Kinetic Modeling Analysis of Ar Addition to Atmospheric Pressure N2-H2 Plasma for Plasma-Assisted Catalytic Synthesis of NH3.

Zero-dimensional kinetic modeling of atmospheric pressure Ar-N2-H2 nonthermal plasma was carried out to gain mechanistic insights into plasma-assisted catalytic synthesis of ammonia. Ar dilution is a common technique for tailoring plasma discharge properties and has been shown to enhance NH3 formation when added to N2-H2 plasma. The kinetic model was developed for a coaxial dielectric barrier discharge quartz wool-packed bed reactor operating at near room temperature using a kHz-frequency plasma source. With 30% Ar mixed in a 1:1 N2-H2 plasma at 760 Torr, we find that NH3 production is dominated by Eley-Rideal (E-R) surface reactions, which heavily involve surface NHx species derived from N and H radicals in the gas phase, while the influence of excited N2 molecules is negligible. This is contrary to the commonly proposed mechanism that excited N2 molecules created by Penning excitation of N2 by Ar(4s) and Ar(4p) play a significant role in assisting NH3 formation. Our model shows that the enhanced NH3 formation upon Ar dilution is unlikely due to the interactions between Ar and H species, as excited Ar atoms have a weak effect on H radical formation through H2 dissociation compared to electrons. We find that excited Ar atoms contribute to 28% of the N radical production in the gas phase via N2 dissociation, while the rest are dominated by electron-impact dissociation. Furthermore, Ar species play a negligible role in the product NH3 dissociation. N2 conversion sensitivity analyses were carried out for electron number density (ne) and reduced electric field (E/N), and contributions from Ar to gas-phase N radical production were quantified. The model can provide guidance on potential reasons for observing enhanced NH3 formation upon Ar dilution in N2-H2 plasma beyond changes in the discharge characteristics.

Ion concentration ratio measurements of ion beams generated by a commercial microwave electron cyclotron resonance plasma source.

A commercially available electron cyclotron resonance (ECR) plasma source (GenII Plasma Source, tectra GmbH) is widely used for surface processing. This plasma source is compatible with ultrahigh vacuum systems, and its working pressure is relatively low, around 10-6-10-4 Torr even without differential pumping. Here, we report ion flux concentration ratios for each ion species in an ion beam from this source, as measured by a mass/energy analyzer that is a combination of a quadrupole mass spectrometer, an electrostatic energy analyzer, and focusing ion optics. The examined beams were those arising from plasmas produced from feed gases of H2, D2, N2, O2, Ar, and dry air over a range of input power and working pressures. H2(D2) plasmas are widely used for nuclear fusion applications and, hence, the ion concentration ratios of H+, H2+, and H3+ reported here will be useful information for research that applies this plasma source to well-controlled plasma-material interaction studies. Ion energy distributions, stability of operation, and impurity concentrations were also assessed for each of the plasma species investigated.

Enhanced Feammox activity and perfluorooctanoic acid (PFOA) degradation by Acidimicrobium sp. Strain A6 using PAA-coated ferrihydrite as an electron acceptor.

Acidimicrobium sp. Strain A6 (A6) can degrade perfluoroalkyl acids (PFAAs) by oxidizing NH4+ while reducing Fe(Ⅲ). However, supplying and distributing Fe(III) phases in sediments is challenging since surface charges of Fe(III)-phases are typically positive while those of sediments are negative. Therefore, ferrihydrite particles were coated with polyacrylic acid (PAA) with four different molecular weights, resulting in a negative zeta potential on their surface. Zeta potential was determined as a function of pH and PAA loading, with the lowest value observed when the PAA/ferrihydrite ratio was > 1/5 (w/w) at a pH of 5.5. Several 50-day incubations with an A6-enrichment culture were conducted to determine the effect of PAA-coated ferrihydrite as the electron acceptor of A6 on the Feammox activity and PFOA degradation. NH4+ oxidation, PFOA degradation, production of shorter-chain PFAS, and F- were observed in all PAA-coated samples. The 6 K and 450 K treatments exhibited significant reductions in PFOA concentration and substantial F- production compared to incubations with bare ferrihydrite. Electrochemical impedance spectroscopy showed lowered charge transfer resistance in the presence of PAA-coated ferrihydrite, indicating that PAAs facilitated electron transfer to ferrihydrite. This study highlights the potential of PAA-coated ferrihydrite in accelerating PFAS defluorination, providing novel insights for A6-based bioremediation strategies.

Mechanistic Elucidations of Highly Dispersed Metalloporphyrin Metal-Organic Framework Catalysts for CO2 Electroreduction.

Immobilization of porphyrin complexes into crystalline metal-organic frameworks (MOFs) enables high exposure of porphyrin active sites for CO2 electroreduction. Herein, well-dispersed iron-porphyrin-based MOF (PCN-222(Fe)) on carbon-based electrodes revealed optimal turnover frequencies for CO2 electroreduction to CO at 1 wt.% catalyst loading, beyond which the intrinsic catalyst activity declined due to CO2 mass transport limitations. In situ Raman suggested that PCN-222(Fe) maintained its structure under electrochemical bias, permitting mechanistic investigations. These revealed a stepwise electron transfer-proton transfer mechanism for CO2 electroreduction on PCN-222(Fe) electrodes, which followed a shift from a rate-limiting electron transfer to CO2 mass transfer as the potential increased from -0.6 V to -1.0 V vs. RHE. Our results demonstrate how intrinsic catalytic investigations and in situ spectroscopy are needed to elucidate CO2 electroreduction mechanisms on PCN-222(Fe) MOFs.

Effect of Porous Catalyst Support on Plasma-Assisted Catalysis for Ammonia Synthesis.

We report on the effect of catalyst support particle porosity on the conversion of NH3 synthesis from N2 and H2 in a coaxial dielectric barrier discharge (DBD) plasma reactor. The discharge was created using an AC applied voltage with the reactor at room temperature and near atmospheric pressure (550 Torr). Two different particles of almost equal diameter (∼1.5 mm)─porous silica (SiO2) ceramic beads (average pore size: 8 nm) and smooth, nonporous soda lime glass beads─were compared in the DBD reactor. As the pore size in the SiO2 particles was smaller than the Debye length, penetration of the plasma into the pores of the particles was unlikely; however, reactive species generated in the plasma outside the particles could diffuse into the pores. The N2 conversion and energy yield of NH3 increased with applied voltage for both particle types, and these values were consistently higher when using the SiO2 beads. Discharge and plasma properties were estimated from Lissajous plots and using calculations with the BOLSIG+ software. The effect of these two different catalyst supports on the physical properties of the discharge was negligible. High resolution optical emission spectra revealed that the concentrations of N2+, atomic N, and atomic H (Hα, Hß) in the plasma discharge were lower with the porous SiO2 beads than with the glass beads at every applied voltage tested. This indicates that these active species participate in heterogeneous reactions at support particle surfaces and that the larger surface area presented by the porous particles led to higher rates of depletion of these intermediates and a higher rate of ammonia synthesis.

Spectroscopic observation and structure-insensitivity of hydroxyls on gold.

The O-H stretching vibration of surface hydroxyls remained at 3691 cm-1 for gold structures ranging in size from clusters to nanoparticles, to non-flat bulk surfaces. In contrast, this vibration was not observed on flat gold surfaces. Therefore, this vibration can serve as an indicator of the roughness of the gold surface and associated functional properties, such as catalytic activity.

Increasing Iridium Oxide Activity for the Oxygen Evolution Reaction with Hafnium Modification.

Synthesis and implementation of highly active, stable, and affordable electrocatalysts for the oxygen evolution reaction (OER) is a major challenge in developing energy efficient and economically viable energy conversion devices such as electrolyzers, rechargeable metal-air batteries, and regenerative fuel cells. The current benchmark electrocatalyst for OER is based on iridium oxide (IrOx) due to its superior performance and excellent stability. However, large scale applications using IrOx are impractical due to its low abundance and high cost. Herein, we report a highly active hafnium-modified iridium oxide (IrHfxOy) electrocatalyst for OER. The IrHfxOy electrocatalyst demonstrated ten times higher activity in alkaline conditions (pH = 11) and four times higher activity in acid conditions (pH = 1) than a IrOx electrocatalyst. The highest intrinsic mass activity of the IrHfxOy catalyst in acid conditions was calculated as 6950 A gIrOx-1 at an overpotential (η) of 0.3 V. Combined studies utilizing operando surface enhanced Raman spectroscopy (SERS) and DFT calculations revealed that the active sites for OER are the Ir-O species for both IrOx and IrHfxOy catalysts. The presence of Hf sites leads to more negative charge states on nearby O sites, shortening of the bond lengths of Ir-O, and lowers free energies for OER intermediates that accelerate the OER process.

Mid-Infrared Scattering in γ-Al2O3 Catalytic Powders.

The energy efficiency of heterogeneous catalytic processes may be improved by using mid-infrared light to excite gas-phase reactants during the reaction, since vibrational excitation of molecules has been shown to increase their reactivity at the gas-catalyst interface. A primary challenge for such light-enabled catalysis is the need to ensure close coupling between light-excited molecules and the catalyst throughout the reactor. Thus, it is imperative to understand how to couple infrared light efficiently to molecules near and inside catalytic material. Heterogenous catalysts are often nanoscale metal particles supported on high surface area, porous oxide materials and exhibit feature sizes across multiple scattering regimes with respect to the mid-infrared wavelength. These complex powders make a direct measurement of the scattering properties challenging. Here, we demonstrate that a combination of directional hemispherical measurements along with the in-line transmission measurement allow for a direct measurement of the scattered light signal. We implement this technique to study the scattering behavior of the catalytic support material γ-Al2O3 (with and without metal loading) between 1040 and 1220 cm-1. We first study how both the mean grain size affects the scattering behavior by comparing three different mean grain sizes spanning three orders of magnitude (2, 40, and 900 µm). Furthermore, we study how the addition of metal catalyst nanoparticles, Ru, or Cu, to the support material impacts the light scattering behavior of the powder. We find that the 40 µm grain size scatters the most (up to 97% at 1220 cm-1) and that the addition of metal nanoparticles narrows the scattering angle but does not decrease the scattering efficiency. The strong scattering of the 40 µm grains makes them the most ideal support material of those studied for the given spectrum because of their ability to distribute light within the reactor. Finally, we estimate that less than 100 mW of laser power is needed to cause significant excitation for testing mid-infrared catalysis in a Harrick Praying Mantis diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) reactor, a magnitude easily available using commercial mid-infrared lasers. Our work also provides a mid-infrared foundation for a wide range of studies of light-enabled catalysis and can be extended to other wavelengths of light or to study the scattering behavior of other complex powders in other fields, including ceramics, biomaterials, and geology.

Acetic Acid Adsorption and Reactions on Ni(110).

Acetic acid adsorption and reactions at multiple surface coverage values on Ni(110) were studied with temperature-programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRAS) at 90-500 K. The experimental measurements were interpreted with density functional theory (DFT) calculations that provided information on adsorbate geometries, energies, and vibrational modes. Below the monolayer saturation coverage of 0.36 ML at 90 K, acetic acid adsorbs mostly molecularly. Above this coverage, a physisorbed layer is formed with dimers and catemers, without detectable monomers. Dimers and catemers desorb as molecular acetic acid at 157 and 172 K, respectively. Between 90 and 200 K, the O-H bond in acetic acid breaks to form bridge-bonded bidentate acetate that becomes the dominant surface species. Desorption-limited hydrogen evolution is observed at 265 K. However, even after the acetate formation, acetic acid desorbs molecularly at 200-300 K due to recombination. Minor surface species observed at 200 K, acetyls or acetates with a carbonyl group, decompose below 350 K and generate adsorbed carbon monoxide. At 350 K, the surface likely undergoes restructuring, the extent of which increases with acetic acid coverage. The initial dominant bridge-bonded bidentate acetate species formed below 200 K remain on the surface, but they now mostly adsorb on the restructured sites. The acetates and all other remaining hydrocarbon species decompose simultaneously at 425 K in a narrow temperature range with concurrent evolution of hydrogen, carbon monoxide, and carbon dioxide. Above 425 K, only carbon remains on the surface.

Nitrogen-plasma treated hafnium oxyhydroxide as an efficient acid-stable electrocatalyst for hydrogen evolution and oxidation reactions.

Development of earth-abundant electrocatalysts for hydrogen evolution and oxidation reactions in strong acids represents a great challenge for developing high efficiency, durable, and cost effective electrolyzers and fuel cells. We report herein that hafnium oxyhydroxide with incorporated nitrogen by treatment using an atmospheric nitrogen plasma demonstrates high catalytic activity and stability for both hydrogen evolution and oxidation reactions in strong acidic media using earth-abundant materials. The observed properties are especially important for unitized regenerative fuel cells using polymer electrolyte membranes. Our results indicate that nitrogen-modified hafnium oxyhydroxide could be a true alternative for platinum as an active and stable electrocatalyst, and furthermore that nitrogen plasma treatment may be useful in activating other non-conductive materials to form new active electrocatalysts.

Self-assembling of formic acid on the partially oxidized p(2 × 1) Cu(110) surface reconstruction at low coverages.

Carbon dioxide (CO2) reduction for synthetic fuel generation could be an integral part of a sustainable energy future. Copper (Cu) is the leading electrocatalyst for CO2 reduction to produce multiple C-containing products such as C1 and C2 hydrocarbons and oxygenates. Understanding the mechanisms leading to their production could help optimize these pathways further. Adsorption studies of the many possible intermediates on well-characterized surfaces are crucial to elucidating these mechanisms. In this work, we explore the adsorption configurations of formic acid (HCOOH) on the surface of the partially oxidized p(2 × 1) reconstruction of the Cu(110) surface, using low-temperature scanning tunneling and atomic force microscopy, in conjunction with density functional theory modeling. We find that HCOOH adsorbs favorably on the CuO chain comprising the reconstruction. The adsorption interactions involve dative bonding of the carbonyl O to the oxidized Cu and hydrogen bonding of the OH group to the surface O or to an adjacently adsorbed HCOOH molecule. Cooperative adsorption of the molecules occurs, forming two- to three-molecule-long oligomer chains, facilitated by intermolecular hydrogen bonding and mutual polarization of the CuO acid-base adsorption sites.

Shear-Induced Changes of Electronic Properties in Gallium Nitride.

We show that sliding on the surface of GaN can permanently change the surface band structure, resulting in an increased degree of band bending by more than 0.5 eV. We hypothesize that shear and contact stresses introduce vacancies that cause a spatially variant band bending. Band bending is observed by shifts and broadening of core-level binding energies toward lower values in X-ray photoelectron spectroscopy. The extent of band bending is controlled by humidity, number of sliding cycles and applied load, presenting opportunities for scalable tuning of the degree of band bending on a GaN surface. Scanning transmission electron microscopy revealed that the epitaxy of GaN was preserved up to the surface with regions of defects near the surface. The hypothesized mechanism of band bending is shear-induced defect generation, which has been shown to affect the surface states. The ability to introduce band bending at the GaN surface is promising for applications in photovoltaics, photocatalysis, gas sensing, and photoelectrochemical processes.

Investigation of Water Dissociation and Surface Hydroxyl Stability on Pure and Ni-Modified CoOOH by Ambient Pressure Photoelectron Spectroscopy.

Water adsorption and reaction on pure and Ni-modified CoOOH nanowires were investigated using ambient pressure photoemission spectroscopy (APPES). The unique capabilities of APPES enable us to observe water dissociation and monitor formation of surface species on pure and Ni-modified CoOOH under elevated pressures and temperatures for the first time. Over a large range of pressures (UHV to 1 Torr), water dissociates readily on the pure and Ni-modified CoOOH surfaces at 27 °C. With an increase in H2O pressure, a greater degree of surface hydroxylation was observed for all samples. At 1 Torr H2O, ratios of different oxygen species indicate a transformation of CoOOH to CoOxHy in pure and Ni-modified CoOOH. In temperature dependent studies, desorption of weakly bound water and surface dehydroxylation were observed with increasing temperature. Larger percentages of surface hydroxyl groups at higher temperatures were observed on Ni-modified CoOOH compared to pure CoOOH, which indicates an increased stability of surface hydroxyl groups on these Ni-modified surfaces.

The promoting effect of tetravalent cerium on the oxygen evolution activity of copper oxide catalysts.

A new catalyst is presented for the oxygen evolution reaction (OER) based on cerium-modified copper oxide (CuOx) prepared using a facile electrodeposition procedure. Incorporation of Ce into CuOx leads to greatly improved OER activity, which reached an optimal value at a surface concentration of 6.9 at% Ce. Specifically, the OER current density at 400 mV overpotential for the most active Ce-modified CuOx catalyst (6.9 at% Ce) was 3.3 times greater compared to the pure CuOx. Coincident with the improved OER activity, Ce incorporation also leads to significant structural changes that manifested in increasing degrees of disorder. A further increase in the Ce concentration led to a decrease in the OER performance which can be attributed to the formation of a segregated CeO2 phase. A strong correlation was observed between the OER performance and tetravalent Ce (Ce4+) ion concentration, up to a concentration corresponding to CeO2 phase segregation. No particular trend was observed for the OER activity of these Ce-modified CuOx catalysts with respect to the surface concentration of Cu ions, surface oxygen species or catalyst structure. The stability of these CuOx catalysts at 5 mA cm-2 was also improved with Ce incorporation, and the overpotential required to sustain this current density is much lower than that of pure CuOx. Overall, this study provides new insights regarding the promoting effect of tetravalent Ce ions on the OER activity of CuOx-based OER catalysts in alkaline electrolytes.

Hydrogenation of CO to Methanol on Ni(110) through Subsurface Hydrogen.

We present a combined theoretical and experimental study of CO hydrogenation on a Ni(110) surface, including studies of the role of gas-phase atomic hydrogen, surface hydrogen, and subsurface hydrogen reacting with adsorbed CO. Reaction mechanisms leading both to methane and methanol are considered. In the reaction involving surface or subsurface hydrogen, we investigate four possible pathways, using density functional theory to characterize the relative energetics of each intermediate, including the importance of further hydrogenation versus C-O bond breaking, where the latter may lead to methane production. The most energetically favorable outcome is the production of methanol along a pathway involving the sequential hydrogenation of CO to a H3CO* intermediate, followed by a final hydrogenation to give methanol. In addition, we find that subsurface hydrogen noticeably alters reaction barriers, both passively and through the energy released by diffusion to the surface. Indeed, the effective reaction barriers are even lower than for CO methanolation on Cu(211) and Cu(111) than for Ni(110). In studies of gas-phase H atoms impinging on a CO-adsorbed Ni(110) surface, Born-Oppenheimer molecular dynamics simulations show that direct impact of H is unlikely to result in hydrogenation of CO. This means that Eley-Rideal or hot-atom mechanisms are not important; thus, thermal reactions involving subsurface hydrogen are the primary reaction mechanisms leading to methanol. Finally, we demonstrate experimentally for the first time the production of methanol and formaldehyde from CO hydrogenation on Ni(110) and confirm the role of subsurface hydrogen in the mechanism of this reaction.

Stable synthesis of few-layered boron nitride nanotubes by anodic arc discharge.

Boron nitride nanotubes (BNNTs) were successfully synthesized by a dc arc discharge using a boron-rich anode as synthesis feedstock in a nitrogen gas environment at near atmospheric pressure. The synthesis was achieved independent of the cathode material suggesting that under such conditions the arc operates in so-called anodic mode with the anode material being consumed by evaporation due to the arc heating. To sustain the arc current by thermionic electron emission, the cathode has to be at sufficiently high temperature, which for a typical arc current density of ~100 A/cm2, is above the boron melting point (2350 K). With both electrodes made from the same boron-rich alloy, we found that the arc operation unstable due to frequent sticking between two molten electrodes and formation of molten droplets. Stable and reliable arc operation and arc synthesis were achieved with the boron-rich anode and the cathode made from a refractory metal which has a melting temperature above the melting point of boron. Ex-situ characterization of synthesized BNNTs with electron microscopy and Raman spectroscopy revealed that independent of the cathode material, the tubes are primarily single and double walled. The results also show evidence of root-growth of BNNTs produced in the arc discharge.

Effect of Temperature on the Desorption of Lithium from Molybdenum(110) Surfaces: Implications for Fusion Reactor First Wall Materials.

Determining the strength of Li binding to Mo is critical to assessing the survivability of Li as a potential first wall material in fusion reactors. We present the results of a joint experimental and theoretical investigation into how Li desorbs from Mo(110) surfaces, based on what can be deduced from temperature-programmed desorption measurements and density functional theory (DFT). Li desorption peaks measured at temperatures ranging from 711 K (1 monolayer, ML) to 1030 K (0.04 ML), with corresponding desorption onsets from 489 to 878 K, follow a trend similar to predicted Gibbs free energies for Li adsorption. Bader charge analysis of DFT densities reveals that repulsive forces between neighboring positively charged Li atoms increase with coverage and thus reduce the bond strength between Mo and Li, thereby lowering the desorption temperature as the coverage increases. Additionally, DFT predicts that Li desorbs at higher temperatures from a surface with vacancies than from a perfect surface, offering an explanation for the anomalously high desorption temperatures for the last Li to desorb from Mo(110). Analysis of simulated local densities of states indicates that the stronger binding to the defective surface is correlated with enhanced interaction between Li and Mo, involving the Li 2s electrons and not only the Mo 4d electrons as in the case of the pristine surface, but also the Mo 5s electrons in the case with surface vacancies. We suggest that steps and kinks present on the Mo(110) surface behave similarly and contribute to the high desorption temperatures. These findings imply that roughened Mo surfaces may strengthen Li film adhesion at higher temperatures.

Facet-dependent activity and stability of Co3O4 nanocrystals towards the oxygen evolution reaction.

The electrocatalytic activities and stabilities of spinel cobalt oxides with different morphologies have been investigated for the oxygen evolution reaction (OER) in an alkaline environment. Spinel cobalt oxide nanoparticles with well-defined cubic and octahedral morphologies were prepared, which predominantly expose the (100) and (111) surfaces, respectively. The OER activity of spinel cobalt oxide, measured in terms of current density, increases with higher relative proportion of the (111) surface, which can be attributed to the higher density of cobalt ions on the (111) surface compared to that on the (100) surface. The surfaces of cobalt oxide nanocubes are slighted reduced compared to those of nanooctahedra prior to OER testing. Based on chronoamperometry experiments, the nanocubes exhibited higher stability compared to the nanooctahedra, which could be due to the lower surface energy of the (100) surface compared to the (111) surface. The dependence of OER activity and stability on spinel cobalt oxide crystal facets demonstrates the importance of surface orientation in catalyst performance optimization.

The (0001) surfaces of α-Fe2O3 nanocrystals are preferentially activated for water oxidation by Ni doping.

Photoelectrochemical water oxidation on hematite has been extensively studied, yet the relationship between the various facets exposed, heteroatom doping, and associated electrocatalytic activity has not been adequately explored. Here, hematite nanocrystals were synthesized with continuous tuning of the aspect-ratio and fine control of the surface area ratio of the (0001) facet with respect to other surfaces. The samples were doped with nickel, which was confirmed using the combined results of HRTEM, SEM, XRD, Raman, BET, and XPS measurements. The surface area ratio of the hexagonal (0001) surface with respect to all surfaces was tuned from 98% to 30%. Ni doping was accomplished by diffusion of Ni clusters into the subsurface region, which forms a uniformly doped NixFe2-xO3 surface overlayer that improves the electrocatalytic activity of water oxidation. These results are discussed in the context of a theoretical prediction and subsequent surface science validation that Ni doping facilitates the water oxidation reaction on hematite (0001) surfaces. Electrochemical testing of water oxidation catalysis was carried out on doped and shape-controlled hematite nanocrystals. The enhancement of water oxidation activity by Ni-doping increased as the surface area ratio of the (0001) facet of hematite nanocrystals increased, consistent with the theoretical predictions and surface science studies.

Water oxidation catalysis: effects of nickel incorporation on the structural and chemical properties of the α-Fe2O3(0001) surface.

Photoelectrochemical solar fuel synthesis devices based on photoactive hematite (α-Fe2O3) anodes have been extensively investigated, yet a fundamental understanding regarding its associated water oxidation surface reaction mechanism is still lacking. To help elucidate detailed reaction mechanisms, we studied water chemisorption and reaction as well as structural changes induced by Ni incorporation into the α-Fe2O3(0001) surface. Investigation by scanning probe and electron diffraction techniques show that vapor deposition of Ni and subsequent annealing to 700 K leads to the interdiffusion and incorporation of Ni into the near-surface region of hematite and changes the structure of the (0001) surface by the formation of FeO-like domains on the topmost layer. These results are discussed in the context of a proposed water oxidation mechanism on this surface in which Ni doping facilitates water oxidation by increasing O hole concentrations and forms less negatively charged O anions (*O) and *O···OH species [ Liao, P. L.; Keith, J. A.; Carter, E. A. J. Am. Chem. Soc. 2012 , 134 , 13296 - 13309 . ]. Consistent with predictions from this theory, electrochemical measurements using cyclic voltammetry carried out on the ultrahigh vacuum-prepared surfaces demonstrated that Ni incorporation leads to higher current density and lower onset potential than the unmodified α-Fe2O3 surface. Our work utilizing a surface science approach helps to connect such theoretical predictions of reaction thermodynamics on well-defined structures and the performance of modified hematite model electrocatalysts for water oxidation.