Mono‐/Multinuclear Water Oxidation Catalysts

Abstract

Water splitting, in which water molecules can be transformed into hydrogen and oxygen, is an appealing energy conversion and transformation strategy to address the environmental and energy crisis. The oxygen evolution reaction (OER) is dynamically slow, which limits energy conversion efficiency during the water‐splitting process and requires high‐efficiency water oxidation catalysts (WOCs) to overcome the OER energy barrier. It is generally accepted that multinuclear WOCs possess superior OER performances, as demonstrated by the CaMn4O5 cluster in photosystem II (PSII), which can catalyze the OER efficiently with a very low overpotential. Inspired by the CaMn4O5 cluster in PSII, some multinuclear WOCs were synthesized that could catalyze water oxidation. In addition, some mononuclear molecular WOCs also show high water oxidation activity. However, it cannot be excluded that the high activity arises from the formation of dimeric species. Recently, some mononuclear heterogeneous WOCs showed a high water oxidation activity, which testified that mononuclear active sites with suitable coordination surroundings could also catalyze water oxidation efficiently. This Review focuses on recent progress in the development of mono‐/multinuclear homo‐ and heterogeneous catalysts for water oxidation. The active sites and possible catalytic mechanisms for water oxidation on the mono‐/multinuclear WOCs are provided.

Electrocatalytic Water Oxidation by a Trinuclear Copper(II) Complex

“…In the last decade, there has been increased interest in molecular catalysts for electrocatalytic water oxidation that are based on first-row transition metals. ,− In particular, copper catalysts are of interest due to copper’s earth abundance. , Since Mayer and coworkers reported a molecular copper catalyst precursor for water oxidation in 2012, additional progress has been made studying new molecular copper catalysts. Until recently, most copper mononuclear catalysts only operated under basic conditions (pH ≥ 8), − with limited examples of copper molecular catalysts at neutral pH. − Two copper complexes containing macrocyclic nitrogen-donor ligands, , a copper­(II) species that contains a substituted pyridyl­(ethyl) amine ligand, and a copper­(II) complex with an aryl oxime ligand catalyze water oxidation at pH 7 in phosphate buffer solution.…”

Surface Charge and Electrostatic Spin Crossover Effects in CoN4 Electrocatalysts

“…4−6 Among various noble-metal-free formulations, 3d transition-metal and nitrogen-codoped carbon materials (M-N-C) are among the most promising groups of catalysts for both the ORR 4 and OER. 6 Specifically, Fe-, 7,8 Co-, 9,10 and Mn-N-C 11−13 have been demonstrated to exhibit high ORR and OER activities. Perhaps the most likely active sites of these M-N-C catalysts are single-atom MN 4 centers embedded in the carbon matrices.…”

Catalytic Water Oxidation by a RuII Half Sandwich Complex

“…The suitable water oxidation catalysts must have low overpotential, high efficiency, can undergo proton‐coupled electron transfer mechanism, solubility in an aqueous medium, and redox‐active metal center [12] . Among these WOCs, Mononuclear, binuclear, and bridged Ru‐based polypyridyl water oxidation catalysts have been widely studied because of their redox properties [13–18] . In recent years, half‐sandwich WOCs have been investigated by employing metallocycles and dinitrogen ligands such as 2‐phenylpyridine or 2,2’‐bipyridine [19–20] .…”