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The lack of low-work function materials and the negative space charge effect have long prevented vacuum thermionic energy converters (VTECs) from becoming a practical means of power generation. Advancements in microfabrication have since provided solutions to these challenges, such as the suppression of negative space charge via a micro/nanoscale interelectrode vacuum gap distance, reigniting interest in VTECs as a potential clean energy technology. However, the limited operational lifetimes of many low-work function coatings have hindered their practical device-level implementation. Solid-state thermionic energy converters (SSTECs) have been proposed as a viable alternative to VTECs since they do not require an interelectrode vacuum gap or low-work function electrodes. Nevertheless, SSTECs still require a large temperature gradient between electrodes and are limited to low operating voltages. To address these limitations, we propose a near-field enhanced solid-state thermionic energy converter (NF-SSTEC), which leverages the advantages of SSTECs by eliminating the need for a large temperature gradient between the electrodes and increasing the range of possible operating voltages. We theoretically demonstrate conversion efficiencies of 16.8 % and power densities as high as 13.1 W cm−2 without needing a high-temperature gradient between the radiator and SSTEC. Additionally, we compare its performance under different radiation spectra, showing the potential for improvement via further optimization of the radiator. 

Abstract Experiments have been conducted in which CO₂gases with varying C and O isotopic compositions and with stochastic and nonstochastic Δ₄₇values have been allowed to equilibrate with phosphoric acid of two concentrations in reaction vessels of varying dimensions at temperatures of 25 and 90 °C. Rates of¹³C¹⁸O and¹⁸O exchange between the CO₂and the phosphoric acid varied as a function of the length of exposure, volume of reaction vessel, acid strength, and difference of the initial Δ₄₇and δ¹⁸O values of the CO₂from theoretical equilibrium values. The Δ₄₇values were also altered by heated stainless steel surfaces such as those found within the Kiel device and other preparation systems. These results have been used to explain variations in the differences in the fractionation between 25 and 90 °C reported for calcite by different workers as well as differences in the slopes between temperature and Δ₄₇values produced by reacting samples at different temperatures (25 and 90 °C).