Enhanced Dehydrogenation and Hydrogenation Capacity of Poly(5‐Vinyl‐1‐Indanol) at Low Temperatures

ABSTRACT

Redox‐active polymer‐based hydrogen carriers store hydrogen gas through chemical bonding. Although existing redox‐active polymers utilized as hydrogen storage units (e.g., fluorenone and fluorenol) demonstrate reversible hydrogenation in the presence of iridium complex catalysts, they are often hindered by low weight‐based hydrogen storage density and steric constraints limiting reaction efficiency. To address these limitations, 1‐indanol and 1‐indanone were investigated as promising hydrogen storage units. Initially, 1‐indanol was dehydrogenated at 25°C–50°C in the presence of an iridium complex catalyst (Ir cat.). Subsequently, 1‐indanone was completely hydrogenated at 25°C under hydrogen flow, establishing a reversible hydrogenation–dehydrogenation cycle. Polymers bearing 1‐indanol and 1‐indanone—poly(5‐vinyl‐1‐indanol) and poly(5‐vinyl‐1‐indanone), respectively—were designed as the simplest structural models and synthesized via radical polymerization. Poly(5‐vinyl‐1‐indanol) was completely dehydrogenated using Ir cat. within 1 h at 80°C, releasing hydrogen gas at relatively low temperatures of 25°C–80°C. Among existing polymer‐based hydrogen carriers, their dehydrogenation rate constantly reached the maximum value within this temperature range. While the hydrogen storage density improved from 0.97 (fluorenone polymer) to 1.2 wt% (indanone polymer), the 5 wt% target could not be achieved. This is primarily because the presence of aromatic rings increases the molecular weight per active hydrogen storage unit, placing a theoretical limit on capacity. However, as we reported earlier, a higher hydrogen storage density can be achieved by optimizing structural design, indicating scope for further improvement. With the capability of operating at low temperatures, this dehydrogenation system offers practical advantages, eliminating the need for energy‐intensive heating equipment.