Improvement of electrochemical performance via enhanced reactive oxygen species adsorption at ZnO-NiO@rGO carbon felt cathodes in photosynthetic algal microbial fuel cells

Oxygen and reactive oxygen species (ROS) produced during algal photosynthesis are important electron acceptors in photosynthetic algal microbial fuel cell (PAMFC) cathodes. In this study, spongy and petaline ZnO-NiO@rGO carbon felt cathodes were first fabricated through in situ ZnO-NiO growth and further modified with reduced graphene oxide (rGO) via electrodeposition and cyclic voltammetry reduction. The structural and electrochemical properties of the ZnO-NiO@rGO carbon felt cathodes were characterized, and the ROS adsorption capacity of the cathodes was analyzed via temperature programmed desorption and UV spectrophotometry. The results illustrated that the optimal molar ratio of Zn to Ni was 0.2 for cathode surface modification, and the specific surface areas of spongy and petaline ZnO0.2-NiO@rGO reached 215.26 and 230.88 mg.g(-1), respectively, which were more than 200-fold higher than that of prefabricated carbon felt. The areal capacitance values of spongy and petaline ZnO0.2-NiO@rGO cathodes reached 3033.5 and 6388.92 mC.cm(-2), respectively. The ROS concentrations on the spongy and petaline ZnO0.2-NiO@rGO cathode surfaces reached 52.36 and 64.02 mu mol.L-1, respectively, which were nearly 2-fold higher than that for prefabricated carbon felt cathode. The power densities of PAMFCs using spongy and petaline ZnO0.2-NiO@rGO as cathode electrodes were 20.18 and 31.92 mW.m(-2), respectively. The improvement of electrochemical performance of PAMFCs is partially ascribed to the enhanced ROS adsorption capacity of ZnO-NiO@rGO cathodes. Therefore, ROS adsorption capacity is recommended as an evaluation indicator for PAMFC cathodes.