A Bio-inspired Cu4 O4 Cubane: Effective Molecular Catalysts for Electrocatalytic Water Oxidation in Aqueous Solution

Borate Buffer as a Key Player in Cu-Based Homogeneous Electrocatalytic Water Oxidation

Borate buffer was found to have both structural and functional roles within a low-cost tri-copper electrocatalyst for homogeneous water oxidation that exhibits a high turnover frequency of 310 s^-1 . The borate buffer was shown to facilitate the catalytic activity by both bridging the three Cu ions and participating in O-O bond formation. Phosphate and acetate buffers did not show such roles, making borate a unique player in this catalytic system.

Homogeneous Water Oxidation Catalyzed by First-Row Transition Metal Complexes: Unveiling the Relationship between Turnover Frequency and Reaction Overpotential

The utilization of earth-abundant low-toxicity metal ions in the construction of highly active and efficient molecular catalysts promoting the water oxidation reaction is important for developing a sustainable artificial energy cycle. However, the kinetic and thermodynamic properties of the currently available molecular water oxidation catalysts (MWOCs) have not been comprehensively investigated. This Review summarizes the current status of MWOCs based on first-row transition metals in terms of their turnover frequency (TOF, a kinetic property) and overpotential (η, a thermodynamic property) and uses the relationship between log(TOF) and η to assess catalytic performance. Furthermore, the effects of the same ligand classes on these MWOCs are discussed in terms of TOF and η, and vice versa. The collective analysis of these relationships provides a metric for the direct comparison of catalyst systems and identifying factors crucial for catalyst design.

Soluble lanthanide-transition-metal clusters Ln36Co12 as effective molecular electrocatalysts for water oxidation

Here we report for the first time soluble lanthanide-transition-metal clusters Ln₃₆Co₁₂ (Ln = Eu, Gd and Dy) as effective homogeneous water oxidation electrocatalysts. The stable 48-metal Ln₃₆Co₁₂ clusters show an effective water oxidation activity under acidic conditions because of the synergistic effect between lanthanide and transition metals in O-O bond formation.

Water Oxidation at Neutral pH using a Highly Active Copper-Based Electrocatalyst

The sluggish kinetics of the oxygen evolution reaction (OER) at the anode severely limit hydrogen production at the cathode in water splitting systems. Although electrocatalytic systems based on cheap and earth-abundant copper catalysts have shown promise for water oxidation under basic conditions, only very few examples with high overpotential can be operated under acidic or neutral conditions, even though hydrogen evolution in the latter case is much easier. This work presents an efficient and robust Cu-based molecular catalyst, which self-assembles as a periodic film from its precursors under aqueous conditions on the surface of a glassy carbon electrode. This film catalyzes the OER under neutral conditions with impressively low overpotential. In controlled potential electrolysis, a stable catalytic current of 1.0 mA cm^-2 can be achieved at only 2.0 V (vs. RHE) and no significant decrease in the catalytic current is observed even after prolonged bulk electrolysis. The catalyst displays first-order kinetics and a single site mechanism for water oxidation with a TOF (k_cat ) of 0.6 s^-1 . DFT calculations on of the periodic Cu(TCA)₂ (HTCA=1-mesityl-1H-1,2,3-triazole-4-carboxylic acid) film reveal that TCA defects within the film create Cu^I active sites that provide a low overpotential route for OER, which involves Cu^I , Cu^II -OH, Cu^III =O and Cu^II -OOH intermediates and is enabled at a potential of 1.54 V (vs. RHE), requiring an overpotential of 0.31 V. This corresponds well with an overpotential of approximately 0.29 V obtained experimentally for the grown catalytic film after 100 CV cycles at pH 6. However, to reach a higher current density of 1 mA cm^-2 , an overpotential of 0.72 V is required.

Water Oxidation Catalysts for Artificial Photosynthesis

Water oxidation is the primary reaction of both natural and artificial photosynthesis. Developing active and robust water oxidation catalysts (WOCs) is the key to constructing efficient artificial photosynthesis systems, but it is still facing enormous challenges in both fundamental and applied aspects. Here, the recent developments in molecular catalysts and heterogeneous nanoparticle catalysts are reviewed with special emphasis on biomimetic catalysts and the integration of WOCs into artificial photosystems. The highly efficient artificial photosynthesis depends largely on active WOCs integrated into light harvesting materials via rational interface engineering based on in-depth understanding of charge dynamics and the reaction mechanism.

Quantum Chemical Study of the Mechanism of Water Oxidation Catalyzed by a Heterotrinuclear Ru2 Mn Complex

The heterotrinuclear complex A {[Ru^II (H₂ O)(tpy)]₂ (μ-[Mn^II (H₂ O)₂ (bpp)₂ ])}⁴⁺ [tpy=2,2':6',2''-terpyridine, bpp=3,5-bis(2-pyridyl)pyrazolate] was found to catalyze water oxidation both electrochemically and photochemically with [Ru(bpy)₃ ]³⁺ (bpy=2,2'-bipyridine) as the photosensitizer and Na₂ S₂ O₈ as the electron acceptor in neutral phosphate buffer. The mechanism of water oxidation catalyzed by this unprecedented trinuclear complex was studied by density functional calculations. The calculations showed that a series of oxidation and deprotonation events take place from A, leading to the formation of complex 1 (formal oxidation state of Ru1^IV Mn^III Ru2^III ), which is the starting species for the catalytic cycle. Three sequential oxidations of 1 result in the generation of the catalytically competing species 4 (formal oxidation state of Ru1^IV Mn^V Ru2^IV ), which triggers the O-O bond formation. The direct coupling of two adjacent oxo ligands bound to Ru and Mn leads to the production of a superoxide intermediate Int1. This step was calculated to have a barrier of 7.2 kcal mol^-1 at the B3LYP*-D3 level. Subsequent O₂ release from Int1 turns out to be quite facile. Other possible pathways were found to be much less favorable, including water nucleophilic attack, the coupling of an oxo and a hydroxide, and the direct coupling pathway at a lower oxidation state (Ru^IV Mn^IV Ru^IV ).