Photosynthetic Biohybrids with Carbon Dots for Solar Hydrogen Production from Wastewater

Climate risks and rising energy prices necessitate the adoption of clean energy technologies  like solar fuels to reduce our dependence on fossil fuels. Solar-produced hydrogen (H2) is a  carbon-free fossil fuel alternative. Conventional H2production often requires clean water as  feedstock. In a mature hydrogen economy, this would strain the water sector, and increase  energy costs. To address this challenge,using wastewater as hydrogen feedstockis  proposed as a sustainable solution. Coupling the photonic/electronic properties of inorganic  materials (abiotic) with the metabolic properties of natural microbes (biotic) is a new route to  producing solar fuels. The biohybrids reported so far coupled non-photosynthetic bacteria  likeEscherichia coliwith rare-earth materials like CdS, CdSe, AgInS2Quantum Dots (QDs),  which generate photo-energized electrons under sunlight to stimulate H2production in the  microbe. While these studies are promising, the area is still in its early stage (Technology  Readiness Level: 1-3), and there are several challenges that need to be addressed, namely (1)  Sluggish abiotic-biotic charge transport and a lack of a mechanistic understanding of the  biotic/abiotic interfaces (2) poor H2yield, and (3) Use of expensive, toxic, and rare-earth  inorganic materials in the hybrids.     This project aims to develop and evaluate functional biohybrids by integrating electroactive/photosynthetic microbes with earth-abundant photocatalysts. Efficient  charge transport from an inorganic semiconductor to a microbial enzyme requires energy-level  alignment. Previous works have built biohybrids by pairing various QDs with microbes,  but no detailed evaluation of band alignment has been made. We proposeCarbon-based  Quantum Dots(CDs) as the abiotic photoactive material in the biohybrid, which could be an earth-abundant/low-cost/non-toxic alternativeto the conventional Cd-based QDs. We aim  to enhance the abiotic/biotic charge transport by optimizing theenergy-level alignmentby engineering the QDsthrough chemical doping. The microbe-photocatalyst interfaces will be  probed byPhotoconductive/Kelvin Probe Atomic Force Microscopy at a single-cell level  to widen ourfundamental understanding of the abiotic/biotic interfaces, paving the way  for improved biohybrids. Further to material-level engineering, the H2yield can also be  increased through pragmatic device design. Adopting design principles from microbial-electrochemical  devices, which are more mature than biohybrids, could help in designing  more efficient biohybrid devices. While microbial-electrochemical devices require external  electricity to operate, which is a limitation, the systems have reportedH2yields as high as  8L/L/day.We propose designingtandem-structure prototypeswith integrated microbial-electrochemical  and photo-biocatalytic systems and evaluating their performance forsolar  H2production from wastewaterwithout external electricity input.