Spinel ZnFe2O4 (ZFO) is a widely studied iron-based semiconductor forapplication as photoanode material in photoelectrochemical water splitting tandemcells. However, the current benchmark efficiency reported for photoelectrochemicalwater oxidation at ZFO photoanodes is approximately one order ofmagnitude smaller than the predicted theoretical maximum. In addition, a largedispersion between the efficiencies reported for ZFO photoanodes prepared bydifferent synthetic approaches, as well as poor reproducibility, become obviousfrom published data. It has been recently reported that the cation distribution, i.e.,the ordering of the Fe3+ and Zn2+ cations within the oxygen lattice, has an impact onthe photoelectrochemical activity of the semiconductor. However, the impact of thecation distribution on physicochemical properties directly related to thephotoelectrochemical activity was poorly understood. The parameter employed tocharacterize the cation distribution is the degree of inversion, x, defined asT[Zn1-xFex]O[ZnxFe2-x]O4, with 0 ≤ x ≤ 1 (the superscripts T and O denote tetrahedraland octahedral sites, respectively).In this work, highly pure ZFO samples exhibiting degrees of inversion rangingfrom x ≈ 0.07 to x ≈ 0.20 were synthesized. The samples exhibited, within the limitof the experimental determination, equal particle size, crystallite size, andcrystallinity, as was confirmed by XRD plus Rietveld refinement, Mössbauerspectroscopy, Raman spectroscopy, scanning electron microscopy, and elementalanalysis. Oxygen vacancies were not detected. Therefore, the degree of inversion isassumed to be the only independent variable between the different samples. Thelight absorption, charge carrier transport, and electronic properties wereinvestigated by UV-Vis-NIR reflectivity, impedance spectroscopy, and time-averagedas well as transient photoluminescence spectroscopy, respectively. Thephotoelectrochemical efficiency for the methanol oxidation reaction undersimulated solar irradiation was determined in order to compare the activity of theZFO samples having different degrees of inversion.VIIt was found that the cation distribution does not affect the band gap energyof ZFO but has a large impact on the charge carrier transport and the electronicproperties. An increase in the photoelectrochemical activity was observed byincreasing the degree of inversion. This impact was mainly ascribed to the enhancedcharge carrier transport properties of the samples having higher degrees ofinversion. In addition, changes in the probability of the photoinduced electronictransitions of ZFO produced by increasing the degree of inversion were found toadditionally contribute, to a lesser extent, to the observed enhancement in thephotoelectrochemical activity.This thesis provides a fundamental insight concerning the impact of thedegree of inversion on the photoelectrochemical activity of ZFO. Furthermore, theresults presented herein contribute to the understanding of some factors limitingthe efficiency of ZFO photoanodes.