Interfacial repairing of semiconductor-electrocatalyst interfaces for efficient photoelectrochemical water oxidation

Tailoring the special hole transfer layer between BiVO4 and oxygen evolution co-catalysts interfaces for boosting photoelectrochemical water splitting

Tailoring the hole transport layer (HTL) between BiVO4 (BVO) and oxygen evolution co-catalysts (OECs) interfaces is a leading strategy to improve the performance of photoelectrochemical (PEC) water splitting. Nevertheless, the limited driving force at the BVO/OECs interfaces severely hinders the transport of charge carriers. In this study, we designed a specialized defective transition metal oxide (Vo-MnOx) as the HTL. The integrated photoanode (BVO/Vo-MnOx/CoFe(OH)x) exhibits an impressive photocurrent density at 1.23 V vs. RHE, along with an outstanding ηsurface value of 91.91 %. These remarkable outcomes are due to the fact that Vo-MnOx as HTL effectively enhances the interface driving force and charge migration ability, which is largely attributed to the ability of Vo to accumulate electrons and accelerate rapid cyclic transitions of multivalent Mn. Satisfactorily, microscopic perspective studies reveal that the distinctive Vo-MnOx can efficiently promote photogenerated charge transfer, as shown in dynamic carrier analysis using scanning photoelectrochemical microscope (SPECM). Additionally, the oxygen evolution reaction model suggests that a defective HTL can improve surface catalytic kinetics. This work provides valuable insights into the role of Vo in regulating the valence state changes in PEC water splitting.

Insight into oxygen reduction activity and pathway on pure titanium using scanning electrochemical microscopy and theoretical calculations

HYPOTHESIS

Unlike noble metals, the oxygen reduction reaction (ORR) behavior on Ti is more complicated due to its spontaneously formed oxide film. This film results in sluggish ORR kinetics and tends to be reduced within ORR potential region, causing the weak and multi-reaction coupled current. Though Ti is being used in chemical and biological fields, its ORR research is still underexplored.

EXPERIMENTS

We innovatively employed the modified reactive tip generation-substrate collection (RTG/SC) mode of scanning electrochemical microscopy (SECM) with high efficiency of 97.2 % to quantitatively study the effects of film characteristics, solution environment (pH, anion, dissolved oxygen), and applied potential on the ORR activity and selectivity of Ti. Then, density functional theory (DFT) and molecular dynamics (MD) analyses were employed to elucidate its ORR behavior.

FINDINGS

On highly reduced Ti, film properties dominate ORR behavior with promoted 4e^- selectivity. Rapid film regeneration in alkaline/O₂-saturated conditions inhibits ORR activity. Besides, ORR is sensitive to anion species in neutral solutions while showing enhanced 4e^- reduction in alkaline media. All the improved 4e^- selectivities originate from the hydrogen bond/electrostatic stabilization effect, while the decayed ORR activity by Cl^- arises from the suppressed O₂ adsorption. This work provides theoretical support and possible guidance for ORR research on oxide-covered metals.