In general, doping of hematite increases photoelectrochemical (PEC) water splitting activity by enhancing the bulk conductivity of the photoanode. In this presentation, I report the negative interaction of the two dopants (Sn and heteroatom) in co-doped hematite that was neglected before. We developed an easy heteroatom-doping method that suppressed Sn doping from the FTO substrate. The co-doped hematite converted the incident photons to EHPs with much reduced recombination and exhibited an excellent photocurrent density greater than 4 mA cm^-2 at 1.23V_RHE and an outstanding low turn-on voltage, which is closer to the theoretical efficiency of hematite. Our co-doping strategy provides a straightforward way to addressing the chronic short-hole diffusion length issue that causes a high electron hole recombination rate, to potentially improve the performance of PEC devices.