Changyeon Baek

A flexible energy harvester based on a lead-free and piezoelectric BCTZ nanoparticle–polymer composite

Lead-free piezoelectric 0.5(Ba0.7Ca0.3)TiO3-0.5Ba(Zr0.2Ti0.8)O3 (BCTZ) nanoparticles (NPs) composed of earth-abundant elements were adopted for use in a flexible composite-based piezoelectric energy harvester (PEH) that can convert mechanical deformation into electrical energy. The solid-state synthesized BCTZ NPs and silver nanowires (Ag NWs) chosen to reduce the toxicity of the filler materials were blended with a polydimethylsiloxane (PDMS) matrix to produce a piezoelectric nanocomposite (p-NC). The naturally flexible polymer-based p-NC layers were sandwiched between two conductive polyethylene terephthalate plastic substrates to achieve a flexible energy harvester. The BCTZ NP-based PEH effectively generated an output voltage peak of ∼15 V and a current signal of ∼0.8 μA without time-dependent degradation. This output was adequate to operate a liquid crystal display (LCD) and to turn on six blue light emitting diodes (LEDs).

Piezoelectric energy harvesting from a PMN–PT single nanowire

Flexible piezoelectric generators constructed using one-dimensional nanostructures are well known for their efficient energy harvesting. Herein, we have fabricated a flexible piezoelectric energy harvester (PEH) consisting of a single 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 nanowire (PMN–PT NW) using a facile transferring approach onto a Au electrode-patterned plastic substrate. The well-developed device effectively harvested the maximum output signals (9 mV and 1.5 nA) originating from a single PMN–PT nanowire under mechanical bending/unbending motions. The designed PEH is also expected to be utilized as a versatile tool to evaluate the performance of a one-dimensional nanostructure.

Lead‐Free Perovskite Nanowire‐Employed Piezopolymer for Highly Efficient Flexible Nanocomposite Energy Harvester

In the past two decades, mechanical energy harvesting technologies have been developed in various ways to support or power small-scale electronics. Nevertheless, the strategy for enhancing current and charge performance of flexible piezoelectric energy harvesters using a simple and cost-effective process is still a challenging issue. Herein, a 1D-3D (1-3) fully piezoelectric nanocomposite is developed using perovskite BaTiO3 (BT) nanowire (NW)-employed poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) for a high-performance hybrid nanocomposite generator (hNCG) device. The harvested output of the flexible hNCG reaches up to ≈14 V and ≈4 µA, which is higher than the current levels of even previous piezoceramic film-based flexible energy harvesters. Finite element analysis method simulations study that the outstanding performance of hNCG devices attributes to not only the piezoelectric synergy of well-controlled BT NWs and within P(VDF-TrFE) matrix, but also the effective stress transferability of piezopolymer. As a proof of concept, the flexible hNCG is directly attached to a hand to scavenge energy using a human motion in various biomechanical frequencies for self-powered wearable patch device applications. This research can pave the way for a new approach to high-performance wearable and biocompatible self-sufficient electronics.

Facile hydrothermal synthesis of BaZrxTi1−xO3 nanoparticles and their application to a lead-free nanocomposite generator

A facile form of hydrothermal synthesis was utilized to obtain BaZrxTi1−xO3 (BZT) nanoparticles (NPs) with a wide range of Zr concentrations. The amorphous B-site precursor prepared by the hydrolysis of alkoxide using an ammonia solution, efficiently promotes the reaction with the A-site precursor solution. Subsequently, the BZT NPs were adopted for a flexible piezoelectric energy harvester (PEH) by employing a simple, low-cost, and scalable spin-casting method. The output performance achieved by the fabricated flexible PEH depends on the Zr/Ti ratio inside a piezoelectric nanocomposite. The BZT NP-embedded PEH with Zr concentration of 32 mol% generated a stable output voltage of ∼20 V and a current signal of 400 nA without performance decay.

Understanding the role of oxygen ion (O2−) activity in 1-D crystal growth of rutile TiO2 in molten salts

Controlled synthesis of nanostructured materials using facile and easily scalable synthesis techniques is highly attractive for large-scale production of nanomaterials. In this regard, molten salt synthesis is a well-established technique for large-scale production of nanostructured materials. Few reports have demonstrated the applicability of the molten salt technique for high-aspect-ratio one-dimensional rutile TiO2 synthesis. However, the crystal growth mechanism of 1-D TiO2 in the molten salt is not well understood. Here, various sets of experiments have been delivered to investigate 1-D rutile TiO2 crystal growth starting from anatase TiO2 precursors in molten NaCl with the presence of various inorganic oxy-additives. It was found that the oxygen ion (O2−) activity of the molten salt matrix, which can be controlled by oxy-additives, is the decisive factor for the formation of the 1-D structure. The (NaPO3)6 additive, which reduces the O2− activity of the molten salt matrix, increased the solubility of anatase TiO2. The increased solubility facilitates the easy mobility of ions to the growth site where the crystallographic surface energy is high. The natural tendency to minimize the total surface energy causes the crystal to grow in a particular direction, which eventually leads to 1-D rutile TiO2 nanoparticles.