Abstract
<title>Abstract</title> <p> IrO <sub>2</sub> typically possesses a rigid bulk crystalline structure formed through necessary high-temperature oxidation processes, thus limiting oxygen evolution reaction (OER) in proton exchange membrane water electrolysis (PEMWE). We develop 2D flexible IrO <sub>2</sub> crystal by using doped Ba atoms as atomic-scale pivots to overcome the structural rigidity imposed by strong Ir-O bonds. Through driving [IrO <sub>6</sub> ] octahedral bending and rotation, the Ba-atom pivots endow the IrO <sub>2</sub> lattice with graphene-like flexibility while synergistically optimizing its surface area, active sites, electronic structure, and Ir-O bond covalency. In PEMWE, flexible IrO <sub>2</sub> crystal achieves an ultralow voltage (1.706 V at 3.0 A/cm <sup>2</sup> ), high stability (3000 h at 3 A/cm <sup>2</sup> and 4416 h under fluctuating photovoltaic input), and low hydrogen production cost (4.08 kWh/Nm <sup>3</sup> and $0.90/kg H <sub>2</sub> ), thereby surpassing the DOE targets for activity, stability, and cost. The transformation of IrO <sub>2</sub> catalyst from rigid crystal into flexible crystal represents a significant breakthrough for advancing PEMWE technology. </p>