Identification of Photoexcited Electron Relaxation in a Cobalt Phosphide Modified Carbon Nitride Photocatalyst

Guang Xian Pei,Nelson Y Dzade,Bert M Weckhuysen,Nora H De Leeuw,Yue Zhang,Jan P Hofmann

doi:10.1002/cptc.202000259

Abstract

AbstractTransition metal phosphides have been recognized as efficient co‐catalysts to boost the activity of semiconductor photocatalysts. However, a rigorous and quantitative understanding is still to be developed about how transition metal phosphides influence photoexcited electron dynamics. Here, we present a nanosecond time‐resolved transient absorption spectroscopy (TAS) study of the photoexcited electron dynamics in carbon nitrides (g‐C3N4) before and after Co and/or P modifications. Our spectroscopic study showed that Co or P lowered the initial electron density, whereas they promoted the photoexcited electron relaxation of g‐C3N4, with their half‐life times (t50%) of 2.5 and 1.8 ns, respectively. The formation of a CoP co‐catalyst compound promoted the electron relaxation (t50%=2.8 ns) without significantly lowering the charge separation efficiency. Density functional theory (DFT) calculations were undertaken to explore the underlying fundamental reasons and they further predicted that CoP, compared to Co or P modification, better facilitates photoexcited electron transfer from g‐C3N4 to reactants.

Highlights

Transition metal phosphides have been recognized as efficient cocatalysts to boost the activity of semiconductor photocatalysts
It has been reported that CoP-loaded g-C3N4 has demonstrated higher photocatalytic activity for the H2 evolution reaction than pristine or Co- or P-modified g-C3N4,[9] while the photoexcited electron dynamics of Co- and/or P-loaded g-C3N4 remain elusive
The positive absorption range has been ascribed to the photogenerated electrons,[8c,d] and was confirmed by our transient absorption spectroscopy (TAS) study, which showed that the broad absorption range was obviously enhanced when TEOA was added as the hole scavenger (Figure S5), while significant changes were observed in the TA spectra for the same g-C3N4 after Co or P modification

Summary

Introduction

Transition metal phosphides have been recognized as efficient cocatalysts to boost the activity of semiconductor photocatalysts. The positive absorption range has been ascribed to the photogenerated electrons,[8c,d] and was confirmed by our TAS study, which showed that the broad absorption range was obviously enhanced when TEOA was added as the hole scavenger (Figure S5), while significant changes were observed in the TA spectra for the same g-C3N4 after Co or P modification.

Results

Conclusion