  This paper demonstrates the significant benefits of exploiting highly aligned
porosity in piezoelectric and pyroelectric materials for improved energy
harvesting performance. Porous lead zirconate (PZT) ceramics with aligned pore
channels and varying fractions of porosity were manufactured in a water-based
suspension using freeze casting. The aligned porous PZT ceramics were
characterized in detail for both piezoelectric and pyroelectric properties and
their energy harvesting performance figures of merit were assessed parallel and
perpendicular to the freezing direction. As a result of the introduction of
porosity into the ceramic microstrucutre, high piezoelectric and pyroelectric
harvesting figures of merits were achieved for porous freeze-cast PZT compared
to dense PZT due to the reduced permittivity and volume specific heat capacity.
Experimental results were compared to parallel and series analytical models
with good agreement and the PZT with porosity aligned parallel to the freezing
direction exhibited the highest piezoelectric and pyroelectric harvesting
response; this was a result of the enhanced interconnectivity of the
ferroelectric material along the poling direction and reduced fraction of
unpoled material that leads to a higher polarization. A complete thermal energy
harvesting system, composed of an parallel-aligned PZT harvester element and an
AC/DC converter successfully demonstrated by charging a storage capacitor. The
maximum energy density generated by the 60 vol.% porous parallel-connected PZT
when subjected to thermal oscillations was 1653 {\mu}J/cm3 respectively, which
was 374% higher than that of the dense PZT with an energy density of 446
{\mu}J/cm3. The results are of benefit for the design and manufacture of high
performance porous pyroelectric and piezoelectric materials in devices for
energy harvesting and sensor applications.
