Enhancing Solar-Driven CO₂ Reduction to Multi-Carbon Products via Adapted Whole-Cell Catalysts and a Silicon Nanowire Photocathode

Due to the anthropogenic CO₂ emissions, the atmospheric concentration of CO₂ exceeded 413 ppm in 2020, sharply increasing from 270 ppm at the beginning of the industrial revolution. Dramatic climate changes, such as extreme heat waves, wildfires, and droughts, are affecting human societies and ecosystems at such alarming levels that their influence can no longer be ignored. Thus, developing alternatives to fossil fuels and mitigating CO₂ emissions at a necessary scale is more urgent than ever to establish a carbon-neutral society. Catalytic CO₂ conversion to renewable fuels has been the focus of intensive research with the goal of closing the carbon loop. Photosynthetic biohybrid systems (PBSs), in which a photoactive semiconductor directly interfaces with nonphotosynthetic, CO₂-reducing bacteria, represent a promising approach for the renewable and sustainable production of fuels and chemicals. They combine the best features of semiconducting nanomaterials and biological whole-cell catalysts to power biocatalytic CO₂ conversion with light. Semiconducting nanomaterials can harvest solar energy efficiently. Nature’s catalytic machinery enclosed in its cellular environment provides low activation energies and exquisite product selectivity through its cascade reactions. We demonstrate that by tunning the local chemical environment of a silicon nanowire – acetogen <i>sporomusa ovata </i>(<i>S. ovata</i>) biohybrid, we can maximize the interfacial area between living cells and cathodes and boost the bioelectrochemical CO₂ reduction rate. In addition to optimizing the local environment, the rational design of biocatalysts in PBSs is imperative to reduce CO₂ into valuable chemicals effectively. We introduce a methanol adapted <i>S. ovata</i> to enhance the sluggish biocatalytic activity of wild-type microorganisms into our silicon nanowires (Si NWs) photocathodes for efficient solar-to-chemical conversion. Electrochemical impedance spectroscopy (EIS) is exploited to study the biohybrid system and the biofilm cathodes. We illustrate the fundamental charge transfer mechanisms at the biotic-abiotic interface between silicon nanowires and microorganisms. Using adapted <i>S. ovata</i> decreases the charge transfer resistance at the cathodes and facilitates charge transfer from directly interfaced solid electrodes. Finally, this new generation of biohybrids with adapted <i>S. ovata </i>enables an increase of solar CO₂ fixation under photoelectrochemical reducing environments on the Si NWs photocathode.