Growth of carbon nanotubes on graphene as 3D biocathode for NAD+/NADH balance model and high-rate production in microbial electrochemical synthesis from CO2
Three-dimensional (3D) structured carbon nanomaterials has great potential to be used in microbial electrochemical synthesis (MES) for carbon dioxide reduction. Here, we report the efficiency of 3D architected GN–CNTs hybrid as MES electrodes and state the mechanism of metabonomics with NAD+/NADH balance model in metabolic pathway. Under 3D structure conditions, the balance of NAD+/NADH in bacteria was disturbed. Changing NAD+/NADH pool can promote the transfer of extra electrons from the cathode to bacteria in order to generate NADH. Consequently, the excess NADH is used for CO2 fixation. Correspondingly, the resulting GN–CNTs hybrid showed adjustable electrochemical performance as a MES electrode. It allows for an enhanced interaction and electron transfer between biofilm and its nano-hierarchical structure. 4.4-fold and 5.0-fold higher current density and acetate production rate were reached on GN–CNTs modified electrode versus a carbon cloth control for the microbial reduction of carbon dioxide by C. ljungdahlii. Recovery of electrons consumed in acetate was 70–80% for all electrodes. Importantly, the GN–CNTs exhibited a high specific surface area of 344.17 m−2 g−1, 3.2-fold higher than that of the unmodified electrode. This study paves a feasible pathway to prepare efficient carbon nanomaterials with highly conductive 3D architecture cathode and high performance for energy storage and conversion in MES. It's also an attempt to make a nanomaterial extremely efficient from an engineering perspective for enhancing the bacteria–electrode interaction and microbial extracellular electron transfer.