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

Metal nanoparticles (NP) supported on TiO2 are knownto be efficient photocatalysts for solar-to-chemical energy conversion.While TiO2 decorated with copper NPs has the potentialto become an attractive system, the poor oxidative stability of Cuseverely limits its applicability. In this work, we demonstrate that,when Cu NPs supported on TiO2 nanobelts (NBs) are engagedin the photocatalytic generation of H-2 from water underlight illumination, Cu is not only oxidized in CuO but also dissolvedunder the form of Cu+/Cu2+ ions, leading toa continuous reconstruction of nanoparticles via Ostwald ripening.By nanoencapsulating the CuO x (Cu/CuO/Cu2O) NPs by a few layers of carbon supported on TiO2 (TC@C), Ostwald ripening can be suppressed. Simultaneously, theresulting CuO x @C NPs are photoreducedunder light illumination to generate Cu@C NPs. This photoswitchingstrategy allows the preparation of a Cu plasmonic photocatalyst withenhanced activity for H-2 production. Remarkably, the photocatalystis even active when illuminated with visible light, indicating a clearplasmonic enhancement of photocatalytic activity from the surfaceplasmonic resonance (SPR) effect of Cu NPs. Three-dimensional electromagneticwave-frequency domain (3D-EWFD) simulations were conducted to confirmthe SPR enhancement. This advance bodes for the development of scalablemultifunctional Cu-based plasmonic photocatalysts for solar energytransfer.