Tuning the oxygen evolution reaction activity of Ni- and Co-modified Fe(OH)2 electrodes through structure and composition control

Abstract

NiFe- and CoFe-based (oxy)hydroxides stand out as promising and highly active earth-abundant electrocatalysts for the oxygen evolution reaction (OER) in alkaline media. Fe(OH)2-Ni(OH)2 and Fe(OH)2-Co(OH)2 electrodes have been prepared through a urea-based chemical bath deposition (CBD) method that enables to control and optimize structure and loading. The effect of the spatial arrangement of the metals in the hydroxide deposits on the electrocatalytic activity in alkaline media has been evaluated. Ultrathin films formed by bilayers resulting from the deposition of submonolayer amounts of Ni or Co hydroxides on previously deposited Fe(OH)2 layers were found to exhibit the best electrocatalytic behavior. The turnover frequency for O2 generation increases drastically as the amount of either Ni or Co decreases, reaching maximum values 2.6 and 1.6 times higher than those for FTO/Ni(OH)2 and FTO/Co(OH)2 electrodes, respectively. This shows that the presence of underlying Fe(OH)2 nanoparticles plays a crucial role in enhancing the electrocatalytic properties of Ni or Co sites. The fact that these ultrathin electrodes, formed by extremely small amounts of electrocatalysts, show good stability in alkaline media paves the way for their use as transparent electrodes or co-catalysts for water splitting photoanodes.