Polymeric Metal Salen-Type Complexes as Catalysts for Photoelectrocatalytic Hydrogen Peroxide Production

Electroactive and conductive polymers based on transition metal complexes with salen-type ligands are of interest as potential materials for energy storage and solar energy conversion. The easily tunable structure of monomers allows to modify polymer properties by changing either the central metal atom or the ligand substituents. Herein we report the photoelectrocatalytic activity of [M-II(L)](n) complexes, where M is Ni, Cu or Pd, and L is a tetradentate N,N,O,O salen-type ligand, in the reduction of molecular oxygen to hydrogen peroxide in water solutions on polymer-coated ITO electrodes. The photocathodic current at 0 V vs. Ag/AgCl is pH-dependent, reaching maximum at pH 1 and dropping almost to zero at pH 12. Hydrogen peroxide production is almost quantitative (97 % efficiency measured in 1-compartment cell). Maximal photocurrent and H2O2 concentrations achieved comprise 23 mu A/cm(2) and 1.3x10(-3) M respectively.