An effective strategy for promoting charge separation by integrating heterojunctions and multiple homojunctions in TiO2 nanorods to enhance photoelectrochemical oxygen evolution

Hewei Si; Lilan Zou; Gu Huang; Jianjun Liao; Shiwei Lin

doi:10.1016/j.jcis.2022.10.066

An effective strategy for promoting charge separation by integrating heterojunctions and multiple homojunctions in TiO₂ nanorods to enhance photoelectrochemical oxygen evolution

J Colloid Interface Sci. 2023 Jan 15;630(Pt A):888-900. doi: 10.1016/j.jcis.2022.10.066. Epub 2022 Oct 19.

Authors

Hewei Si¹, Lilan Zou¹, Gu Huang¹, Jianjun Liao², Shiwei Lin³

Affiliations

¹ State Key Laboratory of Marine Resource Utilization in South China Sea, School of Materials Science and Engineering, Hainan University, Haikou 570228, China.
² School of Ecology and Environment, Hainan University, Haikou 570228, China.
³ State Key Laboratory of Marine Resource Utilization in South China Sea, School of Materials Science and Engineering, Hainan University, Haikou 570228, China. Electronic address: [email protected].

PMID: 36306600
DOI: 10.1016/j.jcis.2022.10.066

Abstract

It is important to achieve high photoelectrochemical (PEC) oxygen evolution performance in titanium oxide (TiO₂) via the separation and transportation of photogenerated carriers. Herein, three-dimensional (3D) TiO₂ nanorod arrays growing on flexible carbon cloth (CC) were decorated with graphitic carbon nitride (g-C₃N₄) to yield a 3D g-C₃N₄/TiO₂/CC heterojunction composite (TCN). The photocurrent density of TCN is 10.6 times that of the bare TiO₂ nanorod arrays, which can be attributed to the promoted separation and transportation of photogenerated carriers by the heterojunction. Then, a simple rapid cooling and heating (RCH) treatment was creatively introduced to form a gradient Ti³⁺ self-doping TiO₂ multiple homojunction (GTSD-TiO₂) in the bulk during the hydrothermal growth of the TiO₂ nanorod array. This can further facilitate the separation and transportation of carriers in the bulk owing to the formation of a built-in electric field. The GTSD-TiO₂ was decorated with g-C₃N₄ to form a core-shell heterojunction composite (GTSD-TCN). Notably, the photocurrent density of the GTSD-TCN core-shell heterojunction reached 1.23 mA cm^-2 at 1.23 V (vs reversible hydrogen electrode (RHE)) under air mass (AM) 1.5 G illumination without the use of hole scavengers or cocatalysts; this was twice the photocurrent density of the TCN heterojunction (0.64 mA cm^-2) and is one of the best values obtained from the previously reported TiO₂ and g-C₃N₄ heterojunction. This performance may be ascribed to the enhanced charge separation and transportation efficiency of the heterojunction after the RCH treatment; the efficiency rises from 51 % (TCN) to 71 % (GTSD-TCN). We believe that the RCH treatment is a highly promising method towards fabricating unique multiple homojunctions by gradient self-doping. This simple and novel design provides a new route for the preparation of high-performance PEC photoelectrodes.

Keywords: Gradient self-doping; Heterojunction; Multiple homojunction; Photoelectrochemical oxygen evolution; Photogenerated charge-carrier separation.