Polyhedral 30‐Faceted BiVO₄ Microcrystals Predominantly Enclosed by High‐Index Planes Promoting Photocatalytic Water‐Splitting Activity

Abstract

High-index crystal facets, denoted by a set of Miller indices {hkl} with at least one index greater than unity, possess a high density of low-coordinated atoms, steps, edges, and kinks that serve as highly active catalytic sites. [1][2][3] High-index surfaces normally grow faster than lowindex ones and are usually lost during crystal growth due to minimization of the total surface energy. Although the selective exposure of high-index facets at the surface is an important and challenging research topic, much progress has been made in the formation of many kinds of relevant noble metal nanocrystals, which have been extensively applied in catalytic reactions, including those in fuel cells, [4] photocatalysis, [5][6][7] electrocatalysis, [8,9] and petroleum catalytic reforming. [10] However, the generation of metal oxide micro-and nanocrystallites with high-index surfaces is comparatively more difficult due to the presence of strong metal-oxygen bonds and diverse crystal packing structures. [11] Only a few binary metal oxides, such as Co 3 O 4 , [12] anatase TiO 2 , [13][14][15] Fe 3 O 4 , [16] Cu 2 O, [17,18] and SnO 2 , [19] have been successfully achieved. Multinary metal oxide crystals are relatively more meaningful than binary ones because they not only possess more complex functions, but their properties also be readily adjusted by tuning the ratio of the component elements. Bismuth vanadate (BiVO 4 ) attracts intense interest as one of the most promising visible-light-active photocatalysts for water oxidation, due to its appropriate valence band edge located at ≈2.4 eV versus normal hydrogen electrode (NHE). [20] Varieties of morphological BiVO 4 , which are generally enclosed by lowindex {111}, {110}, or {100} planes, were formed through control of the synthetic methods and experimental conditions. [21][22][23] The photocatalytic behavior of BiVO 4 is highly dependent on its surface structure, in which photogenerated electrons and holes can be preferentially separated and accumulated on {010} and {110} facets, respectively, via the driving force created by the different band energies of the two facets. [24,25] Herein, we report the synthesis unprecedented 30-faceted BiVO 4 polyhedra predominantly surrounded by high-index {132}, {321}, and {121} facets. These BiVO 4 materials exhibit 3-5 time enhancements in O 2 evolution from photocatalytic water oxidation, relatively to that of low-indexed counterparts. Theory calculations reveal that the high-index surfaces are energetically favorable for water dissociation and exhibit a notable reduction in the overpotential (0.77-1.14 V) of the oxygen Unprecedented 30-faceted BiVO 4 polyhedra predominantly surrounded by {132}, {321}, and {121} high-index facets are fabricated through the engineering of high-index surfaces by a trace amount of Au nanoparticles. The growth of high-index facets results in a 3-5 fold enhancement of O 2 evolution from photocatalytic water splitting by the BiVO 4 polyhedron, relative to its low-index counterparts. Theory calculations reveal th...

A Theoretical Perspective on Charge Separation and Transfer in Metal Oxide Photocatalysts for Water Splitting

“…Recently, Li et al . synthesized 30‐faceted BiVO 4 polyhedra mainly exposed by {321}, {132} and {121} facets, which exhibits a 3–5 times enhancement in the activity of OER compared with the single crystals exposed with low‐index facets . GGA‐PBE calculations revealed that water decomposition is easier on these high‐index surfaces than on low‐index surfaces, e. g. (010), (110), and (101), and the predicted overpotentials for OER on high‐index surfaces are smaller than those on low‐index surface by 0.77∼1.14 V. Sun et al .…”

Unprecedented Eighteen‐Faceted BiOCl with a Ternary Facet Junction Boosting Cascade Charge Flow and Photo‐redox

“…Thesamples prepared for 10 h, 50 h, 100 h, and 200 h are denoted as BiOCl-10, BiOCl-50, BiOCl-100, and BiOCl-200, respectively.S EM images show that BiOCl-10 presents regular square-plate morphology with size of approximately 3 mm ( Figure 1a and Figure S1). With the increase of reaction time,t he plates grow gradually thicker (Figure 1b [6] With further extending the reaction time to 200 h, it can be observed that the growth of BiOCl crystals was slow,and the change in facet composition of BiOCl is not obvious (BiOCl-200, Figure 1d). Thec orresponding schemes of BiOCl prepared under different time give an intuitive guide for illustrating the morphology change.The growth the eighteenfaceted BiOCl crystal seems to be spontaneous.The presence of new facets with prolonged hydrothermal treating time is similar to that observed for BiVO 4 .…”

“…With the increase of reaction time,t he plates grow gradually thicker (Figure 1b [6] With further extending the reaction time to 200 h, it can be observed that the growth of BiOCl crystals was slow,and the change in facet composition of BiOCl is not obvious (BiOCl-200, Figure 1d). [6,9] Tr ansmission electron microscopy (TEM) verifies the regular square plate morphology of BiOCl-10 with four sharp corners ( Figure 1e). [6,9] Tr ansmission electron microscopy (TEM) verifies the regular square plate morphology of BiOCl-10 with four sharp corners ( Figure 1e).…”

“…[6] However, fabrication of high-index surfaces is greatly challenging because they lost easily due to minimization of the total surface energy. [6] However, fabrication of high-index surfaces is greatly challenging because they lost easily due to minimization of the total surface energy.…”

Facet, Junction and Electric Field Engineering of Bismuth‐Based Materials for Photocatalysis

“…BiVO 4 has an appropriate VB edge (≈2.4 eV versus NHE) and attracts strong attentions as one of the most promising photocatalysts for water oxidation under visible light. 30‐faceted BiVO 4 polyhedra mainly exposed by {321}, {132}, and {121} high‐index facets are synthesized by Zou et al . The high‐index facets exposed BiVO 4 caused a 3–5 times improvement of oxygen production, and the apparent quantum efficiency (AQE) of O 2 generation achieves 18.3 % under irradiation of 430 nm light.…”