Enzyme Mediated Increase in Methanol Production from Photoelectrochemical Cells and CO₂

While success has been shown in utilizing photocatalytic systems to reduce CO₂ in water, most of these studies have yielded formic acid as the major product with trace amounts of formaldehyde or methanol. One reason for this is the strong equilibrium of formaldehyde toward the hydrate methanediol. To increase methanol yields from CO₂, we show here the combined use of the biological catalyst alcohol dehydrogenase (ADH) from Saccharomyces cerevisiae with CO₂ reduction products obtained from photoelectrochemical cells (PEC). We first show that ADH can reduce very low micromolar amounts of formaldehyde in solution. Upon adding ADH to the PEC products, a rapid three- to four-fold gain in methanol production was observed, which we also attribute to the lack of back reaction by the enzyme. Lastly, because formaldehyde dehydrogenase (FalDH) showed very low reactivity with formate, the addition of FalDH and ADH to the PEC products demonstrated no difference in methanol yields as compared to ADH alone.