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Piezocatalysis, converting mechanical vibration into chemical energy, has emerged as a promising candidate for water‐splitting technology. However, the efficiency of the hydrogen production is quite limited. We herein report well‐defined 10 nm BaTiO3 nanoparticles (NPs) characterized by a large electro‐mechanical coefficient which induces a high piezoelectric effect. Atomic‐resolution high angle annular dark field scanning transmission electron microscopy (HAADF‐STEM) and scanning probe microscopy (SPM) suggests that piezoelectric BaTiO3 NPs display a coexistence of multiple phases with low energy barriers and polarization anisotropy which results in a high electro‐mechanical coefficient. Landau free energy modeling also confirms that the greatly reduced polarization anisotropy facilitates polarization rotation. Employing the high piezoelectric properties of BaTiO3 NPs, we demonstrate an overall water‐splitting process with the highest hydrogen production efficiency hitherto reported, with a H2 production rate of 655 μmol g−1 h−1, which could rival excellent photocatalysis system. This study highlights the potential of piezoelectric catalysis for overall water splitting. [ABSTRACT FROM AUTHOR]

Magnetic metal–organic frameworks (MOFs) with a perovskite structure AMX3 are emerging single‐phased multiferroics with different sources of magnetic and electric ordering. However, the atomic mechanism underlying the multiple ferroic coupling is convincingly clarified. In this work, large single crystals of [(CH3)2NH2][Ni(HCOO)3] are synthesized and shown to exhibit a first‐order ferroelectric phase transition at ≈178 K during heating and at ≈151 K during cooling, as confirmed by temperature‐dependent differential scanning calorimetry, Raman scattering, and X‐ray diffraction studies. Resonant ultrasound spectroscopy (RUS) is used to investigate the elastic and anelastic properties between 5 and 300 K. The RUS results show an abrupt disappearance of resonance peaks above the ferroelectric transition point of ≈178 K. This is probably due to the unfreezing of dimethylammonium cation motion which couples with local strain. Small changes in elastic properties associated with two known magnetic transition at ≈35 and ≈15 K, respectively, are indicative of weak magnetoelastic coupling. An apparent peak in acoustic loss accompanying the canted antiferromagnetic ordering (≈35 K) and spin reorientation transition (≈15 K) is attributed to dynamical magnetoelastic coupling on the RUS time scale of ≈10−6 s. In comparison with the same MOF structures containing Mn2+ and Co2+, the smaller Ni2+ ions effectively generate an internal chemical pressure and induce a compressed ion force on the anion frameworks. This study opens up a new landscape to explore possibilities for ferroic‐order coupling in molecular MOFs. A type‐I multiferroic phase of [(CH3)2NH2][Ni(HCOO)3] creates significant elastic and anelastic anomalies associated with the ferroelectric and magnetic ordering transition. The overlapping strains, from separated ferroic ordering parameters, could provide a mechanism for strong magnetoelectric properties in nickel‐based molecular multiferroics. [ABSTRACT FROM AUTHOR]