Alkali metal cation effects on hydrogen uptake and binding in metal-organic frameworks

A 2-fold interwoven metal-organic framework has been chemically reduced and doped with Li⁺, Na⁺, and K⁺. At low pressures and temperatures, the reduced and doped materials exhibit enhanced H₂ uptake-up to 65% higher than for the neutral framework. Notably, at similar doping levels, H₂ binding is strongest with Li⁺ and decreases as Li⁺ > Na⁺ > K⁺. However, the uptake increases in the opposite order. We attribute the behavior to structural changes accompanying framework reduction.