Porous Cuboidal SrNbO<sub>2</sub>N Crystals Grown on a Nb Substrate as an Active Photoanode for Neutral Seawater Splitting under Sunlight
Van-Huy Trinh, Jeongsuk Seo
Abstract
Photoelectrochemical (PEC) water splitting using n-type SrNbO 2 N is beneficial for hydrogen production because its narrow-band-gap energy allows it to harvest visible light up to 700 nm. However, the oxygen evolution reaction (OER) activity of oxynitride at neutral pH is very limited, hindering its application to commercial PEC devices. Herein, we report enhanced seawater-splitting activity at neutral pH over porous cuboidal SrNbO 2 N crystals grown on a Nb substrate under simulated sunlight. The oxynitride photoanode was prepared via bottom-up fabrication including oxidation of the Nb substrate and flux-assisted nitridation using NaCl–KCl. The oxidation process was necessary for enhancing the oxygen concentration at the Nb surface and producing a crystalline Nb 2 O 5 layer. Then, the Nb 2 O 5 /Nb substrate was subjected to a two-step nitridation, which was very effective in the generation of SrNbO 2 N crystals with a large surface area and high crystallinity. The bottom-up-fabricated SrNbO 2 N/Nb photoanode exhibited milliampere-level photocurrent during seawater splitting in an aqueous 0.5 M NaCl electrolyte at pH 6.4. Chlorine evolution reaction was preferentially catalyzed during seawater splitting compared with competitive OER. This work is the first to demonstrate the PEC neutral seawater splitting by active SrNbO 2 N crystals originating from bottom-up fabrication, which has never been reported in photoreactions using perovskite AB(O,N) 3 .