GOMs and GOMs in general. GO consists of functionalized and graphitic domains. In GOMs the water flux is considered to mainly move along the graphitic domains . The water flux along graphene-based nanochannels is often described based on the Hagen-Poiseuille equation considering a large slip length that exceeds the channel width . The large slip length describes the low friction of water along the graphitic planes. As shown in Figure for pristine graphitic nanochannels, the slip length is large and has been reported to be around 100-1000 Å 2 . This is in line with our calculated value ~400 Å (Figure ) for the original GO based on our experimental result. After cation intercalation, the slip length decreases.