Growth of carbon nanotubes on graphene as 3D biocathode for NAD ⁺ /NADH balance model and high-rate production in microbial electrochemical synthesis from CO ₂

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 CO ₂ 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.