Photoelectrodes for photoelectrochemical water splitting are extensively studied for a future renewable fuel production based on hydrogen.^1,2 The photoactive electrodes have to fulfill a number of criteria to achieve high solar-to-hydrogen conversion efficiencies: Good light absorption for photon energies down to 2.1 eV, high water splitting (half-) reaction kinetics with low overpotentials, good charge carrier transport throughout the active film and high surface area with active sites. Achieving all of these at once is non-trivial, and to date, no perfect material and/or electrode fabrication method has been found. Therefore, the best results are obtained with composite electrodes, employing a wide range of materials for each specific function.³ Among the electrodes studied are photoanodes made of LaTiO₂N (LTON) particles.^3,4 Particle based electrode fabrication is cheap, scalable and suitable for mass production. LTON particles show good light absorption behavior and low overpotential for the oxygen evolution reaction, further enhanced by CoO_x and NiO_x co-catalysts.³ The oxynitride powders are obtained in a solid-gas ammonolysis reaction, whereby an increased surface area is obtained due to a porous particle morphology.⁵ Transferring those particles onto an electrode however leads to efficiency losses due to limited charge transport at particle boundaries.^4,6 Some success has been achieved by necking individual particles with amorphous TiO₂,^4,7 establishing a short range conductivity. An efficient conductive network, however, enables short and long range charge carrier transport connecting the back contact to each individual particle. This network needs to be implemented into the film such that the catalytically active surface area and the surface accessibility is kept unchanged or is improved, while still allowing for fast and scalable processing.

In this contribution we present a composite photoanode preparation method for LTON with multi-wall carbon nanotubes as conductive network. The composite powder is obtained in a simple water-based pH-shift reaction, and the resulting agglomerates are then deposited electrophoretically to form the photoanode thin films. The films were investigated by SEM, UV/Vis, profilometry and the photoelectrochemical performance was tested. The scalability of the process is demonstrated with a 40 cm² electrode.

[1] Grätzel, M. Nature 2001, 414, 338.

[2] van de Krol, R. et al. Photoelectrochemical hydrogen production; Springer, 2011; Vol. 102.

[3] Landsmann, S. et al. ACS Appl Mater Interfaces 2016, 8, 12149.

[4] Landsmann, S. et al. ChemSusChem 2015, 8, 3451.

[5] Pokrant, S. et al. J Mater Res 2016, FirstView

[6] Feng, J. et al. Advanced Functional Materials 2014, 24, 3535.

[7] Nishimura, N. et al. Thin Solid Films 2010, 518, 5855.

The SNSF is gratefully acknowledged for funding the PrecoR project 20PC21_155667