Visible-Light-Driven Water Splitting over Particulate LaNbON₂ Prepared from La-Rich Lanthanum Niobium Oxides

Abstract

A LaNbON2 semiconductor is capable of absorbing long light wavelengths up to 750 nm, which indicates a promising n-type material for solar water splitting to produce hydrogen. In this study, we present enhanced photocatalytic and photoelectrochemical activities over the particulate LaNbON2 during visible-light-driven water oxidation. La-rich oxide mixtures, prepared by the calcination of La2O3–Nb2O5 with La/Nb ratios greater than 1.00, were proposed as a starting precursor for the synthesis of less-defective LaNbON2. The La-rich condition caused the synthesis of smaller LaNbON2 particles with larger BET surface areas, which were favorable for the complete nitridation under mild conditions. The LaNbON2 particles prepared from the La/Nb ratio of 1.20, which were capable of absorbing a wide range of visible light up to approximately 750 nm and above, completed the nitridation at 1123 K for 15 h. The La-rich condition promoted reduced bulk defect density of LaNbON2 and suppressed the formation of Nb3+ species at the oxynitride surface during nitridation. These differences led to water oxidation photocurrent over the particulate LaNbON2 photoanode under AM 1.5 G simulated sunlight, which has never previously been reported. Therefore, the synthesis strategy using La-rich oxide was effective at preparing less-defective LaNbON2, thus improving the photoactivity.

Porous Cuboidal SrNbO2N Crystals Grown on a Nb Substrate as an Active Photoanode for Neutral Seawater Splitting under Sunlight

“…The two-step nitridation led to the growth of porous, cuboidal SrNbO 2 N, and the porous surface considerably increased the ECSA of the photoanode, i.e., the active sites where the seawater splitting occurs. Incidentally, the larger ECSA of AB(O,N) 3 resulted in improved water-splitting activity in our previous reports. − The two times larger ECSA of BaNbO 2 N photoanode resulted in more than two times higher water-splitting activity . Therefore, the significantly high photocurrent observed in Figure A was attributed to the decreased R ct and increased ECSA of the SrNbO 2 N photoanode, originating from the two-step nitridation.…”

Perovskite and layered perovskite oxynitrides for efficient sunlight-driven artificial synthesis

“…This can require a long nitridation period, which sometimes results in a low-crystalline perovskite oxynitride with a high density of defects. 94,95 Moreover, exceptional oxynitrides such as BaBO 2 N (B = Ta, Nb) have no corresponding starting stoichiometric crystalline oxide, so an amorphous mixture of oxides of all the elements within the oxynitride must be used instead. 91,96 Particulate ANbO 2 N (A = Sr, Ba) can be prepared from the nitridation of stoichiometric perovskite ANbO 3 (Nb 4+ ), as shown in Fig.…”

“…In response, the use of A-site-rich precursors has been applied in various syntheses of perovskite and layered perovskite oxynitrides. 62,[94][95][96] Layered perovskite A 5 B 4 O 15 (A = Sr, Ba; B = Ta, Nb) has been employed in the synthesis of photoactive ABO 2 N, as presented in Fig. 9(A).…”

“…In fact, heat treatment with conductive binders to promote the transfer of photogenerated charges between multiple layers of particles and/or the substrate (called necking) is an important step in preparing photoanodes via EPD. 61,95 The water-splitting photocurrent density over a TaON photoanode has been notably increased by necking treatment of the photoanode using TiCl 4 . 110 Nevertheless, the water-splitting activity of the photoanodes prepared via EPD is limited due to many grain boundaries between the oxynitride particles in the multiple layers slowing the migration of photoexcited charges.…”

Enhanced electron collection in a particulate LaTiO2N photoanode assembled with an inserted ZnO nanorod array for photoelectrochemical water oxidation

“…1,2 In a photoanode, the core component of a PEC cell, photogenerated electrons are collected to the conductive substrate, which is an essential process of photoelectrochemical water splitting. However, metal oxynitride semiconductor materials, including LaTiO 2 N, 3,4 SrNbO 2 N, 5 BaTaO 2 N, 6 BaNbO 2 N, 7 LaNbON 2 , 8,9 and so on, which are responsive to wide visible light, are not suitable for growth on transparent conductive substrates due to harsh preparation conditions. Therefore, it is necessary to prepare semiconductor particles independently and assemble the photoanode.…”