Field emission and thermo-electrochemical cell performances of various types of carbon nanotubes

Different types of carbon nanotube (CNT) nanomaterials were fabricated using electrophoretic deposition (EPD) and chemical vapor deposition (CVD) methods to make the field emission (FE) and thermo-electrochemical cell (TEC) electrodes. The morphological and structural properties of CNT electrodes were characterized by SEM, Raman, and TEM. The graphite multi-walled CNT (MWNT) electrode by EPD (EPD-GMWNT) exhibited the best FE properties with the turn on field and threshold field of 1.7 and 2.97 V·μm⁻¹, respectively. In addition, EPD-GMWNT electrodes presented the best TEC properties with the current density of 2.09 mA·m⁻², the maximum power density of 0.37 W·m⁻², and the relative power conversion efficiency of 0.85%, at the temperature difference of 50 °C. MWNT electrode by CVD growth also demonstrated good FE and TEC performances. Both types of emitters, especially GMWNTs, possess low ratio of the D band peak to the G band peak (I_D/I_G), implying the extreme importance of structural crystallinities of CNTs for FE and TEC applications. The results suggest that construction of MWNT electrodes with low I_D/I_G ratio might be a promising way for the practical applications of FE and TEC devices.