Enhancement of the Solar Water Splitting Efficiency Mediated by Surface Segregation in Ti-doped Hematite Nanorods

TL;DR

This study demonstrates a simple, cost-effective surface engineering method involving Ti segregation and surface oxidation to significantly enhance the photoelectrochemical performance of Ti-doped hematite nanorods for solar water splitting.

Contribution

The paper introduces a novel, scalable surface treatment technique that improves hematite photoanodes by inducing Ti segregation and surface states, verified through advanced spectromicroscopy and DFT calculations.

Findings

Over 200% increase in photocurrent with N2 annealing

Surface Ti segregation forms pseudo-brookite clusters

Enhanced charge carrier density improves PEC activity

Abstract

Band engineering is employed thoroughly and targets technologically scalable photoanodes for solar water splitting applications. Complex and costly recipes are necessary, often for average performances. Here we report simple photoanode growth and thermal annealing, with effective band engineering results. By comparing Ti-doped hematite photoanodes annealed under Nitrogen to photoanodes annealed in air, we found strongly enhanced photocurrent, of more than 200 % in the first case. Using electrochemical impedance spectroscopy and synchrotron X-rays spectromicroscopies we demonstrate that oxidized surface states and increased density of charge carriers are responsible for the enhanced photoelectrochemical activity. Surface states are found to be related to the formation of pseudo-brookite clusters by surface Ti segregation. Spectro-ptychography is used for the first time at Ti L3 absorption edge to isolate Ti chemical coordination arising from pseudo-brookite clusters contribution. Correlated with electron microscopy investigation and Density Functional Theory (DFT) calculations, the synchrotron spectromicroscopy data prove unambiguously the origin of the better photoelectrochemical activity of N2- annealed Ti-doped hematite nanorods. Finally, we present here a handy and cheap surface engineering method, beyond the known oxygen vacancy doping, allowing a net gain in the photoelectrochemical activity for the hematite-based photoanodes.