In Operando Photoswitching of Cu Oxidation States in Cu-Based Plasmonic Heterogeneous Photocatalysis for Efficient H2 Evolution

Metal nanoparticles (NP) supported on TiO2 are known to be efficient photocatalysts for solar-to-chemical energy conversion. While TiO2 decorated with copper NPs has the potential to become an attractive system, the poor oxidative stability of Cu severely limits its applicability. In this work, we demonstrate that, when Cu NPs supported on TiO2 nanobelts (NBs) are engaged in the photocatalytic generation of H2 from water under light illumination, Cu is not only oxidized in CuO but also dissolved under the form of Cu+/Cu2+ ions, leading to a continuous reconstruction of nanoparticles via Ostwald ripening. By nanoencapsulating the CuOx (Cu/CuO/Cu2O) NPs by a few layers of carbon supported on TiO2 (TC@C), Ostwald ripening can be suppressed. Simultaneously, the resulting CuOx@C NPs are photoreduced under light illumination to generate Cu@C NPs. This photoswitching strategy allows the preparation of a Cu plasmonic photocatalyst with enhanced activity for H2 production. Remarkably, the photocatalyst is even active when illuminated with visible light, indicating a clear plasmonic enhancement of photocatalytic activity from the surface plasmonic resonance (SPR) effect of Cu NPs. Three-dimensional electromagnetic wave-frequency domain (3D-EWFD) simulations were conducted to confirm the SPR enhancement. This advance bodes for the development of scalable multifunctional Cu-based plasmonic photocatalysts for solar energy transfer.