High salt capacity and high removal rate capacitive deionization enabled by hierarchical porous carbons

Capacitive deionization, CDI, has emerged as an attractive alternative for water desalination. Electrodes based on Hierarchically porous carbons, HPCs, consistently show promising electrosorption performance. However, the typically low mesopore fraction and broad pore size distribution limit their utilization in practical applications. Here we report the CDI performance of a series of HPCs synthesized via ice templation possessing a high fraction of mesopore volume (85–93% of total porosity) and tight control over the amount and the size of mesopores (∼6 nm). Electrochemical measurements indicate high rate capability (82% salt retention) and outstanding cycling stability performance (100% capacitance retention over 600 cycles at 0.76 A g−1). In the CDI experiments, the HPCs display high salt capacity (up to ∼ 13 mg g−1) and consistently outperform other high surface areas commercial carbons. The existence of high fraction of mesoporosities enables better utilization of the accessible surfaces of HPCs where the introduction of micropores leads to more than 80% increase in the salt capacity. The HPCs reported here can serve as model electrode systems in studies to delineate the impact of mesoporosity (pore size and volume) on CDI performance and they may pave the way for practical CDI applications.