Controlled Surface-Assembly of Nanoscale Leaf-Type Cu-Oxide Electrocatalyst for High Activity Water Oxidation

Abstract

ABSTRACT:The controlled surface deposition of a robust and highperformance nanostructured copper-oxide (CuO x -NLs) electrocatalyst for water oxidation is presented. The material exhibits a characteristic leaf-type morphology and self-assembles on a copper substrate by straightforward constant-current anodization. The oxygen onset occurs at about 1.55 V versus RHE (η = 320 mV), which is 400−500 mV less than for amorphous Cu-oxide films. A Tafel slope of 44 mV dec −1 is obtained, which is the lowest observed relative to other copper-based materials. Long-term catalytic performance and stability tests of the electrocatalytic CuO x -NLs sample show a stable current density of >17 mA cm −2 for oxygen evolution, which was sustained for many hours.KEYWORDS: electrocatalyst, water oxidation, copper-oxide, nanoscale leaves, oxygen evolution T here are continuous efforts to develop a strategy to produce renewable and cleaner energy carriers from abundant solar radiation and water.1,2 In this quest, catalytic water oxidation is regarded as a primary process, and many inorganic materials and transition metal-oxides are considered good candidates for this conversion.2,3 Metal-oxide catalysts can be electrodeposited on conducting substrates from carbonate, phosphate, or borate electrolytes in the presence of metal ions. 4−6 To eliminate the possibility for interaction of metal ions with the cathodic sites during electrolysis, membranes or separators are usually employed that make the system more complex and introduce resistance and diffusion limitations in the electrochemical process.7 New preparation methods are required that are easily implemented, and catalytic materials are desired to perform in metal ion free systems for sustained electrochemical operation. 8,9 In addition, control over the catalyst morphology and surface structure is important to induce a high surface area and phase purity, facilitating both charge transfer and mass transport during catalysis reaction. 9,10Stable and efficient metal-oxide derived electrocatalysts can develop in a carbonate/bicarbonate system under mild conditions. 5,11 HCO 3 − /CO 3 2− is suggested to facilitate proton management and prevent the degradation of these catalytic materials under anodic conditions. 12−14 We observed that anodization of a copper electrode via repetitive potentialsweeps or at constant-potential in a carbonate buffer induces the formation of very small copper-oxide particulate materials (CuO x -NPs) having oxygen onset at ∼1.59 V versus RHE (η ≥ 360 mV). In addition, we found that nanoscale leaf-shaped Cuoxide (CuO x -NLs) surface structures ( Figure S1) are formed during controlled anodization of a chemically etched copper substrate at a constant current density of 4.0 mA cm −2 in a carbonate system. The CuO x -NLs exhibit a remarkably low overpotential for water oxidation (η = 320 mV) relative to other Cu-based electrocatalysts 13−15 and many inorganic materials. 16,17 Scanning electron microscopy (SEM) imaging shows a leaves-type copper-oxide matrix (Figur...

Ultrasmall Co@Co(OH)2 Nanoclusters Embedded in N‐Enriched Mesoporous Carbon Networks as Efficient Electrocatalysts for Water Oxidation

“…The formation of a thin layer of (oxy)hydroxide was also observed with the appearance of a characteristic new peak at approximately 595 cm −1 (Figure S15 in the Supporting Information) in the Raman spectrum, which represents the collective vibration of the B g mode of oxygen in the metal‐(oxy)hydroxide owing to the change in their polarizability . The sensitivity of this collective vibration coupled with the electronic charge/state may result in the structural/electronic flexibility, which could facilitate the polarization of water molecules and electron transfer during catalysis . We believe that such a competent and sustained behavior is most likely owing to the inherently generated optimum redox potential induced by the interconvertible redox couple (Co 0/2+/3+ ) .…”

“…[40] The sensitivity of this collective vibration coupled with the electronic charge/state may result in the structural/electronic flexibility,w hich could facilitate the polarization of water molecules and electron transfer during catalysis. [41] We believe that such ac ompetent and sustained behavior is most likely owing to the inherently generated optimum redox potentiali nduced by the interconvertible redox couple (Co 0/2 + /3 + ) . Moreover,t he large number of active sites on the surfaceo ft he ultrasmall supported NCs and their stable/regeneratable behavior are highly regarded to propel the fast transport of electrons (4 e À )b etween the catalysta nd adsorbed speciesf or the dynamic release of O 2 molecules with high selectivity.…”

Atomically monodisperse nickel nanoclusters as highly active electrocatalysts for water oxidation

“…It is anticipated that this investigation will further advance the knowledge and methods to prepare robust and high activity catalytic materials for anodic water splitting. 61 …”

A Dendritic Nanostructured Copper Oxide Electrocatalyst for the Oxygen Evolution Reaction

“…Representative linear sweep voltammograms (LSV) in 1.0 m aqueous NaOH solution are shown in Figure 4. To assess the influence of the high electrochemical surface area (ECSA) of studied materials (values given in the Supporting Information, Table S3) on their catalytic properties,w en ormalized the LSV plots by the ECSA of the electrodes (Supporting Information, Figure S8) and compared them to as tate of the art porous copper oxide OER catalyst [14] (Supporting Information, Figure S9). To assess the influence of the high electrochemical surface area (ECSA) of studied materials (values given in the Supporting Information, Table S3) on their catalytic properties,w en ormalized the LSV plots by the ECSA of the electrodes (Supporting Information, Figure S8) and compared them to as tate of the art porous copper oxide OER catalyst [14] (Supporting Information, Figure S9).…”

“…[1][2][3] However,t he water oxidation half-reaction, also called the oxygen evolution reaction (OER), providing the electrons required for proton reduction, implies the loss of four electrons and four protons from two water molecules with concomitant formation of an O À O bond. [11][12][13][14][15][16][17] While these are still outperformed by state of the art catalysts [6][7][8][9][10] (Supporting Information, Tables S1 and S2), the low cost and large abundance of copper justifies pursuing studies on rationally designed copper oxide electrodes. [4][5][6][7][8][9][10] In that context, few recent examples have indicated that CuO-based materials electrodeposited from molecular Cu complexes or simple Cu salts could display interesting performances for water oxidation.…”