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 (ReNiO3) 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 ReNiO3 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 ReNiO3. 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 NdNiO3 (001)/LaAlO3 (110), compared to that of NdNiO3(010)/LaAlO3 (001) and NdNiO3(1¯10)/LaAlO3 (111). This is attributed to the highest surface atomic density associated with the Ni active-site within NdNiO3 (001), compared to NdNiO3 (010) and NdNiO3 (1¯10), and this kinetically reduces the overpotential of OER and the charge transfer resistance of NdNiO3 (001). The anisotropic OER activity sheds a light on the crystal orientation in the optimization of the ReNiO3 catalyst for water splitting.