Fig. 2

Photobioelectrochemical cells (PBECs). a PBEC with a photoanode. CO₂ is reduced into formate by a formate dehydrogenase (FDH) via NADH [114]. In this system, an IEM separated the electrodes. b PBEC with a photocathode. In the first example, M. barkeri oxidized H₂ coming from the photocathode to reduce CO₂ into methane [90]. In the second example, a carbon monoxide dehydrogenase (CODH) acquired electrons directly from the photocathode to reduce CO₂ into CO [113]. An IEM was present in example 1 while example 2 was a single-chamber reactor. c PBEC with a photoelectrodes tandem. In the first example, S. ovata acquired electrons directly from a photocathode to reduce CO₂ into acetate [98]. Acetate is then converted to other products by E. coli. In the second example, M. barkeri reduced CO₂ into methane with H₂ from the PEC [90]. In the third example, methanol is produced from CO₂ by an enzymatic cascade acquiring electrons from a photocathode via a rhodium complex and NADH [115]. Examples 1 and 2 comprised an IEM, while photoelectrodes in example 3 were separated by a salt bridge