Herein, we report the application of the mononuclear copper complex 1, [Cu(L)], in electrochemical water oxidation catalysis (L = 1,3-bis(((1-methyl-1H-imidazol-2-yl)methyl)amino)propan-2-ol). The complex exhibits a N donor set consisting of two amine and two imidazole units and a dangling OH unit in close proximity to the copper ion. 1 exhibits a moderate apparent rate constant k of 0.12 s in catalysis and operates at an overpotential of 0.83 V. Detailed investigations allowed us to derive a mechanism for water oxidation. The catalysis proceeds only under basic conditions, where [Cu(L)(OH)], 1H, is the main solution species, which indicates that a negatively charged ligand is necessary to drive the catalysis. Initial oxidation of 1H is coupled to proton loss forming a copper(iii) species and further oxidation initiates oxygen evolution. Initial oxidation of 1 under neutral, i.e. non-catalytic, conditions is pH independent, highlighting the importance of PCET steps during catalysis. We collected reasonable evidence that catalysis proceeds via a water nucleophilic attack mechanism. The electrolyte presumably acts as a proton acceptor in catalysis as the onset potential depends on the buffer employed.

Herein, we present the application of a copper(II) complex, [CuL 1 ](ClO 4 ) 2 (L 1 : 1,3-bis{[(1-methyl-1H-imidazol-2yl)methyl]amino}propan-2-ol) (1), as a catalyst in the electrochemically driven hydrogen evolution reaction (HER) in buffered water and standardised artificial seawater. Potentiometric titrations revealed that a [Cu II HL 1 ] 3+ species is the main species in aqueous solutions at pH 4 to 8. Complex solutions of 1 are active in the electrochemical HER at solutions at pH 4 to 8, yet, the active species is different depending on the reaction [a]

Invited for the cover of this issue is the group of Inke Siewert from Universität Göttingen, Germany. The cover image shows a copper complex that catalyzes the electrochemically driven hydrogen evolution reaction (HER) in buffered purified water and seawater.

The water splitting reaction represents an appealing approach to store solar energy. The 4e À /4H + oxidation of water generating O 2 is considered as the bottleneck in this reaction and usually requires a rather large over potential. We report on the synthesis and application of a binuclear cobalt(III) complex, 1, with two μ-OH ligands and tripodal triazole ligands, L, in the electrochemical water oxidation reaction (WOR; L = tris((1phenyl-1H-1,2,3-triazol-4-yl)methyl)amine).The cobalt(III) centres in the complex exhibit an octahedral coordination geometry and the complex is stable in water. Electrochemical studies revealed that solutions of 1 NO3 catalyse the WOR in phosphate or borate buffer. However, further analysis showed, that 1 NO3 is a precursor and decomposes under the applied potential. A smooth deposit is formed on the electrode surface, which is a highly active water oxidation catalysis. The deposit consists of mainly cobalt oxide/hydroxide, which accounts for the catalytic activity, and small amounts of 1 NO3 .