Synergistic Effect of Cobalt/Ferrocene as a Catalyst for the Oxygen Evolution Reaction

Abstract

There is a great deal of interest in the development of electrocatalysts for the oxygen evolution reaction (OER) that are stable and have high activity because this anodic half-reaction is the main bottleneck in water splitting and other key technologies. Cobalt and iron oxide and oxyhydroxide electrocatalysts constitute a cheaper alternative to the highly active and commonly used Ir- and Ru-based catalysts. Most of the described electrocatalysts require tedious synthetic and expensive preparation procedures. We report here a facile and straightforward preparation of an electrocatalyst by a combination of commercial compounds, such as cobalt chloride and ferrocene. A highly active and stable OER electrocatalyst is obtained, which shows a low overpotential in the alkaline medium as a consequence of a synergistic effect between both compounds and is inexpensive.

1

Cyclic voltammograms in a 1 M KOH solution of a Co/Fc-modified electrode at scan rates of (a) 100 and (b) 5 mV s^–1 and (c) the Fc-modified electrode as the control, at a scan rate of 100 mV s^–1.

2

High-resolution XPS spectra for Fc/Co-modified electrodes of the (a) Co 2p energy region and (b) Fe 2p energy region. Abbreviations: EL1, as prepared before any electrochemical process; EL2, after cyclic voltammetry as depicted in Figure a; EL3, after further OER.

3

Linear sweep voltammograms in a 1 M KOH solution of the (a) Co/Fc-modified electrode, (b) Co-modified electrode, (c) Fc-modified electrode, and (d) only Vulcan-modified electrode. All graphite electrodes were prepared by drop-casting of an ink containing the different catalyst configurations mixed with activated carbon Vulcan and Nafion as described in the Supporting Information. The scan rate was 5 mV·s^–1.

4

Chronoamperometry measurements of a Co/Fc catalyst electrode in 1 M KOH at potentials of (a) 0, (b) 1.528, (c) 1.538, (d) 1.548, (e) 1.558, (f) 1.568, (g) 1.588, (h) 1.608, and (i) 1.628 V. The inset shows a Tafel plot derived from current densities obtained as a function of the compensated potential applied.

5

Chronopotentiometry stability test of the Co/Fc catalyst electrode for 24 h at 10 mA cm^–1 in a 1 M KOH solution.