Hydrogen-associated electron-doping Mottronics for d-band correlated oxides (e.g., VO 2 ) opens up a new paradigm to regulate the electronic functionality via directly manipulating the orbital configuration and occupancy. Nevertheless, the role of hydrogen in the Mottronic transition of VO 2 is yet unclear because opposite orbital reconfigurations toward either the metallic or highly insulating states were both reported. Herein, we demonstrate the root cause for such hydrogen-induced multiple electronic phase transitions by 1 H quantification using nuclear reaction analysis. A low hydrogenation temperature is demonstrated to be vital in achieving a large hydrogen concentration (n H ≈ 10 22 cm −3 ) that further enhances the t 2g orbital occupancy to trigger electron localizations. In contrast, elevating the hydrogenation temperatures surprisingly reduces n H to ∼10 21 cm −3 but forms more stable metallic H 0.06 VO 2 . This leads to the recognition of a weaker hydrogen interaction that triggers electron localization within VO 2 via Mottronically enhancing the orbital occupancies.

Although vanadium dioxide (VO 2 ) exhibits the most abrupt metal-to-insulator transition (MIT) properties near room temperature, the present regulation of their MIT functionalities is insufficient owing to the high complexity and susceptibility associated with V 4+ . Herein, we demonstrate a spark plasma-assisted reactive sintering approach to simultaneously achieve in situ doping and sintering of VO 2 within a largely short period (∼10 min). This enables high convenience and flexibility in regulating the electronic structure of VO 2 via dopant elements covering Ti, W, Nb, Mo, Cr, and Fe, leading to a wide adjustment in their MIT temperature (T MIT ) and basic resistivity (ρ). Furthermore, the mechanical strength of the doped VO 2 is meanwhile largely improved via the compositing effect of the highmelting-point dopant oxide. The high adjustability in MIT properties and improved mechanical properties further pave the way toward practical applications of VO 2 in power electronics, thermochromism, and infrared camouflage.

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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([Formula: see text]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 ([Formula: see text]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.