Manipulation of charge transfer in vertically aligned epitaxial ferroelectric KNbO3 nanowire array photoelectrodes

We demonstrate the growth and characterization of an array of ferroelectric nanowires for photoelectrochemical (PEC) hydrogen production. The photoelectrodes are made of vertically aligned one-dimensional nanowires of the “classic” ferroelectric perovskite KNbO3 grown epitaxially on a Nb-doped SrTiO3 substrate. The charge transfer properties of the photoelectrodes can be effectively tuned by controlling the polarization state, thereby optimizing PEC performance. By manipulating the poling bias from +15 V to −15 V, we were able to tune the photocurrent density in the range from ca. 0.7–11.5 μA·cm−2 (at 0 V vs. Ag/AgCl) under irradiation of air mass 1.5 global (AM 1.5 G) full sunlight at 100 mW/cm2, while the onset potential switches from −0.32 to −0.46 V. Our work provides the basis for understanding PEC reactions conducted with ferroelectric nanowire photoelectrodes as well as insights on strategies for constructing high performance nanowire array-based PEC systems.