Tailoring pseudocapacitive materials from a mechanistic perspective

Pseudocapacitive materials are the basis of the emerging pseudocapacitors, but the applicability of this class of electroactive materials is not limited to supercapacitors. In fact, the pseudocapacitive behaviour of electrode materials is of particular importance in battery systems and electrocatalysis as well. Therefore, it is of vital necessity to profoundly understand the electrochemical behaviour of pseudocapacitive materials. The present paper aims to clarify why the solid-state electrochemistry of an electroactive material tends to shift from a well-defined redox system to a pseudocapacitive behaviour. From a practical perspective, the factors controlling or strengthening the pseudocapacitive behaviour are summarised. Contrary to the common perception, it is very difficult (if not impossible) to kinetically differentiate battery and pseudocapacitive behaviours, but the differences in the thermodynamics and the reaction mechanism are evident. A broad distribution of the energy of redox centres results in pseudocapacitive performance. In the light of this feature, practical factors improving the dynamic nature of the pseudocapacitive redox sites are reviewed to assist the design of future supercapacitor materials. (c) 2017 Elsevier Ltd. All rights reserved.