Efficient Nonsacrificial Water Splitting through Two-Step Photoexcitation by Visible Light using a Modified Oxynitride as a Hydrogen Evolution Photocatalyst

Abstract

A two-step photocatalytic water splitting (Z-scheme) system consisting of a modified ZrO(2)/TaON species (H(2) evolution photocatalyst), an O(2) evolution photocatalyst, and a reversible donor/acceptor pair (i.e., redox mediator) was investigated. Among the O(2) evolution photocatalysts and redox mediators examined, Pt-loaded WO(3) (Pt/WO(3)) and the IO(3)(-)/I(-) pair were respectively found to be the most active components. Combining these two components with Pt-loaded ZrO(2)/TaON achieved stoichiometric water splitting into H(2) and O(2) under visible light, achieving an apparent quantum yield of 6.3% under irradiation by 420.5 nm monochromatic light under optimal conditions, 6 times greater than the yield achieved using a TaON analogue. To the best of our knowledge, this is the highest reported value to date for a nonsacrificial visible-light-driven water splitting system. The high activity of this system is due to the efficient reaction of electron donors (I(-) ions) and acceptors (IO(3)(-) ions) on the Pt/ZrO(2)/TaON and Pt/WO(3) photocatalysts, respectively, which suppresses undesirable reverse reactions involving the redox couple that would otherwise occur on the photocatalysts. Photoluminescence and photoelectrochemical measurements indicated that the high activity of this Z-scheme system results from the moderated n-type semiconducting character of ZrO(2)/TaON, which results in a lower probability of undesirable electron-hole recombination in ZrO(2)/TaON than in TaON.

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

“…Thus, it is critical to suppress the backward reactions involving redox mediators that are thermodynamically more favorable than water splitting. In 2010, Domen et al succeeded in water splitting using a Z‐scheme system consisting of Pt‐loaded ZrO 2 /TaON and Pt‐loaded WO 3 as the H 2 ‐ and O 2 ‐evolution photocatalysts, respectively, in the presence of an IO 3 – /I – redox mediator 19. The undesirable backward reactions, such as oxidation of I – ions on the Pt‐loaded WO 3 and the reduction of IO 3 – on the Pt‐loaded ZrO 2 /TaON, were significantly minimized.…”

“…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, …”

Modeling, Simulation, and Implementation of Solar‐Driven Water‐Splitting Devices

“…The Type 2 reactor leverages the tandem design and could achieve a theoretical STH conversion efficiency of about 25 % with band-gap combinations of approximately 1.7 eV/1.1 eV as determined through modeling. [7b] The redox mediator, such as those based on iodine, [67] iron, [68] or cobalt, [69] could provide the necessary ionic transport between the two electrochemical compartments (i.e. it acts as a molecular or ionic wire).…”

Photobiocatalysis: The Power of Combining Photocatalysis and Enzymes

“…It would be also important if this large proportion of NIR energy present in the sunlight could be used in photobiocatalysis. In one clever approach aimed at utilization of NIR wavelengths, Park and coworkers [69] have prepared nanoparticles of NaYF 4 (Taken with permission from ref [69] ).…”

“…In conventional photocatalysis using inorganic semiconductors, this type of configuration and two photons coupled process is denoted as Zscheme. [3,4] The term Z derives from the shape of the common schematic representation of two photon excitations rendering independently electrons and holes in two different semiconductors and the transfer of one electron from the conduction band of one semiconductor to the valence band of the other (Scheme 2). Scheme 1.…”