Activating a Metallization Switch for Record Hydrogen Evolution in Single-Atom Modified Polar MOF Piezocatalysts.

Piezocatalytic hydrogen evolution enables the conversion of mechanical energy into chemical fuels, but its efficiency is constrained by a trade-off between piezoelectric polarization and electronic conductivity. Strong piezoelectric polarization is essential for sufficient driving force, yet highly polar materials typically suffer from poor conductivity, which limits bulk-to-surface charge transport. Conversely, enhancing conductivity often compromises piezoelectric performance, resulting in a bottleneck in piezocatalysis. Herein, we decouple piezoelectricity and conductivity using atomically dispersed nickel single atoms on amino-functionalized UiO-66 (Ni SAs@UiO-66-NH2). Introducing polar amino groups and asymmetric Ni─N coordination significantly enhances the piezoelectric response, increasing the piezoelectric coefficient d33 from 48 to 242 pm V-1. Simultaneously, hydrogen adsorption at Ni sites under mechanical stress triggers a pressure-induced semiconductor-to-metal transition, creating transient metallic conduction pathways that facilitate efficient electron extraction without sacrificing bulk polarization. As a result, hydrogen adsorption sites shift from framework carbons to Ni centers, yielding near-optimal H* adsorption energetics (ΔGH * approximately 0.12 eV at 100 MPa), and enabling rapid polarization-driven hydrogen evolution. Consequently, the Ni SAs@UiO-66-NH2 catalyst achieves exceptional hydrogen evolution rate of 1871 µmol g-1 h-1 in deionized water and 17 613 µmol g-1 h-1 in methanol-containing media, surpassing reported MOF-based piezocatalysts and competing with leading photo-piezocatalytic and photocatalytic systems.