Butanol condensation facilitated by Bias-free and light-driven enzymatic biofuel cell

Fossil fuels are a finite and polluting source of energy. As global energy consumption rises alongside greenhouse gas emissions, future alternatives are needed. Renewable fuels present a promising alternative but require coupling the fuel synthesis with another process to achieve economic viability. Methods for renewable fuel production often employ abiotic catalysts. However, these catalysts can be expensive, non-selective, and frequently require harsh conditions. Alternatively, natural catalysts and processes can be used at ambient conditions. Combining abiotic and biotic elements enabled a greener approach. Herein, we present a bias-free, light-driven system for butanol condensation using solely inexpensive catalysts. The holistic configuration enabled butanol oxidation to butanal, followed by condensation into 2-ethylhexenal. The conversion was facilitated using the alcohol oxidase (AOX) enzyme and beta-alanine organocatalyst. In parallel, the configuration also produced electrical power output using a bismuth vanadate (BiVO₄) based photoanode and a horseradish peroxidase (HRP) biocathode. The hydrogen peroxide produced by the AOX was reduced by HRP, generating more than 300 μW/cm². Furthermore, this configuration converted butanol to 2-ethylhexenal in a one-pot reaction, with and without applied bias. The amounts of 2-ethylhexenal converted reached 160 μM and 60 μM for biased and bias-free configurations over 3 h of activation, respectively.