Reactive Sputtering of Bismuth Vanadate Photoanodes for Solar Water Splitting

Abstract

Bismuth vanadate (BiVO 4 ) has attracted increasing attention as a photoanode for photoelectrochemical (PEC) water splitting. It has a band gap in the visible light range (2.4−2.5 eV) and a valence band position suitable for driving water oxidation under illumination. While a number of methods have been used to make BiVO 4 photoanodes, scalable thin film deposition has remained relatively underexplored. Here, we report the synthesis of BiVO 4 thin films by reactive sputtering. The use of separate Bi and V sputtering targets allows control of the Bi/V ratio in the film. Under optimized, slightly V-rich conditions, monoclinic phase BiVO 4 with photoactivity for water oxidation is obtained. The highest photocurrents, ca. 1 mA cm −2 at the reversible O 2 /H 2 O potential with simulated AM 1.5G illumination, are obtained with bilayer WO 3 /BiVO 4 , where the WO 3 serves as a hole-blocking layer.

BiVO4 photoanodes for water splitting with high injection efficiency, deposited by reactive magnetron co-sputtering

“…, The shoulder located at 28.8 • is ascribed to the strongest (-112) reflex of m-BiVO 4 . This means, we observe a phase separation at V/Bi = 0.60, which is different from the result of Chen et al, 14 who obtained by reactive magnetron sputtering primarily the monoclinic crystal structure at this V-to-Bi ratio. This could be caused by their slightly different sputtering conditions; instead of a metallic Bi target they used a Bi 2 O 3 target, which was excited by an RF power supply at a total pressure of 0.67 Pa (our total pressure was 1 Pa).…”

“…13 Other synthesis method are based on physical vapor deposition, such as reactive ballistic deposition (RBD), 5 and reactive magnetron sputtering. 14,15 An important advantage of physical vapor deposition techniques over chemical solution methods is the much higher purity that can generally be achieved. This is not only because the deposition process takes place under high vacuum conditions, but also because no organic ligands or surfactants are involved.…”

Factors affecting bismuth vanadate photoelectrochemical performance

“…This is similar to reported PEC performance. 21,23,24,28,32,[41][42][43][44] Our observed lm thickness is likely the optimal trade-off between absorption (thicker is better) and majority carrier transport (thinner is better). No trend could be derived from the property A (see below).…”

“…[15][16][17][18][19][20][21] However, typical photocurrents of unmodied BiVO 4 photoanodes are limited by high electron-hole recombination and poor charge transport properties, 16,[22][23][24] and inadequate water oxidation kinetics.…”

Determination of the Intrinsic Defect at the Origin of Poor H2 Evolution Performance of the Monoclinic BiVO4 Photocatalyst Using Density Functional Theory

“…It has a band gap around 2.4 eV absorbing light in the visible range and an appropriate valence band position for O 2 evolution driving water oxidation with an onset potential of 0.3 V vs RHE (0.9 V vs the O 2 /H 2 O potential). 5,6 Its conduction band edge position is fairly negative or just located at the H 2 /H 2 O potential level. For that, sacrificial reagents (e.g.…”