Photo-electric capacitive deionization enabled by solar-driven nano-ionics on the edges of plasma-made vertical graphenes

Abstract

Abstract Unimpeded ion traffic in carbon materials with ionic selectivity remains a challenge in electrochemical energy storage and chemical purifications represented by capacitive deionization (CDI) of potable and industrial water. In this work, a new concept of solar nano-ionics is developed to directly feed solar energy into photocarriers and localized electric fields near the edges of graphene nanostructures that enable effective, mobility-based ion transport with high mass exchange rates and selectivity. This concept is applied to demonstrate the new approach for CDI, namely the photo-electric capacitive deionization (PECDI), enabled by the solar-enhanced ionic transport. Materialized by edge-enhanced vertical graphenes (eVG), the photocarriers are localized along the edge nano-antennas of eVG to boost the edge-localized electric fields by two orders of magnitude, as confirmed by near-field photo-induced force microscopy. The localized photo-electric fields control and restructure the nano-ionic flows leading to selective transport of ions with different mobility and dramatically enhanced kinetics, as validated by in situ electrochemical quartz crystal microbalance measurements and molecular dynamics simulations. With the photo-enhanced ionic transport kinetics, an average adsorption capacity of 33 mg g–1 at 200 mg L–1 (165 mg g–1 at 5000 mg L–1), a fast adsorption/desorption response and the impressive efficiency are achieved. This work opens a new avenue for solar-enhanced nano-ionic manipulation, which can be extended for a broad range of chemical engineering, energy, and environmental applications.