Photoelectrochemical hydrogen evolution on macroscopic electrodes of exfoliated SnSe flakes

Tin(II) selenide (SnSe) is an attractive photocathode candidate for performing photoelectrochemical (PEC) hydrogen evolution reaction (HER), because of its negative conduction band position relative to the HER redox level and a high absorption coefficient for efficiently harvesting solar energy. To prepare thinner layered SnSe flakes from larger size commercial SnSe crystals, liquid phase exfoliation (LPEx) was employed in isopropanol/water mixtures (IPA/H2O) and pure IPA. Macroscopic (1 cm2) electrodes were prepared from the exfoliated SnSe flakes by immobilizing them on glassy carbon electrodes. These flakes obtained by exfoliating the as-received commercial SnSe in pure IPA exhibited 10 times higher PEC activity than those prepared in IPA/H2O. An additional size separation to make three different size fractions of SnSe crystals served to further optimize the LPEx process. Electrodes prepared from the largest flakes showed the highest photocurrent density of 2.44 ± 0.65 mA cm–2 at −0.74 V versus RHE under 1 Sun, and ∼ 30% incident-photon-to-electron conversion efficiency at 900 nm. Decoration of the SnSe surface with Pt catalyst islands further improved the PEC activity to 4.39 ± 0.15 mA cm–2. This photocurrent density represents the highest value reported to date on macroscopic electrodes assembled from SnSe

Cobalt hexacyanoferrate: compound stoichiometry, infrared spectroelectrochemistry and photoinduced electron transfer

The cobalt hexacyanoferrate system, Mh [FeB(CN)6]l, (where M is an alkali metal cation, and the subscripts h, k, and l are stoichiometric coefficients, and A and B are the formal oxidation states of the Co and Fe metal sites in the structure) was shown to contain a rich series of compounds that are inter-linked through various redox processes (involving both electron and cation transfer) either in the dark or under the near-infrared (IR) activation. These processes were studied by a combined use of cyclic voltammetry, in situ IR spectroelectrochemistry (using both intensity or potential modulation), and ex situ X-ray photoelectron spectroscopy.Centro de Investigación y Desarrollo en Tecnología de Pintura

Spectroelectrochemistry of palladium hexacyanoferrate films on platinum substrates

Among the Prussian blue analogs, palladium hexacyanoferrate is of interest from electrochromic and catalytic perspectives, but has not been extensively studied to date. In this paper was report on the combined use of cyclic voltammetry and in situ infrared and UV- vis spectroelectrochemistry of PdHCF films potentiodynamically grown on platinum electrodes.Centro de Investigación y Desarrollo en Tecnología de Pintura

Peeling off the surface: Pt-decoration of WSe2 nanoflakes results in exceptional photoelectrochemical HER activity

Photoelectrochemical (PEC) hydrogen evolution reaction (HER) was studied on exfoliated, pristine and Pt-decorated tungsten diselenide (p-WSe2) nanoflake samples, using a previously developed microdroplet PEC microscopy approach. The WSe2 nanoflakes had well-defined thicknesses as measured by atomic force microscopy, and the Pt nanoparticles (NPs) were deposited by a variable number of atomic layer deposition (ALD) cycles. An exceptionally high photocurrent density of 49.6 mA cm−2 (under 220 mW cm−2 irradiation) and internal-photon-to-electron-conversion efficiency (∼90% at 550 nm) were demonstrated on these Pt-decorated WSe2 (WSe2-Pt) photocathodes. The Pt NP loading and thickness of WSe2 nanoflakes (in the 24–235 nm range) were used to fine-tune their PEC activity for HER. We found similar charge transfer and surface recombination kinetics of pristine and WSe2-Pt specimens (as assessed by intensity-modulated photocurrent spectroscopy), which indicated significant differences in their bulk properties. X-ray and ultraviolet photoelectron spectroscopies were performed to identify defect states and quantify the density of states around the valence band of WSe2. The elevated temperature of the ALD process and the evolving Pt NP phase conspired to passivate the sub-surface (i.e., bulk) defects in the WSe2 nanoflakes, resulting in their vastly improved PEC performance

Hybrid Cathodic/Anodic Electrosynthesis of Phase Pure Ag4V2O7 Thin Films

Here, we demonstrate a two-step electrosynthesis approach for the preparation of silver pyrovanadate, Ag4V2O7 in thin-film form. In the first, cathodic step, polycrystalline Ag was deposited on fluorine doped tin oxide (FTO) substrate from a non-aqueous bath. Aqueous pyrovanadate species were then generated by aging of a CO2-infused sodium orthovanadate (Na3VO4) solution for three weeks. Silver ions were subsequently generated in situ in this medium using anodic stripping of the Ag/ITO films from the first step. Interfacial precipitation of the Ag+ ions with the pyrovanadate species afforded the targeted product in phase pure form. The various stages of the electrosynthesis were monitored in situ via the combined use of voltammetry, electrochemical quartz crystal nanogravimetry (EQCN), and coulometry. The Ag4V2O7 thin films were characterized by a variety of experimental techniques, including X-ray diffraction, laser Raman spectroscopy, diffuse reflectance spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. Surface photovoltage spectroscopy, ambient-pressure photoemission spectroscopy, and Kelvin probe contact potential difference (work function) measurements afforded information on the energy band structure of the p-type Ag4V2O7 semiconductor. Finally, the electrochemical and photoelectrochemical properties of the electrosynthesized Ag4V2O7 thin films were studied in both aqueous and non-aqueous electrolytes