There are known errors in oxidation energies of transition metal oxides caused by an improper treatment of their d-electrons. The Hubbard U is the computationally cheapest addition one can use to capture correct reaction energies, but the specific Hubbard U oftentimes must be empirically determined only when suitable experimental data exists. We evaluated the effect of adding a calculated, linear response U on the predicted adsorption energies, scaling relationships, and activity trends with respect to the oxygen evolution reaction for a set of transition metal dioxides. We find that applying a U greater than zero always causes adsorption energies to be more endothermic.Furthermore, the addition of the Hubbard U greater than zero does not break scaling relationships established without the Hubbard U. The addition of the calculated linear response U value produces shifts of different systems along the activity volcano that results in improved activity trends when compared with experimental results.
Discovering new materials with tailored chemical properties is vital for advancing key technologies in catalysis and energy conversion. One strategy is the modification of a material's crystal structure, and new methods allow for the synthesis and stabilization of potential materials in a range of crystal polymorph structures. We assess the potential reactivity of four metastable oxide polymorphs of MO2 (M = Ru, Rh, Pt, Ir) transition metal oxides. In spite of the similar local geometry and coordination between atoms in the metastable polymorphic and stable rutile structure, we find that polymorph reactivities cannot be explained by strain alone and offer tunable reactivity and increased stability. Atom-projected density of states reveals that the unique reactivity of polymorphs are caused by a redistribution of energy levels of the t2g-states. This structure-activity relationship is induced by slight distortions to the M-O bonds in polymorphic structures and is unattainable by strain. We predict columbite IrO2 to be more active than rutile IrO2 for oxygen evolution.
The
catalyst-free electrochemical di- and trifluoromethylation/cyclization
of N-substituted acrylamides was realized under external oxidant-free
conditions. The strategy provides expedient access to fluoroalkylated
oxindoles and 3,4-dihydroquinolin-2(1H)-ones with
ample scope and broad functional group tolerance by mild, direct electrolysis
of sodium sulfinates in an undivided cell. Detailed mechanistic studies
provided strong support for a SET-based reaction manifold.
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