Wurtzite based materials have the advantages of being cheap, no-toxic and offering excellent opto-electrical, piezoelectric and pyroelectric properties. The nanocrystalline wurtzite ZnS, being a room temperature stable material unlike its bulk counterpart, is interesting because of its potential in piezoelectric and pyroelectric energy harvesting. In this work we aimed to tailor a simple synthesis method for nanocrystalline wurtzite production, which would be easy to scale up. We used the well-known reaction of zinc chloride with thiourea or sodium sulfide dissolved in ethyl glycol at a carefully controlled molar ratio in medium temperature conditions (140-150°C) to produce pure, nanocrystalline ZnS in the hexagonal (wurtzite) phase, via a series of consecutive experiments. The amount of solvent was kept the same (60 ml of ethyl glycol) by re-using what remained of the solvent from the previous reaction and topping up the quantity lost. The productivity yield increased over 6 successive reactions from 156 mg to 446 mg per batch at a constant mMZn/mMS = 1 ratio. The obtained nanopowder has been characterized using TG, BET, FTIR, TEM and SEM techniques. Our plan is to build an in-house pilot plant that should produce substantial amounts of wurtzite ZnS nano-powder in an environmentally friendly and cost effective way. Acknowledgement: This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 797951.
Pyroelectric materials can harvest energy from naturally occurring ambient temperature change, as well as from artificial temperature change, notably from industrial activity. At a time of climate emergency, pyroelectric energy harvesting is a highly promising technology that should ultimately lead to the development of autonomous and self-powered electronic devices and which has the potential to harvest enormous amount of wasted heat. One interesting but rarely studied class of pyroelectric materials are non-ferroelectric pyroelectrics; these include semiconductor materials with a wurtzite crystalline structure such as CdS, ZnO or ZnS. We studied ZnS, and explored a simple, co-precipitation synthesis for nanocrystalline wurtzite ZnS production. The structural, morphological and dielectric properties of two selected samples were investigated to examine the effects of different molar concentrations of precursor Zn and S ions (mMZn/mMS = 0.47 and 1.22) in the reactive solution. Alongside these results, we present our recently built in-house semi-pilot plant that is able to produce substantial amounts of wurtzite ZnS nanopowder in an environmentally friendly and cost effective way. The obtained ZnS nanopowder is intended both as a precursor for pyroelectric ceramics and as a filler for ferroelectric polymer-based composite thin films (PVDF co-polymers). Acknowledgement: This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 797951. This project was also partially supported by the Piano triennale di realizzazione 2019-2021 della ricerca di sistema elettrico nazionale – Progetto 1.3 Materiali di frontiera per usi energetici (C.U.P. code: I34I19005780001). ; This project was also partially supported by the Piano triennale di realizzazione 2019-2021 della ricerca di sistema elettrico nazionale – Progetto 1.3 Materiali di frontiera per usi energetici (C.U.P. code: I34I19005780001).
At a time of climate emergency and the scarcity of fossil fuels, pyroelectric energy harvesting could be the right methodology to rescue some of the enormous quantities of energy wasted as heat. This technology is able to convert thermal fluctuation into electrical energy by using a pyroelectric device that generates voltage when cyclically heated or cooled down [1]. Here we report on the pyroelectric output registered for a wurtzite phase ZnS ceramic. We created a simple device (a "pyro-cell"): the ceramic sample which has evaporated Au electrodes on both sides is mounted on a Cu-metalized rectangular insulating base (vetronite) using either silver paint or conductive epoxy glue; the electrical connection is provided by tiny Cu wires that are welded to the sample and the vetronite base using tin alloy. This device is stable from room temperature up to approximately 180°C. Two different heating and cooling testing set-ups were used to heat and cool the ZnS sample: Set-up n°1 used an industrial scale laser, providing a fast temperature change, and Set-up n°2 had a standard lab hot plate heating element, providing a much slower temperature change. Acknowledgements: This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 797951.
Pyrolectric materials are able to harvest energy both from naturally and artificially occurring temperature changes. These materials could be the right way to recover some of the enormous amount of energy wasted as heat and help to develop new devices for harvesting thermal ambient energy. In this work it was investigated the development of bulk, dense pyroelectric ceramics, ideally with a highly developed texture and small grain size, using a micron-sized powder of the ZnS wurtzite phase as precursor material. The Two-Step Sintering (TSS) process is a useful method to obtain high sintered density and to limit the grain growth associated with the final stage of the sintering process. One of the main advantages of this method is the lowering of the sintering temperature. The microstructural, morphological and electrical properties of TSS-ZnS were determined and compared to ZnS produced by the conventional sintering process, performed at 1250°C. TSS-ZnS showed comparable density and a finer microstructure than conventional ZnS (five times lower grain size). It was demonstrated that the TSS process is a pressureless, simple and cost‐effective sintering method to obtain high density materials with controlled grain growth, without using a dopant or binder. The TSS produced ZnS ceramic was tested for pyroelectric energy harvesting. It is expected that the efficiency of the ceramic in harvested energy could be further improved by decreasing the grain size down to the nanoscale. Acknowledgement: This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 797951.
Metal hydrides are known as a potential efficient, low-risk option for high-density hydrogen storage since the late 1970s. In this paper, the present status and the future perspectives of the use of metal hydrides for hydrogen storage are discussed. Since the early 1990s, interstitial metal hydrides are known as base materials for Ni – metal hydride rechargeable batteries. For hydrogen storage, metal hydride systems have been developed in the 2010s [1] for use in emergency or backup power units, i. e. for stationary applications. With the development and completion of the first submarines of the U212 A series by HDW (now Thyssen Krupp Marine Systems) in 2003 and its export class U214 in 2004, the use of metal hydrides for hydrogen storage in mobile applications has been established, with new application fields coming into focus. In the last decades, a huge number of new intermetallic and partially covalent hydrogen absorbing compounds has been identified and partly more, partly less extensively characterized. In addition, based on the thermodynamic properties of metal hydrides, this class of materials gives the opportunity to develop a new hydrogen compression technology. They allow the direct conversion from thermal energy into the compression of hydrogen gas without the need of any moving parts. Such compressors have been developed and are nowadays commercially available for pressures up to 200 bar. Metal hydride based compressors for higher pressures are under development. Moreover, storage systems consisting of the combination of metal hydrides and high-pressure vessels have been proposed as a realistic solution for on-board hydrogen storage on fuel cell vehicles. In the frame of the "Hydrogen Storage Systems for Mobile and Stationary Applications" Group in the International Energy Agency (IEA) Hydrogen Task 32 "Hydrogen-based energy storage" different compounds have been and will be scaled-up in the near future and tested in the range of 500 g to several hundred kg for use in hydrogen storage applications ; The research for the lab-scale compressor is part of the activities of SCCER HaE, which is financially supported by Innosuisse - Swiss Innovation Agency . The authors thank the Alexander von Humboldt Foundation in the frame of the post-doctoral fellowship of Dr. J. Puszkiel (No. 1187279 STP ) as well as the European Union for their funding of projects STORHY (contract Nr. SES6-CT-2004-502667 , FP6-2002-Energy-1, 6.1.3.2.2), NESSHY (contract Nr. 518271 , FP6-2004-Energy-3, 6.1.3.2.2) and the EU Horizon 2020 /RISE project HYDRIDE4MOBILITY. Financial support from the S02 and KP8 S05), the European Union's Seventh Framework Programme ( FP7/2007e2013 ) for the Fuel Cells and Hydrogen Joint Technology Initiative under grant agreement no. 256653 (SSH2S), from the European Fuel Cells and Hydrogen Joint Undertaking in the framework of BOR4STORE (Grant agreement no. 303428 ), from the Australian Research Council for grants LP120101848 , LP150100730 , and LE0989180 , The Innovation Fund Denmark (project HyFill-Fast), DST within Hydrogen South Africa/HySA programme (projects KP3 National Research Foundation/NRF of South Africa , incentive funding grant number 109092 and the Research Council of Norway (project 285147 ) is thankfully acknowledged
