Growth of single-crystalline SrNbO2N micron particles and assembling of particulate photoanodes

Abstract

The preparation of single-crystalline SrNbO₂N particles using the flux method, in which NbO_xN_y impurities are generated, remains challenging. Herein, Sr₅Nb₄O₁₅ with a Sr : Nb molar ratio of 1.25 was used as the precursor and NaCl served as flux. The reduction of Nb(V) and formation of NbO_xN_y impurities during the molten salt assisted thermal ammonolysis process was suppressed by the excess SrO in the precursor. On the other hand, the excess SrO hindered the growth of SrNbO₂N grains. The concentration of SrO was controlled by adjusting the precursor-to-flux molar ratio. Meanwhile, the NH₃ contact mode of secondary flow or transition flow slowed down the loss of SrO caused by ammonia gas blow-off, and thus controlled the growth of SrNbO₂N crystals and defect formation. Well-defined single-crystalline SrNbO₂N submicron particles and micron particles were prepared thereby. SrNbO₂N particles were assembled into photoanodes by the method of electron-conducting array insertion, and the influence of crystal grain size on the performance of SrNbO₂N photoanodes was investigated.