CoPi-modified mesoporous titania photoelectrodes for water splitting: why less is more

Titanium dioxide is a promising candidate for photoelectrochemical water splitting; however, its performance is limited due to the sluggish oxygen evolution reaction (OER). In this work, a hybrid nanomaterial was developed by combining ordered mesoporous TiO2 thin films with a cobalt oxo-phosphate OER catalyst (CoPi). We conducted a detailed structural and electrochemical characterization of the nanocomposite. We compared the performance of dense and mesoporous TiO2 films on different substrates as photoelectrodes for water splitting. The photoelectrodes exhibit high stability, reproducibility and cycling durability, with consistent photocurrent densities. Controlled amounts of CoPi were deposited on this matrix. Low loadings resulted in a 20% increase in photocurrent, whereas higher loadings suppressed the photocurrent. In this study, we demonstrate the importance of optimizing the co-catalyst loading based on the interaction between different components in a hybrid photoanode, with a focus on understanding the recombination pathways that appear when working with nanostructured semiconductors.