Experimental and Theoretical Investigation of the Light‐Driven Hydrogen Evolution by Polyoxometalate–Photosensitizer Dyads

Abstract

The visible‐light‐driven hydrogen evolution reaction (HER) by covalent photosensitizer–catalyst dyads is one of the most elegant concepts in supramolecular homogeneous solar energy conversion. The intricacies of catalyst reactivity and photosensitizer–catalyst interactions require a detailed fundamental understanding of the system to rationalize the observed reactivities. Here, we report three dyads based on the covalent imine‐bond linkage of an iridium photosensitizer and an organo‐functionalized Anderson polyoxometalate anion [MMo6O18{(OCH2)3CNH2}2]3− (M=Mn3+, Fe3+, Co3+). Modification of the central metal ion M is used to modulate the HER activity. Detailed theoretical and experimental studies examine the role of the central metal ion M and provide critical understanding of the redox activity and light‐driven HER activity of the novel dyads. Thus, the study enables a knowledge‐based optimization of HER dyads by chemical modification of the reactive metal oxide components.

Beyond Charge Balance: Counter‐Cations in Polyoxometalate Chemistry

“…TMA is a notoriously “innocent” counterion that does not promote aggregation and allows high solubility and stability in water, particularly for polyoxoniobates and tantalates . On the other hand, TBA and THA have been commonly used for decades to extract (or precipitate) POMs into nonaqueous solvents for numerous purposes including electrochemical studies and applications involving POM redox chemistry, catalytic studies in organic solvents, and to stabilize water‐ or pH‐sensitive POMs . While TMA salts of POMs generally crystallize well for structure elucidation, the longer‐chain alkylammonium salts are notoriously difficult to crystallize, due to the flexibility and lack of order of the alkyl chains, and the weak intermolecular interactions in the solid‐state.…”

“…[30,[109][110][111][112] On the other hand, TBA and THA have been commonly used for decades to extract (or precipitate) POMs into nonaqueous solvents for numerous purposes including electrochemical studies and applications involving POM redox chemistry, [3] catalytic studies in organic solvents, [113] and to stabilize water-or pH-sensitive POMs. [114] While TMA salts of POMs generally crystallize well for structure elucidation, the longer-chain alkylammonium salts are notoriously difficult to crystallize, due to the flexibility and lack of order of the alkyl chains, and the weak intermolecular interactions in the solid-state. These physical characteristics are the basis for many of the complex QA-(AP)-POM phases discussed below.…”

Jenseits von Ladungsausgleich: Gegenkationen in der Polyoxometallat‐Chemie

“…Dies ermçglichte neue Anwendungen in der POM-Redoxchemie, [3] Katalyse in organischen Lçsungsmitteln [113] und die Stabilisierung wasser-oder pH-empfindlicher POMs. [114] Während TMA-Salze von POMs häufig gut kristallisieren und zur Rçntgendiffraktion genutzt werden kçnnen, sind die langkettigen Ammoniumsalze schwierig zu kristallieren, da die flexiblen, ungeordneten Ketten und schwachen Wechselwirkungen im Festkçrper zu schlechter Kristallinität führen. Diese Eigenschaften bilden jedoch die Grundlage für viele der komplexen QA(AP)-POM-Phasen, die wir nun besprechen.…”

Devisable POM/Ni Foam Composite: Precisely Control Synthesis toward Enhanced Hydrogen Evolution Reaction at High pH

“…Polyoxometalates (POMs), as a class of anionic transition metal oxides, which show a rich diversity of structural types and reversible multi‐electron redox behaviours . Owing to their unique electron sponge behaviour, POMs exhibit proton‐coupled multi‐electron transfers . More importantly, the electrocatalytic efficiency can be tuned by adjusting the chemical composition and microenvironment of POMs .…”

“…[16][17][18] Owing to their unique electron sponge behaviour,P OMs exhibit protoncoupled multi-electron transfers. [19][20][21][22] More importantly,t he electrocatalytic efficiency can be tuned by adjusting the chemical compositiona nd microenvironment of POMs. [23][24][25][26] In terms of POMs applicationinHER, several POM-based electrocatalysts for HER in acidic solution were reporteds of ar.F or example, Zhang etal.…”