Here we propose copper as a high performance and economically viable anode material for microbial bioelectrochemical systems.

The performance of primary and secondary electroactive biofilms grown on layered corrugated carbon (LCC) electrodes was studied over a period of several months. With an average projected current density of 6.7 mA cm −2 , the studied secondary electroactive biofilms outperformed the primary biofilms (3.0 mA cm −2 ) over the entire experimental period. At the same time, both, primary and secondary biofilms, exhibited a constant Coulomb efficiency of about 89%. The study further illustrates that three-dimensional electrodes such as LCC allow a sustained long-term performance without significant decrease in electrode performance.

6182 wileyonlinelibrary.com fi brous segments. Sponges are typically highly porous and easily permeable by gases. Metallization of such sponges could give novel polymer/metal composites with highly interesting properties for a variety of applications, e.g., electrodes in fuel cells, membranes, fi ltration, thermal insulation, heating, ultralight constructions, and catalysis. Well-established metallization techniques for polymer materials include physical or chemical vapor deposition and galvanization. [ 4 ] These techniques are not suitable for achieving high conductivities by the metallization of macroscopic polymer sponges due to their complex 3D structure. The in-depth import of metals inside the pores of sponges and the formation of fully covered metal layers on the polymer fi brous segments are particular problems. A method of choice could be wet metallization, also assigned as electroless plating. There are some reports on wet metallization of porous polymer surfaces following different concepts. For example, gold coating of electrospun poly(methyl methacrylate) nonwovens was achieved by wet deposition of gold nanoparticles (NPs), which yielded conductivities up to 930 S cm −1 .[ 5 ] Here, copper would be more appropriate for many applications. Major pathways for copper plating of polymers are based on the treatment with copper salts and formaldehyde. [ 6 ] Wet chemical deposition of copper, for example, was achieved by treatment of an open-cell polyurethane sponge with CuSO 4 and formaldehyde under basic conditions using PdCl 2 as an activator. [ 7 ] Plasmonic copper nanoparticle coatings were prepared on silanized glass slides following an elegant approach also using CuSO 4 and formaldehyde, but gold as seed. [ 8 ] A number of efforts were undertaken using ultrasound for fast electroless plating. [ 9 ] However, ultrasound-assisted electroless plating required careful adjustment of the ultrasound frequency in order to avoid the pitting of the metal surface due to microjetting, which could also be a major problem in the absence of ultrasound due to evolving hydrogen bubbles. [ 10 ] The importance of the quality of the metal layer obtained by electroless plating on polymer substrates corresponds directly with their electrical properties. Broken and grainy metal layers or pitted surfaces will reduce their electrical conductivity signifi cantly. However, nickel electrodes were produced with polyurethane foams under suitable plating conditions. [ 11 ] The polyurethane foams served as sacrifi cial templates. As a result, highly conductive nickel sponges with high porosities of up to 98% and pore sizes of several

In this publication, we propose metal-polymer hybrid materials as a novel platform for the development of 3 D anode materials for bioelectrochemical systems, such as microbial fuel cells. Extremely low gravimetric density, high porosity, high electric conductivity, and distinct elastic properties are characteristics that are superior for bioelectrochemical applications. As a proof of concept, we investigated copper-melamine foams (Cu-MF) based on a commercially available, open cell melamine foam. With a low amount of copper (16.3 mg cm for Cu-MF ) used for metallization, such electrode material can be manufactured at low price. The Cu-MF sponges are readily colonized by electrochemically active bacteria and are electrochemically stable over an experimental period of more than 75 days. The Cu-MF-biofilm electrodes exhibit volumetric current densities of up to 15.5 mA cm . During long-term operation, overgrowth of the Cu-MF pore structures by the Geobacter-dominated biofilms occurs, from which demands for future electrode developments are derived.