanobranches with low-coordinated surface atoms for highly efficient ethanol oxidation reaction

Pd based bimetallic nanocrystals (NCs) with low-coordinated surface atoms endow a tremendous ability to modify electronic properties and have the synergistic effect to improve electrocatalytic performance. Among various bimetallic NCs with different compositions, intermetallic Pd-Pb NCs can improve the poisoning tolerance of surface active sites during electrocatalytic reactions. In addition, Pb can provide abundant oxygen-containing species (OHads) and has the ability to cleavage the C–C bond during electrocatalysis that can hinder the production of COads intermediate species, thereby improving ethanol oxidation reaction (EOR) performance. Herein, we report a wet-chemical method for synthesizing highly uniform Pd3Pb nanobranches (NBs). The growth process of Pd3Pb NBs was controlled using ascorbic acid as a reductant, oleylamine as a solvent, 1-octadecene as a surfactant, and ammonium bromide as a shape-directing agent. Their unique NB morphology makes them suitable as electrocatalysts, attributed to the effective adsorption of ethanol and (OH)ads and enhanced removal capability of intermediates adsorbed on the active site of Pd3Pb NBs due to the intermetallic Pd–Pb composition and high density of low-coordinated surface atoms in Pd3Pb branches that can enhance EOR in alkaline media. The prepared Pd3Pb NBs exhibited significantly higher mass activity than Pd3Pb nanocubes and commercial Pd/C catalysts.

Bifunctional OER/NRR Catalysts Based on a Thin-Layered Co3O4-x/GO Sandwich Structure.

Due to ample low-coordinated surface atoms, a distorted lattice endows thin-layered transition metal oxides with a flexible electronic structure, making them the ideal candidates for overall ammonia synthesis. This work proposes a novel and facile method for the controllable synthesis of thin-layered Co3O4 catalysts with graphene as a conductive matrix to further enhance the overall N2 fixation performance. X-ray photoelectron spectroscopy (XPS) and synchrotron radiation X-ray absorption spectroscopy (XAS) demonstrate that the sandwiched Co3O4-x/GO catalysts enable exposure of more coordination unsaturated active sites, resulting in numerous oxygen vacancies. With a higher conductivity and distorted crystalline structure, excellent electrochemical NRR activity is realized with a NH3 production rate of 5.19 mmol g-1 h-1 and a Faradaic efficiency of 10.68% at -0.4 V vs reversible hydrogen electrode (RHE). The density functional theory (DFT) calculation demonstrates that introducing oxygen vacancies in thin-layered cobalt oxides could result in an increased density of states (DOS) near the Fermi level, which would accelerate the NRR rate-determining step. Charge transfer could be accelerated through a weak Co 3d-N 2p σ hybrid bond with a lower energy level. No obvious performance decay could be found after six cycles. Furthermore, the sandwiched Co3O4-x/GO catalyst exhibits a low overpotential of 280 mV@10 mA cm-2 and an outstanding durability for the anode OER, even better than those of the benchmark RuO2. Such an inexpensive sandwiched transition metal oxide catalyst shows great potential in the field of overall N2 fixation.

Preparation of 2D Molybdenum Phosphide via Surface-Confined Atomic Substitution.

The emerging nonlayered 2D materials (NL2DMs) are sparking immense interest due to their fascinating physicochemical properties and enhanced performance in many applications. NL2DMs are particularly favored in catalytic applications owing to the extremely large surface area and low-coordinated surface atoms. However, the synthesis of NL2DMs is complex because their crystals are held together by strong isotropic covalent bonds. Here, nonlayered molybdenum phosphide (MoP) with well-defined 2D morphology is synthesized from layered molybdenum dichalcogenides via surface-confined atomic substitution. During the synthesis, the molybdenum dichalcogenide nanosheetfunctions as the host matrix where each layer of Mo maintains their hexagonal arrangement and forms isotropic covalent bonds with P that substitutes S, resulting in the conversion from layered van der Waals material to a covalently bonded NL2DM. The MoP nanosheets converted from few-layer MoS2 are single crystalline, while those converted from monolayers are amorphous. The converted MoP demonstrates metallic charge transport and desirable performance in the electrocatalytic hydrogen evolution reaction (HER). More importantly, in contrast to MoS2 , which shows edge-dominated HER performance, the edge and basal plane of MoP deliver similar HER performance, which is correlated with theoretical calculations. This work provides a new synthetic strategy for high-quality nonlayered materials with well-defined 2D morphology for future exploration.

The Role of Steps on Silver Nanoparticles in Electrocatalytic Oxygen Reduction

Hydrogen fuel cell technology is an essential component of a green economy. However, it is limited in practicality and affordability by the oxygen reduction reaction (ORR). Nanoscale silver particles have been proposed as a cost-effective solution to this problem. However, previous computational studies focused on clean and flat surfaces. High-index surfaces can be used to model active steps presented in nanoparticles. Here, we used the stable stepped Ag(322) surface as a model to understand the ORR performance of steps on Ag nanoparticles. Our density functional theory (DFT) results demonstrate a small dissociation energy barrier for O2 molecules on the Ag(322) surface, which can be ascribed to the existence of low-coordination number surface atoms. Consequently, the adsorption of OOH* led to the associative pathway becoming ineffective. Alternatively, the unusual dissociative mechanism is energetically favored on Ag(322) for ORR. Our findings reveal the importance of the coordination numbers of active sites for catalytic performance, which can further guide electrocatalysts’ design.

Pt core confined within an Au skeletal frame: Pt@Void@Au nanoframes in a molecular dynamics Perspective

Recently, nanoframe structures have attracted high amount of research interest due to their special properties such as open surface structure, high surface-to-volume ratio, large surface areas, and high densities of low-coordination surface atoms in various fields, especially in catalysis research. Since, stability of nanoparticles is an important factor for their application as catalysts, the present study aimed to evaluate the morphological effect of core and frame on the stability of Pt@void@Au nanoframes, where the Pt core is located inside an Au skeleton, using molecular dynamics simulation at room temperature. Hence, cuboctahedral, Marks-decahedral, decahedral, octahedral, icosahedral, cubic, and tetrahedral morphologies were considered for assessment. According to the simulation results, Au frame with various morphologies and coordination numbers from 3 to 6 was unstable at 300 K. In addition, the contraction and collapse of Au atoms in the frame along with the expansion of Pt atoms in the core, lead to void occupation, and increases the coordination number and formation of a more stable Pt@Au structure. The results also demonstrated that stability of the formed Pt@Au core-shell structure depends on initial morphology and obeys the following trend: Marks-decahedral > cubic > octahedral > icosahedral > decahedral > cuboctahedral > tetrahedral

A leaf-like Co-Silicate/CNT hybrid film as free-standing anode for lithium and sodium storage

Electrode materials with high theoretical capacity and high conductivity are critical for high performance rechargeable batteries. Herein, a leaf-like cobalt silicate nanosheet/carbon nanotube (Co-Silicate/CNT) hybrid film is synthesized through a hydrothermal strategy. The Co-Silicate nanosheets provide large accessible surface area and abundant low-coordinated surface atoms with high reactivity. Meanwhile, the Co-Silicate nanosheets are strongly coupled with internally connected CNTs, which afford fast electron transfer and high mechanical stability. Moreover, the open pores can effectively reduce the ion migration distance and alleviate volume changes during charging and discharging cycle. When used as a binder-free anode for LIBs, the Co-Silicate CNT hybrid film exhibits a high initial charge capacity of 846.8 mA h g−1, a good rate performance (1451.3mAhg−1 when reset to 0.1 A g−1 after additional 80 cycles) and excellent cycle performance (331.72mAhg−1 after 1000 cycles at 10 A g−1). As anode materials for sodium storage, it also shows a good rate performance and cycle performance (246.3mAhg−1 after 500 cycles at 1 A g−1). Reaction mechanism analysis reveals that the good performance results from the optimized 3D “branch-leaf” structure and combined effect of capacitance and insertion mechanism. These results indicate that the Co-Silicate/CNT hybrid film has great potential in practical applications as LIB/SIB electrodes.

Formation of extraordinary density alkanethiol self-assembled monolayers on surfaces of digitally photocorroded (001) GaAs/AlGaAs nanoheterostructures

We report the formation of extraordinary density 16-mercaptohexadecanoic acid (MHDA) self-assembled monolayer (SAMs) on surfaces of freshly etched and re-etched bulk (001) GaAs and on GaAs surfaces of a (001) GaAs/Al0.35Ga0.65 As nanoheterostructure exposed by digital photocorrosion (DIP). Our results demonstrate the advantage of a 2-step thiolation process in achieving high-quality MHDA SAMs on (001) GaAs surfaces. However, the development of the systematically increasing quality SAMs, as suggested by the Fourier-transform infrared absorption (FTIR) data, has been observed on the surfaces of GaAs subsequently revealed by DIP of the GaAs/Al0.35Ga0.65 As nanoheterostructure. An MHDA SAM with the maximum absorbance intensity of the asymmetric -CH2 vibrations, νasym = 2919.6 cm−1, equal to 1.08 × 102 and characterized by the full-width-at-half-maximum of 20.3 cm−1, represents the best quality SAM ever obtained on the surface of (001) GaAs. The underlying mechanism has been explained in terms of the formation of nanostructured surfaces with the increasing concentration of low-coordination number surface atoms available for the interaction with MHDA thiolates. The increased surface density of highly-organized SAMs remains in a qualitative agreement with the proposed cone model of DIP nanostructured surfaces.

Correlating 3D Surface Atomic Structure and Catalytic Activities of Pt Nanocrystals.

Active sites and catalytic activity of heterogeneous catalysts is determined by their surface atomic structures. However, probing the surface structure at an atomic resolution is difficult, especially for solution ensembles of catalytic nanocrystals, which consist of heterogeneous particles with irregular shapes and surfaces. Here, we constructed 3D maps of the coordination number (CN) and generalized CN () for individual surface atoms of sub-3 nm Pt nanocrystals. Our results reveal that the synthesized Pt nanocrystals are enclosed by islands of atoms with nonuniform shapes that lead to complex surface structures, including a high ratio of low-coordination surface atoms, reduced domain size of low-index facets, and various types of exposed high-index facets. 3D maps of are directly correlated to catalytic activities assigned to individual surface atoms with distinct local coordination structures, which explains the origin of high catalytic performance of small Pt nanocrystals in important reactions such as oxygen reduction reactions and CO electro-oxidation.

Quantitative Multilayer Cu(410) Structure and Relaxation Determined by QLEED

Industrially relevant catalytically active surfaces exhibit defects. These defects serve as active sites; expose incoming adsorbates to both high and low coordinated surface atoms; determine morphology, reactivity, energetics, and surface relaxation. These, in turn, affect crystal growth, oxidation, catalysis, and corrosion. Systematic experimental analyses of such surface defects pose challenges, esp., when they do not exhibit order. High Miller index surfaces can provide access to these features and information, albeit indirectly. Here, we show that with quantitative low-energy electron diffraction (QLEED) intensity analyses and density functional theory (DFT) calculations, we can visualize the local atomic configuration, the corresponding electron distribution, and local reactivity. The QLEED-determined Cu(410) structure (Pendry reliability factor RP ≃ 0.0797) exhibits alternating sequences of expansion (+) and contraction (−) (of the first 16 atomic interlayers) relative to the bulk-truncated interlayer spacing of ca. 0.437 Å. The corresponding electron distribution shows smoothening relative to the bulk-determined structure. These results should aid us to further gain an atomic-scale understanding of the nature of defects in materials.

The H2-D2 exchange reaction catalyzed by gold nanoparticles supported on γ-Al2O3: Effect of particle size on the reaction rate

Gold nanoparticles supported on γ-Al2O3 catalyzed the hydrogen isotope exchange Н2 + D2 at low temperatures, ca. 77 K. The specific catalytic activity increases by a factor of ~800 as the particle size decreases from 39.3 to 0.7 nm. A correlation has been established between the catalytic activity of nanoparticles of different size and the concentration of low-coordination gold surface atoms. Apparently, the obtained empirical equations can be used to estimate the specific catalytic activity of gold nanoparticles of various sizes.

Low-Coordinated Gold Atoms Boost Electrochemical Nitrogen Reduction Reaction under Ambient Conditions

Exploration of efficient catalysts is a priority for the electrochemical nitrogen reduction reaction (NRR) under ambient temperature and pressure. Recently, several nanostructured gold (Au) catalysts have shown impressive catalytic activities toward NRR. However, the atomic origin of high catalytic activities of Au catalysts is vague. In this work, a quantitative relationship between the generalized coordination number (GCN) and NRR activity is established. In particular, the NRR activity is linearly increased with the decrease of GCN values of Au surface atoms. As a proof-of-concept experiment, the NRR activity of nanoporous gold (NPG) with a high proportion of low-coordinated surface atoms is investigated and compared with that of Au octahedra (OCTA) enclosed with (111) facets. As expected, NPG exhibits a high NH3 production rate of 30.5 μg h–1 mg–1, which is 5.8 times larger than that of Au OCTA. In addition, the excellent catalytic performance of NPG can be retained for 21 h by showing constant curren...

Hierarchical nanoporous Pd1Ag1 alloy enables efficient electrocatalytic nitrogen reduction under ambient conditions.

Nanoporous Pd1Ag1 nanoleaves with the merits of an appropriate atomic ratio, abundant low-coordinated surface atoms, efficient reactant accessibility and fast interfacial electron transfer kinetics exhibit superior catalytic activity towards the electrochemical nitrogen reduction reaction relative to nanoporous Pd1Ag2 and Pd3Ag1 alloys.

Heterogeneity governs diameter-dependent toughness and strength in SiC nanowires

Using a combination of density functional theory and molecular dynamics simulations, this paper reveals the atomistic origin of diameter-dependent extreme mechanical behavior of [111] 3C-SiC nanowires obtained from an energy-based framework. Our results suggest that heterogeneity in atomic stress and variations in diameter-dependent potential-energy density have a profound impact on extreme mechanical properties in the nanowires. The heterogeneity in stress evolves from the nonuniform bond lengths mediated by low coordinated surface atoms---and it penetrates the entire cross section in thinner nanowires and constitutes the atomistic basis for their large reduction in fracture strain, toughness, and strength. Although stress heterogeneity is substantially higher in ultrathin nanowires, its intensity drops and saturates rapidly in larger nanowires following a nonlinear dependence on diameter. The maximum stress heterogeneity in a cross section localizes crack nucleation at the core in ultrathin nanowires but near the surface in larger nanowires. Moreover results show that stiffness, toughness, strength, and fracture strain of the nanowires increase nonlinearly with increasing diameter and saturate at a lower value compared to bulk SiC. In addition to resolving wide discrepancies in the reported values of the first-order elastic modulus in SiC nanowires, the findings highlight heterogeneity as a critical factor for inducing diameter-dependent extreme mechanical behavior in brittle nanowires.

Assembly of TiO2 ultrathin nanosheets with surface lattice distortion for solar-light-driven photocatalytic hydrogen evolution

Atomically two-dimensional semiconductor nanomaterials have drawn tremendous attention in photocatalytic applications due to their unique and remarkable properties. Herein, the assembly of TiO2 ultrathin nanosheets was fabricated from the titanate sheets using a gas-assisted liquid exfoliation method combined with hydrogenation treatment strategy. The hydrogenation treatment can introduce more surface point defects such as oxygen vacancies without damaging the ultrathin two-dimensional structure. The ultrathin two-dimensional assembly has high percentages of low-coordinated surface atoms and large specific surface areas (340 m2/g), which could increase the absorption of photon and accelerate the photocatalytic reaction process. Meanwhile, homogeneous oxygen vacancies and large fraction of low-coordinated surface atoms in TiO2 nanosheets can cause surface lattice distortion, which leads to a reduction in band gap and an upshift of conduction band minimum. The assembly possesses strong solar-light absorption, efficient charge transfer, and more surface-reactive sites for photocatalytic reactions. As a result, the assembly exhibits fast photocatalytic hydrogen evolution rate of 540.7 μmol h−1 (30 mg catalyst) and good cycling stability under simulated solar irradiation. This work may provide perspectives for designing two-dimensional semiconductor materials besides TiO2 ultrathin nanosheets as photocatalysts.

Interaction of water with stepped Co(0001): how is it different from flat Co(0001)?

The adsorption and dissociation of water monomer and dimer on stepped Co(0001) surface were studied by means of first-principles calculations. Present results indicate that the adsorption strength of water is greatly enhanced by the presence of step, while the activity of water monomer dissociation does not exhibit a noticeable improvement. Nevertheless, water dimer partial dissociation on stepped Co(0001) is more active than on flat Co(0001), and the promotion of oxygen atom on O–H bond cleavage of H2O is more prominent on stepped surface than on flat Co(0001). The findings reveal the importance of low coordinated surface atoms on metallic catalysts and the vital role of surface rippling on water dissociation. Together with previous reports, the activity of water dissociation on cobalt-based catalytic surfaces depends dominantly on O-containing species like oxygen atom, H2O or hydroxyl.

Towards Controlling the Electrocatalytic Hydrogenation of Oxygenated Hydrocarbons through Particle Size Effects

Metal-catalyzed hydrogenations are regarded as non-sensitive reactions in the gas phase. However, varying proportions of high- and low-coordination surface atoms may lead to differences in the selectivity when hydrogenation is performed in aqueous phase especially under electrochemical condition where H2 evolution reaction (HER) appeared to be a major competitive route. The aim of this work was to test this hypothesis by performing the electrocatalytic hydrogenation (ECH) of aromatic hydrocarbons on Pt/C and Pd/C catalysts with varying metal particle sizes. Phenol and benzaldehyde, representative model compounds for bio-oils derived from lignocellulosic biomass, were chosen as target compounds. ECH Experiments were performed at ambient conditions using H-cells wherein cathodic potential was varied systematically. The results of these experiments were compared with catalytic thermal hydrogenation, where the reduction equivalents are provided by H2 dissociation. In the studied range (from -0.6 V to -0.8 V vs Ag/AgCl), the rates of both ECH and HER increase with increasing cathodic potentials. These increases, however, depended on the metal loading of the cathode. As an exemplary result, the figure shows that the rates of phenol ECH reached a maximum at the Pt dispersion of 26%, which corresponded to a Pt loading of 5 wt.% on carbon. However, the rates normalized per active site showed a different picture. TOF values increased as the dispersion of the metal decreased. In stark contrast, the rates of the H2 evolution reaction (HER) were proportional to the dispersion. Hence, the main conclusion of this work is that the intrinsic rates of ECH of polar molecules are higher on extended metal surfaces than in the corners and edges exhibited by small metal particles. The intrinsic rates of HER, on the other hand, are favored by small particles under the applied reaction conditions. The combination of these two opposite trends rendered the catalyst with Pt particles with the average size of 4.5 nm (5 wt.% Pt on C in this work) as the most active catalyst per gram. However, the catalyst with average Pt particle size of 10 nm shows the highest intrinsic activity as well as faradaic efficiency (30%) Thermal catalytic hydrogenation (TCH) also followed the negative particle size effect to the activity trend, thus, coincide with ECH experiments. This strongly suggests the particle size effect noted in the electrochemical experiments is primarily related to the aqueous environment of the reaction instead of presence of electric potential or competing HER. It is worth highlighting that ECH rates were higher than TCH rates at cathodic potentials higher than -0.7 V vs Ag/AgCl for all tested substrates, which is ascribed to higher coverages of reactive H. This work contributes to the understanding of metal catalysis at low temperatures in condensed phases. It also shows directions for the development of highly active electrocatalysts for the conversion of polar molecules. In specific, we show that as the dispersion of the metal phase increases, the compromise between increasing concentrations of available active sites and their decreasing reactivity leads to optimum particle sizes. Figure caption. Left: Rates of phenol hydrogenation on Pt/C along with dispersion at varying cathodic potentials (vs Ag/AgCl). Right: Turnover frequency (TOF) for phenol hydrogenation on Pt/C along with dispersion at varying cathodic potentials (vs Ag/AgCl). The points labeled as "thermal" correspond to hydrogenation performed with H2 gas. Figure 1

Surface reconstruction of fluorites in vacuum and aqueous environment

Surfaces and interfaces of bulk materials with liquids are of importance for a wide range of chemical processes. In this work, we systematically explore reconstructions on the (100) surface of calcium fluoride $({\mathrm{CaF}}_{2})$ and other fluorites $(M{\mathrm{F}}_{2})$, $M={\text{Sr},\text{Cd},\text{Ba}}$ by sampling the configurational space with the minima hopping structure prediction method in conjunction with density functional theory calculations. We find a large variety of structures that are energetically very close to each other and are connected by very low barriers, resulting in a high mobility of the topmost surface anions. This high density of configurational states makes the ${\mathrm{CaF}}_{2}$ (100) surface a very dynamic system. The majority of the surface reconstructions found in ${\mathrm{CaF}}_{2}$ are also present in ${\mathrm{SrF}}_{2},{\mathrm{CdF}}_{2}$, and ${\mathrm{BaF}}_{2}$. Furthermore, we investigate in detail the influence of these reconstructions on the crystal growth of ${\mathrm{CaF}}_{2}$ in solvents by modeling the fluorite-water interface and its wetting properties. We perform a global structural search both by explicitly including water molecules and by employing a recently developed soft-sphere solvation model to simulate an implicit aqueous environment. The implicit approach correctly reproduces both our findings with the explicit-water model and the experimentally reported contact angles for the partial-hydrophobic (111) and hydrophilic (100) surfaces. Our simulations show that the high anion mobility and the low coordination of the (100) surface atoms strongly favors the adsorption of water molecules over the (111) surface. The aqueous environment makes terminations with low-coordination surface atoms more stable, promoting (100) growth instead of the (111).

A Photochemical, Room-Temperature, and Aqueous Route to the Synthesis of Pd Nanocubes Enriched with Atomic Steps and Terraces on the Side Faces

Palladium nanocubes enriched with atomic steps and terraces on the side faces were synthesized at room temperature in an aqueous solution containing a salt precursor, ascorbic acid, KBr, and poly(vinylpyrrolidone) under UV–vis irradiation. The key to the success of this synthesis was the use of PdBr42– as a precursor with strong absorption in the region of 300–600 nm. Single-crystal seeds were formed in the reaction system upon exposure to a medium pressure Hg arc lamp, and the seeds then grew into cubic nanocrystals under extended irradiation. Because the adatoms inherently diffuse slowly across the surface at room temperature, the nanocrystals favored an asymmetric growth mode, generating side faces covered by a series of atomic steps and terraces rather than smooth {100} facets. The steps and terraces would disappear to generate smooth side faces if the sample was subjected to postsynthesis annealing at 130 °C. When applied as catalysts toward the electrochemical oxidation of formic acid, the low-coordination surface atoms such as those presented on the atomic steps resulted in significant reduction of activity relative to the smooth {100} facets. This trend could be rationalized through the overbinding of reactive species to the low-coordination sites.