Regulating VO Layer Spacing by a Polyaniline Molecule Chain to Improve Electrochemical Performance in Salinity Gradient Energy Conversion.

Salinity gradient energy is a chemical potential energy between two solutions with different ionic concentrations, which is also an ocean energy at the junction of rivers and seas. In our original work, the device "activated carbon//(0.083 M NaSO, 0.5 M NaSO)//vanadium pentoxide" for the conversion of salinity gradient energy was designed, and the conversion value of 6.29 J g was obtained. However, the low specific surface area of the original VO inevitably resulted in limited active sites and slow ionic transport rates, and the inherent lower conductivity and narrower layer spacing of the original VO also resulted in poor electrode kinetic performance and cycle stability, hindering its practical application. To solve the above problems, the present work provides a strategy of using polyaniline (PANI) molecule chain intercalation to regulate the layer spacing of the original VO, and through the expansion and traction of the layer spacing, the composite PANI/VO (PVO) with high specific surface area is prepared and used as an anode material for electrochemical conversion of salinity gradient energy application. The significantly increased layer spacing of the crystal plane (001) corresponding to the original VO was confirmed with the PANI by the hydrogen bonding and the van der Waals force. The high specific surface area of the composite provides more electrochemical active sites to realize a fast Na migration rate and high specific capacitance. Meanwhile, the inserted PANI molecule chain, which acts not only as a pillar enlarging the Na diffusion channel but also as an anchor locking the gap between VO bilayers, improves the structural stability of the VO electrode during the electrochemical conversion process. The proposed insertion strategy for the conductive polymer PANI has created a new way to improve the cycle stability performance of the salinity gradient energy conversion device.