Atomically dispersed Rh-doped NiFe layered double hydroxides: precise location of Rh and promoting hydrazine electrooxidation properties

Noble metal-based catalysts have attracted huge attention owing to their intriguing activity and selectivity. Revealing noble metal active sites and keeping them in a form of stable and high loading are crucial to improving the catalytic performance and understanding the reaction mechanism. Herein, a feasible preparation method was used to synthesize a Rh-based ultrathin NiFe layered double hydroxide (Rh/NiFe). The detailed study proved that the existence form of Rh atoms is atomically dispersed. Moreover, extended X-ray absorption fine structure (EXAFS) with theoretical calculation of X-ray absorption near-edge structure (XANES) and density functional theory (DFT) were used to identify at the atomic level the precise location and coordination environment of the introduced Rh atoms. It was found that Rh atoms are doped in the LDH layer in a coplanar position with Ni and Fe atoms. With a 5.4 wt% loading amount of Rh, the modified catalyst of Rh/NiFe-5.4 requires 80 mV less than unmodified ultrathin NiFe layered double hydroxide (NiFe) for hydrazine electrooxidation. The XAFS fitting revealed that the doping of Rh atoms results in the distortion of the laminate and then introduces certain defects, which may be attributed to electron transport, thus endowing them with exceptional electrocatalytic performance. Rh atoms were successfully introduced into NiFe layered double hydroxide and their precise location and coordination environment were identified at the atomic level. The Rh/NiFe requires 1.38 V for hydrazine electrooxidation.