A Redox‐Mediator‐Free Solar‐Driven Z‐Scheme Water‐Splitting System Consisting of Modified Ta₃N₅ as an Oxygen‐Evolution Photocatalyst

Abstract

Tantalum nitride (Ta3N5) modified with various O2-evolution cocatalysts was employed as a photocatalyst for water oxidation under visible light (λ>420 nm) in an attempt to construct a redox-mediator-free Z-scheme water-splitting system. Ta3N5 was prepared by nitriding Ta2O5 powder under a flow of NH3 at 1023-1223 K. The activity of Ta3N5 for water oxidation from an aqueous AgNO3 solution as an electron acceptor without cocatalyst was dependent on the generation of a well-crystallized Ta3N5 phase with a low density of anionic defects. Modification of Ta3N5 with nanoparticulate metal oxides as cocatalysts for O2 evolution improved water-oxidation activity. Of the cocatalysts examined, cobalt oxide (CoO(x)) was found to be the most effective, improving the water-oxidation efficiency of Ta3N5 by six to seven times. Further modification of CoO(x)/Ta3N5 with metallic Ir as an electron sink allowed one to achieve Z-scheme water splitting under simulated sunlight through interparticle electron transfer without the need for a shuttle redox mediator in combination with Ru-loaded SrTiO3 doped with Rh as a H2-evolution photocatalyst.

Unique Properties of 2 D Layered Titanate Nanosheets as a Building Block for the Optimization of the Photocatalytic Activity and Photostability of TiO2‐Based Nanohybrids

“…[1][2][3] Many of semiconducting metal oxides such as TiO 2 and ZnO are, however, inactive in visible light-induced photocatalytic reactions because of their wide bandgap energy and improper band positions. [4] To circumvent the drawbacks of metal oxides, various attempts including chemical substitution and surface sensitization have been made to provide visible light harvesting ability.…”

Z‐Scheme Photocatalytic Systems for Promoting Photocatalytic Performance: Recent Progress and Future Challenges

“…Many works studied different connection modes of Z‐scheme photocatalytic systems 13, 17, 18, 19, 20, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, …”

Effect of Porphyrin Molecular Structure on Water Splitting Activity of a KTaO3 Photocatalyst

“…This two-step excitation process, the so-called "Z-scheme", has been widely studied in both fundamental and applied fields of research [2][3][4][5]. In the past decade, various systems capable of Z-scheme water splitting (Figure 1b), such as Pt or Ru/SrTiO 3 :Rh-Fe 3+ /Fe 2+ -WO 3 , BiVO 4 , or Bi 2 MoO 6 [6,7], Pt/TaON-IO 3´/ I´-PtO X /WO 3 or RuO 2 /TaON [8,9], Pt/ZrO 2 /TaON-IO 3´/ I´-Ir/TiO 2 /Ta 3 N 5 or RuO 2 /TaON [10,11], and other systems [12][13][14][15], have been reported. Our research group has also reported Z-scheme water splitting using porphyrin-dye-modified inorganic semiconductors, such as KTa(Zr)O 3 [16][17][18], GaN:ZnO [19] and TaON [20].…”