A solid pseudocapacitive electrochemical capacitor (EC) enabled by a polymer electrolyte and molybdenum nitride electrodes has been developed and has demonstrated ultra-high rate performance. The solid EC can deliver 1 mF cm-2 at 100 Vs(-1) and achieve a 10 ms time constant. This not only exceeds its liquid EC counter-part but also greatly surpasses a similar EC with titanium nitride electrodes as well as nanocarbon based electrochemical double layer capacitors. (C) 2012 Elsevier B.V. All rights reserved.