Backbone Immobilization of the Bis(bipyridyl)pyrazolate Diruthenium Catalyst for Electrochemical Water Oxidation

Highly Efficient and Durable Electrocatalysis by a Molecular Catalyst with Long Alkoxyl Chains Immobilized on a Carbon Electrode for Water Oxidation

A dinuclear Ru complex, proximal,proximal-[Ru₂L(C₈Otpy)₂(OH)(OH₂)]³⁺ (C₈Otpy = 4'-octyloxy-2,2'; 6',2″-terpyridine) (1) with long alkoxyl chains, was synthesized to be immobilized on a carbon paper (CP) electrode via hydrophobic interactions between the long alkoxyl chains and the CP surface. The 1/CP electrode demonstrated efficient electrocatalytic water oxidation with a low overpotential (η_onset) of 0.26 V (based on the onset potential for water oxidation) in an aqueous medium at pH 7.0, which is compared advantageously with those of hitherto-reported molecular anodes for water oxidation. The active species of Ru^IIIRu^III(μ-OO) with a μ-OO bridge was involved in water oxidation at 0.95 V versus Ag/AgCl. As the applied potential increased to 1.40 V, water oxidation was promoted by participation of the more active species of Ru^IIIRu^IV(μ-OO), and very durable electrocatalysis was gained for more than 35 h without elution of 1 into the electrolyte solution. The introduced long alkoxyl chains act as a dual role of the linker of 1 on the CP surface and decrease the η value. Theoretical investigation provides insights into the O-O bond formation mechanism and the activity difference between Ru^IIIRu^III(μ-OO) and Ru^IIIRu^IV(μ-OO) for electrocatalytic water oxidation.

Recent Advances in the Development of Molecular Catalyst-Based Anodes for Water Oxidation toward Artificial Photosynthesis

Catalytic water oxidation represents a bottleneck for developing artificial photosynthetic systems that store solar energy as renewable fuels. A variety of molecular water oxidation catalysts (WOCs) have been reported over the last two decades. In view of their applications in artificial photosynthesis devices, it is essential to immobilize molecular catalysts onto the surfaces of conducting/semiconducting supports for fabricating efficient and stable water oxidation anodes/photoanodes. Molecular WOC-based anodes are essential for developing photovoltaic artificial photosynthesis devices and, moreover, the performance of molecular WOC on anodes will provide important insight into designing extended molecular WOC-based photoanodes for photoelectrochemical (PEC) water oxidation. This Review concerns recent progress in the development of molecular WOC-based anodes over the last two decades and looks at the prospects for using such anodes in artificial photosynthesis.

Efficient Oxygen Electrocatalyst for Zn-Air Batteries: Carbon Dots and Co9S8 Nanoparticles in a N,S-Codoped Carbon Matrix

Non-noble metal-based bifunctional electrocatalysts for both oxygen reduction reactions (ORRs) and oxygen evolution reactions (OERs) are an essential component of high-performance rechargeable Zn-air batteries (ZABs). Herein, we report a novel and simple method for preparing Co₉S₈ nanoparticles embedded in N and S codoped carbon materials with aid of carbon dots (CDs). CDs play a key role in distributing Co₉S₈ nanoparticles in the matrix uniformly and enhancing the specific surface area and the electric conductivity simultaneously. The obtained Co₉S₈/CD@NSC exhibits an excellent ORR and OER bifunctional catalytic activity and a great long-term durability, with a half-wave potential of 0.84 V versus reversible hydrogen electrode (RHE) for the ORR and a low potential of 1.62 V versus RHE at 10 mA cm^-2, which outperform the popular Pt/C and RuO₂ commercial catalysts. Moreover, the Co₉S₈/CD@NSC catalyst also displays a superior activity and cycling stability as a cathode material in ZABs, which is far better than Pt/C + RuO₂ mixture catalysts. Such a ZAB shows a low charge/discharge voltage gap of 0.62 V and great cycling stability over 125 h at 10 mA cm^-2.

Design of Molecular Water Oxidation Catalysts Stabilized by Ultrathin Inorganic Overlayers—Is Active Site Protection Necessary?

Anchored molecular catalysts provide a good step towards bridging the gap between homogeneous and heterogeneous catalysis. However, applications in an aqueous environment pose a serious challenge to anchoring groups in terms of stability. Ultrathin overlayers embedding these catalysts on the surface using atomic layer deposition (ALD) are an elegant solution to tackle the anchoring group instability. The propensity of ALD precursors to react with water leads to the question whether molecules containing aqua ligands, such as most water oxidation complexes, can be protected without side reactions and deactivation during the deposition process. We synthesized two iridium and two ruthenium-based water oxidation catalysts, which contained an aqua ligand (Ir–OH2 and Ru–OH2) or a chloride (Ir–Cl and Ru–Cl) that served as a protecting group for the former. Using a ligand exchange reaction on the anchored and partially embedded Ru–Cl, the optimal overlayer thickness was determined to be 1.6 nm. An electrochemical test of the protected catalysts on meso-ITO showed different behaviors for the Ru and the Ir catalysts. The former showed no onset difference between protected and non-protected versions, but limited stability. Ir–Cl displayed excellent stability, whilst the unprotected catalyst Ir–OH2 showed a later initial onset. Self-regeneration of the catalytic activity of Ir–OH2 under operating conditions was observed. We propose chloride ligands as generally applicable protecting groups for catalysts that are to be stabilized on surfaces using ALD.

ortho-Amino group functionalized 2,2′-bipyridine based Ru(ii) complex catalysed alkylation of secondary alcohols, nitriles and amines using alcohols

The catalytic activity of Ru(ii) complexes in sustainable C–C and C–N bond formation is enhanced by using a functionalized 2,2′-bipyridine ligand.

In operando studies on the electrochemical oxidation of water mediated by molecular catalysts

This feature article describes on-line studies regarding the water oxidation reaction mediated by molecular catalysts.

Frontiers of water oxidation: the quest for true catalysts

Development of advanced analytical techniques is essential for the identification of water oxidation catalysts together with mechanistic studies.