Highly Efficient Photodecomposition of Ammonia by a Nanoporous Semiconductor Photoanode and an O_2-Reducing Cathode with Internal Quantum Efficiency over 300 (=3 × 10~4%)

摘要

UV light-activated and highly efficient photodecomposition of an ammonia aqueous solution was achieved to produce dinitrogen (N_2) by a Biophotochemical Cell (BPCC) comprised of a nanoporous semiconductor film photoanode and an O_2-reducing cathode with high internal quantum efficiency over 300(=3×10~4%). It was shown that a BPCC composed of a photoanode/cathode unit and a large volume reaction chamber is effective as an efficient cell. When the reaction chamber volume was increased, the total decomposition increased to a great deal, almost linearly with the cell volume. Major decomposition reaction was concluded to be dark auto-oxidation of the activated ammonia by the bulk O_2 into N_2, and its internal quantum efficiency, i.e., quantum efficiency of the NH_3 decomposition versus the UV light-activated NH_3, exceeded 300. Even based on the total incident UV light, the photodecomposition quantum yield reached 40 (=4000%).