MnO2 has been widely applied as activation additives in capacitive deionization (CDI) technique due to its low cost and high performance. However, there is no unambiguous pattern concluded on which MnO2 phase could lead the highest CDI performance. To answer this question, different MnO2 phases were synthesized and associated to activated carbon supports to examine their CDI performances (percentage difference in the conductivity) in different pH by a simple batch mode. In addition, their surface chemistry was characterized using alkalimetric-acidimetric titration. Our preliminary results showed that in a first glimpse, beta-phase MnO2 seemed to exhibit the highest CDI performance over other phases did. However, when plotting the surface charge density of different MnO2 phases in different pH against the deionization efficiency, an interesting pattern appeared that the deionization efficiency decreased proportionally with increasing surface charge density. Importantly, this correlation was independent to the pH and the MnO2 phases. Accordingly, we speculate that the discrepancy in CDI efficiency caused by different MnO2 phases might be simply as a result of the structure induced surface charge effect where different MnO2 phases have its own distribution pattern of surface charge density over MnO2 surfaces.

MnO2 structure induced surface charge effect on the performance of capacitive deionization in different pH

254th National Meeting (2017)

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