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GROWTH OF THE WORLD POPULATION AND SHORTAGE OF FOSSIL FUELS MANDATE OUR SOCIETY TO SEARCH FOR ALTERNATIVE CLEAN ENERGY USING APPROPRIATE PHOTOCATALYST. TIO2 HAS BEEN PROVEN TO BE THE MOST ACTIVE PHOTOELECTRODE FOR PHOTOELECTROCHEMICAL (PEC) APPLICATIONS BUT ITS WIDE BAND GAP LIMITS ITS USAGE IN UV REGION OF SOLAR SPECTRUM [1]. TO HARVEST THE UV/VISIBLE PORTION OF THE SOLAR SPECTRUM AND IMPROVE ITS CARRIER ELECTRICAL CONDUCTIVITY, THE PHOTOANODE CAN CONSIST OF TIO2 ACCOMPANIED WITH A VISIBLE ACTIVE NARROWER BAND GAP SEMICONDUCTOR SUCH AS BIVO4 AND GRAPHENE AS A MATERIAL WITH HIGH ELECTRON MOBILITY AND SURFACE AREA. IN THIS PAPER, WE HAVE USED BAND ENERGETIC CALCULATION TO DESIGN VISIBLE ACTIVE BIVO4/TIO2/GRAPHENENANOCOMPOSITE THIN FILM AND THEN SYNTHESIZED IT AS PHOTOANODE IN PEC CELL. THE PEC PERFORMANCE OF THE BIVO4/TIO2/GRAPHENENANOCOMPOSITE WAS COMPARED WITH PURE TIO2 AND TIO2/GRAPHENE PHOTOELECTRODE UNDER SIMILAR CONDITIONS. TIO2/GRAPHENE SOLUTION WAS PREPARED BY COUPLING TIO2 NANOPARTICLES SYNTHESIZED BY SOL-GEL METHOD ON GRAPHENE OXIDE (GO) SHEET VIA PHOTOCATALYTIC PROCESS AND THEN IT COATED ON TRANSPARENT CONDUCTING OXIDE SUBSTRATE (IN HERE FTO) BY SPIN COATING AND SUBSEQUENTLY ANNEALED UNDER ARGON GAS AT 350OC. AN EFFICIENT BIVO4 LAYER WAS FORMED BY DIPPING THE DEPOSITED TIO2/GRAPHENE THIN FILM ELECTRODE IN AN AQUEOUS NITRIC ACID SOLUTION OF BI (NO3)3 AND NH4VO3. SURFACE ANALYTICAL TECHNIQUES SUCH AS SEM, AFM, XPS ANALYSIS AND UV/VIS SPECTROSCOPY WERE USED TO DETERMINE CHEMICAL AND PHYSICAL PROPERTIES OF ALL INVESTIGATED FILMS. A THREE-ELECTRODE GALVANOSTAT/POTENTIOSTAT (AUTOLABPGSTAT302) WITH A PLATINUM AS COUNTER ELECTRODE, AG/AGCL AS REFERENCE ELECTRODE AND THE PREPARED THIN FILM SAMPLES AS WORKING ELECTRODE, 0.1M K2SO4 AQUEOUS SOLUTION AS ELECTROLYTE AND A XENON SHORT ARC LAMP (OSRAM 5000W HBM/OFR AS VISIBLE IRRADIATION SOURCE WITH THE INTENSITY OF ABOUT 1 SUN WERE USED TO EVALUATE THEIR PEC ACTIVITY. FIG.1 DEPICTS THE PHOTOCURRENT DENSITY OF DIFFERENT SAMPLES OBTAINED IN THE CHOPPED I-T CURVES AT CONSTANT APPLIED POTENTIAL OF 0.8 V VERSUS AG/AGCL REFERENCE ELECTRODE. AS SEEN, THE BIVO4/TIO2/GRAPHENENANOCOMPOSITEPHOTOELECTRODE EXHIBITS THE HIGHTESTPHOTOACTIVITY AT ABOUT 3 A/M2 AS COMPARED WITH THE TIO2 AND TIO2/GRAPHENEPHOTOELECTRODES. VISIBLE LIGHT ABSORPTION OF BIVO4, HIGH ELECTRON ACCEPTANCE OF THE GRAPHENE AND THE MULTISTEP ELECTRON TRANSFER ARE BELIEVED TO BE RESPONSIBLE FOR THE OBSERVED PHOTOENHANCEMENT.

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INCREASING WORLDWIDE DEMAND FOR ENERGY AND LIMITED FOSSIL FUELS RESERVES ON THE PLANET REQUIRE DEVELOPMENT OF RELIABLE AND RENEWABLE ENERGY SOURCES [1]. AMONG THE VARIOUS TECHNOLOGIES AVAILABLE NOWADAYS, PHOTOVOLTAIC IS BELIEVED TO BE ONE OF THE CLEANEST WAYS IN ACHIEVING THIS PURPOSE [2]. IN RECENT YEARS, INORGANIC SEMICONDUCTOR NANO CRYSTALS (KNOWN AS THE QUANTUM DOTS) HAVE BEEN FOUND TO BE PROMISING FOR NEXT GENERATION SOLAR CELLS [3]. UNTIL NOW MANY QUANTUM DOTS HAVE BEEN SENSITIZED AND AMONG THEM CDSE QDS HAS A GOOD PERFORMANCE. IN THIS STUDY THE MODIFIED CDS/CDSE/ZNS QUANTUM DOT PHOTO ANODE WITH MN2+ IONS DEPOSITED ON MESOPOROUS TIO2 FILM USING SUCCESSIVE IONIC LAYER ADSORPTION AND REACTION (SILAR) WAS DONE [4]. FOR IMPROVEMENT OF THE CELL PERFORMANCE, THE POLYSULFIDE ELECTROLYTE WAS USED [5]. AMONG DIFFERENT CHOICES EXISTED FOR THE CATHODE, CU2S WAS THE BEST [5]. IN ORDER TO MEASURE THE EFFICIENCY OF THE MODIFIED PHOTO ANODE, I-V CURVES OF THE CELL, VIA SOLAR SIMULATOR AND AUTO LAB SYSTEM, WERE OBTAINED. THE RESULTS SHOWED THAT QUANTUM DOT SENSITIZED SOLAR CELLS (QDSSCS) CONSTRUCTED WITH MN2+ IONS DOPED CDS/CDSE REPRESENT MORE POWER CONVERSION EFFICIENCY [5]. THE EFFICIENCY OF THE MN2+ DOPED QUANTUM DOT SOLAR CELL COMPARED WITH THE UNMODIFIED CELL, HAD AN IMPROVEMENT OF ABOUT 10%.

HYDROGEN IS A POTENTIAL ALTERNATIVE FOR FOSSIL FUELS, AND IT CAN BE PRODUCED FROM WATER IN A REDOX REACTION. THE ENERGY REQUIRED FOR THE WATER SPLITTING REACTION CAN BE OBTAINED FROM SOLAR IRRADIATION. THIS PROCESS IS CALLED PHOTOELECROCHEMICAL HYDROGEN PRODUCTION OR ARTIFICIAL PHOTOSYNTHESIS, ...