A Game Changer: A Multifunctional Perovskite Exhibiting Giant Ferroelectricity and Narrow Bandgap with Potential Application in a Truly Monolithic Multienergy Harvester or Sensor
Bai, Y., Tofel, P., Palosaari, J., Jantunen, H., Juuti, J.
Advanced Materials Volume 29, Issue 29, 4 August 2017, Article number 1700767
An ABO3-type perovskite solid-solution, (K0.5Na0.5)NbO3 (KNN) doped with 2 mol% Ba(Ni0.5Nb0.5)O3− δ (BNNO) is reported. Such a composition yields a much narrower bandgap (≈1.6 eV) compared to the parental composition—pure KNN—and other widely used piezoelectric and pyroelectric materials (e.g., Pb(Zr,Ti)O3, BaTiO3). Meanwhile, it exhibits the same large piezoelectric coefficient as that of KNN (≈100 pC N−1) and a much larger pyroelectric coefficient (≈130 µC m−2 K−1) compared to the previously reported narrow-bandgap material (KNbO3)1− x-BNNOx. The unique combination of these excellent ferroelectric and optical properties opens the door to the development of multisource energy harvesting or multifunctional sensing devices for the simultaneous and efficient conversion of solar, thermal, and kinetic energies into electricity in a single material. Individual and comprehensive characterizations of the optical, ferroelectric, piezoelectric, pyroelectric, and photovoltaic properties are investigated with single and coexisting energy sources. No degrading interaction between ferroelectric and photovoltaic behaviors is observed. This composition may fundamentally change the working principles of state-of-the-art hybrid energy harvesters and sensors, and thus significantly increases the unit-volume energy conversion efficiency and reliability of energy harvesters in ambient environments.
Robust hierarchical 3D carbon foam electrode for efficient water electrolysis
Pham, T.N., Sharifi, T., Sandström, R., Siljebo, W., Shchukarev, A., Kordas, K., Wågberg, T., Mikkola, J.-P.
Scientific Reports, Volume 7, Article number: 6112 (2017)
Herein we report a 3D heterostructure comprising a hierarchical macroporous carbon foam that incorporates mesoporous carbon nanotubes decorated with cobalt oxide nanoparticles as an unique and highly efficient electrode material for the oxygen evolution reaction (OER) in electrocatalytic water splitting. The best performing electrode material showed high stability after 10 h, at constant potential of 1.7 V vs. RHE (reversible hydrogen electrode) in a 0.1 M KOH solution and high electrocatalytic activity in OER with low overpotential (0.38 V vs RHE at 10 mA cm−2). The excellent electrocatalytic performance of the electrode is rationalized by the overall 3D macroporous structure and with the firmly integrated CNTs directly grown on the foam, resulting in a large specific surface area, good electrical conductivity, as well as an efficient electrolyte transport into the whole electrode matrix concurrent with an ability to quickly dispose oxygen bubbles into the electrolyte. The eminent properties of the three-dimensional structured carbon matrix, which can be synthesized through a simple, scalable and cost effective pyrolysis process show that it has potential to be implemented in large-scale water electrolysis systems.
Last updated: 9.3.2018