Enhanced H2O2 Production at Reductive Potentials from Oxidized Boron-Doped Ultrananocrystalline Diamond Electrodes.

This work investigates the surface chemistry of H2O2 generation on a boron-doped ultrananocrystalline diamond (BD-UNCD) electrode. It is motivated by the need to efficiently disinfect liquid waste in resource constrained environments with limited electrical power. X-ray photoelectron spectroscopy was used to identify functional groups on the BD-UNCD electrode surfaces while the electrochemical potentials of generation for these functional groups were determined via cyclic voltammetry, chronocoulometry, and chronoamperometry. A colorimetric technique was employed to determine the concentration and current efficiency of H2O2 produced at different potentials. Results showed that preanodization of an as-grown BD-UNCD electrode can enhance the production of H2O2 in a strong acidic environment (pH 0.5) at reductive potentials. It is proposed that the electrogeneration of functional groups at oxidative potentials during preanodization allows for an increased current density during the successive electrolysis at reductive potentials that correlates to an enhanced production of H2O2. Through potential cycling methods, and by optimizing the applied potentials and duty cycle, the functional groups can be stabilized allowing continuous production of H2O2 more efficiently compared to static potential methods.

Synthesis and Characterization of an Earth-Abundant Cu2BaSn(S,Se)4 Chalcogenide for Photoelectrochemical Cell Application.

Cu2BaSnS4-xSex films consisting of earth-abundant metals have been examined for photocathode application. Films with different Se contents (i.e., Cu2BaSnS4-xSex with x ≤ 2.4) were synthesized using a cosputter system with post-deposition sulfurization/selenization annealing treatments. Each film adopts a trigonal P31 crystal structure, with progressively larger lattice constants and with band gaps shifting from 2.0 to 1.6 eV, as more Se substitutes for S in the parent compound Cu2BaSnS4. Given the suitable bandgap and earth-abundant elements, the Cu2BaSnS4-xSex films were studied as prospective photocathodes for water splitting. Greater than 6 mA/cm2 was obtained under illumination at -0.4 V versus reversible hydrogen electrode for Pt/Cu2BaSnS4-xSex films with ∼60% Se content (i.e., x = 2.4), whereas a bare Cu2BaSnS4-xSex (x = 2.4) film yielded ∼3 mA/cm2 at -0.4 V/RHE.