Overlooked role associated with the active-site density in perovskite nickelates to the anisotropic catalytic activities for water splitting

The d-band correlated rare-earth nickelate ( ReNiO 3 ) is a typical quantum material that exhibits comparable reactivities to the noble metal oxide in oxygen evolution reactions (OER) for water splitting, apart from their well-known correlated electronic functionalities, such as metal to insulator transition. Nevertheless, the potential anisotropy in the catalyst reactivity of OER for ReNiO 3 and its underneath mechanisms are yet under debate. Herein, we demonstrate the previously overlooked role associated with the surface atomic density of the Ni active-site that dominant in the anisotropic OER catalytic activities of ReNiO 3 . Despite its more localized electron configurations as indicated by the near edge x-ray absorption fine structure analysis and correlated transport, the OER catalytic activity was surprisingly observed to be higher for quasi-single crystalline NdNiO 3 (001)/LaAlO 3 (110), compared to that of NdNiO 3 (010)/LaAlO 3 (001) and NdNiO 3 ([Formula: see text]10)/LaAlO 3 (111). This is attributed to the highest surface atomic density associated with the Ni active-site within NdNiO 3 (001), compared to NdNiO 3 (010) and NdNiO 3 ([Formula: see text]10), and this kinetically reduces the overpotential of OER and the charge transfer resistance of NdNiO 3 (001). The anisotropic OER activity sheds a light on the crystal orientation in the optimization of the ReNiO 3 catalyst for water splitting.