Pyro-electro-catalytic Disinfection using the Pyroelectric Effect in Low Curie Temperature, Lead-Free Ferroelectric Ceramics

BST particles were synthesised and used to produce a variety of materials structures, including finely ground powders (1-2µm), porous structures and dense materials, which were full characterised using physical and ferroelectric characterisation techniques. The BST materials were used in pyro-electro-catalytic decontamination of water experiments. The results were very promising, showing a significant 3-log reduction in viable bacterial cell counts (in CFU/ml), which is above the accepted 1-2 log reduction using conventional water treatment processes. Further experiments were carried out with the pyroelectric BST powders and porous structures, using other bacteria strains and indicators commonly found in contaminated water

Pyro-electro-catalytic disinfection using the pyroelectric effect of low Curie temperature, lead-free ferroelectric ceramics

In recent years there has been an increasing interest in pyroelectric materials for energy harvesting applications, as they have the potential to convert temperature fluctuations into electrical energy. This work investigates using low Curie temperature (Tc), lead-free, ferroelectric ceramics for pyroelectric-electrochemical catalytic reactions, such as water splitting, dye degradation and disinfection of water.<br/

Thermal energy harvesting using pyroelectric-electrochemical coupling in ferroelectric materials

Recently, the coupling of ferroelectrics with electrochemical reactions has attracted increasing interest for harvesting waste heat. The change of polarisation of a ferroelectric with temperature can be used to influence chemical reactions, especially when the material is cycled near its Curie temperature. In this perspective, we introduce the principle of pyroelectric controlled electrochemical processes by harvesting waste heat energy and explore their potential electrochemical applications, such as water treatment, air purificiation and hydrogen generation. As an emerging approach for driving electrochemical reactions, the presence of thermal fluctuations and/or transient waste heat in the environment has the potential to be the primary thermal input for driving the change in polarisation of a pyroelectric to release charge for such reactions. There are a number of avenues to explore and we summarize strategies for forming multi-functional or hybrid materials and future directions such as selecting pyroelectrics with low Curie temperature (< 100 {\deg}C), improved heat conductivity, enhanced surface area or porosity, tailored microstructures and systems capable of operating over a broader temperature range

Pyro-electrolytic water splitting for hydrogen generation

Water splitting by thermal cycling of a pyroelectric element that acts as an external charge source offers an alternative method to produce hydrogen from transient low-grade waste heat or natural temperature changes. In contrast to conventional energy harvesting, where the optimised load resistance is used to maximise the combination of current and voltage, for water splitting applications there is a need to optimise the system to achieve a sufficiently high potential difference for water electrolysis, whilst also maintaining a high current output. For the thermal harvesting system examined here, a high impedance 0.5 M KOH electrolyte with working electrodes connected to a rectified pyroelectric harvester produced the highest voltage of 2.34 V, which was sufficient for H2 generation. In addition to electrolyte concentration, the frequency of the temperature oscillations was examined and reducing the heating-cooling frequency led to a larger change in temperature to generate increased pyroelectric charge and a higher potential difference for pyro-water splitting. Finally, in the absence of sacrificial reagents, cyclic production of H2 (0.654 μmol/h) was demonstrated for the optimised processing parameters of electrolyte and thermal cycling frequency using the external pyroelectric element as a charge source for water splitting

Pyro-electrolytic water splitting for hydrogen generation

Water splitting by thermal cycling of a pyroelectric element that acts as an external charge source offers an alternative method to produce hydrogen from transient low-grade waste heat or natural temperature changes. In contrast to conventional energy harvesting, where the optimised load resistance is used to maximise the combination of current and voltage, for water splitting applications there is a need to optimise the system to achieve a sufficiently high potential difference for water electrolysis, whilst also maintaining a high current output. For the thermal harvesting system examined here, a high impedance 0.5 M KOH electrolyte with working electrodes connected to a rectified pyroelectric harvester produced the highest voltage of 2.34 V, which was sufficient for H2 generation. In addition to electrolyte concentration, the frequency of the temperature oscillations was examined and reducing the heating-cooling frequency led to a larger change in temperature to generate increased pyroelectric charge and a higher potential difference for pyro-water splitting. Finally, in the absence of sacrificial reagents, cyclic production of H2 (0.654 μmol/h) was demonstrated for the optimised processing parameters of electrolyte and thermal cycling frequency using the external pyroelectric element as a charge source for water splitting

Piezoelectric catalysis for efficient reduction of CO₂ using lead-free ferroelectric particulates

The increase in global energy demand, together with a rise in carbon dioxide (CO2) levels have encouraged research into the reduction of CO2 into useful chemicals and fuels. In this paper, we demonstrate the piezo-catalytic reduction of CO2 using lead-free lithium-doped potassium sodium niobate (KNN) ferroelectric ceramic particulates. The application of acoustic waves generated by ultrasound to a suspension of the ceramics particles creates pressure waves result in a large change in the spontaneous polarisation of the KNN particles via the piezoelectric effect, which in turn creates surfaces charges for CO2 reduction. The effect of CO2 gas concentration, the presence of dissolved species, and catalyst loading on piezo-catalytic performance are explored. By optimization of the piezo-catalytic effect, a promising piezo-catalytic CO2 reduction rate of 438 μmol g−1 h−1 is achieved, which is much larger than the those obtained from pyro-catalytic effects. This efficient and polarisation tuneable piezo-catalytic route has potential to promote the development of CO2 reduction via the utilisation of vibrational energy for environmental benefit.</p

Piezoelectric catalysis for efficient reduction of CO₂ using lead-free ferroelectric particulates

The increase in global energy demand, together with a rise in carbon dioxide (CO2) levels have encouraged research into the reduction of CO2 into useful chemicals and fuels. In this paper, we demonstrate the piezo-catalytic reduction of CO2 using lead-free lithium-doped potassium sodium niobate (KNN) ferroelectric ceramic particulates. The application of acoustic waves generated by ultrasound to a suspension of the ceramics particles creates pressure waves result in a large change in the spontaneous polarisation of the KNN particles via the piezoelectric effect, which in turn creates surfaces charges for CO2 reduction. The effect of CO2 gas concentration, the presence of dissolved species, and catalyst loading on piezo-catalytic performance are explored. By optimization of the piezo-catalytic effect, a promising piezo-catalytic CO2 reduction rate of 438 μmol g−1 h−1 is achieved, which is much larger than the those obtained from pyro-catalytic effects. This efficient and polarisation tuneable piezo-catalytic route has potential to promote the development of CO2 reduction via the utilisation of vibrational energy for environmental benefit.</p

Hierarchically structured lead-free barium strontium titanate for low-grade thermal energy harvesting

Low-grade heat conversion is one of the most promising strategies to realise carbon-neutral electricity production. Here we present a study on a hierarchically structured porous pyroelectric barium strontium titanate (BST) ceramic with a low Curie temperature and improved thermal energy harvesting performance. The aligned porous structure is beneficial to achieve a greatly reduced permittivity and heat capacity, combined with a high degree of polarisation to maintain a high pyroelectric coefficient. These characteristics contributed to significantly improved sensing and harvesting pyroelectric figures-of-merit, where the thermal energy harvesting figure-of-merit (F E ′) increased by 510% when the porosity reached to 54 vol%, compared to that of the dense BST ceramic. After rectification of the AC pyroelectric current to a DC current, the electric output was stored on a 1 μF capacitor whose voltage after 20 s increased with increasing volume fraction of porosity; namely 5.8 V (dense, 3 vol% porosity), 6.9 V (30 vol%), 7.5 V (43 vol%) and 9.2 V (54 vol%). A maximum energy density of 4.26 μJ/mm 3 was obtained from the BST with 54 vol% porosity, which was 1.6 times higher than that of the dense counterpart (2.71 μJ/mm 3). This aligned porous structure therefore represents a new and promising architecture for facile harvesting and conversion of low-grade waste heat into electrical power.</p