Effects of alkali ion on boosting WO3 photoelectrochemical performance by electrochemical doping

Electrochemical doping is a promising method to modify the photoelectrochemical performance of semiconductors. The published works using H ions as compensated cations have shown increased photocurrents, but theories vary about the causes of the improvement of photoelectrochemical performance. In this paper, we present the effects of cation ion and the key factors of enhancement using alkali sulfates ((Li/Na/K)(2)SO4) as the electrolyte for electrochemical doping. The effective electrode surface area (ECSA) was increased for the WO3 film after electrochemical doping. The Li-ion, with the smallest radius and thereby the highest potential to insert into the WO3 cell, results in the Li ion inserted WO3 with the highest photocurrent in the three electrochemically doped samples. To investigate the possible factors affecting the photoelectrochemical performance, the electrochemically doped samples and a control sample were annealed under inert gas (Ar). The lower photocurrents were observed for the electrochemically doped samples after annealing, confirming that the key factors are the increase of the effective electrode surface area caused by electrochemical doping and ion compensation, rather than the ions themselves and the chemical bonds between alkali ions and W or O. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.