Copper complexes as catalyst precursors in the electrochemical hydrogen evolution reaction

Abstract

Herein, we report the synthesis and species distribution of copper(ii) complexes based on two different ligand scaffolds and the application of the two complexes in the electrochemical proton reduction catalysis. The ligands bind to one or two copper(II) ions and the pH-dependent mono/dinuclear equilibrium depends on the steric bulk of the ligands. The two water soluble copper(II) complexes were investigated for their activities in the electrochemical hydrogen evolution reaction (HER). In both complexes the copper(ii) ions have a N4-coordination environment composed of N-heterocycles, although in different coordination geometries (SPY-5 and TBPY-5). The solutions of the complexes were highly active catalysts in water at acidic pH but the complexes decompose under catalytic conditions. They act as precursors for highly active copper(0) and Cu2O deposits at the electrode surface, which are in turn the active catalysts. The absence or presence of the ligands has neither an influence on the catalytic activity of the solutions nor an influence on the activity of the deposit formed during controlled potential electrolysis. Finally, we can draw some conclusions on the stability of copper catalysts in the aqueous electrochemical HER.

Reactivity and Mechanism of Photo- and Electrocatalytic Hydrogen Evolution by a Diimine Copper(I) Complex

“…The abundance, price and diverse redox activity of copper have attracted particular interest [1][2][3][4] and many copper complexes have been used as photosensitizers [5,6] redox mediators [7,8] and catalysts for CO 2 reduction [9,10] and water oxidation [11][12][13]. Several Cu-based H 2 evolution heterogeneous [14][15][16] electrocatalysts with good performance have been reported, involving Cu(0), Cu 2 O [17][18][19][20][21][22], and Cu2S [23] materials. However, there are only a few examples of molecular copper catalysts with well-defined, rationally tunable structures and a comprehensive H 2 formation mechanism.…”

Activation pathways taking place at molecular copper precatalysts for the oxygen evolution reaction

“…It is likely that upon reduction [Cu II (bdmpza) 2 ] converts to metallic copper(0) at the electrode interface that in turn is oxidized to CuO. For several related systems conversion of molecular species to copper(0) has been observed in relation to the catalytic hydrogen evolution reaction [48][49][50]. From the cyclic voltammetry in Fig.…”

Thin Copper-Based Film for Efficient Electrochemical Hydrogen Production from Neutral Aqueous Solutions

“…Compared with commonly used metals for hydrogen production, a much higher abundance and lower cost copper complex is obviously much more appealing and promising. − Its potential use in HER has been gradually explored. − In 2014, the first copper-based homogeneous catalyst [(bztpen)­Cu]­(BF 4 ) 2 (batpen = N-benzyl-N,N′,N′-tris­(pyridine-2-ylmethyl)­ethylene-diamine) was reported, and it showed a very outstanding activity in pH 2.5 aqueous solutions . Recently, we demonstrated a water-soluble copper complex featuring a planar polypyridine ligand that can promote hydrogen production in a neutral aqueous solution at a low overpotential .…”