HER and OER Activity of Ti4O7@Ti Mesh—Fundamentals Behind Environmental Application

Abstract

Titanium suboxide (TSO) catalysts offer remarkable activity toward pollutant degradation due to their stability at positive potentials, which enables the formation of reactive oxygen species. Herein, TSOs are prepared directly on the surface of Ti mesh, which also serves as the current collector. The evolution of different TSO surface species during temperature treatment is monitored using micro-Raman spectroscopy. The electrochemically active surface area is determined using cyclic voltammetry (CV) and shows a decrease from 9.3 cm² to 1.1 cm² upon increasing temperature, corresponding to the transformation of TSO as seen in micro-Raman spectroscopy. Impedance spectroscopy revealed nearly identical values (≈29 Ohm) for the charge transfer resistance during OER, indicating the presence of the same active centers on the surface. The electrode potential window toward water splitting is examined using oxygen and hydrogen evolution reactions (OER and HER). The Tafel slopes are in the range 400–600 mV dec⁻¹ for OER and 340–440 mV dec⁻¹ for HER, with higher values being desirable in pollutant degradation applications. Onset potential shifted to slightly more negative values with increasing temperature treatment, with samples treated at 850 °C and 950 °C enabling almost tenfold higher currents at the same potential values. The hydrogen evolution potential lies within the optimal region for H* radical formation around −1.2 V vs. RHE. Surface-formed TSOs represent promising biofunctional materials for pollutant degradation.