Photostable p-Type Dye-Sensitized Photoelectrochemical Cells for Water Reduction

Abstract

A photostable p-type NiO photocathode based on a bifunctional cyclometalated ruthenium sensitizer and a cobaloxime catalyst has been created for visible-light-driven water reduction to produce H2. The sensitizer is anchored firmly on the surface of NiO, and the binding is resistant to the hydrolytic cleavage. The bifunctional sensitizer can also immobilize the water reduction catalyst. The resultant photoelectrode exhibits superior stability in aqueous solutions. Stable photocurrents have been observed over a period of hours. This finding is useful for addressing the degradation issue in dye-sensitized photoelectrochemical cells caused by desorption of dyes and catalysts. The high stability of our photocathodes should be important for the practical application of these devices for solar fuel production.

A Dynamic View of Proton-Coupled Electron Transfer in Photocatalytic Water Splitting

“…Furthermore, the coupling between the WOC, the chromophore and an electron accepting semiconductor into a photoanode has been achieved through co-absorption of both the catalyst and the chromophore 16,[29][30][31][32] or through dye-WOC supramolecular complexes. [33][34][35][36] Acquiring a fundamental understanding of the electron transfer processes and catalytic water oxidation mechanism following light excitation of the photoanode is essential for the design and the optimization of solar fuel cells. However, this is a challenging task mainly because of the different time scales of the processes occurring upon photoexcitation.…”

Nanostructured p-Type Semiconductor Electrodes and Photoelectrochemistry of Their Reduction Processes

“…One of the main concerns at the basis of the development of PECs for water splitting [71] which produce molecular H 2 at the (photo)cathode and O 2 at the (photo)anode is the replacement of precious metals like Pt or Ru photoelectrocatalysts with durable semiconducting electrodes of p-type based on cheaper metal oxides, phosphides and sulfides/disulfides or Si, in order to photoactivate HER (hydrogen evolution reaction). Due to the wide employment in p-DSCs, NiO photocathodes have been considered also for the application of photoelectrochemical generation of H 2 in a variety of sensitization schemes and surface decorations (Figures 11-14) [36,[72][73][74][75][76][77][78][79].…”

“…The Co center of CodmgBF2 complex is coordinated by a pendant pyridine group of O22. Reproduced with permission from reference [74]. The Ru-complex O22 immobilized on NiO surface is the dye-sensitizer acting as an electron donor towards the co-catalyst CodmgBF 2 , and as an electron acceptor from NiO.…”

“…The Co center of CodmgBF 2 complex is coordinated by a pendant pyridine group of O22. Reproduced with permission from reference [74]. Two main types of photocathode configuration have been identified with NiO surface being sensitized by a colorant (either organometallic (Figure 11) or organic ( Figure 12)), which is electronically connected to the actual electrocatalyst of molecular hydrogen formation [74,75].…”

“…Upon excitation of the QD this transfers an electron to the co-catalyst (usually a metal complex) and receives an electron from NiO in order to get regenerated for a successive cycle. Two main types of photocathode configuration have been identified with NiO surface being sensitized by a colorant (either organometallic (Figure 11) or organic ( Figure 12)), which is electronically connected to the actual electrocatalyst of molecular hydrogen formation [74,75]. Another main typology of photocathode configuration is represented by the sensitization of NiO with quantum dots (QD) made of a second p-type semiconducting material with lowered VB edge with respect to NiO, e.g., CdSe (Figures 13 and 14) [72,78].…”