Enwrapping graphdiyne (g-CnH2n−2) on hollow NiCo2O4 nanocages derived from a Prussian blue analogue as a p–n heterojunction for highly efficient photocatalytic hydrogen evolution

Abstract

Graphdiyne (GDY) has shown promising application prospects in the photocatalytic splitting of water into hydrogen (H₂). In this work, a new carbon material of GDY was prepared by a reduction elimination reaction assisted by ball milling, and then it was introduced into NiCo₂O₄ by cryogenic mixing. A novel NiCo₂O₄@GDY p–n heterojunction was designed and synthesized, showing an excellent photocatalytic hydrogen performance of 4.84 mmol g⁻¹ h⁻¹, which is 4.84 and 6.91 times that of GDY and NiCo₂O₄, respectively. The improved hydrogen evolution efficiency can be attributed to the built-in electric field establishment between GDY and NiCo₂O₄, which remarkably promotes the transfer and separation of photoexcitons. Additionally, the unique nanocage structure of Prussian blue analogue (PBA)-derived NiCo₂O₄ can increase the reflection/refraction efficiency of incident light and increase the utilization of sunlight. The possible mechanism at the NiCo₂O₄@GDY p–n heterojunction was proposed and discussed in combination with in situ irradiated X-ray photoelectron spectroscopy (ISI-XPS), time-resolved photoluminescence (TRPL) spectroscopy, valence band XPS (VB-XPS), ultraviolet photoelectron spectroscopy (UPS) and density functional theory (DFT) calculations. As a whole, this work provides an effective strategy for the construction of a p–n heterojunction based on graphdiyne and PBA derivatives to improve photocatalytic hydrogen evolution.