Multi-functional Ni3C cocatalyst/g-C3N4 nanoheterojunctions for robust photocatalytic H2 evolution under visible light

Abstract

Developing highly active, non-noble-metal H₂ evolution co-catalysts is appealing yet still remains a great challenge in the promising field of visible-light-driven photocatalytic solar fuel H₂ production. In this work, high quality hexagonal Ni₃C nanoparticles were facilely fabricated through the low-temperature thermolysis of nickel acetylacetonate in oleylamine under a nitrogen atmosphere and were then coupled with g-C₃N₄ by a simple grinding method. The photocatalytic performances of g-C₃N₄/Ni₃C nanoheterojunctions were tested under visible light irradiation using triethanolamine (TEOA) as a hole scavenger. The optimal H₂-production rate of 15.18 μmol h⁻¹ over 15 wt% Ni₃C nanoparticle decorated g-C₃N₄, corresponding to an apparent quantum yield (AQY) of 0.40% at 420 nm, is approximately 116.7 times higher than that of pure g-C₃N₄ and is even larger than that of the 0.5 wt% Pt/g-C₃N₄ sample. Well resolved density functional theory (DFT) calculation reveals that the “TOP” site of Ni₃C(113) with a H adsorption energy of −0.97 eV is likely the dominant reaction site for H₂ evolution, rather than the Hollow and Bridge sites. It was also demonstrated by the polarization curves that the Ni₃C nanoparticles could act as multi-functional electrocatalysts to improve the kinetics for water oxidation, the oxidation of TEOA, and hydrogen evolution in both acidic and basic media. Therefore, the loading of multi-functional Ni₃C cocatalyst nanoparticles onto g-C₃N₄ can fundamentally promote the rapid transportation/separation of charge carriers, enhance the oxidation kinetics of TEOA, and decrease the overpotential of H₂-evolution, thus favoring significantly enhanced photocatalytic activity. It is highly expected that this work will provide new ideas to develop robust metal carbides as noble-metal-free cocatalysts for high-efficiency and low-cost g-C₃N₄-based photocatalytic water splitting.