This work demonstrates the role of different cobalt-based cocatalysts on BiVO₄ for photoelectrochemical water oxidation. The electrochemical oxygen evolution reaction activities of these cobalt specimens were quite similar but the anodic photocurrent density was quite different. Thus, the vital role of contact interface between cocatalysts and semiconductors were revealed.

Abstract

Cocatalysts play a key role in enhancing activity of photoelectrodes while the study of their interaction remains a challenge. Here, we decoupled the relationship between oxygen evolution reaction (OER) performance and photoelectrochemical (PEC) water oxidation performance by modifying an identical BiVO₄ with different cobalt-based OER catalysts including Co, CoO, Co₃O₄, and Co₄N. The electrochemical OER activities of these cobalt specimens were quite similar. Their anodic photocurrent density followed an order of: Co₄N>Co>Co₃O₄>CoO after loading on the BiVO₄ electrode. The kinetics process and energy band diagram were analyzed, revealing that the interface between different cobalt specimens and BiVO₄ electrode influenced the charge recombination and transfer. Accordingly, we propose a corresponding structural model, which shows that the cocatalysts consist of inner part for interface modulation and the outer layer for catalysis. The present work reveals the vital role of contact interface between cocatalysts and semiconductors, and more attention should be paid when selecting the cocatalysts.