Ultra-high thermal effusivity materials for resonant ambient thermal energy harvesting

Abstract

Materials science has made progress in maximizing or minimizing the thermal conductivity of materials; however, the thermal effusivity—related to the product of conductivity and capacity—has received limited attention, despite its importance in the coupling of thermal energy to the environment. Herein, we design materials that maximize the thermal effusivity by impregnating copper and nickel foams with conformal, chemical-vapor-deposited graphene and octadecane as a phase change material. These materials are ideal for ambient energy harvesting in the form of what we call thermal resonators to generate persistent electrical power from thermal fluctuations over large ranges of frequencies. Theory and experiment demonstrate that the harvestable power for these devices is proportional to the thermal effusivity of the dominant thermal mass. To illustrate, we measure persistent energy harvesting from diurnal frequencies, extracting as high as 350 mV and 1.3 mW from approximately 10 °C diurnal temperature differences.

High‐Performance Thermally Conductive Phase Change Composites by Large‐Size Oriented Graphite Sheets for Scalable Thermal Energy Harvesting

“…Figure g shows a comparison of the thermal effusivities (defined as the square root of the product of TC, density (ρ) and the phase change enthalpy (Δ H ); ), which represent a material's ability to exchange thermal energy with its surroundings . In comparison with the latest reports, our PCCs exhibit a substantially higher room‐temperature TC and thermal effusivity by a factor approximately 2–6 …”

“…However, current engineering technologies, based on mechanically cleaving or chemically exfoliating natural graphite flakes into GNPs, MLG, or graphene, intrinsically destroy the vdW bonding and thus are difficult to synthesize scalable high‐quality large‐size/area graphite sheet . The chemical vapor deposition‐grown growth method can produce such a graphite sheet, but it is generally at a high cost …”

Thermally Enhanced Electro-osmosis to Control Foam Stability

“…Indeed, they are extensively used for their lightness, their thermal [9] or acoustic insulating properties, their green efficiency in the building industry [10], and more specifically their large surface area [11]. Recently, these aerated materials have been used, for example, as electrodes for supercapacitors or batteries [12], or as so-called thermal resonators for energy harvesting [13]. Their fabrication often relies on a two-step process, which consists in shaping the liquid and then solidifying it.…”

Progress in wearable electronics/photonics—Moving toward the era of artificial intelligence and internet of things

“…In this case, power becomes a critical issue for a sustainable electronic system. Conventional batteries fail to meet the rising requirements of the energy storage units in wearable or implantable devices, hence various energy harvesting strategies are proposed to address the limitations of the bulky batteries 215,271‐279 . Solar energy as the cleanest and most abundant renewable energy source has been widely adopted by many self‐powered wearable systems.…”