Enhancing photoelectrochemical water splitting by combining work function tuning and heterojunction engineering

Kai-Hang Ye,Yuwen Hu,Wenjie Mai,Duan Huang,Shihe Yang,Hongbing Ji,Haibo Li,Mingyang Li,Shuang Xiao,Weitao Qiu

doi:10.1038/s41467-019-11586-y

Abstract

We herein demonstrate the unusual effectiveness of two strategies in combination to enhance photoelectrochemical water splitting. First, the work function adjustment via molybdenum (Mo) doping significantly reduces the interfacial energy loss and increases the open-circuit photovoltage of bismuth vanadate (BiVO4) photoelectrochemical cells. Second, the creation and optimization of the heterojunction of boron (B) doping carbon nitride (C3N4) and Mo doping BiVO4 to enforce directional charge transfer, accomplished by work function adjustment via B doping for C3N4, substantially boost the charge separation of photo-generated electron-hole pairs at the B-C3N4 and Mo-BiVO4 interface. The synergy between the above efforts have significantly reduced the onset potential, and enhanced charge separation and optical properties of the BiVO4-based photoanode, culminating in achieving a record applied bias photon-to-current efficiency of 2.67% at 0.54 V vs. the reversible hydrogen electrode. This work sheds light on designing and fabricating the semiconductor structures for the next-generation photoelectrodes.

Highlights

We demonstrate the unusual effectiveness of two strategies in combination to enhance photoelectrochemical water splitting
The XRD patterns collected from BiVO4, Mo-BiVO4, BC3N4/Mo-BiVO4, NiFeOx/B-C3N4/Mo-BiVO4 prepared on the Fdoped SnO2 conducting glass (FTO), C3N4 and B-C3N4 are shown in Supplementary Fig. 1
The NiFeOx/B-C3N4/Mo-BiVO4 photoanode has provided an archetype to exploit the potential of boosting the photoelectrochemical performance by the synergistic combination of work function tuning and heterojunction construction

Summary

Introduction

We demonstrate the unusual effectiveness of two strategies in combination to enhance photoelectrochemical water splitting. Due to the presence of numerous trap states and surface defects as well as the associated surface Fermi-level pinning effect, the BiVO4 films variously prepared so far are still plagued by the quite low open-circuit photo-voltage when used as photoanodes[11,14,15] To address this issue, doped photoanodes, such as W-BiVO4, Mo-BiVO4, have been fabricated aiming to enhance charge transport and to reduce the charge recombination[11,12,16,17]. Other problems of the BiVO4-based photoanode include the still low coverage of the solar spectrum which it is able to harvest as well as the low charge separation efficiency To address these problems, carbon quantum dots/BiVO4 and nitrogen doped BiVO4 photoanodes have been reported showing broadened light absorption range, enhanced light harvesting efficiency, and boosted interfacial charge transfer for PEC water splitting[9,18]. As for improving the utilization efficiency of surface charge for oxygen evolution, the combined catalyst/photoelectrode systems, such as FeOOH/

Methods

Results

Conclusion