  Photoelectrochemical impedance spectroscopy (PEIS) is a useful tool for the
characterization of photoelectrodes for solar water splitting. However, the
analysis of PEIS spectra often involves a priori assumptions that might bias
the results. This work puts forward an empirical method that analyzes the
distribution of relaxation times (DRT), obtained directly from the measured
PEIS spectra of a model hematite photoanode. By following how the DRT evolves
as a function of control parameters such as the applied potential and
composition of the electrolyte solution, we obtain unbiased insights into the
underlying mechanisms that shape the photocurrent. In a subsequent step, we fit
the data to a process-oriented equivalent circuit model (ECM) whose makeup is
derived from the DRT analysis in the first step. This yields consistent
quantitative trends of the dominant polarization processes observed. Our
observations reveal a common step for the photo-oxidation reactions of water
and H2O2 in alkaline solution
