Enhanced electron collection in a particulate LaTiO2N photoanode assembled with an inserted ZnO nanorod array for photoelectrochemical water oxidation

Abstract

The collection of photogenerated electrons is an essential part of the photoelectrochemical process on a semiconductor photoanode, which is often a bottleneck in a particulate photoanode. Herein, by ingeniously inserting a transparent electron-conducting ZnO nanorod array into a particulate LaTiO₂N photoanode, bridges for electron transport are constructed between the nanoporous micron oxynitride particles and the AZO substrate, which improves the photocurrent from tens of μA cm⁻² to 2.87 mA cm⁻² at 1.23 V_RHE. Furthermore, the electron transport in LaTiO₂N particles is improved by increasing the electron carrier density of LaTiO₂N micron particles. After a simple annealing treatment in an inert atmosphere at 713 °C, the electron carrier density of LaTiO₂N micron particles is increased significantly as shown by EPR spectroscopy and Mott–Schottky analysis. The bulk resistance of an assembled particulate LaTiO₂N photoanode is reduced with the increase of electron carrier density as shown by electrochemical impedance spectroscopy. The apparent charge separation efficiency on the photoanode assembled from annealed LaTiO₂N micron particles is 1.6 times that assembled from as-prepared LaTiO₂N micron particles, and the photocurrent for water oxidation is increased by 62%, reaching 4.66 mA cm⁻². By improving electron collection, the conductive array insertion strategy together with particle carrier density optimization provides a method to increase the photocurrent by 2 orders of magnitude reaching the mA cm⁻² level on a photoanode prepared from visible-light photocatalyst powder.