Sébastien Pruvost

Thermal energy harvesting from Pb(Zn1/3Nb2/3)0.955Ti0.045O3 single crystals phase transitions

This paper describes the effect of the frequency on energy harvesting in Pb(Zn1/3Nb2/3)0.955Ti0.045O3 single crystals with an Ericsson cycle. At the lowest frequency of 0.01 Hz (which corresponds to the slope for the application of the electric field), the maximum harvested energy was equal to 86 mJ cm−3. With an increase in frequency, the harvested energy demonstrated a nonlinear decrease, and the diminution was particularly rapid at frequencies above the critical frequency of 1 Hz. The inherent mechanism of the frequency effect is discussed in detail. In the present case, the phase transitions due to domain engineering, e.g., R-O during the charge process at low temperature and O-T during the discharging process at high temperature, greatly improved the harvested energy. The study also revealed that various parameters, such as the electric field associated with the phase transition, the polarization relaxation, and polarization variations, influenced the capability of energy harvesting to a certain exte...

Energy harvesting by nonlinear capacitance variation for a relaxor ferroelectric poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer

The present letter describes the investigation of the electrostatic energy harvesting through nonlinear capacitance variation caused by changes in temperature for a poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) [P(VDF-TrFE-CFE)] terpolymer. Owing to the electric tunability of the terpolymer, the harvested energy can-using an Ericsson cycle-be simulated from permittivity under a dc electric field. When going from 25 to 0 °C, it was found, from simulation, that the harvested energy increased up to 240 mJ/cm3 when raising the electric field at 80 kV/mm. Experimental measurement was also carried out, thus confirming the feasibility of electrostatic energy harvesting through low temperature Ericsson cycle.

Probing nanomechanical properties with AFM to understand the structure and behavior of polymer blends compatibilized with ionic liquids

The PeakForce QNM AFM mode was used to investigate the nanoscale mechanical properties of poly(butylene-adipate-co-terephthalate)/poly(lactic acid) (PBAT/PLA) blends successfully compatibilized with phosphonium-based ionic liquids (ILs). This novel AFM mode allowed identification of the phase structuration and also emphasized the effect of the ionic liquids on the mechanical behavior at nanoscale of the polymer phases and interfaces. On one hand, phosphonium-chloride IL (il-Cl) was shown to play an efficient role as an interfacial agent, i.e., causing a finer dispersion of PLA nodules in the PBAT continuous matrix. On the other hand, phosphonium-phosphinate IL (il-TMP), leads to PLA dispersed as a fibril phase and located as an interphase layer between the two polymers. Adhesion force mappings confirmed that the ILs are mainly localized at the interfaces between the two polyesters. The PeakForce QNM AFM study allowed the proposal of complete models for the compatibilization mechanism, establishing relationships between the nanoscale structure and the macroscopic mechanical properties of these blends.

Direct measurement of the electrocaloric effect in poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) terpolymer films

We investigated the entropy change in poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) (P(VDF-TrFE-CTFE)) films in the temperature range between −5 ∘C and 60 ∘C by direct heat flux calorimetry using Peltier cell heat flux sensors. At the electric field E = 50 MVm−1 the isothermal entropy change attains a maximum of |Δs|=4.2 Jkg−1K−1 at 31∘C with an adiabatic temperature change ΔTad=1.1 K. At temperatures below the maximum, in the range from 25 ∘C to −5 ∘C, the entropy change |Δs| rapidly decreases and the unipolar P vs E relationship becomes hysteretic. This phenomenon is interpreted as the fact that the fluctuations of the polar segments of the polymer chain, responsible for the electrocaloric effect ECE in the polymer, becomes progressively frozen below the relaxor transition.

Doubling the electrocaloric cooling of poled ferroelectric materials by bipolar cycling

We have investigated the entropy change in the ferroelectric phase of poly(vinylidene fluoride-trifluoroethylene) 70/30 films by direct heat flux calorimetry using Peltier cell heat flux sensors. We find that by applying a negative electric field to a positively poled state, the entropy can be further increased without any significantly change of the remanent polarization or the domain structure. By cycling between positive and negative values of the electric field, the electrocaloric effect (ECE) can be then improved by a factor of 2. As an example, we measured, around the positive remanence Pr = 60 × 10−3 C m−2, a fully reversible entropy change |Δs| = 1 J kg−1K−1 for a field change from 40 × 106 to −40 × 106 V m−1 and a maximum of |Δs| = 3.2 J kg−1K−1 for an asymmetric field change from 200 × 106 to −40 × 106 V m−1. This effect can be exploited to significantly increase the range of operating temperature for ECE materials below their Curie temperature.

PeakForce QNM AFM study of chitin-silica hybrid films

Chitin-silica hybrid thin films, prepared through the colloidal self-assembly of chitin nanorods and siloxane oligomers, have been studied for the first time by PeakForce QNM AFM mode to explore their structure and mechanical behaviour. The change in structure and mechanical properties of chitin-silica hybrids is mainly driven by the relative quantities in chitin nanorods and silica, expressed as the chitin volume fraction ϕchi. The coating of the chitin polysaccharide by silica leads to an increase of the nanorods diameter and films surface roughness at small ϕchi values. The DMT (Derjaguin-Muller-Toporov) modulus increased both at small ϕchi due to a large amount of silica and at very high ϕchi→1 due to an incomplete tip penetration between nanorods. The local parallel orientation of nanorods observed at different ϕchi values resulted in a modulus increase due to an enhancement of the cohesion between nanorods.

Energy Harvesting from Temperature: Use of Pyroelectric and Electrocaloric Properties

The previous chapters were devoted to the introduction to the electrocaloric effect and an extensive presentation of different materials. The main application target is the solid-state cooling, and its practical implementation was discussed in chap. 8. In this case, the electrical energy is converted into thermal energy. But electrocaloric materials are also pyroelectric, and the thermal energy can be transformed into electrical energy using the same materials. It can be utilized for power supply of autonomous devices (also called energy harvesting), or even for energy production. In this chapter, the principles of electrical energy production from thermal sources using pyroelectric materials are presented. Linear pyroelectric properties may be utilized as a straightforward transfer from piezoelectric energy harvesting. In particular, energy harvesting figure of merit, as well as electrothermal coupling factor are presented. Then, materials properties and their optimization are discussed. Beyond linear materials, nonlinear ones exhibit the highest known electrocaloric properties. Performing thermodynamic cycles (such as Olsen / Ericsson cycles, or Stirling cycles), it is possible to obtain much larger output energies when working in the vicinity of phase transitions. Finally, the correlation between electrocaloric effect and energy harvesting ability is established. It is shown that the best materials for electrocaloric cooling are also the best candidates for energy harvesting as well. Some predictions are then shown with ultra high output energy densities and efficiencies related to Carnot cycle.