# A Living Semiartificial Photoelectrocatalytic Biohybrid for Solar CO2 Fixation and Fermentation to Fatty Acids

## TL;DR

A new system uses sunlight and bacteria to convert CO2 into useful chemicals and fuels, without needing expensive materials or additives.

## Contribution

A semiartificial biophotoelectrochemical platform that achieves stable and efficient CO2 fixation and fermentation into long-chain fatty acids using microbial consortia.

## Key findings

- The system produced acetate and ethanol with high Faradaic efficiency using a CuBi2O4 photocathode and Sporomusa ovata.
- Clostridium kluyveri extended the chain length, producing butyrate and caproate, the longest-chain solar-driven CO2-derived products reported.
- The system operated stably for 140 hours, a record for Cu-based systems, without redox mediators or H2.

## Abstract

To address the global
climate and energy crisis, innovative strategies
are urgently needed to transform CO2 into sustainable fuels
and chemicals. We present a semiartificial biophotoelectrochemical
(BPEC) platform, combining solar energy conversion with naturally
evolved microbes to develop solutions for transforming CO2 and water into multicarbon productswithout sacrificial additives
or precious materials. This remains extremely challenging for fully
artificial photocatalytic systems. Our system features a scalable
and low-cost CuBi2O4 photocathode, stabilized
by a thin MgO interlayer, in direct contact with the CO2-fixing bacterium Sporomusa ovata grown
on the electrode surface. This interface enables direct electron uptake,
eliminating the need for diffusible redox mediators or externally
supplied H2limitations commonly seen in bionic
leaf systems. The BPEC operated stably for 140 h (5.5 days), a record
duration for a Cu-based system, producing 673.2 ±  71.4
μM cm–2 acetate and 683 ± 55.2 μM
cm–2 of ethanol with a Faradaic efficiency of 69%
for C2 products. Subsequent addition of Clostridium kluyveri enabled biological chain elongation,
producing 1.31  ±  0.2 μmol butyrate (C4) and 0.6  ±  0.1 μmol caproate (C6), with 0.72  ±  0.2 μmol H2 as a fermentation byproduct. To our knowledge, this represents the
longest-chain solar-driven CO2-derived product reported
to date, highlighting a critical advance in artificial photosynthesis.
This approach demonstrates the power of pairing stable photoelectrochemical
interfaces with microbial consortia to utilize CO2 as a
feedstock for solar chemical production.