Mechanistic Insights and Scalable Fabrication of a Ni‐Based MOF Bistable Electrochromic Film Toward Energy‐Efficient Displays

ABSTRACT Bistable electrochromic materials capable of retaining their optical states without sustained electrical power are critically important for energy‐saving technologies. Unfortunately, metal‐organic frameworks (MOFs) have remained largely underexplored for such applications, primarily due to the poor stability of radical intermediates involved in the EC processes. Herein, we propose a c‐axis‐dominated Ni‐based MOF film, denoted Ni‐BPA, fabricated via electrostatic spraying deposition, demonstrating remarkable bistable electrochromism with merely 8% transmittance loss after 12 h in the air (17% after 72 h). The film features reversible switching between a highly transparent and a neutral dark‐brown state, affording a large optical modulation of 78% at 490 nm and a high coloration efficiency of 88.57 cm ² C ⁻¹ . Notably, the colored patterns remain clearly visible for over 5 h in electrolyte and more than 24 h in air after powering off. Through in situ Raman and EPR spectroscopy, we identify the Ni ²⁺ /Ni ³⁺ redox couple as the central electrochromic mechanism. Further supported by DFT calculations, we elucidate that strong adsorption of hydroxide ions (−1.5 eV) plays a key role in stabilizing the colored state. This work establishes MOFs as promising platforms for bistable electrochromism, opening new pathways toward advanced energy‐efficient electronic devices.