Significance A new technique of in situ doping of alkali metal (Li+, Na+, K+, Rb+, and Cs+) in Nb2O5 was showcased by the modified anodization of Nb foils at high frequency, negative-to-positive pulsed voltage. At the optimized dopant concentration and synthesis condition, the doped-Nb2O5 shows twofold enhancement in photoelectrochemical water splitting efficiencies compared with the undoped Nb2O5 electrode, as a result of improved charge carrier density and enhanced surface charge transfer. (c) 2015 American Institute of Chemical Engineers