Photocatalysts and Photoelectrodes James L. White,† Maor F. Baruch,† James E. Pander III,† Yuan Hu,† Ivy C. Fortmeyer,† James Eujin Park,† Tao Zhang,† Kuo Liao,† Jing Gu,‡ Yong Yan,‡ Travis W. Shaw,† Esta Abelev,† and Andrew B. Bocarsly*,† †Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States ‡Chemical and Materials Science Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States

Light-Driven Heterogeneous Reduction of Carbon Dioxide: Photocatalysts and Photoelectrodes

Electrochemistry of polynuclear transition metal cyanides: Prussian blue and its analogues

This review focuses on the electrosynthesis, in situ characterization, and technological applications of Prussian blue analogues with the generic formula AhMk[Fe(CN)6]l·mH2O, where h, k, l, and m are stoichiometric numbers, A = alkali metal cation, and M is a transition metal. Six such metal hexacyanoferrate (MHCF) compounds derived from Cu, Pd, In, V, Co, and Ni are featured in this article against the backdrop of the Prussian blue parent compound itself and other related compounds. The use of cyclic voltammetry and complementary techniques including scanning probe microscopies, quartz crystal microgravimetry, and ac impedance spectroscopy, for studying the growth of MHCF films on targeted substrates, is discussed. Spectroelectrochemical in situ characterization of these films in the UV−visible and IR regions is then reviewed. Finally, the use of Prussian blue and its analogues in devices for displays and “smart” windows, photoimaging, environmental remediation, chemical/biological sensing, energy conver...

Metal Hexacyanoferrates: Electrosynthesis, in Situ Characterization, and Applications

Summary It is shown how the well-known photoeffects observed at semiconductor electrodes can be used to construct an electrochemical photocell. The photovoltaic effects in such cells are based on the formation of a Schottky barrier at the interface between a semiconductor and a suitable redox electrolyte. A cell design is developed and some results with CdS, CdSe or GaP electrodes are presented. The characteristics of such photocells and the problems involved in their application as solar cells are discussed.

Electrochemical Solar Cells are Schottky Barrier Devices. A Citation-Classic Commentary on Electrochemical photo and solar cells: Principles and some experiments

Chemistry of Transition Metal Cyanide Compounds: Modern Perspectives

The potential use of II–VI semiconductor–aqueous junction cells for the conversion of optical energy to electricity has previously been limited by semiconductor photodecomposition processes combined with low energy conversion efficiencies. Decomposition processes in the prototypical n-CdS photoelectrochemical cell can be efficiently suppressed by addition of an appropriate polychalcogenide redox couple to the electrolyte1–3. However, conversion efficiencies remain low (∼5% at 488 nm)4. Moreover, although increased optical to electrical energy conversion rates can be obtained by using a redox couple such as Fe(CN)4−/3−6 (∼8% conversion efficiency at 488 nm), the cell lifetime is greatly diminished5–7 (t1/2∼1/2h). We report here that the photodecomposition of n-CdS in a Fe(CN)4−/3−6 electrolyte can be dramatically decreased and cell output parameters significantly improved by the presence of an appropriate combination of K+ and Cs+ ions. Monochromatic (488 m) conversion efficiencies in excess of 20% have been observed, with fill factors (a measure of the ideality of the cell) in the range of 65%. The enhanced stability and efficiency are associated with in situ chemical derivatization of the n-CdS surface with a layer of Kx Csy[CdIIFeII(CN)6]. (This species is an analogue of Prussian blue having a C-bound FeII/III centre and a nitrogen bound CdII centre. See, for example, ref. 8.)

Role of surface reactions in the stabilization of n-CdS-based photoelectrochemical cells

The stability of in a electrolyte is demonstrated to be due to the formation of a overlayer. Mediated hole transfer through the overlayer to solution competes with photoanodic decomposition of the electrode. The charge transfer energetics and kinetics of the overlayer are very sensitive to the supporting electrolyte cation. Variations in supporting electrolyte allow maximization of overlap between the semiconductor states and the filled levels of the surface couple. This leads to enhanced energy conversion efficiencies and minimization of electrode decomposition. For the electrode, a supporting electrolyte containing both K+ and Cs+ is found to maximize cell performance. A surface state responsible for deleterious electron transfer through the barrier is observed ~600 mV positive of the conduction bandedge. Cells with monochromatic efficiencies in excess of 20% (488 nm) can be obtained by considering the overlayer properties.

Holly-Dee Rubin

Papers

Role of surface reactions in the stabilization of n-CdS-based photoelectrochemical cells

Overlayer Formation as a Source of Stability in the N‐Type Photoelectrochemical Cell: The Cell

Overlayer Formation as a Source of Stability in the N-Type Photoelectrochemical Cell. The N-CdS/Fe(CN)4-/3- 6 Cell.

The n-cadmium selenide photoelectrochemical cell: wavelength-dependent photostability