Morphology-Dependent CO Reduction Kinetics and Surface Copper Species Evolution of Cu₂O Nanocrystals

Abstract

Various Cu2O nanocrystals (NCs), including cubes exposing {100} crystal planes (c-Cu2O), octahedra exposing {111} crystal planes (o-Cu2O), and rhombic dodecahedra exposing {110} crystal planes (d-Cu2O), were employed to study the morphology-dependent reduction kinetics and surface copper species evolution of Cu2O catalyst under a reductive CO atmosphere. Remarkable morphology dependence of Cu2O NCs reduced by CO was observed that varies with CO concentration. When CO concentrations are 0.1 and 1%, the reduction of Cu2O is dominated by the density of CO reduction sites and thus o-Cu2O NCs exhibit the strongest reducibility due to their better CO adsorption capacity, while the strongest reducibility was observed on c-Cu2O NCs at CO concentrations of 5 and 10% due to the reduction dominantly switching to the diffusivity of subsurface/bulk lattice O into the surface. X-ray photoelectron spectroscopy (XPS) results without exposure to air display that metallic Cu is easily enriched on the o-Cu2O surface but the surface copper species is exclusively composed of Cu­(I) on c-Cu2O NCs during the CO reduction process. Moreover, the reducibility of o-Cu2O NCs was significantly influenced by H2O while that of c-Cu2O NCs was hardly affected, which was mainly ascribed to their distinctly different surface compositions. These results not only clearly reveal the morphology-dependent reducibility of Cu2O NCs in different CO concentrations but also provide direct evidence in efficiently guiding the in situ adsorbate-induced restructuring process of Cu2O in CO-involved reduction reactions.

Morphology‐Dependent Catalysis of CeO2‐Based Nanocrystal Model Catalysts

“…This provides an excellent candidate to realize the study of structure‐activity relationships by employing oxide‐based NC model catalysts with one or two types of crystal planes exposed. In the past several years, increasing number of examples of morphology‐dependent catalytic properties of uniform oxide‐based NCs, such as Cu 2 O, [ 31‐36 ] Co 3 O 4 , [ 37 ] TiO 2 , [ 38‐39 ] ZnO, [ 40‐41 ] and Fe 2 O 3 [ 42‐43 ] have been comprehensively explored, also including several nice reviews published on this topic. [ 16‐24,44‐52 ]…”

Cu2O Nanocrystal Model Catalysts

“…Various Cu 2 O NCs were observed to exhibit morphology‐dependent reactivity in a series of redox reactions. [ 95‐103 ]…”

“…Reduced in 0.1%CO/Ar, a very low CO concentration (Figure 4C), CO adsorption is a dominant factor for the reduction reaction and o‐Cu 2 O NCs with a stronger CO adsorption capacity is much easier to be reduced, while reduced in 10%CO/Ar (Figure 4D), the diffusion of subsurface/bulk lattice O to the surface, instead of CO adsorption, becomes a dominant factor for the reduction reaction. [ 99 ]…”

Investigation into the Re-Arrangement of Copper Foams Pre- and Post-CO2 Electrocatalysis

“…Copper is an important CO 2 reduction catalyst due to its unique properties; until 2018, it was the only metal reported capable of generating higher value products than carbon monoxide (CO) and formate from CO 2 in appreciable quantities [12][13][14][15]. Therefore, the use of copper as an electrocatalyst for CO 2 reductions is widely extended, employing solid copper surfaces [16][17][18][19], copper foil [20][21][22][23], copper nanoparticles [24][25][26], copper nanocrystals [27][28][29], or hollow copper metal-organic framework (MOF) [30][31][32]. However, frequently, they are sensitive to minor contaminants present in water or bicarbonate solution [33][34][35][36], requiring extensive purification of both the copper surface and reaction medium before electrocatalysis.…”