title: Parameters affecting the chemical work output of a hybrid photoelectrochemical biofuel cell.
abstract: A hybrid photoelectrochemical biofuel cell employing the photoanode architecture of a dye-sensitized solar cell has been assembled. A porphyrin dye sensitizes a TiO(2) semiconductor over the visible range to beyond 650 nm. Photoinduced charge separation at the dye-TiO(2) interface results in electron migration to a cathode, and the holes generated on surface bound dyes oxidize soluble electron mediators. The increased [Ox] : [Red] ratio of the mediator drives the solution-based enzymatic oxidation of appropriate substrates. In this report we investigate how the accumulation of anodic and cathodic products limits cell performance. The NAD(+)/NADH and benzoquinone/hydroquinone redox couples were studied as sacrificial electron donors in the absence of appropriate enzymes or substrates. Comparatively poor cell performance was observed using the benzoquinone/hydroquinone couple. This effect is explained in terms of rapid charge recombination by electron donation from the electrode to benzoquinone in solution, as compared to much less recombination with NAD(+). With the NAD(+)/NADH couple the cell performance is relatively independent of the redox poise of the anode solution, but limited by accumulation of reduction products in the cathodic compartment. Using the NAD(+)/NADH couple, the photochemical reforming of ethanol to hydrogen was demonstrated under conditions where the process would be endergonic in the dark.
authors.affiliation: The Center for the Study of Early Events in Photosynthesis, Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287-1604, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Hambourger
authors.forename: Paul A
authors.initials: PA
authors.lastname: Liddell
authors.forename: Devens
authors.initials: D
authors.lastname: Gust
authors.forename: Ana L
authors.initials: AL
authors.lastname: Moore
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Moore
mesh_terms: D016227:Benzoquinones / Q000737:chemistry; D001674:Bioelectric Energy Sources / Q000592:standards*; D004396:Coloring Agents / Q000737:chemistry*; D004563:Electrochemistry; D004566:Electrodes; D006873:Hydroquinones / Q000737:chemistry; D009243:NAD / Q000737:chemistry; D010084:Oxidation-Reduction; D010777:Photochemistry; D011166:Porphyrins / Q000737:chemistry*; D012666:Semiconductors; D013499:Surface Properties; D013816:Thermodynamics; D014025:Titanium / Q000737:chemistry
chemical_list: D016227:Benzoquinones; D004396:Coloring Agents; D006873:Hydroquinones; D011166:Porphyrins; D009243:NAD; C009495:titanium dioxide; C004532:quinone; D014025:Titanium; C031927:hydroquinone