Highly conductive alumina/NCN composites electrodes fabricated by gelcasting and reduction-sintering—An electrochemical behavior study in aggressive environments

A novel highly conductive alumina/nano-carbon network composites (alumina/NCN composites) was fabricated by gelcasting and reduction-sintering method under argon atmosphere. The electrochemical behaviors of the alumina/NCN composites were studied systematically in some aggressive solutions (HCl, H2SO4, HNO3, NaOH, and KOH), using potentiodynamic polarization and chronoamperometry and X-ray diffraction and SEM observations. The results showed that the electrochemical stability and reproducibility of the composite electrodes in these diluted acids and alkalis were very good and had, in some extent, an electro-catalytic activity toward formation of hydrogen evolution and reduction of dissolved oxygen in aqueous solutions in comparison with a commercial graphite electrode. In addition, the pyrolyzed nano-carbon contents, size, and shape in the alumina matrix, have greatly effects on the electrochemical performances and electrode reactions in these solutions. It is found that the minimal residual carbon content of 0.62 wt.% in the matrix is enough to improve electrochemical performances and avoid to loss the ceramics physical properties at the same time. When the additional potential in all the tested electrolytes was at +1700 mV (vs. SCE), alumina particles at the electrode surface were not observed to dissolve into solution in this case, indicating the material being suitable for electrodes in aggressive solutions.