A direct borohydride fuel cell (DBFC) employing hydrogen peroxide as oxidant with a power density of about 350 mW cm(-2) at the cell voltage of almost 1.2 V at 70 degrees C is reported. The use of liquid reactants in DBFCs not only simplifies the engineering problems at the front end of the fuel cell, driving down complexity and hence cost, but operating a DBFC with an oxidant such as hydrogen peroxide also extends the operational environment for fuel cells to locations where free convection of air is limited, e.g., underwater applications. (C) 2004 The Electrochemical Society.