Synthesis of Large‐Area 2D Prussian Blue as Ion‐Transport Channels for Non‐Volatile Memristors

2D Prussian blue and its analogues hold great promise for applications in catalysis, energy conversion, sensing, and memory devices, thanks to their open frameworks, surface activity, and directional ion transport. However, synthesizing high-quality and large-area 2D films remains a major challenge. Here, we present a robust and scalable liquid-liquid interfacial synthesis that enables the formation of continuous, 2D flakes of Prussian blue (Fe³⁺[Fe²⁺(CN)₆]_0.75) with tunable thicknesses from ∼2 nm to several hundred nanometers. The controlled reduction of [Fe³⁺(CN)₆]^3- to [Fe²⁺(CN)₆]^4- enables slow, directed growth of 2D-FeFe layers. Unlike films formed from nanoparticles, this method yields high-quality flakes suitable for integration into devices. As a demonstration, we incorporated these films into Ag filament-based electrochemical metallization memristors. The 2D-FeFe devices ≥50 nm thick exhibited reliable bipolar electrical switching, with high Roff/on ratios (∼10⁶), >6 h retention, and stability over 150 cycles. Strikingly, switching was observed across 1.5 µm lateral gaps, far exceeding conventional silver filament formation distances, highlighting the superior ion transport and structural integrity of these 2D frameworks. This scalable approach to 2D Prussian blue, which has the potential to be extended to other related coordination polymers, offers exciting opportunities beyond memristors, enabling integration into technologies where thin-film compatibility, directional ion transport, and high surface activity are critical, such as catalysis, energy storage, and neuromorphic computing.