Tailoring oxygen vacancies of W-doped TiO2 to stabilize Ir for boosting oxygen evolution activity in proton-exchange membrane water electrolysis

초록

To commercialize proton-exchange membrane water electrolysis, the overpotential of the oxygen evolution reaction, which is a key bottleneck, must be reduced while minimizing the use of expensive precious metal Ir. However, reducing the amount of Ir results in significantly fewer active sites, rapid catalyst degradation, and uneven electron flow, thereby significantly decreasing the performance and stability of the proton exchange membrane water electrolysis (PEMWE) system. In this study, W-doped TiO2 supports were fabricated to address these issues by using a polyol reduction method to deposit Ir. When subjected to a reduction atmosphere heat treatment, the W-doped supports exhibited an increased specific surface area owing to the reduced grain size, enabling Ir to be uniformly deposited in small sizes (similar to 2 nm). The increased number of oxygen vacancies promotes n-type semiconductor characteristics with electron-rich properties in the TiO2 lattice. When Ir metal is deposited on the support, Fermi level alignment occurs, facilitating electron transfer from the support to Ir and enhancing both the inherent activity and durability of the Ir catalyst. Notably, the Ir/WTO-10 catalyst demonstrated excellent performance in full-cell electrochemical tests, achieving a current density of 3.13 A cm(-2) at 2 V and a stability of 0.37 mV h(-1) over 150 h at 1 A cm(-2). Furthermore, Gibbs free energy calculations confirmed that the Ir-4/W1Ti17O35 structure has a lower rate-determining-step energy (1.58 eV) than the Ir-4 structure.

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