Enhanced thermopower wave via nanowire bonding and grain boundary fusion in combustion of fuel/CuO–Cu₂O–Cu hybrid composites

Abstract

Understanding the chemical-thermal-electrical energy conversion in micro/nanostructures is crucial for making breakthroughs in new fields related to energy research, as well as in improving the existing energy technologies. Thermopower wave utilizing this chemical-thermal-electrical energy conversion in hybrid structures of nanomaterials and combustible fuel has recently attracted much attention as an enhanced combustion wave with the concomitant voltage generation. In this study, we have explored thermopower waves in the hybrid composite of the chemical fuel and surface-oxidized copper submicroparticles (SCuMPs) films during combustion. Here, we have demonstrated that the manipulations of micro/nanostructures in SCuMPs films by annealing are capable of converting the energy released during chemical combustion to a significantly large amount of thermal and electrical energy (average combustion velocity 32.6 mm s À1 , output voltages up to 6.2 V; average 2.02 V) in comparison with the as-prepared SCuMPs films (19.2 mm s À1 , up to 1.0 V; average 0.75 V) from thermopower waves. Owing to the inter grain boundary fusions and inner/surface nanowire-bonding by annealing, the chemical combustion rate, the corresponding thermal transport, and the electrical energy generation were greatly enhanced in the micro/nanostructured films. This work can contribute to the enhanced combustion wave and voltage generation in thermopower waves as well as further understanding of the fundamental phenomena in chemical-thermal-electrical energy conversions using micro/nanostructured materials.

Giant Peak Voltage of Thermopower Waves Driven by the Chemical Potential Gradient of Single‐Crystalline Bi2Te3

“…Figure a shows an exemplary output voltage waveform from an SC‐BT device. Unlike other multipeak thermopower waves in the literature, a single peak with a very high peak potential of ≈8 V was observed. Figure a, inset, shows another waveform measured in a finer time window.…”

“…This could be due to the tradeoff relationship between electrical conductivity and Seebeck coefficient with regard to the carrier concentration . The highest peak voltage reported so far was 6.2 V from the combination of nitrocellulose and Cu–CuO–Cu 2 O powders, although the corresponding mass‐specific power was not provided in the literature …”

“…Materials with greater Seebeck coefficients were investigated as substrates because the low Seebeck coefficient (≈80 µV K −1 ) of MWNTs was regarded as a hurdle to increase electrical potential of thermopower waves . These include Bi 2 Te 3 (≈−287 µV K −1 ), Sb 2 Te 3 (≈243 µV K −1 ), ZnO (≈−360 µV K −1 ), MnO 2 (≈−1900 µV K −1 ), and Cu–CuO–Cu 2 O powders (≈10 000 µV K −1 ) . The effect of chemical composition of fuel on thermopower waves was also explored .…”

“…The effect of chemical composition of fuel on thermopower waves was also explored . Nitrobenzene‐functionalized MWNTs, TNA, nitrocellulose, sodium azide, sucrose with potassium nitrate, and picric acid were investigated . Bilayered substrates (Bi 2 Te 3 or Sb 2 Te 3 on alumina or terracotta) were also explored .…”

“…The SC‐BT flake was cut into rectangular shape (1 × 10 mm 2 ), and fuel was coated on the top surface. The exothermic chemical reaction was initiated at the right end of the device using a hot nickel–chromium wire, and the induced electrical potential was monitored using an oscilloscope. Figure e shows a self‐propagating heat wave, toward the left end, recorded by a high‐speed camera.…”