To improve the photoelectrochemical (PEC) performance of BiVO4, three different modifications (doping, heterojunction, and catalyst deposition) using earth-abundant elements are performed and their effects are compared in a 0.1 M phosphate electrolyte at pH 7 under AM1.5 light (100 mW/cm2). When a hexavalent element (Cr6+, W6+, or Mo6+) is doped at various levels, the Mo6+-doping effect is most significant at 10 atomic % with about two times higher photocurrent generation at the oxygen evolution potential (1.23 VRHE). Such enhancement is attributed to a decrease in charge transfer resistance (R ct) by donor doping, resulting in an approximate 2-fold increase in charge separation efficiency (ηsep) to about 25%. W6+ is less effective than Mo6+, whereas Cr6+ has a detrimental effect. To further improve the charge separation efficiency of Mo6+-doped BiVO4 (Mo-BiVO4), a approximate 600 nm thick WO3 layer is deposited under a similarly thick Mo-BiVO4 layer. This binary heterojunction (WO3/Mo-BiVO4) exhibits ηsep of about 50% along with more than 3 times higher photocurrent generation. On the other hand, an oxygen evolving cobalt-phosphate (Co-Pi) catalyst electrodeposited to Mo-BiVO4 (Mo-BiVO4/Co-Pi) enhances charge injection efficiency (ηinj) from ∼50 to ∼70% at 1.23 V RHE. These two binaries are coupled into a ternary heterojunction (WO3/Mo-BiVO4/Co-Pi) in order to improve the charge transfer efficiencies (ηsep and ηinj). The PEC performance of this ternary is significantly high with photocurrent density of about 2.4 mA/cm2 at 1.23 VRHE (corresponding to the solar-to-hydrogen efficiency of ca. 3%) due to ηsep and ηinj of ∼60 and 90%, respectively.

The photoelectrochemical properties of template-engineered epitaxial BiVO4 photoanodes have been enhanced approximately 10 times that of bare BiVO4.

No abstract

No abstract

We demonstrate the use of graphene based transparent sheets as a p-type current spreading layer in GaN light emitting diodes (LEDs). Very thin Ni/Au was inserted between graphene and p-type GaN to reduce contact resistance, which reduced contact resistance from ∼5.5 to ∼0.6Ω/cm2, with no critical optical loss. As a result, LEDs with metal-graphene provided current spreading and injection into the p-type GaN layer, enabling three times enhanced electroluminescent intensity compared with those with graphene alone. We confirmed very strong blue light emission in a large area of the metal-graphene layer by analyzing image brightness.

No abstract

To enhance the charge separation and kinetics of water oxidation using a BiVO4 photoanode, a BiVO4/ZnO nanowire heterostructure decorated with gold (Au) nanoparticles is fabricated as a photoanode for photoelectrochemical water splitting.

ZnO particles with rod and plate configurations were synthesized using a solvothermal method using zinc acetate and zinc chloride, respectively. The surface of the as-synthesized ZnO rods and plates were characterized using various analysis tools (XRD, XPS, photoluminescence, FE-SEM, HR-TEM, BET, and UV− vis) and their photocatalytic activities were examined for six different redox reactions. The surface areas and bandgaps of the two ZnO samples were nearly identical; however, XPS and photoluminescence (PL) studies showed that the rods and the plates have relatively pronounced oxygen vacancy and oxygen interstitial contributions, respectively. ZnO rods were found to be active for the decomposition of methylene blue and phenol, the production of OH radicals, and the generation of photocurrents, all of which are associated with single-electron transfer reactions. On the other hand, ZnO plates were more effective for the production of molecular hydrogen and hydrogen peroxide, both of which are initiated by two-electron transfer reactions. These single versus multiple charge transfers are discussed with regard to the roles of oxygen vacancies and oxygen interstitials, which are located near the conduction and the valence bands, respectively.