Earth-abundant first-row (3d) transition metal-based catalysts have been developed for the oxygen-evolution reaction (OER); however, they operate at overpotentials substantially above thermodynamic requirements. Density functional theory suggested that non-3d high-valency metals such as tungsten can modulate 3d metal oxides, providing near-optimal adsorption energies for OER intermediates. We developed a room-temperature synthesis to produce gelled oxyhydroxides materials with an atomically homogeneous metal distribution. These gelled FeCoW oxyhydroxides exhibit the lowest overpotential (191 millivolts) reported at 10 milliamperes per square centimeter in alkaline electrolyte. The catalyst shows no evidence of degradation after more than 500 hours of operation. X-ray absorption and computational studies reveal a synergistic interplay between tungsten, iron, and cobalt in producing a favorable local coordination environment and electronic structure that enhance the energetics for OER.

The development of high-performance catalysts for the oxygen evolution reaction (OER) is paramount for cost-effective conversion of renewable electricity to fuels and chemicals. Here we report the significant enhancement of the OER activity of electrodeposited NiOx films resulting from the combined effects of using cerium as a dopant and gold as a metal support. This NiCeOx-Au catalyst delivers high OER activity in alkaline media, and is among the most active OER electrocatalysts reported to date. Based on experimental observations and theoretical modelling, we ascribe the activity to a combination of electronic, geometric and support effects, where highly active under-coordinated sites at the oxide support interface are modified by the local chemical binding environment and by doping the host Ni oxide with Ce. The NiCeOx-Au catalyst is further demonstrated in a device context by pairing it with a nickel-molybdenum hydrogen evolution catalyst in a water electrolyser, which delivers 50 mA consistently at 1.5 V over 24 hours of continuous operation.

Mechanisms for H 2 dissociation on metal oxides have been typically inferred from the infrared spectra of reaction products on the basis of the presence or lack of M-H fingerprints. Here, we demonstrate by means of Density Functional Theory that oxides with polar M-O bonds favor heterolytic dissociation. Moreover, we report that the resulting heterolytic product can further evolve to the homolytic one provided that metal ions are reducible. Hence, it follows that the redox capacity of the metal determines the reaction outcome. This finding sheds light on why both M-H and O-H bands appear in the infrared spectra of non-reducible oxides such as MgO or γ-Al 2 O 3 , while only O-H bands are observed for reducible oxides like CeO 2. It results in a unified mechanism for polar oxides that can be generalized to other materials exhibiting significant charge separation. Importantly, we also show that the low activity of CeO 2 towards

Palladium-catalyzed C-C cross-coupling reactions (Suzuki-Miyaura, Negishi, Stille, Sonogashira, etc.) are among the most useful reactions in modern organic synthesis because of their wide scope and selectivity under mild conditions. The many steps involved and the availability of competing pathways with similar energy barriers cause the mechanism to be quite complicated. In addition, the short-lived intermediates are difficult to detect, making it challenging to fully characterize the mechanism of these reactions using purely experimental techniques. Therefore, computational chemistry has proven crucial for elucidating the mechanism and shaping our current understanding of these processes. This mechanistic elucidation provides an opportunity to further expand these reactions to new substrates and to refine the selectivity of these reactions. During the past decade, we have applied computational chemistry, mostly using density functional theory (DFT), to the study of the mechanism of C-C cross-coupling reactions. This Account summarizes the results of our work, as well as significant contributions from others. Apart from a few studies on the general features of the catalytic cycles that have highlighted the existence of manifold competing pathways, most studies have focused on a specific reaction step, leading to the analysis of the oxidative addition, transmetalation, and reductive elimination steps of these processes. In oxidative addition, computational studies have clarified the connection between coordination number and selectivity. For transmetalation, computation has increased the understanding of different issues for the various named reactions: the role of the base in the Suzuki-Miyaura cross-coupling, the factors distinguishing the cyclic and open mechanisms in the Stille reaction, the identity of the active intermediates in the Negishi cross-coupling, and the different mechanistic alternatives in the Sonogashira reaction. We have also studied the closely related direct arylation process and highlighted the role of an external base as proton abstractor. Finally, we have also rationalized the effect of ligand substitution on the reductive elimination process. Computational chemistry has improved our understanding of palladium-catalyzed cross-coupling processes, allowing us to identify the mechanistic complexity of these reactions and, in a few selected cases, to fully clarify their mechanisms. Modern computational tools can deal with systems of the size and complexity involved in cross-coupling and have a continuing role in solving specific problems in this field.

A DFT study of R-R reductive elimination (R = Me, Ph, vinyl) in plausible intermediates of Pd-catalyzed processes is reported. These include the square-planar tetracoordinated systems cis-[PdR(2)(PMe(3))(2)] themselves, possible intermediates cis-[PdR(2)(PMe(3))L] formed in solution or upon addition of coupling promoters (L = acetonitrile, ethylene, maleic anhydride (ma)), and tricoordinated intermediates cis-[PdR(2)(PMe(3))] (represented as L = empty). The activation energy ranges from 0.6 to 28.6 kcal/mol in the gas phase, increasing in the order vinyl-vinyl < Ph-Ph < Me-Me, depending on R, and ma < "empty" < ethylene < PMe(3) approximately MeCN, depending on L. The effect of added olefins was studied for a series of olefins, providing the following order of activation energy: p-benzoquinone < ma < trans-1,2-dicyanoethylene < 3,5-dimethylcyclopent-1-ene < 2,5-dihydrofuran < ethylene < trans-2-butene. Comparison of the calculated energies with experimental data for the coupling of cis-[PdMe(2)(PPh(3))(2)] in the presence of additives (PPh(3), p-benzoquinone, ma, trans-1,2-dicyanoethylene, 2,5-dihydrofuran, and 1-hexene) reveals that: (1) There is no universal coupling mechanism. (2) The coupling mechanism calculated for cis-[PdMe(2)(PMe(3))(2)] is direct, but PPh(3) retards the coupling for cis-[PdMe(2)(PPh(3))(2)], and DFT calculations support a switch of the coupling mechanism to dissociative for PPh(3). (3) Additives that would provide intermediates with coupling activation energies higher than a dissociative mechanism (e.g., common olefins) produce no effect on coupling. (4) Olefins with electron-withdrawing substituents facilitate the coupling through cis-[PdMe(2)(PR(3))(olefin)] intermediates with much lower activation energies than the starting complex or a tricoordinated intermediate. Practical consequences are discussed.

While natural gas is an abundant chemical fuel, its low volumetric energy density has prompted a search for catalysts able to transform methane into more useful chemicals. This search has often been aided through the use of transition state (TS) scaling relationships, which estimate methane activation TS energies as a linear function of a more easily calculated descriptor, such as final state energy, thus avoiding tedious TS energy calculations. It has been shown that methane can be activated via a radical or surface-stabilized pathway, both of which possess a unique TS scaling relationship. Herein, we present a simple model to aid in the prediction of methane activation barriers on heterogeneous catalysts. Analogous to the universal radical TS scaling relationship introduced in a previous publication, we show that a universal TS scaling relationship that transcends catalysts classes also seems to exist for surface-stabilized methane activation if the relevant final state energy is used. We demonstrate that this scaling relationship holds for several reducible and irreducible oxides, promoted metals, and sulfides. By combining the universal scaling relationships for both radical and surface-stabilized methane activation pathways, we show that catalyst reactivity must be considered in addition to catalyst geometry to obtain an accurate estimation for the TS energy. This model can yield fast and accurate predictions of methane activation barriers on a wide range of catalysts, thus accelerating the discovery of more active catalysts for methane conversion.

A major roadblock in realizing large-scale production of hydrogen via electrochemical water splitting is the cost and inefficiency of current catalysts for the oxygen evolution reaction (OER). Computational research has driven important developments in understanding and designing heterogeneous OER catalysts using linear scaling relationships derived from computed binding energies. Herein, we interrogate 17 of the most active molecular OER catalysts, based on different transition metals (Ru, Mn, Fe, Co, Ni, and Cu), and show they obey similar scaling relations to those established for heterogeneous systems. However, we find that the conventional OER descriptor underestimates the activity for very active OER complexes as the standard approach neglects a crucial one-electron oxidation that many molecular catalysts undergo prior to O-O bond formation. Importantly, this additional step allows certain molecular catalysts to circumvent the "overpotential wall", leading to enhanced performance. With this knowledge, we establish fundamental principles for the design of ideal molecular OER catalysts.

Transition metal oxides show great promise as Earth-abundant catalysts for the oxygen evolution reaction in electrochemical water splitting. However, progress in the development of highly active oxide nanostructures is hampered by a lack of knowledge of the location and nature of the active sites. Here we show, through atom-resolved scanning tunnelling microscopy, X-ray spectroscopy and computational modelling, how hydroxyls form from water dissociation at under coordinated cobalt edge sites of cobalt oxide nanoislands. Surprisingly, we find that an additional water molecule acts to promote all the elementary steps of the dissociation process and subsequent hydrogen migration, revealing the important assisting role of a water molecule in its own dissociation process on a metal oxide. Inspired by the experimental findings, we theoretically model the oxygen evolution reaction activity of cobalt oxide nanoislands and show that the nanoparticle metal edges also display favourable adsorption energetics for water oxidation under electrochemical conditions.