Insight into anions and cations effect on charge carrier generation and transportation of flake-like Co-doped ZnO thin films for stable PEC water splitting activity

Abstract

Developing a stable interface interaction between photoelectrode and electrolyte is crucial for achieving superior photoelectrochemical (PEC) water splitting activity. In this aspect, the contribution of anions and cations present in the electrolyte play a decisive role during its interaction with the solvent and surface functional groups on the developed photoelectrode, which greatly determine the charge carrier generation and transportation. Herein, we developed the flake-like Co (1.7 at.%)-doped ZnO (Co-ZnO) thin films by employing simultaneous RF and DC magnetron sputtering, which were post annealed at 250 °C for 2 h. The developed films were used to demonstrate the PEC activity under different aqueous electrolytes (KCl, KOH, NaOH, Na2SO3 and Na2SO4). Most importantly, owing to the promising flake-like features of Co-ZnO, efficient electrode-electrolyte interface interaction has been achieved for stable and improved PEC activity. In turn, detailed PEC activity in KCl, KOH and NaOH electrolytes demonstrated that K+ cations and OH− anions in KOH greatly influenced the photocurrents than KCl (Cl−) and NaOH (Na+) due to the high ionic conductive and diffusion properties. On the other hand, SO32− (Na2SO3) anions tailor the charge carrier generation by the advantage of hole scavenging activity compared to SO42− (Na2SO4). Comprehensively, our results provide new insight into the selection of aqueous electrolyte to improve the PEC water splitting activity through adopting the ionic conductivity and constructive interaction with photoelectrode.