Boron/nitrogen substituted carbons were synthesized by co-pyrolysis of polyborazylene/coal tar pitch blends to yield a carbon with a boron and nitrogen content of 14 at% and 10 at%, respectively. The presence of heteroatoms in these carbons shifted the hydrogen evolution overpotential to 1.4 V vs Ag/AgCI in aqueous electrolytes, providing a large electrochemical potential window (similar to 2.4V) as well as a specific capacitance of 0.6 F/m(2). An asymmetric capacitor was fabricated using the as-prepared low surface area carbon as the negative electrode along with a redox active manganese dioxide as the positive electrode. The energy density of the capacitor exceeded 10 Wh/kg at a power density of 1 kW/kg and had a cycle life greater than 1000 cycles. (C) 2011 Elsevier Ltd. All rights reserved.