An activated carbon fiber felt (ACFF) cathode lacking metal catalysts is used in an upflow microbial fuel cell (UMFC). The maximum power density with the ACFF cathode is 315 mW m(-2), compared to lower values with cathodes made of plain carbon paper (67 mW m(-2)), carbon felt (77 mW m(-2)), or platinum-coated carbon paper (124 mW m(-2), 0.2 mg-Pt cm(-2)). The addition of platinum to the ACFF cathode (0.2 mg-Pt cm(-2)) increases the maximum power density to 391 mW m(-2). Power production is further increased to 784 mW m(-2) by increasing the cathode surface area and shaping it into a tubular form. With ACFF cutting into granules, the maximum power is 481 mW m(-2) (0.5 cm granules), and 667 mW m(-2) (1.0 cm granules). These results show that ACFF cathodes lacking metal catalysts can be used to substantially increase power production in UMFC compared to traditional materials lacking a precious metal catalyst. (C) 2009 Elsevier B.V. All rights reserved.