Chemically modified carbon nanomaterials, such as nanodiamond (ND) soot, onionlike carbon (OLC), and carbon nanotubes (CNTs), were investigated as electrodes for electrochemical capacitors in high rate applications, that is, applications that drain power very fast. A layer of Keggin-type polyphosphomolybdate (PMo12) was coated on carbons through "layer-by-layer" deposition by alternating electrostatic adsorption of cationic [i.e., poly (diallyldimethylammonium) chloride] and anionic (i.e., PMo12) species to add pseudocapacitance to improve current response and increase capacitance. This modification was successful on OLCs and CNTs but not on ND soot. This difference is due to variations in surface chemistry, structure, and sp(2)/sp(3) content of those materials. In particular, the modified OLC exhibited a 20% increase in capacitance with up to 600 mF/cm(2) capacitance at 5 V/s, illustrating its high rate capability. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3223964] All rights reserved.