Elsevier

Nano Energy

Volume 81, March 2021, 105607
Nano Energy

Communication
Nanogenerators facilitated piezoelectric and flexoelectric characterizations for bioinspired energy harvesting materials

https://doi.org/10.1016/j.nanoen.2020.105607Get rights and content

Highlights

  • Flexible energy harvesting devices that experience multiple degrees of deformation.

  • Elucidating mechanistic polarization origins is challenging in the device scale.

  • Nanogenerators that enable a facile characterization of piezoelectricity and flexoelectricity in the device scale.

  • A simple solution that provided for the framework to separate the piezoelectric and flexoelectric effects in electric outputs.

Abstract

Deformation-derived electric polarization has been adopted as a core technology for electromechanics devices. Now, as the device experiences the multiple degrees of deformation, such as compressing, bending and stretching, upon the development of technology, the characterization techniques for devices need to be retrofitted to account for the different mechanistic origins of electric polarization. Here, we report the nanogenerators that enable a facile characterization of piezoelectricity and flexoelectricity in the device scale. The quadrant electrode NG along with nematically organized M13 bacteriophage provides the comprehensive piezoelectric coefficients while the flexoelectric coefficient was extracted from sandwich electrode NG. This approach offers a perspective on how to separate the piezoelectric and flexoelectric effects from the electric outputs. Such characterization will not only allow us an understanding of fundamental flexoelectric mechanisms but also help us to establish design rules for flexible electromechanical devices.

Graphical Abstract

Flexible energy harvesting devices that experience multiple degrees of deformation hold the promise for next-generation wearable and portable technologies. Elucidating mechanistic polarization origins is challenging in the device scale. A simple solution is provided for the framework to separate the piezoelectric and flexoelectric effects from the electric outputs of devices, allowing the nanogenerator field moving forward.

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Introduction

Electric charge accumulations in response to applied mechanical agitation have facilitated the conversion from mechanical energy to electrical energy, being employed as building blocks for electromechanical devices including actuators [1], [2], energy harvesting devices [3], [4], [5], and sensors [6], [7], [8]. In the presence of homogeneous strain, crystalline dielectric materials possessing a lack of inversion symmetry yield a piezoelectric polarization as a result of charge accumulation [9] whereas a strain gradient also leads to the characteristic flexoelectric polarization even in the centrosymmetric dielectric and semiconductor materials at the inhomogeneous stress (Fig. 1) [10], [11], [12], [13], [14]. In particular, under the inhomogeneous mechanical deformation, the polarization in the piezoelectric materials is formed by the coupling of piezoelectric and flexoelectric effects, but many researchers have assumed that they only measured piezoelectric outputs. The flexoelectricity in the most dielectric materials have been known to exhibit a low contribution to polarization (the flexoelectric coefficient of 10−10–10−8 C m−1) [15], [16], but recent studies revealed that the flexoelectric polarization was significantly enhanced in the nanomaterials with no inversion symmetry (the flexoelectric coefficient of 10−8–10−4 C m−1) [17], [18], [19], [20]. Hence, the extraction of flexoelectric contribution from the electric outputs is crucial not only to understand the fundamental flexoelectric mechanism but also to establish design rules for flexible electromechanical devices.

The flexoelectric response has been assessed using two different geometries [17]: a cantilever-beam and a truncated pyramid. The dynamic bending of the cantilever-beam generates the transverse strain gradient whereas the uniaxial compression of the truncated pyramid results in the longitudinal strain gradient. In practice, such complex approaches have limited giving us insight on flexoelectric contribution in the electromechanical devices. Ever since the introduction of the piezoelectric nanogenerator (NG) [21], it has been one of the emerging research fields due to many benefits including simple device geometry, easy fabrication, portability, and high conversion efficiency compared to conventional renewable energy technologies [22], [23], [24]. Many researchers have successfully demonstrated the flexible NG by scaling the rigid piezoelectric materials down to the nanometer [25], [26], [27], [28], [29], [30], [31]. Furthermore, organic piezoelectric biomaterials exhibit relatively weak piezoelectricity compared to inorganic materials, but they provide several advantages over conventional inorganic materials in terms of high biocompatibility, excellent flexibility, environmental friendliness, and a high level of processability [9] so that they have been employed as building blocks for the flexible NG [32], [33], [34]. With their excellent flexibility, therefore the NG incorporated with the organic piezoelectric materials can be a promising platform to characterize the device-scaled piezoelectricity and flexoelectricity of active materials by applying the inhomogeneous stress to the NG. Herein, we report an NG that facilitated the characterizations for piezoelectricity and flexoelectricity of the device. The electric output characterizations of quadrant electrode NG involving organic piezoelectric material offer the directional piezoelectric coefficients whereas the sandwich electrode NG provides a facile approach for characterizing the flexoelectric coefficient. With two different geometric NGs, we found that the M13 bacteriophage (phage) film that nematically organized exhibits the piezoelectricity of d11 = 6.5 ± 0.5 pm V−1, d21 = 7.6 ± 1.0 pm V−1, and d31 = 12.1 ± 1.0 pm V−1, together with the flexoelectricity of μwild = 78.3 ± 5.7 nC m−1 and μ4E = 167 ± 14.3 nC m−1. This strategy provides the platform for readily characterizing the flexoelectric figures of merit, allowing us an in-depth understanding of electric outputs at inhomogeneous stress.

Section snippets

Phage mass amplification and purification

To prepare a phage solution, a typical phage mass amplification protocol was conducted. At first, a wild phage plaque was selected from a cultivation dish and dispersed in 1 mL lysogeny broth (LB) containing Escherichia coli (E. coli). The mixture was incubated at 37 °C for 8 h with vigorous shaking. 1 mL resulting mixture and 1 mL E. coli mixture was added to 100 mL LB followed by vigorous shaking at 37 °C for approximately 8 h. Polyethylene glycol (PEG) precipitation was utilized to conduct

Nanogenerators designed for piezoelectricity and flexoelectricity characterization

We thereby have chosen a phage as a model organic piezoelectric nanomaterial for characterizing the piezoelectricity and flexoelectricity of bioinspired piezoelectric material. Phage is a filamentous bacterial virus featuring single-stranded DNA in axis that covered by 2700 copies of the major coat protein (pVIII) and capped with five copies of minor coat proteins (pIII/pVI and pVIII/pIX) on either end. As phage has a narrow size distribution and a well-defined dimension of 880 nm in length and

Conclusion

It is of crucial importance to identify the contributions from multiple mechanistic origins on electric polarization. We have established the measurement protocols to help the elucidation of either piezoelectric or flexoelectric effects in the device deformed. The directional piezoelectric coefficients are obtained from the quadrant electrode NG along with piezoelectric biomaterials at homogeneous stress whereas the flexoelectric coefficient is acquired from the sandwich electrode NG at

Author contributions

Y.Y., J.W.O, D.M.S., and Y.H.H formulated the project. Y.Y. fabricated the device and collected all electrical outputs, SEM, optical microscope, and effective stress and strain data. W.G.K and T.M.N. synthesized the bacteriophage and fabricated nematically organized phage. X.M. calculated the effective stress and strain and simulated the strain distribution. H.A. and S.H.H. assisted in design and fabrication of device. T.T, J.M.L., E.J.C., K.K., and J.M.K. contributed valuable theoretical

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (Nos. 2017R1A2B2006852 and 2020R1A2C2007590). This research was also supported by the Creative Materials Discovery Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (NRF-2017M3D1A1039287). The computational and stress/strain calculations were supported by the Seed and Startup Fund, funded by the Department of Mechanical

Yan Yan is currently a master candidate in Department of Nano Energy Engineering at Pusan National University, He is under the supervision of Prof. Yoon-Hwae Hwang, Prof. Hyung Kook Kim and Prof. Dong-Myeong Shin, His current research interests focuses on flexible electronics and energy harvesting.

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  • Cited by (0)

    Yan Yan is currently a master candidate in Department of Nano Energy Engineering at Pusan National University, He is under the supervision of Prof. Yoon-Hwae Hwang, Prof. Hyung Kook Kim and Prof. Dong-Myeong Shin, His current research interests focuses on flexible electronics and energy harvesting.

    Won-Geun Kim is currently a Ph.D. candidate under the supervision of Prof. Jin-Woo Oh at Pusan National University, Korea. He received his Bachelor’s degree (2015) in Pusan National University in Korea. His current research focuses on self-assembly of biomolecules.

    Xiaoting Ma obtained his B.Eng. from Zhejiang University in 2008, and got his M.Sc. in Chemistry from the same university under the supervision of Prof. Bao-ku Zhu in 2011, working on the development of polymer electrolytes for lithium batteries. Then, he moved to Shenzhen, a wonderful rising city in south China, and joined a company continuing his research on lithium battery separators. After eight years of his industrial experience, in 2020, with the growing eagerness to explore more in the field of Energy and Environmental Science, he joined the Shin group at The University of Hong Kong as a Ph.D. student.

    Tirusew Tegafaw is a postdoctoral research fellow under the supervision of Prof. Yoon-Hwae Hwang in Department of Nano Energy Engineering at Pusan National University. He received a Ph.D. degree from Kyungpook National University in Department of Chemistry. Now his research interests focus on piezoelectric nanomaterials for energy harvesting.

    Thanh Mien Nguyen is currently a graduate student under the supervision of Prof. Jin-Woo Oh at Pusan National University, Korea. His current research focuses on self-assembly of biomolecules

    Dr. Jong-Min Lee is currently a postdoctoral research fellow at Bio-IT Fusion Technology Research Institute in Pusan National University, Korea. He received a Ph.D. degree (2016) from Chungnam National University in the field of nanophotonics. His research interests focus on nano-bio optical structure and biosensor using it.

    Dr. Eun-Jung Choi is currently a research professor at Bio-IT Fusion Technology Research Institute in Pusan National University, Korea. She received a Ph.D. degree (2005) from Ulsan university in the field of molecular neuro-biology. She worked as a research professor at Dong-A University, Korea (2005–2006) and research professor at InJe University, Korea (2006–2012). Her research interests focus on color complex solution-based sensors and functional M13 phage.

    Heesang Ahn is currently is currently a Ph.D. candidate under the supervision of Prof. Kyujung Kim at Pusan National University, Korea. He received his bachelor’s degree (2015) in Pusan National University in Korea. His current research focuses on the development of optical analysis, sensing and imaging techniques integrated with nanoscience.

    Sung-Hun Ha is currently a Ph.D. candidate under the supervision of Prof. Jong-Man Kim at Pusan National University, Korea. He received his Bachelor’s degree (2014) in Pusan National University in Korea. His current research focuses on wearable conductor and sensor

    Kyujung Kim is currently Associate Professor in Department of Optics and Mechatronics Engineering at Pusan National University(PNU). He received B.S. in a school of Electronic engineering in 2006 and Ph.D. degree in a program for Nanomedical Science and Technology from Yensei University, Korea in 2012. He worked as a postdoctoral researcher at the Max-Plank-Institute for the science of light in Erlangen, Germany from 2012 to 2013. He joined Pusan National University in 2013. His recent research interest is focused on understanding the plasmon coupling effects on biosensing, imaging and optical trapping using nanostructures.

    Jong-Man Kim received the Ph.D. degree in Electrical Engineering and Computer Science from the Seoul National University, Republic of Korea, in 2007. In 2008, he joined the Pusan National University, where he is currently a Professor in Department of Nanoenergy Engineering. His current research interests include design, fabrication, and characterization of MEMS sensors and actuators, biomimetic engineering, synthesis and applications of functional nanomaterials, and flexible/stretchable electronics.

    Hyung Kook Kim is a Professor in Department of Nano Energy Engineering at Pusan National University (PNU). He received his Ph.D. from Pennsylvania state university in Department of Physics in 1985 under the supervision of Prof. Moses H. W. Chen, and joined Pusan National University in 1986. From 2012–2014, he was a president in Institute for Research and Industry Cooperation at PNU, and was the chairman in Department of Advanced Integrated Circuit at PNU. His recent research interest is focused on piezoelectric and triboelectric nanogenerators, photovoltaics, and phosphor nanomaterials.

    Jin-Woo Oh received a B.S., M.S., and Ph.D. degree in chemistry from Hanyang University, Korea. After a postdoctoral fellowship at UC Berkeley (2010–2012), he is currently an Associate Professor in the Department of Nanoenergy Engineering at Pusan National University, Korea. His research interest includes bio-photonics, synthesis of nanobiomaterials, biomimetic self-assembly and color sensor/color display using biomaterials.

    Dong-Myeong Shin is currently an Assistant Professor of Mechanical Engineering at the University of Hong Kong (HKU). He was inspired to work in nanoscience as an undergraduate researcher with Prof. Yoon-Hwae Hwang and Prof. Hyung Kook Kim at Pusan National University (B.S., 2009). He obtained his M.S. (2011) and Ph.D. (2016) degrees in nanomaterials at PNU, continuously working with his two mentors. In 2016, he joined the Research Center for Energy Convergence Technology (RCECT) at PNU to work with Prof. Kyujung Kim as a postdoctoral researcher. Following his Ph.D. and Postdoctoral research at PNU, in 2017, he moved to the University of California, Berkeley as a postdoctoral scholar with Prof. Jeffrey R. Long. Upon completion of his postdoctoral studies in the summer of 2019, Dong-Myeong traveled back to Asia to assume his current position of Assistant Professor of Mechanical Engineering at HKU, where his group has devoted to developing the self-powered nanoelectronics, with an emphasis on important components such as energy harvesting/storage devices and bioinspired electronics.

    Yoon-Hwae Hwang is a Professor in Department of Nanoenergy Engineering at Pusan National University (PNU). He received his Ph.D. from University of Pittsburgh in Department of Physics and Astronomy in 1995 under the supervision of Prof. Xiaomin Wu. After working as the postdoctoral researcher at the City College of New York, City University of New York under the supervision of the late Prof. Herman Z. Cummins, he joined PNU in 1997. Now he is the Dean of the College of Nanoscience and Nanotechnology at PNU. His recent research interests focus on piezoelectric and triboelectric nanogenerators, solar water splitting, capacitor based bionanosensors.

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    Y. Y. and W.-G. K contributed equally to this work.

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