Toward enduring pyroelectric energy harvesting without external bias field

Narrow-temperature-fluctuation waste heat is abundant in data centers. Ferroelectric materials exhibit the pyroelectric effect, which enables direct conversion of thermal energy into electricity. Power-source-free pyroelectric energy conversion is a new approach that generates electricity without any external bias or battery connection. It represents a bias-field-free thermodynamic cycle that fundamentally differs from the conventional Olsen/Ericsson cycles. The device performance is governed by a figure-of-merit that considers both the pyroelectric coefficient and the latent heat across the phase transformation. Long-cycle electricity generation is achieved by continuously driven phase transformations. Recent progress has demonstrated microampere-level electricity output over more than 7000 phase-transformation cycles, showing compelling potential for practical applications. This review summarizes the fundamental mechanisms, material design strategies, device demonstrations, and future outlook of power-source-free pyroelectric conversion. We aim to provide a comprehensive understanding of this emerging method and offer useful insights for long-cycle electricity generation from waste heat in data centers.