Solar-driven selective conversion of millimolar dissolved carbon to fuels with molecular flux generation.

The direct utilization of dissolved inorganic carbon in seawater for CO conversion promises chemical production on-demand and with zero carbon footprint. Photoelectrochemical (PEC) CO reduction (COR) devices promise the sustainable conversion of dissolved carbon in seawater to carbon products using sunlight as the only energy input. However, the diffusion-dominant transport mechanism and the near-zero concentration of CO(aq) (CO dissolved in aqueous solution) in static seawater has made it extremely challenging to achieve high solar-to-fuel (STF) efficiency and high carbon-product selectivity. Here, where CO(aq) as a reactant generated in situ by acidification of HCO flows continuously from BiVO photoanodes to Si photocathodes, enabling a single-step conversion of dissolved carbon into products. Our PEC device significantly increases the CO selectivity from 3% to 21%, which approaches the 30% theoretical limit according to multi-physics modeling. Meanwhile, the Si/BiVO PEC COR device achieved a STF efficiency of 0.71%. Such flow engineering achieves flow-dependent selectivity, rate, and stability in simulated seawater, thus promising practical solar fuel production at scale.