Quantifying Per‐Pulse Growth of BiOI for Thickness Optimization of Converted BiVO 4 Photoanodes

Precise thickness control is essential for optimizing BiVO 4 photoanodes because increasing film thickness enhances visible‐light absorption but can simultaneously aggravate carrier‐transport loss. Here, we report a pulse‐electrodeposition route for the fabrication of BiVO 4 /FTO photoanodes via BiOI precursor films and compare it with conventional continuous electrodeposition. Pulse electrodeposition enabled cycle‐resolved growth of BiVO 4 with an average thickness increment of 34.0 nm per cycle and allowed film thicknesses up to ~1700 nm without severe delamination from the FTO conductive substrate, whereas continuous electrodeposition reached a thickness limit of ~600 nm. Structural analyses revealed that pulse‐electrodeposition modified the internal growth structure of the precursor and converted films while maintaining the same BiVO 4 phase identity. Photoelectrochemical measurements under simulated AM 1.5G illumination showed that the photocurrent density at 1.23 V RHE increased with pulse cycle number up to 25 cycles and then decreased at higher cycle numbers, reaching a maximum of 3.5 ± 0.1 mA cm −2 , significantly higher than that of an electrodeposition‐time‐matched continuous reference (approximately 1.2 mA cm −2 ). Optical, IPCE, and numerical analyses indicate that this optimum arises from a trade‐off between enhanced light harvesting below a critical thickness of approximately 850 nm and increasing carrier‐transport/recombination losses at larger thicknesses.