Fig. 4From: WS2–WC–WO3 nano-hollow spheres as an efficient and durable catalyst for hydrogen evolution reactiona XPS survey profiles of the WS2–WC–WO3 NH spheres and WS2 NFs, high-resolution W4f XPS profiles of the b WS2–WC–WO3 NH spheres and c WS2 NFsBack to article page