Enhancing the photoresponse of electrodeposited WO3 film: Structure and thickness effect

Abstract

Electrodeposited WO3 thin films were prepared on the W, Ti, and Nb metal substrates in strongly acidic solution containing a tungsten precursor of (0.025 M sodium tungstate dihydrate powder (Na2WO4 center dot 2H(2)O)) and by varying the applied potential. The applied potential determined the thickness and crystallite size of the deposited WO3 thin films, irrespective of the metal substrate. The thickness and crystallite size of the films, as well as the total consumed electric charge (Q), increased as the applied potential was increased from -0.27 to -0.47 V. Conversely, the photoelectrochemical (PEC) activity declined as the deposition potential increased; the optimal performance was achieved at a deposition potential of -0.27 V for all metal substrates. This potential generated a porous WO3 film or a very thin WO3 layer composed of small nanoparticles, both of which were favorable for electrolyte penetration leading to enhanced charge transport/transfer behavior and providing a large contact area for the electrolyte. Furthermore, the PEC performance of WO3 on the W substrate was higher than those on the Ti and Nb substrates because of the homogenous composition of the W substrate that resulted in the least lattice disturbance. Thus, the maximum photocurrent density of 1.68 mA/c