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.