Enhancement of H2-water mass transfer using methyl-modified hollow mesoporous silica nanoparticles for efficient microbial CO2 reduction

• Outstanding H 2 dissolution in bacterial medium. • High volumetric mass transfer coefficient of H 2 . • Development of a hybrid catalysis system. • High PHB yield. Inorganic-microbial hybrid catalysis is an emerging technology that uses electrical energy to drive microorganisms to reduce CO 2 into high value-added compounds, and it has broad application prospects in CO 2 reduction. However, the low current density (production yield) limits its practical application. Hydrogen-mediated inorganic-microbial hybrid catalysis system can achieve higher current density, but it is limited by low H 2 mass transfer. Here, silica nanoparticles were used to enhance the hydrogen mass transfer for highly efficient CO 2 reduction. Solid silica (SN), mesoporous silica (MSN), hollow mesoporous silica (HMSN), and methyl-modified hollow mesoporous silica (MHMSN) were firstly prepared and tested for the enhancement of hydrogen mass transfer. Of these, MHMSN nanoparticles at a concentration of 0.3 wt% were the best at enhancing gas-liquid mass transfer, the volumetric mass transfer coefficient (K L a) and saturated dissolved hydrogen concentration of H 2 are 0.53 min -1 and 1.81 mg l -1 , respectively. Compared with the control group without added nanoparticles, MHMSN significantly increased the solubility and K L a of H 2 . This can be attributed that the addition of MHMSN promoted the detached process of hydrogen bubbles from the electrode surface, which made the diameter of hydrogen bubbles smaller, increased the gas-liquid mass transfer area, and strengthened the mass transfer process of H 2 . Furthermore, it was added to the inorganic-microbial hybrid catalysis system to effectively promote the microbial carbon reduction process, achieving a polyhydroxybutyrate (PHB) yield of up to 700 mg l -1 , and the electron utilization rate and CO 2 conversion rate were 51 % and 58 % higher than the control group, respectively. These results demonstrated that the addition of MHMSN is an effective approach to enhancing the performance of H 2 -mediated inorganic-microbial hybrid catalysis system.