Preparation of nanostructured Cu(OH) 2 and CuO electrocatalysts for water oxidation by electrophoresis deposition
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Herein, we report the synthesis of Cu(OH)2 nanobelts with high yield at low cost by a simple aqueous solution reaction. The Cu(OH)2-FTO electrode was then fabricated by a facile electrophoresis deposition method with the as-prepared Cu(OH)2 nanobelts, which require no binding agents. By subsequent heat treatment at 300 °C for 2 h, the Cu(OH)2-FTO electrode was converted to the CuO-FTO electrode. The investigation of electrocatalysis of the Cu(OH)2-FTO and CuO-FTO electrodes for water oxidation was conducted in a 0.2 M phosphate buffer solution at pH 12. The CuO-FTO electrode can catalyze water oxidation with an impressive onset overpotential of 370 mV and an overpotential of 500 mV for a current density of 1 mA/cm2 with a low Tafel slope of 57 mV/dec. This facile fabrication strategy is appealing for realizing the practical application of Cu-based electrocatalysts for water oxidation and is expected to be extended to prepare other heterocatalyst electrodes.
I. INTRODUCTION
Water splitting is a promising approach to transform solar energy and to store it in the form of green chemicals or fuels, such as hydrogen.1–6 As one of the half reactions, the oxygen evolution reaction (OER) is the key step in providing the reductive equivalents and protons for performing reduction of proton to hydrogen.7,8 However, the water oxidation reaction is the bottleneck step, due to the formation of the O–O bond, which typically leads to slow kinetics and high overpotentials.9 Thus, there is a high demand for an electrocatalyst with high activity, excellent stability, and low overpotential for OER. The materials based on precious metals, such as IrO2 and RuO2, have been extensively studied as water oxidation catalysts since the late 1970s, but the low abundance and high-cost of these noble metals significantly hamper their practical applications.10–12 Therefore, recent efforts have been dedicated to the development of OER catalysts based on earthabundant metals.13–15 Over the past decade, significant advances have been achieved in developing water oxidation catalysts based on the first–row transition metals such as manganese,16 iron,13,17 cobalt,18 and nickel,14,19 due to their high abundance and low cost. Besides these earth-abundant elements, copper is an attractive low-cost metal and is relatively less harmful to the environment compared with Contributing Editor: Rui Cao a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2017.378
elements like cobalt and nickel. However, it is only recently that a handful of Cu-based electrocatalysts have been shown to electrocatalyze water oxidation in weakly basic to basic solutions.15,20–27 To obtain more economical and efficient catalysts for practical applications, the catalysts should be prepared in a way that is as simple as possible.23,28–30 Recently, some methods have been developed to prepare electrocatalyst electrodes for water oxidation, such as hydrothermal or solid–state reactions22,31 and electrodeposition.24–27,32 The Cu-based electrocatalysts
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