Energy harvesting is an important developing technology for a new generation of self-powered sensor networks. This paper demonstrates the significant improvement in the piezoelectric energy harvesting performance of barium titanate by forming highly aligned porosity using freeze casting. Firstly, a finite element model demonstrating the effect of pore morphology and angle with respect to poling field on the poling behaviour of porous ferroelectrics was developed. A second model was then developed to understand the influence of microstructure-property relationships on the poling behaviour of porous freeze cast ferroelectric materials and their resultant piezoelectric and energy harvesting properties. To compare with model predictions, porous barium titanate was fabricated using freeze casting to form highly aligned microstructures with excellent longitudinal piezoelectric strain coefficients, d33. The freeze cast barium titanate with 45 vol.% porosity had a d33 = 134.5 pC/N, which compared favourably to d33= 144.5 pC/N for dense barium titanate. The d33 coefficients of the freeze cast materials were also higher than materials with uniformly distributed spherical porosity due to improved poling of the aligned microstructures, as predicted by the models. Both model and experimental data indicated that introducing porosity provides a large reduction in the permittivity (𝜀 "" # ) of barium titanate, which leads to a substantial increase in energy harvesting figure of merit, 𝑑 "" % /𝜀 "" # , with a maximum of 3.79 pm 2 /N for barium titanate with 45 vol.% porosity, compared to only 1.40 pm 2 /N for dense barium titanate. Dense and porous barium titanate materials were then used to harvest energy from a mechanical excitation by rectification and storage of the piezoelectric charge on a capacitor. The porous barium titanate charged the capacitor to a voltage of 234 mV compared to 96 mV for the dense material, indicating a 2.4-fold increase that was similar to that predicted by the energy harvesting figures of merit.
Ammonia (NH3) is essential for modern agriculture and industry, and due to its high hydrogen density and no carbon emission, NH3 is also expected to be the next‐generation of “clean” energy carrier. Herein, directly from air and water, the plasma‐electrocatalytic reaction system for NH3 production, which combines two steps of plasma‐air‐to‐NOx− and electrochemical NOx− reduction reaction (eNOxRR) with a bifunctional catalyst, have been successfully established. Especially, the bifunctional catalyst of CuCo2O4/Ni can simultaneously promote the plasma‐air‐to‐NOx− and eNOxRR processes. The easy adsorption and activation of O2 by CuCo2O4/Ni greatly improve the NOx− production rate at the first step. Further, CuCo2O4/Ni can also resolve the over bonding of the key intermediate of *NO, and thus reduce the energy barrier of the second step of eNOxRR. And finally, the “green” NH3 production achievs the excellent FENH3 (96.8%) and high‐record NH3 yield rate of 145.8 mg h−1 cm−2 with large partial current denstity (1384.7 mA cm−2). Moreover, an enlarged self‐made H‐type electrolyzer improves the NH3 yield to be 3.6 g h−1, and the obtained NH3 is then rapidly converted to a solid of magnesium ammonium phosphate hexahydrate, which favors the easy storage and transportation of NH3.This article is protected by copyright. All rights reserved
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