Piezoelectric sensors and energy harvesters have received considerable

interest due to their self-powered capability and potential applications in

various electronic devices. However, it is still a challenge to fabricate stretchable

piezoelectric devices because piezoelectrics mainly consists of stiff

crystalline structures. Here, extremely stretchable and tough piezoelectric

gels are reported, which are prepared simply by swelling poly(ethylene glycol)

(PEG)-based poly(urethane-urea) (PUU) gels with aqueous solution of molecular

ferroelectrics. The hydrogen interactions between the PEG segments

in the gels and the molecular ferroelectrics (dabcoHReO4, DH) enable well

dispersion and crystallization of DH in the PEG segments. The resulted PUU/

DH composite piezoelectric gels exhibit unique tensile mechanical properties,

including superior strain (>1000%), high breaking strength (>10 MPa),

modulus (>2 MPa), and toughness (>57 MJ cm?3). The extremely stretchable

and tough piezoelectric gels show excellent piezoelectric properties (d33 ≈

62 pC N?1 for films with a 10 wt% of DH and light transparency (>90%), and

can quantitatively detect different mechanical deformations. Additionally,

the energy generators can harvest mechanical energy with a power density

of 1.7 μW cm?2. This work is expected to motivate new design principles for

fabricating piezoelectric materials with excellent mechanical and piezoelectric

properties for various applications.