Fabricating efficient bifunctional catalysts for both hydrogen/oxygen evolution reactions (HER/OER) in an easy and mass-productive way is highly attractive for alkaline water electrolyzers. Perovskite oxides show compositional flexibility and high property tunability, while poor electrical conductivity and relatively low HER activity hamper their application in overall water splitting. Here, a conductive monoclinic SrIrO3 perovskite is developed as an excellent alkaline electrocatalyst with bifunctionality which can be easily synthesized under normal conditions. Toward the HER, it experiences progressive surface self-reconstruction during the activation process because of lattice Sr2+ leaching, eventually leading to a remarkable apparent activity with an approximately 11-fold enhancement at 200 mV overpotential relative to the fresh sample. Experimental and theoretical evidence reveals that etching of lattice Sr2+ in relatively less-stable SrIrO3 compared to IrO2 is crucial for triggering this self-reconstruction. Toward the OER, no obvious surface reconstruction occurs, and an overpotential of only 300 mV is required to realize 10 mA cmgeo –2, significantly lower than that for most perovskites reported previously (340–450 mV). The activated SrIrO3 from HER operation can be used alternatively as an OER electrocatalyst with further improved performance. A SrIrO3-based two-electrode water-splitting cell shows exceptional performance, that is, 1.59 V@10 mA cmgeo –2 with negligible performance degradation over 10 h.

Developing a versatile electrocatalyst with remarkable performance viable for pH-universal overall water splitting is increasingly important for the industrial production of renewable energy conversion. Herein, our theoretical calculations predicate that...

Tuning the Fermi level (EF) in Bi2Te3 topological-insulator (TI) films is demonstrated on controlling the temperature of growth with molecular-beam epitaxy (MBE).

The simple ABO3 and A-site-ordered AA′3B4O12 perovskites represent two types of classical perovskite functional materials. There are well-known simple perovskites with ferroelectric properties, while there is still no report of ferroelectricity due to symmetry breaking transition in A-site-ordered quadruple perovskites. Here we report the high pressure synthesis of an A-site-ordered perovskite PbHg3Ti4O12, the only known quadruple perovskite that transforms from high-temperature centrosymmetric paraelectric phase to low-temperature non-centrosymmetric ferroelectric phase. The coordination chemistry of Hg2+ is changed from square planar as in typical A-site-ordered quadruple perovskite to a rare stereo type with 8 ligands in PbHg3Ti4O12. Thus PbHg3Ti4O12 appears to be a combinatory link from simple ABO3 perovskites to A-site-ordered AA′3Ti4O12 perovskites, sharing both displacive ferroelectricity with former and structure coordination with latter. This is the only example so far showing ferroelectricity due to symmetry breaking phase transition in AA′3B4O12-type A-site-ordered perovskites, and opens a direction to search for ferroelectric materials.

A dramatic band gap narrowing of 1.61 eV has been observed in Co-doped nanocrystals of CeO2 (ceria), as a result of thermal annealing, without changing the ceria crystal structure and the Co concentration. As demonstrated by x-ray absorption fine structures, thermal annealing incurs an oxygen coordination rearrangement around Co atoms from an octahedral coordination to a square-planar coordination. First principle calculation using density functional theory reveals two stable oxygen coordination types surrounding Co, consistent with the experimental observation. The band gap values calculated for the two stable coordination types differ dramatically, reproducing the experimentally observed band gap narrowing. These prominent effects due to local structure rearrangement around dopant atoms can lead to unprecedented methods for band gap engineering in doped nanocrystal oxides.