Oxygen Evolution Reaction Driven by Charge Transfer from a Cr Complex to Co-Containing Polyoxometalate in a Porous Ionic Crystal

Abstract

Considerable efforts have been devoted to developing oxygen evolution reaction (OER) catalysts based on transition metal oxides. Polyoxometalates (POMs) can be regarded as model compounds of transition metal oxides, and cobalt-containing POMs (Co-POMs) have received significant interest as candidates. Nanocomposites based on Co-POMs have been reported to show high OER activities due to synergistic effects among the components; however, the role of each component is unclear due to its complex structure. Herein, we utilize porous ionic crystals (PICs) based on Co-POMs, which enable a composition–structure–function relationship to be established to understand the origin of the synergistic catalysis. Specifically, a Keggin-type POM [α-CoW12O40]6– and a Cr complex [Cr3O­(OOCCH2CN)6(H2O)3]+ are implemented as PIC building blocks for the OER under nonbasic conditions. The potentially OER-active but highly soluble [α-CoW12O40]6– was successfully anchored in the crystalline PIC matrix via Coulomb interactions and hydrogen bonding induced by polar cyano groups of the Cr complex. The PIC exhibits efficient and sustained OER catalytic activity, while each building block is inactive. The Tafel slope of the linear sweep voltammetry curve and the relatively large kinetic isotope effect value suggest that elementary steps closely related to the OER rate involve single-electron and proton transfer reactions. Electrochemical and spectroscopic studies clearly show that the synergistic catalysis originates from the charge transfer from the Cr complex to [α-CoW12O40]6–; the increased electron density of [α-CoW12O40]6– may increase its basicity and accelerate proton abstraction as well as enhance electron transfer to stabilize the reaction intermediates adsorbed on [α-CoW12O40]6–.

Electrocatalytic activity of metal encapsulated, doped, and engineered fullerene-based nanostructured materials towards hydrogen evolution reaction

“…As such, natural bond order (NBO) instituted an enhanced technique for investigating the bonding interactions within atomic orbitals and between atomic orbitals, providing an insight for studying the intermolecular charge transfer in molecule 31 . Thus, the charge transfers for the studied bare systems and the hydrogenated engineered systems were calculated using the equation 32 , 33 . where n is the orbital occupancy, are the diagonal elements, and is the off diagonal natural bond orbital Fock matrix element.…”

En route to artificial photosynthesis: the role of polyoxometalate based photocatalysts

“…POMs are a large group of molecular metal oxide anions based on early transition metals (W, Mo, V, Nb, and Ta) in their highest oxidation states (d 0 or d 1 electronic conguration) connected by oxygen atoms. [66][67][68][69][70][71] POMs are structurally and chemically diverse, with reactivity leading to their use in catalysis, 63,[72][73][74][75][76][77] technological applications, 78,79 batteries, 80,81 macromolecular crystallography, 82 electrochemistry, [83][84][85] materials sciences, 86 and molecular magnetism. [87][88][89][90] Among several applications, POM chemistry has enabled breakthroughs in catalysis because of its fascinating properties.…”

Sulfur‐Doped Hydrogen‐Bonded Organic Framework for Improved Oxygen Evolution Reaction

“…Whereas, the oxygen evolution reaction (OER), as the half-cell reaction, limits the entire energy conversion efficiency of electrochemical water splitting reaction due to its sluggish kinetics. [1][2][3][4][5][6] Developments of efficient electrocatalysts to accelerate the OER reaction are thus required. At present, iridium (Ir) and ruthenium (Ru) based noble-metal materials are utilized as OER catalysts with the benchmark performance, but their scarce and expensive nature seriously hinders their widespread utilization.…”

“…The concerns of the growing global warming and energy consumption have boosted the developments in electrochemical water splitting technologies to create the clean H 2 . Whereas, the oxygen evolution reaction (OER), as the half‐cell reaction, limits the entire energy conversion efficiency of electrochemical water splitting reaction due to its sluggish kinetics [1–6] . Developments of efficient electrocatalysts to accelerate the OER reaction are thus required.…”