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

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 cm² 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 Ni²⁺/Ni³⁺ 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.