Spontaneous Solar Syngas Production from CO₂ Driven by Energetically Favorable Wastewater Microbial Anodes

The photoelectrochemical (PEC) reduction of CO₂ to syngas is an attractive strategy for solar-to-fuel conversion. However, the high overpotential, inadequate selectivity, and high cost demand for alternative solutions. Here, we demonstrate a hybrid microbial photoelectrochemical (MPEC) system that contains a microbial anode capable of oxidizing waste organics in wastewater and reducing the oxidation potential by 1.1 V compared with abiotic water oxidation using a PEC anode. Moreover, the MPEC employs a power management circuit (PMC) to enable parallel low-energy-producing reactions operated in the same solution medium to conquer high-overpotential reactions. The nanowire silicon photocathode integrated with a selective single-atom nickel catalyst (Si NW/Ni SA) achieved up to ∼80% faradic efficiency for CO generation with a highly tunable CO:H₂ generation ratio (0.1 to 6.8). When the bioanode was coupled with the Si NW/Ni SA, up to 1.1 mA cm⁻² of spontaneous photocurrent density was obtained for high-rate syngas generation.