Nanostructured Anodic Copper Oxides as Catalysts in Electrochemical and Photoelectrochemical Reactions

Abstract

Recently, nanostructured copper oxides formed via anodizing have been intensively researched due to their potential catalytic applications in emerging issues. The anodic Cu2O and CuO nanowires or nanoneedles are attractive photo- and electrocatalysts since they show wide array of desired electronic and morphological features, such as highly-developed surface area. In CO2 electrochemical reduction reaction (CO2RR) copper and copper-based nanostructures indicate unique adsorption properties to crucial reaction intermediates. Furthermore, anodized copper-based materials enable formation of C2+ hydrocarbons and alcohols with enhanced selectivity. Moreover, anodic copper oxides provide outstanding turnover frequencies in electrochemical methanol oxidation at lowered overpotentials. Therefore, they can be considered as precious metals electrodes substituents in direct methanol fuel cells. Additionally, due to the presence of Cu(III)/Cu(II) redox couple, these materials find application as electrodes for non-enzymatic glucose sensors. In photoelectrochemistry, Cu2O-CuO heterostructures of anodic copper oxides with highly-developed surface area are attractive for water splitting. All the above-mentioned aspects of anodic copper oxides derived catalysts with state-of-the-art background have been reviewed within this paper.

Electrochemical Reduction of CO2 on Flame Annealed Cu

“…[46,47] C 2 formation on OCÀ Cu and FAÀ Cu can be ascribed to the high surface roughness of the annealed Cu (as seen in Table 3) and higher electrochemically active surface area. [41] Stability measurements performed for 3 h showed an initial reduction of Cu oxides followed by constant current density, as illustrated in Figure S7. The characterisation by XRD ( Figure S8) and SEM ( Figure S9) of the oxidised Cu samples before and after CO 2 reduction depicts the reduction of oxides to the metal in par with the literature results, [3] and a newly formed Cu surface helps in C 2 formation.…”

“…[40] However, with the increase in oxidation temperature, C 2 (ethane and ethylene) formation reached a plateau with the increase in the thickness of the electrode ( Figure S6), emphasising that the thickness of the oxide layer governs the product formation rate. [3] In the literature, the selectivity of oxide-derived copper towards C 2 products has been attributed to several factors, such as (i) a higher local pH at the catalyst surface, favouring the CÀ C coupling pathway over the formation of C 1 product; [41] (ii) more grain boundaries, defect sites and crystal planes; and (iii) the presence of oxides, which provide Cu sites with multiple valences to increase the catalytic activity. [37,42,43,44] Eilert et al reported the existence of subsurface oxygen during CO 2 reduction-enhanced C 2 selectivity because of changes in the electronic structure of the Cu, improving the binding of CO. [45] Furthermore, the selectivity for C 2 products depends on the higher surface roughness, leading to increased local current density and the mode of CO 2 adsorption during the reduction.…”

“…In the literature, the selectivity of oxide‐derived copper towards C 2 products has been attributed to several factors, such as (i) a higher local pH at the catalyst surface, favouring the C−C coupling pathway over the formation of C 1 product; [41] (ii) more grain boundaries, defect sites and crystal planes; and (iii) the presence of oxides, which provide Cu sites with multiple valences to increase the catalytic activity [37,42,43,44] . Eilert et al.…”

“…Furthermore, the selectivity for C 2 products depends on the higher surface roughness, leading to increased local current density and the mode of CO 2 adsorption during the reduction [46,47] . C 2 formation on OC−Cu and FA−Cu can be ascribed to the high surface roughness of the annealed Cu (as seen in Table 3) and higher electrochemically active surface area [41] …”

The Use of Anodic Oxides in Practical and Sustainable Devices for Energy Conversion and Storage

“…Papers essentially describing synthetic routes, a material's characterization, or the investigation of a material's properties are not addressed in this review. For such topics, we recommended the excellent review papers in the anodic oxide field [2,8,[34][35][36][37][38][39][40].…”