Multifunctional Coatings from Scalable Single Source Precursor Chemistry in Tandem Photoelectrochemical Water Splitting

The straightforward and inexpensive fabrication of stabilized and activated photoelectrodes for application to tandem photoelectrochemical (PEC) water splitting is reported. Semiconductors such as Si, WO₃, and BiVO₄ can be coated with a composite layer formed upon hydrolytic decomposition of heterobimetallic single source precursors (SSPs) based on Ti and Ni, or Ti and Co in a simple single-step process under ambient conditions. The resulting 3d-transition metal oxide composite films are multifunctional, as they protect the semiconductor electrode from corrosion with an amorphous TiO₂ coating and act as bifunctional electrocatalysts for H₂ and O₂ evolution based on catalytic Ni or Co species. Thus, this approach enables the use of the same precursors for both photoelectrodes in tandem PEC water splitting, and SSP chemistry is thereby established as a highly versatile low-cost approach to protect and activate photoelectrodes. In an optimized system, SSP coating of a Si photocathode and a BiVO₄ photoanode resulted in a benchmark noble metal-free dual-photoelectrode tandem PEC cell for overall solar water splitting with an applied bias solar-to-hydrogen conversion efficiency of 0.59% and a half-life photostability of 5 h. Scalable multifunctional composite films are prepared from simple single source precursor chemistry using solely inexpensive materials and techniques. The films provide protection and the integration of bifunctional water splitting catalysts onto photoelectrodes, thus enabling the assembly of a low-cost photoelectrochemical tandem device with a benchmark performance.