Efficient H2 production and TN removal for urine disposal using a novel photoelectrocatalytic system of Co3O4/BiVO4 - MoNiCuOx/Cu

Urea is considered as the potential hydrogen carrier. However, decomposition of urea to generate hydrogen gas (H2) is severely constrained by sluggish kinetics and the high over-potential of HER. In this study, we propose a novel photoelectriccatalytic (PEC) system of Co3O4/BiVO4 - MoNiCuOx/Cu to realize efficiently H2 production and TN removal in urine treatment. The key design is that an appropriate valence band position of BiVO4 photoanode, which can generate Cl• selectively and suppress HO• extremely, is selected for rapidly converting urea to N2 instead of NO3-. Co3O4, as a co-catalyst of photoanode, matches exactly the Fermi level with BiVO4, driving the separation and transfer of photogenerated charge of BiVO4 greatly due to the built-in electric field of p-n heterojunction of Co3O4/BiVO4. Meanwhile, the yield of Cl• by Co3O4/BiVO4 has been improved by an orders of magnitude compared with BiVO4, WO3 and TiO2. On the other hand, the over-potential of HER is reduced to 49 mV ( −10 mA cm−2) by using MoNiCuOx nanowires cathode, which is prepared by in-situ growth of nanowires and the load of MoNi sites on copper foam. The PEC system exhibits excellent performance, in which the H2 production and TN removal were reached 0.68 mmol and 93.6% after 120 min, which is 2.4, 3.5, 11.0 times and 3.1, 4.6, 17.9 times respectively higher than those of BiVO4, WO3 and TiO2. Therefore, this study provides new insights in urine treatment and H2 generation.