Photoelectrochemical (PEC) water splitting has been a promising approach for solar energy conversion to meet the clean energy demand. Design and fabrication of high-quality photoelectrode for water splitting with enhanced light absorption, as well as efficient charge separation and transport are challenging. Herein, two-dimensional (2D) WO3-x nanosheets with unique fullerene shell-like nanostructure are prepared with assistance of supercritical CO2(SC CO2). Then a novel plasmonic photoanode heterostructure composed of plasmonic Ag and fullerene shell-WO3-x is synthesized for PEC water splitting and photooxidation degradation. The unique coexistence of amorphous and crystalline structure of WO3-x leads to uniformly distribution of Ag nanoparticles, simultaneously increasing the active site density and improving the electron transport. Femtosecond time-resolved IR absorption spectrum analysis indicates the surface plasmonic resonance (SPR) effect of Ag nanoparticles can mediate efficient electron transfer to fullerene shell-WO3-x nanosheets. The photoresponse of the plasmonic Ag/fullerene shell-WO3-x heterostructure is 2.5 times higher than that of fullerene shell-WO3-x. By combining the synergistic effects of the special microstructures of plasmonic Ag and fullerene shell-WO3-x, we are able to design a low-cost photoelectronic catalyst for efficient PEC water splitting and photooxidation degradation. The strategy developed here provides a fascinating way to synthesize high efficient photoelectronic catalysts for solar energy conversion.