ZnO/CdS nanorod arrays decorated by layered double hydroxides for efficient solar water oxidation

Abstract

Developing efficient photoanode without either hole scavenger or noble-metal co-catalyst is extremely important for solar water oxidation. However, in most cases, hole scavengers such as Na2S and/or Na2SO3 are usually used to inhibit carrier recombination while blocking the real water oxidation process. To avoid this, non-noble metal co-catalyst, that is, CoNi layered double hydroxides (LDHs), has been successfully deposited onto ZnO/CdS core-shell nanorod arrays for efficient photoelectrochemical water oxidation in KOH aqueous solution. By changing the deposition cycle numbers from 10 to 25 for CdS and tuning the electrodeposition charge quantities from 0.1 to 0.4 C for CoNi LDHs layers, the effect of thickness or loading of CdS and CoNi LDHs on light absorption and photocurrent was systematically studied. A transformation from M(OH)2 to MOOH (M═Co, Ni) is found when the photoexcited holes in CdS are transferred to CoNi LDHs, making the co-catalyst more active than before. These high active M3+ sites, combined with the high absorption over visible light, fast-charge transfer along the 1D ZnO tunnels, and low-charge transfer resistance at photoanode/electrolyte interfaces, endow the ZnO/CdS/CoNi LDHs nanoarrays photoanode with a photocurrent of 2.87 mA/cm2 at 1.0 VRHE and incident photon-to-current efficiency of 36% at 450 nm. The work provides an effective strategy toward efficient solar water oxidation free of hole scavengers. Copyright © 2017 John Wiley & Sons, Ltd.