Combinatorial Synthesis and High-Throughput Characterization of Fe-V-O Thin-Film Materials Libraries for Solar Water Splitting

The search for suitable materials for solar water splitting is addressed with combinatorial material science methods. Thin film Fe-V-O materials libraries were synthesized using combinatorial reactive magnetron cosputtering and subsequent annealing in air. The design of the libraries comprises a combination of large compositional gradients (from Fe10V90Ox to Fe79V21Ox) and thickness gradients (from 140 to 425 nm). These material libraries were investigated by high-throughput characterization techniques in terms of composition, structure, optical, and photoelectrochemical properties to establish correlations between composition, thickness, crystallinity, microstructure, and photocurrent density. Results show the presence of the Fe2V4O13 phase from similar to 11 to 42 at. % Fe (toward low-Fe region) and the FeVO4 phase from similar to 37 to 79 at. % Fe (toward Fe-rich region). However, as a third phase, Fe2O3 is present throughout the compositional gradients (from low-Fe to Fe-rich region). Material compositions with increasing crystallinity of the FeVO4 phase show enhanced photocurrent densities (similar to 160 to 190 mu A/cm(2)) throughout the thickness gradients whereas compositions with the Fe2V4O13 phase show comparatively low photocurrent densities (similar to 28 mu A/cm(2)). The band gap energies of Fe-V-O films were inferred from Tauc plots. The highest photocurrent density of similar to 190 mu A/cm(2 )was obtained for films with similar to 54 to 66 at. % Fe for the FeVO4 phase with similar to 2.04 eV for the indirect and similar to 2.80 eV for the direct band gap energies.