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In this work, the mechanism of water oxidation catalyzed by a tricopper-containing polyoxometalate (POM) [(SbW9O33)2CuII3(H2O)3]12− ([POM-CuII2CuII OH2]12−), including (i) the deprotonation oxidation and (ii) O O bond formation steps, was theoretically investigated for the first time. Calculations suggest that the Cu center is redox-inert and remains bivalence throughout the catalytic reaction. This is significantly different from the Ru-, Co- and Mn-containing POM-based water oxidation catalysts in which the metal centers (Ru, Co, Mn) are sequentially oxidized and reduced during catalytic reaction. In deprotonation oxidation step, two hydrogen atoms are removed from one water ligand. Therefore, an unusual metal-oxyl-radical species [POM-CuII2CuII O ]12− is obtained, in which two unpaired electrons are assigned to the active O center. A monocopper-containing keggin POM [CuII(O )SbW11O39]5− ([POM-CuII O ]5−) was selected as the model to explore the O O bond formation mediated by [POM-CuII2CuII O ]12−. The O O bond formation was proposed to proceed via the single electron transfer-water nucleophilic attack (SET-WNA) mechanism. Two electrons from the incoming water molecule is step by step transferred to the oxyl-radical ligand of [POM-CuII O ]5−. Furthermore, the SET-WNA process is characterized by two-state reactivity and the observed spin inversions between two potential energy surfaces effectively reduce the activation barrier. Therefore, the present work would provide the promising information for further designing water oxidation catalysts (WOCs).

In this work, the key O O bond formation step in water oxidation catalyzed by a polyoxometalate-based complex [Mn3(H2O)3(SbW9O33)2]12− was theoretically investigated. The MnV-oxo species rather than MnIV-oxo species, is computed to be responsible for O O bond formation via water nucleophilic attack mechanism. During O O bond formation based on MnV-oxo species, two-state reactivity is found and the energy profile switches from the 13et state to the 15et state through a minimum energy crossing point, which significantly reduces the activation barrier. The observed spin inversion phenomenon in O O bond formation is attributed to the exchange-enhanced reactivity for 15et state, but not for 13et state.

The activity of the biomimetic CoII-based cuboidal water oxidation catalyst (WOC) [CoII4(hmp)4(μ-OAc)2(μ2-OAc)2(H2O)] ([CoII4O4]) and its Ca2+-substitute [CoII3CaO4] were theoretically investigated to evaluate the effect of redox-inactive Ca2+ on water oxidation by CoII-based cuboidal catalyst. Compared with [CoII4O4], the smaller redox potential of [CoII3CaO4] results in the more efficient oxidation-equivalents accumulation for water oxidation. By contrast, the water oxidation by [CoII3CaO4] is identified to be more thermodynamically superior than that for [CoII4O4]. The energy barrier of key O O bond formation step in water oxidation by [CoII3CaO4] is 22.0 kcal/mol and lower than that found for [CoII4O4] (25.0 kcal/mol).

A complete mechanism for electrocatalytic reduction of CO2 to CO by nanographene − rhenium complex (Re(gpy-bpy)(CO)3Cl, gpy = nanographene connected with pyrazine; bpy = 2,2’-bipyridyl) was investigated by using density functional theory (DFT) calculations. The reaction free energies, reaction barrier heights, charge decomposition analysis (CDA), spin densities and mulliken populations provide deep insight into the reaction mechanism as well as the origin of selectivity for this catalyst. Protonation and then reduction of Re(gpy-bpy)(CO)3COOH (Re-COOH) precedes Bronsted-acid-catalyzed C − OH bond cleavage and then CO release at external applied potential. It is expected that the present work would provide valuable information for designing catalyst.