Identification of the Miller indices of a crystallographic plane: a tutorial and a comprehensive review on fundamental theory, universal methods based on different case studies and matters needing attention

Micro-/nanostructures exposed with special crystallographic planes (surface or crystal facets) exhibit distinctive physicochemical properties because of their unique atomic arrangements, resulting in their widespread applications in the fields of catalysis, energy conversion, sensors, electrical devices and so on. Therefore, tremendous progress has been made in facet-dependent investigation of various micro-/nanocrystals over the past decades. However, a lot of beginners including undergraduate students as well as graduate students lack systematic knowledge and don't know how to identify the Miller indices of a crystallographic plane in the actual research process. So far, to the best of our knowledge, there is no specialized review article in this respect. Herein, we present a tutorial and a comprehensive review on the identification of the Miller indices of a crystallographic plane, including fundamental theory, universal methods based on different case studies, and matters needing attention. Hopefully, this tutorial review will be a beneficial theoretical and practical reference for beginners currently focusing on the controllable preparation and facet-dependent investigation of micro-/nanocrystals.

High-index faceted metal oxide micro-/nanostructures: a review on their characterization, synthesis and applications

Exposed high-index facets with a high density of low-coordinated atoms (including edges, steps and kinks) can provide more high-active sites for chemical reactions. Therefore, great progress has made in the facet-dependent application of various high-index faceted micro-/nanostructures in the past decades. Previous review papers have mainly highlighted the advances in high-index faceted noble metal nanocrystals. However, to date, there is no specialized review paper on high-index faceted metal oxides and their facet-dependent applications. Thus, in this review, the existing high-index faceted metal oxide micro-/nanostructures, including Cu2O, TiO2, Fe2O3, ZnO, SnO2 and BiVO4, are reviewed based on their characterization, synthesis engineering and facet-dependent applications in the fields of catalysis, sensors, lithium-ion batteries and carbon monoxide oxidation. Also, several challenges and perspectives are presented. Hopefully, this review article will be a useful guideline and resource for researchers currently concentrating on high-index faceted metal oxides to design and synthesize novel micro-/nanostructures for overcoming the practical environment-, biology- and energy-related problems.

Core-Shell Prussian Blue Analogs with Compositional Heterogeneity and Open Cages for Oxygen Evolution Reaction

Here, a reduction-cation exchange (RCE) strategy is proposed for synthesizing Fe-Co based bimetallic Prussian blue analogs (PBAs) with heterogeneous composition distribution and open cage nanocage architecture. Specially, bivalent cobalt is introduced into a potassium ferricyanide solution containing hydrochloric acid and polyvinyl pyrrolidone. The uniform PBAs with opened cages are formed tardily after hydrothermal reaction. Time-dependent evolution characterization on composition elucidating the RCE mechanism is based on the sequential reduction of ferric iron and cation exchange reaction between divalent iron and cobalt. The PBA structures are confirmed by electron tomography technology, and the heterogeneous element distribution is verified by energy-dispersive X-ray spectroscopy elemental analysis, leading to the formation of core-shell PBAs with compositional heterogeneity (Fe rich shell and Co rich core) and open cage architecture. When the PBA catalysts are used to boost the oxygen evolution reaction (OER), superior OER activity and long-term stability (low overpotential of 271 mV at 10 mA cm-2 and ≈5.3% potential increase for 24 h) are achieved, which is attributed to the unique compositional and structural properties as well as high special surface areas (576.2 m2 g-1). The strategies offer insights for developing PBAs with compositional and structural multiplicity, which encourages more practical catalytic applications.

Graphene oxide nanosheet-supported Pt concave nanocubes with high-index facets for high-performance H2O2 sensing

As is known, the catalytic activity of metal nanocrystals is strongly affected by their size and shape, and the shape has a greater impact. Among them, metal nanocrystals enclosed by high-index facets have attracted significant attention due to their excellent properties. In this study, platinum concave nanocubes (Pt CNC) with different sizes and angles distributed on polyvinyl pyrrolidone-functional graphene oxide (GO) were synthesized by a one-pot hydrothermal process. The platinum concave nanocubes mainly enclosed by {410}, {510}, and {610} were prepared and used as modified glassy carbon electrodes; cyclic voltammetry and chronoamperometry were applied to investigate the difference between the catalytic activities of platinum concave nanocubes with different facets. The electrodes induced efficient electrocatalysis of hydrogen peroxide (H2O2), and the electrode modified with Pt CNC/rGO-220 showed the highest reduction current. H2O2 was detected with a detection limit of 0.7 μM over two wide linear ranges (from 3 μM to 1 mM and from 1 mM to 0.1 M) and with high sensitivities (757.4 μA mM-1 cm-2 and 315.4 μA mM-1 cm-2), respectively. The modified glassy carbon electrodes also exhibited good stability and selectivity.