Tunable ambipolar photoelectrochemical behavior emerges from microdomains of nanostructured p-type CuFeO2 and n-type Fe2O3 that arise from a single facile solution-processed thin fi lm. The switchable operation of this system is controlled by chemical, optical, or electronic inputs with a uniquely high photocurrent response (on the order of 1 mA cm(-2)), suitable for robust practical application as an oxygen photoregulator.