Effect of Cerium\nPrecursors on Ce-Doped BiVO<sub>4</sub> Nanoscale-Thick Films as Photoanodes:\nImplications for Water Splitting

The use of the BiVO<sub>4</sub> semiconductor to generate\nH<sub>2</sub> via water splitting has recently been studied to meet\nthe\nglobal energy demand. However, BiVO<sub>4</sub> has some limitations\nsuch as higher electron–hole recombination and poor stability,\nbeing necessary studies that aim to give better performance. In this\nscenario, the use of the rare earths as a doping agent should be considered.\nThis work explores the nanoscale-thick film BiVO<sub>4</sub> electrochemical\nsynthesis via BiOI film obtention and the effects of the use of different\ncerium precursors on the physical and photoelectrochemical (PEC) properties.\nCerium(III) nitrate, cerium(IV) oxide, and ammonium cerium(IV) nitrate\nwere evaluated as precursors and added into the plating solution before\nthe electrochemical deposition. The films obtained underwent characterization\nthrough X-ray diffraction, SEM-EDS, and micro-Raman analyses. The\nresults indicate that cerium is incorporated into the BiVO<sub>4</sub> structure and that this incorporation did not alter its monoclinic\nstructure, confirming the successful execution of the doping process.\nThe PEC film characterization was evaluated by cyclic voltammetry,\nlinear sweep voltammetry, and electrochemical impedance spectroscopy,\nshowing a different PEC activity that depends on the used cerium precursors.\nThe use of ammonium cerium(IV) nitrate improves the activity of the\nCe–BiVO<sub>4</sub> films, increasing the photocurrent by almost\n2 times compared with pure BiVO<sub>4</sub>. Otherwise, the other\nprecursors decrease the activity. Analysis of the ultraviolet–visible\nreflectance spectra and Mott–Schottky plots showed the difference\nbetween the material band gap and conduction band, highlighting that\nthe use of different cerium precursors must be carefully evaluated\nto obtain a Ce–BiVO<sub>4</sub> film with a lower electron–hole\nrecombination. These achievements highlight the importance of understanding\nthe effect of a cerium precursor on nanoscale-thick Ce-doped BiVO<sub>4</sub> obtention for water-splitting applications as a photoanode.