Benzoporphyrin-Based Nanocomposites for Photoelectrochemical O2 Reduction

This research presents a new series of tetrabenzoporphyrins (TBPs) bearing p-diphenylaminophenylethynyl and p-carboxylphenylethynyl groups or two p-carboxylphenylethynyl groups in a trans-fashion on a TBP core for photoelectrochemical O-2 reduction. Impact of electron-donating diphenylamino and electron-withdrawing surface-anchoring carboxyl groups on photophysical and electrochemical properties of the target TBPs was experimentally and theoretically investigated in comparison with those of their benchmark analog. The results show that while the p-carboxylphenylethynyl group give an electronic contribution to the molecules by lowering energy gap, the role of the p-diphenylaminophenylethynyl group is found to be trivial. Preliminary investigation on electrochemical O-2 reduction indicates significant catalytic activities of TBP-modified TiO2/fluorene-doped tin oxide electrodes at potentials of -0.2 V and -0.3 V vs. normal hydrogen electrode (NHE) in a pH-neutral and ambient aqueous condition, leading to H2O2 formation. Upon photoirradiation, catalytic performance of such TBP-based electrodes is further enhanced with the optimum yield obtained when the dicarboxyl derivatives and the potential of -0.3 V vs. NHE are applied. Proposed photoinjection mechanism of the dye/TiO2 simulated by time-dependent density functional theory calculations supported the experimental results indicating the favorable role of the target TBPs as photoelectrocatalysts in the O-2 reduction.

Automated summary

This research investigates the impact of electron-donating and electron-withdrawing groups on the photophysical and electrochemical properties of tetrabenzoporphyrins. The results show that carboxyl groups can lower energy gap, while diphenylamino groups have a trivial effect. TBP-modified electrodes exhibit significant catalytic activities for O-2 reduction, with the best performance seen at -0.3 V potential.