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Low-temperature hydrothermal epitaxial growth and topochemical conversion (TC) reactions offer unexploited possibilities for the morphological engineering of heterostructural and non-equilibrium shape (photo)catalyst particles. The hydrothermal epitaxial growth of SrTiO 3 on Bi 4 Ti 3 O 12 platelets is studied as a new route for the formation of novel nanoheterostructural SrTiO 3 /Bi 4 Ti 3 O 12 platelets at an intermediate stage or (100)-oriented mesocrystalline SrTiO 3 nanoplatelets at the completed stage of the TC reaction. The Bi 4 Ti 3 O 12 platelets act as a source of Ti(OH) 6 2- species and, at the same time, as a substrate for the epitaxial growth of SrTiO 3 . The dissolution of the Bi 4 Ti 3 O 12 platelets proceeds faster from the lateral direction, whereas the epitaxial growth of SrTiO 3 occurs on both bismuth-oxide-terminated basal surface planes of the Bi 4 Ti 3 O 12 platelets. In the progress of the TC reaction, the Bi 4 Ti 3 O 12 platelet is replaced from the lateral ends toward the interior by SrTiO 3 , while Bi 4 Ti 3 O 12 is preserved in the core of the heterostructural platelet. Without any support from noble-metal doping or cocatalysts, the SrTiO 3 /Bi 4 Ti 3 O 12 platelets show stable and 15 times higher photocatalytic H 2 production (1265 μmol·g -1 ·h -1 ; solar-to-hydrogen (STH) efficiency = 0.19%) than commercial SrTiO 3 nanopowders (81 μmol·g -1 ·h -1 ; STH = 0.012%) in pH-neutral water/methanol solutions. A plausible Z scheme is proposed to describe the charge-transfer mechanism during the photocatalysis.

Despite the recent promise of transition metal carbides as nonprecious catalysts for the hydrogen evolution reaction (HER), their extension to the oxygen evolution reaction (OER) to achieve the goal of overall water splitting remains a significant challenge. Herein, a new Ni/Mo x C (MoC, Mo 2 C) nanoparticle-supported N-doped graphene/carbon nanotube hybrid (NC) catalyst is developed via a facile, one-step integrated strategy, which can catalyze both the HER and OER in an efficient and robust manner. The catalyst affords low overpotentials of 162 and 328 mV to achieve a current density of 10 mA/cm 2 for HER and OER, respectively, in alkaline medium, which either compares favorably or exceeds most of the Mo-based catalysts documented in the literature. It is believed that there is an electronic synergistic effect among Mo x C, Ni, and NC, wherein a tandem electron transfer process (Ni → Mo x C → NC) may be responsible for promoting the HER as well as OER activity. This work opens a new avenue toward the development of multicomponent, highly efficient but inexpensive electrocatalysts for overall water splitting.