Unconventional Substitution for BiVO 4 to Enhance Photoelectrocatalytic Performance by Accelerating Polaron Hopping.

Bismuth vanadate (BiVO 4 ) as a fascinating semiconductor for photoelectrocatalytic (PEC) water oxidation with suitable band gap ( E g ) has been limited by the issue of poor separation and transportation of charge carriers. Herein, we propose an unconventional substitution of V 5+ sites by Ti 4+ in BiVO 4 (Ti:BiVO 4 ) for the similar ionic radii and accelerated polaron hopping. Ti:BiVO 4 increased the photocurrent density 1.90 times up to 2.51 mA cm -2 at 1.23 V vs RHE and increased the charge carrier density 1.81 times to 5.86 × 10 18 cm -3 . Compared with bare BiVO 4 , Ti:BiVO 4 improves the bulk separation efficiency to 88.3% at 1.23 V vs RHE. The DFT calculations have illustrated that Ti-doping modification could decrease the polaron hopping energy barrier, narrow the E g , and decrease the overpotential of the oxygen evolution reaction (OER) concurrently. With further spin-coated FeOOH cocatalyst, the photoanode has a photocurrent density of 3.99 mA cm -2 at 1.23 V vs RHE. The excellent PEC performance of FeOOH/Ti:BiVO 4 is attributed to the synergistic effect of the FeOOH layer and Ti doping, which could promote charge carrier separation and transfer by expediting polaron migration.