ZnO-Ta3N5 core-shell nanowire photoanodes with pyridine passivation for efficient and stable photoelectrochemical water-splitting

Abstract

Core-shell nanowire (C/S NW) photoanodes for photoelectrochemical water splitting (PEC-WS) are an effective and promising strategy to enhance light harvesting. Here, ZnO/Ta3N5 C/S NWs passivated by pyridine are fabricated for the first time as photoanodes in PEC-WS. The ZnO/Ta3N5/Pyridine C/S NW with an optimal Ta3N5 shell coating, 10 nm thick, exhibit a maximum photocurrent density of 4.46 mA/cm2 at 1.23 V vs. RHE and a photoconversion efficiency of 2.21 % at 0.35 V vs. RHE, representing 12.53-fold and 36.83-fold enhancements, respectively, compared to the ZnO NW. This optimized photoanode displays remarkable stability over 24 hours with 98 % retention, in contrast to the ZnO NW, which fails after 1.5 hours. Furthermore, we confirm that the ZnO/Ta3N5 C/S NW outperforms the ZnO/TaON and ZnO/Ta2O5 C/S NWs in PEC-WS due to the extensively staggered type-II band alignment for efficient charge separation and the smaller bandgap for efficient light absorption. The pyridine grafting produces a surface dipole, creating a built-in electric field at the surface, and passivates the surface defects of Ta3N5, impeding surface charge recombination. Detailed analyses clarifying the band alignments and charge transport/transfer mechanisms of the aforementioned C/S NW photoanodes have been provided. © 2024 Elsevier B.V.