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

Why It Matters

Bistable electrochromic displays retain images without continuous power, cutting energy use for signage and wearable electronics. Demonstrating scalable MOF fabrication positions this technology for commercial, low‑power visual interfaces.

Key Takeaways

• Ni‑BPA film shows 78% optical modulation at 490 nm
• Colored state persists >5 h in electrolyte, >24 h in air
• Strong –1.5 eV OH⁻ adsorption stabilizes Ni³⁺ state
• Electrostatic spray enables scalable, uniform MOF coating
• Coloration efficiency reaches 88.57 cm² C⁻¹

Pulse Analysis

Electrochromic (EC) technologies have long promised dynamic visual displays that consume power only during state changes. Traditional EC materials, however, require continuous voltage to maintain coloration, limiting their suitability for battery‑operated or off‑grid applications. Bistable EC systems—capable of holding a visual state after power removal—address this gap, but achieving long‑term stability has been challenging, especially with organic or inorganic thin films that degrade under ambient conditions. Recent advances in metal‑organic frameworks (MOFs) suggest a pathway to combine tunable chemistry with structural robustness, opening new horizons for energy‑efficient displays.

The Ni‑BPA film leverages a c‑axis‑oriented nickel coordination network that undergoes a reversible Ni²⁺/Ni³⁺ redox transition. In‑situ Raman and electron paramagnetic resonance spectroscopy pinpoint the redox couple as the primary chromophore, while density‑functional theory calculations reveal that hydroxide ions bind to Ni sites with an adsorption energy of roughly ‑1.5 eV. This strong interaction locks the oxidized Ni³⁺ state, dramatically extending the colored‑state lifetime—over five hours in electrolyte and a full day in ambient air. Optical performance metrics are equally impressive: a 78% transmittance swing at 490 nm and a coloration efficiency of 88.57 cm² C⁻¹, rivaling commercial EC polymers but with the added benefit of bistability.

Scalability is a critical hurdle for MOF‑based devices, yet the researchers demonstrate that electrostatic spray deposition produces uniform, large‑area films compatible with roll‑to‑roll manufacturing. This method reduces material waste and aligns with existing coating infrastructure, making the technology attractive for smart windows, low‑power signage, and wearable displays. As the industry seeks greener, battery‑friendly visual solutions, the Ni‑based MOF platform offers a compelling blend of durability, efficiency, and manufacturability, likely spurring further investment in bistable EC research.