The capture of solar energy and its direct conversion into chemical energy using artificial photosystems is one of the most promising routes to satisfy the global demand of energy in a sustainable way. Among the different existing approaches, photoelectrochemistry (PEC) has attracted considerable interest in solar energy storage through the formation of chemical bonds in the form of dihydrogen molecules or carbon-based fuels. ^[1] Metal oxides are the most studied materials as photoanodes since they have a valence band with a thermodynamically favourable energy for the oxygen evolution reaction (OER). Several semiconductors have been widely studied, such as titanium dioxide (TiO₂), hematite (α-Fe₂O₃), bismuth vanadate (BiVO₄) and tungsten trioxide (WO₃) among others. ^[2]

Here, we focus our attention on Bismuth vanadate (BiVO₄), which in the last two decades has emerged as one of the most robust, efficient, and inexpensive photoanodes for water electrolysis.^[3] However, the practical conversion efficiency of BiVO₄ photoelectrodes is below the theoretical maximum photocurrent density under standard sunlight for water splitting processes (7.5 mA/cm²).^[4] This difference could be explained by the excessive hole-electron recombination, the slow charge transport and poor water oxidation kinetics.^[5] Nowadays, most of the BiVO4 reported performances/photocurrents (put example/number) have been measured in photoanodes with a exposed area of 0.2 cm², however, reproducing similar results with larger exposed areas remains a challenge. Understanding these limitations is the initial step to obtain photoanodes with competitive photocurrents.

 In the present work, different strategies to obtain efficient photoanodes based on optimization of the exposed area, hetero junction fabrication or surface co-catalyst deposition were carried out. We report here a dependence of the observed photocurrent/performance with the photoanode exposed area. In order to understand the nature of such dependency, Linear Sweep Voltammetries (LSV) and Impedance Spectroscopy (IS) with different exposed areas where studied. Therefore, to reduce the hole-electron surface recombination, different overlayers were tried such as Al₂O₃ by atomic layer deposition (ALD) and metallic surface-cocatalysts based on vanadium and iron by spin coating technique. The combination of an optimal PEC measurement area and the use of overlayers we can improve the PEC performance.