Physical Barricading at the Nanoscale: Protecting Pyrite from Weathering toward Efficient and Stable Electrocatalysis of the Oxygen Evolution Reaction

The unique atomic arrangement and excellent charge transfer properties of two-dimensional (2D) metal chalcogenides (MX2; M = transition metal, X = S, Se) make them effective electrocatalysts toward water splitting. But, so far, none of them have been able to replace noble-metal catalysts for the oxygen evolution reaction (OER), and it remains a great challenge to develop these catalysts. Specifically, cost-effective and earth-abundant FeS2 has shown potential, but it is less acknowledged due to the associated weathering process. Here, we report a spin-coated TiO2 layer on hydrothermally synthesized 2D-FeS2 nanoplates to control weathering through physical barricading at the nanoscale. Notably, the electrochemical and chemical weathering studies suggest that the TiO2 layer stabilized FeS2 oxidation in alkaline solution, while the latter gets oxidized without TiO2 overlayers. To the best of our knowledge, this would be the first report on an FeS2/TiO2 photoanode for efficient and stable OER without any composite or doping. It displayed improved long-term durability of OER activity. Moreover, the annealed crystalline leaky TiO2 layer (similar to 72 nm) remarkably displayed enhanced charge transfer at the FeS2/TiO2 interface. Also, Mott-Schottky measurements confirmed that the leaky TiO2 served as a protective layer (physical barrier) against the weathering of FeS2. The current study may provide new insights into the rational design of low-cost FeS2/TiO2 layered electrocatalysts for OER and renewable energy applications.