Promising Performance Indicators for Water Desalination and Aqueous Capacitors Obtained by Engineering the Electric Double Layer in Nano-Structured Carbon Electrodes

It is well-known that the electric double layer plays important roles in a variety of applications, ranging from biology to materials sciences. Many studied the electric double layer using a variety of techniques, and as a result our understanding is mature, although not complete. Based on detailed understanding, we expect that by manipulating the electric double layer we could advance tremendously applications in the water-energy nexus. This is particularly true for electric double layer capacitors and capacitive desalination devices. However, such manipulation is not straightforward because of a competition of phenomena that occur within the electric double layer itself, including solvation effects, excluded volume phenomena, and ionion correlations. Using molecular dynamics simulations, we designed a composite graphene-based electrode to manipulate structural and dynamical properties of the electric double layer. Our design favors the formation of the compact Helmholtz layer. Inherent to our design is that the compact Helmholtz layer not only is atomically thick, but it is also highly mobile in the direction parallel to the charged surface. We suggest here how to exploit the properties of the engineered electric double layer toward developing a new continuous desalination process that combines the advantages of membrane and capacitive desalination processes, reducing their shortcomings. Insights on the molecular mechanisms relevant to the water-energy nexus are provided.