Photoelectrocatalytic Production Of Hydrogen Peroxide From Tantalum Nitride-ordered Mesoporous Carbon

The conversion of the earth’s abundant renewable resources（solar energy,water and air）into H₂O₂ by means of photoelectrocatalysis（PEC）has a wide economic value and application potential.The process is easy to operate,the reaction conditions are mild and no secondary pollution is generated.However,the high overpotential of the water oxidation reaction（OER）at the photoanode,the low two-electron selectivity of the cathodic oxygen reduction process and the low overall mass transfer efficiency of the PEC device combine to limit the overall efficiency of H₂O₂ production by PEC.In this paper,a high-performance Mg:Ta₃N₅ tantalum nitride photoanode for water oxidation and a highly selective ordered mesoporous carbon（CC/CMK-3）cathode for oxygen reduction reactions（ORR）were prepared,and the Mg:Ta₃N₅ photoanode and CC/CMK-3 cathode were assembled into a custom-made PEC device.The results of the study are as follows:（1）The Mg:Ta₃N₅ photoanode was prepared by double electron beam evaporation and high temperature nitridation,and the small area（1 cm²）Ni Co Fe-B_i/Mg:Ta₃N₅photocurrent density reached 8.4 m A/cm² at 1.23 V_RHE after modification by Ni Co Fe-Bi co-catalyst,which could be stabilised for more than 200 min,and a larger area（10cm²）of Mg:Ta₃N₅ photoanodes were prepared.In parallel,the highly selective CC/CMK-3 cathode prepared by using the coating method to load ordered mesoporous carbon（CMK-3）catalysts onto carbon cloth（CC）substrates achieved a current density of～30 m A/cm² at 0.5 V_RHE bias and was tested for stability at 0.65 V_RHE with a Faraday efficiency of～80%.（2）Based on the excellent half-electrode reaction properties described above,it can be speculated that bias-free production of H₂O₂ may be achieved by combining the prepared photoanodes and cathodes.using Mg:Ta₃N₅ photoanodes with a wide visible light absorption range and suitable band positions for H₂O₂ production,and CC/CMK-3 cathodes with high activity and selectivity,the Mg:Ta₃N₅||CC/CMK-3 and Mg:Ta₃N₅||Nafion||CC/CMK-3 devices.The solar-to-H₂O₂ conversion efficiency of the Mg:Ta₃N₅||Nafion||CC/CMK-3 devices reaches up to 2.33%in the AM1.5G simulated sunlight unbiased case.