Nanochannel geometry-depended behaviors on ion selectivity for salinity gradient energy harvesting

Nanofluidic osmotic energy, which can be directly converted into electricity, is considered a clean and sustainable energy that effectively utilizes salinity gradients. The rational construction of nanochannel is of great significance to ion transport and osmotic energy conversion, but there is currently little attention paid to naturally formed rough and irregular channels. In this study, a model that considers the effects of nanochannel cone angle and waveform surface on interface reaction coupling was established for osmotic energy conversion. The results indicate that cone angle and waveform have a significant effect on osmotic energy conversion. It is found that the reduction of cone angle and the addition of waveform will improve ion selectivity and increase energy conversion efficiency, and ion rectification effect of corrugated cylindrical channel is the most obvious. Meanwhile, enlarging waveform dimensions leads to a significant overlap of electric double layer, resulting in a growth in cation transference number and selectivity, thereby enhancing the system's energy conversion efficiency, which can reach 49.62%. At low concentration ratios, the waveform dimensions are inversely proportional to the maximum output power, whereas at high concentration ratios, increasing the waveform dimensions and applying the waveform at channel entrance can efficiently improve the maximum output power.