Upgrading algae waste into 3-D bio-cathode to enhance acetate synthesis by microbial electrosynthesis

[Display omitted] •Algae was upgraded into 3-D porous cathode via coupling phenolic resins and CaCO3.•Phenolic resins could improve N-doped by preventing N element loss in pyrolysis.•Acetate titer of the porous algal electrode was 1.7-fold higher than carbon felt.•Developed pores and high catalytic activity lead to efficient acetate synthesis.•C-O and N-doped was identified as active sites for enhanced electron transfer. Microbial electrosynthesis (MES) technology has already obtained widespread attraction for CO2 conversion and high value-added chemicals production. However, MES has been challenged by the high cost and poor electrocatalytic activity of bio-cathodes. This study proposed a solution for upgrading algae waste into 3-D porous block bio-cathode through the coupling of template modification with phenolic resin cross-linking. The resulting porous algal electrode (PAE) exhibited an enhanced structure with 3.22 % N-doped, high content of oxygen-containing functional groups (22.67 %), and macropore structure with an average pore size of 70 µm. Consequently, the PAE showed impressive acetate synthesis performance, reaching a remarkable 1020.86 mol/m3 and surpassing the commercial carbon felts (CF) by 1.7-fold at −1.1 V (vs. Ag/AgCl). Mechanistic studies indicated that microbial loading capacity in PAE was 1.31 times higher than that in CF. Additionally, the improved N-doped and oxygen-containing functional groups enhanced direct and indirect electron transfer between the electrode and the microorganisms, respectively. All of which contributed to the efficient synthesis of acetate. Therefore, this study not only developed an innovative 3-D porous bio-cathode for efficient CO2 conversion and high value-added chemicals production, but also provided a promising sustainable strategy for algae waste treatment and recycling.