Manipulation of charge carrier flow in Bi4NbO8Cl nanoplate photocatalyst with metal loading.

Kanta Ogawa,Osamu Tomita,Kosaku Kato,Hiroshi Kageyama,Hajime Suzuki,Chengchao Zhong,Ryota Sakamoto,Kouichi Nakashima,Ryu Abe,Akinori Saeki,Takashi Tachikawa,Akira Yamakata

doi:10.1039/d1sc06054f

Abstract

Separation of photoexcited charge carriers in semiconductors is important for efficient solar energy conversion and yet the control strategies and underlying mechanisms are not fully established. Although layered compounds have been widely studied as photocatalysts, spatial separation between oxidation and reduction reaction sites is a challenging issue due to the parallel flow of photoexcited carriers along the layers. Here we demonstrate orthogonal carrier flow in layered Bi4NbO8Cl by depositing a Rh cocatalyst at the edges of nanoplates, resulting in spatial charge separation and significant enhancement of the photocatalytic activity. Combined experimental and theoretical studies revealed that lighter photogenerated electrons, due to a greater in-plane dispersion of the conduction band (vs. valence band), can travel along the plane and are readily trapped by the cocatalyst, whereas the remaining holes hop perpendicular to the plane because of the anisotropic crystal geometry. Our results propose manipulating carrier flow via cocatalyst deposition to achieve desirable carrier dynamics for photocatalytic reactions in layered compounds.

Highlights

Semiconductor photocatalysis is a promising solar energy conversion method
An extraordinarily high quantum efficiency of nearly 100% has recently been demonstrated under UV light on an Al-doped SrTiO3 particulate photocatalyst,[3] such highly efficient charge separation has not yet been achieved on aDepartment of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan bGraduate School of Engineering, Toyota Technological Institute, 2-12-1 Hisakata, Tempaku, Nagoya 468-8511, Japan cDepartment of Materials Science and Engineering, College of Engineering, Ibaraki University, 4-12-1, Nakanarusawa, Hitachi, Ibaraki 316-8511, Japan dMolecular Photoscience Research Center, Kobe University, 1-1 Rokkodai-cho, Kobe 657-8501, Japan eDepartment of Applied Chemistry, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan † Electronic supplementary information (ESI) available: Photocatalytic activity, Scanning electron microscopy (SEM), and Transmission electron microscopy (TEM) images, PL images
We successfully manipulated the carrier ow in a layered Bi4NbO8Cl nanoplate suffering from charge recombination by Rh deposition at the edge, which leads to the spatial charge separation and signi cantly improves the photocatalytic activity

Summary

Introduction

Semiconductor photocatalysis is a promising solar energy conversion method. Therein, photogenerated charge carriers migrate from the bulk to the surface to induce redox reactions – water splitting being the primary target.[1,2,3] For practical solar-tohydrogen conversion systems via photocatalytic water splitting, both the effective absorption of photons in the visible light region and the efficient charge separation of photoexcited charge carriers (electrons and holes) are crucial. We demonstrate orthogonal carrier flow in layered Bi4NbO8Cl by depositing a Rh cocatalyst at the edges of nanoplates, resulting in spatial charge separation and significant enhancement of the photocatalytic activity.

Results

Conclusion