Enhanced oxygen evolution reaction by stacking single-crystalline freestanding SrRuO3

Single-crystalline transition metal oxide thin film has been employed to perceive the fundamental functions of electronic structure and charge transfer processes in water splitting processes. However, the surface area enlargement and strain tunability in a single-crystalline transition metal oxide are restricted in conventional epitaxy. In this study, we report the oxygen evolution reaction (OER) enhancement by a stack of multilayer SrRuO 3 featured single-crystallinity, flexibility, and stackability. The controllable stack of multiple cylindrical SrRuO 3 for surface enlargement in a magnitude of order and the emergent electronic structure transition, from t 2g (3↑, 1↓) to t 2g (3↑) e g (1↑), of Ru efficiently enhances the OER performance, the overpotential can be reduced by ~74 % and ~78 % in KOH and HClO 4 respectively at 5 mA/cm 2 . Our study provides an approach for fine manipulation of single-crystalline freestanding oxide morphologically, and an efficient strategy aiming at the extreme enhancement of the electrochemically active surface area and the electronic structure engineering by strain. We report the oxygen evolution reaction enhancement by a stack of multilayer SrRuO 3 (SRO) featured with single-crystallinity, flexibility, and stackability, which was achieved from the rigid heterostructure via a water-dissolution of Sr 3 Al 2 O 6 sacrifice interlayers. Benefiting from the combination of electrochemical reaction surface area enlargement and high-spin state, our freestanding SROs exhibit a dramatic improvement of OER activity. • Freestanding single-crystalline SrRuO 3 thin film is fabricated. • The high/low-spin state transition of Ru occurs in the strain engineered SrRuO 3 . • Stacking cylindrical SrRuO 3 offers a tremendous enlargement of surface area. • These approaches improve the performance of oxygen evolution reaction.