Mesoporous structures can increase catalytic activity by maximizing the ratio of surface area to volume, but current synthesis techniques utilize expensive polymers and toxic chemicals. A Geobacter sulfurreducens biofilm was used as a sustainable template to form mesoporous Pd structures while eliminating the need for synthetic chemicals. The bulk of the biofilm material was removed by thermal treatments after nanoparticle formation, producing a catalytic Pd mesoporous (pore size 9.7 +/- 0.1 nm) structure attached to the graphite electrode with a 1.5-2 mm thick backbone composed of nanoparticles (similar to 200 nm). A control electrode electrochemically plated with Pd in the absence of a biofilm exhibited a variable planar Pd base (similar to 0.5-3 mu m thick) with sporadic Pd extrusions (similar to 2 mu m across, 1-5 mu m tall) from the surface. The biotemplated mesoporous structure produced 15-20% higher stable current densities during H-2 oxidation tests than the electrochemically plated control electrode, even though 30% less Pd was present in the biotemplated catalyst. These results indicate that electroactive biofilms can be used as a sustainable base material to produce nanoporous structures without the need for synthetic polymers. (C) 2014 Wiley Periodicals, Inc.