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ZnS Wurtzite Nanotextured Ceramic Materials for Pyroelectric Energy Harvesting

Periodic Reporting for period 1 - NanoPyroMat (ZnS Wurtzite Nanotextured Ceramic Materials for Pyroelectric Energy Harvesting)

Reporting period: 2018-09-01 to 2020-08-31

The topic of this research was pyroelectric materials, and in particular the hexagonal, wurtzite phase of zinc sulfide, which is among the structurally simplest of pyroelectric materials. The NanoPyroMat project examined the development of wurtzite-based ZnS ceramics and explored the pyroelectric potential of this cost-effective and lead-free material for potential use as an ambient energy harvesting material.
One key property of all pyroelectric materials is that they exhibit temperature dependent spontaneous polarisation and can generate power from temperature fluctuations. This means they have the potential to “harvest” energy and produce electricity based on either naturally or artificially occurring temperature changes, such as changes in ambient temperature, or in industrial settings. Practically, they represent a potential route to technologies that can convert thermal fluctuation into electrical energy by using a pyroelectric device that generates voltage when cyclically heated up or cooled down.

At a time of climate emergency and the scarcity of fossil fuels, pyroelectric energy harvesting could be the right, “green” methodology to rescue some of the enormous quantities of energy wasted as heat. In the United States, more than 50% of the energy generated is lost in this way each year; in Europe, on the other hand, more heat is wasted annually than is needed to heat all of the buildings in the EU. Looking at this from the perspective of pyroelectric materials, all this lost heat represents a potential abundant and omnipresent source of free energy, which is currently being lost from the energy cycle. Enhancing energy efficiency solutions would help citizens both in economic (lower electricity bills) and ecological (clean, green energy) terms.

The first objective of the project was to tailor a simple synthesis method for nanocrystalline wurtzite ZnS (w-ZnS) production, which would be easy to scale-up and produce abundant precursor material for production of w-ZnS ceramics. This was successfully realized with modified co-precipitation synthesis. The second objective was to fabricate w-ZnS dense ceramics while suppressing the grain growth at the same time. Finally, the third objective was to completely characterize both the precursor material and the ceramics and provide useful feedback to optimize their fabrication conditions. The pyroelectric potential of the resultant ceramics was investigated through the creation of a small device, a so called “pyro-cell”.

A secondary goal of this project was to enable the professional development of the researcher, with special attention paid to the continuous development of their transferable skills and competences, in particular leadership, communication and networking.
The main results can be summarized as follows:
1) A co-precipitation synthesis procedure for w-ZnS nanopowder production has been established Following the lab tests, an in-house semi-pilot plant was built, able to produce substantial amounts of wurtzite ZnS nanopowder in an environmentally friendly and cost-effective way; A successful procedure for recycling of the solvent was introduced, enabling a greener, “circular approach” and the productivity yield increase of 3.5 times.
2) The inherent properties of ZnS ceramics produced with pleasureless Two Step Sintering method that could be used as qualitative indicators for pyroelectric productivity were determined thus simplifying the analysis of the results (pre-screening and pre-selection of the ceramic samples).
3) Two different heating and cooling testing set-ups were established. To probe the pyroelectric output for a w-ZnS ceramic a simple device (a “pyro-cell”), stable from room temperature up to approximately 180°C, was created.

The results obtained in the NanoPyroMat were reported in: 1) one publication in an Open Access journal, 2) one Conference Proceeding, 3) five poster presentations at scientific conferences, 4) three seminars at the host institution, 5) one seminar for industry representatives, 6) one invited lecture given by the researcher at La Sapienza University of Rome and 7) via social media activities (Twitter, LinkedIn and Facebook) undertaken by the researcher for further dissemination. One publication is in preparation, and several others are planned over the next 2 years.

Over the course of the project, the researcher communicated the action activities, and promoted new ways of harvesting clean and renewable energy to the general public, in particular the younger generation (for example to students at La Sapienza University and young researchers in Montenegro), policy-makers (Dr Mark Kozdras, co-lead of Mission Innovation, Innovation Challenge 6: Clean Energy Materials and the Montenegrin Ministry of Science), industry ( the Italian companies SOL S.p.A and Technores Srl) and fellow scientists (via the NanoInnovation Conference and Exhibition). In addition, the researcher used every opportunity to act as a Marie Curie Ambassador and promote the MSCA and in particular the MSCA IF programme, and the Marie Curie Alumni Association (MCAA) where the researcher is the founding Chair of the Western Balkans Chapter; the researcher is involved in running the Chapter’s portal and Twitter account @MCAA_WB. The researcher published 5 popular articles (with 1 further submitted for publication) on online platforms, in international journals and in a national newspaper in Montenegro; she had 2 appearances on Montenegrin national TV, and participated 3 times in the European Researchers’ Night (2018 in Italy, and 2020 in Italy and in Montenegro). The researcher promotes gender equality in the scientific setting, and argued that scientists have a duty to be an active and engaged part of society. The undertaken communication activities exceeded the planned ones by many times both in terms of the number of activities and the number of people reached.
To the best of our knowledge, this is the first time that a wurtzite ZnS ceramic has been prepared using the Two-Step-Sintering method without any additive or binder. This is important, as ZnS ceramics are known to be very difficult to sinter conventionally without additives. This ceramic was used to create a simple “pyro-cell” and using two different heating and cooling testing set-ups, it was confirmed that the studied ceramic material can operate at higher temperature that are good match with the working temperature of power plants and cars (mostly lower that 200 °C). This is a key insight, showing the potential of the material in practical, real world applications ie. the creation of future prototypes of pyroelectric generators.
More generally, pyroelectric energy harvesting has the ability to transform wasted heat into useful energy and as such has a potential to create “green” energy from omnipotent and freely available sources such as ambient temperature changes, and contribute to the fight against climate change. Current pyroelectrics applications are limited to low-power electronics, portable systems or tasks needing only very low range of power (μW–mW). Developing further this highly promising technology should ultimately lead to the creation of more powerful, autonomous and self-powered electronic devices that could one day replace millions of batteries used in everyday life, recycling currently “lost” energy to power electronic devices in both domestic and industrial settings.