Optimizing Electrodeposited Manganese Oxide at Carbon Cloth Electrodes for Harvesting Salinity-Gradient Energy

Electrical power can be generated from the controlled mixing of salinity gradients when solutions of differing salt concentration bathe opposing electrodes in a flow-cell configuration. The power density of such salinity-gradient cells is enhanced by moving beyond the double-layer capacitance of high-surface-area carbons to electrode materials that store charge via pseudocapacitance (e.g., manganese oxides; MnOx). We investigate the effects of MnOx loading on salinity-gradient power production, using anodic electrodeposition to coat carbon cloth (CC) electrodes with nanostructured Akhtenskite-type MnOx at controlled incremental mass loadings. Uniform MnOx deposition at exposed CC surfaces is confirmed by scanning electron microscopy with elemental mapping. Power-density measurements with the resulting MnOx@CC electrodes in a salinity-gradient cell fed by low (0.02 M NaCl) and high (0.5 M NaCl) concentration solutions show a positive correlation with MnOx loading, reaching a competitive peak average power density of 0.221 0.001 mW cm(-2) at 1.90 mg cm(-2) MnOx. By comparing flow-cell data with results from half-cell electroanalytical characterization of individual electrodes, we show that salinity-gradient performance is ultimately limited by resistive losses in the modestly conductive MnOx coating at higher mass loading/thickness.

Automated summary

This study investigates the generation of electric power through controlled mixing of salinity gradients and the use of manganese oxides (MnOx) as electrode materials to enhance power density. The results show that increasing MnOx loading helps to improve the power density of salinity-gradient cells. However, resistive losses in the moderately conductive MnOx coating at higher mass loading/thickness ultimately limit the performance of the salinity-gradient cell.