Performance Enhancement of Moisture-driven Power Generators by Photofragmentation of Inorganic Salt Particles

Abstract

We developed a novel method based on the photofragmentation of inorganic salt particles for improving the moisture-electric energy transformation performance of a moisturedriven power generator (MPG). Infrared laser irradiation on cellulose nanofiber films (CNFs) prepared by a TEMPO (2,2,6,6tetramethylpiperidine-1-oxyl radical)-mediated oxidation of bleached pulp induced a photothermal conversion of CNFs to porous graphitic carbon films (GCFs) with the catalyst-derived Na 2 O 2 particles. Since the laser beam was focused on the top surface of CNF, the gradients of the photothermal conversion of CNFs and Na 2 O 2 concentration were created along the thickness direction. Subsequent irradiation with ultraviolet (UV) light induced the photofragmentation of the micrometer-sized Na 2 O 2 particles into smaller ones, which increased the surface area of the salt particles in contact with the GCFs and consequently increased the number of effective dissociable charge carriers. When the GCF was exposed to moisture, the dissociated sodium ions migrated along the preformed concentration gradient, producing continuous outputs of current and voltage. At 90% relative humidity, the maximum voltage and current density outputs of the MPG increased from 0.91 V and 18.7 μA/cm 2 before UV irradiation to 1.10 V and 56.2 μA/cm 2 after UV irradiation, respectively. Additionally, we demonstrated that a green light-emitting diode could be turned on without capacitors or rectifiers during normal breathing while wearing a face mask with three GCF arrays attached (each 3 mm × 3 mm × 0.1 mm in size).

Highly Efficient Moisture-Induced Power Generators through Flashlight-Induced Graphitization of FeCl3-Impregnated Cellulose Papers

“…Figure b compares the voltage and current outputs of BCP9 with those of MPGs reported in the literature, which generated continuous outputs under ambient humidity conditions (<50% RH) rather than pulsed outputs. Although BCP9 did not exhibit the highest voltage output, it had the highest current density among the MPGs reported so far to the best of our knowledge. − ,,− Note that the voltage output of BCP9 can be easily increased by stacking the devices in series without significantly increasing the size due to its very thin thickness (535 μm). The maximum power density of BCP9 at 45% RH was calculated to be 11.2 μW/cm 2 , which is remarkably high, considering that most previously reported MPGs failed to generate sufficiently high power under ambient humidity conditions (<50% RH). − Figure c,d shows the voltage–current density outputs and power density, respectively, of BCP9 when connected to various load resistances ranging from 100 Ω to 100 MΩ.…”

“…LIG utilizes an infrared (IR) laser to photothermally convert organic materials into graphitic carbon. − In the case of cellulose graphitization, LIG not only converts cellulose into porous graphitic carbons but also creates an ion concentration gradient within it . The resulting MPG offers abundant ion carriers with an ion concentration gradient, high surface area, and ionic conductivity. − However, LIG does have disadvantages: achieving uniformity of graphitization and reducing fabrication time for large-scale production become challenging due to the reliance on focused laser scanning for the graphitization process …”

Moisture Power Generation: From Material Selection to Device Structure Optimization

“…(g) Inorganic salt MPG device . Reprinted with permission from ref . Copyright 2022, American Chemical Society.…”

“…In 2022, Eun and Jeon proposed an inorganic salt MPG device on cellulose nanofibrous membranes (CNFs) prepared by the TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-mediated oxidation of bleached paper pulp with infrared laser irradiation to induce photothermal conversion of CNFs with Na 2 O 2 particles to generate porous graphitic carbon films (GCFs) (Figure g), where the Na 2 O 2 particles were derived from the catalyst used in the TEMPO-mediated oxidation reaction. The Na 2 O 2 particles were then reacted with the CO 2 generated in the GCF photolysis by UV irradiation, resulting in Na 2 CO 3 particles; thus, preparation of GCF-based MPG devices loaded with Na 2 CO 3 particles was achieved . The GCF-based MPG device is capable of generating a voltage of 1.10 V and a current density of 56.2 μA/cm 2 using copper as electrodes on both sides.…”

Assembly of Natural Clay Minerals as Highly Robust Evaporation-Driven Power Generator

“…Carbon-based materials like carbon soot, graphene oxide, and carbon films are top choices for this application. 25,26 These carbon nanomaterial-based generators rely on the gradient of water flowing through narrow pores or channels within the carbon particles, converting ambient thermal energy into electricity. Several polymers, proteins, and layered doublehydroxide-based materials were also proven successful in generating electrical power via the evaporation process at microwatts per cubic centimeter levels.…”