Microbial electrosynthesis (MES) of organics from carbon dioxide has been recently put forward as an attractive technology for the renewable production of valuable multi-carbon reduced end-products and as a promising CO 2 transformation strategy. MES is a biocathode-driven process that relies on the conversion of electrical energy into high energy-density chemicals. However, MES remains a nascent concept and there is still limited knowledge on many aspects.It is still unclear whether autotrophic microbial biocathode biofilms are able to selfregenerate under purely cathodic conditions without any external electron or organic carbon sources. Here we report on the successful development and long-term operation of an autotrophic biocathode whereby an electroactive biofilm was able to grow and sustain itself with CO 2 and the cathode as sole carbon and electron source, respectively, with H 2 as sole product. From a small inoculum of 15 mg COD (in 250 mL), the bioelectrochemical system operating at -0.5 V vs. SHE enabled an estimated biofilm growth of 300 mg as COD over a period of 276 days.A critical aspect is that reported performances of bioelectrosynthesis of organics are still insufficient for scaling MES to practical applications. Selective microbial consortia and biocathode material development are of paramount importance towards performance enhancement. A novel biocompatible, highly conductive three-dimensional cathode was manufactured by direct growth of flexible multiwalled carbon nanotubes on reticulated vitreous carbon (NanoWeb-RVC) by chemical vapour deposition (CVD). The results demonstrated that: (i) the high surface area to volume ratio of the macroporous RVC maximizes the available biofilm area while ensuring effective mass transfer to and from the biofilm, and (ii) the nanostructure enhances the bacteria-electrode interaction, biofilm development, microbial extracellular electron transfer, and acetate bioproduction rate.However, for scale-up beyond certain sizes, there are some limitations with the CVD technique. We harnessed the throwing power of electrophoretic deposition technique (EPD), suitable for industrial scale production, to form multi-walled CNT coatings onto RVC to generate a new hierarchical porous structure, hereafter called EPD-3D. A very effective mixed microbial consortium was successfully enriched and transferred to EPD-3D reactors and demonstrated drastic performance enhancement reaching biocathode current density of -102 ± 1 A m -2 and acetate production rate of 685 ± 30 g m -2 day -1 .ii An in-depth understanding on how electrons flow from the cathode to the terminal electron acceptor is still missing but crucial (e.g. for improved reactor design). High rates of acetate production by microbial electrosynthesis was shown to occur via biologically-induced hydrogen, likely through the biological synthesis of metal copper particles, with 99 ± 1% electron recovery into acetate. The acetate-producing bacteria showed the remarkable ability to consume a high H 2 flux (ca. 1.15 m ...