Page 50 - Multifunctional Photocatalytic Materials for Energy

Metal oxide electrodes for photo-activated water splitting 39

(A) (B)

(C) (D) Fe charge (mC¥cm )
–2
0 5 10 15 20 25 30 35
1.5 1.0
0.8
J(mA¥cm –2 ) 1.0 D C B E j ph @ 1.23V RHE (mA cm –2 ) 0.6

0.4
0.5
A 0.2
dark
0.0
0.0
0.4 0.6 0.8 1.0 1.2 1.4 1.6 0 2 4 6 8 10 12
Voltage (V) vs. RHE Zr concentration (mole %)

Fig. 3.11 High resolution TEM images of: (A) BiVO 4 -ZrO 2 photoanodes (2.5% Zr addition);
(B) BiVO 4 -ZrO 2 -Fe 2 O 3 electrodes (2.5 mole% Zr addition and Fe electrodeposition,
−2
2 mC × cm ). BiVO 4 photoanodes were fabricated by Bi electrodeposition on FTO substrates
from ethylene glycol solutions containing Bi(III) ions, followed by vanadium introduction
by drop casting from VO(acac) 2 (Hacac = 2,4-pentanedione) and annealing at 500°C for 2 h.
Different amounts of Zr 2 Cl 2 O were incorporated into the Bi(III) plating bath as the Zr source.
(C) J/V curves of the synthesized systems obtained in the dark (dashed lines) and under
−2
illumination at 100 mW × cm (solid lines) in phosphate buffer solution (pH = 7.6) for the
reference Fe 2 O 3 (A) and BiVO 4 (B), along with the best modified BiVO 4 -based electrodes:
(C) BiVO 4 -ZrO 2 ; (D) BiVO 4 -Fe 2 O 3 ; (E) BiVO 4 -ZrO 2 -Fe 2 O 3 . (D) Photocurrents obtained
at 1.23 V vs. RHE for different additions of Zr (blue spheres) and Fe (red triangles) in the
phosphate buffer solution. The photocurrent density values for the different Zr and Fe amounts
shown in (D) were used to determine the optimum synthetic conditions corresponding to (C).
Adapted with permission from M.N. Shaddad, M.A. Ghanem, A.M. Al-Mayouf, S. Gimenez,
J. Bisquert, I. Herraiz-Cardona, Cooperative catalytic effect of ZrO 2 and α-Fe 2 O 3 nanoparticles
on BiVO 4 photoanodes for enhanced photoelectrochemical water splitting, ChemSusChem 9
(2016) 2779–2783. Copyright Wiley, 2016.

In this chapter, we have presented various research attempts aimed at improving
the performances of PEC devices adopted in sunlight-driven water splitting. The main
focus has been given to selected oxide-based photoanodes, namely Fe 2 O 3 , WO 3 , ZnO,
and BiVO 4 . The key factors boosting the performances of such materials have been