Copper And Iron Complexes Modified Electrodes Towards Photoelectro-and Electrochemical Water Oxidation

Solar energy conversion has attracted worldwide attention due to its importance to the rising global energy demand and environmental concerns.A renewable and sustainable method to address these questions is to split water into oxygen and hydrogen powered by sunlight.In general.water splitting is hindered by the oxidation of water to oxygen due to its demanded 4e-,4H+ processes.To overcome this obstacle,the robust,low-cost water oxidation catalysts(WOCs)and anodes that perform fast oxygen evolution at low onset potentials and benign conditions are highly desired.In this thesis,a molecular copper complex[Cu(TMC)(H2O)](NO3)2(1,TMC =1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane)which catalyzes water oxidation in neutral phosphate buffer with low overpotentials was developed.Under the same test conditions,complex 1 led to a cathodic shift of approximately 200 mV in potential to reach a current density of 1 mA/cm2 in comparison with that of the previously reported dinuclear copper complex[Cu2(BPMAN)(?-OH)](CF3SO3)3(2).Immobilization of complex 1 on carbon cloth,it showed greatly improved activity than other state-of-the-art copper-based WOCs such as CuOx and Cu2+.For example,a high current density of 4 mA/cm2 at 1.64 V(vs.Normal Hydrogen Electrode,NHE)was maintained with high durability and a Faradaic efficiency of 98%was obtained.Electrochemical kinetic study and Pourbaix diagram suggested the involvement of[Cu?(TMC')(OH)]3+ or[Cu?(TMC)(OH)]3+ as a key intermediate in catalysis,which undergoes the nucleophilic attack by water for O-O bond formation.In addition to homogenous catalysts,heterogenous WOCs have drawn great attentions.We have developed the first example of copper based WOC easily prepared by electrodepostion from the Cu2+ salt solution in borate electrolyte at pH 9(Bi).The in situ formed copper oxide thin film is inert to corrosion and exhibits high catalytic activity with the steady current densities up to 1.2 mA/cm2 at 1.3 V(vs.NHE)without iR compensation in borate buffer.The high activity at relatively low overpotential,the easy accessibility,and benign working conditions of Cu-Bi provide obvious advantages over the reported copper-based WOCs.In the last part,ferrihydrite(Fh)as a cocatalyst was decorated on a worm-like nanoporous BiVO4 photoanode.Surface kinetics study of Fh/BiVO4 by intensity modulated photocurrent spectroscopy(IMPS)evidenced the primary role of Fh on PEC performance enhancement varying with the loading of Fh.It was found that dispersed Fh nanoparticles primarily play the role of accelerating hole transfer for water oxidation,while a compact layer of Fh reduces both surface charge recombination and hole transfer rates.Modification of BiVO4 film with a discrete layer of Fh nanoflakes effectively suppresses charge recombination by surface passivation when maintaining the rate constant of hole transfer,leading to a high AM 1.5 G photocurrent of 4.78 mA/crrm2 at 1.23 V versus the reversible hydrogen electrode and an applied bias photon-to-current efficiency of 1.81%at 0.61 V.These values are comparable to the best results reported for undoped BiVO4.