A mesoporous silica-supported CeO2/cellulose cathode catalyst for efficient bioelectrochemical reduction of inorganic carbon to biofuels

In this study, a novel efficient cathode electrode was fabricated to convert inorganic carbon to volatile fatty acids (VFAs) through microbial electrosynthesis (MES) in a single chamber reactor. The cathode catalyst was made up of mesoporous silica (mS) coated with cerium oxide (CeO2) and carbonized cellulose (C) in which mS acted as a core material and both CeO2 and C acted as a shell material. CeO2/C was loaded on the porous surface of mS, which acted as catalytic centers to enhance the biochemical reactions. The C/CeO2@mS composite catalyst coated on carbon cloth (Cc) was characterized by XRD and FESEM and showed high crystallinity and a porous core–shell morphology. The cyclic voltammetry analysis indicated that the cathode with C/CeO2@mS exhibited higher catalytic activity (−0.59 mA cm−2 (background current)) than the other controls (0.26 mA cm−2 for MES-C and −0.06 mA cm−2 for MES-mS). Three MES reactors with different cathodes were comparatively operated for the conversion of CO2 (8 g L−1 of HCO3−), and MES-C/CeO2@mS exhibited maximum acetate production (19.1 ± 0.95 mM) followed by MES-C (10.8 ± 0.51 mM) and MES-mS (9.5 ± 0.33 mM). The coulombic efficiency (CE%) in MES-C/CeO2@mS was 76%, and it was 42% and 34% for MES-mS and MES-C, respectively. The maximum current generation (0.48 ± 0.21 mA cm−2) was obtained with MES-C/CeO2@mS at a relatively higher cathode potential (−0.61 mV) as compared with the other cathodes. MES-C/CeO2@mS showed a lower Tafel slope of 220 mV dec−1, which was 2.71 times lower than that of abiotic MES-C/CeO2@mS (598 mV dec−1) suggesting enhanced electrokinetics with exoelectrogenic biofilm development on the cathode electrode. This study clearly demonstrates that the C/CeO2@mS catalyst can be successfully used for highly efficient bioelectrochemical conversion of CO2 to value added products via a MES route.