Development of a New System for Photocatalytic Water Splitting into H2 and O2 under Visible Light Irradiation

Abstract

Photocatalytic water splitting using semiconductor materials has attracted considerable interest due to its potential for clean production of H 2 from water by utilizing abundant solar light. The developments of water-splitting systems that can efficiently use visible light have been a major challenge for many years in order to realize efficient conversion of solar light. We have developed a new type of photocatalysis system that can split water into H 2 and O 2 under visible light irradiation, which was inspired by the two-step photoexcitation (Z-scheme) mechanism of natural photosynthesis in green plants. In this system, the water-splitting reaction is broken up into two stages: one for H 2 evolution and the other for O 2 evolution; these are combined by using a shuttle redox couple (Red/Ox) in the solution. The introduction of a Z-scheme mechanism reduces the energy required to drive each photocatalysis process, extending the usable wavelengths significantly (μ660 nm for H 2 evolution and μ600 nm for O 2 evolution) from that in conventional water splitting systems (μ460 nm) based on one-step photoexcitation in single semiconductor material.

Water Splitting on Rutile TiO2‐Based Photocatalysts

“…[5][6][7][8][9][10][11][12][13][14][15][16] Water splitting into H 2 and O 2 [Eq. [5][6][7][8][9][10][11][12][13][14][15][16] Water splitting into H 2 and O 2 [Eq.…”

“…The photogenerated electrons and holes can facilitater eduction and oxidation reactions, respectively.T oa ccomplish overall water splitting into H 2 and O 2 ,t he conduction band minimum (CBM) must be more negative than the reduction potentialo fH + to H 2 (0 Vv s. NHE at pH 0), while the valence band maximum (VBM) must lie at ap ositionm ore positive than the oxidation potential of H 2 Ot oO 2 (1.23 Vv s. NHE). [5,11] As chematic illustration of Z-schemewater splitting is shown in Figure 2. However,t here is an activation barrier in the charge transfer process betweent he solid photocatalyst and water molecules, which requires ap hoton energy greater than the bandgapo ft he photocatalystt os plit pure water at ar easonable rate.…”

Recent progress in oxynitride photocatalysts for visible-light-driven water splitting

“…However, remarkable progress has been made, and many difficulties and problems have been overcome. In fact, overall water splitting with a high reaction efficiency on many UV light-sensitive photocatalysts had been achieved until a decade ago [3–5], and recently, photocatalysts have been developed that are capable of overall water splitting under visible-light irradiation [5–7]. The present review introduces the progress in the study of photocatalysts for overall water splitting, with a focus on recent advances in visible-light water splitting on oxynitride photocatalysts.…”

Effect of inserted Si p-n junction on GaN-based photo-electrochemical CO2 conversion system

“…8 Since then, numerous photo-catalysts have been synthesized for hydrogen production. [9][10][11][12][13] The key point in photo-catalytic reactions is to give the photo-catalyst a band-gap that matches the reaction energies needed for splitting water. Here, water oxidation as a counter-reaction is crucial for hydrogen generation as well as in CO 2 reduction; however, a higher cathode energy is necessary for CO 2 reduction.…”