Carbon containing conductive networks in composite particle-based photoanodes for solar water splitting
Composite materials are formed between carbon nanotubes or graphene oxide and photocatalytically active LaTiO2N particles by a scalable solution-based method. Structural analysis by SEM, UV/Vis and profilometry reveals that long carbon nanotubes are able to form large agglomerates with LaTiO2N. These agglomerates result in photoelectrodes with a rough, open structure and freely accessible LaTiO2N surface. Graphene oxide, however, forms smaller agglomerates and, in consequence, smoother electrode surfaces. In addition, it covers the LaTiO2N surface already at low C content (>0.05 wt%). Graphene oxide does not improve the photoelectrochemical performance significantly. Carbon nanotubes, however, build a conductive network throughout the electrode film resulting in nearly identical performances under front and back side illumination. While electrodes prepared without carbon material exhibit a drop in performance for thicker films, carbon nanotubes composite films see an increase with a best in class performance for co-catalyst free electrodes of nearly 400 μA cm−2 at 1.23 V vs. RHE at 10.7 μm thickness. The addition of co-catalysts improves the performance further to 2.1 mA cm−2. These results demonstrate that limitations in the photoelectrochemical performance of particle-based photoelectrodes induced by high charge transfer resistance can be overcome by composite formation with carbon nanotubes, opening up a route towards cheap and scalable fabrication of efficient photoelectrodes.