Enhancement of nitrate reduction in microbial fuel cells by acclimating biocathode potential: Performance, microbial community, and mechanism

The performance of pseudocapacitive electrodes at fast charging rates are typically limited by the slow kinetics of Faradaic reactions and sluggish ion diffusion in the bulk structure. This is particularly problematic for thick electrodes and electrodes highly loaded with active materials. Here, a surface-functionalized 3D-printed graphene aerogel (SF-3D GA) is presented that achieves not only a benchmark areal capacitance of 2195 mF cm-2 at a high current density of 100 mA cm-2 but also an ultrahigh intrinsic capacitance of 309.1 µF cm-2 even at a high mass loading of 12.8 mg cm-2 . Importantly, the kinetic analysis reveals that the capacitance of SF-3D GA electrode is primarily (93.3%) contributed from fast kinetic processes. This is because the 3D-printed electrode has an open structure that ensures excellent coverage of functional groups on carbon surface and facilitates the ion accessibility of these surface functional groups even at high current densities and large mass loading/electrode thickness. An asymmetric device assembled with SF-3D GA as anode and 3D-printed GA decorated with MnO2 as cathode achieves a remarkable energy density of 0.65 mWh cm-2 at an ultrahigh power density of 164.5 mW cm-2 , outperforming carbon-based supercapacitors operated at the same power density.