In photoelectrochemical (PEC) water oxidation, a low onset potential and a high photocurrent are desired and a cocatalyst on the photoanode could improve the performance. For better use of a NiFe layered double hydroxide (LDH) cocatalyst, concept of exfoliation is applied. Exfoliation gives higher electrochemical surface area and better water oxidation kinetics, which is reflected in improved charge injection efficiency at low bias potentials. Exfoliated NiFe LDH shows increased photocurrent density by 50 % at 1.0 VRHE and reduced onset potential by 140 mV relative to those of stacked bulk LDH under 1 sun illumination, making it a much more effective cocatalyst for α-Fe2O3 photoanode. The intensity modulated photocurrent spectroscopy shows that the improved photocurrents and early onset potentials of exfLDH/α-Fe2O3 photoanode are attributed to fast charge transfer and, more importantly, suppressed charge recombination due to passivation of α-Fe2O3 surface by the LDH monolayer sheet.