Precision decoupling nucleation and growth kinetics remains a grand challenge to enable high-performance MOFs for efficient hydrogen storage. Herein, by using a decelerating nucleation kinetics (denuk) strategy (knucleation/kgrowth = 0.0002), a fully-coordinated acetic acid-tethered MOF-808 (MOF-808-0.5AA-mm) is synthesized with a volumetric hydrogen storage capacity of 50 g L−1 under 77 K and 100 bar, retaining 100% hydrogen uptake after 2000 cycles. In situ neutron powder diffraction (NPD), grand canonical Monte Carlo (GCMC) simulation, and density functional theory (DFT) calculation results collectively suggest that hydrogen initially occupies the small tetrahedral cage (site I) and gradually fills both small (site I) and large adamantane cages (site II) as pressure increases. A 100g-H2-scale MOF-based solid-state hydrogen storage system integrated with a 200-W fuel cell demonstrates ultrafast H2 adsorption and release kinetics, maintaining 100% capacity after 100 cycles. Techno-economic analysis (TEA) results suggest MOF-808-0.5AA-mm can achieve a 45% lower levelized cost of hydrogen storage (2.34 $ kgH2−1) than liquid hydrogen (4.3 $ kgH2−1), approaching the compressed gas (0.9–1.2 $ kgH2−1) under identical conditions. The work thus prospects a new crystallization control paradigm to achieve high-capacity, mechanically robust, long-duration, and cost-effective MOF adsorbents for speed-demanding and space-limiting hydrogen storage applications.