Fig. 7. Nanowire PEC systems for overall solar fuel production.

(A to D) Nanowire photochemical diodes for water splitting. (A and B) Bilayer Ru/Rh-SrTiO₃–BiVO₄ nanowire mesh, reproduced with permission from Liu et al. (34). (C and D) Si/TiO₂ nanotree, adapted with permission from Liu et al. (35). (A and C) False color: SEM images. (B and D) Energy schemes. (E and F) Bacteria-nanowire interfaces for light-driven acetate production. (E) S. ovata bacteria are interfaced to a Si nanowire electrode. Unassisted acetate production is performed by wiring the Si nanowire photocathode to a TiO₂ photoanode, reproduced with permission from Liu et al. (72). (F) Wood-Ljungdahl pathway for acetate production within an S. ovata bacterium, adapted with permission from Su et al. (161). (G) Efficient nanowire photochemical diodes require further development on the light harvesting and catalysis sides. A positive shift in the cathodic signal can be obtained by using catalysts with lower overpotentials for CO₂RR and HER or photocathodes providing higher photovoltages and photocurrent outputs. Similar effects can increase the activity of a photoanode on the OER side. A suitable integration of the oxidative and reductive sides in a single–optical path system is required to maximize light absorption.