Development of a Core–Shell Heterojunction Ta₃N₅-Nanorods/BaTaO₂N Photoanode for Solar Water Splitting

Abstract

Heterostructure-based photoanodes have been investigated to enhance light absorption and promote the generation and extraction of charge carriers for efficient solarto-hydrogen energy conversion. Oxy(nitride) semiconducting materials are promising candidates to harvest the visible solar spectrum; however, the realization of stable and efficient oxy(nitride) heterostructure-based photoanodes remains a challenge. Here, we demonstrate a core−shell heterojunction photoanode of Ta 3 N 5 -nanorods/BaTaO 2 N that is obtained by combining glancing angle deposition and dip coating techniques. The heterojunction photoanode homogeneously covered by a FeNiO x cocatalyst (Ta 3 N 5 -NRs/BaTaO 2 N/FeNiO x ) generates a stable photocurrent of ∼4.5 mA cm −2 at 1.23 V RHE under simulated AM 1.5G sunlight. The stoichiometric evolution of O 2 and H 2 from water occurs steadily over an hour when the covered heterojunction photoanode is connected to a Pt counter electrode with faradaic efficiencies of 90%−95%. This work may open a new path to fabricating efficient and stable oxy(nitride) photoactive materials for solar energy conversion.

High-performance and stable photoelectrochemical water splitting cell with organic-photoactive-layer-based photoanode

“…In addition to their sufficient earth abundance and stability in water, photoelectrode materials must exhibit solar-to-hydrogen (STH) conversion efficiency of above 10% for their commercial viability 2 . Since the first successful demonstration of water splitting with a TiO 2 photoanode by Honda and Fujishima 3 , extensive research has been focused on strategies to maximize the STH efficiency of inorganic photocatalysts, such as SrTiO 3 , NaTaO 3 , WO 3 , Fe 2 O 3 , BiVO 4 , and Ta 3 N 5 because they are typically earth-abundant compounds and are stable in water [4][5][6][7][8][9][10] .…”

Probing fundamental losses in nanostructured Ta3N5 photoanodes: design principles for efficient water oxidation

“…Prior to photoelectrochemical (PEC) measurements using previously reported protocols, 20,21 the Ta/Ba:Ta 3 N 5 -NRs specimens were uniformly coated with FeNiO x as a co-catalyst (see the EDS elemental map in Fig. S6, ESI †) to prevent photo-corrosion of the NRs surfaces as well as to facilitate the oxygen evolution reaction.…”

“…2 shows the PEC performance of the Ta/Ba:Ta 3 N 5 -NRs/ FeNiO x photoanode and compares it with that recently reported by our group for a Ta/Ta 3 N 5 -NRs/FeNiO x photoanode. 20 Fig. S7, ESI † demonstrates that the PEC performance of the Ba:Ta 3 N 5 -NRs photoanode was affected by the Ba precursor concentration and that the best performance was obtained at a concentration of 0.125 M. Since the dimensions of the NRs in the Ba:Ta 3 N 5 -NRs were similar to those of the Ta 3 N 5 -NRs, these materials could be used to examine the effects of Ba doping on the Ta 3 N 5 physical properties and the resultant impact on PEC performance.…”

“…Various nanostructured Ta 3 N 5 -based photoanodes, with morphologies such as nanorods (NRs), nanotubes and nanowires, have been employed to decouple the optical and electrical characteristic lengths to allow for efficient light absorption and charge transport. [17][18][19][20][21] Recently, we demonstrated that a photoanode based on vertically aligned Ta 3 N 5 -NRs exhibited the highest photocurrent density yet reported (close to 10 mA cm À2 ) together with an STH efficiency of approximately 2.7%. 21 This prior work indicated that high performance photoanodes could be realized by the careful optimization of the NR lengths and diameters.…”

Semi-transparent quaternary oxynitride photoanodes on GaN underlayers

“…11 Recently, Domen et al have demonstrated a core-shell heterojunction photoanode of Ta 3 N 5 -nanorods/BaTaO 2 N, generating a stable photocurrent owing to efficient generation and extraction of charge carriers. 31 For the reproducible fabrication of thin films exhibiting controllable thickness on the atomic scale and conformal features, Atomic Layer Deposition (ALD) is a promising technique for the deposition of oxidic precursor layers for subsequent nitridation. 32 In this communication, we demonstrate the synthesis of semi-transparent quaternary photoanodes on the examples of SrTaO 2 N and LaTiO 2 N. First, ALD was explored to obtain semitransparent TaO x N y thin films on conductive n-type GaN substrate.…”