Non‐Stoichiometric Molybdenum Oxides Enable Phase‐Stable Proton Storage

ABSTRACT

Aqueous proton batteries are promising alternatives to lithium‐ion batteries owing to their intrinsic safety, low cost, and fast proton transport. However, the small size, high charge density, and strong protonating ability of H ⁺ often perturb host frameworks during repeated insertion/extraction, causing phase transformations, lattice strain, and rapid capacity decay. Herein, we synthesis we report a non‐stoichiometric tunnel‐structured molybdenum oxide, Mo ₅ O ₁₄ , as a highly reversible proton‐storage electrode. The interconnected tunnel framework enables direct and reversible H ₃ O ⁺ intercalation without phase transition, pronounced structural distortion, or significant volume variation, thereby ensuring excellent structural stability and rapid ion transport. As a result, Mo ₅ O ₁₄ delivers a high capacity of 271 mAh g ⁻¹ at 1.5 A g ⁻¹ (∼5C) and retains 142.2 mAh g ⁻¹ even at 300 A g ⁻¹ (∼1000C) and sustains stable operation for over 310 000 cycles. When paired with a VHCF cathode, the full cell achieves 73.3 Wh kg ⁻¹ and maximum power density of 43.4 kW kg ⁻¹ , and over 60 000 stable cycles. Furthermore, a flexible interdigital proton micro‐cell array demonstrates rapid‐charge capability, powering a red light‐emitting diode for over 5 min after only 10 s of high‐rate charging.