In this work, we report the use of pseudocapacitive RuO2 in a porous carbon-based substrate as a composite electrode for high-performance capacitive deionization (CDI). RuO2 was electrodeposited onto inexpensive activated carbon (AC) via cyclic voltammetry to optimize the composite electrode (denoted as RuO2(20)-AC) fabrication. The electrochemical measurements indicate that the composite electrode with a specific surface area of 576 m(2)/g and hydrophilicity yields an improved specific capacitance and good cycling stability. The notably enhanced performance is attributed to the presence of RuO2, which allows rapid Faradaic charge-transfer reactions as well as pseudocapacitive charge storage. These results confirm that incorporating RuO2 onto an AC electrode effectively reduces the electrical resistance and enhances the charge efficiency. Furthermore, batch-mode CDI experiments were conducted at 1.2 V in a 5 mM NaCl solution. As evidenced, the RuO2(20)-AC composite has a promising salt adsorption capacity of 11.26 mg/g, which is 3.7-fold higher than that of pristine AC. Therefore, using the RuO2(20)-AC composite as the cathode, an enhanced desalination performance can be achieved through a mixed capacitive-Faradaic process, resulting from two removal mechanisms of capacitive electrosorption and pseudocapacitive redox reactions. This work provides an efficient strategy to utilize RuO2 on porous carbon-based substrates to improve CDI performance. (C) 2018 Elsevier Ltd. All rights reserved.