Enhanced Photoelectrochemical Water Splitting with Er- and W-Codoped Bismuth Vanadate with WO Heterojunction-Based Two-Dimensional Photoelectrode.

A novel two-dimensional (2D) heterojunction photoelectrode composed of WO and (Er,W):BiVO is proposed for water oxidation with efficient photoinduced charge carrier separation and transfer. Er stoichiometric along with W nonstoichiometric codoping was introduced to simultaneously manage vacancy creation during substitutional doping, enhance light absorption, and reduce overall impedance. It was found that Er is substituted at the Bi sites in the BiVO lattice to provide expanded light absorption from 400 to 680 nm. The fabricated WO/(Er,W):BiVO electrode shows photocurrent densities of 4.1 and 7.2 mA cm at 1.23 and 2.3 V (vs reversible hydrogen electrode, RHE), respectively, under a 1 sun illumination in KHPO electrolyte. This electrode has shown remarkably high charge separation efficiency of 93% at 1.23 V (vs RHE). With the addition of a standard surface catalyst (i.e., Co-Pi), the WO/(Er,W):BiVO/Co-Pi electrode exhibits the highest photocurrent of 5.6 ± 0.3 mA cm at 1.23 V (vs RHE), nearing the theoretical limit (i.e., 7.5 mA cm) while retaining 98% of the photoelectrochemical cell performance after 3 h. By concomitantly doping the Bi and V sites to enhance absorption, this study demonstrates for the first time a planar WO/BiVO heterojunction that reaches 88% of the record-high performance of its nanostructured counterpart. Through a detailed characterization of the electrodes, it is concluded that the stoichiometric Er and nonstoichiometric W codoping extend light absorption region and improve charge separation efficiency by reducing bulk resistance. The photoactive materials with 2D morphology were synthesized using a facile ultrasonic spray-coating technique without any complex process steps and thus it can be scaled for commercial development.