Boosting the performance of a silicon photocathode for photoelectrochemical hydrogen production by immobilization of a cobalt tetraazamacrocyclic catalyst

Abstract

Modification of the surface of semiconductor photoelectrodes with molecular catalysts provides a way to realize atom-efficient catalysis for photoelectrochemical (PEC) water splitting; however, only a few molecular catalysts have been applied for PEC H₂ production to date. Herein we present an efficient and stable Si-based photocathode modified with a highly active cobalt tetraazamacrocyclic catalyst (denoted as Co(CR-DCP)) through a 2,6-dicarboxypyridin-4-yl (DCP) anchor. The immobilization of Co(CR-DCP) boosted the photocurrent density of the electrode up to −682 μA cm⁻² at 0 V vs. RHE, which was increased by a factor of 31 compared to that of bare Si/TiO₂. Meanwhile, the Si/TiO₂/Co(CR-DCP) photocathode displayed a steady photocurrent over 10 h of controlled potential photoelectrolysis experiment. In terms of PEC activity and stability, the Si/TiO₂/Co(CR-DCP) electrode outperforms previously reported molecular catalyst-modified hybrid photocathodes based on Ga- and In-free semiconductors without an extra TiO₂ outer layer. The kinetic studies revealed that the surface-bound cobalt catalyst substantially improved the PEC activity of the Si-based electrode not only by evidently accelerating the electron transfer rate, but also by retarding the surface electron–hole recombination rate.