Efficient BiVO4 Photoanodes by Postsynthetic Treatment: Remarkable Improvements in Photoelectrochemical Performance from Facile Borate Modification

Qijun Meng,Haidong Liu,Kristina Edström,Biaobiao Zhang,Licheng Sun,Maria Cuartero,Lizhou Fan,Gaston A Crespo,Roland De Marco,Mario Valvo

doi:10.1002/ange.201911303

Abstract

AbstractWater‐splitting photoanodes based on semiconductor materials typically require a dopant in the structure and co‐catalysts on the surface to overcome the problems of charge recombination and high catalytic barrier. Unlike these conventional strategies, a simple treatment is reported that involves soaking a sample of pristine BiVO4 in a borate buffer solution. This modifies the catalytic local environment of BiVO4 by the introduction of a borate moiety at the molecular level. The self‐anchored borate plays the role of a passivator in reducing the surface charge recombination as well as that of a ligand in modifying the catalytic site to facilitate faster water oxidation. The modified BiVO4 photoanode, without typical doping or catalyst modification, achieved a photocurrent density of 3.5 mA cm−2 at 1.23 V and a cathodically shifted onset potential of 250 mV. This work provides an extremely simple method to improve the intrinsic photoelectrochemical performance of BiVO4 photoanodes.

Highlights

Water splitting by photoelectrochemical (PEC) cells is one of the most promising ways to obtain a renewable H2fuel.[1]
Nanoporous BiVO4 photoanodes were prepared according to an established method, with a few minor modifications.[5c]. A typical worm-like nanostructure of the resulting BiVO4 with a thickness of about 600 nm is shown in the SEM images (Supporting Information, Figure S1a,b)
Borate modification of the BiVO4 photoanode was performed by dipping the pristine BiVO4 in a 0.5 m borate buffer solution in a capped dark brown bottle (Figure 1 a)

Summary

Introduction

Water splitting by photoelectrochemical (PEC) cells is one of the most promising ways to obtain a renewable H2. The PEC performance of pure BiVO4 photoanode is greatly limited by its low carrier mobility The efficiency of BiVO4 photoanodes is still far from an application level.[5a] Beside these well-studied techniques, a series of postsynthetic treatments, a concept proposed by Smith and Stefik, have recently emerged as a simple and effective strategy to enhance the intrinsic photocatalytic activity of BiVO4 photoanodes.[14] Instead of requiring the use of additional materials, such posttreatments stand out as methods to change the defect chemistry, both at the surface and in the bulk of BiVO4. It provides new mechanisms and opportunities to understand and enhance the intrinsic properties of BiVO4 photoanodes for higher PEC performance. Chemie tently exhibit excellent PEC performance for water oxidation under AM 1.5 G illumination, with a near tenfold enhancement of photocurrent at 0.7 VRHE and a cathodic shift of the onset potential by 250 mV. A series of control experiments were performed; detailed physical characterizations, electrochemical impedance spectroscopy (EIS), and kinetic isotope effect (KIE) studies were conducted to reveal the significant role played by the addition of the borate moiety

Results and Discussion

Conclusion

Conflict of interest