Striking a balance between the stability and activity of metal nanoparticles (NPs) is crucial in designing efficient heterogeneous catalysts. This challenge requires supporters with highly tunable behaviour enabling metal active sites with appropriate electronic properties. Herein, we demonstrate a newly synthesized pyridine-functionalized covalent organic framework (COF) rendering Pt NPs with enhanced stability and electronic density. Periodic channels with pendant pyridine groups can efficiently stabilize Pt NPs as active sites. Local charge transfer from the COF to Pt was confirmed by experimental and theoretical methods. The increased electron density on Pt promotes the rate-limiting cleavage of the O–H band in H₂O, resulting in enhanced catalytic activity for the hydrolysis of ammonia borane (AB) for H₂ production compared to other non-pyridine-functionalized COF-based catalysts. The mechanistic insights into the local charge transfer advance the applicability of COFs for heterogeneous catalysis.